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How to linearize the Vtune vs. OSC freq

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lllxb

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yig filter linearization

Hi, guys

I am designing a LC VCO using MOS varactor. And I need ur help.

The OSC freq vs. vtune is a nonlinear curve. I am required to linearize it.

I have tried to use resistors to bias a group of Varactors at different voltage level. But the Phase Noise suffers from the resistors, and additional current consumed by the resistor.

So is there any way to linearize the Vtune vs. OSC freq without degrading the VCO phase noise?

Thanks a lot!
 

Download this book and go to chapter 7:
 

u need to use a liear varactor , which is hard to implement , there are many research about this issue

khouly
 

how can you have a linear relation between frequency and capacitance of the varactor is the varactor is linear w.r.t. the control voltage ?

Freq = 1/sqrt(L*C) right ?
 

A hyperabrupt varactor has C=C0/(1+Vtune/V0)^M where M>1. This provides a more linear F vs. V.
 

Hi, Vifone
Thanks for ur help, but the book doesn't exist.


khouly & madengr

in my project, I can only use MOS Var.

Added after 6 minutes:

n1cm0c

I don't care wether the C is linear to V. I just want a constant VCO gain.
 

It looks like you are doing discrete element design, not IC. In this case you may use operational amplifier circuit to linearize VCO tuning characteristic. Check books on analog design and you will find such circuits.The second ay depends on frequency. If it is low enough you may use varactor on mostly linear part of volt-farad characteristic. In this case you sacrifice the VCO gain.

Best regards,
RF-OM
 

The book is there but you don't have enough points to download.
I am attaching part of ch7
 

Thanks vfone. Hope I can see the whole chapter.
I will download it when I have enough points.
 

Rule 1 in microwaves: never do anything in microwave technology when it can be done with low frequency technology!

Use an op amp and some low frequency diodes to design a "break point linearizer". This will provide differing slopes of tuning voltage as a function of the input voltage.
 

vfone said:
The book is there but you don't have enough points to download.
I am attaching part of ch7
Click to expand...

I searched for the book
RF_and_Microwave_Transistor_Oscillator_Design

Unfortunately i couldnt find it.
Please tell as its location.

Thanks.
 

search in "EDA e-books upload/download" forum for this:

RF and Microwave Transistor Oscillator Design
Andrei Grebennikov
2007 John Wiley & Sons Ltd
ISBN 978-0-470-02535-2 (HB)
 

RF-OM & biff44

I am doing RF IC design rather than discrete component design. In that case, can I still use Opamps, as u suggested?

Thanks & Best Regards
 

Sure you can. If your design is not finalized yet you may use OP amp circuit and linearized almost any process. I am not IC designer and cannot help with such a task, but I think that this is the best way to solve your problem.

Best regards,
RF-OM
 

    L

    lllxb

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RF-OM

Could u pls provide some document on this issue, I mean the Opamp Linearization Technique?

Or could u pls this explain the basic theory on this technique in simple words?

Thanks
 

I am sorry but I doubt I can help you to design such linearization circuit. I did it about 30 or 35 years ago with very first ICs like 709 and 741. Frankly speaking I do not remember all the details and definitely schematic technology changes much since that. Moreover, I did not work with OP amps for at least 15 years, so my experience in this area definitely not up to date. I think you may search and find a lot of materials on linearization methods and schematics.

Best regards,
RF-OM
 

Thanks a lot, RF-OM.

At least, u show me a direction.
 

I can try to ask my colleges who are excellent RF IC designers with very good experience. If they give me a good idea I share it with you.

Br,
RF-OM
 

That will be great! Thanks a lot!
 

I did this years ago to linearize a YIG oscillator for FMCW radar. IIRC I plotted F vs Vtune (F is the dependent variable), fit a polynomial, and then used Analog Devices multipliers to generate the polynomial.

If you can get a hold of Analog Devices Nonlinear Circuits Handbook from 1976 it shows how to build multipliers, dividers, RMS and LOG detectors, etc.. with opamps.

Maybe that's overkill for an IC though. However LOG detectors are usually several parallel FETs (current sources) width-scaled and biased in such a way as to provide a non-linear curve of RF drive vs sum of bias currents. Research this and you will probably see a simple way to do it in an IC.
 

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