Patent ID: 8981437
Filing Date: 2015-03-17
Classification: H01L

Abstract:
1. A pixel front end for interfacing to at least one photodetector comprising a first terminal and a second terminal connected to a detector common, comprising; an n-type device acting as a direct injection device, with one end of its channel connected to the first terminal of the photodetector and the other end of its channel connected to a voltage mode pixel backend, and the gate signal applied to the device sets the bias across the detector, a p-type current source connected between the detector first terminal and another common, acting to reduce current to the direct injection device; and, a first p-type switch, connected across the current source from gate to drain, wherein the first p-type switch is turned on during a calibration period, thereby sampling the gate signal on the current source related to the current flow during calibration (background current), such that when the first p-type switch is turned off, the sampled voltage is held on the gate of the current source causing the background current to be subtracted from injection an n-type current sink connected with its channel as a current sink between the first terminal of the detector and another common and its gate connected to an external bias voltage; and, when properly biased, the n-type current sink will apply a predetermined compensation current to be added to the sampled background current of the proper magnitude whereby when the p-type switch and n-type current source are switched off in consecutive order before image collection begins, the resulting background current continues to flow through the p-type current source due to the held values on its gate capacitance and is compensated to remove the effects of charge injection pedestal error from the p-type switch shutting off.