Multi-stage digitally controlled delay line linearity enhancing by redundancy and randomization

1. A circuit for reducing fractional spurs, comprising:

a digital to time converter (DTC) comprising a plurality of delay stages electrically coupled to one another in series, configured such that each delay stage of the plurality of delay stages is binary switched till a total code exceeds cell range and then it is fully turned ON, and thereafter it is moved to the next stage, wherein the each delay stage comprises a digitally controlled delay line (DCDL), wherein each of the DCDL of the each delay stage has code-dependent integrated nonlinearity (INL), and wherein the maximal value of the INL occurs at a mid-code position of the each delay stage; and

an offset stage comprising another DCDL electrically coupled to the DTC in series, configured to generate random codes for each required time delay of the DTC to ensure the probability of landing at the mid-code position is reduced and landing point is kept as far away as possible from the mid-code position for every required time delay in the DTC, thereby improving the INL and therefore the fractional spurs.

2. The device of claim 1 , wherein the each of the DCDL of the each delay stage is a variable slope DCDL.

3. The device of claim 2 , wherein the each of the DCDL of the each delay stage comprises an inverter followed by a capacitor, configured such that, through controlling different aspects of either the inverter or the capacitor, the slope of an input clock signal is changed to provide different delays.

4. The device of claim 3 , wherein the capacitor comprises at least one metal capacitor with at least one switch, or at least one varactor.

5. The device of claim 3 , wherein the inverter comprises a plurality of inverters.

6. The device of claim 3 , wherein the each of the DCDL of the each delay stage further comprises a variable resistor coupled between the inverter and the capacitor.

7. The device of claim 2 , wherein the each of the DCDL of the each delay stage comprises a first inverter, a second inverter, a binary weighted metal-oxide-metal (MOM) capacitors array V x , a first buffer, and a second buffer electrically coupled to one another in series between an input and an output of the DCDL.

8. The device of claim 7 , wherein the binary MOM capacitors array V x comprises N capacitors with switches that are operably switched on and off in a binary fashion to achieve a code range of 2 N codes for the each of the DCDL of the each delay stage, wherein N is an integer equal to or greater than 1.

9. The device of claim 8 , wherein the first buffer has a delay that is a function of the V x 's slope, wherein the more the code range increases, the more the delay varies.

10. The device of claim 1 , wherein the random codes are generated by a pseudorandom binary sequence (PRBS).

11. A method for reducing fractional spurs, comprising:

providing a circuit comprising:

a digital to time converter (DTC) comprising a plurality of delay stages electrically coupled to one another in series, configured such that each delay stage of the plurality of delay stages is binary switched till a total code exceeds cell range and then it is fully turned ON, and thereafter it is moved to the next stage, wherein the each delay stage comprises a digitally controlled delay line (DCDL), wherein each of the DCDL of the each delay stage has code-dependent integrated nonlinearity (INL), and wherein the maximal value of the INL occurs at a mid-code position of the each delay stage;

an offset stage comprising another DCDL electrically coupled to the DTC in series; and

generating random codes for each required time delay of the DTC by the offset stage to ensure the probability of landing at the mid-code position is reduced and landing point is kept as far away as possible from the mid-code position for every required time delay in the DTC, thereby improving the INL and therefore the fractional spurs.

12. The method of claim 11 , wherein the each of the DCDL of the each delay stage is a variable slope DCDL.

13. The method of claim 12 , wherein the each of the DCDL of the each delay stage comprises an inverter followed by a capacitor, configured such that, through controlling different aspects of either the inverter or the capacitor, the slope of an input clock signal is changed to provide different delays.

14. The method of claim 13 , wherein the capacitor comprises at least one metal capacitor with at least one switch, or at least one varactor.

15. The method of claim 13 , wherein the inverter comprises a plurality of inverters.

16. The method of claim 13 , wherein the each of the DCDL of the each delay stage further comprises a variable resistor coupled between the inverter and the capacitor.

17. The method of claim 12 , wherein the each of the DCDL of the each delay stage comprises a first inverter, a second inverter, a binary weighted metal-oxide-metal (MOM) capacitors array V x , a first buffer, and a second buffer electrically coupled to one another in series between an input and an output of the DCDL.

18. The method of claim 17 , wherein the binary MOM capacitors array V x comprises N capacitors with switches that are operably switched on and off in a binary fashion to achieve a code range of 2codes for the each of the DCDL of the each delay stage, wherein N is an integer equal to or greater than 1.

19. The method of claim 18 , wherein the first buffer has a delay that is a function of the V x 's slope, wherein the more the code range increases, the more the delay varies.

20. The method of claim 11 , wherein the random codes are generated by a pseudorandom binary sequence (PRBS).