METHODS AND APPARATUS FOR SELECTIVE HISTOGRAMMING

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

a phase counter configured to generate a phase count value; and

a plurality of physical bins responsive to the phase count value and configured to:

increment in value according to the TDC codes; and

generate a plurality of histograms according to the TDC codes and the phase count value, wherein the plurality of histograms comprises:

a first histogram, wherein each physical bin from the first histogram is defined by a number N of TDC codes; and

a second histogram of the physical bin from the first histogram having the highest value, wherein each physical bin from the second histogram is defined by a number M of TDC codes, and wherein the number of TDC codes from the second histogram is less than the number of TDC codes from the first histogram.

2 . The apparatus of claim 1 , wherein the phase counter is further configured to receive a sequence of laser clock pulses.

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

4 . The apparatus of claim 1 , further 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, wherein the plurality of physical bins increment in value based on the identified portion of bits.

5 . The apparatus of claim 4 , further comprising an encoder configured to:

identify the physical bin, from the plurality of physical bins, with the highest value;

generate a mask code for the physical bin with the highest value; and

transmit the mask code to the controller.

6 . The apparatus of claim 5 , wherein the controller is further configured to:

reset the value of each physical bin;

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 physical bin number from the plurality of physical bins.

7 . The apparatus of claim 6 , 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.

8 . The apparatus of claim 6 , 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.

9 . A method for histogramming using a fixed number of physical bins and TDC codes from a time-to-digital converter (TDC), comprising:

generating a first histogram of a first range of TDC codes during a first phase using the fixed number of physical bins, wherein each physical bin is defined by a number N of TDC codes;

determining the physical bin from the first histogram that has the highest value; and

generating a second histogram of a second range of TDC codes during a second phase using the fixed number of physical bins, wherein each physical bin in defined by a number M of TDC codes, N is greater than M, and the second range of TDC codes corresponds to the TDC codes of the physical bin from the first histogram that has the highest value.

10 . The method of claim 9 , further comprising:

receiving a sequence of laser clock pulses; and

incrementing a phase count value after a predetermined number of the laser clock pulses.

11 . The method of claim 10 , wherein:

generating the first histogram comprises:

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

incrementing a count value of each physical bin from the first histogram based on the first portion of bits from the total number of bits;

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

resetting the value of each physical bin after the predetermined number of laser clock pulses; and

generating the second histogram comprises:

receiving a second set of TDC codes from the TDC;

querying the second set of TDC codes using at least the first mask code; and

incrementing a count value of each physical bin from the second histogram based on the second portion of bits from the total number of bits;

generating a second mask code for the physical bin with the highest second count value; and

generating a peak code using the first mask code and the second mask code, wherein the peak code represents a single bin number from the plurality of physical bins.

12 . The apparatus of claim 11 , wherein querying the second set of TDC codes comprises determining whether the portion of bits in the second set of TDC codes contains the first mask code.

13 . The apparatus of claim 11 , 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 first mask code.

14 . The method of claim 11 , wherein generating the peak code using the first mask code and the second mask code comprises stringing together the first mask code and the second mask code.

15 . 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 conversion circuit connected to the receiver and configured to convert the reception signal to one or more time-to-digital (TDC) codes;

a phase counter configured to generate a phase count value; and

a fixed number N of physical bins responsive to the phase count value and configured to:

increment in value according to the TDC codes; and

generate a plurality of histograms according to the TDC codes and the phase count value, wherein the plurality of histograms comprises:

a first histogram of a first range of TDC codes using the fixed number N of physical bins; and

a second histogram of a second range of TDC codes using the fixed number N of physical bins, wherein the second range of TDC codes corresponds to the physical bin from the first histogram having the highest value.

16 . The system of claim 15 , wherein the number of TDC codes in the first range is greater than the number of TDC codes in the second range.

17 . The system of claim 16 , further comprising a processor configured to:

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

identify a portion of bits, from the total number of bits, in the first set of TDC codes, wherein each physical bin increments in value based on the identified portion of bits;

identify the physical bin, from the plurality of physical bins, with the highest value; and

generate a mask code for the physical bin with the highest value.

18 . The system of claim 17 , wherein the processor is further configured to:

reset the value of each physical bin after the predetermined number of laser clock pulses;

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 physical bin number from the plurality of physical bins.

19 . The system of claim 18 , 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.

20 . The system of claim 18 , 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.