Auto-Zero Amplifier Circuit With Switched-Capacitor Noise Filtering
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Solution Overview
Problem
Existing auto-zero amplifier circuits face a tradeoff between acquisition bandwidth and sampling noise, making it difficult to simultaneously achieve high acquisition bandwidth and low input-referred auto-zero noise.
Innovation Solution
The introduction of a low noise auto-zero circuit with a pair of switch-controlled auxiliary capacitors that function as switched-capacitor low-pass filters, allowing for the reduction of effective sampling noise while maintaining high acquisition bandwidth by sharing charge between auto-zero and auxiliary capacitors during the hold phase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the capacitance of auto-zero capacitors is increased to reduce sampling noise, then auto-zero noise is reduced, but acquisition bandwidth is negatively affected
Solution Approach 1:
The patent divides the capacitance function into two separate components: auto-zero capacitors (C1.1, C1.2) for offset cancellation and auxiliary capacitors (C2.1, C2.2) for noise filtering. This segmentation allows each capacitor to be optimized for its specific function without compromising the other, resolving the contradiction between noise reduction and bandwidth maintenance
Solution Approach 2:
The auxiliary capacitors act as an intermediary element that filters sampling noise from the auto-zero capacitors. By introducing this intermediate noise-filtering stage, the system can maintain small auto-zero capacitors (preserving bandwidth) while still achieving low noise through the auxiliary capacitors' filtering action
2Measurement precision
If the capacitance of auto-zero capacitors is increased to reduce sampling noise, then auto-zero noise is reduced, but the circuit complexity increases
Solution Approach 1:
The patent merges the auto-zero capacitor and auxiliary capacitor into a unified switched-capacitor filter structure that operates together during the hold phase. This combined structure achieves noise reduction without requiring separate, complex noise-filtering circuits, thereby limiting the increase in overall circuit complexity
3Productivity
If ping-ponging is used to increase throughput in amplifier signal chain, then productivity is improved, but image artifacts are generated due to offset differences
Solution Approach 1:
The patent implements an auto-zero feedback mechanism that measures and cancels offset voltages in each amplifier channel. By continuously monitoring and compensating for offset differences between amplifiers, the system maintains high throughput from ping-ponging operation while eliminating the image artifacts that would otherwise be generated
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 effectively decouples acquisition bandwidth from auto-zero noise, allowing for high bandwidth and low noise performance, with the auxiliary capacitors attenuating cycle-to-cycle noise and enabling efficient offset cancellation.
Implementation Method 1
a pair of switch-controlled auxiliary capacitors that function as switched-capacitor low-pass filters, allowing for the reduction of effective sampling noise while maintaining high acquisition bandwidth by sharing charge between auto-zero and auxiliary capacitors during the hold phase
Data Source
AI summary
An amplifier may include a low noise auto-zero circuit with auto-zero capacitors and switch-controlled auxiliary capacitors that function as switched-capacitor low-pass filters. In an acquisition phase of the auto-zero operation, the inputs of an amplifier may be shorted to a common voltage, and a representation of the offset voltage may be acquired by the auto-zero capacitors. In a hold phase of the auto-zero operation, the auto-zero capacitors may be connected to the auxiliary capacitors, and the resulting voltages may be applied to the circuit such that the original offset voltage is cancelled. Moreover, the switched-capacitor filters may reduce the effective sampling noise while maintaining high acquisition bandwidth.