ZHCSI30G March 2002 – April 2018 OPA2354 , OPA354 , OPA4354
PRODUCTION DATA.
To achieve the best performance, components must be selected according to the following guidelines:
1. For lowest noise, select R(F) to create the total required gain. Using a lower value for R(F) and adding gain after the transimpedance amplifier generally produces poorer noise performance. The noise produced by R(F) increases with the square-root of R(F), whereas the signal increases linearly. Therefore, signal-to-noise ratio improves when all the required gain is placed in the transimpedance stage.
2. Minimize photodiode capacitance and stray capacitance at the summing junction (inverting input). This capacitance causes the voltage noise of the op amp to amplify (increasing amplification at high frequency). Using a low-noise voltage source to reverse-bias a photodiode reduce the capacitance. Smaller photodiodes have lower capacitance. Use optics to concentrate light on a small photodiode.
3. Noise increases with increased bandwidth. Limit the circuit bandwidth to only the required bandwidth. Use a capacitor across the R(F) to limit bandwidth, even if a capacitor not required for stability.
4. Circuit board leakage degrades the performance of an otherwise well-designed amplifier. Clean the circuit board carefully. A circuit board guard trace that encircles the summing junction and is driven at the same voltage helps control leakage.