SBOA585 March   2024 ADS127L11 , ADS127L11 , ADS127L21 , ADS127L21 , PGA855 , PGA855

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1PGA855 and ADS127L21, 24-Bit, Delta-Sigma ADC Driver Circuit
  5. 2PGA855 Analog Front-End Filters
  6. 3ADS127Lx1 Delta-Sigma ADC and Digital Filter
  7. 4Approximate PGA855 Intrinsic Noise Analysis
    1. 4.1 Simplified Noise Model for the PGA855
    2. 4.2 PGA855 Spectral Noise Density vs Frequency
    3. 4.3 PGA855 Effective Noise Bandwidth
    4. 4.4 PGA855 Low Frequency (1/f) Noise Calculation
    5. 4.5 PGA855 Voltage Broadband Noise
    6. 4.6 PGA855 Current Noise and Source Resistance
    7. 4.7 PGA855 Total Noise
  8. 5PGA855 and ADS127Lx1 System Noise
  9. 6PGA855 and ADS127Lx1 SNR and Noise Calculator
  10. 7PGA855 and ADS127Lx1 FFT Measured Performance
  11. 8Summary
  12. 9References

4.4 PGA855 Low Frequency (1/f) Noise Calculation

To calculate the 1/f noise contribution of the PGA855, obtain the noise density at the lowest given frequency on the voltage spectrum noise density curve (enf), and the lowest frequency (fL) from Figure 7-13. The upper cutoff frequency fH is set to the ENBW of 45.5kHz. Equation 9 calculates the 1/f noise normalized to 1Hz:

Equation 9. ennormal  =enf  ×fL

Equation 10 provides the total RMS noise from the 1/f region in µVRMS. Table 7-6 shows the calculation results for the referred-to-input (RTI) 1/f noise.

Equation 10. En1/f(RTI)  = ennormal ×ln fHfL
Table 4-1 PGA855 Input-Referred 1/f Noise
PGA GAIN
(V/V)		fL
(Hz)		fH
(Hz)		enf
(nV / √Hz)		ennormal
(nV / √Hz)		En1/f(RTI)
(µVRMS)
0.1250.2455001000447.21.57
0.2500.245500500223.60.79
0.500.245500250111.80.39
10.24550013058.10.20
20.2455007031.30.11
40.2455004520.10.07
80.2455003716.50.06
160.2455003515.70.05