How to Evaluate the Common Mode Rejection Ratio (CMRR) of a Differential Probe to Meet Usage Requirements

In the field of electronic measurement, differential probes are widely used in various circuit tests as an important measurement tool. Differential probes acquire signals by measuring the potential difference between two inputs while suppressing common mode signals, thus improving the accuracy and stability of measurements. However, in practical applications, the common mode rejection ratio (CMRR) of differential probes is a key performance indicator, which is directly related to the probe's ability to suppress common mode signals. Therefore, how to evaluate the CMRR of differential probes to meet the needs of the use of electronic engineers must face the problem!

Take MOS tube as an example

1. Short the red and black clips of the differential probe to ensure that there is no potential difference between them. 2.

2. Hook the shorted differential probe clamp to the upper G-pole of the MOS tube (or other electronic component) under test. 3.

3. Observe the output of the differential probe, if the output is not zero, it means that there is a common mode voltage to ground at the point under test and the CMRR of the differential probe is limited.

4. Observe the output of the oscilloscope, the smaller the output, the stronger the CMRR capability of the differential probe; conversely, the larger the output, the worse the CMRR capability

5. Measure the waveform of the circuit, if the measured voltage is much larger than the output of the common-mode signal, it will have almost no effect on the waveform.