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Input impedance matching ADS131 (or other if better) with TIPD118

Intellectual 335 points

Replies: 11

Views: 1661

Hello,

I've found very useful circuit design in your resources: http://www.ti.com/tool/TIPD118#1

I have a prototype with ADS131E04, single supply AVDD=5V, internal Vref=4V also taken out from Vref+ and divided by 2 and buffered to provide CM of single ended input.

U1=OPA376, R1=36k, R2=14,3k, C2=1200p, R4=62, C9=100n 

I usually notice about -7 value when nothing is connected to input circuit. I assume it is caused by not matched input impedances, am I right? How should I calculate IN- branch? I have used same 62R + 100n as low pass filter but it's sourced from "+" terminal of U1, which is sourced from buffered Vref/2 via 1k + 1uF.

This effect can be seen regardless of OFFSETCAL opcode using so I assume this command is executed with disconnected IN+/IN- inputs and can't compensate that.

I'm mostly interested in signals from range 10..2000Hz but I usually use 8ksps, 16bit is enough.

Or maybe there is another ADS better suited for 4 single ended signals?

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