Created on 2010-11-25 04:45:00
Question:
How do I measure CMRR (Common Mode Rejection Ratio)?
Answer:
Use the following procedure:
- Select File > New > Test.
- Set the Analog Generator output Configuration to Bal – Float or Bal – Gnd as appropriate for the DUT (generally, whichever results in lower noise).
- Set the Analog Analyzer inputs to XLR–Bal or BNC–Unbal as appropriate for the DUT.
- Set the Function Reading Meter to Amplitude.
- Set the Function Reading Meter units to dBrA.
- Turn the generator on and set it to the desired level.
- Press F4 to capture the reference level.
- Set the Analog Generator output Configuration to CMTST (Common Mode Test).
- The CMRR will appear on the Function Reading Meter as a negative amount, but it is interpreted to be positive, as CMRR is always expressed as a positive number.
The 2700 Series and ATS-2 analyzers do not have the IEC CMRR test as a built-in option. However, the IEC CMRR test can be done by making one XLR barrel adapter with a 10 Ω resistor in series with pin 2 (and the other pins wired direct), and another with a 10 Ω resistor in series with pin 3. The CMRR test is then run three times, following the procedure above. The first time it is run with no adapter, the second time it is run with the pin 2 resistor adapters inserted in series between the Analog Output and the XLR connecting cable, and the third time it is run with the pin 3 resistor adapter inserted in series. The worst ratio of the three is reported as the measurement result.
Applies to: 2700 Series, ATS-2.
