| Electronics > Projects, Designs, and Technical Stuff |
| Diffrential amp design |
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| SiliconWizard:
--- Quote from: Warhawk on January 23, 2020, 10:32:09 am --- --- Quote from: magic on January 23, 2020, 08:43:14 am ---You can eat your cake and have it too: buy AD620 from AliExpress 8) --- End quote --- Yeah, 100% genuine --- End quote --- ;D |
| technix:
There might be some ADC with true differential inputs and has enough resolution natively. If that is the case, scratch the whole front end and have your sensor hooked directly to that ADC and call it a day. Maybe put a can over that, but anyway use as short an analog section as possible. As long as the noise is under control, systematic biases and nonlinearity can be trimmed out afterwards in software. You don't even need to know exactly what kind of nonlinearity you may have, just assume the inverse transfer function is a polynomial (actually the first few terms of the function's Taylor series, but that is usually enough since you have a limited range anyway) and grab a few calibration points so you can work out the coefficients. |
| Marco:
--- Quote from: OwO on January 23, 2020, 09:53:42 am ---I looked for cheap instrumentation amplifiers a while ago and didn't find any. There are probably 10 different Chinese op amp manufacturers and you can find everything from 500MHz op-amps to low offset op-amps, but it seems no one has ever heard of instrumentation amplifiers. I think it's probably because trimming the resistors is expensive. --- End quote --- That's no excuse, the transconductance based differential amplifiers like MAX4208 don't rely on resistor matching. |
| MasterT:
--- Quote from: Marco on January 23, 2020, 07:01:37 pm --- --- Quote from: OwO on January 23, 2020, 09:53:42 am ---I looked for cheap instrumentation amplifiers a while ago and didn't find any. There are probably 10 different Chinese op amp manufacturers and you can find everything from 500MHz op-amps to low offset op-amps, but it seems no one has ever heard of instrumentation amplifiers. I think it's probably because trimming the resistors is expensive. --- End quote --- That's no excuse, the transconductance based differential amplifiers like MAX4208 don't rely on resistor matching. --- End quote --- Probably, they can't produce instrumental amp due copyright issue. |
| Zero999:
--- Quote from: Marco on January 23, 2020, 07:01:37 pm --- --- Quote from: OwO on January 23, 2020, 09:53:42 am ---I looked for cheap instrumentation amplifiers a while ago and didn't find any. There are probably 10 different Chinese op amp manufacturers and you can find everything from 500MHz op-amps to low offset op-amps, but it seems no one has ever heard of instrumentation amplifiers. I think it's probably because trimming the resistors is expensive. --- End quote --- That's no excuse, the transconductance based differential amplifiers like MAX4208 don't rely on resistor matching. --- End quote --- The MAX4208 is very noisy compared to the AD620, around ten times as bad, so completely unsuitable for μV level signals. https://datasheets.maximintegrated.com/en/ds/MAX4208-MAX4209.pdf https://www.analog.com/media/en/technical-documentation/data-sheets/AD620.pdf |
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