Re: Programming Languages

On Sun, 3 Nov 2024 15:58:25 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:

On 3/11/2024 8:12 am, Cursitor Doom wrote:

On Sat, 2 Nov 2024 15:57:39 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
 

"Cursitor Doom" <cd@notformail.com> wrote in message news:ahucij5dt50fihbuenl766e80isr227gqa@4ax.com...

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.

>
Well it's all exactly what you would expect because as was previously pointed out, a gain of 1.0000000001 (with as many 0s as you
want) will grow to limiting but a gain of 0.99999999999 (with as many 9s as you want) will die to nothing. So in any real circuit
you must constantly control the gain so that never goes into limiting and never dies. Yes this will usually be a knife-edge thing.
>
If you try to do this manually then the slightest change in anything (supply voltage, temperature, humidity, wind direction,
Halloween) will tip it one way or another.
>
Pure sine waves are surprisingly difficult to generate for this reason. Real analogue hardware just doesn't want to do it naturally
(unless the frequency is so high that the next harmonic is barely noticed or easy to filter). It would much rather produce a square
(limited) wave or nothing at all.

 
Indeed. And that's why it's really quite remarkable that this tiny
passive device enables the generation of such spectrally pure
sinewaves; an 'ancient' technology that still holds a candle in the
digital world of today.

>
They can generate tolerably spectrally pure sine waves if engineered in
with sufficient expertise, which is pretty thin on the ground.
>
It's not an area where digital technology has a lot to offer. Today's
word isn't exactly digital either - every system has a analog front end

Even SDR?

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?

>
And Cursitor Doom hasn't a clue about that.

True enough, Bill. I've not yet encountered capacitors.