# US 2022/0037540 A1 · Avalanche photodiode gain control

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- Number: US 2022/0037540 A1
- Document ID: US20220037540A1
- Status: Published application
- Kind: A1
- Application number: 17/347,822
- Filed: 2021-06-15
- Published: 2022-02-03
- Earliest claimed: 2020-08-03
- Assignees: Texas Instruments Incorporated
- Applicants: Texas Instruments Incorporated
- Inventors: Gerd SCHUPPENER; Miaad ALIROTEH; Srinath RAMASWAMY; Baher HAROUN
- Web page: https://patentgrep.com/patent/US20220037540A1

## CPC

- H10F 77/959: {for devices working in avalanche mode}
- H03F 3/08: controlled by light
- H04B 10/6911: {Photodiode bias control, e.g. for compensating temperature variations}
- H04B 10/6931: {Automatic gain control of the preamplifier}
- H10F 30/225: the potential barrier working in avalanche mode, e.g. avalanche photodiodes
- H10F 30/2255: {in which the active layers form heterostructures, e.g. SAM structures}
- H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
- H03F: AMPLIFIERS
- H04B: TRANSMISSION

## Abstract

An avalanche photo-diode (APD) circuit includes a first APD and a bias circuit. The first APD is configured to detect light. The bias circuit is configured to control a gain of the first APD. The bias circuit includes a second APD, a reference voltage source, a bias voltage generation circuit, and a metal layer configured to shield the second APD from the light. The reference voltage source is configured to bias the second APD. The bias voltage generation circuit is configured to generate a bias voltage for biasing the first APD based on dark current output by the second APD.

## Claims

### Claim 1

An avalanche photo-diode (APD) circuit, comprising:
a first APD including an anode;
a reference voltage source; and
a bias circuit including:
a bias output coupled to the anode of the APD;
a second APD including:
a cathode coupled to the bias output; and
an anode coupled to the reference voltage source; and
a layer of metal covering the second APD.

### Claim 2 (depends on 1)

The APD circuit of claim 1, wherein the bias circuit further includes:
a current multiplier circuit including:
an input coupled to the cathode of the second APD; and
an output coupled to the bias output.

### Claim 3 (depends on 2)

The APD circuit of claim 2, wherein the bias circuit further includes:
a variable current source including:
a control input coupled to the output of the current multiplier circuit; and
an output coupled to the bias output.

### Claim 4 (depends on 3)

The APD circuit of claim 3, wherein:
the bias circuit further includes:
a third APD including:
an anode coupled to the output of the variable current source; and
the layer of metal covers the third APD.

### Claim 5 (depends on 3)

The APD circuit of claim 3, wherein the bias circuit further includes:
a buffer circuit including:
an input coupled to the output of the variable current source; and
an output coupled to the bias output.

### Claim 6 (depends on 2)

The APD circuit of claim 2, wherein:
the bias circuit further includes:
a third APD including:
an anode coupled to the bias output; and
the layer of metal covers the third APD.

### Claim 7 (depends on 6)

The APD circuit of claim 6, wherein:
the third APD includes a cathode; and
the bias circuit further includes:
an amplifier including:
a first input coupled to the output of the current multiplier circuit;
a second input coupled to the cathode of the third APD; and
an output coupled to the bias output.

### Claim 8 (depends on 7)

The APD circuit of claim 7, wherein the bias circuit further includes:
a bias voltage generation circuit including:
an input coupled to the output of the amplifier; and
an output coupled to the bias output.

### Claim 9

An avalanche photo-diode (APD) circuit, comprising:
a first APD configured to detect light;
a bias circuit configured to control a gain of the first APD, and includes:
a second APD;
a reference voltage source configured to bias the second APD;
a metal layer configured to shield the second APD from the light; and
a bias voltage generation circuit configured to generate a bias voltage for biasing the first APD based on dark current output by the second APD.

### Claim 10 (depends on 9)

The APD circuit of claim 9, wherein the bias circuit further includes:
a current multiplier circuit coupled to the second APD, and configured to provide, to the bias voltage generation circuit, an output current that is a predetermined multiple of the current output by the second APD.

### Claim 11 (depends on 10)

The APD circuit of claim 10, wherein:
the first APD includes an anode; and
the bias voltage generation circuit further includes:
a variable current source including a current output coupled to the anode of the first APD, the variable current source configured to generate, at the current output, a bias current based on the output current of the current multiplier circuit.

### Claim 12 (depends on 11)

The APD circuit of claim 11, wherein:
the bias voltage generation circuit further includes:
a third APD including:
an anode coupled to the current output of the variable current source;
the metal layer is configured to shield the third APD from the light.

### Claim 13 (depends on 11)

The APD circuit of claim 11, wherein the bias voltage generation circuit further includes:
a buffer circuit coupled to the current output of the variable current source, configured to provide the bias voltage to the first APD.

### Claim 14 (depends on 10)

The APD circuit of claim 10, wherein:
the bias circuit further includes:
a third APD biased by the bias voltage; and
an amplifier configured to generate a difference voltage as a difference of current output by the second APD and a current output by the third APD; and
the metal layer is configured to shield the third APD from the light.

### Claim 15 (depends on 14)

The APD circuit of claim 14, wherein the bias voltage generation circuit is configured to generate the bias voltage based on the difference voltage.

### Claim 16

A light detection circuit, comprising:
an avalanche photo-diode (APD) array configured to detect light, and including:
a first APD; and
a transimpedance amplifier coupled to first APD; and
a bias circuit coupled to the APD array, and configured to control a gain of the first APD, the bias circuit including:
a second APD;
a reference voltage source configured to bias the second APD;
a metal layer configured to shield the second APD from the light;
a current multiplier circuit coupled to the second APD, and configured to provide an output current that is a predetermined multiple of a dark current output by the second APD; and
a bias voltage generation circuit configured to generate a bias voltage for biasing the first APD based on the output current of the current multiplier circuit.

### Claim 17 (depends on 16)

The light detection circuit of claim 16, wherein:
the first APD includes an anode; and
the bias voltage generation circuit further includes:
a variable current source including a current output coupled to the anode of the first APD, the variable current source configured to generate, at the current output, a bias current based on the output current of the current multiplier circuit.

### Claim 18 (depends on 17)

The light detection circuit of claim 17, wherein:
the transimpedance amplifier is a first transimpedance amplifier;
the bias voltage generation circuit further includes:
a third APD including:
an anode coupled to the current output of the variable current source; and
a cathode;
a second transimpedance amplifier coupled to the cathode of the third APD;
a buffer circuit coupled to the current output of the variable current source, and configured to provide the bias voltage to the first APD; and
the metal layer is configured to shield the third APD from the light.

### Claim 19 (depends on 16)

The light detection circuit of claim 16, wherein:
the bias circuit further includes:
a third APD biased by the bias voltage; and
an amplifier configured to generate a difference voltage as a difference of current output by the second APD and a current output by the third APD; and
the metal layer is configured to shield the third APD from the light.

### Claim 20 (depends on 19)

The light detection circuit of claim 19, wherein the bias voltage generation circuit is configured to generate the bias voltage based on the difference voltage.