2005-04-19 Application filed by Koninklijke Philips Electronics N.V. filed Critical Koninklijke Philips Electronics N.V.
A novel high-speed differential receiver (100) is disclosed that provides a new method and apparatus receiving and amplifying a small differential voltage with a rail-to-rail common mode voltage. The receiver output signals are differential signals with low skew and high symmetry. This high-speed differential receiver (100) is based on a common mode voltage normalization, which is based on a differential phase splitting methodology, before the resulting signal is recombined, normalized and amplified. The method involves using a differential signal splitting stage (110) followed by a common mode voltage normalization stage (130), then a controlled gain transimpedance amplification stage (150), and then amplification using one or two rail to rail amplification stages (170) that are symmetrical and balanced in nature.
The invention relates to the field of differential receiver circuits and more specifically to the field of differential receiver circuits with rail-to-rail common mode operation with differential output signal low skew and symmetry. One conventional technique used for receiving of low swing differential signals, 5 having a rail to rail common mode voltage (CMV) range, is to utilize two receiver circuits. The first receiver circuit is, for example, a NMOS type input transistor, which is used to receive a signal with a CMV close to a supply voltage potential (Vdd) and a PMOS type input transistor for receiving a signal with a CMV close to ground potential, gnd. Output signals from the two receiver circuits are then combined into a single ended output signal 0 from an output port thereof. The differential receiver circuits are typically of any form of differential amplifier, however, the most common differential amplifiers are typically highly accurate folded cascode ones. United States Patent Number 5,801,564 discloses a reduced skew differential receiver that utilizes first and second differential amplifiers. Unfortunately, careful coupling5 of the two differential amplifiers is required in order to attain predetermined operation. Additionally, this circuit is quite complex and as a result affects the creation of low skew and symmetry in the differential output signal. A need therefore exists to provide a high-speed performance differential receiver with low skew and a symmetrical differential output signal at a low design cost. It is0 therefore an object of the invention to provide a differential receiver circuit with rail-to-rail common mode operation while providing differential output signal low skew and symmetry. In accordance with the invention there is provided a differential receiver circuit comprising: a first supply voltage port as a first rail for receiving of a first potential; and a second supply voltage port as a second rail for receiving of a second potential that is lower5 than the first potential, a differential signal splitter comprising a first branch and a second branch disposed between the first and second supply voltage ports and first and second input ports for receiving of a differential input signal and first through fourth output ports for providing of two complementary differential output signals therefrom; a common mode voltage (CMV) normalization stage for level shifting the two complementary differential0 output signals to form one complementary differential output signal, the CMV normalization stage comprising first through fourth input ports electrically coupled with the first through fourth output ports of the differential signal splitter stage and first and second output ports; a transimpedance amplifier comprising first and second input ports electrically coupled with the first and second output ports of the CMN normalization stage and first and second output ports for providing a rail to rail complementary differential output signal having low signal skew and symmetry, wherein the differential signal splitter, the common mode voltage (CMN) normalization stage and the amplifier are disposed between the first and second supply voltage port for receiving of the first and second potentials therefrom. In accordance with the invention there is provided a method of providing a differential output signal comprising: providing a first voltage as a first rail and a second other voltage as a second other rail; receiving of a differential input signal having a common mode voltage (CMV) and being other than rail to rail from the second voltage to the first voltage; phase splitting the differential input signal into two complementary differential output signals having a crossover voltage and that other than overlap being spaced one from the other in potential; level shifting the two complementary differential output signals and summing of analogous signals within each the complimentary differential signals to form one complementary output signal that is other than rail to rail; and, amplifying the one complementary output signal to form a rail to rail complimentary differential signal having similar temporal characteristics to the level shifted signals and a transition approximately from rail to rail between the first and second voltages. In accordance with the invention there is provided a circuit comprising: means for providing a first voltage as a first rail and a second other voltage as a second other rail; means for receiving of a differential input signal having a common mode voltage (CMN) and being other than rail to rail from the second voltage to the first voltage; means for phase splitting the differential input signal into two complementary differential output signals having a crossover voltage and that other than overlap being spaced one from the other in potential; means for level shifting the two complementary differential output signals and summing of analogous signals within each the complimentary differential signals to form one complementary output signal that is other than rail to rail; and, means for amplifying the one complementary output signal to form a rail to rail complimentary differential signal having similar temporal characteristics to the level shifted signals and a transition approximately from rail to rail between the first and second voltages. In accordance with the invention there is provided a storage medium for storing of instruction data comprising: first instruction data for providing a first voltage as a first rail and a second other voltage as a second other rail; second instruction data for receiving of a differential input signal having a common mode voltage (CMN) and being other than rail to rail from the second voltage to the first voltage; third instruction data for phase splitting the differential input signal into two complementary differential output signals having a crossover voltage and that other than overlap being spaced one from the other in potential; fourth instruction data for level shifting the two complementary differential output signals and summing of analogous signals within each the complimentary differential signals to form one complementary output signal that is other than rail to rail; and, fifth instruction data for amplifying the one complementary output signal to form a rail to rail complimentary differential signal having similar temporal characteristics to the level shifted signals and a transition approximately from rail to rail between the first and second voltages. Exemplary embodiments of the invention will now be described in conjunction with the following drawings, in which: FIG. la illustrates a differential signal splitter input stage, which is the first stage of a rail-to-rail common mode voltage (CMN) differential receiver circuit; FIG. lb illustrates a CMN normalization stage, which is a second stage of the rail- to-rail CMN differential receiver circuit; FIG. le a transimpedance amplifier stage, which is a third stage of the rail-to-rail CMN differential receiver circuit; FIG. Id illustrates a buffer stage, which is a rail-to-rail output driver stage, which is a fourth stage of the rail-to-rail CMN differential receiver circuit; FIG. 2a graphically depicts small differential signal input signal, "in+" and "in-", which is provided to differential input ports of the rail-to-rail CMN differential receiver circuit; FIG. 2b illustrates an increase in the "dn" voltage and decrease the "sn" voltage as a result of the "in+" voltage rising; FIG. 2c illustrates a decrease in the "sp" voltage and an increase in the "dp" voltage as a result of the "in+" voltage rising; FIG. 3a illustrates output signals, "in2-" and "in2+", provided from output ports of the second stage; FIG. 3b illustrates output signals, "in3-" and "in3+", provided from output ports of the third stage; and, FIG. 3c illustrates output signals, "out-" and "out+", provided from output ports of the rail-to-rail CMN differential receiver circuit. FIGs. la through Id illustrate multiple stages of a rail-to-rail common mode voltage (CMV) differential receiver circuit 100 in accordance with the preferred embodiment of the invention. The differential receiver circuit 100 is comprised of four stages of symmetrical circuits that are disposed in series. FIG. la illustrates a differential signal splitter input stage 110, which is the first stage. FIG. lb illustrates the second stage, the CMN normalization stage 130. FIG. lc illustrates the third stage, a transimpedance amplifier stage 150. FIG. Id illustrates the fourth stage, a buffer stage, which is a rail-to-rail output driver stage 150. Referring to FIG. la, the first stage 110 is comprised of two symmetrical circuit branches, a first branch 111 and a second branch 112. Disposed within the first branch 111 are a first n channel metal oxide semiconductor (ΝMOS) transistor (ΝMOS1) 113 and a first p channel metal oxide semiconductor (PMOS) transistor (PMOS1) 114. Disposed within the second branch 112 are a second ΝMOS transistor (ΝMOS2) 115 and a second PMOS transistor (PMOS2) 116. Four resistive loads, labeled Rl , 117a through 117d, electrically couple the drain and source terminals of devices NMOS1 113, PMOS1 114 and NMOS2 115, PMOS2 116 to a first and second supply voltage ports, 110c and 1 lOd, connected for receiving of potential voltages, Vdd and Nss, respectively. The gate terminals of transistors PMOS1 114 and ΝMOS2 115 are electrically coupled together and are electrically coupled with a first input port 110a, which his labeled "In+." Gate terminals of transistors PMOS2 116 and NMOS1 113 are electrically coupled together to a second input port 110b, which is labeled "In-." The first and second input ports, 110a and 110b, form the differential input ports to the first stage 110. The first stage 110 additionally has four output ports, 1 lOe through 1 lOh, which are labeled: innl, inpl, inn2, inp2, for providing of respective signals dn, sn, sp, dp, therefrom. In use, the first 110 stage functions as a differential signal phase splitting stage. The input signal provided to the differential input ports, 110 and 110b, of this stage is a small differential signal with a potential of approximately 50mv to 400mv having a rail-to-rail common mode voltage (CMV). The first branch 111 is comprised of the NMOS1 and PMOS1 devices, 113 and 114, which are electrically coupled together in a pass-gate configuration. Each side of this pass- gate is electrically coupled to a respective resistor, where resistors 117a and 117b respectively electrically couple the drain and source terminals of NMOS 1 and PMOS1 devices, 113 and 114, to the 110c and 1 lOd supply voltage ports. Resistors 117c and 117d are used for respective coupling of the drain and source terminals of NMOS2 and PMOS2 devices, 115 and 116, to the 110c and 1 lOd supply voltage ports. Referring to FIG. 2a, this figure graphically depicts what occurs when a small differential signal, "in+" and "in-," is applied to the input ports, 110 and 110b, which are the gate terminals of the MOS devices 113 and 114. As the "in+" voltage rises the PMOS1 device 114 conduct less current and the same, but opposite, occurs for the NMOS1 device 113. For the input port 110b, as the potential of the signal "In-" falls the NMOS1 device 113 conduct less current. The total effect is to increase pass-gate impedance and therefore a decrease in the current that propagates through this first branch 111. As is shown in FIG. 2b, for output ports 1 lOe and 11 Of, an increase in the "dn" voltage and decrease in the "sn" voltage is observed as a result of the "in+" voltage rising. A similar type of event is observed in the second branch 112, but with opposite effects to that of the first branch 111. Referring to FIG. 2c, this transition of the "in+" voltage rising results in a decrease in the "sp" voltage and an increase in the "dp" voltage, as observed on the 1 lOg and 1 lOh output ports. FIG. 2d illustrates four superimposed output signals, dn, sn, sp and dp, provided from respective output ports 1 lOe through 1 lOh for this first stage 110. This figure also illustrates that starting with one differential signal, results in the generation of two complementary differential signals with a very small skew of approximately a few Pico seconds between the upper and lower sets of crossover points, labeled "A", 201a and 201b, and "B", 202a and 202b. Furthermore, as the input CMV change, the corresponding crossover voltage moves up or down in potential but remains relatively constant in time or in a timing relashionship. Also, as the differential amplitude changes so does the differential amplitude of both complementary differential output signals. Referring back to FIG. la, as the input CMV moves toward higher Vdd potentials, the pass-gate structure conducts current even when the PMOS1 device 114 is either turned off or close to being turned off. As the input CMV moves toward ground, the pass-gate structure conducts current even when the NMOS1 device 113 is either turned off or is close to being turned off. So in extreme cases for the CMN, either towards higher Ndd or lower Nss, the differential phase splitting is performed by one of the MOS devices, which is either the ΝMOS1 device 113 or the PMOS1 device 114, respectively. In the case of extreme CMN, when the first branch 111 is conducting more current than the second branch 112, the differential phase splitting works with a rail to rail CMN. Optionally, the differential gain of this first stage is less than unity, where it is optionally 50% of the differential input voltage. Preferably, during integrated manufacturing, the dimensions of each of the PMOS and ΝMOS devices, 113 through 116, as well as the resistors, 117a through 117d, are chosen in order to approximately optimize for best performance of cross-over voltage and differential phase splitting. Referring back to FIG. lb, the CMN normalization stage is shown with two ΝMOS devices, labeled MΝ1 134 and MΝ2 136, and two PMOS devices, labeled MPl 133 and MP2 135. Drain terminals of devices MPl 133 and MP2 135 are electrically coupled together and are further electrically coupled to a first supply voltage port 130c, for receiving of Vdd, through resistor R2 137a. Source terminals of devices MN1 134 and MN2 136 are electrically coupled together and are further electrically coupled to a second supply voltage port 130d, for receiving of Nss, through resistor R2 137b. A third resistor R3 137c is disposed between a junction formed between the source terminal of device MPl 133 and the drain terminal of device MΝ1 134 and a junction formed between the source terminal of device MP2 135 and the drain terminal of device MΝ2 136. Gate terminals of the PMOS devices, MPl 133 and MP2 135, form input ports 130e and 13 Of to the second stage 130 and are electrically coupled with output ports 11 Of and 1 lOh, respectively, of the first stage bottom side. Gate terminals of the NMOS devices, MN1 134 and MN2 136, are electrically coupled to the output ports, 1 lOe and llOg, of the first stage top side. This second stage is a complementary differential stage, which is used to normalize the common mode voltage (CMV) to approximately Vdd/2. Referring to FIG. 3a, when the input voltage "inpl," provided to input port 130e, is lower than the input voltage "inp2," provided to input port 130g, and when the input voltage "inn2," provided to input port 13 Of, is higher than "innl," provided to input port 13 Oh, a positive current path flows through resistor R3 137c from node 131a, as is indicated by signal "in2-", toward node 131b, as is indicated by signal "in2+". A main current path is formed from the first supply voltage port 130c, resistor R2 137a through transistor MPl 133, through resistor R3 137c, through transistor MN2 136, through resistor R2 137b and finally into the second supply voltage port 130d, which is ground, Vss. When the input conditions are reversed, the reverse is true. A positive current propagates through resistor R3 from node 131b, "in2+", to node 131a, "in2-". Preferably, the PMOS and NMOS devices, 133, 135, 134, 136 are designed to have equal active areas and comparable gain, gm. This equalizes capacitive loading of the first stage 110 and aids in skew and symmetry of the output signals provided from output ports, 131a and 131b of this second stage 130. With an equal gain, gm, for the transistors MPl 133, MP2 135 and MN1 134, MN2 136, positive and negative currents flowing in resistor R3 137c are equal.
110, the four output signals provided from the output ports, 1 lOe through 1 lOh, shift up and down in potential. Referring to FIG. 3b, as the second stage 130 differential output signal, provided from output ports 131a and 131b, changes in differential amplitude, its CMV stays constant - around Vdd/2. Referring back to FIGs. lc and Id, these figures illustrate the transimpedance stages.
170b electrically coupled with the output ports 150c and 150c of the third stage 150. This fourth stage 170 receives the output signals from the third stage 150 and buffers them using buffer circuits 171 and 172 in order to form output signals, "out+" and "out-", on output ports 170c and 170d. Referring to FIG.3d, the resulting output signals, "out+" and "out-", are rail to rail. By design, this fourth stage 170 is optimized to amplify and buffer the third stage 150 output signals and to preserve the low skew and rise and fall symmetry of the waveforms and the CMN. Advantageously, the differential receiver in accordance with the embodiment of the invention is useable with high speed, or optionally low speed, differential signal amplification and signal communication where low skew and high symmetry are preferred. Numerous other embodiments may be envisaged without departing from the spirit or scope of the invention.
13 Oh) electrically coupled with the first through fourth output ports (1 lOe, 1 lOf, 1 lOg, 11 Oh) of the differential signal splitter stage (110) and first and second output ports (131a, 13 lb); a transimpedance amplifier (150) comprising first and second input ports (150a, 150b) electrically coupled with the first and second output ports (131a, 131b) of the CMN normalization stage (130) and first and second output ports (150c, 150d) for providing a rail to rail complementary differential output signal having low signal skew and symmetry, wherein the differential signal splitter (110), the common mode voltage (CMN) normalization stage (130) and the transimpedance amplifier (150) are disposed between the first supply voltage port (110c; 130c) and the second supply voltage port (1 lOd; 130d) for receiving of the first and second potentials therefrom. 2. A differential receiver circuit according to claim 1 comprising a buffer stage (170) comprising a first input port (170a) and a second input port (170b) electrically coupled with the first output port (150c) and the second output port (150d) of the transimpedance amplifier (150) and a first output port (170c) and a second output port (170d) for providing the rail to rail complimentary differential output signal. 3. A differential receiver circuit according to claim 1 wherein the first branch (111) comprises: a first PMOS device (114) having gate, drain and source terminals; a first ΝMOS device (113) having a gate terminal and drain and source terminals electrically coupled with the drain and source terminals of the first PMOS device (114).
4. A differential receiver circuit according to claim 3 wherein the second branch (112) comprises: a second PMOS device (116) having gate, drain and source terminals; a second NMOS device (115) having a gate terminal and drain and source terminals electrically coupled with the drain and source terminals of the second PMOS device (116), where the gate terminals of the first PMOS device (114) and the second NMOS device (115) are electrically coupled together and form the first input port (110a) of the differential signal splitter stage (110) and the gate terminals of the second PMOS device (116) and the first NMOS device (113) form the second input port (110b) of the differential signal splitter stage (110).
5. A differential receiver circuit according to claim 4 wherein the NMOS (113, 115) devices and PMOS devices (114, 116) comprise approximately equal active areas and approximately equal gains.
6. A differential receiver circuit according to claim 4 comprising: wherein the first branch (111) comprises a first set of two approximately identical resistors (117a, 117b) respectively disposed between the drain terminals of the electrically coupled first NMOS (113) device and first PMOS device (114) and the first supply voltage port (110c) and between the source terminals of the electrically coupled first NMOS device (113) and first PMOS device (114) and the second supply voltage port (1 lOd), wherein the first output port (1 lOe) and the second output port (11 Of) of the differential signal splitter stage (110) are formed respectively at the electrically coupled drain and source terminals of the first NMOS device (113) and the first PMOS device (114).
( 11 Og) and the fourth output port ( 11 Oh) of the differential signal splitter stage ( 110) are formed respectively at the electrically coupled drain and source terminals of the second NMOS device (115) and second PMOS device (116).
8. A differential receiver circuit according to claim 1 wherein the common mode voltage (CMV) normalization stage (130) comprises: a first branch; a second branch; and, a first resistive coupling (137a) between a first end of both branches to the first supply voltage port (130c) and a second resistive coupling (137b) between a second end of both branches to the second supply voltage port (130d), wherein resistance values for the first resistive coupling (137a) and second resistive coupling (137b) are approximately equal.
9. A differential receiver circuit according to claim 8 wherein the first branch of the CMN normalization stage (130) comprises: a first PMOS device (133) having a gate terminal electrically coupled with the first input port (130e) of the CMN normalization stage (130), a drain terminal electrically coupled to the first end of the first branch and a source terminal; and, a first ΝMOS device (134) having a gate terminal electrically coupled with the second input port (130f) of the CMN normalization stage (130), a drain terminal electrically coupled to the source terminal of the first PMOS device (133), for forming the first output port (131a) of the CMN normalization stage (130), and the source terminal thereof electrically coupled to the second end of the first branch.
10. A differential receiver circuit according to claim 9 wherein the second branch of the CMV normalization stage (130) comprises: a second PMOS device (135) having a gate terminal electrically coupled with the third input port (130g) of the CMV normalization stage (130), a drain terminal electrically coupled to the first end of the second branch and a source terminal; and, a second ΝMOS device (136) having a gate terminal electrically coupled with the fourth input port (130h) of the CMN normalization stage (130), a drain terminal electrically coupled to the source terminal of the second PMOS device (135), for forming the second output port (131b) of the CMN normalization stage (130), and the source terminal thereof electrically coupled to the second end of the second branch.
11. A differential receiver circuit according to claim 10 wherein the ΝMOS devices (134, 136) and PMOS devices (133, 135) comprise approximately equal active areas and approximately equal gains.
12. A differential receiver circuit according to claim 1 comprising a third resistor (137c) disposed between the first output port (131a) and the second output port (131b) of the CMN normalization stage (130).
13. A differential receiver circuit according to claim 1 wherein the transimpedance amplifier (150) comprises: a first inverter circuit (151) disposed between the first input port (150a) and the first output port (150c) of the transimpedance amplification stage (150); and, a fourth resistor (157a) disposed in parallel with the first inverter circuit (151).
14. A differential receiver circuit according to claim 13 wherein the transimpedance amplifier comprises: a second inverter circuit (152) disposed between the second input port (150b) and the second output port (150d) of the transimpedance amplification stage (150); and, a fourth resistor (157b) disposed in parallel with the second inverter circuit (152).
15. A differential receiver circuit according to claim 2 wherein the buffer stage (170) comprises a first buffer circuit (171) disposed between the first input port (170a) and the first output port (170c) of the buffer stage (170).
16. A differential receiver circuit according to claim 15 wherein the buffer stage (170) comprises a second buffer circuit (172) disposed between the second input port (170b) and the second output port (170d) of the buffer stage (170).
17. A differential receiver circuit according to claim 1 wherein the differential input signal has a potential of approximately 50mv to 400mv and has a rail-to-rail common mode voltage (CMV).
18. A differential receiver circuit according to claim 2 comprising a same integrated circuit semiconductor substrate, wherein the differential signal splitter (110), the CMN normalization stage (130), the transimpedance amplifier circuit (150) and the buffer stage (170) are integrated within the same integrated circuit semiconductor substrate.
19. A method of providing a differential output signal comprising: providing a first voltage as a first rail and a second other voltage as a second other rail; receiving of a differential input signal having a common mode voltage (CMN) and being other than rail to rail from the second voltage to the first voltage; phase splitting the differential input signal into two complementary differential output signals having a crossover voltage and that other than overlap being spaced one from the other in potential; level shifting the two complementary differential output signals and summing of analogous signals within each the complimentary differential signals to form one complementary output signal that is other than rail to rail; and, amplifying the one complementary output signal to form a rail to rail complimentary differential signal having similar temporal characteristics to the level shifted signals and a transition approximately from rail to rail between the first and second voltages.
20. A method according to claim 19 comprising normalizing of the CMN to approximately half of the potential between the second voltage level and the first voltage level.
21. A method according to claim 19 wherein for changes in the input signal CMN the crossover voltage for the input signal changes.
22. A method according to claim 19 wherein for changes in a differential amplitude of the input signal a differential amplitude of both complementary differential output signals also changes.
23. A method according to claim 19 comprising providing of a first stage for receiving of the differential input signal, wherein a differential gain of this first stage is less than unity.
24. A method according to claim 19 wherein the differential gain of the first stage is approximately half of a differential input voltage for the differential input signal.
25. A storage medium for storing of instruction data comprising: first instruction data for providing a first voltage as a first rail and a second other voltage as a second other rail; second instruction data for receiving of a differential input signal having a common mode voltage (CMN) and being other than rail to rail from the second voltage to the first voltage; third instruction data for phase splitting the differential input signal into two complementary differential output signals having a crossover voltage and that other than overlap being spaced one from the other in potential; fourth instruction data for level shifting the two complementary differential output signals and summing of analogous signals within each the complimentary differential signals to form one complementary output signal that is other than rail to rail; and, fifth instruction data for amplifying the one complementary output signal to form a rail to rail complimentary differential signal having similar temporal characteristics to the level shifted signals and a transition approximately from rail to rail between the first and second voltages.