High speed rail to rail phase splitter for providing a symmetrical differential output signal having low skew
A novel high-speed phase splitter circuit ( 100 ) and method of operation are disclosed. This high-speed phase splitter ( 100 ) creates a differential rail-to-rail output signal from a single ended input signal, with an inherent low skew and symmetrical output. The circuit ( 100 ) uses a phase splitting input stage ( 110, 130 ) followed by several amplification stages ( 150, 170 ) that are symmetrical and balanced in nature.
1. A rail-to-rail phase splitter circuit comprising:
a first supply voltage port as a first rail configured to receive a first potential; and
a second supply voltage port as a second rail configured to receive a second potential that is lower than the received first potential;
a phase splitter comprising a first branch and a second branch disposed between the first supply voltage port and the second supply voltage port, first through fourth phase splitter output ports, and a phase splitter input port configured to receive a first input signal having rail to rail voltage transitions about a known voltage level;
a complementary differential amplifier configured to split the input signal into two complementary differential output signals, the complementary differential amplifier comprising a first differential amplifier output port, a second differential amplifier output port, and first through fourth differential amplifier input ports electrically coupled with the first through fourth phase splitter output ports; and
a transimpedance amplifier comprising a first transimpedance amplifier input port and a second transimpedance amplifier input port electrically coupled with the complementary differential amplifier, and a first transimpedance amplifier output port and a second transimpedance amplifier output port configured to provide complementary output signals therefrom that transition from rail to rail between the first and second potentials, wherein the phase splitter, the complementary differential amplifier, and the transimpedance amplifier are disposed between the first supply voltage port and second supply voltage port and configured to receive the first and second potentials.
2. The rail-to-rail phase splitter circuit according to claim 1 , further comprising:
a buffer circuit comprising a first buffer input port and a second buffer input port electrically coupled with the first transimpedance amplifier output port and the second transimpedance amplifier output port, wherein the first transimpedance amplifier output port and the second transimpedance amplifier output port are configured to provide the complementary output signals.
3. The rail-to-rail phase splitter circuit according to claim 1 , wherein the first branch comprises a first NMOS device having gate, drain, and source terminals.
4. The rail-to-rail phase splitter circuit according to claim 3 , wherein the second branch comprises a first PMOS device having a gate terminal electrically coupled with a gate terminal of the first NMOS device and configured to form the phase splitter input port.
5. The rail-to-rail phase splitter circuit according to claim 4 , wherein the first NMOS device and the first PMOS device comprise approximately equal active areas and approximately equal gains.
6. The rail-to-rail phase splitter circuit according to claim 4 , wherein the first branch comprises a first set of two approximately identical resistors respectively disposed between the drain terminal of the first NMOS device and the first supply voltage port and between the source terminal of the first NMOS device and the second supply voltage port, wherein the first differential amplifier output port and the second differential amplifier output port are formed respectively at the drain and source terminals of the first NMOS device.
7. The rail-to-rail phase splitter circuit according to claim 6 , wherein the second branch comprises a second set of two approximately identical resistors respectively disposed between the drain terminal of the first PMOS device and the first supply voltage port and between the source terminal of the first PMOS device and the second supply voltage port, wherein the second phase splitter output port and the third phase splitter output port are formed respectively at the drain and source terminals of the first PMOS device.
8. The rail-to-rail phase splitter circuit according to claim 1 , wherein the complementary differential amplifier comprises:
a first branch;
a second branch;
a first resistive coupling between a first end of both branches to the first supply voltage port; and
a second resistive coupling between a second end of both branches to the second supply voltage port, wherein resistance values for the first resistive coupling and the second resistive coupling are approximately equal.
9. The rail-to-rail phase splitter circuit according to claim 8 , wherein the first branch of the complementary differential amplifier comprises:
a first PMOS device having a gate terminal electrically coupled with the first differential amplifier input port and a drain terminal electrically coupled to the first end of the first branch and a source terminal; and,
a first NMOS device having a gate terminal electrically coupled with the second differential amplifier input port, a drain terminal electrically coupled to the source terminal of the first PMOS device for forming the first differential amplifier output port and the source terminal thereof electrically coupled to the second end of the first branch.
10. The rail-to-rail phase splitter circuit according to claim 9 , wherein the second branch of the complementary differential amplifier comprises:
a second PMOS device having a gate terminal electrically coupled with the third differential amplifier input port, a drain terminal electrically coupled to the first end of the second branch, and a source terminal; and,
a second NMOS device having a gate terminal electrically coupled with the fourth differential amplifier input port, a drain terminal electrically coupled to the source terminal of the second PMOS device for forming the second differential amplifier output port of, and the source terminal thereof electrically coupled to the second end of the second branch.
11. The rail-to-rail phase splitter circuit according to claim 10 , wherein the second NMOS device and the second PMOS device comprise approximately equal active areas and approximately equal gains.
12. The rail-to-rail phase splitter circuit according to claim 1 , wherein the phase splitter comprises a PMOS differential stage and, a NMOS differential stage electrically coupled with the PMOS differential stage.
13. The rail-to-rail phase splitter circuit according to claim 1 , comprising a virtual resistor disposed between the first and second differential amplifier output ports.
14. The rail-to-rail phase splitter circuit according to claim 1 , wherein the transimpedance amplifier comprises:
a first inverter disposed between the first transimpedance amplifier input port and the first transimpedance amplifier output port; and
a fourth resistor disposed in parallel with the first inverter.
15. The rail-to-rail phase splitter circuit according to claim 14 , wherein the transimpedance amplifier comprises:
a second inverter disposed between the second transimpedance amplifier input port and the second transimpedance amplifier output port; and
a fifth resistor disposed in parallel with the second inverter.
16. The rail-to-rail phase splitter circuit according to claim 2 , wherein the buffer circuit comprises:
a first buffer circuit disposed between the first buffer circuit input port and the first buffer circuit output port.
17. The rail-to-rail phase splitter circuit according to claim 16 , wherein the buffer circuit comprises:
a second buffer circuit disposed between the second buffer circuit input port and the second buffer circuit output port, wherein the first buffer circuit and the second buffer circuit are configured to provide the complementary output signals therefrom.
18. The rail-to-rail phase splitter circuit according to claim 1 , wherein the known voltage level is at a potential of approximately halfway between the first and second potentials.
19. A method of providing a differential output signal comprising:
receiving an input signal having rail to rail voltage transitions about a known voltage level from a second voltage level to a first voltage level;
phase splitting the received input signal into two complementary differential output signals that are spaced one from the other in potential and do not overlap;
level shifting the two complementary differential output signals to form two level shifted complementary output signals that are other than rail to rail; and,
amplifying the two level shifted complementary output signals.
20. The method according to claim 19 , wherein a crossover point between these two complementary differential output signals is at a potential of approximately halfway between the first and second voltage levels.
21. The method according to claim 20 , wherein the two complementary differential output signals are symmetrical about the crossover point.
22. The method according to claim 19 , wherein the two complementary differential output signals are on different voltage planes from each other.
23. The method according to claim 19 , wherein the two complementary differential output signals comprise approximately equal rise and fall times.
24. The method according to claim 19 , wherein the phase splitting step further comprises:
differentially splitting the input signal into a first set of opposite signals and into a second set of opposite signals.
25. The method according to claim 19 , wherein the skew is more than 50 ps.
26. The method according to claim 19 , wherein the amplifying step further comprises:
inverting of each of the two level shifted complementary output signals.
27. The method according to claim 19 , wherein the step of amplifying further comprises:
providing a NMOS device having a first sized active area and a first gain;
providing a PMOS device having a second sized active area that is the same as the first sized active area and a second gain that is the same as the first gain, wherein shifts in crossover voltages for each of the two complementary differential output signals occur at approximately the same times for both of the complementary differential output signals because of the approximately equal first and second gains of the NMOS device and PMOS device.
28. The method according to claim 27 , wherein the shifts in crossover voltages for each of the two complementary differential output signals occur at approximately the same times for both of the complementary differential output signals because of the approximately same size active areas for the NMOS device and PMOS device.
29. A non-transitory storage medium configured to store instruction data comprising:
first instruction data for receiving of an input signal having rail to rail voltage transitions about a known voltage level from a second voltage level to a first voltage level;
second instruction data for phase splitting the input signal into two complementary differential output signals that are spaced one from the other in potential and do not overlap;
third instruction data for level shifting the two complementary differential output signals to form two level shifted complementary output signals that are other than rail to rail; and,
fourth instruction data for amplifying the two level shifted complementary output signals.