Switched-Feedback Sample-and-Hold Amplifier for Offset and Noise Reduction
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Solution Overview
Problem
Existing sample-and-hold amplifiers face challenges in accurately eliminating offset voltage and low-frequency noise due to high input current and noise limitations, particularly in auto-zero and chopping methods.
Innovation Solution
A sample-and-hold amplifier design that adjusts the feedback path in two operating stages, using a switching circuit to sample and hold offset voltage on a capacitor, allowing for unity gain and inverted holding modes to eliminate offset voltage and reduce noise, with a dummy component to maintain system stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the sampling capacitor is directly driven by the input terminal to store offset voltage, then the offset voltage elimination is achieved, but the input current becomes relatively large
Solution Approach 1:
The patent introduces an operational amplifier as an intermediary component between the input terminal and the sampling capacitor. The operational amplifier drives the sampling capacitor instead of the input terminal directly, thereby reducing the input current while maintaining the offset voltage storage function. This mediator approach resolves the contradiction by decoupling the direct drive relationship.
2Object-affected harmful factors
If the sampling capacitor is made larger to reduce noise, then the noise is reduced, but the input current increases due to the larger capacitor requiring more drive current
Solution Approach 1:
The operational amplifier serves as a mediator that can drive larger capacitors without proportionally increasing the input current burden. By placing the operational amplifier between the input terminal and the sampling capacitor, the system can use larger capacitors for noise reduction while the operational amplifier handles the increased drive requirements, isolating the input terminal from the high current demands.
3Measurement precision
If the feedback path is fixed, then the circuit structure is simple, but the ability to eliminate offset voltage and reduce noise is limited
Solution Approach 1:
The patent implements a dynamic feedback path that can switch between different configurations based on operational requirements. The feedback path includes switching elements that allow the circuit to adapt between unity gain mode and inverted holding mode, enabling offset voltage elimination and noise reduction functions. This dynamic reconfiguration resolves the contradiction by allowing the system to become more complex only when needed for precise offset elimination.
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 design effectively reduces input current and noise while maintaining system stability, enabling precise offset voltage elimination and improved accuracy.
Implementation Method 1
using a switching circuit to sample and hold offset voltage on a capacitor
Data Source
AI summary
A sample-and-hold amplifier can include: an operational amplifier; a sampling capacitor having a first terminal coupled to an inverting input terminal of the operational amplifier, and a second terminal coupled to a reference ground; and a switching circuit configured to switch feedback paths of the sample-and-hold amplifier in a first stage and a second stage, such that an offset voltage of the operational amplifier is at least partially eliminated.