JKowalski wrote ...

The PLL system is just a phase detector -> loop filter -> VCO -> back to phase detector.

The 4046 chip is a medley of the above. Phase detectors of all types and a VCO. It's meant as a modular chip that provides all the parts to build a PLL.

If all you have is a VCO (XR2206), then you need a phase detector. Simplest solution is to use a 4046's phase comparators. That brings up the question. Are you trying to use the XR2206 to get sine/triangle wave output? Or just a square wave? If the answer is square wave, then ditch the XR2206 and just use a 4046.

Using a different VCO shouldn't be much harder than using the 4046's, provided you know what you are doing. All you really need to know is the gain of the VCO (Hz/V), which is given explicitly on the XR2206 datasheet. Account for any quirks of the new VCO and the different gain.

Inducktion wrote ...


It's not the XR2206, its the XR2207. Different chip. Not made specifically for PLL, it just says it can be used for PLL. And what is a phase detector? Could I use an XOR gate for this purpose? And, I don't have any way of getting a 4046 so...

JKowalski wrote ...


Ah, well it's almost the same thing just with a different I/O configuration.

Phase detector = phase comparator. Yes, an XOR gate would work (if you look at the 4046 datasheet you can see that the "type I" phase comparator is just that - an XOR gate. )

Inducktion wrote ...


Unfortunately I would have NO idea of how to hook up the XOR gate to the XR2207 to make it PLL.

JKowalski wrote ...



Then you need to study up on PLL design some more. It's a very difficult circuit concept to get working correctly and reliably.

Put simply, the phase comparator compares the input signal (signal to be locked onto) to the output of the VCO (with an XOR gate, preferably both logic level square waves). If you look at a timing diagram, the output of the XOR gate will be 1 whenever the two signals are not the same. By filtering the phase comparator pulse output correctly, you get a mostly-DC waveform which you apply to the VCO input. This will change the VCO frequency. If conditions are right (and they have to be carefully tailored) the VCO will tweak the output frequency, changing the phase comparator output pulses and therefore it's own control voltage until a stable condition is reached (hopefully a lock condition)

IamSmooth wrote ...

Induktion,

I don't know if you read the tutorial I suggested before, but it describes how the PLL works. It talks about the VCO and phase detector. I put up a lot of diagrams showing the waveforms.