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Grounding in mixed synthesizer circuit - RF Cafe Forums

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Below are all of the forum threads, including all the responses to the original posts.


Guest
Post subject: Grounding in mixed synthesizer circuit
Unread postPosted: Wed Apr 06, 2005 8:02 am

Hello everyone!
I want to design a frequency synthesizer circuit; but I don't know how design analog and digital grounds. Should these two grounds be connected together or isolated from each other?
Thanks for help and time.
mohammad


Top


Itay
Post subject:
Unread postPosted: Wed Apr 06, 2005 8:21 am

Hi mohamad,

The analog and digital voltages should be provided from different regulators, each will have its own ground. Then you should connect both grounds by a wide trace near the regulators.

This will provide good isolation between the voltages, and eliminate ground loops and noise usually associated with such designs.

Another advice for synthesizer is to use a "super filter" circuit for the VCO supply. This circuit is based on NPN transistor with bypass capacitors at both base and collector (use a tantalum capacitor at the base) that is used to filter the supply voltage of the VCO. This circuit reduces the supply voltage from the regulator to the level required by the VCO. Make sure that the transistor is in the active region of operation. Use a voltage divider at the base. This circuit will enhance your phase noise performance.

Hope this helps,
Itay


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Guest
Post subject:
Unread postPosted: Thu Apr 07, 2005 1:40 am

In The Name of God
Dear Itay.
Thanks for your help and time. Some companies produce integrated microwave frequency synthesizers that include VCO. Should the RF and digital grounds for these products be isolated too?
Thanks if you give me your email address.
Also I want to have PDF of some of microwave books. Can you help me?
Thanks.
With best regards, Mohammad
Itay wrote:
Hi mohamad,

The analog and digital voltages should be provided from different regulators, each will have its own ground. Then you should connect both grounds by a wide trace near the regulators.

This will provide good isolation between the voltages, and eliminate ground loops and noise usually associated with such designs.

Another advice for synthesizer is to use a "super filter" circuit for the VCO supply. This circuit is based on NPN transistor with bypass capacitors at both base and collector (use a tantalum capacitor at the base) that is used to filter the supply voltage of the VCO. This circuit reduces the supply voltage from the regulator to the level required by the VCO. Make sure that the transistor is in the active region of operation. Use a voltage divider at the base. This circuit will enhance your phase noise performance.

Hope this helps,
Itay


Top


Guest
Post subject:
Unread postPosted: Thu Apr 07, 2005 3:26 am

Hi Mohammad,

Yes the grounds should be connected as I mentioned in this type of synthesizers too. I have used this kind of synthesizers as well (ADF4360 series of Analog Devices)

My email address is: itre27@012.net.il

Thanks,
Itay






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