SBASB74 October 2024 ADS127L21B
PRODUCTION DATA
Power-supply rejection ratio (PSRR) specifies the ability of the ADC to reject power-supply interference. PSRR is expressed as ac and dc parameters. For PSRR (dc) measurement, the power-supply voltage is changed over the range of minimum, nominal, and maximum specified voltages with the inputs externally shorted together. The maximum change of ADC offset voltage is recorded versus the change in power-supply voltage. PSRR (dc) is computed as shown in Equation 12 as the ratio of change of the power-supply voltage step to the change of offset voltage.
where:
For PSRR (ac) measurement, the power-supply voltage is modulated by a 100mVPP (35mVRMS) signal at various test frequencies. An FFT of the ADC data with power-supply modulation is performed. As shown in Equation 7, the nine largest amplitude spurious frequencies in the frequency spectrum are summed as powers. These frequencies are also related to the amplitude of the power-supply modulation signal.
where: