Time to digital converter and all digital phase-locked-loop

1. A time to digital converter, comprising:

a multiphase circuit that generates multiphase signals of which phases are different from each other by 180/M degrees by dividing a differential oscillation signal by M (M is an integral number not smaller than 2);

a flip-flop that captures the multiphase signals in synchronization with an input of a reference signal; and

a decoder that decodes an output signal of the flip-flop, wherein

the multiphase circuit comprises a divide-by-2 circuit that generates the multiphase signals of which phases are different from each other by 90 degrees by dividing the differential oscillation signal by 2, and

an interpolation circuit that interpolates an interval between the phases of the multiphase signals at regular intervals by synthesizing a plurality of inverter outputs driven by the multiphase signals of which phases are different from each other.

2. The time to digital converter according to claim 1 , wherein

the interpolation circuit interpolates such that K (K is an integral number not smaller than 3) or more edges are generated between the phases of the multiphase signals by changing combination of the outputs of the inverters of which driving forces are different from each other.

3. The time to digital converter according to claim 1 , wherein

the interpolation circuit generates 2 M+1 multiphase signals of which phases are different from one another by 180/2 M+1 degrees by interpolating 2 M multiphase signals of which phases are different from one another by 180/2 M degrees.

4. The time to digital converter according to claim 3 , wherein

K (K is a positive integral number) stage of the interpolation circuit is connected, thereby generating 2 K+2 multiphase signals of which phases are different from one another by 180/2 K+2 degrees from four multiphase signals of which phases are different from one another by 90 degrees.

5. The time to digital converter according to claim 4 , wherein

a 4-input-8-output interpolation circuit is obtained by combining four 2-input-3-output sub interpolation circuits that generate three multiphase signals of which phases are different from one another by 45 degrees from two multiphase signals of which phases are different from each other by 90 degrees.

6. The time to digital converter according to claim 5 , wherein

the sub interpolation circuit comprises

a first inverter that generates a first multiphase output signal by inverting a first multiphase input signal,

second and third inverters that generate a second multiphase output signal of which phase is different from the phase of the first multiphase output signal by 45 degrees by synthesizing signals obtained by inverting the first multiphase input signal and a second multiphase input signal of which phase is different from the phase of the first multiphase input signal by 90 degrees, and

a fourth inverter that generates a third multiphase output signal of which phase is different from the phase of the first multiphase output signal by 90 degrees by inverting the second multiphase input signal.

7. The time to digital converter according to claim 1 , comprising:

a switch that stops the inverter output for each phase of the multiphase signals obtained by the interpolation;

a prediction circuit that predicts a phase of a next reference signal based on a comparison result between a present reference signal and the multiphase signals; and

a switching controller that on/off controls the switch based on a prediction result by the prediction circuit.

8. The time to digital converter according to claim 7 , wherein

the switching controller on/off controls the switch such that only the multiphase signals that generate phases before and after the phase of the reference signal predicted by the prediction circuit are generated.

9. The time to digital converter according to claim 7 , wherein

the switching controller on/off controls the switch such that only the multiphase signals that generate phases in the vicinity of the phase of the reference signal predicted by the prediction circuit are generated.

10. The time to digital converter according to claim 7 , wherein

the switching controller on/off controls the switch such that only the multiphase signals that generate phases before and after the phase of the reference signal predicted by the prediction circuit and a phase of a higher-bit are generated.

11. The time to digital converter according to claim 7 , wherein

the switching controller on/off controls the switch such that only the multiphase signals that generate phases in the vicinity of the phase of the reference signal predicted by the prediction circuit and a phase of a higher-bit are generated.

12. The time to digital converter according to claim 7 , wherein

the inverter comprises a P-channel field effect transistor and an N-channel field effect transistor, and

the switch comprises

a first switch connected between a gate of the P-channel field effect transistor and an input point of the multiphase signals,

a second switch connected between a gate of the N-channel field effect transistor and the input point of the multiphase signals,

a third switch connected between the gate and a source of the P-channel field effect transistor, and

a fourth switch connected between the gate and a source of the N-channel field effect transistor.

13. The time to digital converter according to claim 7 , wherein

the inverter comprises a P-channel field effect transistor and an N-channel field effect transistor, and

the switch comprises

a first switch connected between a source of the P-channel field effect transistor and supply potential, and

a second switch connected between a source of the N-channel field effect transistor and ground potential.

14. An all digital phase-locked-loop, comprising:

a time to digital converter that detects phase shift between a differential oscillation signal and a reference signal based on a multiphase signal generated based on a cycle of the differential oscillation signal; and

a digital control oscillator provided with a differential oscillator to generate the differential oscillation signal that controls an oscillation frequency of the differential oscillation signal based on a detection result by the time to digital converter, wherein

the time to digital converter comprises

a multiphase circuit that generates multiphase signals of which phases are different from each other by 180/M degrees by dividing the differential oscillation signal by M (M is an integral number not smaller than 2);

a flip-flop that captures the multiphase signals in synchronization with an input of a reference signal; and

a decoder that decodes an output signal of the flip-flop, wherein

the multiphase circuit comprises

a divide-by-2 circuit that generates the multiphase signals of which phases are different from each other by 90 degrees by dividing the differential oscillation signal by 2, and

an interpolation circuit that interpolates an interval between the phases of the multiphase signals at regular intervals by synthesizing a plurality of inverter outputs driven by the multiphase signals of which phases are different from each other.

15. The all digital phase-locked-loop according to claim 14 , wherein

the interpolation circuit interpolates such that K (K is an integral number not smaller than 3) or more edges are generated between the phases of the multiphase signals by changing combination of the outputs of the inverters having different driving forces.

16. The all digital phase-locked-loop according to claim 14 , wherein

the interpolation circuit generates 2 M+1 multiphase signals of which phases are different from one another by 180/2 M+1 degrees by interpolating 2 M multiphase signals of which phases are different from one another by 180/2 M degrees.

17. The all digital phase-locked-loop according to claim 16 , wherein

K (K is a positive integral number) stage of the interpolation circuit is connected, thereby generating 2 K+2 multiphase signals of which phases are different from each other by 180/2 K+2 degrees from four multiphase signals of which phases are different from each other by 90 degrees.