Method of and apparatus for reducing the influence of a common mode signal on a differential signal and to systems including such an apparatus

Patent metadata

Field	Value
Publication number	US-10892722-B2
Application number	US-201816015657-A
Country	US
Kind code	B2
Filing date	Jun 22, 2018
Priority date	Sep 8, 2017
Publication date	Jan 12, 2021
Grant date	Jan 12, 2021

Abstract

Differential sampling circuits may be adversely affected by changes in common mode voltage. Changes in the common mode voltage may alter the on resistance of transistor switches which it turn may mean that small signal changes are not correctly observed against a bigger common mode signal. The present disclosure relates to a way of improving the ability to resolve small differential signal changes by varying the supply or drive voltage to a component to compensate for common mode voltage changes.

First claim

The invention claimed is:

1. An apparatus comprising:
an active circuit that is configured to:
determine an adjustment to a control voltage of a differential signal processing circuit by using an indication of a time varying perturbation of a common mode voltage of a differential pair of signals determined by a first circuit and, processed by the differential signal processing circuit to estimate the common mode voltage generated using the differential pair of signals; and
adjust the control voltage of the differential signal processing circuit based on a stimulation signal being applied to the first circuit.

2. An apparatus as claimed in claim 1 , wherein the differential signal processing circuit comprises at least one transistor switch that is configured to receive at least one signal of the differential pair of signals, and to adjust the control voltage of the differential signal processing circuit, the active circuit being configured to adjust a control voltage of the at least one transistor switch.

3. An apparatus as claimed in claim 2 , wherein the apparatus is configured to:
monitor an output of an excitation circuit that is configured to apply the stimulation signal; and
adjust the control voltage of the at least one transistor switch in response to the output of the excitation circuit.

4. An apparatus as claimed in claim 2 in which the apparatus monitors a control signal supplied to an excitation circuit applying the stimulation signal and varies a gate voltage of the at least one transistor switch in response to the control signal.

5. An apparatus as claimed in claim 2 , wherein to adjust the control voltage of the differential signal processing circuit, the active circuit is configured to adjust the control voltage of the at least one transistor switch responsive to a perturbation of the common mode voltage resulting from the stimulation signal.

6. An apparatus as claimed in claim 5 , wherein to adjust the control voltage of the differential signalprocessing circuit, the active circuit is configured to adjust the control voltage of the at least one transistor switch responsive to a change in the common mode voltage resulting from a change in the stimulation signal.

7. An apparatus as claimed in claim 2 , further comprising a sampling circuit, the sampling circuit comprising the at least one transistor switch.

8. An apparatus as claimed in claim 7 , wherein the sampling circuit further comprises an amplifier, an integrator, or an analog to digital converter.

9. An apparatus as claimed in claim 7 , further comprising:
a stimulus generator for providing the stimulation signal to the first circuit, wherein the stimulus generator is coupled to the differential signal processing circuit to cause the stimulation signal to modify differential and common mode voltages at inputs of the differential signal processing circuit.

10. An apparatus as claimed in claim 9 , wherein the first circuit includes a voltage divider having a first input node, a second input node and an output node, wherein the first input node is configured to receive a voltage to be attenuated and processed, the second input node is configured to receive the stimulation signal, and a first input of the differential signal processing circuit is coupled to the output node and a second input of the differential signal processing circuit is coupled to the second input node or to a second output.

11. An apparatus as claimed in claim 9 , further comprising a correction signal generator responsive to the stimulus generator for generating a correction signal for controlling the adjustment of the control voltage of the differential signal processing circuit.

12. An apparatus as claimed in claim 2 , wherein the active circuit is configured to apply the adjustment to the control voltage by applying a modulation or a voltage translation to a digital switch driving signal that is configured to drive the at least one transistor switch.

13. An apparatus as claimed in claim 1 , wherein the active circuit is configured to adjust the control voltage of the differential signal processing circuit based on a magnitude or a timing parameter of the stimulation signal.

14. An apparatus as claimed in claim 1 , wherein a magnitude of the stimulation signal is known or measured to sufficient accuracy to enable a response of the first circuit and a response of the differential signal processing circuit to be characterized to a desired accuracy as a result of a change made to the stimulation signal.

15. An apparatus as claimed in claim 1 , included in a voltage measurement circuit, an electricity meter, or a power measurement apparatus.

16. An apparatus as claimed in claim 1 , wherein to adjust the control voltage of the differential signal processing circuit, the active circuit is configured to adjust supply voltage of the differential signal processing circuit.

17. An apparatus as claimed in claim 1 , further comprising a correction signal generator responsive to a stimulus generator for generating a correction signal for controlling adjustment of a supply voltage of the differential signal processing circuit.

18. An apparatus as claimed in claim 1 , wherein to adjust a supply voltage of the differential signal processing circuit, the active circuit is configured to adjust a voltage applied to a back-gate node of an at least one transistor switch of the differential signal processing circuit.

19. An apparatus comprising:
a differential signal processing circuit and a stimulus signal generator, wherein the stimulus signal generator is arranged to apply a stimulation signal to an input circuit that is arranged to supply first and second signals that together form a differential signal to signal inputs of the differential signal processing circuit;
a correction signal generator circuit to receive the stimulation signal and generate a correction signal based on an estimated change in a common mode voltage developed between the inputs of the differential signal processing circuit responsive to the stimulation signal, the correction signal generator circuit configured to determine the estimated change using an indication of a time varying perturbation of a common mode voltage in the stimulation signal; and
a further circuit that is configured to adjust a resistance of a transistor switch of the differential signal processing circuit to offset a change in the resistance of the transistor switch caused by the stimulation signal.

20. An apparatus as claimed in claim 19 , wherein the differential signal processing circuit comprises a switched capacitor analog to digital converter circuit comprising the transistor switch, and to adjust the resistance of the transistor switch, the further circuit is configured to modify first and second supply voltages of the switched capacitor analog to digital converter circuit responsive to the correction signal.

21. An apparatus as claimed in claim 19 , wherein to adjust the resistance of the transistor switch, the further circuit is configured to adjust a control voltage that is configured to control the transistor switch.

22. An apparatus as claimed in claim 19 , wherein to adjust the resistance of the transistor switch, the further circuit is configured to adjust a reference voltage or a signal ground voltage of the differential signal processing circuit.

23. A method of improving a common mode rejection ratio of a differential circuit, the method comprising:
generating a correction sign

Assignees

• Analog Devices International Unlimited Co

Inventors

• Hurwitz Jonathan Ephraim David
• Spalding Jr George Redfield
• Danesh Seyed Amir Ali

Classifications

• G01R19/00 Primary

  Arrangements for measuring currents or voltages or for indicating presence or sign thereof (G01R5/00 takes precedence; for measuring bioelectric currents or voltages A61B5/24) · CPC title

• G01R15/144

  Measuring arrangements for voltage not covered by other subgroups of G01R15/14 · CPC title

• G01L9/02 Primary

  by making use of variations in ohmic resistance, e.g. of potentiometers {, electric circuits therefor, e.g. bridges, amplifiers or signal conditioning} · CPC title

• H03M1/1295

  Clamping, i.e. adjusting the DC level of the input signal to a predetermined value · CPC title

• G01R17/00

  Measuring arrangements involving comparison with a reference value, e.g. bridge · CPC title