Return-Path: Received: (qmail 3521 invoked from network); 16 Sep 2002 17:37:35 -0000 Received: from warrior.services.quay.plus.net (212.159.14.227) by mailstore with SMTP; 16 Sep 2002 17:37:35 -0000 Content-Transfer-Encoding: 8bit Received: (qmail 4989 invoked from network); 16 Sep 2002 17:37:28 -0000 X-Priority: 3 X-MSMail-Priority: Normal Received: from post.thorcom.com (193.82.116.70) by warrior.services.quay.plus.net with SMTP; 16 Sep 2002 17:37:28 -0000 X-SQ: A X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Received: from majordom by post.thorcom.com with local (Exim 4.10) id 17qzo0-0007Dt-00 for rsgb_lf_group-outgoing@blacksheep.org; Mon, 16 Sep 2002 18:37:04 +0100 Received: from [147.197.200.9] (helo=hestia.herts.ac.uk) by post.thorcom.com with esmtp (Exim 4.10) id 17qznz-0007Dj-00 for rsgb_lf_group@blacksheep.org; Mon, 16 Sep 2002 18:37:03 +0100 Received: from gemini ([147.197.200.44] helo=gemini.herts.ac.uk) by hestia.herts.ac.uk with esmtp (Exim 3.22 #1) id 17qznN-0000Qv-00 for rsgb_lf_group@blacksheep.org; Mon, 16 Sep 2002 18:36:25 +0100 Received: from [147.197.232.252] (helo=rsch-15.herts.ac.uk) by gemini.herts.ac.uk with esmtp (Exim 3.33 #1) id 17qznC-0004o8-00 for rsgb_lf_group@blacksheep.org; Mon, 16 Sep 2002 18:36:14 +0100 Message-ID: <5.1.0.14.0.20020916180814.00b02648@gemini.herts.ac.uk> X-Sender: mj9ar@gemini.herts.ac.uk X-Mailer: QUALCOMM Windows Eudora Version 5.1 Date: Mon, 16 Sep 2002 18:36:12 +0100 To: rsgb_lf_group@blacksheep.org From: "James Moritz" In-reply-to: <3D85FD53.7090901@usa.net> References: <3A5B37BB.11936.1878C3D@localhost> MIME-Version: 1.0 X-MailScanner: No Virus detected Subject: Re: LF: PSpice question Content-Type: text/plain; charset=us-ascii; format=flowed X-Spam-Status: No, hits=-4.1 required=5.0tests=IN_REP_TO,DEAR_SOMEBODYversion=2.31 Sender: Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group > If I simulate it with Electronics Workbench it happily oscillates. >With PSpice it doesn't, no matter how I change the feedback. >I suspect that some noise source should be added to trigger the >oscillation, but >don't know how, nor I am sure that this is indeed true. > >Any help is gratefully accepted, thanks. > >73 Alberto I2PHD Dear Alberto, LF group, Try connecting a pulsed voltage source (VPULSE) in series with the tank circuit - set it to generate a pulse width of, say, 1/2 a cycle of the expected oscillator frequency, starting at t=0. The pulse will cause the tank circuit to "ring", and the oscillations should build up from there. Once the pulse has finished, the source just behaves as a short circuit . You will want to play with the amplitude of the pulse so that the ringing has roughly similar amplitude to the steady-state oscillator level, otherwise it will take a long time to settle. In any case, the simulation must run for a large number of oscillator cycles in order for the circuit to reach equilibrium - this is also true of a real oscillator! You may also find it necessary to set the transient simulation "step ceiling" to a value that is a small fraction of a cycle, otherwise peculiar waveforms will result, because the default time step size selected by PSpice is normally too big for a high Q circuit. Cheers, Jim Moritz 73 de M0BMU