SMU Diode Clamp Circuit for Faster Low-Current Settling
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Solution Overview
Problem
Device under test (DUT) measurement systems face challenges in reducing settling time, especially in low current ranges, due to the use of large current sense resistors, which increases measurement time and limits manufacturing throughput.
Innovation Solution
The implementation of a diode clamp and slew detection circuitry in the source measurement unit (SMU) reduces settling time by bypassing sense resistors during initial charging of the DUT, allowing faster voltage achievement and minimizing interference during measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If large current sense resistors are used in low current ranges, then measurement precision is improved, but settling time increases significantly
Solution Approach 1:
The patent segments the current sensing function into two paths: a high-precision path through large sense resistors for accurate measurement, and a fast charging path through the diode clamp for rapid voltage establishment. This segmentation allows the system to use different sensing mechanisms during different phases of the measurement process, resolving the contradiction between precision and speed.
Solution Approach 2:
The diode clamp performs preliminary action by rapidly charging the DUT to the target voltage before the main measurement phase begins. This preliminary charging action through the low-impedance diode path establishes the voltage quickly, after which the high-precision resistor path takes over for accurate current measurement, thus reducing overall settling time while maintaining precision.
2Measurement precision
If large current sense resistors are used, then measurement accuracy in low current ranges is improved, but manufacturing throughput decreases
Solution Approach 1:
The measurement system is segmented into a fast charging phase using the diode clamp and a precision measurement phase using the sense resistors. This allows rapid testing cycles where the DUT is quickly charged and then measured, significantly improving manufacturing throughput while maintaining measurement accuracy through the dedicated precision path.
Solution Approach 2:
The system maintains continuous useful action by seamlessly transitioning from the diode clamp charging phase to the resistor measurement phase without interruption. This continuous operation eliminates idle time between charging and measurement, maximizing manufacturing throughput while preserving measurement accuracy through the uninterrupted handoff between components.
3Measurement precision
If sense resistors are used during initial charging, then current measurement is available, but voltage achievement time increases
Solution Approach 1:
The diode clamp acts as an intermediary component that provides a low-impedance charging path during the initial voltage establishment phase. This intermediary element enables rapid voltage achievement without requiring current measurement through the sense resistors, as the clamp temporarily handles the high-current charging function before the measurement phase begins.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The diode clamp and slew detection circuitry significantly reduce settling time from approximately 5.6 seconds to around 200 milliseconds, enhancing measurement efficiency and accuracy in low current ranges.
Implementation Method 1
a diode clamp and slew detection circuitry in the source measurement unit (SMU) reduces settling time by bypassing sense resistors during initial charging of the DUT
Implementation Method 2
a first diode having a first terminal coupled to the first terminal of the resistor, and having a second terminal coupled to the second terminal of the resistor, the first diode having a first orientation. The example diode clamp also includes a second diode coupled in parallel with the first diode between the first and second terminals of the resistor, the second diode having a second orientation opposite than the first diode
Data Source
AI summary
An apparatus includes a circuit including a force amplifier having an output, a resistor having a first terminal coupled to the output of the force amplifier, and a second terminal. The circuit also includes a diode clamp including a first diode having a first terminal coupled to the first terminal of the resistor, and having a second terminal coupled to the second terminal of the resistor, the first diode having a first orientation. The diode clamp also includes a second diode coupled in parallel with the first diode between the first and second terminals of the resistor, the second diode having a second orientation opposite than the first diode.