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I have a high impedance differential sensor (stable 600k impedance Rth, 10mV signal, Fout=1kHz). I need to amplify this signal to about 1V (40dB gain). Due to layout/system constraints only the TLV9061 OpAmp stage can be used. Any suggestions on what topology would enable this? The problem I run into is that any difference amplifier or transimpedence amplifier needs feedback resistors that are unreasonably high (10s or 100s of Megohm) for a real world implementation.

I was looking into T-Network solutions as in this thread but it seems they suffer from high current noise.

Looking for any advice on other topologies to explore or methods to consider. Thanks!

enter image description here

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  • \$\begingroup\$ (1) What's the nature of the sensor? (2) Is it connected through a cable? Or, is it mounted on the same PCB as the amplifier? (3) Is using an instrumentation amplifier an option for you? If not, why not? \$\endgroup\$ – Nick Alexeev Jul 5 '18 at 20:52
  • \$\begingroup\$ Sample rate or bandwidth? Is there a reason you cannot use an integrator? The (-) terminal of your opamp may need a guard ring. \$\endgroup\$ – jonk Jul 5 '18 at 21:00
  • \$\begingroup\$ There are ICs which pack 4 OpAmps into one small footprint, including feedback resistors. So the layout constraints can't be an excuse. Any so-called "instrumental amplifiers" should do the job, especially at 1 kHz range. \$\endgroup\$ – Ale..chenski Jul 5 '18 at 21:52
  • \$\begingroup\$ Single supply? Needs Vcc/2 ref not 0V . Long cable? Needs better CM balanced impedance on Vin(+) \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 5 '18 at 21:55
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Why not just use the op-amp in non-inverting mode: -

enter image description here

The impedance it presents to the transducer is giga ohms and the feedback resistors are isolated from the transducer hence don't need to be mega ohms; they just need to have the correct ratio i.e. 99:1 to give 100x amplification.

For the TLV9061, be aware that if used in single supply rail applications the output won't quite get down to 0 volts.

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  • \$\begingroup\$ Yes, I have come to this conclusion as well so focusing on this implementation. With dual rail supply. Thanks! \$\endgroup\$ – EasyOhm Jul 7 '18 at 7:45
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If by "single op amp" you mean you can accept an 8-pin package, an AD621R in 8-pin SOIC will give you a gain of 100 with no external components and extremely high input impedance.

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  • \$\begingroup\$ +1 Yep, modern silicon technology makes real wonders! \$\endgroup\$ – Ale..chenski Jul 5 '18 at 23:37
  • \$\begingroup\$ Sorry updated description due to size constraints have to use X2SON package \$\endgroup\$ – EasyOhm Jul 6 '18 at 6:08

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