Cross-Coupled Dummy Circuit for Differential Charge Cancellation

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Solution Overview

Problem

Differential amplifier inputs in electronic systems are prone to unwanted charge injections, which can reduce the accuracy of the amplifier's output by creating an imbalance between the non-inverted and inverted inputs.

Innovation Solution

The implementation of a differential charge cancellation circuit using cross-coupled dummy circuit elements that inject charge on one node to cancel out charge injected on the other node when the corresponding switch is off, ensuring that the net differential charge is approximately zero, thereby compensating for voltage glitches or other unwanted charge injections.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If switches are used to selectively connect differential inputs to the amplifier, then channel multiplexing and electrical decoupling are enabled, but unwanted charge injections occur on the differential inputs when switches are off

Engineering Contradiction:

Improvechannel multiplexingVSAvoidcharge injection

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

Dummy circuit elements are introduced as intermediary components that mediate between the switches and the differential amplifier inputs. These dummy elements generate compensating charge to cancel the unwanted charge injection from the switches, thereby protecting the sensitive differential inputs while maintaining the switch-based channel multiplexing functionality

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The circuit employs a feedback mechanism where the dummy circuit elements sense the charge injection state of the switches and generate opposing charge in response. This feedback loop continuously compensates for charge imbalances on the differential inputs, maintaining accuracy despite the presence of switches in the signal path

Inventive Principle:

Principle #23Feedback

2Reliability

If differential inputs are designed to be matched and electrically decoupled, then noise immunity is improved, but charge imbalance between inputs still occurs due to switch effects

Engineering Contradiction:

Improvenoise immunityVSAvoiddifferential accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The dummy circuit elements act as counterweight components that generate equal and opposite charge to the unwanted charge injected by the switches. This counterbalancing approach directly addresses charge imbalance while preserving the matched differential input design, thereby maintaining both noise immunity and measurement precision

Inventive Principle:

Principle #8Anti-weight (Counterweight)

Data Source

PatentUS8941439B2Differential charge reduction

Publication Date: 2015.01.27 ANALOG DEVICES INC

AI summary

One embodiment relates to an apparatus configured to cancel charge injected on a node of a differential pair of nodes. A dummy circuit element can inject charge on an inverted node to cancel charge injected on a non-inverted node by a switch when the switch is switched off. In addition, another dummy circuit element can inject charge on the non-inverted node to cancel charge injected on the inverted node by another switch when the other switch is switched off. These dummy circuits elements can be cross-coupled.