Image sensor with non-destructive readout

摘要

An image sensor particularly suitable for use in an autofocus camera includes a light measuring means, a capacitance element for accumulating picture element information which is photoelectrically converted by the light measuring means, a source follower circuit that outputs as picture element information the voltage across the capacitance element with low output impedance, a switching element for reading out the picture element information from the source follower to a video line, and a load element for outputting the output voltage of the source follower to a monitor line. The output voltage from the source follower to the monitor line is compared with a reference voltage which has been preset to a desired output voltage level. The light measuring operation of the light measuring means is caused to stop when the output voltage of the source follower is equal to the reference voltage thereby storing and maintaining across the capacitance element the picture element information which has the desired voltage level.