While searching the web about ideas to improve the GWB (lets call it speed) of transimpedance amplifiers there came up many a lot of suggestions to introduce several bootstrapping methods using additional opamps and JFET and also several other components.
But when the phrase "high gain" was mentioned, that usually meant something around 1M or maybe 10M of transimpedance.
In my daily business I would call that quite low gain, because I'm using transimpedance resistors of 1G to 25G typically.
Low current consumption (<<1mA) and very small packages (such as SC70) are welcome.
Let's consider the following as a starting point:
Cf = 1pF, Rf=25G, Ip = 80pA, Ci=10pF with OPA291 or LPV521
All that tightly integrated with a careful PCB design to control leakage currents and stray capacitance turns out to work properly.
The several opamps offer different current consumption and temperature dependence but pure dc performance is ok.
The bandwidth limit is by no surprise at a few Hz, the step response is nearly perfect Rf*Cf-discharge curve, so fall-time around 200ms.
I'm looking for ideas or techniques to improve the step response speed.
Is any bootstrapping approach working at such high gains (found no example beyond 10M)?
Any other ideas to improve the step response, even by only little?