Method and device for detecting the temporal variation of the light intensity in a matrix of photosensors

A device for detecting temporal variation of the light intensity in a matrix of photosensors, characterised in that it comprises at least:

• a matrix of pixels, wherein each pixel comprises at least:
• a) a photosensor which generates a photocurrent proportional to a light striking its surface;
• b) an adjustable gain current mirror (8) comprising an input branch, a first output branch with adjustable current gain and a second output branch with a fixed gain, which copy the input photocurrent to respective outputs and where the output branch with fixed gain is connected to a collector transistor (T4c1) connected in diode configuration and whose nodes are connected to the collector transistors of the other pixels of the matrix;
• c) a transimpedance amplifier (T6a1-T6d1) arranged in the output of the adjustable gain current mirror, the amplifier comprising at least two MOS transistors polarised in weak inversion and arranged in series, each MOS transistor being in diode configuration, for the conversion of the photocurrent into a logarithmic voltage;
• d) a switched capacitor circuit (14) comprising a first capacitor (C4) connected to the output of the transimpedance amplifier (T6a1-T6d1), a voltage amplifier (T10a1-T10b1) connected to the first capacitor (C4), and a second capacitor (C3) connected in series to the first capacitor (C4) and feedback connected to the voltage amplifier, the second capacitor being connected in parallel to a MOS transistor (T111) which acts as a reset key;
• and,
• e) a first threshold detector to determine if the voltage exceeds a higher threshold and a second threshold detector to determine if the voltage drops below a lower threshold, both detectors being connected to the output of the second voltage amplifier (T10a1-T10b1) and said higher and lower thresholds being previously set by a user,
• a block for the automatic adjustment of the amplification of the photocurrent, which calculates the average of the photocurrents of the pixels of the matrix;
• and,
• an arbitrating and event-encoding block connected to the output of the pixel matrix.