De-skew Method for Dynamic Testing Using Current Sensor Transfer Function
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Solution Overview
Problem
Existing methods for compensating skew in oscilloscope measurements of power semiconductor devices are either incompatible, require special fixtures or modifications, or suffer from reduced accuracy due to the inability to account for the frequency response of current sensors, particularly when evaluating high-frequency wide gap semiconductor devices like GaN power transistors.
Innovation Solution
A dynamic test method that de-skews voltage probes and current measurement cables using a standard square-wave signal and applies a transfer function of the current sensor to the current waveform, allowing for accurate alignment and compensation of timing measurements without the need for special fixtures or circuit modifications, and accounting for the frequency response of the current sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a power measurement de-skew and calibration fixture is used, then de-skewing is convenient, but compatibility is reduced and special fixtures are required
Solution Approach 1:
The patent introduces a calibration circuit as an intermediary component that enables de-skewing through standard oscilloscope functions. This circuit includes a voltage source connected to a known impedance, creating a standardized test signal path that mediates between the oscilloscope and various probe configurations, allowing de-skewing without special fixtures while maintaining compatibility
Solution Approach 2:
The patent creates a standardized calibration model that copies the essential characteristics needed for de-skewing into a universal test circuit. This model can be replicated across different measurement setups, allowing the same de-skewing procedure to be applied universally without requiring manufacturer-specific fixtures or modifications
2Ease of operation
If probe compensation output is used as standard square waveform signal source, then de-skewing is easy to perform, but accuracy is reduced because current sensor delay is not de-skewed
Solution Approach 1:
The patent segments the de-skewing process into distinct components: voltage probe de-skewing and current sensor de-skewing. By using separate calibration procedures for each channel type and applying individual delay measurements, the system achieves both ease of operation and high precision, as each component can be optimized independently
Solution Approach 2:
The patent applies partial de-skewing to the voltage channels using the compensation output, then adds excessive action by further de-skewing the current sensor using the standardized calibration circuit. This two-stage approach ensures that the minimum required action is performed easily, then additional precision is achieved through the extended calibration process
3Measurement precision
If inductor is removed and replaced with low inductance resistor, then V-I alignment accuracy is improved, but test circuit modification cost and inconvenience increase
Solution Approach 1:
The patent changes the electrical parameters of the calibration circuit by using a low-inductance resistor with specific impedance values. This parameter selection achieves accurate V-I alignment by minimizing parasitic inductance effects while maintaining a simple, standard component that requires no complex circuit modifications
Solution Approach 2:
The patent uses a simple, inexpensive low-inductance resistor as a temporary calibration element rather than permanently modifying the test circuit. This disposable-like approach allows accurate calibration to be achieved with a cheap, easily replaceable component that doesn't require complex installation or permanent circuit changes
4Adaptability or versatility
If actual DPT switching waveform is used for de-skew, then no external fixture or circuit modification is needed, but difficulty increases when ringing or noise magnitude is comparable to waveform magnitude
Solution Approach 1:
The patent performs preliminary de-skewing of the voltage and current channels using the standardized calibration circuit before acquiring the actual switching waveform. This preliminary action removes the skew artifacts that would otherwise complicate the analysis of the actual device under test, making the subsequent measurement easier and more accurate
Solution Approach 2:
The standardized calibration circuit acts as an intermediary that provides a clean, controlled test signal with known characteristics. This intermediary enables accurate de-skew measurement by providing a reference signal that is not contaminated by device switching transients, ringing, or noise, thus simplifying the overall measurement process
Data Source
AI summary
A dynamic test method includes configuring a dynamic test set-up for a device under test (DUT), the dynamic test set-up including at least one de-skewed voltage probe and at least one de-skewed current measurement cable connected to respective channels of an oscilloscope, and a current sensor connected to the de-skewed current measurement cable and configured to measure a current of the DUT. The method further includes conducting a dynamic test set-up for the DUT using the dynamic test set-up to obtain a current waveform for display on the oscilloscope, and applying a transfer function of the current sensor to the current waveform to display a corresponding de-embedded current waveform on the oscilloscope.