Multistage amplifier circuit with improved settling time

Patent metadata

Field	Value
Publication number	US-2016006403-A1
Application number	US-201514790592-A
Country	US
Kind code	A1
Filing date	Jul 2, 2015
Priority date	Jul 2, 2014
Publication date	Jan 7, 2016
Grant date	—

Abstract

Described examples include multistage amplifier circuits having first and second forward circuits, a comparator or sensor circuit coupled to sense a signal in the second forward circuit to identify nonlinear operation or slewing conditions in the multistage amplifier circuit, and one or more sample hold circuits operative according to a sensor circuit output signal to selectively maintain the amplitude of an amplifier input signal in the second forward circuit and/or in a feedback circuit in response to the sensor circuit output signal indicating nonlinear operation or slewing conditions in the multistage amplifier circuit. Certain examples further include a clamping circuit operative to selectively maintain a voltage at a terminal of a Miller compensation capacitance responsive to the comparator output signal indicating nonlinear operation or slewing conditions.

First claim

The following is claimed:

1 . A multistage amplifier circuit, comprising:
a first forward circuit, including a first amplifier having a first amplifier input to receive an input signal, and a second amplifier having a second amplifier input coupled with an output of the first amplifier, the second amplifier including a second amplifier output providing an output signal; a second forward circuit, including a third amplifier having a third amplifier input coupled to receive the input signal, a fourth amplifier having a fourth amplifier input coupled with an output of the third amplifier, and a fifth amplifier having a fifth amplifier input coupled with an output of the fourth amplifier, the fifth amplifier having a fifth amplifier output coupled with the second amplifier input; a sensor circuit coupled with the second forward circuit to sense nonlinear operation or slewing conditions of the multistage amplifier circuit, the comparator having a sensor circuit output providing a sensor circuit output signal in a first state when nonlinear operation or slewing conditions are sensed in the multistage amplifier circuit, and a second state when no nonlinear operation or slewing conditions are sensed in the multistage amplifier circuit; and a first sample hold circuit coupled with the fifth amplifier input to maintain an amplitude of a signal at the fifth amplifier input when the sensor circuit output signal is in the first state.

2 . The multistage amplifier circuit of claim 1 , wherein the sensor circuit is a comparator circuit including a first comparator input coupled with a first differential input of the fourth amplifier, a second comparator input coupled with a second differential input of the fourth amplifier, and comparator output providing the sensor circuit output signal.

3 . The multistage amplifier circuit of claim 2 , wherein the input signal is a differential signal, and wherein the second forward circuit comprises:
a first chopper circuit coupled between the first amplifier input and the third amplifier, the first chopper circuit including a first switching circuit to alternately invert the input signal according to a clock signal to provide a first chopped differential input signal to the third amplifier input; and a second chopper circuit coupled between the third amplifier and the fourth amplifier, the second chopper circuit including a second switching circuit to alternately invert a differential output signal from the output of the third amplifier according to the clock signal to provide a second chopped differential input signal to the fourth amplifier input.

4 . The multistage amplifier circuit of claim 2 , comprising:
a compensation capacitance including a first terminal coupled with the second amplifier output, and a second terminal coupled with the fourth amplifier input; and a clamp circuit coupled with the fourth amplifier input to selectively maintain a voltage at the second terminal of the compensation capacitance when the sensor circuit output signal is in the first state.

5 . The multistage amplifier circuit of claim 4 , wherein the clamp circuit is operative to drive a voltage at the first differential input of the fourth amplifier to a voltage at the second differential input of the fourth amplifier when the sensor circuit output signal is in the first state.

6 . The multistage amplifier circuit of claim 5 , comprising:
a third circuit providing a feedback loop to the second forward circuit, the third circuit including:
a sixth amplifier having a sixth amplifier input coupled with the fourth amplifier input,
a seventh amplifier having a seventh amplifier input coupled with an output of the sixth amplifier, and
a notch filter coupled between the output of the sixth amplifier and the seventh amplifier input; and
a second sample hold circuit coupled with the seventh amplifier input to maintain an amplitude of a signal at the seventh amplifier input when the sensor circuit output signal is in the first state.

7 . The multistage amplifier circuit of claim 6 , wherein the input signal is a differential signal, and wherein the second forward circuit comprises:
a first chopper circuit coupled between the first amplifier input and the third amplifier, the first chopper circuit including a first switching circuit to alternately invert the input signal according to a clock signal to provide a first chopped differential input signal to the third amplifier input; and a second chopper circuit coupled between the third amplifier and the fourth amplifier, the second chopper circuit including a second switching circuit to alternately invert a differential output signal from the output of the third amplifier according to the clock signal to provide a second chopped differential input signal to the fourth amplifier input.

8 . The multistage amplifier circuit of claim 7 , wherein the third circuit includes a third chopper circuit coupled between the output of the sixth amplifier and the notch filter, the third chopper circuit including a third switching circuit to alternately invert a differential output signal of the sixth amplifier according to the clock signal to provide a third chopped differential input signal to the notch filter.

9 . The multistage amplifier circuit of claim 1 , comprising:
a compensation capacitance including a first terminal coupled with the second amplifier output, and a second terminal coupled with the fourth amplifier input; and a clamp circuit coupled with the fourth amplifier input to selectively maintain a voltage at the second terminal of the compensation capacitance when the sensor circuit output signal is in the first state.

10 . The multistage amplifier circuit of claim 9 , wherein the clamp circuit is operative to drive a voltage at the first differential input of the fourth amplifier to a voltage at the second differential input of the fourth amplifier when the sensor circuit output signal is in the first state.

11 . The multistage amplifier circuit of claim 1 , comprising:
a third circuit providing a feedback loop to the second forward circuit, the third circuit including:
a sixth amplifier having a sixth amplifier input coupled with the fourth amplifier input,
a seventh amplifier having a seventh amplifier input coupled with an output of the sixth amplifier, and
a notch filter coupled between the output of the sixth amplifier and the seventh amplifier input; and
a second sample hold circuit coupled with the seventh amplifier input to maintain an amplitude of a signal at the seventh amplifier input when the sensor circuit output signal is in the first state.

12 . The multistage amplifier circuit of claim 1 , comprising:
a third circuit providing a feedback loop to the second forward circuit, the third circuit including:
a sixth amplifier having a sixth amplifier input coupled with the fourth amplifier input, and
a seventh amplifier having a seventh amplifier input coupled with an output of the sixth amplifier; and
a second sample hold circuit coupled with the seventh amplifier input to maintain an amplitude of a signal at the seventh amplifier input when the sensor circuit output signal is in the first state.

13 . The multistage amplifier circuit of claim 12 , wherein the third circuit includes a notch filter coupled between the output of the sixth amplifier and the seventh amplifier input.

14 . The multistage amplifier circuit of claim 12 , wherein the first, third, fourth, fifth, sixth and seventh amplifiers are transconductance amplifiers with differential inputs and differential outputs.

15 . The multistage am

Assignees

• Texas Instruments Inc

Inventors

• Ivanov Vadim V
• Kumar Vaibhav
• Shaik Munaf H

Classifications

• H03F3/45273

  Mirror types · CPC title

• H03F1/3211

  in differential amplifiers · CPC title

• H03F1/14

  by use of neutralising means · CPC title

• H03F1/086

  with FET's · CPC title

• H03F2200/135

  there being a feedback over one or more internal stages in the global amplifier · CPC title