Return-Path: Received: (qmail 49292 invoked from network); 13 May 2004 11:33:36 -0000 Received: from unknown (HELO ptb-mxscan03.plus.net) (212.159.14.237) by ptb-mailstore04.plus.net with SMTP; 13 May 2004 11:33:36 -0000 Received: (qmail 48218 invoked from network); 13 May 2004 11:33:36 -0000 X-Filtered-by: Plusnet (hmail v1.01) X-Spam-detection-level: 11 Received: from ptb-mxcore03.plus.net (212.159.14.217) by ptb-mxscan03.plus.net with SMTP; 13 May 2004 11:33:35 -0000 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore03.plus.net with esmtp (Exim) id 1BOET0-000CHv-TW for dave@picks.force9.co.uk; Thu, 13 May 2004 12:33:34 +0100 X-Fake-Domain: majordom Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1BOESa-0008Qy-KR for rs_out_1@blacksheep.org; Thu, 13 May 2004 12:33:08 +0100 Received: from [213.232.95.59] (helo=relay.salmark.net) by post.thorcom.com with esmtp (Exim 4.14) id 1BOESZ-0008Qp-R2 for rsgb_lf_group@blacksheep.org; Thu, 13 May 2004 12:33:07 +0100 Received: from hestia.herts.ac.uk ([147.197.200.9]) by relay.salmark.net with esmtp (Exim 4.24) id 1BOL0y-0006Jy-7E for rsgb_lf_group@blacksheep.org; Thu, 13 May 2004 19:33:04 +0100 X-Fake-Domain: altair Received: from altair ([147.197.200.45] helo=altair.herts.ac.uk) by hestia.herts.ac.uk with esmtp (Exim 3.22 #1) id 1BOEQJ-0004JK-00 for rsgb_lf_group@blacksheep.org; Thu, 13 May 2004 12:30:47 +0100 X-No-DNS-For: 147.197.164.230 Received: from [147.197.164.230] (helo=JamesMorrits) by altair.herts.ac.uk with esmtp (Exim 3.36 #1) id 1BOEQI-0007WJ-00 for rsgb_lf_group@blacksheep.org; Thu, 13 May 2004 12:30:46 +0100 From: "James Moritz" To: rsgb_lf_group@blacksheep.org Date: Thu, 13 May 2004 12:30:42 +0100 Message-ID: MIME-Version: 1.0 X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.4510 Importance: Normal In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1409 X-UH-MailScanner: No Virus detected X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=no, Subject: LF: RE: Re: VDC source with microvolt resolution Content-Type: text/plain; charset=us-ascii; 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: 1 >.....This is more or less what I had in mind when I wrote of a charge pump. >The AVR micro I am using offers a >PWM output, but unfortunately it has a resolution of only ten bits, so >it must be done in software. Dear Alberto, LF Group, How about this - generate your output DC voltage using the 10 bit PWM. Additionally, have an external 10 bit DAC, driven from the reference voltage source used by the PWM. Attenuate the DAC output by a factor of 1/(2^10)(or whatever factor gives a full-scale output equal to a 1 LSB change in the PWM output), and sum it with the PWM output to interpolate with 10 bit resolution between the "coarse" PWM output steps. I think it would be quite easy to get 20bit resolution like this, but 20 bit accuracy would be another problem... Another thought occurs - implement a software DDS with 20bit phase accumulator, then use the output to drive a frequency to voltage converter (essentially a pulse generator or charge pump with a low pass filter). One problem there would be the output ripple at low voltage outputs. Cheers, Jim Moritz 73 de M0BMU