Building Earth Observation Cameras

131Optomechanical Scanners

=

π

f

RC

1

2



c

ff

(5.7)

The thermal noise due to R

f

is the dominating noise, and the SNR is propor-

tional to

R

f

. However, the maximum R

f

value is limited by the bandwidth

requirement. Also, the maximum value of feedback resistance is chosen such

that the output does not get saturated for an expected maximum signal cur-

rent. The actual input resistance of an operational amplier is not innite,

and some bias current ows at the input terminal causing some offset. FET-

input-type operational ampliers have a much lower bias current compared

to bipolar operational ampliers and are the preferred choice. The other cri-

teria for ...