Sample and Hold Compensation Circuit for Charge Leakage

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Solution Overview

Problem

In high accuracy converters for battery management systems, the source capacitor discharges due to a lower cut-off frequency of the low pass filter, leading to input charge leakage and degradation of accuracy, especially in high resolution applications.

Innovation Solution

A compensation circuit that generates a compensation charge equivalent to the input charge, stored in a compensation capacitor during sampling, and re-injected during the holding phase to maintain a stable voltage, thereby restoring the input charge and preventing leakage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a low pass filter with low cut-off frequency is used to attenuate spurious high frequency components, then noise attenuation is improved, but the source capacitor discharges to the input capacitor causing input charge leakage and degrading converter accuracy

Engineering Contradiction:

Improvespurious high frequency componentsVSAvoidconverter accuracy

Core Design Contradiction:

Object-affected harmful factorsVSMeasurement precision

Solution Approach 1:

The compensation circuit proactively generates a compensation charge equal to the input charge transferred during sampling, and re-injects it during the holding phase to counteract the charge leakage effect before it degrades accuracy. This preliminary anti-action prevents the harmful effect of charge transfer on measurement precision.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The patent converts the harmful charge transfer effect into a beneficial compensation mechanism by capturing the input charge during sampling and re-injecting it during holding, thereby transforming the charge leakage problem into a controlled charge restoration process that maintains voltage stability.

Inventive Principle:

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

2Productivity

If the source capacitor is used to sample the analogue voltage signal, then sampling function is achieved, but the source capacitor discharges due to low cut-off frequency causing input charge leakage

Engineering Contradiction:

Improvesampling functionVSAvoidvoltage stability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

During the sampling phase, the compensation circuit captures the input charge transferred from the source capacitor to the input capacitor. This preliminary action of storing the compensation charge allows the source capacitor to maintain its charge level, preventing discharge and maintaining voltage stability for reliable sampling.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent recovers the input charge that was transferred during sampling by storing it in a compensation capacitor and then re-injecting it during the holding phase. This recovering process prevents the permanent loss of charge from the source capacitor, maintaining system reliability.

Inventive Principle:

Principle #34Discarding and recovering

3Productivity

If digital processing assigns digital values to transferred input charge, then conversion function is achieved, but charge leakage degrades the accuracy of this conversion

Engineering Contradiction:

Improveconversion functionVSAvoiddigital value accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The compensation circuit implements a feedback mechanism where the input charge transferred during sampling is captured and then re-injected during the holding phase. This feedback loop ensures that the charge level at the input capacitor remains stable, providing accurate baseline conditions for subsequent conversions and maintaining digital value accuracy.

Inventive Principle:

Principle #23Feedback

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

This solution maintains the sampled analogue input voltage around a stable value, improving the accuracy of high resolution converters with minimal component usage and simplified design by synchronizing with sampling and holding phases.

Implementation Method 1

The control circuit controls the compensation circuit such that a compensation charge equivalent to the input charge is stored in a compensation capacitor when the sample and hold circuit is sampling the analogue input voltage

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS10115475B2Compensation circuit for compensating for an input charge in a sample and hold circuit

Publication Date: 2018.10.30 FREESCALE SEMICON INC

AI summary

A compensation circuit for compensating for an input charge at a first input of a sample and hold circuit, comprising: a first buffer, a first compensation capacitor comprising a first compensation terminal switchable between a first buffer input and a first buffer output, and a second compensation terminal switchable between the first buffer output and a reference terminal, and a control circuit to switch the first compensation terminal to the first buffer1 output and the second compensation terminal to the reference terminal during sampling, for storing a compensation charge into the first compensation capacitor, and to switch the first compensation terminal to the first buffer input and the second compensation terminal to the first buffer output during holding, for discharging the first compensation capacitor into the first input. The compensation charge is substantially equal to the input charge.