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, take special care 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. The REF35-Q1 device also offers noise reduction functionality by adding an optional capacitor between NR (pin 5) and ground pins. Figure 8-12 and Figure 8-13 show the noise spectrum for REF35250 and REF35500 devices respectively across various NR pin capacitance.

Figure 8-12 Noise Spectrum 10 Hz to 100 kHz (V_REF = 2.5 V)

Figure 8-13 Noise Spectrum 10 Hz to 100 kHz (V_REF = 5 V)