Pixel with switchable high gain and high capacity modes
Provided herein is a novel pixel circuit for image sensors such as IR ROIC image sensors. The design provides a switchable pixel with two modes. In the first mode, the pixel performs in-pixel correlated double sampling to remove reset noise. In the second mode, the pixel is configured in a high-capacity mode to avoid saturation. The pixel may be dynamically switched between modes, for example in response to lighting conditions in the scene to be imaged.
1. A charge transimpedance amplifier readout circuit which can be alternately switched between a correlated double sampling configuration and a high capacity configuration, wherein
the charge transimpedance amplifier readout circuit comprises a single output differential amplifier, wherein the positive input of the amplifier is a reset voltage source and the negative input is the output of a photodetector;
wherein a feedback capacitor is present in a feedback loop between the amplifier output and the negative amplifier input;
wherein a reset switch can be closed to short the amplifier output to its negative input and the two plates of the feedback capacitor to each other;
wherein the circuit comprises a clamping voltage source which can be connected or disconnected to the circuit by a clamping voltage switch;
wherein the circuit comprises a dual-use capacitor which can be connected to the circuit in alternate configurations by the action of switches;
wherein the correlated double sampling configuration comprises the dual-use capacitor being connected in series between the amplifier output and transiently being connected to the clamping voltage source, such that the dual-use capacitor may store a reset value for correlated double sampling operation; and
wherein the high capacity configuration comprises the dual-use capacitor being connected in parallel with the feedback capacitor, increasing the total feedback capacitance and decreasing the gain of the amplifier.
2. The charge transimpedance amplifier readout circuit of claims 1
wherein the photodetector is an infrared detector.
3. A method of operating a charge transimpedance amplifier readout circuit in two alternate modes comprising a correlated double sampling mode and a high capacity mode,
wherein the charge transimpedance amplifier readout circuit comprises a single output differential amplifier, wherein the positive input of the amplifier is a reset voltage source and the negative input is the output of a photodetector;
wherein a feedback capacitor is present in a feedback loop between the amplifier output and the negative amplifier input;
wherein a reset switch can be closed to short the amplifier output to its negative input and the two plates of the feedback capacitor to each other;
wherein the circuit comprises a clamping voltage source which can be connected or disconnected to the circuit by a clamping voltage switch;
wherein the circuit comprises a dual-use capacitor which can be connected in a first and a second configuration by the action of switches which are under the control of a controller;
the method comprising the steps of
enabling the correlated double sampling mode by controlling the switches such that the dual-use capacitor is configured such that it is transiently connected in series between the amplifier output and the clamping voltage source, such that it may store a reset value for correlated double sampling operation; and
enabling the high capacity mode by controlling the switches such that the dual-use capacitor is configured such that it is connected in parallel with the feedback capacitor, increasing the total feedback capacitance and decreasing the gain of the amplifier.
4. The method of claim 3 , wherein
the switching between modes is activated by a human user.
5. The method of claim 3 , wherein
the switching between modes is automated and is activated in response to detection of light conditions in the scene to be imaged.