Duplexer/Multiplexer Having Filters That Include At Least One Band Reject Filter
Technical Field
[0001 ] The invention relates generally to a duplexer/multiplexer that has filters
including at least one band reject filter.
Background
[0002] Wireless communications devices, such as wireless terminals or wireless base
stations, include wireless transceivers to perform wireless communications, such as radio
frequency (RF) communications. A wireless communications device can include a duplexer
(or multiplexer) to allow simultaneous transmission and reception in different frequency
bands using the same antenna while ensuring that relatively high power transmit signals
transmitted by the wireless transceiver do not swamp relatively low power receive signals
received by the wireless transceiver.
[0003] A duplexer has an antenna port (for connection to an antenna), a receive port (to
receive a signal from the antenna port) and transmit port (to transmit a signal to the antenna
port). A multiplexer has an antenna port and one or more receive ports and one or more
transmit ports. Note that a duplexer is a type of multiplexer.
[0004] A duplexer or multiplexer can include bandpass filters implemented with
acoustic-type resonators. Conventional duplexers/multiplexers including bandpass filters
implemented with acoustic-type resonators have relatively limited maximum power handling
capabilities, which can prevent use of such conventional duplexers/multiplexers in
high-power, high-frequency applications, such as in Worldwide Interoperability for
Microwave Access (WiMax) applications or Long-Term Evolution (LTE) applications.
WiMax is based on the IEEE (Institute of Electrical and Electronics Engineers) 802.16
Standard (as amended by the IEEE 802.16e or IEEE 802.16e-005). WiMax is able to provide
broadband wireless connectivity for mobile stations at relatively high data rates. LTE is a
technology that provides an enhancement to the Universal Mobile Telecommunications
System (UMTS) technology. LTE is described in 3GPP TS 23.401 and 23.402.
[0005] In conventional duplexers/multiplexers that employ bandpass filters with
acoustic-type resonators, high-power and high-frequency communications can cause
ultrasonic vibration in metallic electrodes of the acoustic-type resonators, which can lead to a
phenomenon referred to as acousto-migration, in which metal grain boundaries in the
resonators migrate. The acousto-migration phenomenon can reduce the lifetime of the filters.
Therefore, such filters may not survive for a desirable length of time at desired power levels
and frequencies that may be required in certain types of wireless networks.
Summary
[0006] In general, according to an embodiment, a wireless communications device
includes an antenna and a multi-port path selection structure (e.g., a duplexer or multiplexer)
having an antenna port connected to the antenna, and plural ports connected to respective
receive and transmit paths of the wireless communications device. The multi-port path
selection structure has a band reject filter connected to the transmit path and a second filter
connected to the receive path.
[0007] Other or alternative features will become apparent from the following
description, from the drawings, and from the claims.
Brief Description Of The Drawings
[0008] Fig. 1 is a block diagram of a wireless communications device that includes a
duplexer or multiplexer according to an embodiment.
[0009] Fig. 2 is a schematic diagram of a conventional duplexer that includes bandpass
filters connected to a receive port and a transmit port of the duplexer.
[0010] Fig. 3 is a graph illustrating the transmit and receive bands provided by the
bandpass filters of Fig. 2.
[0011] Fig. 4 is a schematic diagram of a duplexer that includes a receive filter
connected to a receive port, and a band reject filter connected to a transmit port, according to
an embodiment.
[0012] Fig. 5 is a graph illustrating the transmit and receive bands provided by the
filters of Fig. 4.
[0013] Fig. 6 illustrates acoustic-type resonators arranged in a ladder-type configuration
for implementing a band reject filter for use in a duplexer or multiplexer according to an
embodiment.
[0014] Fig. 7 is a graph illustrating the resonance and anti-resonance frequencies of the
resonators of Fig. 6.
[0015] Fig. 8 is a schematic diagram of a duplexer according to another embodiment
that includes a band reject filter connected to a receive port, and a band reject filter connected
to a transmit port.
[0016] Fig. 9 is a graph illustrating the transmit and receive bands provided by the
filters of Fig. 8.
[0017] Fig. 10 is a schematic diagram of a multiplexer that includes bandpass filters
connected to receive ports, and band reject filters connected to transmit ports, according to
another embodiment.
[0018] Fig. 11 is a graph illustrating the transmit and receive bands provided by the
filters of Fig. 10.
[0019] Fig. 12 is a schematic diagram of a multiplexer that includes bandpass filters
connected to receive ports, and a band reject filter connected to a transmit port, according to a
further embodiment.
[0020] Fig. 13 is a graph illustrating the transmit and receive bands provided by the
filters of Fig. 12.
[0021 ] Fig. 14 is a schematic diagram of a band reject filter formed of cascaded band
reject filter units to provide multiple reject bands, according to an embodiment.
[0022] Fig. 15 is a graph illustrating the multiple reject bands provided by the band
reject filter of Fig. 14.
[0023] Fig. 16 is a schematic diagram of a duplexer according to a further embodiment
that includes a bandpass filter connected to a receive port, and a band reject filter connected
to a transmit port.
[0024] Fig. 17 is a graph illustrating the transmit and receive bands provided by the
filters of Fig. 16.
[0025] Fig. 18 is a schematic diagram of a duplexer according to yet a further
embodiment that includes a band reject filter connected to a receive port, and a band reject
filter connected to a transmit port.
[0026] Fig. 19 is a graph illustrating the transmit and receive bands provided by the
filters of Fig. 18.
[0027] Fig. 20 is a schematic diagram of a multiplexer that includes a band reject filter
connected to a receive port, and a band reject filter connected to a transmit port, according to
a further embodiment.
[0028] Fig. 21 is a graph illustrating the transmit and receive bands provided by the
filters of Fig. 20.
Detailed Description
[0029] In the following description, numerous details are set forth to provide an
understanding of some embodiments. However, it will be understood by those skilled in the
art that some embodiments may be practiced without these details and that numerous
variations or modifications from the described embodiments may be possible.
[0030] In accordance with some embodiments, a multi-port path selection structure for
use in a wireless communications device is provided that has an antenna port connected to an
antenna of the wireless communications device, and plural ports connected to respective
receive and transmit paths of the wireless communications device. Examples of the wireless
communications device include a wireless terminal (mobile station), a wireless base station,
and other devices that are capable of performing wireless communications.
[0031 ] A multi-port path selection structure can be a duplexer or a multiplexer.
Generally, a multi-port path selection structure includes circuitry to selectively route signals
that are communicated along transmit and receive paths of the wireless communications
device. Such circuitry can receive a signal from the antenna of the wireless communications
device, and route the received signal to the receive path of the wireless communications
device. Similarly, the multi-port path selection structure can route a transmitted signal from
transmission circuitry in the transmit path of the wireless communications device to the
antenna. The "routing" of the received and transmitted signals is accomplished by use of
filters provided in the multi-port path selection structure, where the filters are designed to
pass signals in respective receive and transmit frequency bands. In accordance with some
embodiments, the filter connected to the transmit path is a band reject filter, and the filter
connected to the receive path can either be a bandpass filter or band reject filter.
[0032] A duplexer has an antenna port connected to the antenna of the wireless
communications device, and a single receive port and a single transmit port for connection to
respective receive and transmit paths of the wireless communications device. A multiplexer
includes an antenna port for connection to the antenna of the wireless communications
device, and two or more ports connected to respective receive and transmit paths. Note that a
duplexer is a type of multiplexer.
[0033] A multiplexer can have plural receive ports (corresponding to different receive
frequency bands) and/or plural transmit ports (corresponding to different transmit frequency
bands). The multiple receive ports can be connected to one or plural receive paths in the
wireless communications device. The multiple transmit ports can be connected to one or
plural transmit paths in the wireless communications device. Note that it is possible for
multiple receive frequency bands and/or multiple transmit frequency bands to share just one
receive path or transmit path, respectively, since a wireless communications device normally
operates at just a single receive or transmit frequency band at any given time. Alternatively,
separate paths in the wireless communications device can be provided for different receive
frequency bands or different transmit frequency bands.
[0034] Fig. 1 illustrates an exemplary wireless communications device 100 that
includes a duplexer or multiplexer 102 according to an embodiment. In the ensuing
discussion, reference is made to "multiplexer" 102, although it is to be understood that the
discussion applies equally to a duplexer. The wireless communications device 100 has an
antenna 104 for communicating radio frequency (RF) signals with another communications
device. For example, the wireless communications device 100 can be a wireless terminal
(e.g., mobile station) to communicate wirelessly with a wireless base station. Alternatively,
the wireless communications device 100 can be base station for communicating with a
wireless terminal.
[0035] The wireless communications device can be used in a wireless communications
network, such as a WiMax (Worldwide Interoperability for Microwave Access) network, a
Long-Term Evaluation (LTE) network, or any other type of network. Reference to LTE is to
any technology based on LTE, such as defined by current standards 3GPP TS 23.401 and
23.402 or any subsequent standard. Reference to LTE can also refer to any subsequent
standard derived from an evolution of LTE, whether or not such subsequent standard is
referred to as "LTE" by name.
[0036] The multiplexer 102 has an antenna port 106 that is connected to the antenna
104. The antenna port 106 of the multiplexer 102 is "connected" to the antenna 104 either
directly or indirectly (through other circuitry).
[0037] The multiplexer also has a receive port 108 for connection to a receive path 110
of the wireless communications device 100, and a transmit port 112 for connection to a
transmit path 114 of the wireless communications device. The receive path 110 includes
receive circuitry 116 to receive a signal from the antenna 104 through the multiplexer 102.
The transmit path 114 includes transmit circuitry 118 to generate a transmit signal to be sent
through the multiplexer 102 onto the antenna 104.
[0038] The multiplexer 102 has filters 120 and 122 for passing signals in the receive
and transmit frequency bands, respectively. Also shown in dashed profile is another filter
124 and another port 126, where the other filter 124 and port 126 can be connected to a
transmit path or a receive path, depending upon the specific configuration of the wireless
communications device 100.
[0039] A conventional duplexer 10 is depicted in Fig. 2, where the conventional
duplexer 10 has an antenna port 12, a receive port 14 (that is connected to a receive path of a
wireless communications device), and a transmit port 16 (that is connected to a transmit path
of the wireless communications device). The conventional duplexer 10 uses bandpass filters
(BPFs) 18 and 20 connected to the receive and transmit ports 14 and 16, respectively. The
bandpass filters 18 and 20 can be implemented with acoustic-type resonators.
[0040] Fig. 3 is a graph of the transmit frequency band 22 and receive frequency band
24 provided by the bandpass filters 20 and 18, respectively. The graph of Fig. 3 plots
insertion loss (in terms of decibel or dB) as a function of frequency. Insertion loss is the
decrease in signal power resulting from insertion of a device in a communications path. As
discussed above, the bandpass filters 18 and 20 of a conventional duplexer such as duplexer
10 are subject to deterioration caused by the acousto-migration phenomenon at high power
and high frequencies.
[0041] In accordance with some embodiments, instead of using bandpass filters 18 and
20 in the duplexer 10 as conventionally done, a duplexer 200 (depicted in Fig. 4) can be
provided that includes a band reject filter 202 connected to a transmit port of the duplexer
200, and a receive filter 204 connected to a receive port of the duplexer 200. Both the band
reject filter 202 and receive filter 204 are connected to an antenna port. The receive filter 204
can either be a bandpass filter or a band reject filter, in accordance with some embodiments.
[0042] Typically, the transmit signals that are sent from the transmit port to the antenna
port through the duplexer 200 are associated with relatively high power, while the receive
signals communicated from the antenna port to the receive port through the duplexer 200 are
associated with relatively low power. The receive filter 204 operates to protect the receive
port (and receive circuitry connected to the receive port) against the high-power transmit
signals communicated through the duplexer 200.
[0043] Note that with the band reject filter 202, the acoustic vibration is relatively
strong in the reject band, but relatively weak in the pass band of the band reject filter. This
enables the band reject filter 202 to handle relatively high power transmit signals with
reduced acousto-migration issues. Moreover, another characteristic of a band reject filter is
that it has lower phase distortion and less ripple in the pass band, as compared to a bandpass
filter.
[0044] Assuming the receive filter 204 is implemented with a bandpass filter, then the
receive and transmit frequency bands are depicted in Fig. 5, which plots insertion loss as a
function of frequency. The bandpass filter 204 provides a pass band 302—any signal having
a frequency below or above the pass band 302 is attenuated or rejected by the bandpass filter
204. The band reject filter 202 provides a reject band 304—any signal having a frequency
within the reject band 304 is attenuated or rejected, and any signal having a frequency above
or below the reject band 304 is passed through the band reject filter 202. The pass band 302
and reject band 304 of Fig. 5 overlap. The pass band for the transmit path provided by the
band reject filter 202 is represented by reference numerals 306A and 306B, which are on the
two sides of the reject band 304 (and of the pass band 302 provided by the bandpass filter
204).
[0045] In the receive direction, the bandpass filter 204 passes a signal from the antenna
port to the receive port of the duplexer 200 if the signal has a frequency within the receive
band 302. On the other hand, in the transmit direction, the band reject filter 202 passes a
signal having a frequency outside the reject band 304 through the band reject filter 202 from
the transmit port to the antenna port.
[0046] A band reject filter can be implemented with acoustic-type resonators RES1 and
RES2 arranged in a ladder-type configuration, as depicted in Fig. 6. The ladder-type
configuration includes a first acoustic-type resonator RES1 (referred to as "series resonator")
connected in series between two ports PORT1 and PORT2, and a second acoustic-type
resonator RES2 (referred to as "shunt resonator") connected between PORT2 and ground.
Note that in the ladder-type configuration, there can be two (or more) series resonators
between PORT1 and PORT2, and two (or more) shunt resonators connected between nodes
of the filter and ground.
[0047] Each of the resonators RES 1 and RES2 can be any one of a surface acoustic
wave (SAW) resonator, a thin film bulk acoustic resonator (FBAR), a bulk acoustic wave
(BAW) resonator, or any other type of acoustic-type resonator. The BAW resonator can be a
surface mounted resonator (SMR)-type BAW resonator.
[0048] The series resonator RES1 of Fig. 6 is designed to present a high impedance at
the reject band 304 of interest. The series resonator RES1 is configured to be anti-resonance
at a reject band frequency (the anti-resonance frequency for the series resonator RES1 is
depicted in Fig. 7, according to one example), which means that the series resonator RES1
presents a high impedance at the anti-resonance frequency. In contrast, the shunt resonator
RES2 is configured to provide a low impedance at a reject band frequency (a frequency
within reject band 304). This is achieved by designing the shunt resonator RES2 to be at or
near resonance in the reject band 304. The resonance frequency of the shunt resonator RES2
is represented as 404 in Fig. 7.
[0049] The resonance frequency of series resonator RES 1 is represented as 406 in Fig.
7, while the anti-resonance frequency of the shunt resonator RES2 is represented as 408 in
Fig. 7. The resonance frequency 406 of the series resonator RES1 is immediately below the
reject band 304 and is between the pass band 306A and the reject band 304 of the band reject
filter—at the resonance frequency 406, the series resonator RES1 has a low impedance. In
the pass band 306A, the shunt resonator RES2 simply presents a capacitive load to ground.
[0050] The anti-resonance frequency 408 of the shunt resonator RES2 is immediately
above the reject band 304 and is between the reject band 304 and the pass band 306B—at the
anti-resonance frequency 408, the shunt resonator RES2 presents a high impedance to
ground. However, in the pass band 306B, the series resonator RES1 presents a capacitive
series impedance. At frequencies much above or below the reject band 304, the series and
shunt resonators simply behave as high-Q capacitors.
[0051 ] In this manner, the overall effect of the filter provided by resonators RES 1 and
RES2 is to provide a high impedance for signals passing between ports PORT1 and PORT2
having frequencies in the reject band 304.
[0052] Fig. 8 shows an implementation of the duplexer 200 in which the receive filter
204 is implemented with a band reject filter (instead of a bandpass filter as depicted in Fig.
4). In this configuration, both the receive and transmit ports of the duplexer 200 are
connected to band reject filters.
[0053] As depicted in Fig. 9, the band reject filter 202 for the transmit port is associated
with the transmit reject band 304, while the band reject filter 204 for the receive port has a
receive reject band 402. The band reject filter 204 allows a signal having a frequency outside
the receive reject band 402 to be passed through the band reject filter 204, whereas the band
reject filter 202 allows a signal having a frequency outside the transmit reject band 304 to
pass through the band reject filter 202.
[0054] Fig. 10 shows a multiplexer 500 that has an antenna port, two receive ports
(RX1 port and RX2 port), and two transmit ports (TX1 port and TX2 port). Note that the two
receive ports can be connected to just one receive path (and the associated receive circuitry,
such as circuitry 116 in Fig. 1), or alternatively, the two receive ports can be connected to two
different receive paths. Similarly, the transmit ports can be connected to just one transmit
path (and the associated transmit circuitry, such as 118 in Fig. 1), or alternatively, the
transmit ports can be connected to multiple transmit paths. In other implementations, the
multiplexer 500 can have more than two transmit ports and/or more than two receive ports.
The different receive ports are associated with different receive frequency bands, and the
different transmit ports are associated with different transmit frequency bands.
[0055] The receive ports of the multiplexer 500 are connected to corresponding
bandpass filters 502 and 504, whereas the transmit ports are connected to band reject filters
506 and 508. Each of the bandpass filters and band reject filters 502, 504, 506, and 508 is
connected to the antenna port of the multiplexer 500.
[0056] As depicted in the graph of Fig. 11, a receive pass band 602 corresponds to the
pass band provided by the bandpass filter 502 for the RX1 port, and a receive pass band 604
is provided by the bandpass filter 504 for the RX2 port.
[0057] A transmit reject band 606 is provided by the band reject filter 506 for the TX1
port, and a transmit reject band 608 is provided by the band reject filter 508 for the TX2 port.
[0058] While Fig. 10 shows separate band reject filters 506 and 508 to provide two
respective reject bands 606 and 608 (Fig. 11), note that a single band reject filter can be used
instead, such as band reject filter 702 in a multiplexer 700 depicted in Fig. 12, to provide
multiple reject bands. The multiplexer 700 has one transmit port connected to the band reject
filter 702.
[0059] The chart of Fig. 13 depicts receive pass bands 602 and 604 and transmit reject
bands 606 and 608 that are the same as those depicted in Fig. 11, except that the reject bands
606 and 608 of Fig. 13 are provided by one band reject filter 702 (Fig. 12), instead of two
distinct band reject filters 506 and 508 (Fig. 10).
[0060] The band reject filter 702 includes multiple cascaded band reject filter units to
provide the multiple reject bands 606 and 608. Cascading multiple band reject filter units
means that the band reject filter units are connected in series. For example, as depicted in
Fig. 14, three band reject filter units 802, 804, and 806 are connected in series (cascaded)
between PORT1 and PORT 2. Each of the band reject filter units 802, 804, and 806 defines a
respective reject band, as depicted in Fig. 15. The band reject filter unit 802 provides reject
band 902, the band reject filter unit 804 provides reject band 904, and the band reject filter
unit 806 provides reject band 906. Each of the band reject filter units contains an
arrangement of resonators; in the embodiment of Fig. 14, each band reject filter unit includes
two series resonators and two shunt resonators arranged in the ladder-type configuration. To
provide the two transmit reject bands 606 and 608 of Fig. 13, two band reject filter units (e.g.,
any two of 802, 804, and 806) can be connected in series (cascaded) to form the band reject
filter 702. In other implementations, the resonators of all band reject filter units can be
arranged in a mixed configuration for their locations in the ladder-type structure, namely each
of the band reject filter units can have its resonators distributed in the entire filter structure
and does not have to have all its resonators arranged together.
[0061] Fig. 16 shows an alternative embodiment of a duplexer 1000 that has a band
reject filter 1002 for the transmit port that provides multiple reject bands 1102, 1104, and
1106 (Fig. 17). The band reject filter 1002 is thus able to block signals having frequencies in
any of the reject bands 1102, 1104, and 1106.
[0062] A bandpass filter 1004 connected to the receive port of the duplexer 1000
provides a pass band 1108 (Fig. 17).
[0063] Fig. 18 shows another embodiment of a duplexer 1200 that includes band reject
filter 1202 connected to a receive port of the duplexer 1200, and band reject filter 1204
connected to the transmit port of the duplexer 1200. Each of the band reject filters 1202 and
1204 provides multiple reject bands, as depicted in Fig. 19. The band reject filter 1202 for
the receive port provides reject bands 1312, 1310, and 1314, while the band reject filter 1204
for the transmit port provides reject bands 1304,1302, and 1306.
[0064] Fig. 20 shows another embodiment of a multiplexer 1300 that includes a first
band reject filter 1302 for the RX1, RX2,..., RXn port, and a second band reject filter 1304
for the TX1, TX2,..., TXn port. The band reject filter 1302 provides reject bands 1402,
1404, and 1406, whereas the band reject filter 1304 provides reject bands 1408,1410, and
1412, as depicted in Fig. 21.
[0065] In the foregoing description, numerous details are set forth to provide an
understanding of the present invention. However, it will be understood by those skilled in the
art that the present invention may be practiced without these details. While the invention has
been disclosed with respect to a limited number of embodiments, those skilled in the art will
appreciate numerous modifications and variations therefrom. It is intended that the appended
claims cover such modifications and variations as fall within the true spirit and scope of the
invention.
What is claimed is:
1. A wireless communications device comprising:
an antenna;
a multi-port path selection structure having an antenna port connected to the antenna,
and plural ports connected to respective one or more receive and transmit paths of the
wireless communications device,
wherein the multi-port path selection structure has a transmit band reject filter
connected to the transmit path and a second filter connected to the receive path.
2. The wireless communications device of claim 1, wherein the second filter comprises a
bandpass filter.
3. The wireless communications device of claim 2, wherein the multi-port path selection
structure further comprises another bandpass filter connected to the receive path.
4. The wireless communications device of claim 1, wherein the multi-port path selection
structure is a duplexer.
5. The wireless communications device of claim 1, wherein the multi-port path selection
structure is a multiplexer.
6. The wireless communications device of claim 1, wherein the wireless
communications device comprises a wireless mobile station.
7. The wireless communications device of claim 1, wherein the wireless
communications device comprises a wireless base station.
8. The wireless communications device of claim 1, wherein the transmit band reject
filter provides multiple reject bands.
9. The wireless communications device of claim 8, wherein the second filter comprises a
receive band reject filter.
10. The wireless communications device of claim 9, wherein the receive band reject filter

provides multiple reject bands.
11. The wireless communications device of claim 1, wherein the transmit band reject
filter includes acoustic-type resonators.
12. The wireless communications device of claim 11, wherein the acoustic-type
resonators are selected from among surface acoustic wave (SAW) resonators, thin film bulk
acoustic resonators (FBAR), and bulk acoustic wave (BAW) resonators.
13. The wireless communications device of claim 11, wherein the acoustic-type
resonators are arranged in a ladder-type configuration.
14. The wireless communications device of claim 1, wherein the transmit band reject
filter has relatively weak acoustic vibration in a pass band of the transmit band reject filter,
and relatively strong acoustic vibration in a reject band of the transmit band reject filter.
15. A wireless communications device comprising:
an antenna;
a multiplexer having an antenna port connected to the antenna, at least one receive
port connected to at least one receive path of the wireless communications device, and at least
one transmit port connected to at least one transmit path of the wireless communications
device,
wherein the multiplexer has a transmit band reject filter connected to the transmit port
and a second filter connected to the receive port.
16. The wireless communications device of claim 15, wherein the second filter comprises
a band reject filter.
17. The wireless communications device of claim 16, wherein the second band reject
filter provides multiple reject bands.
18. The wireless communications device of claim 15, wherein the transmit band reject
filter provides multiple reject bands.
19. The wireless communications device of claim 15, wherein the band reject filter
includes acoustic-type resonators.
20. A method of enabling wireless communications, comprising:
providing an antenna at a wireless communications device;
providing a multi-port path selection structure having an antenna port connected to the
antenna, and transmit and receive ports connected to respective transmit and receive paths of
the wireless communications device;
providing a transmit band reject filter to provide a reject band for the transmit port;
and
providing a second filter connected to the receive port.
21. The method of claim 20, wherein the second filter comprises a second band reject
filter.

A wireless communications device includes an antenna, a multi-port path selection structure having an antenna port connected to the antenna, and plural ports connected to respective one or more receive and transmit paths of the wireless communications device. The multi-port path selection structure has a transmit band reject filter connected to the transmit path and a second filter connnected to the receive path.