SBAA591 December   2023 REF54

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Flicker Noise Measurement Method
  6. 30.1 Hz to 10 Hz Band Pass Filter Design for Reference Noise Measurement
    1. 3.1 Filter Schematic
    2. 3.2 TINA - TI simulations
    3. 3.3 Component Selection
  7. 4Measurement Setup
    1. 4.1 REF54250CDR Noise Measurement Setup
  8. 5Filter Board Design
    1. 5.1 Schematic
      1. 5.1.1 Schematics Images
    2. 5.2 Layout
    3. 5.3 Bill of Materials
  9. 6References

2 Flicker Noise Measurement Method

A voltage reference data sheet specifies flicker noise from 0.1 Hz to 10 Hz frequency band in the units of peak to peak variation over 10 seconds. A simple method is to measure this noise on DMM for 10 seconds with an averaging time of 100 ms (1/10 Hz) to capture peak to peak response. The peak to peak noise from the reference signal gets coupled with the DMM signal chain noise (around 0.5 μV measured at TI lab for HP3458A at 10 V range). SNR of this method is not good enough for ultra-low noise high precision references, such as REF7012, which has flicker noise = 312 nV pk-pk over 10 seconds, or REF54250CDR has 275 nV pk-pk (0.11 ppmpp) noise with 100 uF capacitor on NR pin as the DMM’s signal chain noise is more than the device noise.

Pre-amplify the reference noise to improve SNR of the measurement setup. This requires eliminating the DC and providing sufficient gain to noise signal as shown in Figure 3-2. Section 3 discusses the filter design to measure flicker noise with high SNR.