Digital SMU Control Loop for Accurate Range Switching
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Solution Overview
Problem
Existing source-measure units (SMUs) are limited by their analog control loops, which lack flexibility and accuracy, and are complex, especially when switching between ranges, and digital power supplies do not offer full programmability or dynamic range of true SMUs.
Innovation Solution
Implementing a digital control loop in the SMU using dedicated ADCs to measure output voltage and current, with setpoints set in an FPGA or DSP chip, allowing for regulation and compliance limit checking, and enabling configuration to source one signal while measuring another, reducing DAC accuracy requirements and offering flexibility in range-switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If analog control loops are used in SMU, then the system can operate with simpler architecture, but the flexibility and accuracy are limited
Solution Approach 1:
The patent replaces the traditional analog control loop with a digital control loop. The digital controller receives digital values from ADCs representing output current and voltage, compares these to setpoints, and generates control signals to regulate the output. This substitution of digital for analog control improves measurement precision and flexibility while managing complexity through software-based control algorithms.
2Adaptability or versatility
If range switching is implemented in analog SMU, then the device can cover broader measurement ranges, but the complexity and potential for errors increase
Solution Approach 1:
The patent implements dynamic range switching through the digital control loop. The system can switch between different measurement ranges (e.g., voltage ranges, current ranges) by adjusting the ADC reference voltages and control parameters digitally. This dynamic approach allows the SMU to adapt to different measurement requirements without complex mechanical switching mechanisms, reducing complexity while maintaining versatility.
3Manufacturing precision
If high accuracy DACs are used in SMU, then the output regulation is more precise, but the cost and complexity increase
Solution Approach 1:
The patent employs a feedback mechanism where ADCs continuously measure the actual output current and voltage, and the digital controller compares these measurements to the desired setpoints. The controller adjusts the DAC output based on the error between measured and target values. This feedback loop allows the use of lower-precision DACs while achieving high output regulation precision through iterative correction, reducing cost and complexity.
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 digital control loop enhances flexibility, reduces DAC accuracy needs, and allows for novel approaches to range-switching issues, enabling functions beyond standard current-limited voltage sources and voltage-limited current sources, such as constant power or resistance, while minimizing glitches during switching.
Implementation Method 1
The output voltage and output current may be measured with dedicated ADCs
Implementation Method 2
The FPGA or DSP chip may be used accordingly to produce an output to drive a DAC
Data Source
AI summary
A source-measure unit (SMU) may be implemented with a control loop configured in the digital domain. The output voltage and output current may be measured with dedicated ADCs (analog-to-digital converters). The readings obtained by the ADCs may be compared to a setpoint, which may be set in an FPGA (field programmable gate array) or DSP (digital signal processing) chip. The FPGA or DSP chip may then be used to produce an output to drive a DAC (digital-to-analog converter) until the output voltage and/or output current reach the respective desired levels. The readback values may be obtained by averaging the voltage and/or current readings provided by the ADCs. The averaging may be weighted to improve noise rejection. The digital control loop provides added flexibility to the SMU and a decrease in the accuracy requirements on the DAC, while also for solving potential range-switching issues that may arise within the SMU.