Understanding Power Supply Rejection Ratio

What is PSRR?

Power Supply Rejection Ratio or Power Supply Ripple Rejection (PSRR) is a measure of how well a circuit rejects noise, of various frequencies, injected at its voltage input.  The ripple can be induced from a number of sources, such as a 50Hz/60Hz supply ripple, a switching ripple from a DC/DC converter, or a ripple due to the sharing of an input supply between different circuit blocks on the board.  In the timing solutions world, when discussing PSRR we are typically referring to supply ripple.

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