Low power current integration DAC ramp 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 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 the ramp signal;
• an integration current source coupled to 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;
• a reset switch coupled between the first input and the output of the operational amplifier, wherein the reset switch is configured to be turned on to reset the ramp generator, wherein a ramp event is configured to be generated in the ramp signal at the output of the operational amplifier in response to the reset switch being turned off;
• and
• an assist current source coupled between the output of the operational amplifier and ground, wherein the assist current source is configured to conduct an assist current from the output of the operational amplifier to ground in response to the reset switch being turned off, and wherein the feedback capacitor is coupled between the assist current source and the first input of the operational amplifier.