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opamp sine wave oscillator

W

Winfield

Jan 1, 1970
0
That's not even my main concern. I can wait. What I'm worried about is: How
is the community going to get their hands on what's finished of AoE3 when
Win dies of old age 20 or 30 years from now?

robert

Actually, we've ramped up our work pace, and
plan on introducing H&H AoE 3rd-ed early in
2010. We also committed to this in an edit
of the Wikipedia "Art of Electronics" entry,
so now it must be true. :)
 
J

John Devereux

Jan 1, 1970
0
Winfield said:
Actually, we've ramped up our work pace, and
plan on introducing H&H AoE 3rd-ed early in
2010. We also committed to this in an edit
of the Wikipedia "Art of Electronics" entry,
so now it must be true. :)

It is such a wide ranging book, that (unlike most textbooks) also
tries to describe the actual current state of the art. By the time it
is finished it is ten years later and out of date - it's a moving
target, and you will always be trying to catch up without a huge,
sustained effort.

But I guess you know that :)
 
F

Fred Bloggs

Jan 1, 1970
0
Inventor said:
Inventor said:
[...]

Well, then maybe the circuit is not for you. You know, I am really
quite surprised at all the negativity in these responses. I figured
out something interesting, I wrote it up, and I posted it on the web
for you to enjoy. I'm not asking for anything from anyone other than
a plain, simple peer review and I've gotten some of that, thank you
very much. The circuit might prove very useful, it might not. I had
fun with the process of discovery so it was a pleasant, positive
experience for me. Why don't we all play nice for a change?
Thanks!

I thought your article itself was quite interesting, nicely laid out
too. I think some people are having a problem with your perceived
claim to "inventing" something new. These circuit arrangements are no
doubt obvous and well known for decades, to those here more
experienced. And for the stated goal of a sine wave oscillator there
are better solutions.

Well, I can't really be certain, but I kind of thought there was
something new here, yes. I thought that stuff about using the inverse
dual voltage divider on opposite sides of the circuit was new, the
fact that it's a whole family of oscillators not just one was new, and
features like the amplitude stabilization and amplitude modulation
were new as well. I think people are reminded of familiar circuits by
the new circuit, and then they reply: "that's been done before!", but
at this point I'm still thinking there is novelty here. If it's an
old familiar circuit, would someone please post a reference, perhaps
an existing web link?

Well you could be right - I am not an expert - but some of the people
commenting *are*.

I don't see that your amplitude stabilisation can work as
advertised. You initially claim to replace the "light bulb"
stabilisation by putting part of the network in the negative feedback
path. But all you are doing is rearranging the network, the overall
effect is the same as far as I can see. You are still left with a
system that requires a slight positive gain to startup reliably, which
will inevitably lead to clipping in the steady state condition.

Any feedback mechanism that operates at the level of a single cycle
will create distortion or require impossibly accurate matching. That
is why the classic "light bulb" is used, it has a relatively long
thermal time constant so as to *gradually* adjust the amplitude over
hundreds of cycles.

And in fact I see you show this with your test results.


Yes, that is an interesting question. I also do not quite see how the
amplitude is stabilized by this circuit. I think it is simply
clipping at the peaks. There's not all that much I can do with that
old scope in the photo, but one thing I did was I looked at the peak
on all three waveforms: Vo, V-, and V+. I noticed that during the
distortion V- was not equal to V+, so as expected the circuit is not
in the linear mode during the peak distortion interval. Then, sure
enough, after the peak distortion interval, the circuit transitions
into the linear mode where V- = V+.

Right, and that is the problem with that particular feedback
configuration, the oscillator has no breathing room in frequency, it has
to go non-linear. Most , if not all, linear oscillator configurations
settle into 0o loop phase by allowing the active element operating
frequency, and loop phase, to shift however minutely. Your circuit does
not do that because the active element phase shift is common to both
feedback paths and therefore cannot influence the differential feedback
in(+)-in(-) drive, at least in linear mode. Then because your 0o loop
phase frequency coincides with a zero drive in(+)-in(-)=0, you have
problems because even an ideal amplifier requires a finite non-zero
input to produce any kind of output. The end result is the circuit has
to go non-linear, clip, and produce harmonics for a non-zero feedback
self-sustaining drive. That circuits works *because* of the harmonics,
not despite them, it requires harmonics for its operation, it *has* to clip.

Don't write any more papers like that. Your use of undefined terminology
such as "inverse voltage dividers" and "duals" is at first mystifying
and then aggravating. Then the microscopic focus on some trivial
algebraic manipulations and the complete absence of any discussion
within the framework of conventional analysis of oscillator circuits
makes for a very bad presentation.
 
F

Fred Bloggs

Jan 1, 1970
0
Winfield said:
Actually, we've ramped up our work pace, and
plan on introducing H&H AoE 3rd-ed early in
2010. We also committed to this in an edit
of the Wikipedia "Art of Electronics" entry,
so now it must be true. :)

You should have broken the thing up into multiple volumes, we'll all be
dead by 2010...
 
V

Vladimir Vassilevsky

Jan 1, 1970
0
Our new 2-opamp "AoE oscillator" (a modified
Wien bridge made with two inverting opamps and
G=2) has about 0.0002% (2ppm) distortion, IIRC.

That is awesome. IIRC Williams's sinewave generator of four opamps claimed
the THD of 3 ppm.
How do you measure the distortion levels that low? The design of the notch
filter for the measurement should be as challenging as the design of the
oscillator itself.

Vladimir Vassilevsky
DSP and Mixed Signal Consultant
www.abvolt.com
 
W

Winfield

Jan 1, 1970
0
Fred said:
You should have broken the thing up into multiple volumes,
we'll all be dead by 2010...

Wait, what year is it now? I meant to say 2009.
 
B

BobW

Jan 1, 1970
0
Vladimir Vassilevsky said:
That is awesome. IIRC Williams's sinewave generator of four opamps claimed
the THD of 3 ppm.
How do you measure the distortion levels that low? The design of the notch
filter for the measurement should be as challenging as the design of the
oscillator itself.

Vladimir Vassilevsky
DSP and Mixed Signal Consultant
www.abvolt.com

It's easy. You build a couple hundred of them, sum their outputs, and THEN
measure the distortion.

Bob
 
J

Joerg

Jan 1, 1970
0
Winfield said:
Wait, what year is it now? I meant to say 2009.


So when good old analog TV goes kaputt and we finally have free time in
the evening, voila, a new AoE appears? Great!
 
S

Spehro Pefhany

Jan 1, 1970
0
So when good old analog TV goes kaputt and we finally have free time in
the evening, voila, a new AoE appears? Great!

Pre-orders, with a penalty clause? ;-)
 
W

Winfield Hill

Jan 1, 1970
0
MooseFET said:
Yes, it adds distortion for even fairly modest swings.
"deleveraging" the JFET with capacitors and not resistors like:

!
=== C1
!
!------+
Control-->! !
!-- === C2
! !
GND GND

helps.

It divides down the amplitude the JFET sees and C2 also
tends to short out the harmonics.

Interesting. We didn't choose to do that,
and instead placed the JFET directly in the
DC signal pathway. Hmm, would you say we
could have further reduced our distortion
below the 2ppm = 0.0002% we observed?
 
J

Jim Thompson

Jan 1, 1970
0
Interesting. We didn't choose to do that,
and instead placed the JFET directly in the
DC signal pathway. Hmm, would you say we
could have further reduced our distortion
below the 2ppm = 0.0002% we observed?

Win, How was that measured?

My old hp distortion analyzer (can't remember the model number) only
worked down to about 0.001% (IIRC).

...Jim Thompson
 
S

Spehro Pefhany

Jan 1, 1970
0
Like one bottle of Samuel Adams per week?

A wee dram of Glenfiddich per week would do just fine.
Best regards,
Spehro Pefhany
 
J

Joerg

Jan 1, 1970
0
Spehro said:
A wee dram of Glenfiddich per week would do just fine.


Oh yeah! After some of the booze went bad on our last move (across the
pond) we pretty much abandoned the occasional glass of Whiskey or Cognac.
 
F

Frank Buss

Jan 1, 1970
0
Jim said:
Win, How was that measured?

My old hp distortion analyzer (can't remember the model number) only
worked down to about 0.001% (IIRC).

0.0002% sounds like the -112 dB THD+N, at least for audio frequencies, of
really expensive products (but really cool, I'm working with one at a
clients site) like this one: http://ap.com/products/2700.htm
 
R

Rich Grise

Jan 1, 1970
0
Oh yeah! After some of the booze went bad on our last move (across the
pond) we pretty much abandoned the occasional glass of Whiskey or Cognac.

How does booze "[go] bad"?

Thanks,
Rich
 
J

Joerg

Jan 1, 1970
0
Rich said:
Oh yeah! After some of the booze went bad on our last move (across the
pond) we pretty much abandoned the occasional glass of Whiskey or Cognac.

How does booze "[go] bad"?

No idea but what we did is pack whatever was in our booze cabinet,
estimate how much is in the bottles and declare it all on the customs
forms. Meaning most of the bottles had been opened, of course. I guess
that and the salty air plus a northerly (frosty) ship route in January
didn't exactly help. On top of that the container must have been dropped
somewhere, a lot of stuff was squished.
 
C

Clifford Heath

Jan 1, 1970
0
Joerg said:
Rich said:
How does booze "[go] bad"?
No idea but...

Actually I think Rich was asking how the booze doesn't get
consumed immediately it's in your possession, instead being
kept for long enough for *anything* else to happen to it :)
 
P

Phil Hobbs

Jan 1, 1970
0
MooseFET said:
Mine doesn't clip at all when run on normal supply voltages. It makes
a sawtoothy waveform that doesn't get tot he rails.

Sure, but it clips on the inputs.

[...]
That's usually cad sulphide (CdS), cad selenide (CdSe), or an alloy of
the two. They're very sensitive, adequately slow for lots of things,
but unfortunately their photoresponse depends on their previous
history...would you believe 5:1 change in resistance for CdSe based on
how recently it's been in room light?

The ones I was speaking of are in a black housing. The no-light
resistance depends on what happened last week but the full light
resistance only really depends on the last minute or so.

If you keep them nearly fully illuminated, they're better behaved, it's
true. I'd still much rather use something else.
For oscillators that tends to
turn into lots and lots of amplitude drift unless you're careful.

You just tell the user to leave it on for a week before use. A
nonlinear feedback gets it settled more quickly. For large errors,
you turn the LED to full power or off.
;)
[....]
And you need to linearize it really carefully---Jim Williams's chapter
on ALC oscillators is a classic. (It's in one of his books, but I don't
have it handy.) Residual nonlinearity in the JFET (even with the 1:1
voltage divider between gate and drain) turns out to be one of the big
problems, iirc.

Yes, it adds distortion for even fairly modest swings. "deleveraging"
the JFET with capacitors and not resistors like:


!
=== C1
!
!------+
Control-->! !
!-- === C2
! !
GND GND

helps.

It divides down the amplitude the JFET sees and C2 also tends to short
out the harmonics.

Cute--that's like tapping a varactor down on a tank circuit. With an op
amp it isn't hard to know the total range of gains you can have, so you
can use a vernier control and get better nonlinearity.

Cheers,

Phil Hobbs
 
J

John Larkin

Jan 1, 1970
0
0.0002% sounds like the -112 dB THD+N, at least for audio frequencies, of
really expensive products (but really cool, I'm working with one at a
clients site) like this one: http://ap.com/products/2700.htm


What sort of harmonic distortion does a speaker have? I've seen
numbers like 6% called "good."

John
 
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