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ADS8584S: how to reduce oscillation in adc value in ADS8584s for measuring millivolts ranging from (1mv - 40mv)

Ramachandran V
Prodigy 150 points
Part Number: ADS8584S

hi

 i have designed  an ADC board using two ADS8584 ic to measure Millivolts, I have a voltage source meter (Keithley) which can source from 1mv to 20v,

The two ADC's are designed to operate in the range of -5v to +5v(Range pin to be 0),

They have a  minimum resolution of 0.00015259 uv and also they are made to operate in oversampling mode by making os0 - 0,os1-1,os2-1

So they operate in   5.156 Ksps sampling rate,

the problem is when i give 5mv to the ADC from the source meter directly to the input terminal of  ADC channel 1  ,the value I get is 4.5mv or 4.8mv or 5.2mv or 4.9

sometimes the voltage is 3mv for 5mv it keeps on oscillating 

the input which i have given to the ADC is from Keithley source meter which is constant

Should i have to ADD some external signal conditioner to reduce this oscillation

some one just give me a solution

  • 0
    TI__Mastermind 45315 points
    Hi Ramachandran,
    You have configured the ADCs in serial interface mode, so the data bus (DB[6:0], DB[9:14]) should be tied to GND. I have few questions, are you using a dedicated ground plane (whole layer) for all GND connections? are you doing offset calibration?
    You have an option to use external voltage reference, did you use internal voltage reference with default configurations in the schematic for your test? 
    Thanks&regards,
    Dale