Assuming I used the word "tank" correctly (something that has a resonant frequency) I have been working on a circuit that has 4 leads--two for DC input and two for AC output--such that you can attach something with a resonant frequency to the AC outputs, and the device will automatically adjust the frequency of the AC current to resonate with the tank.
I actually came up with a simple design using just two n-channel mosfets, two p-channel mosfets and four diodes. The principle of operation is that whatever voltage the tank produces, the mosfets direct the DC current to counter it (assuming the tank's voltage is above the threshold of the mosfets.) However, I found it in part by a lot of trial and error, and I was wondering if there was a standard IC that does this that I missed.