I want to measure an oscillating magnetic field using a coil. Using a small self-spun coil, I can already measure very decent 100 KHz signals by hooking each end of the coil up to an oscilloscope.
I want to eventually pump the frequency up to 10 MHz. Using my extremely basic coil+oscilloscope setup I can already measure this for fairly strong oscillating magnetic fields but the fields that I'll be measuring will be much smaller. I can therefore not just hook my coil up directly to the oscilloscope anymore, but will need to amplify the signal.
My problem is as follows: if I want to push my signal through some filters, then those filters will invariably have some capacitance and resistance. Hooking up my coil to non-neglectable capacitances turns the whole thing into an electric oscillator, whose resonance frequency lies (for decent coils) far below 10 Mhz!
The solution I came up with was first passing the signal through an opamp, to "restart" the circuit:
I do have some opamps that can handle 10 MHz signals. The datasheet for the OPA6999 shows that it works just fine for these frequencies (page 7).
But won't I run into the same problem using this circuit? Won't the opamp introduce capacitance and inductance on the left side of the circuit that could significantly decrease my resonance frequency, unless I use a tiny coil?