Solid State Switch Guard Circuit Mitigates Leakage

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Solution Overview

Problem

Solid state switches used in test and measurement systems face issues such as high leakage current, poor voltage isolation, and charge injection, which affect measurement accuracy and reliability, especially in high voltage applications.

Innovation Solution

A solid state switching network is employed with a double tee arrangement using guard switches to mitigate current leakage and optical isolation to reduce charge injection, maintaining low on-state resistance and high voltage isolation while minimizing size and safety constraints.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If solid state switches are used to achieve fast switching speeds, then switching speed is improved, but leakage current increases

Engineering Contradiction:

Improveswitching speedVSAvoidleakage current

Core Design Contradiction:

SpeedVSObject-generated harmful factors

Solution Approach 1:

The patent introduces guard switches as intermediary components connected to the solid state switch through guard circuits. These guard switches act as mediators that provide alternative current paths and compensate for leakage current from the solid state switch, thereby maintaining measurement accuracy while preserving the fast switching speed advantage of solid state devices

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent dynamically adjusts the resistance values of guard resistors based on the operating conditions and the specific characteristics of the solid state switch being used. By changing the resistance parameters of the guard circuit components, the system optimizes the compensation of leakage current across different switching states and operating voltages

Inventive Principle:

Principle #35Parameter changes

2Reliability

If solid state switches are used to achieve high voltage isolation, then voltage isolation is improved, but charge injection occurs

Engineering Contradiction:

Improvevoltage isolationVSAvoidcharge injection

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent employs guard switches and guard circuits as intermediary elements between the high voltage solid state switch and the measurement circuitry. These intermediaries provide controlled current paths that prevent charge injection from the solid state switch from reaching the measurement equipment, while maintaining the high voltage isolation capability

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent converts the harmful charge injection effect into a beneficial outcome by using the guard circuit to deliberately provide a controlled path for charge dissipation. The guard circuit uses the charge injection phenomenon to its advantage by directing it through known resistance paths, thereby neutralizing its harmful effects while maintaining voltage isolation

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Reliability

If mechanical relays are used to achieve high voltage isolation, then voltage isolation is improved, but switching lifetime is limited

Engineering Contradiction:

Improvevoltage isolationVSAvoidswitching lifetime

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

The patent replaces the mechanical relay system with a solid state switch system that uses optical isolation and guard circuits to achieve voltage isolation. This substitution eliminates the mechanical wear and tear that limits relay lifetime, while maintaining the voltage isolation performance through electronic and optical means rather than mechanical contacts

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Reliability

If solid state switches with low on-state resistance are used, then on-state resistance is improved, but leakage current increases

Engineering Contradiction:

Improveon-state resistanceVSAvoidleakage current

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent introduces guard switches and guard circuits as intermediary components that compensate for the increased leakage current from solid state switches with low on-state resistance. The guard circuit provides alternative current paths that balance the leakage current, allowing the use of low resistance solid state switches without compromising measurement accuracy

Inventive Principle:

Principle #24Intermediary (Mediator)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The solution effectively reduces current leakage and charge injection, enhancing measurement accuracy and reliability by isolating leakage currents and redirecting injected charge away from the Device Under Test, thus improving the overall performance of the test and measurement system.

Implementation Method 1

an optical isolator is coupled to the gate of each switch

Methodology Applied

Scientific EffectOptical coupling: Optical Fibre

Data Source

PatentUS10725105B2Current leakage and charge injection mitigating solid state switch

Publication Date: 2020.07.28 KEITHLEY INSTRUMENTS LLC

AI summary

Disclosed is a test and measurement switch matrix. The test and measurement switch matrix includes a solid state switch to couple a test signal from a Device Under Test (DUT) to a test system. The solid state switch has a dual tee guard arrangement providing low leakage when off. The solid state switch also includes an optically coupled drive, which further improves isolation and reduces undesirable charge injection when changing switch states.