Designer’s Guide Community

aaron_do Senior Fellow Offline Posts: 1398	VCO pulling, Sep 16^th, 2007, 8:10pm Hi, just wondering, how big of a problem is VCO pulling? I have a receiver which uses a direct conversion transmitter, and furthermore, the PA is not ON in receive mode. Therefore, i'm thinking that VCO pulling will not be a big issue. cheers, Aaron hmm......seems direct conversion transmitters have a worse VCO pulling problem...
Back to top	there is no energy in matter other than that received from the environment - Nikola Tesla IP Logged

Aigneryu

Senior Member

Offline

Posts: 102

Re: VCO pulling,
Reply #1 - Sep 16^th, 2007, 9:47pm

Hi,

When your transmitter is on, the output of PA will be a carrier-modulated signal, which will be different from your VCO. So if you have some feedback path, the PA will still pull your VCO. So that is why the VCO frequency should avoid to be the same as your LO in a "integrated" "direct-conversion" (or low-IF). If you lock your VCO at 2x of the required LO, then you can prevent the pulling.

Sincerely,

Back to top

IP Logged

aaron_do Senior Fellow Offline Posts: 1398	Re: VCO pulling, Reply #2 - Sep 17^th, 2007, 6:27pm thanks for the reply, one thing though, if we have a direct conversion transmitter and the modulated signal is symmetric about 0 Hz, the upconverted signal will also be symmetric about the LO. So therefore, can we expect much pulling effect. i.e. which way would it pull? thanks, Aaron
Back to top	there is no energy in matter other than that received from the environment - Nikola Tesla IP Logged

nxing Community Member Offline God help the person who help themselves Posts: 46 China	Re: VCO pulling, Reply #3 - Sep 19^th, 2007, 4:20pm It really depends on how strong your PA output and how linear it is. 2X LO is not necessary enough to prevent the pulling. THat's why some companies use 4X VCO or 3 X VCO.
Back to top	IP Logged

aaron_do Senior Fellow Offline Posts: 1398	Re: VCO pulling, Reply #4 - Sep 19^th, 2007, 6:34pm thanks for the advice :) I was quoting from memory, but i guess i was quite far off. Aaron
Back to top	there is no energy in matter other than that received from the environment - Nikola Tesla IP Logged

yang

New Member

Offline

Posts: 4

Re: VCO pulling,
Reply #5 - Sep 20^th, 2007, 6:55am

Aigneryu wrote on Sep 16^th, 2007, 9:47pm:

Hi,

So if you have some feedback path, the PA will still pull your VCO. So that is why the VCO frequency should avoid to be the same as your LO in a "integrated" "direct-conversion" (or low-IF).

Sincerely, �

Hi Aigneryu,

Could you please give us some examples of " So if you have some feedback path"? In my experience, the common VCC and Ground maybe a feedback path.

Best regards,
Yang

Back to top

IP Logged