VCO requirement in the GPS system?

Dear all,

Could anyone give me an information about the VCO requirement in the GPS system? I means what is the phase noise or required output power do they need usually?

Thanks

wccheng

Because GPS is a spread spectrum system, phase noise is not a critical parameter, and even a value around 80?85 dBc/Hz at 100 kHz offset is still acceptable.

Normal values for LO phase noise of the GPS receivers on the market are better than ?95dBc/Hz @ 100kHz.

Output level of the LO is dictated by the mixer type, and in this case could be somewhere between ?10dBm and 0dBm.

very thanks for your reply.
then how about the frequency band of the VCO need to vary?

GPS is spread spectrum modulation (there's no bands, just one common band with all the signals on top of each other) so you just design for a fixed frequency which ensures downconversion of the GPS signal to the IF you have chosen.

Dear Sir:

Allow me to add one question:

Seems to me frequency resoluation (accuracy) of
carrier and code tracking loops critical to GPS receiver sensitivity.

Does LO (VCO+PLL) close-in phase noise affecting accuracy of
this carrier and code tracking loops?

Thanks.

it affects, but not much

one more question Sir:

For the reference clock source of RF PLL in GPS receiver,
do we need TCXO?

Hi Jcpu,

GPS need both TCXO (25M or 16M) for RF section as well as RTC (32K).

Hi PK:

Could u please explain us more how much degrade with poor VCO PN in terms
of quantity of PN and C/I ...

Thanks !