Temperature compensation schemes for APD detectors in PET

A temperature compensation circuit for APD detectors includes a low voltage (LV) temperature compensation section and a high voltage (HV) regulation section. The HV section includes (1) a high voltage regulation circuit to regulate the external HV power supply (HVPS); (2) a high voltage adjustment circuit with I²C digital potentiometers to preset the APD operating voltage in each detector; (3) a HV monitor with voltage attenuator, I²C multiplexer, Hi-Z OPAMP to ensure accurate HV measurement, and a low-power I²C ADC. The LV section includes (1) a remote temperature sensing circuit; (2) a low-voltage DC biasing circuit with an I²C digital potentiometer to adjust the temperature slope and a Hi-Z operational amplifier (OPAMP) to provide low-impedance voltage level adjustment based on the sensed temperature; (3) a LV monitor circuit with a low power I²C ADC to read out and monitor the LV value. Hence the photosensors in each detector block are biased from both the HV node for setting the proper photosensor operating voltage and the LV node for automatically compensating the APD gain versus temperature due to ambient temperature variations and MR gradient influences. This hardware temperature compensation scheme is intended to stabilize the APD detector timing and energy performances in MR/PET applications.