I am learning about how VCO modules operate and I am rekindling an old interest in electronics in general. For one particular VCO, the manufacturer has provided a circuit diagram. Does anybody know the purpose of the capacitors in series between the tuning voltage source and the mains voltage source?
closed as unclear what you're asking by Andy aka, The Photon, RoyC, Sparky256, Finbarr Feb 23 '18 at 9:46
Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.
Your terminology is incorrect but the shunt caps on the supply and tuning voltage is to provide low ESR to noise over many decades of frequency. Often the Self Resonant Freq. or SRF limits the useful RF spectrum and a smaller 1nF is needed to take over when the 10uF becomes inductive. Hence these parts are 5 & 4 decades apart in value to extend the low impedance to ripple for potentially 8 decades in bandwidth. Each source Zo(f) must be known to demonstrate precisely.
Superimposing the impedance charts may be more instructive. There are many similar answers on this site if you search; Shunt caps, SRF.
It often extremely important to remove all ripple noise V to reduce phase noise on the VCO. However if were used in a PLL where negative feedback requires more bandwidth to track a lower noise XO & phase detector, then the Vtune caps may be smaller.
They are decoupling capacitors to keep VCC power rails devoid of high frequency noise. Without it, the frequency of the output wave will fluctuate with the noise in power rails.
The clearest thing to say about those capacitors is that they are there to remove noise on the power supply and the tuning voltage.
Noise on either of those will cause the generated frequency from the VCO to be noisy. That is, the frequency will wander up and down in response to the noise.
Your generated signal would be frequency modulated by whatever crap is on the power supply or the tuning voltage. You want a clean signal, so you need a clean power supply and a clean tuning voltage.