Return-Path: Received: (qmail 3261 invoked from network); 13 May 2004 14:43:40 -0000 Received: from unknown (HELO ptb-mxscan01.plus.net) (212.159.14.235) by ptb-mailstore02.plus.net with SMTP; 13 May 2004 14:43:40 -0000 Received: (qmail 2007 invoked from network); 13 May 2004 14:43:40 -0000 X-Filtered-by: Plusnet (hmail v1.01) X-Spam-detection-level: 11 Received: from ptb-mxcore01.plus.net (212.159.14.215) by ptb-mxscan01.plus.net with SMTP; 13 May 2004 14:43:38 -0000 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore01.plus.net with esmtp (Exim 4.30; FreeBSD) id 1BOHQw-0000Ir-5m for dave@picks.force9.co.uk; Thu, 13 May 2004 14:43:38 +0000 X-Fake-Domain: majordom Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1BOHQR-00049Z-DI for rs_out_1@blacksheep.org; Thu, 13 May 2004 15:43:07 +0100 Received: from [213.232.95.59] (helo=relay.salmark.net) by post.thorcom.com with esmtp (Exim 4.14) id 1BOHQQ-00049Q-LC for rsgb_lf_group@blacksheep.org; Thu, 13 May 2004 15:43:06 +0100 Received: from mailfe05.swip.net ([212.247.154.129]) by relay.salmark.net with esmtp (Exim 4.24) id 1BONyn-0006fe-0M for rsgb_lf_group@blacksheep.org; Thu, 13 May 2004 22:43:01 +0100 X-T2-Posting-ID: 3bgU4LVfFOB/SKpu7D1OzA== Received: from [212.151.18.81] (HELO oemcomputer) by mailfe05.swip.net (CommuniGate Pro SMTP 4.2b4a) with SMTP id 39076081 for rsgb_lf_group@blacksheep.org; Thu, 13 May 2004 16:43:00 +0200 X-Bad-Message-ID: no DNS (oemcomputer) Message-ID: <003301c438f8$97eaaa40$511297d4@oemcomputer> From: "Johan Bodin" To: rsgb_lf_group@blacksheep.org References: <40A2578C.2080600@usa.net> Date: Thu, 13 May 2004 14:42:30 -0000 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1409 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1409 X-Spam-Score: 0.1 (/) X-Spam-Report: autolearn=no,RCVD_IN_SORBS=0.1 Subject: LF: Re: VDC source with microvolt resolution Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Status: No, hits=0.0 required=5.0 tests=none autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-PN-SPAMFiltered: yes X-Spam-Rating: 2 Hi Alberto, Jim mentioned using a DAC to interpolate between the PWM steps. The interpolation can also be done by "PWMing the PWM" between two adjacent PWM steps (sort of "controlled dithering" :-). 1024 main PWM cycles = 1 sub-PWM cycle. For example, if the MSWord = 705 and the LSWord = 442 (10-bit words) then the main PWM should be set to 706 for 442 of the PWM cycles and to 705 for the remaining 1024-442=582 cycles. I recall we discussed this approach for VCXO control some time ago. The downside is that the output signal will contain frequency components as low as the main PWM frequency divided by the sub-PWM resolution so you'll need a very "slow" lowpass filter to get rid of the ripple. A DC accurate multi-pole filter with good (perhaps chopper stabilised) op-amps should do the trick. 73 Johan SM6LKM