Trimming control circuit for current integration ramp DAC settling assist circuit

An imaging system, comprising:

• an array of pixels to receive image light and generate an image charge voltage signal in response;
• and
• readout circuitry coupled to the receive the image charge voltage signal from the array of pixels and provide a digital representation of the image charge voltage signal in response, the readout circuitry including a comparator to receive the image charge voltage signal, compare the image charge voltage signal to a ramp signal from a ramp generator, and provide the digital representation of the image charge voltage signal in response, wherein the ramp generator comprises:
• an operational amplifier having a first input, a second input, and an output to generate a ramp signal;
• an integration current source coupled the first input of the operational amplifier;
• a reference voltage coupled to the second input of the operational amplifier;
• a feedback capacitor coupled between the first input and the output of the operational amplifier;
• an assist current source coupled between the output of the operational amplifier and ground;
• a monitor circuit coupled to the first and second inputs of the operational amplifier, wherein the monitor circuit is configured to generate an output flag in response to a comparison of the first and second inputs of the operational amplifier;
• and
• a trimming control circuit coupled to the assist current source, wherein the trimming control circuit is configured to generate a trimming signal in response to the output flag generated by the monitor circuit, wherein the assist current source is configured to conduct an assist current from the output of the operational amplifier to ground in response the trimming signal generated by the trimming control circuit.