-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Somebody in the thread at some point said: | On Wed, Aug 20, 2008 at 09:39:14AM +0100, Andy Green wrote: | |> IMO it doesn't make any harm to see MOSFET switches on the power rails |> to whole GSM side so there is no question. | | no, it actually causes problems
I heard from Tony having a current limit on the switch caused problems, nothing else. |> This was done on a previous prototype I saw in .tw, but the low Rdson switch |> they used had built-in currently limit (1.6A IIRC?) that got triggered at low |> temperature and highest TX setting destroying TX action. So they removed it |> from PA side... maybe we can bring this back in the future. | | to the best of my knowledge it is industry standard practise to have the GSM PA | cunnected directly to the battery. the RdsON of the mosfet switches (even of | those optimized for very low RdsON) is not constant but current-dependent. | This causes spectral impurity and can easily have (and actually has in | practise) effects on violating the regulatory requirements on the extremely | strict regulations on GSM/GPRS/3G signals. Sounds like problems with the PA design, but it is hard to argue about since it's hearsay. | So I really vote strongly against tryign to do this for no apparent reason. There's a very good obvious reason to stop a wideband RF amp from having autonomous power supply even when the device is "off". It's such a bizarre design that doing it is the thing that needs the special pleading, not the insertion of control over its power which is normal design action. | The GSM PA is an analog circuit without any digital logic. Thus, it can never | lock up internally. It has an input pin that switches it off/on depending on | the logic state, i.e. a built-in power switch. This is what should be used | (and is used in GTA02) to ensure acutal power-off. No I disagree -- removing the power ensures "actual power off". Everything else is something different than "ensure actual power off" but "ensure powered but allegedly inactive while we keep that enable level right". - -Andy -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org iEYEARECAAYFAkiyvugACgkQOjLpvpq7dMpjBwCeJqL/rmx3OuRSoXWWmlUG4rND 1mQAn1Lj/iXwYMM5oLayZYVSPrdhj1La =jbYc -----END PGP SIGNATURE----- _______________________________________________ hardware mailing list [email protected] http://lists.openmoko.org/mailman/listinfo/hardware
