Q1:How to select the amp when the input signal is curret?
Q2:Why not all the manuals have input impedance information?
Basically, these types of application uses operational amplifier in transimpedance configuration. A transimpedance amplifier or TIA is a current to voltage converter wherein the current from the sensors are transform into useable output voltage level. One of the main factor to make accurate TIA is the bias current of the amplifiers. If you could give us more details of your application maybe we can help you better.
On your next question. We always tried to put every necessary information in the datasheet for the benefits of the user, however, sometimes some parameters are not included for some reason. If the imput impedance is not included in the specifiaction table, you can try to look at the typical performance characteristics section and look for some plots like" input bias current vs VCM". From there we can figure out the input impedance of the device.
please let me know if you have any question.
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