From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail.kapsi.fi ([217.30.184.167]:52279 "EHLO mail.kapsi.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752086AbbGPHNU (ORCPT ); Thu, 16 Jul 2015 03:13:20 -0400 From: Antti Palosaari Subject: Re: [PATCH 2/9] v4l2: add RF gain control To: Hans Verkuil , linux-media@vger.kernel.org References: <1433592188-31748-1-git-send-email-crope@iki.fi> <1433592188-31748-2-git-send-email-crope@iki.fi> <55755A6A.9080300@xs4all.nl> Message-ID: <55A7598D.9050004@iki.fi> Date: Thu, 16 Jul 2015 10:13:17 +0300 MIME-Version: 1.0 In-Reply-To: <55755A6A.9080300@xs4all.nl> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-media-owner@vger.kernel.org List-ID: On 06/08/2015 12:03 PM, Hans Verkuil wrote: > On 06/06/2015 02:03 PM, Antti Palosaari wrote: >> Add new RF tuner gain control named RF gain. That is aimed for >> external LNA (amplifier) chip just right after antenna connector. > > I don't follow. Do you mean: > > This feeds into the external LNA... > > But if that's the case, then the LNA chip isn't right after the antenna connector, > since there is a RF amplified in between. On that case, there is amplifier between antenna and tuner chip. And I named it as a RF gain. It is quite same thing than LNA gain, but I would call LNA gain as a "RF gain" inside the tuner chip - integrated into tuner chip. These terms are not 100% established as LNA gain and RF gain are considered as a same thing very often. The fact is that almost every silicon tuner nowadays has integrated RF/LNA amplifier, but there is devices having still separate amplifier between tuner and antenna. For DVB side there is multiple such devices, for example PCTV 290e and PCTV 292. HackRF SDR has separate RF amplifier and multiple other amplifiers. So all in all, I needed second "LNA/RF" gain control and as LNA gain was already defined, I defined another as a RF gain. RF in +----+ +-----+ +-------+ +----+ IF out -------> | RF | --> | LNA | --> | Mixer | --> | IF | --------> +----+ +-----+ +-------+ +----+ Those boxes (RF/LNA/Mixer/IF) are gain controls and signal travels in order shown from gain to gain. In real life there is usually even more gains withing gain stage, eg. Mixer gain stage could contain 3 different amplifiers. RF in = antenna input IF out = connected to ADC (demod) Hope the RF gain / LNA gain documentation is now a bit better. regards Antti -- http://palosaari.fi/