Switched-Capacitor Glitch Filter for Burst Reset Stability
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Solution Overview
Problem
Process variation in glitch filters, such as RC filters, leads to uncertainty in operation parameters, causing inconsistent filtering of glitches, particularly in bursts of signal transitions shorter than 50 nanoseconds.
Innovation Solution
The implementation of a switched capacitance filter with coupled switching and reset stages that charge or discharge capacitances based on clock signals to mitigate glitches, ensuring consistent filtering across varying process conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an RC filter is implemented in a glitch filter, then the filtering function is achieved, but process variation causes the time constant to vary between 50% and 150%, leading to inconsistent operation
Solution Approach 1:
The patent replaces the RC filter with a switched-capacitor filter, fundamentally changing the filtering mechanism from resistance-based to capacitance-based. This parameter change eliminates the time constant variation issue because the switched-capacitor filter's filtering characteristic depends on the clock frequency and capacitance ratio, which are much more stable against process variation than RC time constants.
Solution Approach 2:
The patent substitutes the passive RC filtering mechanism with an active switched-capacitor filtering mechanism controlled by clock signals. This substitution allows precise control of the filtering behavior through the clock frequency and capacitance values, replacing the unreliable passive RC time constant with an active, controllable system.
2Manufacturing precision
If a switched capacitance filter is used, then process variation is reduced, but the circuit complexity increases with additional switching stages and reset stages
Solution Approach 1:
The patent divides the switched-capacitor filter into multiple discrete stages, each with its own switching transistors and capacitances. This segmentation allows independent optimization of each stage and makes the overall complex function manageable through modular design, where each stage contributes to the overall filtering performance.
Solution Approach 2:
The patent employs periodic clock signals to control the switching of capacitances in the filter. This periodic action creates a time-varying filter characteristic that achieves the desired filtering function while maintaining stability against process variation. The regular clocking rhythm provides predictable and repeatable operation.
3Reliability
If reset stages are added to mitigate bursts of glitches, then glitch filtering is improved, but the device complexity and number of components increase
Solution Approach 1:
The reset stages are controlled by detecting the output state of the filter and providing feedback to reset the capacitances when needed. This feedback mechanism automatically mitigates burst glitches without requiring complex external control logic, as the system self-regulates based on its own output state.
Solution Approach 2:
The filter circuit performs its own reset function through the integrated reset stages that are part of the filter structure itself. The circuit serves its own need for glitch mitigation by automatically detecting and resetting charged capacitances when burst glitches occur, without requiring external intervention.
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
Effectively filters glitches and bursts of signal transitions shorter than 50 nanoseconds, decoupling process variations and maintaining consistent output by resetting capacitances during state changes, thereby improving the reliability of glitch filtering.
Implementation Method 1
the glitch filter provided herein utilizes a switched capacitance. In one or more embodiments, the glitch filter also includes switching stages coupled to the switched capacitance. The switching stages operate to charge or discharge the switched capacitance and a filter capacitance
Data Source
AI summary
A glitch filter is provided. The glitch filter receives an input signal and sets a voltage level of an intermediary input node in accordance with a state of the input signal. The glitch filter charges or discharges a switched capacitance based on the voltage level of the intermediary input node and charges or discharges a filter capacitance based on a charge of the switched capacitance. The glitch filter sets a state of an output signal based on the charge of the filter capacitance. The glitch filter includes a reset stage that at least partially filters a burst of glitches in the input signal from the output signal by controlling the charge of the switched capacitance based on the state of the input signal and the state of the output signal.