How to make a 100 MHz frequency counter using PIC

[sajeev]

anybody know how to make 100Mhz a freeq.counter using pic.What is the logic in freeq.counting?

 

[Bacra2k]

Re: freq .counter Help?

You can see this

**broken link removed**

It may be heplful


Greetings

 

[VVV]

Re: freq .counter Help?

Frequency counting is generally done by counting the number of periods of the input signal (# of pulses) in a given time, usually 1ms, 10ms, 100ms, 1s, 10s.

For example, a signal with a frequency of 50kHz will produce 50,000 pulses per second. If you feed this signal to an AND gate and at the other input of the gate you produce a logic HI signal for exactly 1sec, then the output of the gate will produce 50,000 pulses then stop. By counting the pulses at the gate output, you know the frequency. The gate is not really necessary, its function can be simulated in software.
The 1 sec. signal is called "gating signal". If it is 1ms, and you count 50,000 pulses during that time, then the frequency is 50MHz.

This is the principle and it is applied in the circuit Bacra2k provided the link to.
I suggest you use that circuit, since it features a high impedance input amplifier.

For more info, check out AN592 from Microchip: www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en011033

This is just a basic circuit, with no additonal input amplifier.
Microchip claims it can work up to 50MHz.
However, if you add the input buffer, it has to be able to work up to 50MHz, too. Careful layout is thus required.