Resistance simulation and common mode rejection for digital source-measure units
First Claim
1. A source-measure unit (SMU) comprising:
- output terminals configured to couple to corresponding input terminals of a device, and provide an output voltage across the input terminals of the device to effect an output current flowing in the device;
a digital loop controller configured to;
receive a first digital value representative of the output current, and a second digital value representative of the output voltage;
regulate a function of the output voltage and the output current according to the first digital value, the second digital value, and a parameter that is proportional to a specified resistance value simulating effects of a resistance not physically present on a control path between an output of the digital loop controller and the output terminals of the SMU.
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Accused Products
Abstract
A source-measure unit (SMU) may be implemented with digital control loops. The output voltage and output current may be measured with dedicated ADCs (analog-to-digital converters), and the readings obtained by the ADCs may be compared to a setpoint in a digital loop controller, which may produce an output to drive a DAC (digital-to-analog converter) to maintain the output voltage and/or output current at a desired setpoint. The digital loop controller may also digitally implement simulated resistance with high resolution, accuracy, and range, using Thévenin and Norton power supply models. Simulated resistor values may range from 10Ω to 10Ω for output currents in the 100 mA range, with a sub-200μΩ resolution. The range may be expanded up to 100 kΩ for output currents in the 10 μA range. The Norton and Thévenin implementations may be combined, and a “pure resistance” mode may be created for simulating any desired resistance value. A variation of the general resistance-simulation technique may also be used to compensate for Common Mode Voltage effects in the current measurement path, providing tighter output and measurement specifications at a lower component cost.
15 Citations
24 Claims
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1. A source-measure unit (SMU) comprising:
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output terminals configured to couple to corresponding input terminals of a device, and provide an output voltage across the input terminals of the device to effect an output current flowing in the device; a digital loop controller configured to; receive a first digital value representative of the output current, and a second digital value representative of the output voltage; regulate a function of the output voltage and the output current according to the first digital value, the second digital value, and a parameter that is proportional to a specified resistance value simulating effects of a resistance not physically present on a control path between an output of the digital loop controller and the output terminals of the SMU. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A digital loop controller comprising:
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input terminals configured to receive; a first digital value representative of an output current flowing in a device; and a second digital value representative of an output voltage developed across input terminals of the device, wherein the output current is effected by the output voltage; wherein the digital loop controller is configured to; regulate a function of the output voltage and the output current according to the first digital value and the second digital value to maintain one of the output voltage and the output current at a specified setpoint corresponding to a desired value; and adjust one or more of the setpoint, the first digital value, and the second digital value, to adjust the desired value by one of; an amount corresponding to a voltage that would be developed across a specified resistor if the specified resistor were coupled to an output of the digital loop controller; and an amount corresponding to a current that would be developed in the specified resistor if the specified resistor were coupled to an output of the digital loop controller. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
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17. A method for testing a device using a source-measure unit (SMU), the method comprising:
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providing a supply voltage across input terminals of the device to effect a supply current flowing in the device; generating a first digital signal representative of the supply current; generating a second digital signal representative of the supply voltage; regulating one of the supply voltage and the supply current to remain at a specified setpoint value corresponding to the one of the supply voltage and the supply current, according to; the first digital value; the second digital value; and a parameter that is proportional to a value of a specified resistance not physically coupled between the SMU and the device, to simulate effects of the specified resistance on a control path between the SMU and the device. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24)
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Specification