Pulsed AC Current Source Testing Apparatus for High-Frequency Impedance
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Solution Overview
Problem
Measuring AC characteristics of devices under test is challenging due to stray capacitances and rapid impedance changes, especially at high frequencies and narrow pulse widths, which complicates accurate voltage and current control, particularly for devices like PRAM and RRAM.
Innovation Solution
A testing apparatus with a pulsed signal source and a programmable hard current-limiter in series with the device under test, along with a voltage sensor, which operates at a programmed current limit to minimize inaccuracies and includes a transimpedance amplifier for precise current and voltage measurement, and multiple measurement channels for improved accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a voltage is measured across a sense resistor in series with the DUT, then current measurement is enabled, but the voltage applied to the DUT is not the same as the voltage applied by the measurement system across the DUT and sense resistor
Solution Approach 1:
The patent introduces a sense resistor as an intermediary element between the voltage source and the DUT. This sense resistor serves as a mediator that converts current flow into a measurable voltage drop, enabling accurate current measurement while allowing the main voltage source to independently control the voltage applied to the DUT. The sense resistor acts as a separate measurement path that does not interfere with the primary voltage control function.
2Speed
If AC frequency increases and/or pulse width becomes narrow, then high speed measurement capability is improved, but stray capacitances become significant loads
Solution Approach 1:
The patent extracts and isolates the measurement function from the signal path by using a dedicated sense resistor and separate voltage sensing mechanism. This separation removes the measurement function from the main signal path, reducing the impact of stray capacitances on the measurement system. The sense resistor provides a direct current measurement path that is less susceptible to capacitive effects at high frequencies.
Solution Approach 2:
The patent replaces traditional voltage-based measurement methods with a current-based measurement approach using the sense resistor. By substituting the measurement mechanism, the system achieves better performance at high frequencies where stray capacitances would otherwise dominate the measurement characteristics.
3Adaptability or versatility
If DUT exhibits rapid changes in impedance, then device functionality is improved, but it becomes difficult to control voltage and current at the DUT
Solution Approach 1:
The patent implements feedback control by continuously monitoring the voltage across the DUT through a separate voltage sensor and using this information to adjust the voltage source output. This feedback mechanism compensates for rapid impedance changes in the DUT, maintaining stable voltage and current control even when the DUT characteristics change dynamically.
Solution Approach 2:
The patent employs dynamic control mechanisms that allow the voltage source to respond in real-time to changing DUT impedance characteristics. The system adapts its output dynamically based on feedback from voltage sensors, enabling effective control despite rapid impedance transitions in devices like PRAM and RRAM.
Data Source
AI summary
An apparatus for testing a DUT includes a pulsed signal source; a hard current-limiter adapted to be operated in series relationship between the pulsed signal source and the DUT; and a voltage sensor adapted to sense a voltage across the DUT in response to the pulsed signal source.