Hi.
I was wondering if it is possible to compare frequencies with the 4046 PLL. I don't care about phase.
I have an unknown frequency signal output from a XR-2206 IC, over which I have control of the frequency through digital potentiometers.
The goal is to fine tune the XR-2206 automatically.
Based on the 4046 datasheet, I am thinking of inputing a reference, known frequency PWM, 50% duty cycle signal to the comparator input, instead of the 4046 VCO signal. In my setup, this would be synthesized by a MCU.
The unknown XR-2206 frequency signal would be input to the signal in pin 14 of the 4046. This signal would be square too, with 50% duty.
If I understand the datasheet well, putting a low pass filter at the output of the phase comparator I yields a triangle signal output, When both signals are of same frequency, the LP outputs a voltage proportional to the phase difference between signals, that is, a DC signal. let's call it 's'
Then it would be trivial to sample that signal at the MCU level and make an integrator, ex. sum over 100 samples of abs(s(t+1) - s(t)).
Then change slightly the XR-2206 signal frequency every 100 samples, until the integrator output is the lowest value attained.
Am I thinking this setup right ?
I was wondering if it is possible to compare frequencies with the 4046 PLL. I don't care about phase.
I have an unknown frequency signal output from a XR-2206 IC, over which I have control of the frequency through digital potentiometers.
The goal is to fine tune the XR-2206 automatically.
Based on the 4046 datasheet, I am thinking of inputing a reference, known frequency PWM, 50% duty cycle signal to the comparator input, instead of the 4046 VCO signal. In my setup, this would be synthesized by a MCU.
The unknown XR-2206 frequency signal would be input to the signal in pin 14 of the 4046. This signal would be square too, with 50% duty.
If I understand the datasheet well, putting a low pass filter at the output of the phase comparator I yields a triangle signal output, When both signals are of same frequency, the LP outputs a voltage proportional to the phase difference between signals, that is, a DC signal. let's call it 's'
Then it would be trivial to sample that signal at the MCU level and make an integrator, ex. sum over 100 samples of abs(s(t+1) - s(t)).
Then change slightly the XR-2206 signal frequency every 100 samples, until the integrator output is the lowest value attained.
Am I thinking this setup right ?