Designs that require high bandwidth from a large area detector with relatively high transimpedance-gain benefit from the low input voltage noise of the OPAx607 devices. Use the Excel™ calculator available at What You Need To Know About Transimpedance Amplifiers – Part 1 to help with the component selection based on total input capacitance and C_TOT. C_TOT is referred as C_IN in the calculator. C_TOT is the sum of C_D, C_DIFF, and C_CM which is 20 pF. Using this value of C_TOT, and the targeted closed-loop bandwidth (f_–3dB) of 2 MHz and transimpedance gain of 100 kΩ results in amplifier GBW of approximately 50 MHz and a feedback capacitance (C_F) of 1.1 pF as shown in Figure 9-2. These results are for a Butterworth response with a Q = 0.707 and a phase margin of approximately 65° which corresponds to 4.3% overshoot.

Figure 9-2 Results of Inputting Design Parameters in the TIA Calculator

The OPA607's 50 MHz GBW, is suitable for the above design requirements. If the required feedback capacitance C_F comes out to be a very low value capacitor to be practically achievable, a T-Network capacitor circuit as shown below can be used. A very low capacitor value (C_EQ) can be achieved between Port₁ and Port₂ using standard value capacitors in a T-Network circuit as shown in Figure 9-3.

Equation 1.

Figure 9-3 T-Network