Problem with input voltage on frequecy meter

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Can anyone please help me...I'm building a frequency meter using a
Infineon c167 microcontroller to accept signals in the range of 0.1Hz
- 100Mhz. The brief also states that the peak to peak input voltage
levels vary between 0.1v and 20v. This obviously needs to be stepped
down to 0 - +5v be accepted by the prescaler circuitry and the
microcontroller, but if i simply divide it by 4 say, then then lowest
voltage level would become too small. I also need something that will
not affect the frequecies being passed through and the impedence which
needs to stay high...

I'm just a beginner in this subject and would very much appreciate any
wisdom anyone could give me on this matter...

Thanks

 

Look at the limits...

Amplify the .1 Volt signal up to 5 volts, a MMIC would do the job.
Clip the higher level signals DOWN to .3 volts which would not over drive
the MMIC.
(Schottky diodes back to back.)

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| __O Thomas C. Sefranek
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