Analog-to-digital converters

1. A device, comprising:

a first track and hold amplifier (THA) configured to receive an analog input signal; and

a plurality of paths coupled to an output of the first THA, each path of the plurality of paths including:

a second THA coupled to the first THA; and

a successive approximation register analog-to-digital converter (SAR ADC) coupled to an output of the second THA, the SAR ADC including:

a comparator including an input coupled to an output of the second THA;

a latch coupled to an output of the comparator;

a SAR coupled to an output of the latch, the SAR comprising a plurality of cells, each cell of the plurality of cells including an emitter follower coupled to a settable and resettable latch; and

a R-2R DAC coupled between an output of the SAR and another input of the comparator.

2. The device of claim 1 , where the settable and resettable latch includes four-level bi-complementary metal-oxide-semiconductor (BiCMOS) quasi-current mode logic (CML), wherein two levels of the four-level BiCMOS quasi CML comprise one or more metal-oxide-semiconductor field-effect transistors (MOSFETs) and two levels of the four-level BiCMOS quasi CML comprise one or more heterojunction bipolar transistors (HBT).

3. The device of claim 1 , further comprising a pulse generator including a sequencer configured to send one or more clock signals to each path of the plurality of paths.

4. The device of claim 3 , the sequencer comprising:

a plurality of resettable flip-flops; and

a settable flip-flop coupled to the plurality of resettable flip-flops.

5. The device of claim 4 , wherein the settable flip-flop includes a settable latch coupled to a latch.

6. The device of claim 5 , wherein the settable latch includes three-level bi-complementary metal-oxide-semiconductor (BiCMOS) quasi-current mode logic (CML), wherein one level of the three-level BiCMOS quasi CML comprise one or more metal-oxide-semiconductor field-effect transistors (MOSFETs) and two levels of the three-level BiCMOS quasi CML comprise one or more heterojunction bipolar transistors (HBT).

7. The device of claim 4 , wherein each resettable flip-flop of the plurality of resettable flip-flops includes a resettable latch coupled to a latch.

8. The device of claim 7 , wherein the resettable latch includes three-level bi-complementary metal-oxide-semiconductor (BiCMOS) quasi-current mode logic (CML), wherein one level of the three-level BiCMOS quasi CML comprise one or more metal-oxide-semiconductor field-effect transistors (MOSFETs) and two levels of the three-level BiCMOS quasi CML comprise one or more heterojunction bipolar transistors (HBT).

9. The device of claim 1 , wherein the first THA comprises:

an emitter follower transistor coupled to each of an input and an output;

a charging node coupled between the output and a voltage supply, the charging node further coupled to the input via the emitter follower transistor; and

a cascode switch coupled to each of the input and the output and configured to:

cause the emitter follower transistor to operate in a conductive state and charge the charging node during a track mode; and

cause the emitter follower transistor to operate in a non-conductive state to isolate the charging node from the input during a hold mode.

10. The device of claim 9 , the cascode switch comprising:

a first bipolar transistor coupled to the input;

a second bipolar transistor coupled to the output and the first bipolar transistor;

a first field-effect transistor (FET) coupled to the first bipolar transistor and configured to receive a hold signal during the hold mode; and

a second FET coupled to the second bipolar transistor and configured to receive a track signal during the track mode.

11. The device of claim 10 , wherein a gate of the first FET is configured to receive a track signal to cause the first FET to operate in a conductive state during the track mode.

12. The device of claim 10 , wherein a gate of the second FET is configured to receive a hold signal to cause the second FET to operate in a conductive state during the hold mode.

13. The device of claim 1 , wherein the second THA comprises:

an input buffer;

an output buffer; and

a THA core coupled between the input buffer and the output buffer and comprising:

an emitter follower transistor coupled to each of an input and an output;

a charging node coupled between the output and a voltage supply, the charging node further coupled to the input via the emitter follower transistor; and

a cascode switch coupled to each of the input and the output and configured to:

cause the emitter follower transistor to operate in a conductive state and charge the charging node during a track mode; and

cause the emitter follower transistor to operate in a non-conductive state to isolate the charging node from the input during a hold mode.

14. The device of claim 1 , further comprising a pulse generator configured to convey a clock signal to the second THA and the SAR ADC in each path of the plurality of paths.

15. The device of claim 1 , wherein the plurality of paths are configured to sequentially sample an output of the first THA.

16. The device of claim 1 , further comprising:

a third first track and hold amplifier (THA) configured to receive the analog input signal; and

a second plurality of paths coupled to an output of the third THA, each path of the second plurality of paths including:

a fourth THA coupled to the third THA; and

a SAR ADC coupled to an output of the fourth THA.

17. The device of claim 1 , wherein each path of the plurality of paths includes:

a first delay component configured to receive a phase signal and convey a delayed phase signal to the second THA; and

a second delay component configured to receive a master clock signal and convey a second delayed phase signal to a comparator of the associated path.

18. An optical receiver, comprising:

a processor; and

an analog-to-digital converter (ADC) coupled to the processor and including:

a master track and hold amplifier (THA) configured to receive an analog input signal; and

a plurality of paths coupled to an output of the master THA, the plurality of paths comprising N+2 paths, N being equal to a number of bits of the ADC, each path of the plurality of paths including:

a slave THA coupled to the master THA; and

a successive approximation register analog-to-digital converter (SAR ADC) coupled to an output of the slave THA, the SAR ADC including:

a comparator including an input coupled to an output of the slave THA;

a latch coupled to an output of the comparator;

a SAR coupled to an output of the latch; and

a R-2R DAC coupled between an output of the SAR and another input of the comparator.

19. The optical receiver of claim 18 , wherein the master THA comprises:

an emitter follower transistor coupled to each of an input and an output;

a charging node coupled between the output and a voltage supply, the charging node further coupled to the input via the emitter follower transistor;

a cascode switch coupled to each of the input and the output and configured to:

cause the emitter follower transistor to operate in a conductive state and charge the charging node during a track mode; and

cause the emitter follower transistor to operate in a non-conductive state to isolate the charging node from the input during a hold mode.

20. The optical receiver of claim 18 , wherein the slave THA comprises:

an input buffer;

an output buffer; and

a THA core coupled between the input buffer and the output buffer and comprising:

an emitter follower transistor coupled to each of an input and an output;

a charging node coupled between the output and a voltage supply, the charging node further coupled to the input via the emitter follower transistor; and

a cascode switch coupled to each of the input and the output and configured to:

cause the emitter follower transistor to operate in a conductive state and charge the charging node during a track mode; and

cause the emitter follower transistor to operate in a non-conductive state to isolate the charging node from the input during a hold mode.

21. The optical receiver of claim 18 , wherein the plurality of paths are configured to sequentially sample an output of the master THA.

22. A method, comprising:

receiving an analog signal at a master track and hold amplifier (THA);

generating the output of the master THA including:

receiving the analog signal at an input of the master THA coupled to an emitter follower transistor;

configuring a cascode switch to cause the emitter follower transistor to operate in a conductive state to couple the input to each of a charging node and an output during a track mode; and

configuring the cascode switch to cause the emitter follower transistor to operate in a non-conductive state to isolate the input from each of the charging node and the output during a hold mode;

sequentially sampling an output of the master THA with a plurality of slave THAs;

digitizing an output of each slave THA of the plurality of slave THAs via a plurality of successive approximation register analog-to-digital converters (SAR ADC), wherein each SAR ADC of the plurality of SAR ADCs includes a comparator including an input coupled to an output of the second THA, a latch coupled to an output of the comparator, a SAR coupled to an output of the latch, and a R-2R DAC coupled between an output of the SAR and another input of the comparator; and

combining an output of each SAR ADC of the plurality of SAR ADCs to generate a digital signal.

23. The method of claim 22 , wherein sequentially sampling an output of the master THA with a plurality of slave THAs comprises receiving a different sample of the output of the master THA at each slave THA of the plurality of slave THAs.

24. The method of claim 22 , further comprising generating the output of each slave THA including:

receiving a sample of the output of the master THA at an input coupled to an emitter follower transistor;

configuring a cascode switch to cause the emitter follower transistor to operate in a conductive state to couple the input to each of a charging node and an output during a track mode; and

configuring the cascode switch to cause the emitter follower transistor to operate in a non-conductive state to isolate the input from each of the charging node and the output during a hold mode.