# ~1 GHz low phase noise oscillator

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#### rfmw

varicap +oscillator +phase noise

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

tnx,
rfmw

#### Jackal

##### Member level 2
vco low noise 1.4ghz wideband

Hi!

Try to see RF products of Motorola (www.mot.com) and Maxim (www.maxim-ic.com). 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 ).

#### goxy

##### Full Member level 4
fixed oscillator 1 ghz

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

#### flatulent

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.

#### E-design

low phase noise 1 ghz oscillator

Hi

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.

Results:

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.

#### toonafishy

##### Full Member level 6
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.

#### rfmw

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...

regards,
rfmw

#### johnseven

##### Junior Member level 3
rfmw said:
was anybody involved in designing a low phase noise oscillator with varactor/varicap diodes at frequencies around 1 GHz?

tnx,
rfmw

On the subject -

73! klug.

#### tanveerriaz

##### Full Member level 5
1.5 to 2.2 Ghz osc

#### toonafishy

##### Full Member level 6
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.

#### g579

##### Full Member level 6
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

#### IICCEE

##### Full Member level 3
you can find some reference in the alpha-ind.com

#### BigBoss

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

Rgrds

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