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# ADS1294: Measurement of very low voltages (microvolts)

Part Number: ADS1294

Hello,

I'm using an ADC1294 to pick up signals from a sodium chloride solution. For signals larger than 10 Milivolt this works without problems.
I would like to measure signals in the microvolt range and use a low-noise signal generator that can generate 20Hz signals with an amplitude of up to 130µV. Which settings do you recommend? I have currently set a gain factor of 12 and a data rate of 250SPS. Do you think a preamplifier is necessary? The measurements are carried out in a shielded chamber.
AVDD = 3.3V and DVDD = 1.8V

Many thanks in advance!

Jason

• Hi Jason,

We typically recommend customers to not use a preamplifier since the input referred noise will increase and degrade the SNR - but it depends on each system and what is important to that system.

I don't have your reference voltage, but I will assume you're using the internal reference of 2.4V.

LSB = (2 x VREF)/ Gain / (2^24 - 1) = (2 x 2.4V) / 12 / (2^24-1) = 23.8nV

To see how much of the FSR you can take advantage of with an amplitude of up to 130uV:

130uV / 23.8nV = 5462

The FSR code range is 2^24 = 16777216, so 130uV would use only 3% of the FSR. ((5462/16777216)*100)

Another option is to use the ADS1299-4 which has a PGA setting of 24 - this would reduce your LSB size and increase the FSR used.

Using a smaller external reference voltage with either device would also reduce your LSB size and increase the FSR used.

Best regards,

Alex Smith
Applications Engineer | Precision Delta-Sigma Converters

Check out our helpful resources: BIO-FAQ: Common Questions for TI's ADS129x Family of Bio-Potential ADCs

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