Charge recycling amplifier for a high dynamic range CMOS imager

• US 7,919,992 B2
• Filed: 07/16/2009
• Issued: 04/05/2011
• Est. Priority Date: 08/19/2002
• Status: Expired due to Fees

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Inventors: Rossi, Giuseppe
• Primary Examiner(s): LE, DINH THANH
• Application Number:
  US12/504,302
• Publication Number:
  US 20090278575A1
• Time in Patent Office: 628 Days
• Field of Search: 327/124, 327 90- 95, 327/554, 333/9, 330/9, 330/69, 330/86, 330/141, 358/448, 348/300, 348/301
• US Class Current: 327/12
• CPC Class Codes: H03F 3/005 using switched capacitors, e.g. dynamic amplifiers; using switched capacitors as resistors in differential amplifiers H03F3/45 takes precedence
• CPC Class Codes: H03F 3/45475 using IC blocks as the active amplifying circuit
• CPC Class Codes: H03F 3/70 Charge amplifiers
• CPC Class Codes: H04N 25/78 Readout circuits for addressed sensors, e.g. output amplifiers or A/D converters
• CPC Class Codes: H04N 5/148 Video amplifiers amplifiers in general H03F

Abstract

A high dynamic range amplifier circuit for amplifying pixel signals of an imager device is disclosed. The amplifier circuit uses a read-out scheme based on a charge recycling approach, where a pixel signal is first amplified with a low gain during a first amplification phase T1, and then the amplifier output is immediately recycled and the pixel signal amplified with a higher gain during a second amplification phase T2.

Claims

1. An imager comprising:

an array of pixels outputting pixel signals; and

a charge recycling amplifier for processing said output pixel signals comprising;

a differential amplifier;

a pair of input capacitors connected to the inputs of said differential amplifier for receiving a charge from said pixel signals;

a plurality of pairs of feedback capacitors, each connected between the input and output of said differential amplifier; and

a switching circuit coupled to said amplifier and capacitors for causing said differential amplifier to amplify initial signals based on said charge from said input capacitors with a first gain during a first amplification phase, recycle charge to said pair of input capacitors as recycled charge after said first amplification phase and all but a last of at least one additional amplification phase, and after said recycle, amplify subsequent signals associated with said recycled charge with at least one additional gain during the at least one additional amplification phase.

2. The imager of claim 1, wherein said switching circuit comprises:

a crowbar switch, arranged to switchably couple a same side of said pair of input capacitors, for forcing a charge present on said input capacitors through said differential amplifier;

a plurality of pairs of gain switches, connected to said plurality of pairs of feedback capacitors, respectively, for setting the gain of said charge recycling amplifier during said first and at least one additional amplification phases; and

at least one switch, coupled to at least one of the pairs of feedback capacitors, for recycling charge from at least one of the plurality of pairs of feedback capacitors to the inputs of said differential amplifier.

3. The imager of claim 1, wherein said charge recycling amplifier further comprises:

a reset switch connected between the inputs and outputs of said differential amplifier, for resetting said differential amplifier.

4. The imager of claim 2, wherein said at least one switch comprises a pair of serially connected switches.

5. A charge recycling amplifier comprising:

a differential amplifier;

a pair of input capacitors connected to the inputs of said differential amplifier for receiving a charge from pixel signals;

a plurality of pairs of feedback capacitors, each connected between the input and output of said differential amplifier; and

a switching circuit coupled to said amplifier and capacitors for causing said differential amplifier to amplify initial signals based on said charge from said input capacitors with a first gain during a first amplification phase, recycle charge to said pair of input capacitors as recycled charge after said first amplification phase and all but a last of at least one additional amplification phase, and after said recycle, amplify subsequent signals associated with said recycled charge with at least one additional gain during the at least one additional amplification phase.

6. The amplifier of claim 5, wherein said switching circuit comprises:

a crowbar switch, arranged to switchably couple a same side of said pair of input capacitors, for forcing a charge present on said input capacitors through said differential amplifier;

a plurality of pairs of gain switches, connected to said plurality of pairs of feedback capacitors, respectively, for setting the gain of said charge recycling amplifier during said first and at least one additional amplification phases; and

at least one switch, coupled to at least one of the pairs of feedback capacitors, for recycling charge from at least one of the plurality of pairs of feedback capacitors to the inputs of said differential amplifier.

7. The amplifier of claim 5, wherein said charge recycling amplifier further comprises:

a reset switch connected between the inputs and outputs of said differential amplifier, for resetting said differential amplifier.

8. The amplifier of claim 6, wherein said at least one switch comprises a pair of serially connected switches.

9. A method of operating a differential amplifier, said method comprising:

receiving first and second signals into a pair of input capacitors, said first and second signals respectively forming initial charges in said pair of input capacitors;

passing initial charges present on said input capacitors through said differential amplifier set to a first gain value;

recycling charges to said input capacitors as recycled charges; and

passing recycled charges present on said input capacitors through said differential amplifier set to at least one additional gain value.

10. The method of claim 9, further comprising resetting said differential amplifier before passing charge present on said input capacitor through said differential amplifier set to said at least one additional gain value.

11. The method of claim 9 wherein said at least one additional gain value is higher than said first gain value.

12. An imager comprising:

an array of pixels outputting pixel signals; and

a charge recycling amplifier for processing said output pixel signals comprising;

a differential amplifier;

a pair of input capacitors connected to the inputs of said differential amplifier for receiving a charge from said pixel signals;

first, second and third pairs of feedback capacitors, each connected between the input and output of said differential amplifier; and

a switching circuit coupled to said amplifier and capacitors for causing said differential amplifier to amplify initial signals based on said charge from said input capacitors with a first gain during a first amplification phase, recycle charge to said pair of input capacitors as first recycled charge after said first amplification phase, and amplify subsequent signals associated with said first recycled charge with a second gain during a second amplification phase, recycle charge to said pair of input capacitors as second recycled charge after said second amplification phase, and amplify subsequent signals associated with said second recycled charge with a third gain during a third amplification phase.

13. The imager of claim 12 further comprising:

a fourth pair of feedback capacitors connected between the input and output of said differential amplifier, wherein the switching circuit is further configured to recycle charge to said pair of input capacitors as third recycled charge after said third amplification phase, and amplify subsequent signals associated with said third recycled charge with a fourth gain during a fourth amplification phase.