Common-mode feedback circuit, corresponding signal processing circuit and method

Patent metadata

Field	Value
Publication number	US-9628028-B2
Application number	US-201514746124-A
Country	US
Kind code	B2
Filing date	Jun 22, 2015
Priority date	Sep 9, 2014
Publication date	Apr 18, 2017
Grant date	Apr 18, 2017

Abstract

A common-mode feedback circuit includes a transconductor input stage with differential input terminals, and a frequency-compensated gain stage coupled to the transconductor input stage with differential output terminals. The common-mode feedback circuit also includes a feedback loop having a comparator configured to produce a feedback error signal for the transconductor input stage by comparing with a reference a common-mode sensing signal indicative of a common-mode voltage level sensed at the differential output terminals. In addition, the common-mode feedback loop includes a converter for converting the common-mode voltage level sensed at said differential output terminals into a current signal coupled to the comparator.

First claim

The invention claimed is:

1. A common-mode feedback circuit comprising:
a transconductor input stage having differential input terminals;
a frequency-compensated gain stage coupled to said transconductor input stage and having differential output terminals;
a common-mode feedback loop including a comparator configured to produce a feedback error signal for said transconductor input stage by comparing a common-mode sensing signal indicative of a common-mode voltage level sensed at said differential output terminals with a reference;
said common-mode feedback loop including a converter configured to convert the common-mode voltage level sensed at said differential output terminals into a current signal coupled to said comparator, said converter comprising a pair of common-mode detector resistors coupled to said differential output terminals, and said comparator comprising a current amplifier.

2. The common-mode feedback circuit of claim 1 , further comprising a cascode current mirror with a first portion coupled with said comparator and a second portion coupled with said transconductor input stage.

3. The common-mode feedback circuit of claim 1 , further comprising a multi-output current mirror having respective gains towards said transconductor input stage and said comparator.

4. The common-mode feedback circuit of claim 1 , wherein said transconductor input stage comprises output nodes coupled to said frequency-compensated gain stage and the feedback error signal of said common-mode feedback loop is injected into one of said output nodes of said transconductor input stage, and a tail current generator of said transconductor input stage.

5. The common-mode feedback circuit of claim 1 , wherein said comparator comprises a transistor pair sensitive to said reference and said current signal from said converter.

6. The common-mode feedback circuit of claim 5 , wherein said common-mode feedback loop comprises at least one further transistor coupled with a transistor of said transistor pair to generate said feedback error signal for said transconductor input stage.

7. The common-mode feedback circuit of claim 6 , further comprising at least one of:
a start-up current generator coupled with a current generator circuit at said comparator;
a beta helper coupled to a differential transistor pair in said comparator; and
at least one of a first error-compensating resistor and a second self-bias resistor coupled with an input terminal of said comparator for said reference.

8. An integrated circuit comprising:
a transconductor input stage;
a frequency-compensated gain stage coupled to said transconductor input stage and having differential output terminals; and
a common-mode feedback loop including a comparator configured to produce a feedback error signal for said transconductor input stage by comparing a common-mode sensing signal indicative of a common-mode voltage level sensed at said differential output terminals with a reference;
said common-mode feedback loop including a converter configured to convert a common-mode voltage sensing signal into a current signal coupled to said comparator, said converter comprising a pair of common-mode detector resistors coupled to said differential output terminals, and said comparator comprising a current amplifier.

9. The integrated circuit of claim 8 , further comprising a cascode current mirror with a first portion coupled with said comparator and a second portion coupled with said transconductor input stage.

10. The integrated circuit of claim 8 , further comprising a multi-output current mirror having respective gains towards said transconductor input stage and said comparator.

11. A method of providing feedback in a common-mode feedback circuit comprising a transconductor input stage having differential input terminals, a frequency-compensated gain stage coupled to said transconductor input stage and having differential output terminals, a converter comprising a pair of common-mode detector resistors coupled to said differential output terminals, and a comparator comprising a current amplifier, the method comprising:
producing a common-mode feedback error signal by a comparison of a common-mode sensing signal indicative of a common-mode voltage at said differential output terminals with a reference; and
converting said common-mode sensing signal into a current signal for said comparison.

12. The method of claim 11 , further comprising a cascode current mirror with a first portion coupled with said comparator and a second portion coupled with said transconductor input stage.

13. The method of claim 11 , further comprising a multi-output current mirror having respective gains towards said transconductor input stage and said comparator.

14. An integrated circuit comprising:
a transconductor input stage having differential input terminals;
a frequency-compensated gain stage coupled to said transconductor input stage and having differential output terminals;
a common-mode feedback loop including a comparator configured to produce a feedback error signal for said transconductor input stage; and
a multi-output current mirror comprising a first portion coupled with said comparator and a second portion coupled with said transconductor input stage;
said common-mode feedback loop including a converter configured to convert a common-mode voltage level sensed at said differential output terminals into a current signal coupled to said comparator.

15. The integrated circuit of claim 14 , wherein the multi-output current mirror has respective gains towards said transconductor input stage and said comparator.

16. The integrated circuit of claim 14 , wherein said transconductor input stage comprises output nodes coupled to said frequency-compensated gain stage and the feedback error signal of said common-mode feedback loop is injected into one of said output nodes of said transconductor input stage, and a tail current generator of said transconductor input stage.

Assignees

• St Microelectronics Srl

Inventors

• Carrara Francesco
• Torrisi Felice Alberto
• Clerici Francesco

Classifications

• H03F3/45179

  using MOSFET transistors as the active amplifying circuit (H03F3/45278 takes precedence) · CPC title

• H03F2203/45008

  the addition of two signals being made by a resistor addition circuit for producing the common mode signal · CPC title

• H03F1/083 Primary

  in transistor amplifiers (H03F1/10 - H03F1/22 take precedence) · CPC title

• H03F2203/45116

  Feedback coupled to the input of the differential amplifier · CPC title

• H03F2200/456

  A scaled replica of a transistor being present in an amplifier · CPC title