Single phase analog counter for a digital pixel
AssigneeRaytheon Company
InventorsRichard E. Wahl, Joshua J. Cantrell, John L. Vampola, Micky R. Harris
Life of this patent
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Abstract
An analog counter circuit for use with a digital pixel includes: an input; an output; a first stage electrically coupled to the input that is charged to an initial charge voltage; a second stage that includes an accumulating charge storage device; and a charge transfer device between the first and second stages that includes a transfer voltage. The charge transfer device allows charge from the first stage to pass to the second stage and be accumulated on the accumulating charge storage device as long as a voltage at a node in the first stage is greater than the transfer voltage.
Claims17
An analog counter circuit for use with a digital pixel, the analog counter circuit comprising:
- an input connected to an output of a digital pixel that receives RESET signal that provides reset pulses from the digital pixel;
- an output;
- a first stage electrically coupled to the input that is charged to an initial charge voltage;
- a second stage that includes an accumulating charge storage device;
- and
- a charge transfer device between the first and second stages that includes a transfer voltage, wherein the charge transfer device allows charge from the first stage to pass to the second stage and be accumulated on the accumulating charge storage device as long as a voltage at a node in the first stage is greater than the transfer voltage,
- wherein the transfer device includes an input connected to the first stage and an output connected to the second stage,
- wherein the transfer device includes a gate that is connected to a constant gate bias voltage, wherein the transfer voltage is a sum of the gate bias voltage and a threshold voltage of the transfer device.
A method of using an analog counter in a digital pixel circuit, the method comprising:
- receiving a RESET signal at an input to the analog counter from a comparator operatively connected to a photo-current source through an injection transistor and to an integration capacitor, the RESET signal having a low value and a high value;
- charging a first storage device connected to the input to an initial charge voltage when the RESET signal has a low value;
- and
- transferring charge stored on first storage device to an accumulating charge storage device through a charge transfer device connected between the first storage device and the accumulating charge storage device when the RESET transitions from the low value to the high value for long as a voltage at a node between the first storage device and the charge transfer device is greater than a transfer voltage of the charge transfer device;
- wherein the transfer device includes an input connected to the first storage device and an output connected to the second storage device
- wherein the transfer device includes a gate that is connected to a constant gate bias voltage, wherein the transfer voltage is a sum of the gate bias voltage and a threshold voltage of the transfer device.
Dependencies are inferred from the claim text.