From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5E220C43334 for ; Mon, 20 Jun 2022 20:01:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237461AbiFTUBM (ORCPT ); Mon, 20 Jun 2022 16:01:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35220 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229553AbiFTUBL (ORCPT ); Mon, 20 Jun 2022 16:01:11 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 35D991CB0F for ; Mon, 20 Jun 2022 13:01:10 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 7B1826165A for ; Mon, 20 Jun 2022 20:01:10 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 10BD7C3411B; Mon, 20 Jun 2022 20:01:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1655755269; bh=og1nf8zR9WFzNGW4XGzNuCAvcdmYIjHMDBbdsycQtWo=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=W/InKpF+cVYWNcF4klV/WtypPJkuDoZf7bSpJitSd6ChiRspIDBPUxe9z37HuQR1s hroYyKtlHqK0LxV/UeNuzCUCy4r+l4EHZuQrDvWO60I3Z7UAP6hYNVYQLy3uIM/fcK nXnOgE1xE5Yk+Huxzx/FY6NTFEf2UHid2TIZ/sCBrTRNpZkRhuVMtjjIJDUiPKVnUT VGhhrmwhL9MDXAOapppKHHTfwfNUiCthRpr1f1a8O8YU6ezePuPbAWInwxgj5g8PK7 IpPaB+aQftTLvPYwAMTtsARbTLBN7F4ryKe20lFUhJLKE326+yAA7rOx3zVNQTKvRB ujyFOf6CHuzSw== Date: Mon, 20 Jun 2022 21:01:03 +0100 From: Jonathan Cameron To: Andy Shevchenko Cc: linux-iio , Peter Rosin , Michael Hennerich , Lars-Peter Clausen , Vincent Whitchurch , Jonathan Cameron Subject: Re: [PATCH v2 11/17] iio: core: Introduce _inputoffset for differential channels Message-ID: <20220620210103.30504288@jic23-huawei> In-Reply-To: References: <20220619185839.1363503-1-jic23@kernel.org> <20220619185839.1363503-12-jic23@kernel.org> <20220620191307.7f8fefa7@jic23-huawei> X-Mailer: Claws Mail 4.1.0 (GTK 3.24.34; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-iio@vger.kernel.org On Mon, 20 Jun 2022 20:35:57 +0200 Andy Shevchenko wrote: > On Mon, Jun 20, 2022 at 8:13 PM Jonathan Cameron wrote: > > On Mon, 20 Jun 2022 01:20:08 +0200 > > Andy Shevchenko wrote: =20 >=20 > ... >=20 > > So to try and explain what this is doing in more depth. > > > > This is basically applying a negative offset X to both the P(ostitive) = and > > N(egative) lines. Hence > > > > measured capacitance =3D (P - X) - (N - X) > > =3D P - N > > > > the aim of X being to keep the signal hitting some internal point on > > the device within a range that is measurable. > > > > The relevant text on the datasheet is: > > > > "The CAPDAC can be understood as a negative capacitance > > connected internally to the CIN pin." > > > > "Each of the two input capacitances CX and CY between the EXC > > and CIN pins must be less than 4 pF (without using the > > CAPDACs) or must be less than 21 pF and balanced by the > > CAPDACs. Balancing by the CAPDACs means that both > > CX=E2=80=93CAPDAC(+) and CY=E2=80=93CAPDAC(=E2=80=93) are less than 4 p= F." > > > > So basically if you have both sides of the differential pair > > that are too large (>4 pF) then you can drag them together > > down to that range by adding negative capacitance. =20 >=20 > Ah, in a long wording it's "measurement window offset". Dunno how to > make it shorter. > Also, 0-point on the axis in math. >=20 Hmm. Both good descriptions so I'll add something along these lines to the description. Characters are cheap aren't then? :) in_capacitanceY-capacitanceZ_zero_point isn't too bad - will think more. No connection to offset which is what it would be for a single ended channel though... Jonathan