Design of 5 – 15 MHz Voltage Preamplifier


I'm trying to design a power amplifier for the HF band to drive an inductive charger. The stage I'm working on now is a voltage amplifier which needs to be able to amplify 1 Vpp to 10 Vpp.

The input signal (1 Vpp) can vary from 5-15 MHz. The output signal will drive the MOSFET gates of the second stage, so it doesn't need to be able to provide a lot of current.

The question is what kind of circuit topology should I be looking at to solve this problem? Some configuration of BJTs, mosfets, op-amps? Also, what parameters do I need to look for in choosing the proper components?

It would be great if it was non-inverting, with little or no phase offset, but that is definitely not a necessity.

My First Try:
I tried to build the circuit from this page, which says that a common-base amplifier is well suited for high voltage gain, and high frequencies. I chose this BJT to build it since it's specified as an RF transistor. Unfortunately, I can only get a little bit of gain around 10 MHz with the right biasing, but not with a 1V input, not anywhere near 10X, and it only works really close to 10 MHz.

Best Answer

An opamp with GBWP (gain bandwidth product) of 200MHz will probably do the job and is easily configured as a non inverting gain of ten amp. One word of warning though... Driving a mosfet can be tricky because of gate capacitance and you might need to connect the opamp output via 100 ohms. All this assumes sinwave amplification. If wanting to amplify square waves a quite different solution will be required.