8.5 Noise Performance

The reference pin output noise is categorized as low frequency and broadband noise. Following sections

describe these categories in detail.

8.5.1 Low Frequency (1/f) Noise

Flicker noise, also known as 1/f noise, is a low frequency noise that affects the device output voltage which can

affect precision measurements in ADCs. This noise increases proportionally with output voltage and operating

temperature. It is measured by filtering the output from 0.1-Hz to 10-Hz. Since the 1/f noise is an extremely low

value, the frequency of interest needs to be amplified and band-pass filtered. This is done by using a high-pass

filter to block the DC voltage. The resulting noise is then amplified by a gain of 1000. The bandpass filter is

created by a series of high-pass and low-pass filter that adds additional gain to make it more visible on a

oscilloscope as shown in Figure 8-7. Figure 8-8 shows the effect of flicker noise over 10 second. Flicker noise

must be tested in a Faraday cage enclosure to block environmental noise.

Figure 8-7. Low Frequency (1/f) Noise Test Setup

Figure 8-8. 0.1-Hz to 10-Hz Voltage Noise

Figure 8-9 shows the typical 1/f noise (0.1-Hz to 10-Hz) distribution across REF35 devices. REF35 device also

offers noise reduction functionality by adding an optional capacitor between NR (pin 5) and ground pins.

Figure 8-10 shows the typical 1/f noise (0.1-Hz to 10-Hz) distribution across REF35 devices with 10 μF capacitor

between NR pin and GND.

REF35

SNAS809 – DECEMBER 2021

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