Figure 8-9. 0.1-Hz to 10-Hz Noise Distribution (NR =

Open)

Figure 8-10. 0.1-Hz to 10-Hz Noise Distribution (NR

= 10 μF)

8.5.2 Broadband Noise

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

measured by high-pass filtering the output of the reference device, followed by a gain stage and measuring the

result on a spectrum analyzer as shown in Figure 8-11

Figure 8-11. 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

ensure 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. The

REF35 device also offers noise reduction functionality by adding an option capacitor between NR (pin 5) and

ground pins. Figure 8-12 shows the noise spectrum for REF35 device when NR pin is open. Figure 8-13 shows

the noise spectrum for REF35 device when 10 μF capacitor is connected between NR pin and GND.

Figure 8-12. Noise Spectrum 10 Hz to 100 kHz (NR

= Open)

Figure 8-13. Noise Spectrum 10 Hz to 100 kHz (NR

= 10 μF)

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REF35

SNAS809 – DECEMBER 2021

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