Input Protection Circuit With Variable Tripping Threshold
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Solution Overview
Problem
High-performance oscilloscopes, particularly RF oscilloscopes, face issues with parasitic elements that degrade performance due to the need for additional mechanisms to prevent over-voltage damage, which introduces time delays and requires high-voltage components, leading to increased parasitic elements and performance degradation.
Innovation Solution
An input protection circuit with a variable tripping threshold and low parasitic elements is implemented, using a control circuit with multiple trip-points and active and passive components to selectively isolate input signals based on voltage ranges, preventing signal propagation into sensitive circuitry without degrading instrument performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage sensing circuit and switching element are added to prevent over-voltage damage, then protection capability is improved, but parasitic elements increase and performance degrades
Solution Approach 1:
The patent implements a variable tripping threshold that dynamically adapts to the selected voltage range on the oscilloscope. Instead of a fixed threshold, the protection circuit adjusts its trip point based on the operating conditions, allowing it to provide effective protection across multiple voltage ranges without requiring separate protection circuits for each range, thereby reducing overall parasitic elements.
Solution Approach 2:
The invention changes the parameter of the tripping threshold voltage to be variable rather than fixed. By implementing multiple trip-points corresponding to different voltage ranges, the protection circuit can adapt its characteristics to match the selected operating range, improving protection effectiveness while minimizing the addition of parasitic elements through shared circuitry.
2Reliability
If additional mechanisms are added to prevent over-voltage damage, then protection reliability is improved, but time delays increase
Solution Approach 1:
The protection circuit continuously monitors the input voltage and pre-charges the switching element in anticipation of over-voltage conditions. The voltage sensing mechanism is always active, so when an over-voltage event occurs, the switching element can respond immediately without the delay of detecting and processing the voltage excursion from a dormant state.
Solution Approach 2:
The dynamic response of the protection circuit is optimized by implementing a variable tripping threshold that can quickly adapt to different voltage ranges. The circuit transitions rapidly between states based on the selected voltage range, minimizing the time required to detect and respond to over-voltage conditions while maintaining protection reliability.
3Reliability
If high-voltage components are used to protect against over-voltage, then protection capability is improved, but parasitic elements increase
Solution Approach 1:
The protection circuit is segmented into multiple operational modes corresponding to different voltage ranges. Each mode has its own trip-point optimized for that range, allowing the circuit to use appropriate protection levels for each operating condition. This segmentation enables the use of lower-voltage components in lower ranges while maintaining protection capability across all ranges, reducing overall parasitic elements.
Solution Approach 2:
The protection circuit dynamically selects which trip-point to use based on the selected voltage range on the oscilloscope. This dynamic selection allows the circuit to adapt its protection characteristics to match the operating conditions, providing effective protection without requiring high-voltage components to be present in all operating modes, thereby reducing parasitic elements.
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 protects oscilloscopes from over-voltage conditions early in the signal path, adapting to selected voltage ranges without introducing significant parasitic elements, thus maintaining performance and feature integrity.
Implementation Method 1
the control circuit to control the first switching element to decouple the input node from the output node when a control voltage exceeds the specified trip-point
Implementation Method 2
A first switching element within the protection circuit may be configured to couple/decouple the input node to/from the output node
Data Source
AI summary
Various embodiments of an input protection circuitry may be configured with a variable tripping threshold and low parasitic elements, which may prevent a signal from propagating into the protected equipment/device if the voltage of the input signal exceeds a certain limit. The input protection circuit may operate to protect a measurement instrument, which may be an oscilloscope, early in the signal path leading into to the instrument, to avoid exposing sensitive circuitry to damaging voltage levels, and without introducing significant parasitic elements that would degrade the performance of the instrument. The protection circuit may be configured to include clamping to provide protection during the circuit response delay time. The input protection threshold of the protection circuit may be adaptive to a selected voltage range on the instrument without trading-off instrument performance and features.