Image sensors and dual ramp analog-to-digital converters and methods

• US 7,804,438 B2
• Filed: 05/01/2009
• Issued: 09/28/2010
• Est. Priority Date: 05/02/2008
• Status: Active Grant

• Current Assignee: Alexander Krymski
• Original Assignee: Alexander Krymski
• Inventors: Krymski, Alexander
• Primary Examiner(s): Nguyen; Linh V
• Application Number:
  US12/434,602
• Publication Number:
  US 20090273500A1
• Time in Patent Office: 515 Days
• Field of Search: 341/113, 341/128, 341/129, 341/155, 341/156, 341/169, 341/170
• US Class Current: 341/167
• CPC Class Codes: H03M 1/144 the steps being performed sequentially in a single stage, i.e. recirculation type H03M1/141, H03M1/143, H03M1/16 take precedence
• CPC Class Codes: H03M 1/56 Input signal compared with linear ramp

Abstract

Dual ramp analog-to-digital converters and methods allow for performing analog-to-digital conversion of an analog signal. Various dual ramp analog-to-digital converters and methods allow for applying the analog signal and a coarse ramp to a same input of a comparator, and applying a fine ramp to another input of the comparator. Some dual ramp analog-to-digital converters and methods allow for applying the analog signal, a coarse ramp, and a fine ramp to a same input of a comparator. Various dual ramp analog-to-digital converters and methods allow for applying the analog signal to an input of a first comparator, applying a coarse ramp to the input of the first comparator through a coarse ramp switch, applying the analog signal to an input of a second comparator, and applying a fine ramp to another input of the second comparator.

Claims

1. A method for performing analog-to-digital conversion of an analog signal, comprising:

applying the analog signal and a coarse ramp to a same input of a comparator; and

applying a fine ramp to another input of the comparator.

2. The method of claim 1,

wherein the analog signal is an output signal of a pixel.

3. The method of claim 1,

wherein the analog signal is an output signal of an amplifier that amplifies a difference between a pixel image signal and a pixel reset signal.

4. The method of claim 1, further comprising:

generating the coarse ramp using a digital-to-analog converter to convert a digital counter value to the coarse ramp.

5. The method of claim 1, further comprising:

generating the fine ramp using a digital-to-analog converter to convert a digital counter value to the fine ramp.

6. The method of claim 1,

wherein the coarse ramp is used to determine most-significant-bits of a digital value for the analog signal;

and

wherein the fine ramp is used to determine least-significant-bits of the digital value for the analog signal.

7. The method of claim 1, said applying the analog signal and the coarse ramp to the same input of the comparator, comprising:

applying the analog signal and the coarse ramp to the same input of the comparator through one or more circuit elements such that a signal at the input of the comparator is based on the analog signal and the coarse ramp.

8. The method of claim 1, said applying the analog signal and the coarse ramp to the same input of the comparator, comprising:

providing the coarse ramp to a first terminal of a first capacitor; and

providing the analog signal to a second terminal of the first capacitor;

wherein the second terminal of the first capacitor is connected to a first terminal of a second capacitor, and a second terminal of the second capacitor is connected to the input of the comparator.

9. A dual ramp analog-to-digital converter for performing analog-to-digital conversion of an analog signal, comprising:

at least one circuit element to which the analog signal and a coarse ramp are applied; and

a comparator comprising an input connected to the at least one circuit element, and another input connected to receive a fine ramp.

10. The dual ramp analog-to-digital converter of claim 9,

said at least one circuit element including a storage element, the storage element having a first terminal connected to receive the coarse ramp and a second terminal connected to receive the analog signal.

11. The dual ramp analog-to-digital converter of claim 10,

said storage element comprising a capacitor.

12. The dual ramp analog-to-digital converter of claim 10,

wherein the second terminal of the storage element is connected to the input of the comparator.

13. The dual ramp analog-to-digital converter of claim 12,

wherein the second terminal of the storage element is connected to the input of the comparator through one or more circuit elements.

14. A method for performing analog-to-digital conversion of an analog signal, comprising:

applying the analog signal to an input of a comparator;

applying a coarse ramp to the same input of the comparator to which the analog signal is applied; and

applying a fine ramp to the same input of the comparator to which the analog signal is applied.

15. The method of claim 14,

wherein the analog signal is an output signal of a pixel or an output signal of an amplifier that amplifies a difference between a pixel image signal and a pixel reset signal.

16. A dual ramp analog-to-digital converter for performing analog-to-digital conversion of an analog signal, comprising:

a comparator; and

one or more circuit elements through which the analog signal, a coarse ramp, and a fine ramp are applied to a same input of the comparator.

17. A method for performing analog-to-digital conversion of an analog signal, comprising:

applying the analog signal to an input of a first comparator;

applying a coarse ramp to the input of the first comparator through a coarse ramp switch;

applying the analog signal to an input of a second comparator; and

applying a fine ramp to another input of the second comparator.

18. The method of claim 17, further comprising:

compensating by the second comparator for switch feedthrough from the coarse ramp switch.

19. A dual ramp analog-to-digital converter for performing analog-to-digital conversion of an analog signal, comprising:

a first comparator comprising an input to which the analog signal is applied;

a coarse ramp switch that is controllable to selectively apply a coarse ramp to the same input of the first comparator to which the analog signal is applied; and

a second comparator for compensating for switch feedthrough from the coarse ramp switch, said second comparator comprising an input to which a fine ramp is applied.

20. The dual ramp analog-to-digital converter of claim 19,

said coarse ramp switch connected to be controlled by an output of the first comparator.