I have a question with regard to the differences between a PLL on a PCB and on a breadboard.
In this test, I have connected the output of the amplifier (LMH6503) to both the PLL on the PCB and the PLL on the breadboard.
Another picture to make it clear:
Then, I have set the following parameters in the function generator:
- fcarrier = 15.75 kHz
- fmod = 1 kHz
- frequency deviation = 3 kHz
- amplitude = 305 mVp
Then I obtained the results, which will be listed here.
The result between the VCO output of both the PLL on the PCB and the breadboard:
In this figure, the yellow channel and the blue channel are the VCO outputs of the PLL on the breadboard and the PCB respectively.
The result between the outputs of the analog filter between the PLLs:
The yellow channel and the blue channel represent the output of the analog filter of the PLL on the breadboard and the PCB respectively.
If I zoom in on this figure, the PLL on the breadboard does demodulate the modulated signal (1 kHz) whereas the PLL on the PCB does not do anything. Furthermore, since this NE564 operates on a single power supply, it should have a particular DC-voltage, which is not zero, at the output when the VCO is on the free running frequency, but the one on PCB does not have an 'offset DC-voltage.'
How can it be that both differ from the output of the analog filter of the PLL even if both of the PLLs are locked on 15.7 kHz? (Both VCO outputs tracks the input signals.)
My circuit of the PLL on the PCB:
The PLL built on the breadboard is exactly the same as the circuit on the PCB. Besides, this circuit is found in the datasheet of the NE564 with the frequency capacitor 39 nF to obtain a free running frequency of approximately 16.1 kHz.