0

0.08

0.16

0.24

0.32

0.4

0.48

0.56

0.64

Figure 8-7. 0.1-Hz to 10-Hz 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 8-8 shows the effect of 1/f noise over 10s.

Time 1s/div

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

8.4.2 Broadband Noise

Broadband noise is a noise that appears at higher frequency compared to 1/f noise. The broadband noise is

usually flat and uniform over frequency as shown in Figure 8-10. The broadband noise is measured by high-pass

filtering the output of the REF70 and measuring the result on a spectrum analyzer as shown in Figure 8-9.

The DC component of the REF70 is removed by using a high-pass filter and then amplified. When measuring

broadband noise, it is not necessary to have high gain in order to achieve maximum bandwidth.

REF70xx

GND

OUTS

OUTF

VIN EN

VIN

VREFP

Spectrum

Analyzer

Post Amplifier

G = 11

High-pass Filter

G = 11

Figure 8-9. Broadband Noise Test Setup

For noise sensitive designs, a low-pass filter can be used to reduce broadband noise output noise levels by

removing the high frequency components. When designing a low-pass filter special care must be taken to

REF70

SNAS781C – OCTOBER 2020 – REVISED SEPTEMBER 2021

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