1/f noise, also known as flicker noise, is dominant mostly in the lower frequency bands. Flicker noise affects the device output voltage which can affect the ENOB of the signal chain. REF80 data sheet specifies flicker noise for 0.1Hz to 10Hz frequency band where 1/f noise has maximum power. Flicker noise is measured by filtering the output from 0.1Hz to 10Hz. Since the 1/f noise is an extremely low value, the frequency of interest needs to be amplified and band-pass filtered as shown in Figure 8-4. 1/f noise must be tested in a Faraday cage enclosure to block environmental noise. Refer to application note Techniques for Noise Measurements in Precision Series References for more detail on noise measurement for precision series references.

Figure 8-4 1/f Noise Test Setup

Typical 1/f noise (0.1Hz to 10Hz) distribution can be seen in Figure 8-5.

Figure 8-5 0.1Hz to 10Hz Voltage Noise Distribution

The 1/f noise is in such a low frequency range that it is not practical to filter out which makes it a key parameter for ultra-low noise measurements. Noise sensitive designs must use the lowest 1/f noise for the highest precision measurements. Figure 8-6 shows the effect of 1/f noise over 10s.

Figure 8-6 0.1Hz to 10Hz Voltage Noise