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MXR104A power supply noise measurement with 1Mohms input + 50Ohms feedthrough termination

Question asked by malli1729 on Nov 24, 2020
Latest reply on Nov 30, 2020 by malli1729


We need to measure power supply noise measurement for 0.82V,1.0V,1.2V,1.8V rails.

Setup will be:

50Ω, RF176 Co-axial probe directly soldered across output capacitor, configure oscilloscope input to 50Ω and with lowest vertical division to measure the ripple.

Low end scopes like DSOX3024A have offset ranges up to ±2V, but new scopes can't offer more offset with 50Ω impedance. With AC coupling impedance is 1MΩ which is not matched.


I am planning to use MXR104A(this is common scope which i can use for other measurements also) to do the Power supply noise ripple measurement, But with 50Ω Input impedance offset ranges are as below

≤55 mV/div: ±0.8 V,
≤120 mV/div: ±1.6 V,
≤260 mV/div: ±3.2 V.

with 1MΩ input impedance

<10 mV/div: ±5 V,
≤200 mV/div: ±20 V.


I am thinking to use 1MΩ input impedance on MXR104A so, that i will have more OFFSET range of ±5 V, but to have 50Ω input impedance for impedance matching use a 50Ω feedthrough termination before MXR104A input.


I don't have option to use high cost Power rail probes/differential probes, only this Option i have.


Do you see any issue with this setup for measurement of ripple.