hi i choosed the VCO resistor & capacitor According to the formula ( f min= 1/(R2(C1+32pf)), f max =(1/(R1(C1+32pf)))+f min) my Fmin is 10KHZ and Fmax is 20KHZ.
And i have not connected any loop filter. i have checked the offset frequency.
But the output is very worst, I'm not getting the exact squrwave(VCO OUT). I have checked the connection, every thing is correct.
If I connect the capacitor between the VCOout-pin and ground, then the output is somewhat ok.
Warm Regards
What chip are you using?
i am using 4046 pll chip
First point. This PLL is an analog circuit with some digital parts, so it needs a very clean power supply. If other chips operate across the same supply, you may have noise from them getting into the PLL.
Check that your VCO is programmed (by R1, R2 and C1) to operate at the correct range of frequency. Connect the VCO control line to the positive supply line and measure the frequency of the VCO output frequency. This should be the expected maximum frequency. Then connect the VCO control line to the negative supply line. The VCO should produce the expected minimum frequency. The output is not guaranteed to be precisely a 50% duty cycle square wave, but it should be very close.
If these two measurements are correct, then the VCO part of the PLL is set up correctly, and all that remains is to choose the PLL phase detector and design the loop filter.
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