Audio characteristics

AN2583

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2.3

Power supply rejection ratio

The PSRR is a measure of how well the device keeps power supply noise out of its output. It

The output signal is filtered to reject frequencies other than the test signal, in this case 1kHz.

A fast fourier transform engine, or FFT, is helpful in implementing the filter and measuring

the output level.

Since the PSRR is in the range of –55 to –65 dB, the output signal will be on the order of

200 uV. Without the FFT and filtering, the signal will be lost in the noise floor.

Figure 14.

PSRR test setup

The PSRR is calculated as follows using the standard formula for power gain in dB.

Example:

If the output is measured as 350 uV, the PSRR will be

PSRR = 20 log ( 350 u / 200 m ) = –55.1 dB

ai13940

Test signal

Scope

and/or

other test

eqpt

V

DD