Voltage range extension for difference amplifier

Patent metadata

Field	Value
Publication number	US-10312865-B2
Application number	US-201715784842-A
Country	US
Kind code	B2
Filing date	Oct 16, 2017
Priority date	Oct 16, 2017
Publication date	Jun 4, 2019
Grant date	Jun 4, 2019

Abstract

A difference amplifier circuit can be used to amplify a differential input signal representative of a current flowing through a current sensing element, such as a resistor. In certain applications, a common mode voltage established at an input of the difference amplifier circuit can be greater in magnitude than a supply voltage provided to the difference amplifier circuit. A component of the differential input signal, such as one polarity of the differential signal, can be used to power the difference amplifier circuit. Such powering of the difference amplifier by the component of the differential input signal can be performed selectively, such as when a magnitude of the common mode voltage exceeds the supply voltage or another specified threshold. In this manner, a common mode input voltage capability can be greater in magnitude than a magnitude of a supply input voltage provided to an integrated circuit including the difference amplifier circuit.

First claim

The claimed invention is:

1. An electrical apparatus for generating a signal indicative of a monitored voltage difference, the apparatus comprising:
an integrated circuit comprising:
a difference amplifier circuit comprising:
a two-terminal input to receive a differential signal, and
an output to provide the signal indicative of the input differential signal; and

an amplifier control circuit, electrically coupled to the difference amplifier circuit, to compare a signal representative of a common-mode input voltage at the input of the difference amplifier circuit to a specified threshold, and, in response, when the signal representative of the common-mode input voltage exceeds the specified threshold, to electrically couple a first terminal of the two-terminal input to the difference amplifier circuit to power the difference amplifier circuit;
wherein the amplifier control circuit comprises a current source; and
wherein the current source is capable of being electrically coupled to a second terminal of the two-terminal input to compensate for an offset between respective input currents through the first and second terminals, wherein the second terminal comprises a polarity opposite the first terminal.

2. The electrical apparatus of claim 1 , wherein a second terminal of the two-terminal input is inhibited from powering the difference amplifier circuit.

3. The electrical apparatus of claim 2 , wherein a resistance provided between the first terminal and a second terminal is at least an order of magnitude greater in value than a resistance through an electrical path between the first terminal and an internal supply node powering the difference amplifier circuit, when the first terminal is electrically coupled to power the difference amplifier circuit.

4. The electrical apparatus of claim 1 , further comprising a sensing resistor; and
wherein the monitored voltage difference comprises a voltage representative of a current flowing through the sensing resistor.

5. The electrical apparatus of claim 1 , wherein the amplifier control circuit comprises switches controlled by a comparator circuit, the switches configured to respectively electrically couple the first terminal to an internal supply node powering the difference amplifier circuit and to couple the second terminal to the current source.

6. The electrical apparatus of claim 1 , wherein the amplifier control circuit comprises a comparator circuit including a first input coupled to a node providing a voltage representative of the first terminal and a second input coupled to a threshold voltage corresponding to the specified threshold.

7. The electrical apparatus of claim 6 , wherein the second terminal of the difference amplifier circuit is coupled to the first input of the comparator circuit through a resistor circuit, the resistor circuit configured to provide the signal representative of the common-mode input voltage.

8. The electrical apparatus of claim 1 , wherein the amplifier control circuit is configured to inhibit the first terminal from powering the difference amplifier circuit when the signal representative of the common-mode input voltage is less than the specified threshold, and configured to electrically couple a supply input node to the difference amplifier circuit to power the difference amplifier circuit using a voltage corresponding to a supply input voltage when the signal representative of the common-mode input voltage is less than the specified threshold.

9. The electrical apparatus of claim 1 , comprising a current sensing element.

10. The electrical apparatus of claim 9 , further comprising a filter circuit coupled between the current sensing element and the two-terminal input, the current sensing element and the filter circuit separate from the integrated circuit.

11. The electrical apparatus of claim 1 , wherein the difference amplifier circuit comprises a transconductance topology configured to provide a differential current output corresponding to the differential signal received at the input of the difference amplifier circuit.

12. The electrical apparatus of claim 11 , comprising a second amplifier circuit including an input configured to receive a differential current from the output of the difference amplifier circuit, and including an output to provide the signal indicative of a monitored current in response to the received differential current.

13. The electrical apparatus of claim 12 , wherein the second amplifier circuit is configured to be powered using a supply input node using a voltage corresponding to a supply input voltage that is lesser in magnitude than a common-mode input voltage capability.

14. An electrical apparatus for generating a signal indicative of a monitored current, the apparatus comprising:
a current sensing element located in series with an electrical load;
an integrated circuit comprising:
a difference amplifier circuit comprising:
an input compatible with a common-mode input voltage exceeding a supply input voltage of the integrated circuit; and
an output to provide the signal indicative of the monitored current; and
an amplifier control circuit, electrically coupled to the difference amplifier circuit, including a comparator to compare a signal representative of a common-mode input voltage at the input of the difference amplifier circuit to a specified threshold, and, in response, when the signal representative of the common-mode input voltage exceeds the specified threshold, to power the difference amplifier circuit using an input terminal of the difference amplifier circuit, the difference amplifier circuit separate from the comparator included as a portion of the amplifier control circuit;
wherein the amplifier control circuit is configured to compensate for an offset between respective input currents through respective first and second input terminals of the difference amplifier circuit when the difference amplifier circuit is powered using an input terminal amongst the respective first and second input terminals.

15. The electrical apparatus of claim 14 , wherein the amplifier control circuit is configured to inhibit the input terminal from powering the difference amplifier circuit when the signal representative of the common-mode input voltage is less than a specified threshold, and configured to electrically couple a supply input node to the difference amplifier circuit to power the difference amplifier circuit using a voltage corresponding to the supply input voltage that is lesser in magnitude than the common-mode input voltage capability when the signal representative of the common-mode input voltage is less than the specified threshold.

16. A method for generating a signal indicative of a monitored current through a current sensing element, the method comprising:
amplifying a differential signal indicative of the monitored current using a difference amplifier circuit; and
when an input common mode voltage of the difference amplifier circuit exceeds a specified threshold voltage, changing powering of the difference amplifier circuit from using a power supply rail to using a component of the differential signal to power the difference amplifier circuit, including compensating for an offset between respective input currents through respective first and second input terminals of the difference amplifier circuit when the difference amplifier circuit is powered using the component of the differential signal.

17. The method of claim 16 , comprising comparing a signal representative of a common-mode input voltage at the input of the difference amplifier ci

Assignees

• Analog Devices Inc

Inventors

• Wan Quan

Classifications

• H03F3/45179

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

• H03F2203/45288

  Differential amplifier with circuit arrangements to enhance the transconductance · CPC title

• H03F2200/462

  the current being sensed · CPC title

• H03F2203/45151

  At least one resistor being added at the input of a dif amp · CPC title

• H03F2203/45136

  One differential amplifier in IC-block form being shown · CPC title