wide range (2-20MHz) VCO

20 mhz vco


Hi all!
I want to design a wide range (2-20MHz) discrete VCO, as part of a PLL frequency synthesis and I need some ideas.
I think there are few ways to do this:

1. A oscillator controlled with wide range varactor diodes ---but I can't find special varactors to use---

2. Mixing 2 higher frequency signals, for example one at 100MHz and the second from a 102-120MHz VCO (controlled with "normal" range varactors) ---but the schematic is more complex and the output signal contains more harmonics---

3. Using a ring oscillator, which is suitable for IC design.

So, who can help me with some ideas in designing this VCO with general purpose parts and a moderate complexity schematic? I appreciate your help!
Thanks in advance!
Best regards,
eugen

wide vco

A ring oscillator in general can help you with that range.If not,you could further use mixer to generate the frequency that you want.

vco 20mhz

I need to design a discrete VCO and I don't want to use the mixer choice because of the complex schematic, the need for precise measurements and tuning and the harmonics present in the output signal.
I want to use a classical LC oscillator and I think I should use "something" that will replace the hard to find wide range varactors.
So I want to ask if you know a method to obtain a wide tuning range by controlling the capacitance, inductance, or both with a voltage.

vco wide

you can use 74hc4046, a very popular pll device which includes two PD and a vco.

20mhz vco

I think that a traditioonal approach is not possible, because the frequency range is nearly ten times and this requires a change in capacitance of 100 times ( excluding the capacitances of the circuit. )
An easier approach is with the old CD40HC46 of in a new fashion with the DDS AD 9850.

Mandi