Time (1s/div)

Figure 8-8. 0.1Hz to 10Hz REF_Z 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

dominated by white noise as shown in Figure 6-10. The broadband noise is measured by high-pass filtering

the output of the REF80 and measuring the result on a spectrum analyzer as shown in Figure 8-9. The DC

component of the REF80 is removed by using a high-pass filter and then amplified. When measuring broadband

noise, you do not need high gain to achieve maximum bandwidth.

Spectrum

Analyzer

Post Amplifier

G = 11

High-pass Filter

G = 11

VDD

REF_Z

REF_GND

HEATP

HEATM

+30 V

10 V

REF80

CL

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 make

sure the output impedance of the filter does not degrade ac performance. This can occur in RC low-pass filters

where a large series resistance can impact the load transients due to output current fluctuations.

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REF80

SNAS856A – SEPTEMBER 2024 – REVISED MARCH 2025

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