PSRR

PSRR is a significant performance concern for many applications and especially for high speed clocks and low noise amplifiers.  Even very small amounts of ripple on the power supply can result in significant clock jitter, limiting the performance of high speed ADC’s and resulting in increased noise figure in low noise amplifiers (LNA’s).  Even opamps often offer high PSRR at low frequencies, but this degrades very significantly at higher frequencies.

The measurement of PSRR requires very high dynamic range and an excellent measurement noise floor.   The following measurement shows the measurement noise floor and the PSRR measurement of a very high PSRR regulator.

PSRR measurement and noise floor of a high performance voltage regulator, designed for the J2170A injector power supply.

The next PSRR measurement of a precision voltage reference again shows nearly 100dB measurement result and also shows the impact that control loop stability has on the PSRR performance.  The addition of a 0.1uF output capacitor (solid trace) shows a significant dip in PSRR at the78kHz bandwidth of the control loop

PSRR measurement of a REF-03 with (solid) and without (dashed) an output capacitor.  

Note that the non-invasive phase margin cursor measurement can also be used in the PSRR measurement.  In the example above, with the 0.1uF output capacitor, the reference control loop exhibits 8.9 Deg phase margin as indicated in the cursor measurement.