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Simple DC AFE for ADC chips with unipolar diff inputs

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David Hess:

--- Quote from: imo on January 23, 2019, 08:43:04 pm ---Do you mean to use fets in the bootstrap?
The divider there - what to use? - a capacitive divider ? :)
--- End quote ---

Buffer the output of the precision operational amplifier to drive the bootstrap circuit which currently as shown has a parallel load resistance of about 10k which is not particularly low but every bit helps.

iMo:
This is with buffering the bootstrap, and 18k/2k divider. The larger the source impedance feeding the ADC, the worse..

David Hess:
Many implementations work in exactly that way with an operational voltage follower to drive just the bootstrap circuit.

iMo:
And these are the simulation results with above v7.
Note:
1. source resistance of the input Voltage source is 1Meg
2. optimal resistor's tempcos with the two dividers
3. LM741 model used for the rail splitter and the bootstrap buffer.

iMo:
v32 with low leakage input protection..

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