SCDS397 November 2018 TMUX6136
One example to take advantage of TMUX6136’s precision performance is the implementation of parametric measurement unit (PMU) in the semiconductor automatic test equipment (ATE) application. The PMU is frequently used to characterize and measure the digital pin’s DC characteristics of a device under test (DUT). Among all the PMU’s capabilities, force voltage, measure current (FVMC), and force current, measure voltage (FCMV) are the two most typical configurations in DC characterizations.
Figure 32 shows a simplified diagram of the PMU in FVMC configuration. The control loop consists of the force amplifier with the voltage sense amplifier (unity gain in this example) making up the feedback path. Current flowing through the DUT is measured by sensing the current flowing through a sense resistor (RSENSE) in series with the DUT. The current sense amplifier with a gain of Av generates a voltage (VOUT) at its output and the voltage can then be measured by an ADC. The voltage produced at the DUT pin stays at the input voltage level (IN) as long as the force amplifier doesn’t rail out (ie. IDUT × RSENSE x Av stays within the input voltage range of the force amplifier). Depending on level of the DUT current to be measured, different gain settings need to be configured for the current sense amplifier.
Figure 33 shows a simplified diagram of the PMU in FCMV mode. The voltage VIN is now converted to a current through the following relationship:
The control loop consists of the force amplifier with the current sense amplifier making up the feedback path. The voltage at the DUT is sensed across the voltage sense amplifier (unity gain in this example) and presented at the output for sample.