VCO output power +flatness!?

[kd]

hello!

I'm designing a VCO for my school project and need a help..
Could anybody tell me how does the output power (and the power
flatness) depends on the capacitors and inductance in the tank
circuit? You may find this question silly, but I realy need to know
this
I work with Colpitts and a varactor.

Thank you in advance,

Konrad

 

[John Popelish]

hello!

I'm designing a VCO for my school project and need a help..
Could anybody tell me how does the output power (and the power
flatness) depends on the capacitors and inductance in the tank
circuit? You may find this question silly, but I realy need to know
this
I work with Colpitts and a varactor.

Thank you in advance,

Konrad

Can you point us to the actual schematic of your circuit? Details
matter.

 

[Ken Smith]

hello!

I'm designing a VCO for my school project and need a help..
Could anybody tell me how does the output power (and the power
flatness) depends on the capacitors and inductance in the tank
circuit? You may find this question silly, but I realy need to know
this
I work with Colpitts and a varactor.

I assume that the limiting in your oscillator is done by "bottoming" in
the transistor. (ie: the transistor's voltage swinging down to zero)

If this is the case, the output voltage swing will be nearly constant over
the whole range of the VCO, assuming it continues to oscillator over the
whole control range. You have an excess of drive to the transistor and
the gain is limited only by the transistor's voltage falling to near zero.

If the limiting is done by the loss of gm method (unlikely), you will have
to look at the tank circuit losses and the feedback ratio to see how they
vary with variactor voltage.