Chopper Ripple Reduction via Sample-Hold Notch Filter
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Solution Overview
Problem
Existing notch filters for chopper stabilized circuits require precise 90-degree phase control signals and multiple signal paths, leading to increased circuit complexity and area, while still allowing residual ripple in the output signal.
Innovation Solution
A notch filter design that uses a sample and hold circuit with a zeroing switch, operating during non-overlap times between chopper phases, which eliminates chopper ripple without requiring precise phase control and reduces circuit complexity by using a single signal path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a switched capacitor notch filter operating at precisely 90 degrees out of phase with choppers is used, then chopper ripple is filtered out, but the circuit complexity and area increase due to multiple signal paths
Solution Approach 1:
The circuit is divided into two distinct operational phases: a charge phase where capacitors are charged during chopper transitions, and a hold phase where capacitors maintain their charge during non-overlap periods. This segmentation allows ripple filtering without requiring complex multi-path signal processing
Solution Approach 2:
The harmful ripple component is extracted and isolated from the main signal path by using separate charge and hold phases. The capacitors capture ripple during charge phase and isolate it during hold phase, eliminating the need for complex continuous filtering circuits
2Object-affected harmful factors
If a switched capacitor notch filter with two ping-ponged signal paths is used, then ripple suppression is achieved, but the device area increases
Solution Approach 1:
Multiple filtering functions are merged into a single capacitor structure that operates in different phases. The same capacitor serves both charge accumulation and ripple holding functions at different times, eliminating the need for separate parallel filtering paths and reducing overall device area
Solution Approach 2:
The capacitor operates periodically alternating between charge phase and hold phase. During charge phase, capacitors accumulate charge; during hold phase, they maintain charge. This periodic operation allows a single capacitor to perform what would traditionally require multiple continuous filtering components
3Object-affected harmful factors
If precise 90-degree phase control signals are generated for the notch filter, then ripple filtering is effective, but the control complexity increases
Solution Approach 1:
The capacitor automatically charges and discharges based on the natural timing of chopper phases without requiring external precise phase control. The circuit self-regulates by capturing ripple during chopper transitions and holding charge during non-overlap periods, eliminating the need for complex phase synchronization control
Data Source
AI summary
A notch filter is controlled synchronously with a chopper to filter out chopping ripple. In one embodiment, the notch filter is coupled to the differential output of the chopper and includes a sampling capacitor, a hold capacitor, and a second set of switches between the sampling capacitor and the hold capacitor. The second set of switches is temporarily closed once per chopper switching cycle to transfer charge from the sampling capacitor to the hold capacitor such that the ripple from the chopper is not transferred to the hold capacitor. The voltage across the hold capacitor may be coupled to any other circuit, such as to the differential inputs of an amplifier.