Advanced temperature compensation and control circuit for single photon counters

A radiation detector for use in imaging comprising:

• a plurality of avalanche photodiodes, at least one of the avalanche photodiodes being a reference photodiode which is shielded from light;
• a biasing circuit configured to bias the avalanche photodiodes to operate in a Geiger mode in which the avalanche photodiodes breakdown in response to receiving radiation generating an output pulse and the biasing circuit being configured to bias each photodiode back to the Geiger mode after each breakdown;
• a first cooling element thermally coupled to the photodiodes and configured to remove heat from the photodiodes;
• a control circuit configured to:
• measure a breakdown voltage across the at least one reference photodiode and adjust the bias voltage of the photodiodes to a predetermined characteristic logic voltage level,
• measure the breakdowns of the at least one reference photodiode and
• control the first cooling element in accordance with a rate of the output pulses from the at least one shielded avalanche photodiode.

A radiation detector for use in imaging comprising:

• a plurality of avalanche photodiodes, the plurality of avalanche photodiodes including:
• a first plurality of avalanche photodiodes configured to be optically connected with a scintillator, the first plurality of avalanche photodiodes generating output voltage pulses (i) in response to light photons from the scintillator in response to incident radiation and (ii) in response to dark currents,
• at least one shielded avalanche photodiode, the at least one shielded avalanche photodiodes being shielded from the light photons from the scintillator, the at least one shielded avalanche photodiode generating the output voltage pulses in response to dark currents,
• a biasing circuit configured to bias the avalanche photodiodes to operate in a Geiger mode in which (i) the first plurality of avalanche photodiodes breakdown in response to at least one of receiving the light photons from the scintillator and the dark currents, (ii) the at least one shielded avalanche photodiode breaks down in response to the dark currents, and (iii) each breakdown generates an output voltage pulse, wherein the biasing circuit is further configured to bias each of the first plurality of avalanche photodiodes and the at least one shielded avalanche photodiode back to the Geiger mode after each breakdown;
• a cooling element thermally coupled to the first avalanche photodiodes and the at least one shielded avalanche photodiode, the cooling element being configured to remove heat from the first plurality of avalanche photodiodes and the at least one shielded avalanche photodiode;
• a control circuit configured to count the breakdowns of the first plurality of avalanche photodiodes, the control circuit including two feedback paths, a first feedback path configured to control a bias voltage to the first and shielded avalanche photodiodes to bring the output voltage pulses to a preselected common voltage level and a second feedback path configured to control the cooling element in accordance with a rate of the counted breakdowns of the at least one shielded avalanche photodiode.