Integratable DC blocking circuit

• US 5,389,839 A
• Filed: 03/03/1993
• Issued: 02/14/1995
• Est. Priority Date: 03/03/1993
• Status: Expired due to Term

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Heck, Joseph P.
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): Abraham, Fetsum
• Application Number:
  US08/025,517
• Time in Patent Office: 713 Days
• Field of Search: 307/264, 307/259, 307/491, 307/520, 307/521, 307/522, 358/171
• US Class Current: 327/307
• CPC Class Codes: H03F 1/303 using a switching device H03F1/305, H03F3/005, H03F3/38 take precedence
• CPC Class Codes: H03K 5/088 modified by switching, e.g. by a periodic signal or by a signal in synchronism with the transitions of the output signal

Abstract

An electronic circuit (100) includes an output (110) and a filter circuitry (104, 106 and 108) coupled across this forward transmission path is a feedback loop having an error amplifier (112) and a coupling amplifier (116). Switches (118, 120, 122, and 124) are situated around the error amplifier to form an auto zero circuit. A capacitor (114) in conjunction with the error amplifier (112) provides an integrator for the circuit (100). The auto zero circuit allows the output (110) to follow a desired DC voltage namely (VAG) independent of the offset voltage of the error amplifier (112) or the coupler amplifier (116).

Claims

1. An electronic circuit having an output, comprising:

a forward transmission path;

feedback means coupled across the forward path;

an error amplifier having an offset voltage; and

auto-zero circuit for forcing the output to accurately follow a desired DC voltage independent of the offset voltage.

2. The electronic circuit of claim 1, wherein the auto-zero circuit includes a plurality of switches.

3. The electronic circuit of claim 1, wherein the auto-zero circuit includes a hold capacitor.

4. The electronic circuit of claim 1, wherein the feedback means includes an integrator.

5. The electronic circuit of claim 1, wherein the forward path includes a filter.

6. An integrated circuit with Direct Current (DC) blocking, comprising:

at least one electronic circuit having an input and an output;

a feedback loop comprising;

an error amplifier having an offset voltage for comparing the DC voltage level of a signal at the output with a reference voltage, the error amplifier includes an auto-zeroing circuit for producing an error signal independent of the offset voltage;

an integrator for integrating the error signal to produce an integrated error signal; and

a coupler for coupling the integrated error signal to the input.

7. The integrated circuit of claim 6, wherein the coupler includes a transconductance amplifier.

8. The integrated circuit of claim 6, wherein the error amplifier includes a transconductance amplifier.

9. An integrated circuit having, comprising:

at least one integrated electronic circuit having an input and an output; and

a feedback loop coupled from the output to the input, the feedback loop comprising;

an error amplifier with offset voltage, including an auto-zeroing circuit for correcting out the offset voltage.

10. A fully integrated electronic circuit, comprising:

an input;

an output;

a forward transmission path coupling the input to the output; and

a feedback loop configured around the forward transmission path for forcing a signal at the output to have a desired DC voltage level, the feedback loop having an auto-zeroing circuit.

11. The integrated electronic circuit of claim 10, wherein the circuit includes a low pass filter.

12. The integrated electronic circuit of claim 10, wherein feedback loop includes an error amplifier.

13. The integrated electronic circuit of claim 10, wherein feedback loop includes an integrator.

14. The integrated electronic circuit of claim 10, wherein feedback loop includes an amplifier.

15. The integrated electronic circuit of claim 14, wherein amplifier includes a current amplifier.

16. A communication device, comprising:

a receiver, having an electronic circuit, the circuit comprising;

a forward transmission path;

feedback means coupled across the forward path;

an error amplifier having an offset voltage; and

auto-zero circuit for forcing the output to accurately follow a desired DC voltage independent of the offset voltage.

17. The communication device of claim 16, wherein the electronic circuit includes a filter.