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Geert

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Posts: 2
Delft, The Netherlands

PSRR of VCO
Mar 06^th, 2006, 1:49am

Dear All,

I want to simulate the PSRR of a free running LC VCO.

I can do this by inserting a tone of eg 10kHz at the VCC. The VCO frequency is 200MHz.
When I run a transient and look at the VCO spectrum the simulation becomes too long.

Trying this in PSS gives a problem since the VCO is an autonome system and it is not
allowed to have another signal source in the circuit.

Is there another, relative quick, way to simulate this? QPSS for example? And where can
I find some remarks, articles about this topic.

Thanks.

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Ken Kundert Global Moderator Offline Posts: 2386 Silicon Valley	Re: PSRR of VCO Reply #1 - Mar 6^th, 2006, 7:18am If the 10kHz signal is small, you can get this using PSS/PAC or PSS/PXF. -Ken
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hrkhari

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Posts: 21

Re: PSRR of VCO
Reply #2 - Mar 12^th, 2006, 8:10pm

Hi Guys:

I have a related problem. I simulated my LC-VCO and it has around -84dBc/Hz of phase noise at 10kHz, I used an open drain 50Ohms Ft doubler circuit as a buffer, when I replace the biasing point with a BGR, the phase noise drops to -60dBc/Hz. My BGR has a 70dB of PSRR for flat band of 10kHz, with no external capacitor and 2mV of VREF variation with respect to temperature. The question is:

1. Is BGR referencing a common practice in biasing RF-VCO?, if no, any suggestion?
2. How do I increase my Phase noise

Thanks in advance

Rgds

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Visjnoe

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Posts: 233

Re: PSRR of VCO
Reply #3 - Apr 17^th, 2006, 3:15am

Hi,

including the BGR in your VCO testbench makes sure you include the noise of the BGR, thus degrading your phase noise performance compared to the situation with an ideal/noiseless biasing.

You basically have some options here:

1. Decrease the noise of the BGR by design.
2. Keep the BGR noise the same, but filter it in the (local) VCO biasing (current mirror). This might take some area,
but is very effective.
3. Try to minimize the noise upconversion by carefully choosing Vgs-Vt and L for your VCO transistors.

Kind Regards,

Peter

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longma New Member Offline Posts: 3	Re: PSRR of VCO Reply #4 - Apr 18^th, 2006, 11:11am SpectreRF has app note on this: PSRR simulation using spectreRF for driven and autonomous circuits.
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zhaojiayuan New Member Offline Love to talk Posts: 3	Re: PSRR of VCO Reply #5 - May 18^th, 2006, 9:14pm Could you tell me where can find this application note? Thanks a lot!
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bernd Senior Member Offline Posts: 229 Munich/Germany	Re: PSRR of VCO Reply #6 - May 19^th, 2006, 12:33am Try it at sourcelink http://sourcelink.cadence.com or http://sourcelink.cadence.com/en/infomgmt/AppNoteHomePage.jhtml but you have to register. Bernd
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