Analog current mode assisted differential to single-ended read-out channel operable with an active pixel sensor

• US 6,201,572 B1
• Filed: 02/02/1998
• Issued: 03/13/2001
• Est. Priority Date: 02/02/1998
• Status: Expired due to Term

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Agilent Technologies, Inc.
• Inventors: Chou, Eric Y.
• Primary Examiner(s): Garber, Wendy
• Assistant Examiner(s): Vu, Ngoc-Yen, VU, NGOC YEN T
• Application Number:
  US09/018,022
• Time in Patent Office: 1,135 Days
• Field of Search: H04/N.5217, H04/N.314, H04/N.964, 250/208.1, 257/239, 257/291, 257/292, 257/294, 257/443, 348/241, 348/250, 348/294, 348/300, 348/301, 348/302, 348/307-311, 348/315
• US Class Current: 348/241
• CPC Class Codes: H03F 3/082 with FET's H03F3/085 takes precedence
• CPC Class Codes: H04N 25/616 involving a correlated sampling function, e.g. correlated double sampling [CDS] or triple sampling
• CPC Class Codes: H04N 25/677 for reducing the column or line fixed pattern noise
• CPC Class Codes: H04N 25/75 Circuitry for providing, modifying or processing image signals from the pixel array
• CPC Class Codes: H04N 25/77 Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components

Abstract

The present invention provides an active pixel sensor read-out channel that includes an active pixel. The active pixel drives an active pixel output to a signal voltage having an amplitude proportional to an intensity of light received by the active pixel. The active pixel drives the active pixel output to a reference voltage when the active pixel is not exposed to light. The active pixel output is connected to a sample and hold circuit. The sample and hold circuit samples and stores the signal voltage and samples and stores the reference voltage. A buffer amplifier generates a difference voltage between the sampled and stored signal voltage and the sampled and stored reference voltage.

Claims

1. An active pixel sensor read-out channel comprising:

an active pixel, the active pixel driving an active pixel output to a signal voltage having an amplitude proportional to an intensity of light received by the active pixel, the active pixel driving the active pixel output to a reference voltage when the active pixel is not receiving light;

a sample and hold circuit for receiving the active pixel output, the sample and hold circuit sampling and storing the signal voltage and sampling and storing the reference voltage; and

a buffer amplifier generating a single output difference voltage between the sampled and stored signal voltage and the sampled and stored reference voltage, and generating an output current having an amplitude which is presetably greater than an amplitude of a buffer current of a buffer stage of the buffer amplifier.

2. The active pixel sensor read-out channel as recited in claim 1, wherein the buffer amplifier comprises:

a differential to single end amplifier stage receiving the sampled and stored signal voltage and the sampled and stored reference voltage and generating a single output voltage which has a voltage potential proportional to the difference between the sampled and stored signal voltage and the sampled and stored reference voltage;

the buffer stage receiving the single output voltage and generating the buffer current having an amplitude which is proportional to the voltage potential of the single output voltage; and

a gain stage which receives the buffer current and generates the single output difference voltage and the output current having an amplitude which is presetably greater than the amplitude of the buffer current.

3. The active pixel sensor read-out channel as recited in claim 2, wherein the buffer stage comprises a source follower.

4. The active pixel sensor read-out channel as recited in claim 2, wherein the gain stage comprises a gain stage output that is connected to a multiplexed bitline within an array of bitlines.

5. The active pixel sensor read-out channel as recited in claim 1, wherein the sample and hold circuit comprises:

a signal storage element;

a signal voltage switch for connecting the active pixel output to the signal storage element to allow the signal storage element to store the signal voltage;

a reference storage element; and

a reference voltage switch for connecting the active pixel output to the reference storage element to allow the reference storage element to store the reference voltage.

6. The active pixel sensor read-out channel as recited in claim 5, wherein the sample and hold circuit further comprises means for setting a voltage stored by the signal storage element to be equal to a voltage stored by the reference storage element.

7. The active pixel sensor read-out channel as recited in claim 5, further comprising means for discharging the signal storage element and the reference storage element.

8. The active pixel sensor read-out channel as recited in claim 5, wherein the signal storage element is a signal capacitor and the reference storage element is a reference capacitor.

9. The active pixel sensor read-out channel as recited in claim 1, wherein the active pixel sensor read-out channel further comprises means for equalizing inputs to the buffer amplifier to allow offset errors within the buffer amplifier to be determined.

10. The active pixel sensor read-out channel as recited in claim 1, wherein the buffer amplifier has a gain of greater than one.