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Testing LDMOS transistors with DMM multimeter

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Testing LDMOS transistors with DMM multimeter
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All too often today, one or more of the following field-testing issues are encountered:

Issue #1
Technicians literally grabbing an RF power transistor and testing it “free form” with a battery powered multimeter (using either the ohmmeter or diode setting).

Problems Caused
It is impossible to properly test leakage current with a battery powered multimeter. The output voltage and the meter’s impedance are completely unknown. This will certainly lead to invalid and/or unreliable readings. Remember, the DUT must be tested under the correct voltages, and the correct conditions, to guarantee reliable and repeatable results. Using a multimeter, no details regarding the DUT’s actual leakage current level can actually be measured or recorded in any meaningful way. A battery-powered multimeter can only reliably be used to test whether a clearly already defective DUT is either “open” or “shorted.”

Issue #3
Static discharge is applied to the DUT (improper device handling).

Problems Caused
Static discharge can and likely will ruin (forever) an otherwise good device.

Issue #4
Improper grounding/shielding/isolation methods are employed with the DUT.

Problems Caused
Testing with improper shielding, grounding, and isolation will lead to erroneous and invalid measurements; and it may also damage the part.

Improper Testing Lead to These Unfortunate Consequences:
- Both “good” and “bad” devices are being damaged unnecessarily, and this makes further analysis impossible.
- Some devices that are actually within specification are being thrown away or being rejected/returned because of erroneous test results.

Conclusion: DO NOT TEST RF LDMOS WITH DMM multimeter!

Best regards,
Marko - PCS Electronics
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