Voltage Limiting Circuit for SMU Current Sensing Overload Protection
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Solution Overview
Problem
Source Measurement Units (SMUs) face challenges in measuring device currents over a wide range due to logarithmic IV characteristics, leading to excessive burden voltage across current sense resistors, causing overload and undesirable voltage transients when current levels change significantly, which can damage the Device Under Test.
Innovation Solution
A voltage limiting circuit is introduced, comprising a voltage sense circuit, activation circuit, and level shifting circuit, which detects predefined threshold voltages and activates the voltage limiting circuit to shunt current, preventing overload by maintaining optimal voltage across the current sense resistor network.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-value current sense resistor is used to measure low current levels, then measurement precision is improved, but burden voltage increases causing overload and reliability deterioration
Solution Approach 1:
The patent implements dynamic switching between multiple current sense resistors with different values based on the measured current level. The system automatically selects appropriate resistors (e.g., 1GΩ for pA range, 1kΩ for mA range) to maintain measurement precision while preventing burden voltage from causing overload conditions
Solution Approach 2:
The patent changes the resistance parameter of the current sense resistor based on the measured current magnitude. By switching resistor values dynamically, the system adapts the measurement range to match the actual current level, ensuring both precision and reliability across different operating conditions
2Power
If voltage is increased during device parametric sweep, then measurement capability is improved, but transient voltage signals increase causing harmful effects
Solution Approach 1:
The patent places diodes in parallel with the current sense resistors to provide a voltage clamping mechanism. When transient voltage exceeds the diode breakdown voltage, the diode conducts and limits the voltage spike, protecting the Device Under Test from damage while allowing normal measurement operation
Solution Approach 2:
The diode acts as an intermediary protective element between the voltage source and the Device Under Test. It absorbs excess voltage energy during transients through reverse breakdown, preventing harmful voltage spikes from reaching the DUT while maintaining circuit functionality
Data Source
AI summary
A voltage limiting circuit for limiting the voltage developed across a current sensing circuit and a method are disclosed. The voltage limiting circuit includes an input terminal configured to receive an input signal from the current sensing circuit, and an output terminal configured to receive an output signal from the current sensing circuit. A voltage sense circuit is connected to the input terminal and output terminal to detect that a predefined threshold voltage is developed between the input terminal and output terminal. An activation circuit receives a signal from the voltage sense circuit to activate the voltage limiting circuit, and a level shifting circuit interfaces the voltage sense circuitry to the activation circuitry and other circuits by level shifting signals to required levels.