Low-Pass Filter Feedback Logic for Glitch-Free Output Transitions
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Solution Overview
Problem
Low-pass filter circuits lack an effective arbitration mechanism, leading to incorrect output signal transitions due to incomplete charge removal from the integrating capacitor, resulting in short pulses when the input signal's pulse width is close to the preset filter pulse width, which can cause errors in downstream circuits.
Innovation Solution
Incorporating a feedback logic circuit mechanism that prioritizes the transition state of the hysteresis signal generated by the Schmitt trigger to ensure complete charging or discharging of the capacitor, thereby preventing short pulses in the output signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a low-pass filter circuit uses an integrating circuit with a resistor and capacitor to filter glitches, then the circuit can eliminate interference from input signals, but when the pulse width of the input signal is close to the preset filter pulse width, the capacitor does not discharge properly, resulting in short pulses at the output signal edge
Solution Approach 1:
The patent introduces a feedback logic circuit that detects the state of the integrating capacitor and provides feedback control signals to adjust the charging and discharging processes. When the pulse width of the input signal is close to the preset filter pulse width, the feedback mechanism ensures the capacitor discharges completely before the next charging cycle, preventing short pulses at the output signal edge while maintaining reliable glitch filtering.
2Device complexity
If the low-pass filter circuit lacks a charge removal mechanism of the integrating capacitor, then the circuit structure remains simple, but the low-pass filter result has considerable dependence on the waveform or pattern of the input signal, causing incorrect output signal transitions
Solution Approach 1:
The patent implements a self-service mechanism where the feedback logic circuit automatically detects when the integrating capacitor needs to be discharged and activates the charge removal process without external intervention. This self-regulating mechanism ensures the capacitor is always in the correct state for accurate filtering, making the circuit reliable across various input signal waveforms and patterns while adding minimal structural complexity.
3Ease of manufacture
If the designed charge/discharge time constant does not match the pattern of the input signal, then the circuit can maintain fixed component values, but the glitch or interference in the input signal cannot be filtered out, resulting in incorrect output signal transitions
Solution Approach 1:
The patent introduces dynamic control of the charge/discharge time constant through the feedback logic circuit. While the resistor and capacitor components maintain fixed values for ease of manufacture, the feedback mechanism dynamically adjusts the effective time constant by controlling the switching of charging and discharging paths based on the actual input signal pattern, ensuring reliable glitch filtering across different signal conditions.
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 solution effectively prevents output signal transitions caused by input signal pulse widths smaller than expected, ensuring correct operation of subsequent load circuits and eliminating glitches in clock signals, thus enhancing the reliability of the low-pass filter circuit.
Implementation Method 1
the integrating circuit comprises a resistor R1 and a capacitor C1
Implementation Method 2
the Schmitt trigger SCHTRG...generate an output signal VOUT...utilizing the low-pass filter characteristics of the integrating circuit and the hysteresis characteristics of the Schmitt trigger SCHTRG
Data Source
AI summary
A glitch-free low-pass filter circuit includes an integrating circuit, a Schmitt trigger, a first feedback logic circuit and a second feedback logic circuit. The integrating circuit is used to integrate an input signal to generate an integral signal. The Schmitt trigger is used to receive the integral signal to generate a hysteresis signal. The first feedback logic circuit is used to pull the integral signal to a reset voltage or up to the set voltage based on an inverted input signal and an inverted hysteresis signal, wherein the inverted input signal and the inverted hysteresis signal are generated by performing an inversion process. The second feedback logic circuit is used to pull the integral signal down to the reset voltage or up to the set voltage based on the inverted hysteresis signal and an output signal, wherein the output signal is generated by performing the inversion process twice.