Sample and Hold Circuit Offset Voltage Control
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Solution Overview
Problem
Sample and hold circuits face challenges in achieving long hold times due to leakage in the sampling switch, which reduces the voltage on the sampling capacitor and limits the power-saving potential by requiring frequent reactivation of reference voltage generation circuitry.
Innovation Solution
The proposed sample and hold circuits incorporate an amplifier, a capacitor, and a switch configuration that measures and applies offset voltage to reduce the voltage across the sampling switch during hold time, thereby minimizing leakage and extending hold time, with additional implementations using multiple amplifiers to alternately measure and control the switch voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If a conventional sample and hold circuit uses a simple switch and capacitor configuration, then the circuit structure is simple, but the hold time is short due to leakage in the sampling switch
Solution Approach 1:
An operational amplifier is introduced as an intermediary component between the sampling switch and the holding capacitor. The amplifier buffers the sampled voltage, isolating the capacitor from the switch's leakage effects and enabling significantly extended hold times while maintaining reasonable circuit complexity
Solution Approach 2:
The circuit is divided into distinct functional segments: a sampling network with switch, an operational amplifier stage, and a holding capacitor. This segmentation allows each component to perform its specific function optimally, with the amplifier acting as a buffer between the sampling and holding stages to minimize leakage impact
2Reliability
If the sampling switch is kept simple to reduce circuit complexity, then manufacturing is easier, but leakage current reduces the voltage on the sampling capacitor
Solution Approach 1:
The operational amplifier serves as a mediator that protects the sampling capacitor from the detrimental effects of switch leakage. By placing the amplifier between the switch and capacitor, the capacitor voltage is maintained stable despite leakage currents in the sampling switch
3Use of energy by moving object
If hold time is extended to reduce power consumption, then energy efficiency improves, but the sampling switch leakage reduces the voltage on the sampling capacitor
Solution Approach 1:
The operational amplifier acts as an energy-preserving intermediary that prevents leakage current from discharging the sampling capacitor. This allows the circuit to maintain stable voltages over extended periods, enabling longer hold times and reduced power consumption without sacrificing voltage integrity
Solution Approach 2:
The amplifier maintains continuous voltage stabilization on the sampling capacitor, ensuring that the stored voltage remains valid throughout the extended hold period. This continuous action prevents the voltage decay that would otherwise occur due to leakage, enabling energy-efficient operation
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 configuration significantly increases the hold time of the sample and hold circuit, allowing the reference voltage generation circuit to remain disabled for longer periods, thereby reducing power consumption and extending battery life in battery-powered devices.
Implementation Method 1
The capacitor is coupled to an inverting input of the amplifier, and is configured to store offset voltage of the amplifier
Implementation Method 2
The switch is configured to switchable couple an output of the amplifier to an inverting input of the amplifier
Data Source
AI summary
A sample and hold circuit with long hold time. A sample and hold circuit includes an amplifier, a capacitor, a switch, and a sampling network. The capacitor includes a first terminal coupled to an inverting input of the amplifier. The switch includes a first terminal that is coupled to an output of the amplifier, and a second terminal that is coupled to the inverting input of the amplifier. The sampling network is coupled to a non-inverting input of the amplifier.