Path: ...!weretis.net!feeder9.news.weretis.net!i2pn.org!i2pn2.org!.POSTED!not-for-mail
From: RodionGork <rodiongork@github.com>
Newsgroups: sci.electronics.design
Subject: Re: How 3-capacitor sine generator works =?UTF-8?B?cmVhbGx5Pw==?=
Date: Sat, 4 May 2024 21:00:23 +0000
Organization: novaBBS
Message-ID: <996510dbea043eaeaa8b600026bcf2e1@www.novabbs.com>
References: <804485177e123558699ce859cc4d496a@www.novabbs.com> <v121vo$db1f$1@dont-email.me>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
Injection-Info: i2pn2.org;
	logging-data="93837"; mail-complaints-to="usenet@i2pn2.org";
	posting-account="PetDxtfYxGIz8HKnOUw23jUTBLp0s6zcpeRK8b5yfAk";
User-Agent: Rocksolid Light
X-Rslight-Posting-User: d7f835980493bcbf332e1f3bae1201d566d49944
X-Spam-Checker-Version: SpamAssassin 4.0.0
X-Rslight-Site: $2y$10$pKcJpKSvGdXRGNY4/d7CnO0PbL2qPoUsj.uIilNhWY3S094hfOfIO
Bytes: 2578
Lines: 43

> It's a phase shift oscillator - one of many.

Thanks a lot, so the "keywords" were on the surface, I just missed. It
could be googled by
phase shift or even by RC-oscillator. Great!

> Here's a solution I came up with back in 1986

Wow, thanks for curious story. I haven't yet went to school then :) Golden
age of electronics!

> For oscillation you need to put the output back in phase to the input.
The tansistor gives 180 degrees phese shift

Thanks, I see I was mistaken thinking that each stage "shifts" phase by 90
degrees (obviously I forgotten university lectures) and that confused me.

> and as gain is >1 it wil oscillate

supposedly, it is about overall gain - transistor gain multiplied by (less
than 1) gains of filter stages - it seems they "eat" quite a lot of an
amplitude.

> The 100K base resistor was probably selected to match the
beta of the transistor

please note here is some cheat - resistor is connected not to the positive
supply but to the collector - it reduces the pull-up effect, but allows for
wider range of resistance (effectively removing necessity of adding proper
pull-down resistor at the base and small another one at emitter).

> The lesson for your students is more general

Thanks, it is a good lesson for myself - as for the students, they are a
bit too beginners to
get into such depth of idea, but I'll try to communicate your explanations
:)

> Another phase-shift osc form uses three RC integrators

That's curious, I'll look for this variant.

-- 
to email me substitute github with gmail please