DESCRIPTION
GAIN CONTROL CIRCUIT, COMMUNICATION DEVICE, ELECTRONIC
APPLIANCE, AND GAIN CONTROL METHOD
5 TECHNICAL FIELD
[OOOl]
The technology disclosed i n the present s p e c i f i c a t i o n
r e l a t e s t o a gain control c i r c u i t , a communication device,
an e l e c t r o n i c appliance, and a gain c o n t r o l method.
10
BACKGROUND ART
[0002]
In an e l e c t r o n i c c i r c u i t , i n a case a p l u r a l i t y of s i g n a l s
atdifferentfrequenciesareinput, so-calledintermodulation
15 d i s t o r t i o n a r i s e s a problem. For example, a case of an
amplifier c i r c u i t provided a t an input stage of a receiving
c i r c u i t is t y p i c a l . For example, i n a case the d i f f e r e n c e
of two c a r r i e r frequencies is p r e s e n t n e a r the frequency of
a d e s i r e d wave, t h e r e is a problem of "intermodulation
20 distortion"whereaninterferingcomponentisalsodemodulated.
~ y p i c a l l y , w h e n s i g n a l s a t a p l u r a l i t y o f f r e q u e n c i e s a d j a c e r ~ t
t o the receiving band of a s e l f s t a t i o n a r e received, i f the
l i n e a r performance of an amplifier c i r c u i t o r a frequencymixer
c i r c u i t is poor, third-order d i s t o r t i o n is c a u s e d w i t h i n t h e
25 receiving band (normally, only a f i r s t - o r d e r component of a
modulated s i g n a l has t o be taken i n t o account), and the
reception q u a l i t y is s i g n i f i c a n t l y reduced.
[0003]
As amethodof preventing the problemof "intermodulation
30 d i s t o r t i o n " , t h e r e is known a method of adding a wavelength
s e l e c t i v e bandpass f i l t e r t o an input u n i t of a receiving
c i r c u i t , forexample. However, thismethodincreasesthecost
regarding the bandpass f i l t e r , or increases the size of the
substrate, for example. Also, since generally the bandpass
f i l t e r acts only with respect to a fixed frequency, using the
5 same while making the corresponding frequency variable is
d i f f i c u l t , andthebandpass f i l t e r h a s tobeprepared for each
communication channel ( i n other words, a c a r r i e r frequency;
h e r e i n a f t e r a l s o referred t o as a "band").
[0004]
10 As another method of preventing the problem of
intermodulation distortion, there is also known a method of
improving "non-linear operation of a c i r c u i t member" which
is the causeof occurrenceinthe f i r s t p l a c e . Thisis amethod
where a c i r c u i t member is not added. For example, t o improve
15 the l i n e a r performance of a c i r c u i t , a measure of increasing
the bias current or optimizing the DC bias point such t h a t
operation is in a linear region asmuch as possible is effective,
but t h i s increases the power supply voltage or increases the
consumption power. O r , it is also conceivable to use an
20 expensive c i r c u i t member with improved l i n e a r i t y , but even
i f an expensive c i r c u i t member is used, the non-linearity
cannot, in principle, be made zero.
[0005]
I n c o n t r a s t , for example, Japanese Patent Application
25 Laid-OpenNo. 2000-244353proposesatechnologywhichassumes
that occurrence of intermodulation d i s t o r t i o n is inevitable,
and which includes a gain control c i r c u i t ( a variable gain
amplifier c i r c u i t ) a t an input stage to r e s t r i c t the gain a t
the time of large input such t h a t the intermodulation
30 distortionmaybe suppressedinause s t a t e , t o thereby suppress
d i s t o r t i o n a t the gain control c i r c u i t or a t a frequency
conversioncircuit (amixercircuit, amixer) atalaterstage.
[0006]
However, the technology proposed in Japanese Patent
Application Laid-OpenNo. 2000-244353 includes two stages of
5 gain control circuits in a system for input signals, and
includes aleveldetectioncircuit (awave detector) for each
gain control circuit, and thus, the circuit is complicated.
CITATION LIST
10 PATENT DOCUMENT
[0007]
Patent Document 1: Japanese Patent Application Laid-Open No.
2000-244353
15 SUMMARY OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
[0008]
In the present technical field, another technology
capable of suppressing the intermodulation distortion is
20 desired.
[ooo~']
The present disclosure aims to provide a technology
capable of suppressing the intermodulation distortion.
25 SOLUTIONS TO PROBLEMS
[0010]
A gain control circuit according to a first aspect of
the present disclosure includes a first amplifier for
amplifying an input signal and a signal determination unit
I
30 for determining the input signal to be input to the first
amplifier, and controlling anamplification factor of the first
amplifierbasedonadeterminationresult. Eachgaincontrol
circuit described in a dependent claim for the gain control
circuit according to the first aspect of the present disclosure
defines another advantageous concrete example of the gain
5 , control circuit according to the first aspect of the present
disclosure.
[ 0011]
A communication device according to a second aspect of
the present disclosure includes a first amplifier for
10 amplifyinga receivedsignal, areceivingunitforperforming
a receiving process based on a signal output from the first
amplifier, and a signal determination unit for determining
the received signal to be input to the first amplifier, and
controlling an amplification factor of the first amplifier
15 based on a determination result. The same technologies and
methodsdescribedinthedependentclaims forthegaincontrol
circuit according to the first aspect may be applied to the
communication device according to the second aspect of the
present disclosure, and structures where these are applied
20 define other advantageous concrete examples of the
communication device according to the second aspect.
[0012]
An electronic appliance according to a third aspect of
the present disclosure includes a first amplifier for
25 amplifying an input signal, a signal processing unit for
performing signal processing based on a signal output from
the first amplifier, and a signal determination unit for
determining the input signal to be input to the first amplifier,
andcontrollinganamplificationfactorofthe firstamplifier
30 based on a determination result. The same technologies and
methodsdescribedinthedependentclaims forthegaincontrol
c i r c u i t according to the f i r s t aspect may be applied t o the
electronic appliance according t o the third aspect of the
present disclosure, and structures where these are applied
defineotheradvantageous concreteexamples o f t h e e l e c t r o n i c
5 appliance according to the t h i r d aspect.
[0013]
An electronic appliance according to a fourth aspect
of the present disclosure includes a f i r s t amplifier f o r
amplifyingareceivedsignal, a receivingunitforperforming
10 a receiving process based on a signal output from the f i r s t
amplifier, and a signal determination unit for determining
the received signal to be input t o the f i r s t amplifier, and
controlling an amplification factor of the f i r s t amplifier
based on a determination r e s u l t . The same technologies and
15 methodsdescribedinthedependentclaims f o r t h e g a i n c o n t r o l
c i r c u i t according to the f i r s t aspect may be applied to the
electronic appliance according t o the fourth aspect of the
present disclosure, and structures where these are applied
defineotheradvantageous concreteexamples o f t h e e l e c t r o n i c
20 appliance according to the fourth aspect.
[0014]
In a gain control method 'according t o a f i f t h aspect
o f t h e p r e s e n t disclosure, the input signal includes adesired
wave and an interfering wave, and the amplification factor
25 of the f i r s t amplifier i s controlled with a fixed difference
i n levels of the desired wave and the i n t e r f e r i n g wave. The
sametechnologiesandmethodsdescribedinthedependentclaims
f o r the gain control c i r c u i t according to the f i r s t aspect
may be applied t o the gain control method according to the
30 f i f t h aspect of the present disclosure, and structures where
theseareapplieddefineotheradvantageous concreteexamples
of the gain control method according to the fifth aspect.
[0015]
In short, the technology of the present disclosure
controls the amplification factor of a first amplifier by a
5 feed forward system. There is no need to provide two stages
of gain control circuits in a system for input signals as with
the technology proposed in Japanese Patent Application
Laid-Open No. 2000-244353.
10 EFFECTS OF THE INVENTION
[0016]
Accordingtothegaincontrolcircuit, thecommunication
device, the electronicappliance, andthe gaincontrolmethod
of the present disclosure, since the amplification factor of
15 afirstamplifieriscontrolledbyfeedforward, againcontrol
method different from the technology proposed in Japanese
PatentApplicationLaid-OpenNo. 2000-244353mayberealized.
BRIEF DESCRIPTION OF DRAWINGS
20 [0017]
Fig. 1 is a diagram for describing cross modulation
distortion.
Fig. 2 is a diagram for describing a basic structure
of a gain control circuit of a present embodiment.
25 Fig. 3 is a diagram for describing a first modified
structure of the gain control circuit of the present
embodiment.
Fig. 4 is a diagram for describing a second modified
structure of the gain control circuit of the present
30 embodiment.
Fig. 5 is a diagram for describing a communication device
(including a receiving circuit) of Example 1.
Fig. 6 is a diagram showing an example structure of an
input amplifier unit (a gain control circuit).
Fig. 7 is a diagram showing a relationship between an
5 input level and an SN ratio (SNR) of a communication device.
Fig. 8 is a diagram showing a relationship between the
amount of attenuation of an input amplifier unit and an SN
ratio and IIP3 where a desired wave is at -30 dBm.
Fig. 9 is a diagram showing a relationship between the
10 amount of attenuation of an input amplifier unit and an SN
ratio and IIP3 where a desired wave is at -14 dBm.
Fig. 10 is a diagram for describing a communication
device (including a receiving circuit) of Example 2.
Fig. 11 is a diagram for describing an operation of the
15 communication device of Example 2.
Figs. 12(A) to12(C) arediagrams fordescribingExample
3 .
MODE FOR CARRYING OUT THE INVENTION
20 [0018]
Hereinafter, embodiments of the technology disclosed
inthe present specificationwillbe describedindetailwith
reference to the drawings. If each functional element is to
be distinguished between modes, an alphabet or " n" (n is a
25 number) or a combination of these signs are attached, and if
distinction is not particularly necessary, the sign(s) is
omitted. The same can be said for the drawings.
[0019]
The description will be given in the following order.
1. General Outline
2. Cross Modulation Distortion
3. Basic Structure
4. Modified Structure 1
5. Modified Structure 2
6. Concrete Example Application
Example 1: Corresponding to Basic Structure
Example 2: Modified Structure 1
Example 3: Application to Communication Device,
Electronic Appliance
[0020]
10
First, basic matters will be described below.
[0021]
Inastructure ofthepresentembodiment, againcontrol
circuit, a communication device, and an electronic appliance
15 include a first amplifier for amplifying an input signal (for
example, a received signal), and a signal determination unit
for determining an input signal to be input to the first
amplifier andcontrolling the amplification factor of the first
amplifier based on the determination result. The gain control
20 system for the first amplifier is realized by feed forward.
Accordingly, basically, there isnoneedtoprovide twostages
of gain control circuits to the system for input signals.
Moreover, as a whole, the circuit will be simpler. In the
case of an electronic appliance, there may be a plurality of
25 communication units including the first amplifier, the
receiving unit, and the signal determination unit.
[0022]
For example, in a case an input signal (for example,
a receivedsignal) includes a desiredwave andan interfering
30 wave, the signal determination unit determines each of the
levels of the desired wave and the interfering wave.
LO0231
A t t h i s time, as a f i r s t method, t h e s i g n a l processing
unit may determine the level o f t h e desiredwave and the level
of the i n t e r f e r i n g wave without distinguishing the two. If
5 the level o f t h e desiredwaveis g r e a t e r , c o n t r o l is performed
based on the absolute value of the level of the desired wave,
and i f the level of the interfering wave is greater, control
is performed based on the absolute value of t h e l e v e l of the
i n t e r f e r i n g wave.
10 [0024]
In the case of applying the f i r s t method, the signal
determinationunitpreferablyincludesasecondamplifierfor
a m p l i f y i n g a n i n p u t s i g n a l t o b e i n p u t t o t h e f i r s t amplifier,
andaleveldetectionunitfordetectingthelevelofanoutput
15 signal of the second amplifier. In t h i s case, the level
detection unit controls the f i r s t amplifier with a r e l a t i v e
relationship between the amplification factor of the f i r s t
amplifier andthe amplification factor of the secondamplifier.
[0025]
20 In t h i s case, the amplification factor of the f i r s t
amplifierandtheamplificationfactorofthesecondamplifier
are preferably controlled to be the same. An additional
c i r c u i t f o r o f f s e t a d j u s t m e n t o r t h e l i k e w i l l b e u n n e c e s s a r y .
[0026]
25 Also, i n t h i s case, the second amplifier i s preferably
proportionally s m a l l e r i n s i z e t h a n t h e f i r s t amplifier. The
f i r s t amplifier preferably has a good noise characteristic,
but t h i s is not necessary for the second amplifier, because
it is enough i f t h e l e v e l of the desired wave and the level
30 oftheinterferingwave canbe distinguished fromeachother.
[0027]
As a second method, the signal determination unit
preferablyincludesafirstleveldetectionunitfordetecting
the level of a desired wave, a second level detection unit
for detecting the level of an interfering wave, and a level
5 determination unit for controlling the amplification factor
of the first amplifier based on the detection results of the
first level detection unit and the second detection unit. That
is, this is a structurewheredeterminationisperformedwhile
distinguishing between the level of the desired wave and the
10 level of the interfering wave.
[0028]
With either of the first method and the second method,
theamplification factor ofthe first amplifier is preferably
controlledwitha fixeddifferenceinthelevels ofthedesired
15 wave and the interfering wave.
[0029]
In the structure of the present embodiment, the gain
controlcircuit, thecommunicationdevice, andtheelectronic
appliancemaybe provided, for the output of the first amplifier,
20 with a bandwidth limitation unit for limiting the bandwidth
of an output signal to the bandwidth of a desired wave. This
is because, since the gain control system for the first
amplifier is realized by feed forward, the influence of
bandwidth limitation for the output of the first amplifier
25 is not felt.
[0030]
In the structure of the present embodiment, the gain
control circuit, the communicationdevice, and the electronic
appliance may be provided, at a later stage of the first
30 amplifier,withafeedbackcontrolloopfordetectingthelevel
of a signal corresponding to the level of an output signal
of the first amplifier andcontrolling the amplification factor
of the first amplifier. This is because a gain control loop
ispreferablyprovidedforwhenaninputsignalis small. This
control loop preferably uses negative feedback, but is not
5 necessarily limited to negative feedback.
[0031]

Before describing the basic structure, example
modifications and examples to be described later, cross
10 modulationdistort.ion,w hich is an important evaluation factor,
will be first described. Fig. 1 is a diagram for describing
the cross modulation distortion.
[0032]
In the case of evaluating the characteristics of an
15 amplifier circuit, not only AC characteristics (bandwidth,
slew rate, settling time, etc .) , but also item such as harmonic
distortion, spurious free dynamic range (SFDR) ,
intermodulation distortion (IMD) , intercept point (IP, IP2,
IP3, etc.), noise (S/N: Signal to Noise Ratio), noise figure
20 (NF) and the like are included, for example.
[0033]
For example, in a case a sine wave of a purely single
frequencypassesthroughanamplifiercircuit(thesameapplies
for other active elements), harmonic distortion is caused
25 according to the characteristics and the non-linearity.
Merely measuring the harmonic distortion while changing the
frequency of the sine wave is not enough to evaluate the true
performance of an amplifier circuit that is to be used for
a case where signals at different frequencies are to be input
30 (forexample, communicationuse). Inmanycommunicationuses,
alarge number ofchannelsthataremultiplexedina frequency
domain are used, and thus, the amplifier circuit has to be
evaluated using the amount of intermodulation distortion at
two or more specified frequencies.
[0034]
5 When studying the occurrence of distortion due to two
signals (referred to as a two-tone signal), it can be seen
that second-order and third-order intermodulation products
are caused. Fig. 1 shows this state, and the state is shown
focusingonthe second-order andthird-order intermodulation
10 products occurring when two signals whose frequencies are fl
and f2 are added to a non-linear element. Generally, the
second-order intermodulation distortion is specified using
the value of IP2, and the third-order intermodulation
distortion is specifiedusing the value of IP3. Additionally,
15 a number read on the input level side is expressed by IIP,
and a number read on the output level side is expressed by
OIP, and degrees (multipliers) are further applied thereto
to be expressed by IIP2, IIP3, OIP2, OIP3, and the like.
[0035]
20 This is an evaluation result in a state where two sine
waves at close frequencies (two-tone signal) are
simultaneously appliedto a receiving circuit. In addition
to single tone output signal power (dBm), relative values
(relative to the single tone) of the second-order
25 intermodulation distortion and the third-order
intermodulation distortion are plotted as functions of input
signal power. A function of a fundamental wave is expressed
by a curve of inclination 1. If the non-linearity of the
circuit is approximated by power series expansion, the
30 amplitude of the second-order intermodulation distortion is
increased by 2 dB every time signal input is increased by 1
dB, and this is shown in the drawing as a curve of inclination
2. In the same manner, the amplitude of the third-order
intermodulation distortion is increased by 3 dB every time
an input signal is increased by 1 dB, and this is shown as
5 a curve of inclination 3. Additionally, in reality, when an
input signal exceeds a specific level, the increase in an output
signal starts to be clipped (peaked) . That is, in a domain
where a straight line of ideal inclination 1 is shown by a
dottedline, output is actuallycompressedinthemanner shown
10 by a solid line.
[0036]
Here, if the straight lines ofthe second-order and the
third-order intermodulation distortions are extended, these
intersect with an extendedportion of aline showing an ideal
15 output response. These are second-order and third-order
inter,cept points (IP2, IP3). Additionally, these show the
output power that the circuit supplies to matched load (for ..
example, 500) in dBm.
[0037]
20
Fig. 2 is a diagram for describing a basic structure
of a gain control circuit of the present embodiment. A gain
controlcircuit10Ais embeddedinasignalprocessingcircuit
1, and includes a variable amplifier unit 12, a signal
25 processing unit 14 having a level detection function, and a
signal determination unit 20.
[0038]
The variable amplifier unit 12 is provided on a main
signal path, and its output signal is input to the signal
30 processing unit 14, and predetermined signal processing is
performed at the signal processing unit14. Accordingly, as
the variable amplifier unit 12, a low noise amplifier with
a good noise characteristic (and, generally, a large size)
is used. For example, in a case the signal processing unit
14 is for performing a receivingprocess, it is providedwith
5 a demodulation circuit. In order toperformrequired signal
processing, the signal processing unit 14 detects the input
level (the output level of the variable amplifier unit 12)
or the signal level of a predetermined function unit inside
the signal processing unit 14 corresponding to the input level,
10 and supplies the detection result to the variable amplifier
unit 12. Thus, with respect to the main signal path, when
the input level of the variable amplifier unit 12 is lower
than a predetermined level, an automatic gain control (AGC)
function is made to act between the variable amplifier unit
15 12 and the signal processing unit 14 based on a feedback loop
(NFB) so that the input level of the signal processing unit
14willbe constant. Additionally, thegaincontrol function
regarding the main signal path for causing the input level
ofthe signal processingunit14 tobe constant when the input
20 level of the variable amplifier unit 12 is low does not have
to be based on the feedback loop, and any other circuit
structures may be applied.
[0039]
The s i g n a l d e t e r m i n a t i o n u n i t 2 0 i s p r o v i d e d o n a s i g n a l
25 path (referred to as a replica signal path) different from
the main signal path, and determines the state of a signal
to be input to the variable amplifier unit 12, and when the
input level of the variable amplifier unit 12 is higher than
a predetermined level, the automatic gain control function
30 acts on the variable amplifier unit 12 based on feed forward
(FF) so that the input level of the signal processing unit
14 w i l l be constant.
[0040]
Now, the s t a r t point (AGC - s t a r t ) of AGC of the feed
forward system by t h e s i g n a l determination u n i t 20 and the
5 variable amplifier unit 12 i s given as cx dBm. A threshold
(Threshold) of t h e s i g n a l determination u n i t 20 is given as
p dBm.
[0041]
As a d e s i r e d s i g n a l becomes l a r g e r , the gain of the
10 variable amplifier u n i t 12 is reduced according t o the
determination output o f t h e signaldeterminationunit20. In
thecaseoflowsignalinput,thegainofthevariableamplifier
unit12ismaximizedandthedeteriorationofNF (noise f a c t o r )
is prevented, and i n contrast, i n the case of large input,
15 the gain is r e s t r i c t e d t o suppress t h e d i s t o r t i o n a t the
variable amplifier u n i t 1 2 and the s i g n a l p r o c e s s i n g u n i t 1 4 ,
andthe signal transmissiondevice1 (for example, a r e c e i v i n g
c i r c u i t ) with a wide dynamic range is structured.
[0042]
20 With the gain control c i r c u i t 10A structured i n t h i s
manner, i f an input signal is smaller than a predetermined
l e v e l , t h e input level of t h e s i g n a l processing u n i t 14 is
prevented frombeingloweredby an amplification function of
t h e v a r i a b l e a m p l i f i e r u n i t 1 2 . Ontheotherhand, i f aninput
25 signal is greaterthanapredeterminedlevel, the input l e v e l
of the signal processing u n i t 1 4 is prevented from becoming
excessivelylarge by an attenuation function o f t h e variable
amplifier u n i t 12 i n response t o the determination r e s u l t of
t h e s i g n a l determination u n i t 20, and d i s t o r t i o n a t the
30 variable amplifier unit 12 and the signal processing u n i t 14
may be suppressed. For example, i f t h e input level is higher
than a t the s t a r t point of AGC, and higher than the threshold
o f t h e s i g n a l d e t e r m i n a t i o n u n i t 2 0 , t h i s function comes i n t o
e f f e c t . In the case of applying the technology proposed i n
Japanese Patent Application Laid-Open No. 2000-244353, two
5 stages of gain control c i r c u i t s a r e provided t o the system
for i n p u t s i g n a l s r a t h e r than t o t h e signal processing u n i t
14, but i n the present embodiment, the number of the gain control
c i r c u i t s may be only one. Also, control by the signal
determination unit 20 is not feedback control, and thus, the
10 influenceofbandwidthlimitationofthecircuitatthelater
stage than the variable amplifier unit 12 is not f e l t , and
an i n t e r f e r e n c e s i g n a l may be detected i n a wide bandwidth.
LO0431
Additionally, since t h e s i g n a l determination unit 20
determines the s t a t e of each of the s i g n a l l e v e l s of the desired
signal and the i n t e r f e r i n g signal, it is important t h a t the
bandwidth is wider than for t h e v a r i a b l e amplifier u n i t 1 2 .
That is, it is desired t h a t the frequency band of not only
adesiredsignalcomponentbutaninterferingsignalcomponent
can be dealt with. On the other hand, it is enough i f the
v a r i a b l e amplifier unit 12 can deal with the frequency band
of a desired signal component, and the frequency
c h a r a c t e r i s t i c s for the i n t e r f e r i n g signal component are
b e t t e r reduced.
[0044]
Since there is no document c e r t i f y i n g t h a t Fig. 1 i n
the proposal is known outside the company, Fig. 1 in the proposal
is a l s o i n c l u d e d w i t h i n t h e scope o f t h e present application.
[0045]

Fig. 3 is a diagram for describing a f i r s t modified
structure of againcontrol circuit ofthepresent embodiment.
A gain control circuit 10B of the first modified structure
is different from the gain control circuit 10A of the basic
structure in that a variable amplifier unit 22 and a level
5 detection unit 24 are provided to the signal determination
unit 20. Other aspects are the same as the gain control circuit
10A.
[0046]
The signal determination unit20 of Modified Structure
10 1 is characteristic in that, in a case a plurality of types
of signals at different frequencies are to be supplied to the
variable amplifier unit 12, -control is performed such that
the variable amplifier unit 12 operates in an appropriate state,
based on the state of each of the signal levels of a signal
15 at a desired frequency (a desired signal) and other signals
(interfering signals). What is meant by "such that the
variable amplifier unit 12 operates in an appropriate state"
is that the variable amplifier unit 12 operates in a state
where IIP3 is at a required level regardless of the states
20 ofthe desiredsignallevelandtheinterfering signal level.
[0047]
Forexample,therelationshipbetweenthedesiredsignal
level, the interfering signal level and IIP3 is as shown in
Fig. 1. That is, in a logarithmic expression, the function
25 for a desired signal is expressedby the curve of inclination
1, andthethird-orderintermodulationdistortionisexpressed
by the curve of inclination 3, or in other words, it is increased
in proportion to the cube of the product of two signals. In
the case of achieving a required IIP3 level, the level is not
30 determined based on one of the desired signal level and the
interfering signal level, andboth are involved. Taking this
point in account, the variable amplifier unit 12 is made t o
operate i n a s t a t e where IIP3 is a t a required level.
Specifically, the gain control operation of the variable
a m p l i f i e r u n i t 1 2 i s t o b e p e r f o r m e d i n a statewhere the r a t i o
5 ( D / U ) between the desired signal level (D: Desire - I nput) and
theinterferingsignallevel (U: Undesire- I nput) is constant.
[0048]
Accordingtothis function, thevariable amplifierunit
12 may be appropriately controlled without being influenced
10 by the level difference between a desired signal and an
i n t e r f e r i n g signal. As a desired signal becomes larger, the
gain of the variable amplifier unit 12 is reduced according
t o the determination output o f t h e signal determinationunit
20. I n the case of low signal input, the gain of the variable
15 amplifier unit 12 i s maximized and the deterioration of NF
(noise factor) is prevented, and in contrast, i n the case of
large input, the g a i n i s r e s t r i c t e d t o s u p p r e s s t h e d i s t o r t i o n
a t the variable amplifier unit 1 2 and the signal processing
unit 1 4 , and the signal transmission device 1 (for example,
20 a r e c e i v i n g c i r c u i t ) with awide dynamic range is structured.
[0049]
In Modified Structure 1, t o realize t h i s function, the
signal determination unit 20 uses, as the variable amplifier
unit 22, a variable gain amplifier t h a t operates with a variable
25 width corresponding to the variable width of the variable
amplifier unit 12 on themain signal path. As canbe understood
from the description of t h e s i g n a l determination unit 20, it
isimportantthatthebandwidthofthevariableamplifierunit
22 is wider than t h a t of the variable amplifier unit 1 2 . On
30 the other hand, the noise characteristicisnotmuchof aproblem
and it is enough i f level determination can be appropriately
performed, and thus, a low noise amplifier does not have to
be used. Taking this point into account, the variable
amplifier unit 22 is preferably proportionally smaller in size
than the variable amplifier unit 12 on the main signal path.
5 Being "proportional in size" has an advantage that other
characteristics may be made approximately the same as those
of the variable amplifier unit 12.
[0050]
To "operate with a variable width corresponding to the
10 variable width of the variable amplifier unit 12 on the main
signal path", it is enough if the amplification factor of the
variable amplifier unit 12, which is an example of the first
amplifier, and the amplification factor of the variable
amplifier unit 22, which is an example of the second amplifier,
15 are controlledwhilemaintaininga relative relationship, and
although, as atypical example, the variable widthis the same
as that of the variable amplifier unit 12, this is not
restrictive, and there may be a certain degree of difference
therebetween. This is because this difference may be
20 cancelled by causing the level detection unit 24 to include
an offset function or the like.
[0051]
An output signal of the variable amplifier unit 22 is
s u p p l i e d t o t h e l e v e l d e t e c t i o n u n i t 2 4 . The level detection
25 unit 24 detects the signal level based on the output of the
variable amplifier unit 22, and controls the variable amplifier
unit12 onthemainsignalpath. Againcontrolmethodcapable
of enlargingthe dynamicrange ofthe variable amplifier unit
12 without wasting S/Nmay therebybe realized. With the effect
30 of the variable amplifier unit 22 on the replica signal path,
gain control may be performed with a fixed difference in the
l e v e l s of a desired s i g n a l and an i n t e r f e r i n g signal ( f i x e d
D/U) . Thegaincontrol canbeperformedat an optimal operating
point a t a l l times withoutbeinginfluencedbythe d i f f e r e n c e
i n the l e v e l s of an i n t e r f e r i n g s i g n a l and a desired s i g n a l
5 a t the input of the v a r i a b l e a m p l i f i e r u n i t 12 (regardless
of the input l e v e l ) , and the v a r i a b l e amplifier u n i t 12 may
beappropriatelycontrolled. The s i g n a l transmissiondevice
1 which is d e s i r a b l e i n both NF and dynamic range may be
s t r u c t u r e d .
10 [0052}

Fig. 4 i s a diagram f o r describing a second modified
structureofagaincontrolcircuitofthepresentembodiment.
A gain control c i r c u i t 10C of the second modified s t r u c t u r e
15 is d i f f e r e n t from the gain control c i r c u i t 10A of the basic
s t r u c t u r e i n t h a t a l e v e l d e t e c t i o n u n i t 26A and a l e v e l
detection u n i t 26B, and a l e v e l determination u n i t 28 a r e
p r o v i d e d t o the s i g n a l determination u n i t 20. Other aspects
a r e the same a s t h e gain control c i r c u i t 10A.
20 [0053]
Like Modified Structure 1, Modified Structure 2 causes
the g a i n c o n t r o l operation of the variable amplifier u n i t 12
t o be performed i n a s t a t e where the r a t i o between a desired
s i g n a l l e v e l D and an i n t e r f e r i n g s i g n a l l e v e l U ( D / U ) is fixed.
25 With t h i s function, the v a r i a b l e a m p l i f i e r u n i t 12 may be
a p p r o p r i a t e l y c o n t r o l l e d without being influenced by the
differenceinthelevelsofadesiredsignalandaninterfering
s i g n a l .
[ 0 0 5 4 ]
30 With Modified Structure 2, t o r e a l i z e t h i s function,
a function u n i t f o r detecting the l e v e l of a desired signal
and a function u n i t for d e t e c t i n g t h e l e v e l of an i n t e r f e r i n g
signal a r e separately provided, and the v a r i a b l e a m p l i f i e r
u n i t 12 is controlled based on the r e s u l t s , i n a s t a t e where
the D/U r a t i o is fixed. Specifically, t h e l e v e l detection
5 u n i t 26A is for d e t e c t i n g t h e level of a d e s i r e d s i g n a l , and
for example, a bandpass f i l t e r for passing frequency band
components of t h e d e s i r e d signal i s used a t the input stage.
On the other hand, t h e l e v e l d e t e c t i o n u n i t 26B is f o r d e t e c t i n g
the level of an i n t e r f e r i n g signal, and for example, a band
10 stop ( l i m i t . ) f i l t e r ( a b a n d e l i m i n a t i o n f i l t e r , a n o t c h f i l t e r )
for l i m i t i n g the frequency band components of t h e d e s i r e d
signal is used a t the input stage. The detection r e s u l t of
the level detection unit 26A and the detection r e s u l t of the
level detection unit 26B are supplied t o the level
15 determination unit 28. The level determination u n i t 28
detects the signal levels based on the detection r e s u l t of
. .
the level detection unit 26A and t h e d e t e c t i o n r e s u l t of the
l e ~ e l d e t e c t i o n u n i t 2 6 Ba~nd controls the v a r i a b l e a m p l i f i e r
unit12 onthemain s i g n a l p a t h . Againcontrolmethodcapable
20 of enlarging the dynamic range of the variable amplifier u n i t
12 without wasting S/N may thereby be r e a l i z e d . With the
e f f e c t s of the level detection unit 26A, t h e l e v e l detection
u n i t 26B, and the leve.1 determination u n i t 28 on the r e p l i c a
signal path, gain control may be performed with a fixed
25 differenceinthelevelsofadesiredsignalandaninterfering
s i g n a l ( f i x e d D/U) . The gain control may be performed a t an
optimal operatingpoint a t a l l times without being influenced
by the difference i n the l e v e l s of an i n t e r f e r i n g signal and
a desired signal a t the input of the variable amplifier unit
30 12. The s i g n a l transmission device 1 which is desirable i n
both NF and dynamic range may be structured.
[0055]

Hereinafter, aconcrete example applicationofthe gain
control circuit10 described above will be described. In the
5 following, an example of application to an automatic gain
control circuit (AGC circuit) usedina receiving circuit for
wireless communication will be described. For example,
application to an AGC circuit used in a receiving circuit of
a communication device, a TV, or Digital Audio Broadcasting
10 (DAB) forperformingmobile communication, orthe like, where
a received signal fluctuates, and where a large signal level
may be received in an adjacent channel from another
transmission antenna is desirable.
Example 1
15 [0056]
[Structure]
Fig. 5 is a diagram for describing a communication device
(includingareceivingcircuit) ofExample1. Acommunication
device 810A includes an input amplifier unit 812, a
20 receiving-side localoscillatot-814 for generating a carrier
frequencyF - @,afrequencymixingunit815 (aso-calledmixer),
a demodulated signal processing unit 816 (for example, a
bandpass filter), an output amplifier unit 817, and a
demodulation circuit 818, and a receiving antenna 811 is
25 connected to the input amplifier unit 812. The receiving-side
local oscillator 814 and the frequency mixing unit 815 form
a frequency conversion unit. The input amplifier unit 812
is for gain multiplying the amplitude of a received signal
receivedbythe receiving antenna 811, and corresponds tothe
30 variable amplifier unit 12 described above. A gain control
signal GC1 is supplied from the demodulation circuit 818 to
t h e i n p u t amplifier unit 812, anda negative feedback amplifier
c i r c u i t is structured.
[0057]
The communication device 810A s e l e c t s only a d e s i r e d
5 frequency by imposing bandwidth l i m i t a t i o n on received
frequencies, and a f i l t e r c i r c u i t 813 (a tank c i r c u i t ) is
provided for a load on input amplifier unit 812. The f i l t e r
c i r c u i t 813 is an example of a bandwidth l i m i t a t i o n unit for
l i m i t i n g the bandwidth of an output signal of the input
10 amplifier u n i t 812 t o the bandwidth of the -desired .wave. A
signal determination unit 820A (corresponding t o the signal
determinationunit20 describeabove) fordetermininganinput
signalleveloftheinputamplifierunit812iscorrespondingly
providedona replica signal p a t h d i f f e r e n t fromamain signal
15 path. The signal determination u n i t 820A includes a level
detection u n i t 824 (corresponding t o the level detection u'nit
24) . The level d e t e c t i o n u n i t 824 is providedbefore the input
amplifier u n i t 812, and the detection r e s u l t is usedas a gain
c o n t r o l s i g n a l GC2 t o control t h e i n p u t amplifier unit 812.
20 [0058]
[Gain Control Circuit]
Fig. 6 is a diagram showing an example s t r u c t u r e of the
input amplifier unit 812 (the gain control c i r c u i t ) .
[0059]
25 A n a t t e n u a t o r c i r c u i t 8 3 0 i s p r o v i d e d a t a n i n p u t s t a g e ,
tap output. Incidentally, aninput e n d i s directlyconnected
t o t h e d i f f e r e n t i a l amplifier c i r c u i t 8 4 0 a t the f i r s t stage.
As the attenuator c i r c u i t 830, a r e s i s t o r ladder c i r c u i t may
30 beused, for example. The d i f f e r e n t i a l amplifier c i r c u i t 840
includes a t r a n s i s t o r 842 and a t r a n s i s t o r 844, which are a
d i f f e r e n t i a l p a i r , a n d a t r a n s i s t o r 846servingasthecurrent
source for the two.
[0060]
Each of taps o f t h e attenuator c i r c u i t 830is connected
5 t o t h e i n p u t e n d o f o n e o f t h e t r a n s i s t o r 8 4 2 a n d t h e t r a n s i s t o r
844, which are the d i f f e r e n t i a l pair. The other input ends
of t h e t r a n s i s t o r 842 and the t r a n s i s t o r 844, which are the
d i f f e r e n t i a l pair, are connected together, and a r e f u r t h e r
connectedto a feedbackcircuit for determiningagain. This
10 feedbackcircuitcorrespondstoonewhichoperatesbythegain
control signal GC1. The d i f f e r e n t i a l p a i r operates as a
current control transconductance (gm) amplifier c i r c u i t
(Gm-AMP) . A control signal (corresponding to the gain control
signal GC2) for operating one of the d i f f e r e n t i a l pair is
15 supplied t o a control input end (a gate) of the t r a n s i s t o r
846. An operation s t a t e (a gain) a t the time of excessively
large input i s determined depending on which stagef s
d i f f e r e n t i a l pair is to be operated.
[0061]
20 [Operation of Example 11
Figs. 7 to 9 a r e diagrams for describing an operation
of the communication device 810A of Example 1. Here, Fig.
7 is a diagram showing a relationship between an input level
and an SN r a t i o (SNR) of the communication device 810A. Fig.
25 8 is a diagram showing a relationship between the amount of
attenuation of the input amplifier unit 812 and an SN r a t i o
andIIP3whereadesiredwaveisat-30dBm. Fig. 9isadiagram
showing a relationship between the amount of attenuation of
the input amplifier unit 812 and an SN r a t i o and IIP3 where
30 a desired wave i s a t -14 dBm.
[0062]
As shown in Fig. 7, the start point of AGC is at -50
dBm. Itcanbeseenthatthenoisecharacteristicisdesirable
when the input level is high.
[0063]
5 Fig. 8 shows operating points where the desired wave
is at -30 dBm, and at this time, the threshold of the level
detection unit 824 is set at -30 dBm. For example, when
assuming the required IIP3 where the signal level of an
interfering wave is at -14 dBm to be +12 dBm, it can be seen
10 thatreceptionbecomespossiblewhentheinputamplifierunit
812 is attenuated by 16 dB.
[0064]
By restricting the gain at the time of large input,
distortion at the input amplifier unit 812 or at a circuit
15 at a later stage can be suppressed. However, there are some
drawbacks. For example, Fig. 9 shows operating points where
the desired wave is at -14 dBm, and in this case, the required
IIP3 is already satisfiedby the operatingpoints of the desired
wave, but an operation of further deteriorating the S/N is
20 performed. That is, with the communication device 810A of
Example 1, the gain is controlled by performing detection at
the level of an absolute value of an interfering wave until
the desired wave level exceeds the interfering wave level,
and there is adrawbackthat operationat an optimal operating
25 point is not performed for all the receiving levels.
Example 2
[0065]
[Structure]
Fig. 10 is adiagramfor describingacommunicationdevice
30 (includingareceivingcircuit) ofExample2. Acommunication
device 810B is different from the communication device 810A
of Example l i n t h e s t r u c t u r e o f t h e signal determinationunit
820. Specifically, asignaldeterminationunit820Bincludes
a variable amplifier u n i t 822 (corresponding t o t h e v a r i a b l e
amplifier u n i t 22), and a l e v e l detection u n i t 824
(corresponding t o the l e v e l detection u n i t 24). As the
variable amplifier unit 822, a wide bandwidth v a r i a b l e g a i n
amplifier is used so t h a t t h e i n t e r f e r i n g wave can also be
appropriately processed, b u t s i n c e the noise c h a r a c t e r i s t i c
does not have t o be good, one which is proportionally smaller
10 i n s i z e t h a n t h e v a r i a b l e amplifierunit812 onthemainsignal
path is used. The s i g n a l determinationunit 820Bis provided
b e f o r e t h e i n p u t a m p l i f i e r u n i t 8 1 2 , and the detection r e s u l t
i s u s e d a s t h e gaincontrolsignalGC2, andthe input amplifier
u n i t 812 is thereby controlled.
15 100661
The v a r i a b l e a m p l i f i e r unit 822 has a variable width
the same as the input amplifier unit 812 on the main s i g n a l
path, andalso, includes a v a r i a b l e g a i n a m p l i f i e r w i t h a w i d e
bandwidth. By including t h i s replica signal path, an
20 interferingwavemaybedetectedoverawidebandwithoutbeing
i n f l u e n c e d b y t h e bandwidth l i m i t a t i o n o f t h e f i l t e r c i r c u i t
813, and also, due t o the e f f e c t of the v a r i a b l e a m p l i f i e r
u n i t 822, gain control may be performed i n a s t a t e where the
difference i n the l e v e l s o f t h e desired wave and the i n t e r f e r i n g
25 wave is fixed (fixed D/U).
[0067]
[Operation of Example 21
Fig. 11 is diagram for describing an operation of the
communication device 810B of Example 2 . Here, Fig. 11
30 corresponds t o Fig. 9 for Example 1, and shows a desired wave
a t -14 dBm, and the amount of attenuation of the input amplifier
unit 812, an S/N ratio and IIP3 where the desired wave is at
-14 dBm (that is, in a case where D/U = 0 dB).
[0068]
The input level of the communication device 810B and
5 the SN ratio are the same as the characteristics in Example
1 shown in Fig. 7. The threshold of the level detection unit
824 is -30 dBm as in Example 1. When the desired wave is at
-30 dBm and the interfering wave is at -14 dBm, the operation
as shown in Fig. 8 is performed, as in Example 1.
10 [0069]
The level calculation by the level detection unit 824
of the communication device 810B in Example 2 is as shown in
Fig. 11. For example, a detection threshold is at -30 dBm,
andanAGCstartis at-50 dBm, andthus, the gain is controlled
15 with D/U = -20 dB. For example, in Fig. 11, when the desired
wave is at -14 dBm and the interfering wave is at -14 dBm,
as shown by Condition 1 in the drawing, control by the level
detection unit 824 on the input amplifier unit 812 will be
an attenuation (ATT) operation of -36 dB (because -14-36 =
20 -50). At this time, D/U is 0 dB, and the level of input to
the level detection unit 824 is at -50 dBm and is lower than
the threshold, and thus, no operation is performed in this
case. Accordingly, unnecessary deterioration in S/N is not
caused.
25 [0070]
On the other hand, as shown by Condition 2 in the drawing,
when the desired wave is at -14 dBm and the interfering wave
is at +6 dBm, the level of input to the level detection unit
824 is -30 dBm and is at the threshold, and thus, beyond this
30 state (that is, when the interferingwave is at +6 dBmor higher)
will be the critical point for the start of AGC operation.
It can be seen t h a t the c r i t i c a l point is D/U = -20 dB.
[0071]
Moreover, as shown by Condition 3 in the drawing, when
the desired wave is a t -50 dBm and t h e i n t e r f e r i n g wave is
5 a t -30 dBm, control by the level detection unit 824 on the
inputamplifierunit812willbeanattenuation (ATT) operation
of +O dB (because -50-0 = -50). A t t h i s time, the level of
input t o the level detection unit 824 is a t -30 dBm and is
a t the threshold, and beyond t h i s s t a t e ( t h a t i s , when the
10 i n t e r f e r i n g w a v e i s a t - 3 0 dBmorhigher) w i l l b e t h e c r i t i c a l
point for the s t a r t of AGC operation. It can be seen that,
also i n t h i s case, the c r i t i c a l point i s D/U = -20 dB.
[0072]
AccordingtoExample2, d u e t o t h e e f f e c t o f t h e v a r i a b l e
15 amplifier unit 822, gain control may be performed with the
D/Uratio correspondingtothe differencebetweenadetection
threshold and AGC s t a r t being fixed with respect t o the
difference i n the levels of the desired wave and the i n t e r f e r i n g
wave. As described, unlike Example 1 where the gain is
20 controlledbyperformingdetectionatthelevelofanabsolute
value of an i n t e r f e r i n g wave, in Example 2, gain control is
performed with the D/U being fixed, and gain control may be
performed with an optimal operating point a t a l l times
regardless of the input level of each of the desired wave and
25 the i n t e r f e r i n g wave. As described above, by carrying out
the present invention of performing gain control with fixed
D/U, gain control can be performed with an optimal operating
point a t a l l times regardless of the input level.
Example 3
30 [0073]
Fig. 12 is a diagram for describing Example 3. Here,
I
(A) of Fig. 12 shows an arrangement image of a plurality of
communication devices within an electronic appliance, (B) of
Fig. 12 shows an example detailed structure of the
communication devices, and (C) of Fig. 12 shows an example
5 of frequency arrangement of carrier frequencies.
[0074]
Example 3 is an example application where a plurality
of communication'devices are arranged inside the housing of
oneelectronicapplianceandcommunicationisperformed. For
10 .example, this is a mode where all the communication devices
(communication chips) are mounted on the same board in one
electronic appliance, and each carrier carrier frequency is
set in advance. A case is assumed where more than three sets
15 circuit boardinside the electronicappliance withno respect
to the arrangement, the directivity of the radio wave or the
like.
[0075]
For example, in Fig. 12, a case where 3-band frequency
20 arrangement is applied is shown. As shown in (A) of Fig. 12,
a signal transmission device 1A is hous@d on a circuit board
701insideanelectronicappliance751, thesignaltransmission
device 1A including three sets regarding
transmission/reception, namely, a set of a communication
25 device 710 - 1 having a function of a transmitter and a
communication device 810 1 having a function of a receiver,
a set of a communication device 710 2 having a - function of
a transmitter and a communication device 810 - 2 having a
function of a receiver, and a set of a communication device
30 710 - 3 having a function of a transmitter and a communication
device 810 - 3 having a function of a receiver.
[0076]
As shown in (B) in Fig. 12, each of the communication
device 710 - 1, the communication device 710 - 2 and the
communicationdevice710 - 3includesamodulationtargetsignal
5 processing unit 712, a signal amplifier unit 713, a
transmission-side local oscillator 714 for generating a
carrier frequency F - n (where n is any of 1, 2 and 3) as a local
frequency, a frequency mixing unit 715 (a so-called mixer),
and an output amplifier unit 717, and a transmission antenna
10 718 is connected to the output amplifier unit 717. The
transmission-side local oscillator 714 and the frequency
mixingunit715 formamodulationunit. Themodulationtarget
signal processing unit 712 includes a low pass filter, for
example, andrestrictsthereceptionbandwidthofamodulation
15 signal. The signal amplifier unit 713 gain multiplies the
amplitudeofasignaloutputfromthemodulationtargetsignal
processing unit 712. The frequency mixing unit 715 performs
a modulation process by multiplying a signal output from the
signal amplifier unit 713 and a carrier signal (a carrier
20 frequency F - n) from the transmission-side local oscillator
714. The output amplifier unit 717 gain multiplies the
amplitude of a signalmodulatedbythe frequencymixing unit
715.
[0077]
25 As shown in (B) in Fig. 12, each of the communication
device 810 - 1, the communication device 810 - 2 and the
communication device 810 - 3 includes an input amplifier unit
812, a receiving-side local oscillator 814 for generating a
carrierfrequencyF - n, afrequencymixingunit815 (aso-called
30 mixer), ademodulatedsignalprocessingunit816 (forexample,
a low pass filter), and an output amplifier unit 817, and a
receivingantenna 811is connectedtothe input amplifierunit
812. The receiving-side local oscillator 814 and the
frequencymixingunit815 formademodulationunit. Theinput
amplifierunit812 gainmultipliestheamplitudeofareceived
5 signalreceivedbythe receiving antenna 811. The frequency
mixingunit815performsademodulationprocessbymultiplying
a received signal output from the input amplifier unit 812
and a carrier signal (a carrier frequency F - n) from the
receiving-side localoscillator 814. The demodulatedsignal
10 processing unit 816 includes a low pass filter, for example,
andrestrictsthereceptionbandwidthofademodulatedsignal.
The output amplifier unit 817 gain multiplies the amplitude
of a demodulated signal output fromthe demodulated signal
processing unit 816.
15 [0078]
As shown in (B) in Fig. 12, a modulation signal S711
in a whole reception bandwidth Bwl is input to the communication
device 710 - 1, a n d i s m o d u l a t e d b y t h e t r a n s m i s s i o n - s i d e l o c a l
oscillator 714 at a carrier frequency F - 1, and a radio wave
20 is transmitted from the transmission antenna 718. The
receivingantenna811receivesthismodulatedsignalandinputs
the same tothe communication device 810 - 1, and demodulation
is performed at the demodulation unit, and a demodulated signal
S811 is output from the output amplifier unit 817.
25 [0079]
As shown in (B) in Fig. 12, a modulation signal S721
in a whole receptionbandwidthBw2 is input to the communication
device 710 - 2, a n d i s m o d u l a t e d b y t h e t r a n s m i s s i o n - s i d e l o c a l
oscillator 714 at a carrier frequency F - 2, and a radio wave
30 is transmitted from the transmission antenna 718. The
receivingantenna811receivesthismodulatedsignalandinputs
the same tothe communication device 810 2, -2 , and demodulation
is performed at the demodulation unit, and a demodulated signal
5821 is output from the output amplifier unit 817.
[0080]
5 As shown in (B) in Fig. 12, a modulation signal S731
ina whole reception bandwidthBw3 is input to the communication
device 710 - 3, a n d i s m o d u l a t e d b y t h e t r a n s m i s s i o n - s i d e l o c a l
oscillator 714 at a carrier frequency F- 3 , and a radio wave
is transmitted from the transmission antenna 718. The
10 receivingantenna811receivesthismodulatedsignalandinputs
the same to the communication device 810- 3 , and demodulation
is performedat the demodulationunit, and a demodulated signal
S831 is output from the output amplifier unit 817.
[ 00811
Here, as shown in (C) in Fig. 12, as the frequency
arrangementofthecarrierfrequencyF- 1 , thecarrierfrequency
F- 2 and the carrier frequency F- 3 , the carrier frequency F- 1
and the carrier frequency F- 2 are arranged with a frequency
difference Dl2 therebetween, and the carrier frequency F- 2
20 and the carrier frequency F- 3 are arranged with a frequency
differenceD23 (=D12) therebetween. Thebandgapbetweenthe
modulated signal based on the carrier frequency F- 1 and the
modulated signal based on the carrier frequency F- 2 is H12,
and the band gap between the modulated signal based on the
25 carrier frequency F- 2 and the modulated signal based on the
carrier frequency F 3 is H23 (=H12) . -
[0082]
In the case of such a frequency arrangement, the frequency
use efficiency is high, but cross modulation may become a
30 problem. For example, if signals at two carrier frequencies
not related to a desired wave (self station) are received and
input t o a non-linear amplifier c i r c u i t or frequency mixer
c i r c u i t , a s i g n a l of a d i f f e r e n c e between the two c a r r i e r
frequencies (an i n t e r f e r i n g wave component) is also output.
In the case of the frequency arrangement shown i n (C) i n Fig.
5 12, the difference between the two c a r r i e r frequencies is
present near the frequency of the desired wave, and there is
the problem of "intermodulation d i s t o r t i o n " where the
i n t e r f e r i n g wave component is a l s o demodulated. Typically,
when signals a t a p l u r a l i t y of frequencies adjacent t o the
10 r e c e i v i n g b a n d o f t h e s e l f s t a t i o n a r e r e c e i v e d , i f the l i n e a r
performance of the amplifier c i r c u i t or the frequency mixer
circuitispoor,third-orderdistortionoccursinthereceiving
band (normally, onlythe first-order componentof amodulated
s i g n a l h a s t o b e t a k e n i n t o a c c o u n t ) , andthe r e c e p t i o n q u a l i t y
15 is s i g n i f i c a n t l y reduced.
[0083]
In such a case, by applying the present embodiment (the
b a s i c s t r u c t u r e , orModifiedStructure1orModifiedStructure
2, or Example 1 or Example 2 ) ,
20 [0084]
Heretofore, embodiments have been described with
respect t o the technology disclosed i n the present
specification,butthetechnicalscopedescribedintheclaims
is not limited t o the embodiments described above. Various
25 a l t e r a t i o n s or modifications may be made t o the embodiments
described above without departing from the g i s t of the
technology d i s c l o s e d i n t h e p r e s e n t s p e c i f i c a t i o n , andmodes
where s u c h a l t e r a t i o n s ormodifications aremade are included
i n the t e c h n i c a l scope of the technology disclosed i n the
30 present s p e c i f i c a t i o n . The embodiments described above do
not l i m i t the technology according t o t h e claims, andnot a l l
of the combinations of the features described in the
embodiments are indispensable for solvingtheproblems which
are the targets of the technology disclosed in the present
specification. The embodiments described above include
5 technologies forvarious stages, andvarioustechnologiesmay
be extracted by appropriately combining a plurality of
structural elements that are disclosed. If effects for the
problems that are the targets of the technology disclosed in
the present specification may be achieved even if some
10 structuralelementsareeliminatedfromtheentirestructural
elements shown in the embodiments, structures where the
structural elements are eliminated may also be extracted as
the technologies disclosed in the present specification.
[0085]
15 Based on the description of the embodiments above, the
following technologies, for example, may be extracted in
additiontothetechnologiesaccordingtotheclaimsdescribed
in the scope of claims. They are listed as follows.
[Supplemental Note 11
20 A gain control circuit including:
a first amplifier for amplifying an input signal; and
a signal determination unit for determining the input
signal to be input to the first amplifier, and controlling
an amplification factor of the first amplifier based on a
25 determination result.
[Supplemental Note 21
The gaincontrol circuit according to SupplementalNote
1
in which the input signal includes a desired wave and
30 an interfering wave, and
in which the signal determination unit determines each
of levels of the desired wave and the interfering wave.
[Supplemental Note 31
The gaincontrol circuit according to SupplementalNote
2, in which the signal determination unit determines, while
5 notdistinguishingbetween, the level ofthe desiredwave and
the level of the interfering wave.
[Supplemental Note 41
The gaincontrol circuit accordingto SupplementalNote
3 ,
10 in which the signal determination unit includes
a second amplifier for amplifying the input signal
input to the first amplifier, and
a level detection unit for detecting a level of
an output signal of the second amplifier, and
15 inwhichtheamplification factor ofthe first amplifier
and an amplification factor of the second amplifier are
controlled with a relative relationship.
[Supplemental Note 51
The gaincontrol circuit according to SupplementalNote
20 4, in which the amplification factor of the first amplifier
and the amplification factor of the second amplifier are
controlled to be same.
[Supplemental Note 61
The gaincontrol circuit according to SupplementalNote
25 4 or5, inwhichthe secondamplifier isproportionally smaller
in size than the first amplifier.
[Supplemental Note 71
The gaincontrol circuit according to SupplementalNote
2,
in which the signal determination unit includes
a first level detection unit for detecting the
level of the desired wave,
a second level detection unit for detecting the
level of the interfering wave, and
a level determination unit for controlling the
amplificationfactorofthefirstamplifierbasedondetection
results of the first level detection unit and the second
detection unit.
[Supplemental Note 81
The gain control circuit according to any one of
10 Supplemental Notes 4 to 7, in which the amplification factor
of the first amplifier is controlled with a fixed difference
in the levels of the desired wave and the interfering wave.
[Supplemental Note 91
The gain control circuit according to any one of
15 Supplemental Notes 1 to 8, in which a bandwidth limitation
unit is provided for an output of the first amplifier, for
limiting a bandwidth of an output signal to a bandwidth of
the desired wave.
[Supplemental Note 101
20 The gain control circuit according to any one of
Supplemental Notes 1to 9, in which a control loop is provided
at a following stage of the first amplifier, for detecting
a l e v e l o f a s i g n a l c o r r e s p o n d i n g t o a l e v e l o f a n o u t p u t s i g n a l
ofthefirstamplifierandcontrollingtheamplificationfactor
25 of the first amplifier.
[Supplemental Notell]
. - -
A communication device including:
a first amplifier for amplifying a received signal;
a receivingunit for performing a receivingprocess based
30 on a signal output from the first amplifier; and
asignaldeterminationunitfordeterminingthereceived
signal to be input to the first amplifier, and controlling
an amplification factor of the first amplifier based on a
determination result.
[Supplemental Note 121
5 An electronic appliance including:
a first amplifier for amplifying an input signal;
a signal processing unit for performing signal
processingbasedon a signal output fromthe first amplifier;
and
10 a signal determination unit for determining the input
signal to be input to the first amplifier, and controlling
an amplification factor of the first amplifier based on a
determination result.
[Supplemental Note 131
An electronic appliance including:
a first amplifier for amplifying a received signal;
a receivingunit for performing a receivingprocess based
on a signal output from the first amplifier; and
asignaldeterminationunitfordeterminingthereceived
20 signal to be input to the first amplifier, and controlling
an amplification factor of the first amplifier based on a
determination result.
[Supplemental Note 141
TheelectronicapplianceaccordingtoSupplementalNote
25 13, including:
a pluralityof communicationunits includingthe first
amplifier, the receiving unit, and the signal determination
unit.
[Supplemental Note 151
A gain control method including:
determining an input signal to be input to a first
amplifier for amplifying the input signal, and controlling
anamplification factor of the first amplifierbya feed forward
system based on a determination result.
[Supplemental Note 161
5 The gain control method according to Supplemental Note
15,
in which the input signal includes a desired wave and
an interfering wave, and
inwhichthe amplification factorofthe first amplifier
10 is controlledwitha fixeddifference inlevels ofthe desired
wave and the interfering wave.
REFERENCE SIGNS LIST
[0086]
15 1 Signal processing circuit
10 Gain control circuit
12 Variable amplifier unit
14 Signal processing unit
20 Signal determination unit
20 22 Variable amplifier unit
24 Level detection unit
26A Level detection unit
26B Level detection unit
28 Level determination unit

CLAIMS
1. A gain control circuit comprising:
a first amplifier for amplifying an input signal; and
a signal determination unit for determining the input
signal to be input to the first amplifier, and controlling
an amplification factor of the first amplifier based on a
determination result.
10 2. The gain control circuit according to claim 1,
wherein the input signal includes a desired wave and
an interfering wave, and
wherein the signal determination unit determines each
of levels of the desired wave and the interfering wave.
15
3 . The gain control circuit according to claim 2, wherein
the signal determination unit determines, while not
distinguishingbetween, the level ofthe desiredwave andthe
level of the interfering wave.
20
4. The gain control circuit according to claim 3,
wherein the signal determination unit includes
a second amplifier for amplifying the input signal
input to the first amplifier, and
25 a level detection unit for detecting a level of
an output signal of the second amplifier, and
whereintheamplification factor ofthe first amplifier
and an amplification factor of the second amplifier are
controlled with a relative relationship.
30
5. The gain control circuit according to claim 4, wherein
the amplification factor ofthe first amplifier is controlled
with a fixed difference in the levels of the desired wave and
the interfering wave.
5 6. The gain control circuit according to claim 5, wherein
the amplification factor of the first amplifier and the
amplification factor of the second amplifier are controlled
to be same.
10 7. The gain control circuit according to claim 6, wherein
the second amplifier is proportionally smaller in size than
the first amplifier.
8. The gain control circuit according to claim 2,
wherein the signal determination unit includes
a first level detection unit for detecting the
level of the desired wave,
a second level detection unit for detecting the
level of the interfering wave, and
20 a level determination unit for controlling the
mplificationfactorofthefirstamplifierbasedondetection
results of the first level detection unit and the second
detection unit.
25 9. The gain control circuit according to claim 8, wherein
the amplification factor ofthe first amplifier is controlled
with a fixed difference in the levels of the desired wave and
the interfering wave.
30 10. The gain control circuit according to claim 1, wherein
a bandwidth limitation unit is provided for an output of the
first amplifier, for limiting abandwidthof an output signal
to a bandwidth of the desired wave.
11. The gain control circuit according to claim 1, wherein
5 a control loop is provided at a following stage of the first
amplifier, for detecting a level of a signal corresponding
to a level of an output signal of the first amplifier and
controlling the. amplification factor ofthe first amplifier.
10 12. A.comrnunication device comprising:
a first amplifier for amplifying a received signal;
a receivingunit forperforminga receivingprocess based
on a signal output from the first amplifier; and
asignaldeterminationunitfordeterminingthereceived
15 signal to be input to the first amplifier, and controlling
an amplification factor of the first amplifier based on a
determination result.
13. An electronic appliance comprising:
a first amplifier for amplifying an input signal;
a signal processing unit for performing signal
processing based on a signal output fromthe first amplifier;
and
a signal determination unit for determining the input
25 signal to be input to the first amplifier, and controlling
an amplification factor of the first amplifier based on a
determination result.
14. An electronic appliance comprising:
a first amplifier for amplifying a received signal;
a receivingunit for performing a receivingprocess based
on a signal output from the first amplifier; and
a signal determination unit for determining the received
signal to be input to the first amplifier, and controlling,
an amplification factor of the first amplifier based on a
5 determination result.
15. The electronic appliance according to claim 14,
comprising:
aplurality of communicationunits includingthe first
10 amplifier, the receiving unit, and the signal determination
unit.
16. A gain control method comprising:
determining an input signal to be input to a first
15 amplifier for amplifying the input signal, and controlling
anamplification factor of the first amplifierbya feed forward
system based on a determination result.
17. The gain control method according to claim 16,
20 wherein the input signal includes a desired wave and
an interfering wave, and
whereintheamplification factorofthe first amplifier
is controlledwitha fixeddifference inlevels ofthe desired
wave and the interfering wave.