I have a primary inductor L1 connected to a voltage source with frequencies varying from 0.5MHz to 15MHz. This primary inductor induces a voltage across a secondary inductor via coupling and I want to investigate the response generated in L2.
So I am trying to amplify a voltage from an inductor using an op amp in non-inverting configuration (image1). Upon doing an AC sweep I find that there is resonant frequency peaking at 3.5MHz which is presumably due to L2 forming an LC tank with the input capacitance(2pf) of the LT1886 amp (image1).
Now this is a problem because I want a reasonably flat band frequency response from 0.5MHz to 15MHz, so I was wondering how can I achieve such a thing if possible?
Here's a few things I've tried:
Place a reasonably large resistor R3 in the non inverting input to decrease the quality factor of the LC tank which should smooth out the frequency response (image2). However looking at the frequency response (image2) the roll off after 3.5MHz is still unacceptable, because I want a flat band response upto 15MHz.
Move the resonant frequency further away by decreasing L2 and then adjusting R3 accordingly (image3). This worked out quite well however I'm afraid that if the inductance L2 is too low the coupling will be insignificant and so the final amplified voltage is dominated by the amplifier's noise due to low signal to noise ratio.
I was also wondering if looking into current sensing would be a better option instead of directly sensing the inductor's voltage?