Reference Filter Increases 32-Bit ADC SNR by 6dB

Attaining optimal SNR performance from an ADC isn’t just a matter of providing a low noise signal to the ADC’s input. Providing a low noise reference voltage is just as important. While reference noise has no effect at zero-scale, at full-scale any noise on the reference will be visible in the output code. This is why dynamic range (DR) which is measured at zero-scale is usually several dB better for a given ADC than the signal-to-noise ratio (SNR) which is measured at or near full-scale. Providing a low noise reference voltage is particularly important in an oversampling application where it ’s possible for the ADC’s SNR to exceed 140dB. To achieve an SNR at this level, even the best low noise references need some help to reduce their noise levels.