Avalanche photodiode gain compensation for wide dynamic range
An optical receiver includes a parasitic current compensation circuit having a reference diode, a sense avalanche photodiode (APD), at least one DC voltage source, and a measurement node. The at least one DC voltage source is configured to generate a first DC bias voltage that varies over time and drives the reference diode, and generates a second DC bias voltage that varies over time and drives the sense APD. A reference parasitic current travels through the reference diode based on the first DC bias voltage. A sense current travels through the sense APD based on the second DC bias voltage and exposure of the sense APD to a light signal. The measurement node receives a sense photocurrent, which is generated by the sense APD in response to the exposure of the sense APD to the light signal, the sense photocurrent including the sense current less the reference parasitic current.
1 . An optical receiver comprising:
a parasitic current compensation circuit comprising a reference diode;
a sense avalanche photodiode (APD);
at least one DC voltage source configured to generate a first DC bias voltage that varies over time and drives the reference diode, and generate a second DC bias voltage that varies over time and drives the sense APD;
and
a measurement node,
wherein:
a reference parasitic current travels through the reference diode based on the first DC bias voltage;
a sense current travels through the sense APD based on the second DC bias voltage and exposure of the sense APD to a light signal; and
the measurement node receives a sense photocurrent, which is generated by the sense APD in response to the exposure of the sense APD to the light signal, the sense photocurrent comprising the sense current less the reference parasitic current.
2 . The optical receiver of claim 1 , wherein the reference diode comprises an APD that is shielded from light signals.
3 . The optical receiver of claim 2 , wherein the first and second DC bias voltages are waveforms that comprise a ramp waveform or a sawtooth waveform.
4 . The optical receiver of claim 3 , wherein the waveforms traverse a voltage range of 20 VDC-60 VDC, and the waveforms have a frequency of 0.8 MHz-1.2 MHz.
5 . The optical receiver of claim 1 , wherein the first DC bias voltage varies at a first rate, and the second DC bias voltage varies at a second rate that is opposite the first rate.
6 . The optical receiver of claim 5 , wherein the reference diode and the sense APD are connected in parallel with the measurement node.
7 . The optical receiver of claim 1 , wherein the first and second DC bias voltages are equal and change over time at a change rate.
8 . The optical receiver of claim 7 , wherein:
the reference diode and the sense APD are connected in parallel with the measurement node; and
the parasitic current compensation circuit comprises a shunt that extracts twice the reference current from the measurement node.
9 . A light detector comprising: the optical receiver of claim 1 ; and
a light detection circuit coupled to the measurement node and configured to detect the light signal based on the sense photocurrent.
10 . A light detection and ranging (LIDAR) device comprising:
a light emitter; and the light detector of claim 9 ,
wherein the light detector comprises:
a transimpedance amplifier configured to produce a voltage pulse in response to the sense photocurrent;
a comparator configured to compare the voltage pulse to a threshold voltage and produce a comparator output signal; and
a time-to-digital converter configured to receive the comparator output signal and determine an interval of time between the transmission of a transmitted light signal from the light signal emitter and an exposure of the sense APD to a reflection of the transmitted light signal from an external object based on the sense photocurrent.