Switched Capacitor Notch Filter With Parallel Charge Averaging
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Solution Overview
Problem
Conventional notch filters for chopper stabilized Hall effect sensors require large sampling capacitors and output buffers, leading to area consumption and offset issues, and are susceptible to sampling non-ideal effects like charge injection and clock feed-through.
Innovation Solution
A switched capacitor notch filter design that alternately charges sampling capacitors and couples them in parallel to an operational amplifier during an averaging time period, eliminating the need for conventional buffering and allowing for smaller capacitor sizes and reduced area consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional notch filters use two sampling stages with large sampling capacitors (4-10 picofarads) and output buffers, then the filtering performance is improved, but the circuit area consumption increases and offset issues arise
Solution Approach 1:
The patent combines the sampling and averaging functions into a single stage by coupling sampling capacitors in parallel during an averaging time period, eliminating the need for separate buffering stages while maintaining filtering performance. This merging reduces the overall circuit area by removing redundant components.
Solution Approach 2:
The sampling capacitors serve multiple functions: they perform sampling during their charged state and simultaneously perform averaging when coupled in parallel during the averaging time period. This multi-functionality eliminates the need for dedicated buffering stages, reducing circuit area while maintaining filtering effectiveness.
2Stability of the object's composition
If conventional notch filters use output buffers to isolate sampling stages from averaging stage, then the stability is improved, but the offset contribution increases and dynamic offset cancellation becomes difficult
Solution Approach 1:
The patent extracts and eliminates the output buffer stage from the conventional filter architecture. By directly coupling sampling capacitors in parallel during the averaging time period, the design removes the source of buffer-induced offset while maintaining circuit stability through the inherent charge redistribution mechanism.
Solution Approach 2:
The sampling capacitors themselves perform the averaging function by being coupled in parallel during a dedicated averaging time period, eliminating the need for separate buffering stages. This self-service approach reduces offset contribution while maintaining stability through the natural charge equalization process.
3Measurement precision
If notch filters use continuous time approaches with two sampling stages, then the filtering accuracy is improved, but the device complexity and area consumption increase
Solution Approach 1:
The patent merges the sampling and averaging operations into a single unified stage. Sampling capacitors are charged during sampling phases and then coupled in parallel during an averaging time period, achieving accurate filtering without requiring separate two-stage sampling architectures, thereby reducing device complexity.
4Object-generated harmful factors
If charge redistribution discrete time approach is used, then the offset issues are reduced, but the sampling capacitor sizes remain large (4-10 picofarads) and area consumption is high
Solution Approach 1:
The patent employs periodic switching to control the coupling and decoupling of sampling capacitors. During specific averaging time periods, capacitors are coupled in parallel to perform charge redistribution, while during other periods they are independently charged. This periodic action enables effective averaging with reduced capacitor sizes compared to continuous approaches.
Data Source
AI summary
A switched capacitor notch filter for sampling an input signal using multiple sampling capacitors and multiple non-overlapping time periods. The charge from the sampling capacitors is averaged and transferred to the filter output during another non-overlapping time period.