Signal Clamp Circuit Using MOSFET Detection for Overrange Protection
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Solution Overview
Problem
Existing diode-based clamps in electronic circuits are inaccurate due to temperature-dependent threshold voltages, require high-speed voltage references, suffer from leakage that impacts signal distortion, and introduce non-linear capacitances, degrading system linearity.
Innovation Solution
A detector circuit and clamping switch system using a multi-terminal active device, such as a PMOSFET, NMOSFET, or BJT, that detects signal levels exceeding thresholds and adjusts impedance to clamp the signal, minimizing distortion and maintaining linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a diode-based clamp is used to limit voltage, then the second circuit is protected against overrange signals, but the clamp becomes inaccurate due to temperature-dependent threshold voltage shifts
Solution Approach 1:
The patent replaces the diode-based clamp with a transistor-based clamp (MOSFET or BJT) whose clamping threshold is determined by externally controllable voltage references rather than fixed diode threshold voltages. This allows the clamping level to be stabilized against temperature variations through regulated reference voltages, directly addressing the temperature stability issue while maintaining protection accuracy.
2Measurement precision
If a diode-based clamp is used to limit voltage, then overrange signals are protected, but high-speed voltage references are required to maintain accurate clamping levels
Solution Approach 1:
The patent introduces detector circuits as intermediary components that monitor signal levels and control the clamping action. These detectors compare the input signal against reference levels and activate the clamp only when needed, eliminating the requirement for continuously operating high-speed voltage references while maintaining accurate clamping precision through controlled activation.
3Reliability
If a diode-based clamp is used to limit voltage, then overrange protection is provided, but leakage current impacts distortion in high dynamic range signal paths
Solution Approach 1:
The patent employs dynamically controllable transistor switches (MOSFETs or BJTs) instead of fixed diode clamps. These transistors can be precisely controlled to remain in a high-impedance off state during normal operation, minimizing leakage current to negligible levels. When overrange conditions are detected, the transistors dynamically switch to a low-impedance on state to provide effective clamping, thus protecting against distortion while maintaining overrange protection.
4Reliability
If relatively large diodes are used for effective clamping, then overrange signals are limited, but non-linear capacitances are added to the signal path, degrading system linearity
Solution Approach 1:
The patent substitutes the physical diode structure with a transistor-based switching mechanism controlled by electrical signals. This replacement eliminates the inherent non-linear capacitance of diode junctions, as the transistor switches operate in a more linear manner when properly biased and controlled. The clamping effectiveness is maintained through the transistor's ability to conduct heavily when activated, while the signal path linearity is preserved due to the reduced parasitic capacitance and more controlled switching behavior.
Data Source
AI summary
One embodiment is an apparatus including a detector circuit electrically coupled between a signal source and a second circuit, the signal source generating a first signal, the detector circuit detecting a level of the first signal and generating a first control signal when the detected level of the first signal exceeds a first threshold value, and a clamping switch electrically coupled to receive the first control signal from the detector circuit, the clamping switch including a multi-terminal active device. The first control signal controls a state of the clamping switch such that the clamping switch clamps a level of a signal applied to the second circuit when the level of the first signal exceeds the first threshold value.