I was trying to simulate (In LTSPICE) buffer for ADC 08200 that would have 1Meg input impedance it is about to be used with standart oscilloscope probes. But I am having problem with bandwidth limiting. So far I have tried OPA354 and LMH6702 and both suffer from this pitfall.
What is correct way to make high impedance ADC buffer?
So far I have came to this as circuit with best result (as far as bandwidth goes, but it's having very high attenuation). I am simulating 1:10 probe with 9Meg resistor.
I have redesigned the circuit but I am having weird problem with simulation and I think that circuit should work but I am getting very small negative voltage out of OPAMP even thought it's supplied by positive rail only.
This is my schematic now:
Blue trace is output of OPA355 and green trace is non-inverting input.
R11 and R12 are used for offset adjustment. C5 is AC coupling capacitor (if used).
//Edit3: Fixed model of OPA355 now, but I am having different problem.. on certain frequency it seems that there is some parasitic capacitance charging, but I have no clue where .. Same trace is for non-inverting input, output and inverting input...