[FAQ] How does the digital filter frequency response of a Delta-Sigma ADC scale with clock frequency?

Before explaining how the clock frequency of a Delta-Sigma ADC influences its digital filter frequency response it will be beneficial to get a basic understanding of the digital filters typically used in Delta-Sigma ADCs. The following application note provides a brief overview: Digital Filter Types in Delta-Sigma ADCs

In general the digital filter frequency response and also the output data rate of a Delta-Sigma ADC scale directly with clock frequency.

Consider the following example. Imagine a SINC filter with an output data rate of 10 SPS at the ADC’s nominal clock frequency.
The output data rate would double to 20 SPS if the clock frequency were doubled. At the same time the -3-dB corner frequency increases by 2x and the filter notches now occur at multiples of 20 Hz instead of a multiples of 10 Hz.

The following diagram shows an example using the SINC3 filter of ADS124S08.
The red colored line shows the frequency response using a 2.048 MHz clock, the black colored line shows the frequency response using a 4.096 MHz clock.
The same OSR (oversampling ratio) of 256 kHz / 20 Hz = 128 has been used in both cases.

Regards,