Hello.
I'm building a virtual ground for a customer IC using an opamp (LT1802). The circuit that it interfaces to is an NMOS, whose gate samples at 10MHz and outputs a current between 100uA and 200uA. The virtual ground connects to the drain of the NMOS. I'm also using a feedback resistor of 10KOhm to act as a I-to-V converter.
My problem is.. I need a capacitor of about 10pF in parallel with the feedback resistor in order to be stable. However, the settling of this configuration is too slow. The voltage output cannot track the samples at 10MHz. From the LT1802 documentation, I see that a pole is formed by the capacitance at the noninverting input as well as the feedback resistor. It is this pole that determines the stability. However, I have little control of this pole except to use the parallel capacitor which lowers the bandwidth.
My question is.. how can I make it stable and fast at the same time?
Thanks for your time.
Scott