Path: ...!eternal-september.org!feeder2.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: Programming Languages
Date: Sun, 3 Nov 2024 13:27:26 +1100
Organization: A noiseless patient Spider
Lines: 81
Message-ID: <vg6n2g$295s$3@dont-email.me>
References: <vg3575$3bio0$1@dont-email.me>
 <vg3tkh$1kht$1@nnrp.usenet.blueworldhosting.com>
 <vg4fff$3lok1$1@dont-email.me>
 <vg5m8l$21fg$1@nnrp.usenet.blueworldhosting.com>
 <ahucij5dt50fihbuenl766e80isr227gqa@4ax.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Injection-Date: Sun, 03 Nov 2024 03:27:29 +0100 (CET)
Injection-Info: dont-email.me; posting-host="f48fba85c9bfbf253fad93eba184ff84";
	logging-data="74940"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1/fQXPR47ZSA5lD4rqUaUfryvN5/pUYHAQ="
User-Agent: Mozilla Thunderbird
Cancel-Lock: sha1:6GAlZsB2AOdjDEwXGrubqxAk9f8=
X-Antivirus: Norton (VPS 241102-0, 2/11/2024), Outbound message
Content-Language: en-US
In-Reply-To: <ahucij5dt50fihbuenl766e80isr227gqa@4ax.com>
X-Antivirus-Status: Clean
Bytes: 5666

On 3/11/2024 6:21 am, Cursitor Doom wrote:
> On Sat, 2 Nov 2024 13:07:32 -0400, "Edward Rawde"
> <invalid@invalid.invalid> wrote:
> 
>> "Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vg4fff$3lok1$1@dont-email.me...
>>> On 2/11/2024 12:01 pm, Edward Rawde wrote:
>>>> "Cursitor Doom" <cd999666@notformail.com> wrote in message news:vg3575$3bio0$1@dont-email.me...
>>>>> You can call me old fashioned, but I still believe there's never been a
>>>>> more elegant computer language than the original K&R C. You can keep the
>>>>> rest; I'll stick with that.
>>>>
>>>> Having just got back from a vacation I thought I'd give my input to this before looking into whether it's worthwhile getting back
>>>> into sinewave oscillators.
>>>
>>> John May has come up with a much better sine wave oscillator than yours.
>>
>> That's no surprise. I can remember one or two other occasions when I thought I had a brilliant way to do it but someone else came up
>> with a better way.
>> I don't specifically mean sinewave oscillators.
>>
>>> It also has more components, and I'm not sure that all of them are strictly necessary. Getting deep enough into the design to be
>>> sure where the harmonics are coming from is going to be difficult. I think I'm getting there, but I'm not all that motivated to
>>> put in the rest of the
>>> work.
>>>
>>> One obvious point is that a FET channel isn't a perfect resistor - as the voltage across it rises above zero it starts looking
>>> more like a constant current diode (and you can buy FET-based constant current diodes).
>>>
>>> In theory, if you added a second harmonic component to the FET gate drive you could make it look like a resistor over a wider
>>> range of voltage, if the phasing was close enough to right.
>>>
>>> You've also got the point that when there's a voltage drop across the FET channel, it adds to the gate-to-channel voltage (as has
>>> been mentioned here) and you can cancel that with an in-phase fundamental component
>>
>> The last circuit of my own had both an n fet and a p fet.
>> I found that by adding a capacitor from one gate to the other (to try to cancel the unwanted signals in opposite phase) I could get
>> the unwanted gate signal below 100uV. I then had harmonics approaching 60dB down except one at 50dB (I think 2KHz). Not brilliant
>> but not bad.
>>
>> There are some useful pointers here:
>> https://sound-au.com/articles/sinewave.htm
>> In particular where it says "Done properly, a JFET can provide distortion performance that is as good or better than a lamp or
>> thermistor."
>>
>> Perhaps I'll concentrate on how to make the FET behave as a voltage variable resistor over the widest possible range.
>>
>> I also what to look into what I meant by crud and non crud mode in LTSpice.
>> This mysterious effect can depend on things such as which specific computer is used and how long is specified before collecting
>> simulation data.
>> You can see it in the gate voltage after startup. It looks a bit like a PLL hunting and eventually locking but it doesn't happen at
>> startup, it happens after seconds.
>> So I'll need to be able to post some pictures to show that. I'll get to that.
> 
> Hi Edward,
> I've been messing around with a real-life WB oscillator - the busted
> one I originally posted about. AFAIK, everyone else here has just been
> simming them, so I thought it might be useful if I provided some
> detail that others may have overlooked.
> The thing that stands out in my experiments in replacing the broken
> thermistor with a pot and attempting to twiddle for the optimum sine
> wave is just how close the waveform has to get to collapsing from
> insufficient feedback in order to get a nice sine wave. It's a
> knife-edge adjustment to get it right and then of course, with
> constantly shifting temperatures it goes out of adjustment again
> within a few seconds. But the sweet spot for the best waveshape is
> *just* a whisker above collapse.
> HTH.

Of course it is.That's why Wein bridges need a non-linear element that 
can be adjust to get the gain exactly right and keep it there.

>> Is there an easy way to remove a DC offset from a simulation trace so that my n and p gate signals can be superimposed after
>> startup?

There is but Cursitor Doom doesn't know it.

-- 
Bill Sloman, Sydney