Multi-Phase Auto-Zero Amplifier Circuit for Input Offset Reduction
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Solution Overview
Problem
Existing amplifier circuits face challenges in reducing effective input offset voltage, particularly in analog front-end (AFE) circuitry, due to manufacturing imperfections and noise, which can lead to errors in signal processing, especially when dealing with small signals.
Innovation Solution
The implementation of a multi-phase auto-zeroing amplifier circuitry that utilizes multiple switches and capacitors to separate the auto-zero phase into sub-phases, allowing for more accurate compensation of input offset voltage by storing coarser and finer charge approximations on capacitors, thereby reducing pedestal and sampling noise errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional auto-zeroing is used with a single phase, then the circuit complexity is low, but the input offset voltage compensation accuracy is insufficient
Solution Approach 1:
The auto-zero phase is segmented into multiple sub-phases (first sub-phase and second sub-phase) with different switching configurations. During the first sub-phase, switches S1 and S2 are closed to provide a first approximation of offset compensation. During the second sub-phase, switches S1 and S2 are opened to provide a second, more accurate approximation. This segmentation allows progressive refinement of offset compensation without requiring complete circuit redesign.
Solution Approach 2:
The circuit employs dynamic switching of capacitors C1 and C2 between different connection states during the auto-zero phase. The switches S1 and S2 dynamically change their states between sub-phases to reconfigure the feedback path and capacitor connections, enabling the circuit to adapt its compensation precision based on the current sub-phase requirements.
2Measurement precision
If multi-phase auto-zeroing is implemented, then the input offset voltage reduction is significant, but the switching complexity increases
Solution Approach 1:
The switching complexity is managed by segmenting the auto-zero operation into distinct sub-phases with well-defined switch states. Each sub-phase has a specific configuration (S1/S2 closed or open) that can be controlled by simple phase signals, making the switching sequence manageable and predictable despite multiple phases involved.
Solution Approach 2:
The circuit performs preliminary offset compensation during the first sub-phase before proceeding to the second sub-phase. This preliminary action establishes a baseline compensation that reduces the burden on subsequent phases, allowing the switching complexity to be distributed progressively rather than all at once.
3Measurement precision
If coarser charge approximation is stored first, then the auto-zero phase can be divided into sub-phases, but the total auto-zero time increases
Solution Approach 1:
The auto-zero time is segmented into sub-phases that can be efficiently executed. By dividing the compensation task into first and second sub-phases with different precision levels, the circuit avoids the inefficiency of a single long high-precision phase while still achieving the desired overall accuracy through cumulative compensation effects.
Solution Approach 2:
The first sub-phase provides a coarser but sufficient initial compensation that addresses the majority of the offset error. The second sub-phase then provides additional refinement. This partial action approach prevents over-engineering the first phase while ensuring adequate overall compensation, optimizing the time-precision tradeoff.
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 approach significantly reduces the effective input offset voltage, improving the accuracy of signal processing by attenuating referred-to-input errors during the auto-zero phase, as demonstrated by computer simulations showing a reduction from 40mV to 0.22mV input-referred offset voltage.
Implementation Method 1
an input capacitor, having a first input capacitor terminal and a second input capacitor terminal, the second input capacitor terminal coupled to the inverting amplifier input terminal
Data Source
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AI summary
An enhanced auto-zero circuitry and technique for reducing the effective input offset voltage of an amplifier. The circuitry includes a multi-phase auto-zeroing amplifier circuitry including several capacitor and switch components and a switch controller circuit. The switch controller circuit is configured to provide control signals for controlling the switches, where during a first sub-phase of an auto-zero phase, multiple switches are turned on to store an amplifier input offset coarser compensation charge on the input capacitor, and where during a second sub-phase of the auto-zero phase, at least one switch is turned off before turning on another switch to store an amplifier input offset finer compensation charge on the input capacitor via the first auto-zero capacitor.