Assume I have an input voltage ranging from 5-10 MHz and want to amplify it. The case is pretty simple as any device as FET,BJT or high frequency op-amp can do the amplification well but I have a problem: the input frequency range (amplitude) changes by the frequency as it is 2.5 volt pk-pk at 5MHz and reduces to 5 milli volts pk-pk at 10 MHz. I need a constant output amplitude ( at any voltage ). I tried a high-pass filter to reduce the high range at lower frequencies but unfortunately it is not that precise and some changes remains ( even with good frequency calculations and active filters) and some distortion at extremities noticed. Is there any standard way to do that? Any helps appreciated in advance.
Adding as an answer because comment dialog became too long:
AG: A simple set of experiments with a DDS module (AD9850 prebuilt DDS module, less than $5 shipped internationally) should address your concerns. Creamy smooth low THD pure sine waves with an extremely fine frequency resolution of under 0.05 Hertz.
AG: No point debating in theory when practical experiments are so easy, you won't even have to make a PCB.
OP: I looked at at the AD9850 data sheet. That looks great but needs a 125MHz input clock to produce half frequency (62.5 MHz). What is the best input circuit for that? a common Colpitts/Hartely can produce the required clock? Is there any suitable IC for that? If that works, can be definite solution for my question.
AG: You would not need to look for any external "good clock source" - The device uses any standard oscillator crystal: For 10 MHz maximum output, a 20 MHz crystal is sufficient, but use a 40 MHz for some room to grow. Crystals are a few cents each.
AG: Also, the link I provided is a ready-made AD9850 signal generator board with crystal and all associated parts already assembled and tested, so you can initially experiment with it to see how well it meets your requirements.
OP: I got a little confused. the datasheet requires a clock source as CMOS level( squre 0-5 volt wave) or a sine wave with 1/2 volt bias. Are you sure a crystal alone works fine?
Yes, an XO works fine as a clock source. See the first application schematic in the datasheet:
Also see this answer to another question, for more discussion on DDS ICs and sine wave generation.
The standard approach for generating precision signals in this frequency range is a direct digital synthesis (DDS) chip. Analog Devices has a wide selection of chips of this type, and so do several other manufacturers.
If this is for a medical experiment, one of their DDS evaluation boards might be all you need.