Multi-Phase Auto-Zero Amplifier Circuit for Offset Cancellation
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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, where manufacturing imperfections and device noise lead to errors in signal processing, especially when dealing with small signals.
Innovation Solution
The implementation of a multi-phase auto-zeroing circuitry with additional switches and capacitors allows for multiple sub-phases in the auto-zeroing process, enabling more accurate cancellation of input offset voltage by storing and compensating for the offset voltage in a series of steps, thereby reducing pedestal and noise errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional auto-zeroing methods are used, then the input offset voltage is reduced, but the reduction is insufficient (only to about 3.35 mV) due to manufacturing imperfections and device noise
Solution Approach 1:
The patent divides the auto-zeroing process into multiple sequential sub-phases (first sub-phase, second sub-phase, third sub-phase) instead of using a single auto-zeroing phase. Each sub-phase uses specific switch configurations and capacitor connections to progressively reduce the offset voltage. This segmentation allows the circuit to address different components of the offset voltage in stages, overcoming the limitations of traditional single-phase auto-zeroing affected by manufacturing imperfections.
2Measurement precision
If more switches and capacitors are added to implement multi-phase auto-zeroing, then the offset voltage cancellation accuracy is improved, but the circuit complexity increases
Solution Approach 1:
The patent performs preliminary offset voltage sampling and compensation actions in the first and second sub-phases before the main signal processing occurs in the third sub-phase. During the first sub-phase, switches are configured to sample the offset voltage onto capacitors. In the second sub-phase, additional compensation actions are performed. This preliminary action sequence allows the circuit to pre-compensate for offset errors before amplifying the actual signal, improving accuracy without requiring continuous complex circuitry during signal processing.
Solution Approach 2:
The patent implements periodic switching sequences that cycle through different switch configurations in distinct sub-phases. The switches are periodically opened and closed in specific patterns during each sub-phase, creating a time-multiplexed operation mode. This periodic action allows the same physical components to perform multiple functions at different times, achieving high precision offset cancellation while managing circuit complexity through temporal rather than spatial multiplication of components.
3Measurement precision
If multi-phase auto-zeroing is implemented, then the effective input offset voltage is significantly reduced (to as low as 0.22 mV), but the processing time increases due to multiple sub-phases
Solution Approach 1:
The patent changes the operational parameters of the circuit by dynamically reconfiguring switch states and capacitor connections across different sub-phases. Each sub-phase uses specific parameter settings (switch open/closed states, capacitor charging/discharging conditions) optimized for that particular compensation stage. This parameter changing approach allows the circuit to achieve high precision offset reduction (0.22 mV) by adapting its operational characteristics to the specific requirements of each compensation phase, rather than using fixed parameters throughout.
Data Source
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.