How to Measure Power Supply Rejection Ratio

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Measure Supply Ripple Rejection

Power supply disturbances can couple into a circuit’s output differently as frequency changes, making rejection a frequency-dependent characteristic rather than a single value. Accurately characterizing this behavior requires distinguishing the circuit’s response to supply ripple from changes caused by operating conditions, loading, noise, and the measurement setup.

Power supply rejection ratio (PSRR) testing measures how much of a known disturbance on the supply rail appears at the circuit output. The disturbance is evaluated across the frequency range of interest while the device remains at its intended operating point. Comparing the applied supply ripple with the resulting output ripple produces a rejection-versus-frequency response that identifies where supply variations are most strongly suppressed or coupled into the output.

Power Supply Rejection Ratio Solution

Perform the test by injecting a controlled sinusoidal disturbance onto the device under test’s DC supply rail while monitoring the applied ripple and resulting output ripple. Advanced Benchtop Waveform and Function Generators provide the AC stimulus, with adjustable frequency and amplitude for evaluating rejection across the required test range. Combine the generated signal with the DC supply through an appropriate injection network so the device remains at its intended operating point. An oscilloscope or analyzer measures the ripple at the supply and output as the stimulus frequency is stepped. Comparing these measurements produces the PSRR versus frequency.

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