Hamamatsu-Photonics K.k.

Tsuyoshi Ohta

Shigeyuki Nakamura

Shunsuke Adachi

Michito Hirayanagi

Hiroki Suzuki

Shigeki Nakase

Kenichi Sato

Shogo Kamakura

A readout circuit for reading out an output current from a photoelectric conversion element which collectively outputs currents generated in a plurality of pixels, each of which includes an avalanche photodiode, includes a current mirror circuit configured to receive the output current and output first and second currents having magnitudes in proportion to the output current, a photon counting circuit configured to count the number of photons incident on the photoelectric conversion element on the basis of the first current, an integral circuit configured to integrate the second current to generate a voltage signal, and a signal processing unit configured to determine a magnitude of light incident on the photoelectric conversion element on the basis of a counting result output from the photon counting circuit and a magnitude of the voltage signal output from the integral circuit.

Readout circuit

A reverse bias voltage is applied to a photodiode array provided with a plurality of avalanche photodiodes operated in Geiger mode and with quenching resistors connected in series to the respective avalanche photodiodes. Electric current is measured with change of the reverse bias voltage applied, and the reverse bias voltage at an inflection point in change of electric current measured is determined as a reference voltage. A voltage obtained by adding a predetermined value to the determined reference voltage is determined as a recommended operating voltage.

Photodiode array, method for determining reference voltage, and method for determining recommended operating voltage

A bias circuit for applying a bias voltage to an avalanche photodiode APD2 for detecting light comprises a first diode APD1, a power supply V.sub.H connected to the first diode APD1, for applying a voltage to make the diode in breakdown between an anode and a cathode of the first diode APD1, and a constant voltage circuit V2 connected to the avalanche photodiode APD2 for detecting light, for applying a voltage difference of a breakdown voltage generated between the anode and the cathode of the first diode APD1 minus a constant voltage to the avalanche photodiode. The constant voltage is substantially independent from current flowing in the avalanche photodiode APD2 for detecting light to the avalanche photodiode.

Bias circuit for maintaining a constant potential difference between

A photodetecting circuit using an avalanche photodiode of the present invention has an avalanche photodiode, and a bias control means for applying a bias voltage to the avalanche photodiode to drive the avalanche photodiode at a high multiplication factor. The bias control means has a diode having the same temperature dependence of a breakdown voltage as that of the avalanche photodiode, and a control circuit for applying positive and negative potentials with respect to the ground potential between the anode and the cathode of the diode such that the diode is set in a breakdown state at a predetermined current. A positive or negative potential is applied from one of the anode and the cathode of the avalanche photodiode as a bias voltage, and a photocurrent is output from the other terminal of the avalanche photodiode.

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Hamamatsu, Japan

Tsuyoshi Ohta