ADS8900B: Single-ended bipolar to differential unipolar conversion

Erik Anderson41

Part Number: ADS8900B
Other Parts Discussed in Thread: OPA625

Hi,

Is there an app note that shows the best parts to use to convert a single-ended bipolar signal to the 0-VREF differential unipolar input of the ADC?

The ADS8900B seems to be one of the lowest noise ADCs out there, but our application is measuring bio-potential signals that swing around ground. Just checking if there is a particular circuit that is proven to do this for the ADS8900B before I start messing around with level translation (diff-amps with common mode). Ideally, the solution is lower noise than the ADC itself (something like <5uV-RMS @ 8kHz bandwidth).

Thanks!

Erik

over 4 years ago

0 Erik Anderson41 over 4 years ago

Intellectual 915 points

Looks like this is what I needed:

http://www.ti.com/lit/an/sbaa246a/sbaa246a.pdf

0 Keith Nicholas over 4 years ago in reply to Erik Anderson41

TI__Mastermind 40710 points

Hi Erik,

You found the application note that I normally recommend. This is the easiest way to translate from single ended bipolar to differential.

Regards,
Keith Nicholas
Precision ADC Applications

0 Erik Anderson41 over 4 years ago in reply to Erik Anderson41

Intellectual 915 points

Even better since I don't need high speed and I need low-ish power, is this instrumentation amplifier method:

https://m.eet.com/media/1134731/15496-81904di.pdf

Figure 2.

0 Keith Nicholas over 4 years ago in reply to Erik Anderson41

TI__Mastermind 40710 points

Hi Erik,

You can use this method, but the bandwidth of the amplifier must be high to support the fast settling times for the input sampling capacitor.

For the ADS8900B converting at 1Msps, you will need an input amplifier bandwidth close to 22MHz, which exceeds most Instrumentation amplifiers. The suggested work-around is to drive the inputs with a high speed amplifier, similar to the OPA625 used on the ADS8900BEVM board, and connect the Instrumentation amplifier outputs to the OPA625 inputs.

Regards,
Keith

0 Erik Anderson41 over 4 years ago in reply to Keith Nicholas

Intellectual 915 points

Yes, after more reading I came to the same conclusion. Thanks.

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ADS8900B: Single-ended bipolar to differential unipolar conversion