Avalanche photodiode operating voltage selection algorithm

• US 8,653,434 B2
• Filed: 04/08/2011
• Issued: 02/18/2014
• Est. Priority Date: 04/08/2010
• Status: Active Grant

• Current Assignee: BAE Systems Information and Electronic Systems Integration Incorporated (BAE Systems Plc)
• Original Assignee: BAE Systems Information and Electronic Systems Integration Incorporated (BAE Systems Plc)
• Inventors: Johnson, Aaron, Schorr, David, Steenson, James H. Jr.
• Primary Examiner(s): PYO, KEVIN K
• Application Number:
  US13/377,084
• Publication Number:
  US 20120080583A1
• Time in Patent Office: 1,047 Days
• Field of Search: 250/214.R, 250/214.1, 250/214.VT, 250/214.AG, 250/207, 327/422, 327/514, 257/186
• US Class Current: 250/214.R
• CPC Class Codes: G01J 1/44 Electric circuits for command of an exposure part G03B7/02
• CPC Class Codes: G01J 2001/4466 Avalanche
• CPC Class Codes: G01S 7/4868 Controlling received signal intensity or exposure of sensor
• CPC Class Codes: H01L 31/107 the potential barrier working in avalanche mode, e.g. avalanche photodiodes
• CPC Class Codes: H03G 3/3084 in receivers or transmitters for electromagnetic waves other than radiowaves, e.g. lightwaves H03G3/32, H03G3/34 take precedence

Abstract

An accurate and rapid method for characterizing the performance of an APD and setting its operating voltage Vop to an optimal value uses an on-board LED or other pulsed light source to measure APD responses at different operating voltages Vop. An estimated breakdown voltage Vb is determined by comparing the measured responses, and the Vop is adjusted to a new value at a fixed offset from the estimated Vb. The fixed offset is selected according to ambient light conditions, including the presence or absence of light background noise, and whether the sun is partially or fully in the field of view. The method is iterated until convergence, or until a maximum number of iterations is reached. In embodiments, a plurality of APD'"'"'s having a common Vop can be adjusted, and the Vop is never set below a minimum value VopBW necessary to meet timing requirements for a missile guidance system.

Claims

1. A method for optimizing the operating voltage Vop of an avalanche photo-diode (APD), the method comprising:

setting Vop to a first value which is less than an initially estimated breakdown voltage for the APD;

determining a first response of the APD to an on-board light source at the first Vop value;

setting Vop to an updated value which is less than the initially estimated breakdown voltage and different from the previous value of Vop;

determining an updated response of the APD to the on-board light source;

determining an updated estimated breakdown voltage according to the updated value of Vop, the updated response, the immediately previous value of Vop, and the immediately previous response;

setting Vop to an offset value which is offset below the updated estimated breakdown voltage by a fixed offset amount; and

repeating the steps of determining an updated response, determining an updated estimated breakdown voltage, and setting the Vop to an offset value, until at least one of a convergence criterion is met and a maximum number of repetitions is reached, each estimated breakdown voltage being determined according to a most recently set value of Vop, a most recent response, an immediately previous value of Vop, and an immediately previous response.

2. The method of claim 1, wherein determining the updated estimated breakdown voltage Vb includes applying the formula

Vb=(R2*Vop2−

R1*Vop1)/(R2−

R1)

where Vop1 is the immediately previous value of Vop, R1 is the response of the APD for Vop=Vop1, Vop2 is the updated value of Vop, and R2 is the response of the APD for Vop=Vop2.

3. The method of claim 1, wherein the initially estimated breakdown voltage is estimated according to an ambient temperature and typical characteristics applicable to an APD type to which the APD belongs.

4. The method of claim 1, wherein the method further includes determining a field of view illumination status, and the fixed offset amount is determined according to the field of view illumination status.

5. The method of claim 4, wherein the field of view illumination status is selected from among a group of status conditions, the group of status conditions including at least one of:

night;

day, sun not in field of view;

day, sun partially in field of view; and

day, sun fully in field of view.

6. The method of claim 4, wherein the fixed offset amount for a field of view illumination status of “

night”

is about approximately 40 volts.

7. The method of claim 4, wherein the fixed offset amount for a field of view illumination status of “

day, sun not in field of view”

is about approximately 80 volts.

8. The method of claim 4, wherein the fixed offset amount for a field of view illumination status of “

day, sun partially in field of view”

is an amount which sets Vop to a minimum value VopBW below which the response of the APD might not meet a timing (bandwidth) required to evaluate laser pulses.

9. The method of claim 4, wherein the fixed offset amount for a field of view illumination status of “

day, sun fully in field of view”

is an amount which sets Vop to a minimum value VopBW below which the response of the APD might not meet a timing (bandwidth) required to evaluate laser pulses.

10. The method of claim 1, wherein the convergence criterion is that the difference between the updated value of Vop and the immediately previous value of Vop is less than or equal to 5 Volts in one embodiment.

11. The method of claim 1, wherein the maximum number of repetitions is 5 repetitions.

12. The method of claim 1, wherein the fixed offset is adjusted if necessary so as to ensure that Vop is not set below a minimum value VopBW necessary to meet timing requirements of the APD.

13. The method of claim 1, wherein the on-board light source is an LED.

14. The method of claim 1, wherein a common Vop is provided to each APD in a group containing a plurality of APD'"'"'s, and the method further includes determining responses of each of the APD'"'"'s in the group to the on-board light source and setting the Vop to a value which is optimal for performance of the group of APD'"'"'s.

15. The method of claim 14, wherein determining responses of each of the APD'"'"'s in the group to the on-board light source includes determining responses of each of the APD'"'"'s to the same on-board light source.

16. The method of claim 14, wherein the group includes exactly seven APD'"'"'s.

17. The method of claim 14, wherein setting the Vop to a value which is optimal for performance of the group of APD'"'"'s includes:

determining a most sensitive APD in the group, the most sensitive APD in the group being that APD in the group which has the lowest breakdown voltage in comparison to the other APD'"'"'s in the group;

optimizing Vop to find an optimal value VopMS for the most sensitive APD in the group; and

setting Vop to a value which is offset from VopMS by a predetermined most-sensitive offset amount.

18. The method of claim 17, wherein setting Vop to a value which is offset from VopMS includes setting Vop to a value which is greater than a minimum value VopBW below which the updated response of the APD to the on-board light source cannot be determined within a specified maximum time period.

19. The method of claim 1, wherein the on-board light source is a pulsed light source.