Question
In a transimpedance (TIA) application, what is an appropriate value of feedback resistor, RF for maximum signal-to-noise (SNR) ratio?
Answer
In TIA configuration, the signal gain increases directly with RF, whereas the resistor noise only increases in square root fashion. Hence, increasingthe value of RF maximizes SNR. There is however an upper limit on the value of RF that can be used. First, the maximum output current from thesensor multiplied by RF must be less than the amplifier swing limitations. Also, depending on the signal bandwidth that is needed, using large RF toachieve high signal bandwidth requires vanishingly small feedback capacitors to implement. Another thing to note is the current noise of theamplifier. When current noise of the amplifier is larger than the noise of RF, SNR stops improving. For more details on using the ADA4530-1 in TIAapplications, refer to the ADA4530-1 data sheet.