Methods and apparatus for selective histogramming

1. An apparatus, capable of receiving TDC codes from a time-to-digital converter (TDC), comprising:

a controller configured to:

receive a first set of TDC codes, wherein each TDC code comprises a total number of bits; and

identify a portion of bits, from the total number of bits, in the first set of TDC codes;

a plurality of counters responsive to the controller, wherein each counter is configured to increment in value based on the identified portion of bits; and

an encoder, in communication with the plurality of counters, and configured to:

identify the counter, from the plurality of counters, with the highest value;

generate a mask code for the counter with the highest value; and

transmit the mask code to the controller;

wherein the controller is further configured to:

query a second set of TDC codes using the mask code; and

generate a peak code using the mask code, wherein the peak code represents a single bin number from a plurality of virtual histogram bins.

2. The apparatus according to claim 1 , further comprising a phase counter configured to:

receive a sequence of laser clock pulses;

generate a phase count value; and

transmit the phase count value to the controller.

3. The apparatus according to claim 2 , wherein the phase count value increments after a predetermined number of laser clock pulses.

4. The apparatus according to claim 1 , wherein the controller is further configured to reset the plurality of counters after the predetermined number of laser clock pulses.

5. The apparatus according to claim 1 , wherein querying the second set of TDC codes comprises determining whether the portion of bits in the second set of TDC codes contains the mask code.

6. The apparatus according to claim 1 , wherein querying the second set of TDC codes comprises ignoring any TDC codes, from the second set of TDC codes, if the portion of bits differs from the mask code.

7. The apparatus according to claim 1 , wherein the controller is further configured to generate the peak code using a second mask code.

8. The apparatus according to claim 1 , wherein the encoder is further configured to:

identify the counter, from the plurality of counters, with the second-highest value; and

generate a third mask code for the counter with the second-highest value.

9. A method for selective histogramming using data from a time-to-digital converter (TDC), comprising:

dividing a total number of virtual bins into a number of groups; and

histogramming the total number of virtual bins over a total number of phases, wherein:

a first phase, from the total number of phases, comprises:

receiving a first set of TDC values from the TDC, wherein each TDC value is represented by a total number of bits;

incrementing a plurality of counters based on a first portion of bits from the total number of bits;

generating a first mask code for the counter with the highest count value; and

resetting the counter; and

each subsequent phase, from the total number of phases, comprises:

dividing a portion of the virtual bins into the number of groups;

receiving a new set of TDC values from the TDC;

querying the new set of TDC values using at least the first mask code;

incrementing the counter based on a new portion of the bits;

generating a new mask code for the counter with the highest count value; and

generating a peak code using the mask codes from each phase, wherein the peak code represents a single bin number from the total number of virtual bins.

10. The method according to claim 9 , further comprising receiving a sequence of laser clock pulses and incrementing a phase count value after a predetermined number of laser clock pulses.

11. The method according to claim 10 , further comprising resetting the plurality of counters after the predetermined number of laser clock pulses.

12. The method according to claim 9 , wherein the number of groups is equal to a total number of counters in the plurality of counters.

13. The method according to claim 9 , wherein generating the peak code using the mask codes comprises stringing together the mask codes from each phase.

14. The method according to claim 9 , wherein querying comprises determining whether the first portion of bits in the new set of TDC codes contains the mask code.

15. The method according to claim 9 , wherein querying comprises ignoring any TDC values, from the new set of TDC codes, if the first portion of bits differs from the first mask code.

16. A system, comprising:

a source configured to transmit a source signal;

a receiver configured to receive a reflected source signal and generate a reception signal according to the reflected source signal;

a phase counter having a phase count value that increments after a predetermined number of clock pulses;

a conversion circuit connected to the receiver and configured to convert the reception signal to a binary code that represents time, wherein the binary code comprises a total number of bits; and

a processor connected to the conversion circuit and the phase counter and configured to:

histogram a total number of virtual bins over a plurality of phases using a total number of counters, wherein the total number of counters is less than the total number of virtual bins, comprising:

for each phase:

incrementing the counters based on a portion of bits of the binary code;

generating a mask code for the counter value with the highest value; and

querying a new portion of bits in a new binary code using the mask code; and

stringing together the mask codes from each phase to form a peak code, wherein the peak code represents a single bin number from the total number of virtual bins.

17. The system according to claim 16 , wherein querying comprises determining whether the new portion of bits in the new binary code contains the mask code.

18. The system according to claim 16 , wherein querying comprises ignoring the new binary code if the new portion of bits differs from the mask code.

19. The system according to claim 16 , wherein the processor is further configured to reset the total number of counters after the predetermined number of laser clock pulses.

20. The system according to claim 16 , wherein the processor is further configured to divide the total number of virtual bins into a number of groups, and wherein the number of groups is equal to the total number of counters.