Signal processing scheme utilizing oversampled switched capacitor filter

• US 5,982,229 A
• Filed: 11/17/1997
• Issued: 11/09/1999
• Est. Priority Date: 11/17/1997
• Status: Expired due to Term

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: LSI Logic Corporation (Broadcom, Inc.)
• Inventors: Liu, Edward, Wong, See-Hoi Caesar
• Primary Examiner(s): LE, DINH THANH
• Application Number:
  US08/971,428
• Time in Patent Office: 722 Days
• Field of Search: 327/552, 327/554, 327/94, 327/100, 330/9
• US Class Current: 327/554
• CPC Class Codes: H03H 19/004 Switched capacitor networks

Abstract

A novel signal processing scheme comprises a digital to analog converter which is clocked at a first frequency, and a switched capacitor filter which receives input from the digital to analog converter and is clocked at a second frequency which is a multiple N times the first frequency. A preferred version of the present invention further comprises an analog signal sychronization circuit which allows the switched capacitor filter to oversample output from the digital to analog converter. The analog signal sychronization circuit comprises a sample and hold circuit, which receives input from the digital to analog converter and holds the input so that the switched capacitor filter can sample the same input N times, and a digital clock generator, which clocks the sample and hold circuit such that the sample and hold circuit only samples settled and valid output data from the digital to analog converter. An RC active filter receives input from the switched capacitor filter and rejects signal images at the first and higher frequencies.

Claims

1. A signal processing system comprising:

a digital to analog converter which is clocked at a first frequency;

a switched capacitor filter which receives input from the digital to analog converter and outputs a filtered signal, wherein the switched capacitor filter is clocked at a second frequency which is a multiple N times the first frequency, wherein N is greater than one; and

an analog signal synchronization circuit which facilitates sampling of an output signal from the digital to analog converter at the second frequency, thereby allowing the switched capacitor filter to oversample said output signal from the digital to analog converter.

2. The signal processing system of claim 1, wherein the analog signal synchronization circuit is connected between the digital to analog converter and the switched capacitor filter, and samples output from the digital to analog converter at the second frequency.

3. The signal processing system of claim 2, wherein the analog signal synchronization circuit comprises a sample and hold circuit which receives said output signal from the digital to analog converter and holds said output signal so that the switched capacitor filter can oversample the output signal N times.

4. The signal processing system of claim 3, wherein the analog signal synchronization circuit further comprises a digital clock generator, which clocks the sample and hold circuit such that the sample and hold circuit samples said output signal from the digital to analog converter.

5. The signal processing system of claim 1, further comprising a second filter which receives said filtered signal from the switched capacitor filter.

6. The signal processing system of claim 5, wherein the second filter comprises an RC active filter.

7. The signal processing system of claim 5, further comprising a buffer driver connected between the switched capacitor filter and the second filter.

8. A signal processing system comprising:

a digital to analog converter which is clocked at a first frequency;

a switched capacitor filter which receives input from the digital to analog converter and outputs a filtered signal, wherein the switched capacitor filter is clocked at a second frequency which is a multiple N times the first frequency, wherein N is greater than one; and

an analog signal synchronization circuit connected between the digital to analog converter and the switched capacitor filter, which samples an output signal from the digital to analog converter at the second frequency, thereby allowing the switched capacitor filter to oversample said output signal from the digital to analog converter, wherein the analog signal synchronization circuit comprises;

a sample and hold circuit which receives said output signal from the digital to analog converter and holds said output signal so that the switched capacitor filter can oversample the output signal N times, and

a digital clock generator, which clocks the sample and hold circuit such that the sample and hold circuit samples said output signal from the digital to analog converter.

9. The signal processing system of claim 8, further comprising a second filter which receives said filtered signal from the switched capacitor filter.

10. The signal processing system of claim 9, wherein the second filter comprises an RC active filter.

11. The signal processing system of claim 9, further comprising a buffer driver connected between the switched capacitor filter and the second filter.

12. A method for use in signal processing, comprising the steps of:

clocking a digital to analog converter at a first frequency;

clocking a switched capacitor filter, which receives input from the digital to analog converter and outputs a filtered signal, at a second frequency which is a multiple N times the first frequency, wherein N is greater than one; and

utilizing an analog signal synchronization circuit which facilitates sampling of an output signal from the digital to analog converter at the second frequency, thereby allowing the switched capacitor filter to oversample said output signal from the digital to analog converter.

13. The method of claim 12, wherein the analog signal synchronization circuit is connected between the digital to analog converter and the switched capacitor filter, and samples output from the digital to analog converter at the second frequency.

14. The method of claim 13, wherein the step of utilizing an analog signal synchronization circuit comprises sampling and holding said output signal from the digital to analog converter so that the switched capacitor filter can oversample the output signal N times.

15. The method of claim 14, wherein the step of sampling and holding comprises clocking a sample and hold circuit such that the sample and hold circuit samples said output signal from the digital to analog converter.

16. The method of claim 12, further comprising the step of filtering said filtered signal from the switched capacitor filter such that signal images are rejected.

17. The method of claim 16, wherein the step of filtering said filtered signal is accomplished using an RC active filter.

18. The method of claim 16, further comprising the step of buffering the filtered signal output from the switched capacitor filter before filtering said filtered signal.