Dear Klaus,Hi,
XOR them.
Klaus
thus the frequency deviation is some 0.001% only.10MHz and 10MHz + some hundred Hz
HI,
You siad:
thus the frequency deviation is some 0.001% only.
now you test with 25% ... for sure this gives different results.
You may simply use a Mixer to obtain the frequency difference then measure how much there is.. Or, you can also use a Phase/Frequency Detector so that the output of this detector will be proportionally related to Input Frequencies. Standard FFs can be used at 10MHz to realize the F/P Detector.
Unless you have real time or very high accuracy requirements a very easy solution is to simply count clocks over a given time period. One second would be a good choice, then pause the counter and you have your frequencies.
Because 10Mhz isn't very fast I'd consider an oversampling implementation and keep track of the remainder for some additional precision. Or at least make sure to count both edges.
Again here you use 25% deviation. Why? Your initial post says about 0.001%. deviation. A factor of 25000! --> use meaningful simulation.Here is latest sim. result using 1 MHz and 1.25 MHz
Well, I have two options as also you said (or what I understand from what you said):
- Count two sources up to 10^7 region and simply calculate the difference
- "Simply" get the frequency difference in a way and count up to ~10^3 region
I don' t want to work with such high frequencies (first option). So I'm forcing for the second option.
Brad: I'm suggesting two counters. One for each clock. Subtract them to get the difference.
Hi,
It makes no sense to give response ... and you don´t care about it...
Klaus
I'm suggesting two counters. One for each clock. Subtract them to get the difference.
Yes, that is the straightforward method.
However my idea (post #9) is to have one counter rather than two normal frequency counters. One clock enables the up direction (simultaneously adding 1), the other clock enables the down direction (simultaneously subtracting 1). A bidirectional counter might be capable (such as 74HC190 4-bit BCD decade Up/Down counter or4029 4-bit Synchronous Up/Down counter).
The readout is the difference in frequencies.
There is the spec as to whether a change of state occurs at a rising edge or a falling edge. It may be a hurdle to enable up/down mode soon enough to handle an incoming clock pulse.
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