Help me with MAX2620 VCO design

[alliedelectronics]

After Finishing Design of a FG.I want to make a 10Mhz to 1Ghz RF Signal Generator with PLL.I found a promising IC the MAX2620.But I want to know if it is possible to make a wideband VCO as all the Circuits have a max Frequency Change range of 30Mhz.Also what would be the ideal Inductor Value Required.Thanking You

 

[DrBob13]

max2620 vco design

Hi,
You will not get the whole frequency range from one resonant component. I have not done any detailed calculations but I suspect that if you try to actively switch the inductor you will almost certainly run into trouble especially at the high frequency end. You will probably need to use a number of independant VCOs using several of the MAX 2620 devices and switch their outputs into your phase comparator when they are required, the master microcontroller will decide when to do this.

You can calculate the inductor values from the standard resonant frequency formula f = 1/(2*Π*√(L*C)). The capacitances will be the range available from your chosen varicap diodes (see their datasheets) and by transposing the formula you can calculate the inductor value eg (L = 1/(4*Π*Π*f*f*C). I hope you can understand the way I have written (f squared) and (PI squared) in the formula.

The design you propose is not trivial and will need a lot of care and thought and calculations to design it if it is to stand any chance of success. You need to carefully read the datasheets and follow the advice contained within them.

A better option may be to use a DDS (direct digital synthesiser) based design but even with this method you will probably find it tricky to do the whole range with one device.
Bob.

 

[Nicholaes]

vco 2ghz

It's not a good idea to use max2620. I've try it two or three times, and have problems with quality of thouse IC's. Possible it was counterfeiht.

It's impossible to build so wideband VCO; but you can use DDS.

 

[rfmw]

max 2620

Make a VCO in the GHz range, that easily covers 1GHz of bandwidth. Then mix its output with a constant LO and filter out the low-frequency mixing product.

For example:

VCO: 2GHz - 3GHz
LO: 2GHz
-----
After mixing and low-pass filtering you get 0-1GHz. All required components you can get at Mini-Circuits.

For example, for hobby use I've managed to cover from 70MHz to 310MHz in a single sweep. So for a 1GHz bandwidth, you would have at least 3-5 of this-kind oscillators.