I am working on the design of a high-bandwidth transimpedance amplifier (TIA) to detect a relatively weak optical signal (100μW) but also be able to withstand short pulse, high power optical signals (>10W peak, 100ns long). The aim is to achieve a 50MHz bandwidth with a transimpedance gain of 5kΩ. I wish to use the FGA21 photodiode and the OPA657 Op-Amp to achieve this, key specifications include:
- Gain Bandwidth Product: GBW = 1.6GHz
- Photodiode Capacitance: C_d > 100pF
To limit the effect of input capacitance and push the bandwidth out I am using the bootstrapped architecture described by Hobbs. The SPICE model of this circuit is illustrated in the figure below:
Simulations suggest that this can achieve the required gain and bandwidth. However, I need to extend this design further so that it can shunt the ~10A pulse generated in an efficient manner. My thought is to use a Zener diode between the inverting and non-inverting op-amp inputs to regulate the differential voltage and provide a low impedance path for the current spike to ground. For this I require a Zener capable of handling high currents and that has low capacitance (as any capacitance >5pF will limit my TIA bandwidth), which is a big ask.
So I am wondering if there alternative methods to shunt high currents with minimal capacitance or is there a way to increase the maximum power dissipation of Zener diodes?