Open-Loop Photodiode Gain Regulation

An avalanche photodiode (APD) based gain control apparatus adapted to generate signals to control relative gain of at least one APD element, the apparatus comprising:

• a sensor configured to measure temperature information indicative of a temperature of an APD element;
• a controller operably coupled to the sensor and configured to:
• (a) receive the measured temperature information;
• and,
• (b) receive a commanded APD relative gain level signal, the commanded APD relative gain level signal representing a desired APD gain level relative to a predetermined reference gain, the desired APD gain level to be generated by the APD element in response to a drive voltage supplied to an input of the APD element;
• a data store operably coupled to the controller, wherein:
• the data store contains information about a predetermined efficiency characteristic that relates the commanded APD relative gain level signal by the APD element to a drive voltage supplied to the APD element,
• the predetermined efficiency characteristic information comprises adjustments responsive to the measured temperature of the APD element for a plurality of temperatures,
• the controller is further configured to retrieve at least a portion of the predetermined efficiency characteristic information sufficient to determine the drive voltage such that, when the drive voltage is supplied to the APD element while operating at the temperature of the APD element indicated by the measured temperature information, the drive voltage is operable to cause the APD element to generate substantially the desired APD gain level;
• when the retrieved predetermined efficiency characteristic information indicates that the desired APD gain level at the measured temperature of the APD element corresponds to a substantially non-linear portion of the predetermined efficiency characteristic, the controller is further configured to determine the drive voltage signal based upon the retrieved predetermined efficiency characteristic as a function of the commanded APD relative gain level signal and the measured temperature information;
• and,
• a driver circuit operatively coupled to the controller and to the input of the APD element, the driver circuit being configured to supply the determined drive voltage signal to the input of the APD element,
• wherein the determined drive voltage signal is operative to generate a gain level from the APD element, relative to the predetermined reference gain, substantially at the desired APD gain level.