Reduction of fixed-pattern noise in digital image sensors by mitigating gain mismatch error

A method for error-modulated pixel readout by a plurality of programmable gain amplifiers (PGAs) of a digital image sensor, the method comprising:

• receiving, by the plurality of PGAs, for each row scan time of a sequence of row scan times of a row scan routine, a swap control signal indicating a swap state generated according to a pseudo-random sequence;
• and
• for each of the plurality of PGAs, in each row scan time:
• receiving a respective pixel signal;
• configuring a respective operational amplifier to couple with a respective first capacitor network and a respective second capacitor network in accordance with the swap state, such that:
• responsive to the swap control signal indicating a first swap state, the respective first capacitor network and the respective second capacitor network are coupled with the respective operational amplifier as a respective input capacitor network and as a respective feedback capacitor network, respectively;
• and
• responsive to the swap control signal indicating a second swap state, the respective first capacitor network and the respective second capacitor network are coupled with the respective operational amplifier as the respective feedback capacitor network and as the respective input capacitor network, respectively;
• and
• generating a respective PGA output signal responsive to the respective pixel signal in response to the configuring by applying a respective gain to the respective pixel signal having a magnitude defined by a ratio of an input capacitance of the respective input capacitor network to a feedback capacitance of the respective feedback capacitor network.

An error-modulatable programmable gain amplifier (PGA) circuit for use with a digital image sensor, the PGA circuit comprising:

• a control input configured to receive, for each row scan time of a sequence of row scan times, a swap control signal indicating a swap state generated according to a pseudo-random sequence;
• a pixel input configured to receive a pixel signal corresponding to one of a plurality of pixels of a pixel array of the digital image sensor;
• a first capacitor network and a second capacitor network;
• and
• an operational amplifier configured to generate a PGA output signal by applying gain to the pixel signal in accordance with the swap state received at the control input, a magnitude of the gain defined by a ratio of an input capacitance to a feedback capacitance, such that:
• responsive to the swap control signal indicating a first swap state, the first capacitor network is coupled with the operational amplifier to provide the input capacitance, and the second capacitor network is coupled with the operational amplifier to provide the feedback capacitance;
• and
• responsive to the swap control signal indicating a second swap state, the first capacitor network is coupled with the operational amplifier to provide the feedback capacitance, and the second capacitor network is coupled with the operational amplifier to provide the input capacitance.