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AD8304 noise estimation

Question asked by tneagoe on Jan 26, 2016
Latest reply on Feb 1, 2016 by jdobler

@

I am just reviewing the spec sheet of this device and am looking for some feedback on noise estimation at 1-KHz to determine ADC performance. 

The shaded table cells are my estimation from the graph data

 

From graph 9 on page 5 of the datasheet…review of 1-KHz noise data

 

FROM GRAPH 9 (page 5)

ESTIMATED VALUES FROM GRAPH DATA

Input Current

1-KHz (uV/rtHz) from graph

Calculated 1-KHz Noise (mVrms)

Calculate Total RMS LSBs (VREF =5)

1-nA

40

  1. 1.3

3846 (or 11.9-Bits)

10-nA

6

  1. 0.19

26315 (or 14.7-Bits)

100-nA

1

  1. 0.032

Ok

1-uA

~0.18

  1. 0.0057

Ok

10-uA

~0.15

  1. 0.0047

Ok

>100-uA

~0.15

  1. 0.0047

Ok

 

Questions:

 

  1. Are my estimations accurate from the graph data.
  2. Is the 1-KHz graph data based on a single pole LPF at VLOG?
  3. Graphs 2 and 3 on datasheet page 4 indicate the use of a small negative supply (VN) to provide the performance indicated.  Is there a significant degradation if VN is 0-Volts?
  4. It seems that 100-pA is the minimum spec input current yet there is a provision to move the intercept lower as indicated on page 11..showing effective intercepts down to 1-pA

    Can Analog devices indicate the noise performance in the 1-pA to 1-nA range using this technique…like the graphs of 8 & 9?

 

Regards, TN

 

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