From bounce-ss-6751@lists.tapr.org Mon Dec 27 02:40:20 1999 Received: from lists.tapr.org (lists.tapr.org [204.17.217.24]) by tapr.org (8.9.3/8.9.3/1.13) with SMTP id CAA12000 for ; Mon, 27 Dec 1999 02:40:19 -0600 (CST) Message-ID: Date: Mon, 27 Dec 1999 19:38:11 +1100 From: Geoff Matthews X-Accept-Language: en MIME-Version: 1.0 To: "TAPR Spread Spectrum Special Interest Group" CC: ss@lists.tapr.org Subject: [ss] Incremental phase modulator Content-Type: text/plain; charset=iso-8859-1 List-Unsubscribe: List-Software: Lyris Server version 3.0 List-Subscribe: List-Owner: X-List-Host: Tucson Amateur Packet Radio Reply-To: "TAPR Spread Spectrum Special Interest Group" X-Message-Id: <38672573.DD3533AB@ozemail.com.au> Sender: bounce-ss-6751@lists.tapr.org Precedence: bulk Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by tapr.org id CAA12000 Hi Guys, I found the enclosed snippet on the web and it looks useful. Do any of you know how I could go about implementing it? I have a CPLD "starter kit" that I am learning to drive (slowly!!). > Incremental Phase Modulator (IPM) -- simply use a clock that is 4 to 16 times the chip rate clock for the system digital timing reference in the receiver. Follow this clock with a programmable frequency divider, e.g. if the clock is 4 x the PN chip rate, use a divide by 3/4/5 counter. In the case of a clock at 8 x the PN chip rate, use a programmable 7/8/9 counter. Make sure this counter is controlled in such a way that it adds or drops only one input clock each time it is adjusted. This gives us single PN chip phase adjustment capability! Also, make sure that the counter can be advanced or retarded only once per data bit time (or one PN Epoch)! This scheme is especially useful in designs using FPGAs or planning to use custom ASICs, because it lends itself to simple, straightforward digital implementation. Note that, by proper design, ONLY advancing OR retarding of the PN chip phase is necessary -- but be careful of long term PN clock oscillator drifts! > 73 de Geoff vk2tfg --- You are currently subscribed to ss as: lyris.ss@tapr.org To unsubscribe send a blank email to leave-ss-6751T@lists.tapr.org