| 摘要 |
In a photodetector, a photodiode and a capacitor are coupled between a sensi ng node and a ground voltage line, and a MOS transistor is coupled between the sensing node and a reference voltage line. Initially, the capacitor is charg ed so that the sensing node voltage is greater than a transition voltage and a predetermined gate voltage is applied to switch the transistor off. During a sampling time, the capacitor initially discharges through the photodiode, th e discharge current being dependent on the intensity of radiation incident on the photodiode, until the sensing node voltage falls to the transition voltage. If the sensing node voltage falls to the transition voltage during the sampling time, the transistor enters its weak inversion operation domain and the current through the photodiode can flow through the transistor such that the sensing node voltage varies logarithmically with the radiation intensity. At the end of the sampling time, a readout circuit coupled to the sensing node generates an output signal dependent on the sensing node voltag e, and the photodetector is reset by recharging the capacitor before the start of another sampling time.
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