Low capacitance switch for programmable gain amplifier or programable gain instrumentation amplifier

Patent metadata

Field	Value
Publication number	US-2018062646-A1
Application number	US-201615254782-A
Country	US
Kind code	A1
Filing date	Sep 1, 2016
Priority date	Sep 1, 2016
Publication date	Mar 1, 2018
Grant date	—

Abstract

A low capacitance n-channel analog switch circuit, a p-channel analog switch circuit, and a full CMOS transmission gate (T-gate) circuit are described. Resistive decoupling can be used to isolate the switch or T-gate from AC grounds. A semiconductor region that is separated from a body region of a pass field-effect transistor (FET), such as by an insulator, can be coupled to or driven to a voltage similar to the input voltage or other desired bias voltage (e.g., an operational amplifier output) to help reduce parasitic capacitance of the switch or T-gate. The switch or T-gate can help provide improved frequency bandwidth or frequency response. The switch can be useful in a programmable gain amplifier (PGA) or programmable gain instrumentation amplifier (PGIA) or other circuit in which excessive switch capacitance could degrade circuit performance.

First claim

The claimed invention is:

1 . An analog switch circuit, comprising:
a first pass FET, including a gate coupled to a first control signal input, a first conduction terminal coupled to a signal input, a second conduction terminal coupled to a signal output, and a first body, wherein the first body is separated from a local first semiconductor region by a first insulator.

2 . The analog switch circuit of claim 1 , wherein the local first semiconductor region is dedicated to the analog switch circuit by being additionally electrically isolated by a second insulator that, together with the first insulator and an underlying third insulator, forms a moat region about or near the first pass FET, and wherein the local first semiconductor region is coupled to a circuit node, or driven to, a bias voltage.

3 . The analog switch circuit of claim 2 , wherein the local first semiconductor region is coupled to, or driven to a voltage like that of, one of the signal input or the signal output.

4 . The analog switch circuit of claim 3 , wherein the local first semiconductor region is coupled to, or driven to a voltage like that of, the signal output.

5 . The analog switch circuit of claim 2 , included in a feedback network of a programmable gain amplifier circuit, wherein the local first semiconductor region is electrically connected to a signal output of an amplifier of the programmable gain amplifier circuit.

6 . The analog switch circuit of claim 2 , included in a feedback network of a programmable gain instrumentation amplifier circuit, wherein the local first semiconductor region is electrically connected to a signal output of an amplifier of the programmable gain instrumentation amplifier circuit.

7 . The analog switch circuit of claim 1 , wherein the first body is switchably coupled to a first bias voltage via a first body decoupling resistor when the first pass FET is off, the first body also switchably coupled to at least one of the signal input or the signal output when the first pass FET is on.

8 . The analog switch circuit of claim 7 , wherein the first body is switchably coupled to the signal input when the first pass FET is on.

9 . The analog switch circuit of claim 1 , wherein the first pass FET includes the gate coupled to the first control signal input via a first gate decoupling resistor.

10 . The analog switch circuit of claim 1 , further comprising:
a second pass FET, including a gate coupled to a second control signal input, a first conduction terminal coupled to the signal input, a second conduction terminal coupled to the signal output, and a second body, wherein the second body is separated from a second local semiconductor region by an insulator, wherein the second local semiconductor region is coupled to a circuit node, or driven to a bias voltage; and wherein the first pass FET is an NFET and the second pass FET is a PFET, and wherein the first pass FET and the second pass FET complement each other to form a transmission gate.

11 . The analog switch circuit of claim 10 , wherein the first semiconductor region and the second semiconductor region are shared in common between the first pass FET and the second pass FET.

12 . The analog switch circuit of claim 10 , wherein the second pass FET, includes the gate coupled to the second control signal input via a second gate decoupling resistor.

13 . An analog switch circuit, comprising:
a first pass FET, including a gate coupled to a first control signal input, a first conduction terminal coupled to a signal input via a first gate decoupling resistor, a second conduction terminal coupled to a signal output, and a first body separated from a local first semiconductor region by a first insulator; and a second pass FET, including a gate coupled to a second control signal input via a second gate decoupling resistor, a first conduction terminal coupled to the signal input, a second conduction terminal coupled to the signal output, and a second body separated from a local second semiconductor region by a second insulator; and wherein the local first and second semiconductor regions are electrically-connected to an amplifier signal output.

14 . The analog switch circuit of claim 13 , included in a feedback network of a programmable gain amplifier circuit, and wherein the local first and second semiconductor regions are connected to a signal output of an amplifier in the programmable gain amplifier circuit.

15 . The analog switch circuit of claim 13 , included in a feedback network of a programmable gain instrumentation amplifier circuit, and wherein the local first and second semiconductor regions are connected to a signal output of an amplifier in the programmable gain instrumentation amplifier circuit.

16 . The analog switch circuit of claim 13 , wherein the local first and second semiconductor regions are shared.

17 . A method of using at least a first pass FET for switchably passing or isolating an analog signal from a signal input to a signal output, the method comprising:
providing a first control signal to a gate of a first pass FET to turn the first pass FET on to pass the analog signal from the signal input to the signal output and to turn the first pass FET off to isolate the analog signal at the signal input from the signal output; and coupling or driving, to a circuit node or a bias voltage, a local first semiconductor region, separated from a body region of the first pass FET by a first insulator, and separated from other circuitry on an integrated circuit by a second insulator.

18 . The method of claim 17 , comprising connecting the local first semiconductor region to the signal output of an amplifier circuit when the first pass FET is on and when the first pass FET is off.

19 . The method of claim 17 , comprising using the first pass FET to selectively switch at least one element in a feedback network of at least one of programmable gain amplifier circuit or a programmable gain instrumentation amplifier circuit.

20 . The method of claim 17 , further comprising:
using a second pass FET, complementary in type to the first pass FET, for switchably passing or isolating an analog signal from a signal input to a signal output; providing a second control signal to a gate of the second pass FET to turn the second pass FET on to pass the analog signal from the signal input to the signal output and to turn the second pass FET off to isolate the analog signal at the signal input from the signal output; and coupling the local first semiconductor region, separated from a body region of the second pass FET by a second insulator, to the signal output of an operational amplifier circuit of a programmable gain amplifier (PGA) or a programmable gain instrumentation amplifier (PGIA) when the second pass FET is on and when the second pass FET is off.

Assignees

• Analog Devices Inc

Inventors

• Herrera Sandro
• Jeffery Alan K

Classifications

• H03F2203/45528

  the FBC comprising one or more passive resistors and being coupled between the LC and the IC · CPC title

• H03K2217/0054

  Gating switches, e.g. pass gates · CPC title

• H03F3/45475

  using IC blocks as the active amplifying circuit · CPC title

• H03G1/0088

  using discontinuously variable devices, e.g. switch-operated · CPC title

• H03F1/342 Primary

  in field-effect transistor amplifiers · CPC title