Broadband noise or white noise is flat over
the whole spectrum which is restricted by the bandwidth of internal bandgap reference. The
broadband noise is measured by high-pass filtering the output of the REF54 and measuring the
result on a precision spectrum analyzer as shown in
Figure 7-7. The DC component of the REF54 is removed by using a high-pass filter and then amplified.
Two stages of small gain has been used to maximize the noise bandwidth analysis.
Figure 7-8 shows the typical white noise floor for REF54. Designer can use NR pin to restrict the
noise bandwidth to achieve required resolution for the signal chain. Connecting 1 μF at NR
pin creates a typical low pass filter of 12 Hz for the band gap noise which reduces the
white noise floor of REF54. Capacitor >1 μF eliminates all the noise in > 10 Hz band.
Figure 7-8 Noise Performance 10 Hz to 100 kHz
(CNR = Open) Figure 7-9 Noise Performance 10 Hz to 100 kHz
(COUT) = 10 μF