Stability compensation for adjustable gain amplifier

• US 20050253651A1
• Filed: 05/12/2004
• Published: 11/17/2005
• Est. Priority Date: 05/12/2004
• Status: Active Grant

• Current Assignee: Avago Technologies Fiber IP Singapore PTE Limited (Broadcom, Inc.)
• Original Assignee: Avago Technologies Fiber IP Singapore PTE Limited (Broadcom, Inc.)
• Inventors: Quek, Irene
• Granted Patent: US 7,154,330 B2
• Time in Patent Office: Days
• US Class Current: 330/107
• CPC Class Codes: H03F 1/08 Modifications of amplifiers to reduce detrimental influences of internal impedances of amplifying elements wide-band amplifiers with inter-stage coupling networks incorporating these impedances H03F1/42
• CPC Class Codes: H03F 1/34 Negative-feedback-circuit arrangements with or without positive feedback H03F1/02 - H03F1/30, H03F1/38 - H03F1/50, H03F3/50 take precedence ; for rejection of common mode signals H03F3/45479

Abstract

Stability compensation for an amplifier with adjustable gain is provided via adjustable capacitance coupled to an input of a gain element within the amplifier. Gain of the amplifier is adjusted by an adjustable resistance coupled between the input and output of the gain element. The adjustable capacitance and the adjustable resistance determine the frequency of a dominant pole of the amplifier.

Claims

1. An amplifier, comprising:

a gain element;

an adjustable capacitance coupled to an input of the gain element; and

an adjustable resistance coupled between an output of the gain element and the input of the gain element, the amplifier having a gain set by the adjustable resistance and having a dominant pole at a frequency according to the adjustable capacitance and the adjustable resistance.

2. The amplifier of claim 1 wherein the adjustable capacitance is adjusted to maintain the frequency of the dominant pole within a predesignated frequency range.

3. The amplifier of claim 1 wherein a decrease in the adjustable resistance is accompanied by an increase in the adjustable capacitance.

4. The amplifier of claim 1 wherein the adjustable capacitance includes a fixed capacitance and a variable capacitance in parallel with the fixed capacitance.

5. The amplifier of claim 3 wherein the adjustable capacitance includes a fixed capacitance and a variable capacitance in parallel with the fixed capacitance.

6. The amplifier of claim 1 wherein the adjustable capacitance includes a semiconductor junction having an associated capacitance that is varied by at least one of a control voltage and a control current.

7. The amplifier of claim 4 wherein the variable capacitance includes at least one parallel capacitor selectively coupled to the input of the gain element via at least one switch.

8. The amplifier of claim 2 wherein the gain element has at least one dominant pole, at at least one corresponding pole frequency that is higher in frequency than the predesignated frequency range.

9. The amplifier of claim 1 further comprising a signal source providing a current to a node connecting the adjustable capacitance to the adjustable resistance.

10. An amplification method, comprising:

forming an amplifier by coupling an adjustable resistance between an input and an output of a gain element, and by coupling an adjustable capacitance to the input of the gain element, wherein the amplifier has a dominant pole at a frequency according to the adjustable capacitance and the adjustable resistance;

adjusting the adjustable resistance to adjust the gain of the amplifier; and

adjusting the adjustable capacitance to maintain the frequency of the dominant pole within a designated frequency range.

11. The amplification method of claim 10 wherein the gain element has at least one pole, at at least one corresponding pole frequency that is higher than the predesignated frequency range.

12. The amplification method of claim 10 wherein a decrease in the adjustable resistance is accompanied by an increase in the adjustable capacitance.

13. The amplification method of claim 10 wherein the adjustable capacitance includes a fixed capacitance and a variable capacitance in parallel with the fixed capacitance.

14. The amplification method of claim 12 wherein the adjustable capacitance includes a fixed capacitance and a variable capacitance in parallel with the fixed capacitance.

15. The amplification method of claim 10 wherein the adjustable capacitance includes a semiconductor junction having an associated capacitance that is varied by at least one of a control voltage and a control current.

16. The amplification method of claim 14 wherein the variable capacitance includes at least one parallel capacitor selectively coupled to the input of the gain element via at least one switch.

17. The amplification method of claim 10 further comprising applying a current to a node connecting the adjustable capacitance to the adjustable resistance.