Abstract: In described examples, a circuit includes an integrator. The integrator receives an input signal. A first sampling network is coupled to the integrator and generates a signal voltage. A second sampling network is coupled to the integrator and generates a pixel sampled noise voltage. The pixel sampled noise voltage generated in a previous cycle is subtracted from the signal voltage generated in a current cycle to generate a true signal voltage.

Abstract: In accordance with one embodiment, an apparatus includes a first amplifier having a noninverting input, an inverting input and an output. The noninverting input is coupled to a first ground reference. The inverting input is coupled to an output of an external sensor. The apparatus also includes a second amplifier having a noninverting input, an inverting input and an output. The noninverting input is coupled to the first ground reference. The inverting input is coupled to the power supply through a first variable capacitor and to the second ground reference through a second variable capacitor. The output is coupled to the inverting input of the first amplifier. The external sensor is coupled to a third ground reference, and the first amplifier and second amplifier are coupled to the second ground reference.

Abstract: A dark current compensation circuit comprises a first comparator having inputs for a detection signal and a first voltage, and a second comparator having inputs for the detection signal and a second voltage. The dark current compensation circuit also comprises a controller coupled to the first and second comparators, which has an input for an event signal. An adjustable current source is coupled to the controller and configured to generate a compensation current. The controller adjusts a value of the compensation current based on the first and second comparator outputs and maintains a constant value in response to the event signal indicating photons incident on a photon detector. In some implementations, the dark current compensation circuit further comprises an analog sub-circuit coupled to the adjustable current source and configured to receive the detection signal. The analog sub-circuit generates an analog compensation current in response to the detection signal.

Abstract: A circuit for use in a system that includes a detector, wherein the circuit comprises an input terminal to receive a detector signal from the detector external to the circuit, the detector signal to include an error charge corresponding to a leakage current. The circuit further comprises an amplifier coupled to the input terminal to receive input signals corresponding to the detector signal, including the error charge applied to an input of the amplifier. The circuit further comprises a feedback path coupled across the amplifier, wherein the feedback path comprises a first switch coupled across a leakage resistor and to a leakage capacitor for discharging a feedback compensation charge from the leakage capacitor and onto the input of the amplifier to substantially cancel the error charge.

Abstract: A dark current compensation circuit comprises a first comparator having inputs for a detection signal and a first voltage, and a second comparator having inputs for the detection signal and a second voltage. The dark current compensation circuit also comprises a controller coupled to the first and second comparators, which has an input for an event signal. An adjustable current source is coupled to the controller and configured to generate a compensation current. The controller adjusts a value of the compensation current based on the first and second comparator outputs and maintains a constant value in response to the event signal indicating photons incident on a photon detector. In some implementations, the dark current compensation circuit further comprises an analog sub-circuit coupled to the adjustable current source and configured to receive the detection signal. The analog sub-circuit generates an analog compensation current in response to the detection signal.

Abstract: In accordance with one embodiment, an apparatus includes a first amplifier having a noninverting input, an inverting input and an output. The noninverting input is coupled to a first ground reference. The inverting input is coupled to an output of an external sensor. The apparatus also includes a second amplifier having a noninverting input, an inverting input and an output. The noninverting input is coupled to the first ground reference. The inverting input is coupled to the power supply through a first variable capacitor and to the second ground reference through a second variable capacitor. The output is coupled to the inverting input of the first amplifier. The external sensor is coupled to a third ground reference, and the first amplifier and second amplifier are coupled to the second ground reference.

Abstract: In described examples, a charge sensitive amplifier (CSA) generates an integrated signal in response to a current signal. A high pass filter is coupled to the CSA and receives the integrated signal and an inverse of an event signal, the high pass filter generates a coarse signal. An active comparator is coupled to the high pass filter and receives the coarse signal and a primary reference voltage signal, the active comparator generates the event signal.

Abstract: In described examples, a charge sensitive amplifier (CSA) generates an integrated signal in response to a current signal. A high pass filter is coupled to the CSA and receives the integrated signal and an inverse of an event signal, the high pass filter generates a coarse signal. An active comparator is coupled to the high pass filter and receives the coarse signal and a primary reference voltage signal, the active comparator generates the event signal.

Abstract: A dark current compensation circuit comprises a first comparator having inputs for a detection signal and a first voltage, and a second comparator having inputs for the detection signal and a second voltage. The dark current compensation circuit also comprises a controller coupled to the first and second comparators, which has an input for an event signal. An adjustable current source is coupled to the controller and configured to generate a compensation current. The controller adjusts a value of the compensation current based on the first and second comparator outputs and maintains a constant value in response to the event signal indicating photons incident on a photon detector. In some implementations, the dark current compensation circuit further comprises an analog sub-circuit coupled to the adjustable current source and configured to receive the detection signal. The analog sub-circuit generates an analog compensation current in response to the detection signal.

Abstract: A circuit for use in a system that includes a detector, wherein the circuit comprises an input terminal to receive a detector signal from the detector external to the circuit, the detector signal to include an error charge corresponding to a leakage current. The circuit further comprises an amplifier coupled to the input terminal to receive input signals corresponding to the detector signal, including the error charge applied to an input of the amplifier. The circuit further comprises a feedback path coupled across the amplifier, wherein the feedback path comprises a first switch coupled across a leakage resistor and to a leakage capacitor for discharging a feedback compensation charge from the leakage capacitor and onto the input of the amplifier to substantially cancel the error charge.

Abstract: In described examples, a charge sensitive amplifier (CSA) generates an integrated signal in response to a current signal. A high pass filter is coupled to the CSA and receives the integrated signal and an inverse of an event signal, the high pass filter generates a coarse signal. An active comparator is coupled to the high pass filter and receives the coarse signal and a primary reference voltage signal, the active comparator generates the event signal.

Abstract: An active pixel sensor a plurality of sensor pixels disposed in a row, a plurality of sensor pixels in a column, and steering circuitry coupled to each of the sensor pixels. Each of the sensor pixels includes a first pixel circuit, and a second pixel circuit. For each of the sensor pixels, the steering circuitry includes a first switch, a second switch, a third switch, and a fourth switch. The first switch and the second switch are connected in series to route an input signal to the first pixel circuit. The third switch and a fourth switch are connected in parallel to route the input signal to the second pixel circuit.

Abstract: A photon counting system includes a photon sensor, a charge-sensitive amplifier (CSA) and an analog-to-digital converter (ADC). The CSA is configured to convert photon energy detected by the photon sensor to voltage pulses. The ADC is configured to digitize the voltage pulses generated by the CSA. The ADC includes successive approximation circuitry. The successive approximation circuitry includes an N-bit digital-to-analog converter (DAC), an N-bit successive approximation register (SAR), a plurality of N-bit registers, and a multiplexer configured to selectively route outputs of the SAR and outputs of the N-bit registers to the DAC for conversion to an analog signal.

Abstract: An active pixel sensor a plurality of sensor pixels disposed in a row, a plurality of sensor pixels in a column, and steering circuitry coupled to each of the sensor pixels. Each of the sensor pixels includes a first pixel circuit, and a second pixel circuit. For each of the sensor pixels, the steering circuitry includes a first switch, a second switch, a third switch, and a fourth switch. The first switch and the second switch are connected in series to route an input signal to the first pixel circuit. The third switch and a fourth switch are connected in parallel to route the input signal to the second pixel circuit.

Abstract: A photon counting system includes a photon sensor, a charge-sensitive amplifier (CSA) and an analog-to-digital converter (ADC). The CSA is configured to convert photon energy detected by the photon sensor to voltage pulses. The ADC is configured to digitize the voltage pulses generated by the CSA. The ADC includes successive approximation circuitry. The successive approximation circuitry includes an N-bit digital-to-analog converter (DAC), an N-bit successive approximation register (SAR), a plurality of N-bit registers, and a multiplexer configured to selectively route outputs of the SAR and outputs of the N-bit registers to the DAC for conversion to an analog signal.

Abstract: A circuit includes a charge sensitive amplifier (CSA) that includes an input to receive current from a photon sensor and generates an output signal that represents photons received by the sensor and dark current of the sensor. A control circuit generates a compensation signal to offset the dark current from the photon sensor at the input of the CSA. The control circuit couples feedback from the CSA to enable the compensation signal if the photon current received from the sensor is below a predetermined threshold. The control circuit decouples the feedback from the CSA to disable the compensation signal if the photon current received from the sensor is above the predetermined threshold.

Abstract: A photon counting system includes a photon sensor, a charge-sensitive amplifier (CSA) and an analog-to-digital converter (ADC). The CSA is configured to convert photon energy detected by the photon sensor to voltage pulses. The ADC is configured to digitize the voltage pulses generated by the CSA. The ADC includes successive approximation circuitry. The successive approximation circuitry includes an N-bit digital-to-analog converter (DAC), an N-bit successive approximation register (SAR), a plurality of N-bit registers, and a multiplexer configured to selectively route outputs of the SAR and outputs of the N-bit registers to the DAC for conversion to an analog signal.

Abstract: The disclosure provides a circuit that includes a charge sensitive amplifier (CSA) that generates an integrated signal in response to a current signal. An active comparator is coupled to the CSA. The active comparator receives the integrated signal and a primary reference voltage signal, and generates an event detect signal. A first delay element is coupled to the active comparator and provides a fixed delay to the event detect signal to generate a convert signal. A discriminator system is coupled to the CSA. The discriminator system samples the integrated signal when activated by the convert signal.

Abstract: The disclosure provides a receiver with reduced noise. The receiver includes a photodiode that generates an input signal in response to received light pulses. A pixel switch is coupled to the photodiode. An operational amplifier is coupled to the photodiode through the pixel switch. A feedback capacitor and a reset switch are coupled between a first input port and an output port of the operational amplifier. A switched resistor network is coupled to the output port of the operational amplifier. A first switched capacitor network is coupled to the switched resistor network and samples a reset voltage. A second switched capacitor network is coupled to the switched resistor network and samples a signal voltage. A subtractor receives the reset voltage and the signal voltage, and generates a sample voltage. The second switched network comprises two or more capacitors.

Abstract: A photon counting system includes a photon sensor and pixel circuitry. The pixel circuitry includes a charge sensitive amplifier (CSA), an analog to digital converter (ADC), an event detector, and a coincidence detector. The CSA is configured to convert photon energy detected by the photon sensor to a voltage pulse. The ADC is coupled to an output of the CSA. The ADC is configured to digitize the voltage pulses generated by the CSA. The event detector is configured to determine whether output voltage of the CSA exceeds an event threshold voltage, and to trigger the ADC to digitize the output voltage based on the output voltage exceeding the event threshold voltage. The coincidence detector is configured to determine whether the output voltage of the CSA exceeds a coincidence threshold voltage, and to trigger the ADC to digitize the output voltage based on the output voltage exceeding the coincidence threshold voltage.