Patent ID: 6348681
Filing Date: 2002-02-19
Classification: H04N

Abstract:
An active pixel sensor cell array, including:at least one active pixel sensor cell having a MOSFET reset transistor and sensing circuitry, wherein the sensing circuitry is coupled to the reset transistor and configured to produce at a signal node, in response to incident radiation, a time-dependent signal potential indicative of said radiation, wherein the reset transistor has a gate, a channel coupled to the signal node, and a threshold voltage, the sensing circuitry is configured to reset the signal potential at the signal node to a first potential in response to a full reset potential at the gate of the reset transistor, and the sensing circuitry has a state in which assertion of an XDR reset potential at the gate of the reset transistor following assertion of the full reset potential resets the signal potential at the signal node to a second potential; and an XDR reset signal generator including a digital-to-analog converter (DAC) and a level shifting circuit, wherein the DAC is configured to assert a first analog voltage in response to control bits indicative of a predetermined value of the XDR reset potential, wherein the level shifting circuit has an input coupled to receive the first analog voltage from the DAC, an output, and a MOSFET reference transistor whose current density matches that of the reset transistor, wherein the reference transistor is coupled to the output, the level shifting circuit is configured to assert a second analog voltage at the output in response to the first analog voltage, and the second analog voltage is shifted by the said threshold voltage of said reference transistor relative to the first analog voltage.