VCO 10 MHz tuning range

[whatever125]

Here is my current schematic for my VCO. I need a 10 MHz range from 0 to 5 V but I can't figure out how to get that. It needs to work from 48 MHz to 58 MHz. Ignore the filter for now.



I got rid of the trim cap and increased C7 to 100 pF and decreased C6 to 30 pF and nothing works. It oscillates fine at around 29 MHz but as I decrease C1 so the frequency goes up it doesn't oscillate. I noticed that it stops oscillating at 1 uH.

 

[biff44]

well, you can change to a hyper abrupt tuning diode to get more capacitance change fro 0 to 5 volts. the one you chose needs to tune to 30 volts to get its full range.

another trick is to partially series resonate the diode with a series inductor.

 

[vfone]

Ignoring the varicap circuit (C7, D1, L3, C8, R4), to get the requested tuning range, the variable cap C1 shall be 20pF to 80pF.
So you have to adjust the varicap components to get all together this capacitance range in parallel to L1.
MV2109 has 33pF maximum, so might need to put more in parallel.

 

[Pavithra18]

I know VCO provides output oscillations for a given input voltage.... it was told that VCO output oscillation can be controlled by a DC voltage... is the control voltage and input voltage the same and does supply voltage got anything to do with the output...also is it possible to only give DC input to VCO or even AC voltage can be given??? Also could anyone please tell what is VCO tuning frequency... I thought VCO output is tuned by control voltage but what is this tuning frequency???