SMU Force Amplifier Feedback for Faster Current Settling
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Solution Overview
Problem
Source measurement units (SMUs) face instability due to RC pole frequency, leading to delayed current measurements and reduced system bandwidth, which increases device testing time and reduces throughput.
Innovation Solution
The SMU employs a GmC pole compensation method by adding a series combination of a resistor and capacitor, independent of the resistance, to stabilize the system and minimize measure current settling time, using a feedback loop to adjust output impedance and improve bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If RC pole frequency compensation is used to stabilize the system, then system stability is improved, but measure current settling time increases and bandwidth decreases
Solution Approach 1:
The patent changes the compensation parameter from RC pole (resistor-capacitor) to GmC pole (transconductance-capacitor) by replacing the resistor with a transconductance circuit. This parameter change maintains system stability while significantly reducing the measure current settling time and increasing bandwidth, as the GmC pole compensation does not introduce the same time delays as RC pole compensation.
Solution Approach 2:
The patent substitutes the traditional RC pole compensation mechanism with a GmC pole compensation mechanism. The resistor-based RC pole is replaced by a transconductance-based GmC pole, fundamentally changing the compensation approach from resistive-capacitive to active transconductance-capacitive, which resolves the trade-off between stability and settling time.
2Stability of the object's composition
If RC pole frequency compensation is used to stabilize the system, then system stability is improved, but system bandwidth decreases
Solution Approach 1:
The patent changes the compensation parameter from RC pole to GmC pole by replacing the resistor with a transconductance circuit. This parameter change maintains system stability while significantly increasing the system bandwidth, as the GmC pole compensation architecture allows for higher frequency operation without the bandwidth limitations imposed by RC pole compensation.
Solution Approach 2:
The patent substitutes the traditional RC pole compensation mechanism with a GmC pole compensation mechanism. The resistor-based RC pole is replaced by a transconductance-based GmC pole, fundamentally changing the compensation approach from resistive-capacitive to active transconductance-capacitive, which resolves the trade-off between stability and bandwidth.
3Reliability
If traditional feedback loop is used, then basic measurement function is maintained, but measure current settling time increases
Solution Approach 1:
The patent changes the feedback loop compensation parameter from RC pole to GmC pole by replacing the resistor with a transconductance circuit. This parameter change maintains the basic measurement function and system reliability while significantly reducing the measure current settling time, enabling faster and more efficient measurements.
Data Source
AI summary
The techniques and circuits, described herein, include solutions for reducing measure current settling time in source measurement units (SMUs) during a force voltage mode of operation. An SMU includes a force amplifier having a first voltage input, a second voltage input, a feedback voltage input, and a output. A resistor has a first terminal coupled to the output of the force amplifier, and a second terminal. A switch is coupled between the second terminal of the resistor and the feedback voltage input of the force amplifier. The switch is closed in the force voltage mode, creating a feedback path which the resistor is contained within. A series combination of a capacitor and a resistor is coupled to a gate of a transistor within the force amplifier, which results in improved measure current settling time compared to alternative techniques.