I have a harebrained idea on how to make a 200Mhz Frequency Counter using an AVR. The basic concept is to use a 74VHC4040 counter that is rated for 200Mhz and the AVR just as the UI / counter reader. The reference is a 1 PPS input signal. Zero the counter. Start the counter using the 1 PPS into a T flip-flop. When the flip-flop goes high, an AND gate feeds the input signal to be counted to the 4040 and the AVR counts the overflows from q12 for the 4096s bit on the INT0 line. When the next PPS signal comes in the T flip-flop goes low, the signal is disconnected from the 4040, the AVR reads the rest of the bits, and lastly resets the counter for the next go-through. So you get one count every 2 seconds. Real basic stuff. The problem is that the PPS signal is 0.5V and the input signal may not be of a TTL triggering strength either. Is this a job for an opamp to boost these incoming signals? What would be the right one to try? I would assume that 200Mhz is not a speed that that most opamps do not operate at. Or is this more of a job for a high speed comparator?P.S. I haven't sampled a part from Linear in a while. Suggest Linear parts and I will test them out for you and report the results here.
This reminds me of a laser control system I built about 35 years ago, when I had to build a counter that would measure the frequency of a very small signal from 0.1 to 500MHz. Getting an ECL-logic divide-by-10 counter that would clock at 500MHz was no problem, but converting the signal to a square wave was hard. Originally I was going to use a tunnel diode, but it took weeks to arrive. So I ended up building a non-saturating Schmitt trigger that worked over the full frequency range.If you want to cover DC-200MHz, then converting the signal to a square wave (when the frequency is too low for the counter to accept a sine wave) is also something that you need to look at carefully. Using a gate with hyteresis is a good idea, however the one that you linked to has a propagation delay of up to 5.1ns @ 5V. The datasheet doesn't specify a maximum frequency, but with a propagation delay that high, there is a possibility that it may not pass 200MHz very well.