CMOS image sensor for direct time of flight measurement

A CMOS imaging sensor for detecting time occurrence of a light pulse having a given pulse duration T, comprising:

• pixels, each pixel having a pixel structure comprising at least:
• a photodetector operating as a current source;
• a nonlinear resistor, connected and operated continuously between a voltage supplying node of the pixel and a sense node,
• wherein the sense node is a capacitive sense node having a capacitance, the nonlinear resistor and capacitance of the sense node configured to operate as a low pass filter and to perform current to voltage conversion in a low frequency range and integration in a high frequency range;
• a control circuit for controlling a measurement phase in at least a selected pixel (P) for measuring a time occurrence of a rising edge of a light pulse reaching the photodetector in the pixel, the control circuit being configured to:
• implement continuous current to voltage conversion inside the pixel through the nonlinear resistor, and
• convert, by the nonlinear resistor and capacitance, the signal received from the photodetector to produce a voltage signal at the sense node that has a main signal component comprising at least a rising edge pulse location information in the high frequency range, and a noise component mainly concentrated in the low frequency range spaced apart from said high frequency range, and
• a readout circuitry of a voltage signal from the sense node of a selected pixel, which comprises at least:
• an analog to digital converter applying a high sampling time in respect of the pulse width duration;
• and
• a filter (F) configured to apply continuously at least one of a band pass or high pass filter, before or after analog to digital conversion, having the effect of increasing the signal to noise ratio in at least a frequency band around the main signal component to recover the rising edge pulse location information.