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Low voltage difference amplifier
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MilkmanCDN:
Hey there,

Have you tried using a difference amplifier with integrated resistors like the INA190 (TI)?   The bandwidth on these types of parts isn't great (50-100kHz), however, the ADS1115 isn't sampling at a very high rate either (<1ksps).   These INA devices are made specifically for the type of circuit you drew.    Some of them even have integrated data-converters with an I2C interface.

Curious, what's the end application?

Edit:   INA233 features an internal 16-bit ADC.    Also if you need a small negative voltage power supply (for those down to ground applications), the LM7705 is a little known device that generates a -0.23V rail from 3.3V or 5V input.    It does have a bit of ripple on the output (single-digit mV), but the op-amp PSRR usually filters that out nicely.   

Edit #2:  I suppose that I should have consolidated all of my research before I started typing away.   Regarding the OPA388, that's a chopper based amplifier and it does have ESD diodes across the inputs, so you can't effectively pull the inputs apart within forward biasing a diode.    In most applications that's a don't care but I figured I'd let you know just the same.    TI's newer precision amplifiers are starting to adopt eTrim, which is essentially EEPROM programmed at manufacturing.   The EEPROM is used to set various trim elements inside the amplifier.    Traditionally, laser trim has been the go to; however it does suffer from two draw backs:  it's expensive, and you have to trim at the wafer stage, which means that you can't factor in package parasitics.    eTrim devices are trimmed at final-test, which means that package parasitics are lumped into the measure/trim function.   INA192 is an example of one such device and features near chopper level performance, without the chopper noise or excessive cost of a laser trim device.    About the best device I found at TI is the OPA189.   3uV offset.   Both the INA192 and INA189 also feature comparator inputs, which means there are no back-to-back diodes across the inputs.    If you're muxing various gains stages together, this can be advantageous.   

If you choose to run with a discrete op-amp, you'll need to match those resistors if you hope to have any CMRR.     You can buy precision resistor arrays, but they're expensive.    You could also add trim potentiometers in the feedback loop (less expensive, but someone has to tune each circuit).   This circles us back to my original suggestion of the INA190 (resistors baked into the device).    You likely know this, but resistors on silicon are very tightly matched, but have horrible accuracy.    If the application is ratiometric, then all is good.   Otherwise not so.

These days, about the only reason I see folks go with discrete op-amps for this application is if they need bandwidth.   Lots of it.    Trading precision for bandwidth is often a delicate proposition.

Good luck with the project!!
Doctorandus_P:
Do you have some ballpark figures for the range of Shunt values and currents you want to use?

As said before, the Shunt tends t be a pretty low impedance source and it seems that an extra opamp justs adds / amplifies noise.
Sometimes I think they add those opamps in AN's just to sell more components.

If your input signal is in the "10's of uV" then using a chip that is designed for thermocouples seems a better choice, for example the ADS1220, which also has a programmable PGA upto 128x.
David Hess:

--- Quote from: Doctorandus_P on January 26, 2019, 07:49:44 am ---If your input signal is in the "10's of uV" then using a chip that is designed for thermocouples seems a better choice, for example the ADS1220, which also has a programmable PGA upto 128x.
--- End quote ---

At high data rates and at low PGA gains the input noise increases significantly on delta-sigma converters so it can be advantageous to use an external operational amplifier depending on the application.  Or an operational amplifier might be used to remove common mode noise if that is an issue.

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