FORM 2
THE PATENTS ACT, 1970 [39 of 1970]
& THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(Section 10; Rule 13)
A SEMICONDUCTOR UNIT WITH PRECISE CONTROL OVER OUTPUT
PARAMETERS
KPIT Cummins Infosystems Ltd.,
35 and 36, Rajiv Gandhi Infotech Park,
Phase 1, MIDC, Hinjewadi,
Pune-411057, India
An Indian Company
The following specification describes the invention and the manner in which it is
to be performed

BACKGROUND OF THE INVENTION
In the semi conductors involved in the high speed transmitters, the phenomenon of variation of bias current of main driver is observed to be proportionate with respect to the variation of resistor used for current generation. The transmitter (Tx), receiver (Rx) on the chip termination resistors and bias current exhibit large variation due to large variation in sheet resistance of on chip resistors.
The output swing of the transmitter, is dependent on main driver bias current and transmitter, receiver termination resistors and are related by the expression, VOD = [RT-TX / (RT-TX + RT-TX + RT-RX)]X 1DRIVER X RT-RX
Hence, it is apparent from the nature of the expression that any variation in percentage of sheet resistance is reflected by further increase in percentage of the output swing. In general it has been observed that for a variation of sheet resistance in the ranges of ±15% and ±25%, the corresponding variation ranges in output swing are ±25% and ±55% respectively.
Such large scale variations in output swing have a negative effect on reception of signal at receiver end. The reception of degraded signal causes increase in Bit error

rate (BER). The occurrence of more bit errors causes bad picture quality due to bad video signals received for instance, when it comes to transmitting of video signals.
Attempts for achieving control over Common mode as discussed in LVDS 1/O Interface for Gb/s - per - Pin Operation in 0.35 - μ rn CMOS by Andrea Boni, Andrea Pierazzi and Davide Veechi ( IEEE journal of solid state circuits, Vol. 36, No. 4, April 2001) have the limitations such as lack of control over output swing variation. Similarly, drawbacks exist in existing prior art which attempt in solving the problem of achieving control over variation in output swing such as absence of feed back mechanism, employing open loop control techniques, non inclusion of local feedback within the driver side and instead taking feedback from receiver (Rx), or adopting multiple local feedback loops.
US Patent 6788116, while attempting to address this problem of checking variation in output swing, encounters drawbacks such as being unable to control output common mode of Low voltage differential signaling (LVDS). Also, it achieves positive results only in controlling pull up current which in turn causes mismatch in impedance levels of pull up and pull down structure. Further, US 6788116 fails to explain as how to achieve, summation or peak detection anywhere. Also, the architecture provided tries to control the top current source to correct swing variation. While this effort is made, in turn it would introduce large pull up and pull down mismatch of impedance levels thereby causing more reflections on line A major drawback in it is that it requires complementary peak detector architectures in its circuitry due to usage of positive (NMOS source follower) and negative (PMOS source follower) peak detectors used to detect V0H and VOL levels respectively. Such architectures will fail to correct variations in swing in cross corners.

Information relevant to attempts to address the problem can be found in US 5065055, US 694388, US 6600346, US 690422, US 7307458 and US6380797. However each one of these references suffers from one or more of the drawbacks listed above.
For the foregoing reasons, there is a need for a semi conducting unit which is incorporated with feedback control circuitry in the architecture and a single peak detector which is advantageous in achieving control over output swing even under cross corner conditions without the above mentioned disadvantages.
SUMMARY OF THE INVENTION
In one aspect of the present invention a semi conducting unit for high speed transmitters is provided which exhibits control over output swing parameters.
In another aspect of the present invention controlling methods of output swing by employing feedback loop are provided which can sense the output swing variation by means of peak detectors and level shifters and comparing the values with that of a reference swing and generate proper bias current for the main driver and compensate variations that occur in the output swing.
In a further aspect of the present invention the output swing is controlled with application of the combined effects of swing sensing and correcting mechanism.
In yet another aspect of the invention output swing control is provided and maintained within the levels of ± 8% without addition of much hardware and associated circuitry saving power or alternatively improved BER. (Bit error rate).
Accordingly the present invention provides a semiconductor unit for a transmitting device for precise controlling of output swing even under cross corner conditions, the semi conductor unit comprising of a feed back circuitry. The feed back circuitry of

the semiconductor unit of the present invention include a level shifter, an operational amplifier for error amplification and a single peak detector which is capable of correcting of swing variation including cross corners and a secondary protection circuit to which the output of the said transmitting device goes into for protection of the input devices of the said lever shifter in the event of Electrostatic Discharge (BSD).
The semiconductor unit of the present invention is capable of achieving control over output swing with precision levels ranging between ± 5% to ± 25%, preferably between ± 6% to ± 15%, and more preferably to a value of ± 6.5%. Further, the semiconductor unit of the present invention is capable of compensating even low frequencies of swing variations within its prescribed bandwidth. Furthermore, the semiconductor unit of the present invention is capable of being applied in Common Mode Feed Back (CMFB) Low Voltage Differential Signaling (LVDS) applications and also power saving can be achieved even in case of smaller transmissions with an improved Bit Error Rate (BER) to the levels of 10'" to 10-13 with an improvement factor of 100.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig.l illustrates the architecture of CIVIL driver with constant current without any control methods adopted (Prior art)
Fig.2 illustrates the proposed controlled current CML driver architecture.
Fig.3, illustrates the schematic view of output swing controlled CML transmitter (3a) with an equivalent view of the top level given in inset (3b)
Fig.4, illustrates a level shifter with output CM control

Fig.5, illustrates a positive peak detector circuit
Fig.6, illustrates the CMFB LVDS architecture (existing)
Fig.7, illustrates CMFB LVDS architecture with constant swing achieved by feedback control
Fig.8, illustrates, the top level schematic view of output swing controlled CMFB LVDS transmitter.
Fig.9, illustrates the waveforms as comparison between output swing variation with (a) conventional CML-TX circuitry without feedback control and (b) present CML-TX circuitry proposed in the invention with feedback control method.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will now be described with reference to the attached figures. Various structures, systems and devices are schematically depicted/illustrated in the drawings for purposes of explanation only and so as to not obscure the present invention with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the present invention. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i. e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional

manner that directly and unequivocally provides the special definition for the term or phrase.
In one embodiment, the present invention provides an architecture which is incorporated in a semi conducting device for a transmitter Tx with a feedback loop which can sense the output swing variation by means of peak detectors and level shifters and comparing the values with that of a reference swing and generate proper bias current for the main driver, thus compensating the variations occurring in the output swing.
As shown in figs 1 and 2, the circuitry of PMOS differential stage, conventional constant current MOS CML driver architecture and proposed controlled current MOS CML driver architecture the swing control is achieved by the sensing and correcting methods applied. The top level schematic view of swing controlled CML transmitter is shown in fig. 3 (a) where main driver is biased by a global loop formed by level shifter, positive peak detector and error amplifier in feedback path.
It is depicted in fig 3 (b) an equivalent view of the system as described in fig 3 (a) where global loop is predominantly shown. The output swing, (VOH-VOL) is compared against the reference swing, (VOHREF - VOLREF) by error amplifier and based upon error value output swing is adjusted to match the reference swing. It must be noted that the gain in low frequency closed loop system is unity, resulting in the output swing value becoming exactly same as the reference swing. Fig. 3 a) shows the output of CML transmitter goes to secondary protection circuit which is used for protection of the input devices of level shifter against ESD event. The peak detector of the feed back circuitry of the semi conductor offers less droops at the output due to peak detection in both of half cycles and the value of capacitance of the peak detector is determined in proportion to the longest zeroes and ones in input data stream. This

single peak detector is capable of correcting of swing variation including cross corners.
It must be noted that care should be taken to ensure that the bandwidth of filter formed by series resistance and input device capacitance of GGNMOS and SGPMOS is not low enough to corrupt the bit. The level shifter stage after this protection circuit fixes the common mode at its output to VCMREF level by controlling top current sources. The architecture of the level shifter is as shown in fig.4 where input swing is shifted across output common mode level, VCMREF- The peak of this level shifted signal is detected by the next peak detector stage. Fig 5, shows the architecture of the peak detector offering small droops at the output due to peak detection in both half cycles. The peak detecting capacitor value is determined based upon the longest zeros/ones in the input data stream where the maximum run length is defined by DC balancing protocol.
The inputs to replica level shifter are VOHREF and VOLREF corresponding to reference swing, (VOHREF-VOLREF). This reference swing is shifted across output common mode level of VCMREF- The said reference voltages are derived from Band Gap Reference circuit (BGR). Further, the following next replica peak detector stage generates reference peak. This peak is the reference against which detected peak is compared by error amplifier and generation of bias voltage (VPBIAS) is done for top current source to compensate the output swing variation.
It must be observed here that since the output common mode of level shifters is controlled to VCMREF, it enables only positive peak detection as a means to sense the swing. Thus, the positive peak detection alone is enough to detect the swing variation, and any variation in positive peak is therefore proportional to swing variation at the output of driver and does not require output low level/negative peak detection.

A compensating output swing variation with respect to variation of remote Rx termination resistor is provided so that variations in Rx termination resistor causes swing variation which reflects on the line and when sensed at transmit side, loop applies correction. Thus the loop effectively compensates for low frequency components of swing variation lying within its bandwidth. As shown in figs. 6, 7, it can be seen that the same concept of feedback control with swing sensing and correcting can further be extended to CMFB LVDS. Fig 8 shows a top level schematic view of output swing controlled CMFB LVDS transmitter. The precision levels of output swing control of the semi conducting unit is in the range of ± 8%. Fig. 9 shows the comparative variations in swing as achieved at the input of the receiver with conventional architecture (9a) of CML transmitter to that of the CML transmitter architecture of the proposed invention (9b). It is evident from the waveforms that higher control over swing is achieved with precision using the architecture of the present invention.
The semi conducting unit enables with power saving by achieving reduction in transmitted swing within the specified swing variation levels or alternatively provide improved Bit Error Rate (BER) by a factor of 100 at given swing. Example 1 :-
Fig 9(a) and 9(b) show the output waveforms achieved under simulated conditions, by the conventional architecture and the proposed architecture respectively. The improvement achieved in swing control can be inferred from the waveforms.
Conditions :-
Process corners: snfp,snsp,fnfp,fnsp Supply variation: 1.2V±10% Resistance variation: 50 Ω±15% Temperature variation: -40° C to 125° C
Results: Conventional architecture: Swing variation = +25%, -23% Proposed architecture: Swing variation = +6.5%, -6.3%.

DESCRIPTION OF TERMINOLOGY
BER-> Bit Error Rate
LVDS -> Low voltage differential signaling
CMFB -> Common mode feedback
Rx → Receiver
Tx → Transmitter
CML -> Current mode logic
ESD -> Electrostatic discharge
VOHREF → Output high reference level
VOLREF → Output low reference level
VCMRGF ~> Common mode output reference level
GGNMOS -> Grounded gateNMOS device
SGPMOS -> Supply gate PMOS device
BGR -> Band gap reference circuit
Ω -> Ohm ( unit of electrical resistance)
V -> Volt

CLAIMS
What is claimed is
1) A semiconductor unit for a transmitting device for precise controlling of output swing even under cross corner conditions, the semi conductor unit comprising of a feed back circuitry to sense the output swing variation.
2) The semiconductor unit as claimed in claim 1 wherein the feed back circuitry essentially consists of

- a peak detector,
- a level shifter,
- an operational amplifier and
- a secondary protection circuit
to receive output from a transmitting device and protect input devices of the said level shifter in the event of Electrostatic discharge (ESD)
3) The semiconductor unit as claimed in claim 1, wherein the level shifter shifts the input swing across fixed output common mode by controlling the top current sources.
4) The semiconductor unit as claimed in claim 1, wherein the single peak detector of the feed back circuitry offers less droops at the output due to peak detection in both of half cycles and the value of capacitance of the said peak detector is determined in proportion to the longest zeroes and ones in input data stream, i.e. DC balancing protocol.
5) The semiconductor unit as claimed in claim 1, wherein the feed back of the global loop circuitry is capable of applying correction to variations in the

main driver bias current and termination resistors thereby achieving precise control over the output swing.
6) The semiconductor unit as claimed in claim 1, is capable of achieving control
over output swing with precision levels ranging between ± 5% to ± 25%.
7) The semiconductor unit as claimed in claim 1, is capable of achieving control
over output swing with precision levels ranging between ± 6% to ± 15%.
8) The semiconductor unit as claimed in claim 1, is capable of compensating low frequencies of swing variations within its prescribed bandwidth.
9) The semiconductor unit as claimed in claim 1, is capable of being applied in Common Mode Feed Back (CMFB) Low Voltage Differential Signaling (LVDS) applications.
10)The semiconductor unit as claimed in claim 1, wherein power is saved even when smaller transmit swing is used, or alternatively an improvement in the BER by a factor of 100.
11) A semi conducting unit for a transmitting device to control the output swing parameters even under cross corner conditions substantially described particularly with reference to the accompanying drawings.