Auto-Zero Amplifier Without Signal-Path Switching Artifacts
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Solution Overview
Problem
Existing differential amplifier circuits amplify both the desired signal and DC offset voltage, leading to noise gain issues that degrade the input signal, and traditional auto-zero circuits introduce artifacts due to switches in the signal path.
Innovation Solution
A circuit that removes noise due to DC offset voltage from the signal frequency band without reversing the input signal, using a two-position switch and a single-bit sigma-delta modulator to change the noise gain and relocate noise errors to harmonic frequencies of the switching signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If traditional auto-zero circuits are used to remove DC offset noise, then noise gain is reduced, but switches in the signal path introduce artifacts and degrade signal quality
Solution Approach 1:
The patent introduces an intermediary auto-zero amplifier that samples the DC offset voltage from the main amplifier without being in the signal path. This intermediary device captures the harmful DC component and generates a compensating signal, thereby removing the noise without introducing artifacts from switches in the critical signal path.
Solution Approach 2:
The patent segments the noise removal function from the main signal amplification path by creating a separate auto-zero amplifier. This segmentation allows the DC offset sampling and compensation to occur in isolation, preventing the switching artifacts from contaminating the primary signal path while still achieving noise reduction.
2Object-affected harmful factors
If switches are placed in the signal path for auto-zero operation, then DC offset voltage can be removed, but the switches introduce artifacts and disturb the input signal
Solution Approach 1:
The patent uses an intermediary auto-zero amplifier as a mediator that performs the DC offset sampling function away from the main signal path. The switch in the auto-zero amplifier handles the DC component removal without affecting the AC signal integrity, as the switch operates in isolation from the critical signal path.
Solution Approach 2:
The patent extracts the DC offset sampling function from the main amplifier circuit and places it in a separate auto-zero amplifier. This extraction removes the harmful effect of switches from the signal path while preserving the beneficial DC offset removal capability.
3Object-affected harmful factors
If noise gain is reduced to remove low frequency noise, then DC offset effects are minimized, but signal quality may be compromised by traditional methods
Solution Approach 1:
The patent employs feedback by having the auto-zero amplifier continuously sample the DC offset voltage from the main amplifier output and feed back a compensating signal. This feedback mechanism dynamically adjusts the noise gain reduction while maintaining signal quality, as the compensation is based on actual measured DC offset rather than fixed circuit parameters.
Data Source
AI summary
An apparatus for removing noise due to a DC offset voltage from the frequency band of interest of a signal. Input noise errors are moved out of the band of interest by changing the noise gain of the system without placing a switch in the signal path. The resistance through which an input signal passes to the amplifier remains unchanged, but the noise gain is selectively changed by use of a single switch that inserts an additional resistance from a zero signal source in response to a switching signal, thus switching the amplifier between two states with different noise gains. The output signal may be passed through a sigma-delta modulator and an exclusive-or gate clocked at a duty cycle such that the signal gain of the amplifier is unchanged while the different noise gain states cancel out, thus relocating the input noise errors to harmonic frequencies of the switching signal.