Return-Path: Received: (qmail 27539 invoked from network); 24 Apr 2002 13:46:22 -0000 Content-Transfer-Encoding: 8bit Received: from unknown (HELO murphys-inbound.services.quay.plus.net) (212.159.14.225) by excalibur.plus.net with SMTP; 24 Apr 2002 13:46:22 -0000 X-Priority: 3 X-MSMail-Priority: Normal Received: (qmail 27114 invoked from network); 24 Apr 2002 13:46:18 -0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by murphys.services.quay.plus.net with SMTP; 24 Apr 2002 13:46:18 -0000 Received: from majordom by post.thorcom.com with local (Exim 3.33 #2) id 170OIj-0000tw-00 for rsgb_lf_group-outgoing@blacksheep.org; Wed, 24 Apr 2002 16:03:21 +0100 Received: from relay.dera.gov.uk ([192.5.29.49]) by post.thorcom.com with smtp (Exim 3.33 #2) id 170OIi-0000tr-00 for rsgb_lf_group@blacksheep.org; Wed, 24 Apr 2002 16:03:20 +0100 Received: (qmail 25364 invoked from network); 24 Apr 2002 14:25:12 +0100 Received: from butterfly.mod.uk (HELO warlock.dstl.gov.uk) (192.5.29.10) by relay.dera.gov.uk with SMTP; 24 Apr 2002 14:25:12 +0100 Message-ID: <7D653C9C42F5D411A27C00508BF8803DCB9A7E@mail.dstl.gov.uk> From: "Talbot Andrew" To: "LF Group \(E-mail\)" Subject: LF: DDS Amplitude control Date: Wed, 24 Apr 2002 14:24:28 +0100 MIME-Version: 1.0 X-Mailer: Internet Mail Service (5.5.2650.21) Content-Type: text/plain; charset=iso-8859-1; format=flowed Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: Not being able to control the amplitude of the AD9850/51 DDS chip output waveform makes it difficult to generate decent signalling waveforms. However, this is possible by changing the current into the Rset, pin 12, which sets the full scale amplitude of the D/A output. On my DDS board this current is set by an innocuous 3.9k resistor. Replacing this with a FET acting as a variable resistor allows a DC level to control the amplitude for non critical applications - such as bandwidth limiting a signal by envelope shaping. The voltage at this Rset pin is maintained at approximately 1.26V and current is sourced through the external resistor. By suitable biassing, this current can be varied, so directly and linearly altering the amplitude of the output waveform. On the Analog Devices web site WWW.ANALOG.COM there is a tecnical note on altering the amplitude by digital control via an external D/A converter. Search for 'AD9851' then under related topics look for technical data. Andy G4JNT "The Information contained in this E-Mail and any subsequent correspondence" "is private and is intended solely for the intended recipient(s)." "For those other than the recipient any disclosure, copying, distribution, " "or any action taken or omitted to be taken in reliance on such information is" "prohibited and may be unlawful."