Switched-Capacitor Low-Pass Filter With Resistor Feedback
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Solution Overview
Problem
Switched capacitor filters face limitations in frequency response due to the sample and hold process, leading to degraded filter performance.
Innovation Solution
A switched capacitor low-pass filter design incorporating a plurality of switched capacitors and resistors, with a clock signal having a duty cycle differing from 50%, to enhance frequency response and reduce DC gain and frequency variations across corners.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If switched capacitors are used instead of resistors, then sensitivity to process variations, temperature variations, and power supply variations is reduced, but the roll-off slope is limited by the sample and hold process
Solution Approach 1:
The patent combines switched capacitors with resistors in a hybrid configuration. Specifically, resistors are placed in series with switched capacitors in the feedback paths, merging the advantages of both components: switched capacitors provide insensitivity to variations while resistors contribute to achieving the desired roll-off slope without being limited by the sample-and-hold effect
Solution Approach 2:
The filter employs a composite structure where resistor-capacitor networks are integrated with switched capacitor networks. This composite approach creates a hybrid filter that leverages the variation-insensitivity of switched capacitors and the frequency-response-shaping capabilities of resistors, achieving both reliability and performance
2Ease of operation
If a 50% duty cycle clock signal is used, then the switched capacitor operates symmetrically, but the frequency response is degraded
Solution Approach 1:
The patent changes the duty cycle parameter of the clock signal from the conventional 50% to a non-50% value (specifically mentioning duty cycles between 40-60% or 60-80%). This parameter modification optimizes the frequency response and reduces DC gain variations while maintaining proper switched capacitor operation
Solution Approach 2:
The invention introduces dynamic asymmetry through the non-50% duty cycle clock signal, allowing the switched capacitor network to operate in an optimized state for frequency response. The asymmetric switching creates beneficial effects on the filter's frequency characteristics and DC gain stability
3Speed
If resistors are added to increase roll-off slope, then frequency response improves, but DC gain variations across corners increase
Solution Approach 1:
The patent employs feedback networks that combine resistors and switched capacitors in specific configurations. The feedback paths are designed to provide DC gain stabilization while maintaining the improved roll-off slope, using the interaction between resistive and switched capacitive elements to achieve both objectives simultaneously
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
The filter achieves improved frequency response, increased roll-off slope, and minimized DC gain and frequency variations, effectively addressing the limitations of existing switched capacitor filters.
Implementation Method 1
The roll-off in a switched-capacitor filter may be limited, however, by the sample and hold process, leading to degraded filter performance.
Data Source
AI summary
A switched capacitor low-pass filter. The filter includes a plurality of switched capacitors, and a plurality of resistors. The resistors increase the slope of the roll-off of the filter, reduce DC gain variations across corners, and minimize the frequency variation across corners. In some embodiments, the clock signal used to control the switched capacitor filters has a duty cycle differing from 50%, to improve the frequency response of the filter.