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The Necessity Pmu In Automatic Testing System

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Parametric Measurement Unit is one of the other testing methods for Automated Test Equipment Systems. The ATE PMU system is an essential means to reduce the test costing. The unit, most commonly known as testers, allows manufacturers to test each device for engineering characterization and production until approval. 

Why is PMU required?

    • To support a variety of test modes and integrate ATE systems’ circuits to decrease the cost, a new test methodology using Parametric Measurement Unit (PMU) is required. 
    • The PMU supplies high voltages of current to charge the capacity loads.
    • The PMU system measures low voltages and current. 
  • The PMU is capable of forcing and measuring positive and negative voltages and currents, and it

has all of the four modes in general, i.e 

 Force Voltage/Measure Current (FVMI)

 Force Voltage/Measure Voltage (FVMV)

 Force Current/Measure Voltage (FIMV)

 Force Current/Measure Current (FIMI)

What is Application of PMU?

VMI mode-Application of the PMU in FVMI mode measures input bias current on a single DUT pin (Device under test), where the PMU forces a voltage onto the DUT pin and measures the corresponding current. 

FIMV mode- Application of the PMU in FIMV mode is continuity testing of a DUT pin, where a current is forced in that is being tested (while every other pin on the DUT is grounded), and the voltage at the pin is


Low current ranges are required when measuring leakage currents, and high current ranges are

required for measuring low input resistances. 

What are the different modes of PMU?

Measure Voltage:

    • It is one of the simplest models of PMU. 
    • It offers a higher degree of accuracy since it is important to measure the voltage that they are forcing accurately.
    • In this mode, the PMU acts as a voltage follower applying to the Measure Out pin as a buffered version of the DUT voltage.
    • The PMU can either Force a current and measure the resulting voltage
    • or force a voltage and measure the resulting voltage.
  • However, it is possible to have the PMU measure the voltage at the DUT pin while not forcing anything. 

Force Voltage:

    • PMU in Force Voltage mode forces an accurate voltage at the DUT pin. 
  • In Force Voltage mode, the PMU acts as a voltage follower applying to the DUT pin as a buffered version of the input voltage VIN. 

Measure Current:

    • In the Measure current mode, the PMU can either Force a current or voltage and measure the resulting current. 
  • PMU measures the input current of a specific DUT pin, where it forces a voltage to the DUT and measures the resulting current.

Force Current:

    • In this mode, the Force V switch is open, and the Force I switch is closed, placing the InAmp inside the feedback path. 
    • Since the feedback is usually negative, the force amp will force the output of the InAmp (Instrumentation Amplifier, which is used to amplify very low-level signals, rejecting noise and interference signals) to be approximately equal to the input voltage.
    • Despite PMU being a DC( direct current) measurement circuit, its output capacity might reduce the bandwidth of the test path.
  • When the PMU is a separate integrated circuit from the DCL, a relay is used to isolate its capacitance from the test path. No output forces need to be applied to minimize its output capacitance. 

Analog Devices’ parametric measurement units (PMUs) and device power supply (DPS) products offer a flexible range of voltage and current source/measurement capability to meet the needs of a wide range of cost-sensitive test applications. With a proven track record, Analog Devices’ PMU and DPS products serve a wide variety of precision test application requirements, such as measurement and control for voltage and current.

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