How to design the calibration circuit of VCO

[incol]

Hi, everyone. I am designing a lcvco, and want to have 5 bit calibration. But I don't know what should concern about the calibration circuit, how to set the size of capactors and switches. Is there any papers about it? thanks a lot!

 

[BradtheRad]

A small capacitor and large inductor will produce more voltage swing and use less current, as compared to a large capacitor and small inductor.

Look at some schematics where a working project uses a tank circuit.

A suitable proportion is 1 to 100. As in 1uF to 100uH (or even 1mH). Scale up or down to your frequency requirements.

 

[incol]

Thanks for your reply. And does decrease the transistor's gm also improve the voltage swing with the same I bias?

 

[BradtheRad]

I suppose you already know that oscillators are finicky beasts to get going.

You'll have to experiment with ways to alter gain, bias, resistances, etc. And finally you'll find the magic combination.

Here are a couple of websites I've seen showing transistor-based LC tank oscillators.

Two-transistor style, with animated simulation:

Emitter-Coupled LC Oscillator

tpub.com --- chapter on oscillators:

 

[leo_o2]

Make sure the switch generating neglectable parasite capacitance comparing with the switched capatitors. For switch, pls also consider its operating condition under various supply voltage.

Hi, everyone. I am designing a lcvco, and want to have 5 bit calibration. But I don't know what should concern about the calibration circuit, how to set the size of capactors and switches. Is there any papers about it? thanks a lot!

 

[incol]

OK, thanks a lot