Power MOSFET I-V Measurement with Load Resistance Compensation
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Solution Overview
Problem
Current-Voltage (I-V) measurements on power MOSFETs are inaccurately affected by high drain currents due to small load resistances causing unwanted voltage drops, leading to incorrect drain current measurements.
Innovation Solution
Methods to compensate for load resistance by iteratively adjusting the forced drain voltage using previous drain current and voltage measurements, employing either a Linear Model Method or an Expected Value Method, to achieve accurate drain current readings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high drain current is measured in power MOSFETs, then the measurement capability is improved, but small load resistances cause large unwanted voltage drops leading to measurement inaccuracy
Solution Approach 1:
The patent implements feedback by measuring the actual drain voltage across the MOSFET and comparing it to the target voltage. Based on this comparison, the system iteratively adjusts the forced drain voltage to compensate for voltage drops across load resistance. This closed-loop feedback mechanism ensures that the measured drain current accurately reflects the true device characteristics despite the presence of load resistance.
Solution Approach 2:
The patent applies preliminary action by pre-characterizing the load resistance in the test circuit before performing I-V measurements. By determining the load resistance value in advance, the system can calculate and apply the necessary voltage compensation beforehand, ensuring that the forced drain voltage accounts for expected voltage drops across the load resistance during subsequent measurements.
2Measurement precision
If load resistance compensation is applied iteratively, then measurement accuracy is improved, but measurement time and complexity increase
Solution Approach 1:
The patent reduces measurement time by performing preliminary characterization of the load resistance before iterative compensation. By determining the load resistance value in advance and storing it for reuse, the system avoids repeatedly measuring it during each iteration, significantly reducing the total measurement time while maintaining accuracy.
Solution Approach 2:
The patent applies partial action by implementing a threshold-based stopping criterion for the iterative compensation process. Instead of performing an fixed number of iterations, the system stops when the difference between measured and target drain voltage falls below a predetermined threshold, thereby avoiding unnecessary iterations and reducing measurement time while still achieving sufficient accuracy.
Data Source
AI summary
A test and measurement instrument, includes a user interface, one or more probes configured to connect to a device under test comprising a MOSFET, and one or more processors configured to execute code that causes the one or more processors to: set a target voltage to be measured across the MOSFET, apply a force voltage to the MOSFET, measure a drain current and a drain voltage of the MOSFET with the one or more probes, determine if a difference between the measured drain voltage and the target voltage meets a threshold, when the difference does not meet the threshold, use the measured drain voltage, the measured drain current, and a load resistance to determine a new force voltage value to compensate for the load resistance, set the force voltage to the new force voltage value, and repeat the apply, measure and determine steps as needed.