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 7-15.

Figure 7-15 Broadband Noise Test Setup

For noise sensitive designs, a low-pass filter can be used to reduce broadband output noise. 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 device also offers noise reduction functionality by adding an optional capacitor between NR (pin 5) and ground pins. Figure 7-16 and Figure 7-17 show the noise spectrum for REF35250 and REF35500 devices respectively across various load capacitance.

Figure 7-16 Noise Spectrum 10Hz to 100kHz (V_REF = 2.5V)

Figure 7-17 Noise Spectrum 10Hz to 100kHz (V_REF = 5V)