Switched capacitor gain stage

• US 5,574,457 A
• Filed: 06/12/1995
• Issued: 11/12/1996
• Est. Priority Date: 06/12/1995
• Status: Expired due to Term

• Current Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Rakers, Patrick L., Garrity, Douglas A.
• Primary Examiner(s): Gaffin, Jeffrey A.
• Assistant Examiner(s): KOST, JASON L
• Application Number:
  US08/489,349
• Time in Patent Office: 519 Days
• Field of Search: 341/133, 341/155, 341/158, 341/159, 341/160, 341/161, 341/162, 341/172
• US Class Current: 341/172
• 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: H03H 19/004 Switched capacitor networks
• CPC Class Codes: H03M 1/442 using switched capacitors

Abstract

A switched capacitor gain stage (21) that samples an input voltage every clock cycle phase for effectively doubling the frequency of operation. The switched capacitor gain stage (21) comprising an amplifier (22), a first capacitor network, and a second capacitor network. Either the first or second capacitor network is sampling an input voltage. For example, the first capacitor network samples an input voltage. Capacitors of the first capacitor network are coupled to sample the input voltage via switches. Capacitors of the second switched capacitor network are coupled around the amplifier (22) in a gain configuration via switches. The capacitors of the second switched capacitor network having a voltage stored from a previous clock phase. In a next clock phase the second switched capacitor network are coupled via switches for sampling an input voltage and the first switched capacitor network is coupled via switches in a gain configuration around the amplifier (22).

Claims

1. A switched capacitor gain stage having an input and an output, the switched capacitor gain stage comprising:

an amplifier having an inverting input, a non-inverting input coupled to a power supply terminal, and an output coupled to the output of the switched capacitor gain stage;

a first capacitor having a first terminal and a second terminal;

a first switch having a first terminal coupled to said first terminal of said first capacitor and a second terminal coupled to said output of said amplifier;

a second switch having a first terminal coupled to the input of the switched capacitor gain stage and a second terminal coupled said first terminal of said first capacitor;

a third switch having a first terminal coupled to said second terminal of said first capacitor and a second terminal coupled to said inverting input of said amplifier;

a fourth switch having a first terminal coupled to said second terminal of said first capacitor and a second terminal coupled to said power supply terminal;

a fifth switch having a first terminal coupled to the input of the switched capacitor gain stage and a second terminal;

a second capacitor having a first terminal coupled to said second terminal of said fifth switch and a second terminal coupled to said second terminal of said first capacitor;

a third capacitor having a first terminal and a second terminal;

a sixth switch having a first terminal coupled to said first terminal of said third capacitor and a second terminal coupled to said output of said amplifier;

a seventh switch having a first terminal coupled to the input of the switched capacitor gain stage and a second terminal coupled said first terminal of said third capacitor;

an eighth switch having a first terminal coupled to said second terminal of said third capacitor and a second terminal coupled to said inverting input of said amplifier;

a ninth switch having a first terminal coupled to said second terminal of said third capacitor and a second terminal coupled to said power supply terminal;

a tenth switch having a first terminal coupled to the input of the switched capacitor gain stage and a second terminal; and

a fourth capacitor having a first terminal coupled to said second terminal of said tenth switch and a second terminal coupled to said second terminal of said third capacitor.

2. The switched capacitor gain stage as recited in claim 1 further including an eleventh switch having a first terminal coupled to a first reference input and a second terminal coupled to said first terminal of said second capacitor.

3. The switched capacitor gain stage as recited in claim 2 further including a twelfth switch having a first terminal coupled to a second reference input and a second terminal coupled to said first terminal of said fourth capacitor.

4. The switched capacitor gain stage as recited in claim 3 wherein said second, fourth, and fifth switches are closed during a first phase of a clock cycle for sampling a voltage on said first and second capacitors corresponding to a voltage of an applied signal to the input of the switched capacitor gain stage.

5. The switched capacitor gain stage as recited in claim 4 wherein said first, third, and eleventh switches are closed during a second phase of said clock cycle for placing said first and second capacitors in a gain configuration around said amplifier.

6. The switched capacitor gain stage as recited in claim 5 wherein said amplifier amplifies said voltage on said first and second capacitors during said second phase of said clock cycle and wherein a reference voltage is applied to said first reference input.

7. The switched capacitor gain stage as recited in claim 3 wherein said seventh, ninth, and tenth switches are closed during a second phase of a clock cycle for sampling a voltage on said third and fourth capacitors corresponding to said voltage of an applied signal to the input of the switched capacitor gain stage.

8. The switched capacitor gain stage as recited in claim 7 wherein said sixth, eighth, and twelfth switches are closed during a first phase of said clock cycle for placing said third and fourth capacitors in a gain configuration around said amplifier.

9. The switched capacitor gain stage as recited in claim 8 wherein said amplifier amplifies a voltage stored on said third and fourth capacitors during a first phase of said clock cycle and wherein a reference voltage is applied to said second reference input.

10. The switched capacitor gain stage as recited in claim 3 wherein said first and second capacitors, and said third and fourth capacitors are coupled to said amplifier respectively during a second and a first phase of a clock cycle for increasing speed of operation and for maintaining said amplifier in a gain configuration throughout said clock cycle.

11. A clocked gain stage having an input and an output comprising:

an amplifier having an inverting input, a non-inverting input coupled to a power supply terminal, and an output coupled to the output of the clocked gain stage;

a first capacitor;

a second capacitor, said first and second capacitor being coupled between the input of the clocked gain stage and said power supply terminal during a first phase of a clock cycle for sampling a voltage of an input signal applied to the input of the clocked gain stage and said first and second capacitor being coupled in a gain configuration around said amplifier during a second phase of said clock cycle for amplifying a voltage sampled during said first phase of said clock cycle;

a third capacitor; and

a fourth capacitor, said third and fourth capacitor being coupled between the input of the clocked gain stage and said power supply terminal during said second phase of said clock cycle for sampling a voltage of said input signal applied to the input of the clocked gain stage and said third and fourth capacitors being coupled in a gain configuration around said amplifier during a first phase of a clock cycle for amplifying a voltage sampled during a second phase of a previous clock cycle.

12. The clocked gain stage as recited in claim 11 wherein either said first and second capacitor or said third and fourth capacitor are coupled around said amplifier for maintaining said amplifier in a gain configuration during an entire clock cycle.

13. The clocked gain stage as recited in claim 11 wherein said first capacitor is coupled between said inverting input and said output of said amplifier during said second phase of said clock cycle and said second capacitor is coupled between a first reference input and said inverting input of said amplifier during said second phase of said clock cycle.

14. The clocked gain stage as recited in claim 13 wherein a reference voltage is applied to said first reference input.

15. The clocked gain stage as recited in claim 11 wherein said third capacitor is coupled between said inverting input and said output of said amplifier during said first phase of said clock cycle and said fourth capacitor is coupled between a second reference input and said inverting input of said amplifier during said first phase of said clock cycle.

16. The clocked gain stage as recited in claim 15 wherein a reference voltage is applied to said second reference input.

17. A pipelined Analog to Digital Converter (ADC) including a plurality of series coupled switched capacitor gain stages, the pipelined ADC wherein at least one switched capacitor gain stage of said plurality of series coupled switched capacitor gain stages samples and amplifies a voltage during both clock phases of a clock signal for increasing an operating speed of the pipelined ADC.

18. The pipelined ADC as recited in claim 17 wherein said at least one switched capacitor gain stage includes an input and an output and said at least one switched capacitor gain stage comprises:

an amplifier having an inverting input, a non-inverting input coupled to a power supply terminal, and an output;

a first capacitor;

a second capacitor, said first and second capacitor being coupled between said input of said at least one switched capacitor gain stage and a power supply terminal during a first phase of a clock cycle and said first and second capacitor being coupled in a gain configuration around said amplifier during a second phase of said clock cycle;

a third capacitor; and

a fourth capacitor, said third and fourth capacitor being coupled between said input of said at least one switched capacitor gain stage and said power supply terminal during said second phase of said clock cycle and said third and fourth capacitors being coupled in a gain configuration around said amplifier during a first phase of a clock cycle.

19. The pipelined ADC as recited in claim 18 wherein during said second phase of said clock cycle said first capacitor is coupled between said inverting input and said output of said amplifier, said second capacitor is coupled between a first reference input and said inverting input of said amplifier, and a first reference voltage is applied to said first reference input.

20. The pipelined ADC as recited in claim 19 wherein said first and second capacitors have equal capacitance thereby placing said at least one switched capacitor gain stage in a gain of two during said second phase of said clock cycle.

21. The pipelined ADC as recited in claim 18 wherein during said first phase of said clock cycle said third capacitor is coupled between said inverting input and said output of said amplifier, said fourth capacitor is coupled between a second reference input and said inverting input of said amplifier, and a second reference voltage is applied to said second reference input.

22. The pipelined ADC as recited in claim 21 wherein said third and fourth capacitors have equal capacitance thereby placing said at least one switched capacitor gain stage in a gain of two during said first phase of said clock cycle.