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~1 GHz low phase noise oscillator

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Advanced Member level 2
May 10, 2001
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varicap +oscillator +phase noise

was anybody involved in designing a low phase noise oscillator with varactor/varicap diodes at frequencies around 1 GHz?

links, pdfs or comments very welcome!


vco low noise 1.4ghz wideband


Try to see RF products of Motorola ( and Maxim ( This firms are produce sigle chips VCO's for this frequencies with low phase noise.But if you need a very stamle frequency and very low phase noise you may use VCXO.

Another way is:
Use Maxim's sigle chip VCO for 2.4Ghz (varicaps and inductors are implemented on a chip, phase noise is -120dB) and use external prescaller (when you devide frequency phase noise devides too :D ).

fixed oscillator 1 ghz

Try this tutorial for designing low noise and low cost 1Ghz VCO on FR4 using CAD.

1ghz osc

One of the major contributors to phase noise is the variable capacitance diode. One of my friends told me that measurements of phase noise using different brands of diodes in the same circuit showed vast differences. It would be worth your effort to try different brands.

low phase noise 1 ghz oscillator


Have a look at the balanced VCO described in the book by James Crawford - Frequency Synthesizer Design Handbook- Basically using 2 active devices sharing a single resonator.


Freq 1-1.4Ghz
O/P 5dBm
Tuning 1-9V
PN 10kHz < -110dBc/Hz
100kHz < -130dBc/Hz
1MHz < -150dBc/Hz

I once designed an experimental unit at 1.2Ghz using 2 MMIC amps and got very good results as well, apart from the current consumption a bit on the high side.

The varactor plays a big part in the phase noise as flatulent mentioned.

1 ghz oscillator low phase noise

another big issue is the Q of the resonator. Its hard to get good Q with an etched resonator on the PCB. the varactor has the same efffect. As the voltage/capacitor varies, the Q also varies and this can harm the phase noise response.


search with Google

and find F3YX

french pages

ex: **broken link removed**

6 * F

Thanks for your help. I agree with the fact that using varicaps and FR4 resonators results in poor phase noise performance. But for amateur application it'll be just fine...


rfmw said:
was anybody involved in designing a low phase noise oscillator with varactor/varicap diodes at frequencies around 1 GHz?

links, pdfs or comments very welcome!


On the subject -
Applied Microwave $ Wireless

Magazine Article
Page 24 October 2002 by Tibor Hajder
Higher Order Loops Improve Phase Noise ......

Hi Friends!

There is a nice idea to exclude varicap from circuit.

There is another method of changing frequency by yttrium iron garnet sphere - it is tuned by changing constant magnetic field. As a rule there are two coils for rough and fine tuning by DC. This method allows to make resonators with very high Q up to 4000. They are working to 26 GHz. Changing of a frequency in a wide band up to one octave. Level of phase noice remains constant on all this band. Another advantage is high linearity of tuning in all band (plus minus of 0.2 %). Also they allow to obtain big power of generator up to +7 dBm on 18 GHz.

This information is from nice book of V. Manassewitsch "Frequency Synthesizers, Theory and Design".

Price for this YIG resonators is high near 200 $, so it is too expencive for home, but idea is interesting.

73! klug.

In the above circuit, it looks like the varicaps are in series with the tank circuit, hence the circuit is at the mercy of the Q of the varactors. I usually put the varactors in shunt across the tank and capacitively couple them in only enough to get the tuning range I need. That keeps the circuit Q much higher.

There is another way of making low phase noise oscillators.
The resonator capacitive element consists of a loosely coupled varicap (meaning high Q and low noise) and fixed capacitors.
In reality the fixed capacitors are switched capacitor bank, where the value of the fixed capacitor changes digitally, through diode switches.
Tuning will mean tuning of the varicap and switching capacitors on and on and on.
For example HP used this idea in his 8662 series low phase noise generators long ago.

Some Examples

A good article of the famous Mr Ulrich Rohde was brought into another section of the board:
**broken link removed**
by jacek100

you can find some reference in the

This is a nice thesis on Oscillators. It includes all neccesary design of components.


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