Return-Path: Received: (qmail 11828 invoked from network); 14 Jan 2003 13:24:44 -0000 Received: from marstons.services.quay.plus.net (212.159.14.223) by mailstore with SMTP; 14 Jan 2003 13:24:44 -0000 Received: (qmail 16199 invoked by uid 10001); 14 Jan 2003 13:24:38 -0000 Content-Transfer-Encoding: 8bit Received: from post.thorcom.com (193.82.116.70) by marstons.services.quay.plus.net with SMTP; 14 Jan 2003 13:24:38 -0000 X-Priority: 3 X-MSMail-Priority: Normal X-SQ: A Received: from majordom by post.thorcom.com with local (Exim 4.12) id 18YR2A-0002QI-00 for rsgb_lf_group-outgoing@blacksheep.org; Tue, 14 Jan 2003 13:23:14 +0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Received: from [134.58.241.13] (helo=mail3.cc.kuleuven.ac.be) by post.thorcom.com with esmtp (Exim 4.12) id 18YR2A-0002Q9-00 for rsgb_lf_group@blacksheep.org; Tue, 14 Jan 2003 13:23:14 +0000 Received: from dell-rik.fys.kuleuven.ac.be (ssl32-dmz.kuleuven.net [134.58.241.97]) by mail3.cc.kuleuven.ac.be (8.12.1/8.12.1) with ESMTP id h0EDMhBV060504 for ; Tue, 14 Jan 2003 14:22:43 +0100 Message-ID: <5.1.0.14.0.20030114093942.01bbcb60@pb623250.kuleuven.be> X-Sender: pb623250@pb623250.kuleuven.be X-Mailer: QUALCOMM Windows Eudora Version 5.1 Date: Tue, 14 Jan 2003 14:30:10 +0100 To: rsgb_lf_group@blacksheep.org From: "Rik Strobbe" In-reply-to: <5.1.0.14.0.20030113182353.00af0e30@gemini.herts.ac.uk> References: <18Xprt-0FPHu4C@fwd02.sul.t-online.com> <003801c2b9e6$7a85c940$0500a8c0@charter.net> MIME-Version: 1.0 Subject: Re: LF: push/pull Content-Type: text/plain; charset=us-ascii; format=flowed X-Spam-Status: No, hits=-0.5 required=6.0tests=IN_REP_TO,REFERENCES,SPAM_PHRASE_00_01version=2.43 X-SA-Exim-Scanned: Yes Sender: Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rsgb_lf_group-outgoing@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false Hello Uwe, power-FETs do have rather large gate-source capacitances that can differ from FET to FET. For the popular IRF450 Cgs is about 2nF, variations between FET's can easily be a few 100pF. If the FETs are driven from a rather high-Z source the variations in Cgs might cause a phase shift, although 10 degrees look very much to me. How did you measure this phase shift ? In the past I have noticed that measuring waveforms at the gate of a FET with the drain open can give very strange results ... 73, Rik ON7YD >Hi all, > >guess many of you built the G0MRF-Quarter-Kilowatt-Amplifier. >I did. the PSU is not finished yet. > >got some trouble with the phase of the 137kHz sines >(es triangular and rectangular) measured at the gates of the MOSFETs. >there is a diff btwn the two channels of estimated 10degr. >that means parasitic oscillation if operating the PA, doesn`t it.