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1. For an inverting amplifier. Choose the feedback (FB) resistor (from Out to -In) Rfb = 0.1*Rin (Rin - from amplifier input to -In pin). Example Rfb = 10k, Rin = 100k.
In this case the input resistance of whole amplifier will be equal to Rin, i.e. 100k.
2. For a non-inverting amplifier. Connect the OA as repeater (-In to Out) and connect the signal input to the OA non-inverting input through voltage divider 10:1. Example:
from input to +In (Rin) 90k, from +In to ground 10k. In this case the input resistance
will be again ~100k.
3. If you need an amplifier with large input resistance, then you should take a double
OA chip. The first one you have to connect as voltage repeater, the second as one of the case 2. But in such way your input signal range will be 10 times smaller, than in cases 1 or 2.
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