Fixed gain amplifier circuit

Patent metadata

Field	Value
Publication number	US-9755597-B2
Application number	US-201514971359-A
Country	US
Kind code	B2
Filing date	Dec 16, 2015
Priority date	Jun 5, 2014
Publication date	Sep 5, 2017
Grant date	Sep 5, 2017

Abstract

An instrumentation amplifier includes first and second resistors for gain setting. The operational amplifiers within the instrumentation amplifier include selectively enabled current drive sources coupled to the amplifier output. The first and second resistors have variable resistances. A control circuit is configured to select the variable resistances of the first and second resistors to implement a fixed gain for the instrumentation amplifier and further selectively enable the current drive sources. The control circuit receives an indication of a downstream programmable gain (for example, from a downstream programmable gain amplifier). The variable resistances of the first and second resistors are selected to be scaled inversely with respect to the downstream programmable gain and the current drive sources are enabled proportionately with respect to the downstream programmable gain.

First claim

What is claimed is:

1. A circuit, comprising:
a differential amplifier having a plurality of selectively enabled current drive sources coupled to an output;
a resistor circuit coupled to the differential amplifier and having a variable resistance;
a control circuit configured to select the variable resistance of the resistor circuit to implement a fixed gain at the output and further selectively enable the current drive sources, said control circuit receiving an indication of a downstream programmable gain; and
wherein a number of the current drive sources that are enabled by the control circuit is proportional to the downstream programmable gain.

2. The circuit of claim 1 , wherein the resistor circuit comprises:
a first resistor having a first variable resistance coupled between the output and inverting input of the first differential amplifier; and
a second resistor having a second variable resistance coupled to the inverting input of the first differential amplifier.

3. The circuit of claim 2 , wherein the first and second variable resistances selected by the control circuit are scaled inversely with respect to the downstream programmable gain.

4. The circuit of claim 2 , wherein the first resistor comprises a plurality of first resistances selectively connectable in parallel in response to said control circuit.

5. The circuit of claim 2 , wherein the second resistor comprises a plurality of second resistances selectively connectable in parallel in response to said control circuit.

6. The circuit of claim 1 , further comprising a programmable gain amplifier having an input coupled to the output of the differential amplifier, said programmable gain amplifier configured to implement said downstream programmable gain.

7. A circuit, comprising:
an instrumentation amplifier including an operational amplifier and first and second resistors coupled to the operational amplifier for gain setting, wherein the operational amplifier includes selectively enabled current drive sources coupled to an amplifier output;
wherein the first and second resistors each have a variable resistance; and
a control circuit configured to select the variable resistances of the first and second resistors to implement a fixed gain for the instrumentation amplifier, the selected variable resistances of the first and second resistors being scaled inversely with respect to a downstream programmable gain;
wherein said control circuit is further configured to selectively enable a number of the current drive sources proportionally with respect to the downstream programmable gain.

8. The circuit of claim 7 , further comprising a programmable gain amplifier having an input coupled to the output of the instrumentation amplifier, said programmable gain amplifier configured to implement said downstream programmable gain.

9. The circuit of claim 8 , wherein the programmable gain amplifier is a component of a modulation circuit.

10. The circuit of claim 8 , further comprising an analog-to-digital converter circuit coupled to an output of the programmable gain amplifier.

11. The circuit of claim 7 , wherein the first resistor comprises a plurality of first resistances selectively connectable in parallel in response to said control circuit.

12. The circuit of claim 7 , wherein the second resistor comprises a plurality of second resistances selectively connectable in parallel in response to said control circuit.

13. A method, comprising:
setting a fixed gain of an instrumentation amplifier;
receiving an indication of a downstream programmable gain; and
enabling a number of output current drive sources of the instrumentation amplifier proportionately with respect to the downstream programmable gain.

14. The method of claim 13 , further comprising amplifying an output of the instrumentation amplifier in accordance with said downstream programmable gain.

15. The method of claim 14 , wherein amplifying the output further comprises modulating the output of the instrumentation amplifier.

16. The method of claim 14 , further comprising converting the output of the instrumentation amplifier from an analog signal to a digital signal.

17. The method of claim 13 , wherein setting the fixed gain comprises setting variable resistances of resistors of the instrumentation amplifier to implement the fixed gain.

18. The method of claim 17 , wherein the resistors including a first resistor and a second resistor, and setting variable resistances comprises selecting the variable resistances scaled inversely with respect to the downstream programmable gain.

Assignees

• St Microelectronics Inc

Inventors

• Choi Davy

Classifications

• H03F2203/45138

  Two or more differential amplifiers in IC-block form are combined, e.g. measuring amplifiers · CPC title

• H03G3/3036

  in high-frequency amplifiers or in frequency-changers (H03G3/3052, H03G3/32, H03G3/34 take precedence) · CPC title

• H03F3/45179

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

• H03F3/45

  Differential amplifiers (differential sense amplifiers G11C7/062) · CPC title

• H03F3/45094

  Folded cascode stages · CPC title