INDEED! A 4046 PLL IC, using the complex phase detector would then produce smaller and smaller correction pulses as the frequencies became closer. Then, feeding that correction signal through a low pass filter and into a window comparator will give a logic high when the signal is stable. Likewise, an exclusive OR gate fed into a low pass filter would provide a similar signal.A phase-lock-loop IC might fit the bill, or even a simple XOR circuit or a beat-frequency detector.
Pass both signals through identical networks tuned to resonate at the osc freq. When the detection osc is pulled off freq, its output will drop relative to the reference osc. In fact, you can eliminate the reference ose and just slope detect (frequency-to-voltage converter) the detection osc.I have a project where I have two oscillators. One reference oscillator and one detection oscillator. I'm looking for a way to output a 5V constant output when the two frequencies are in the same range.
A red trace is when the frequencies coincide (=). Truth is the best case, when the phase shift between the reference signal and the signal being studied is zero. The real signal must be multiplied by Cos(fi). I did such a detector in the form of a chip (for fixed audio frequencies). The bandwidth of that asynchronous filter (my chip) was less than 0.1Hz.What is the Red trace?
It looks like it should be V(out) but the plot says the blue trace is V(out).
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