> wrote in message news:f94en916gp1dmlev5mh9a03ir205hppmgu@4ax.com...
>
> On Fri, 16 May 2014 14:31:31 +0100, "Kevin Aylward"
> <ExtractkevinRemove@kevinaylward.co.uk> wrote:
>
>> "Jim Thompson" wrote in message
>> news:vbj9n9p3gebit51f22nagtmlfo3uaebe7p@4ax.com...
>>
>> On Thu, 15 May 2014 09:29:42 +1000, Clifford Heath
>> <no.spam@please.net> wrote:
>>
>>>> On 15/05/14 04:43, haiticare2011@gmail.com wrote:
>>>>> On Wednesday, May 14, 2014 10:46:54 AM UTC-4, Joerg wrote:
>>>>>> Cheapskates use logic parts for that because you get a six-pack for a
>>>>> OK thanks. - What logic part would produce a sine wave output?
>>>
>>>> One that has no extra gain than what is required to start, so it's not
>>>> constantly slamming against the amplitude limit. One that limits its
>>>> amplitude into a resistive load. Or one fitted with an AGC circuit. It
>>>> helps if the clipping is somewhat soft. Look at the 74HCU04 inverters
>>>> for a start.
>>
>>> "Clipping" is for digital guys. AGC is necessary for low distortion.
>>
>>> Usually, however, clipping/clamping/limiting pretty much invariably
>>> produces
>>> the lowest phase noise. Simple principle, is the more devices, the more
>>> noise.
>>
>>> I have actually spent some time running sims on just about every
>>> reasonable
>>> oscillator topology you can imagine for phase noise. One transistor
>>> wins.
>
>> IIRC, Wes Hayward's book "Introduction to Radio Frequency Design"
>> contained a design around a long-tail pair that with suitable
>> component selection, the transistors wouldn't saturate.
>
> Sure, but something has to limit in an oscillator otherwise the output
> will get to trillions of volts and keep on increasing for ever.
>
Ask a politician, especially the ones current in power in the US. The
word "trillions" leaves them completely unfazed, they don't care. This
nonsense actually started already with the Romans and nothing was
learned from that. So why shouldn't the International Brotherhood of
Oscillators claim the same right?
:-)
[...]
--
SCNR, Joerg
http://www.analogconsultants.com/
Reply by Bill Sloman●May 17, 20142014-05-17
On Sunday, 18 May 2014 03:17:19 UTC+10, Kevin Aylward wrote:
> >wrote in message news:r9len996m7e1rbmk9hn3av20f1ccon0obu@4ax.com...
<snip>
> >Sure you can do all kinds of simulations, but do these have anything=20
> >to do with the real physical world (as in the climate change debate) ?=
=20
>=20
> Yes. Spice simulations for analog ASIC design and development are, =20
> essentially, nuts on, and indispensible. Billions and billions of real wo=
rld =20
> chips of 10,000s of different types, with 10,000s of transistors per asic=
, =20
> have been designed purely in the virtual world, in simulation. Period.
>=20
> Climate debate is several orders of magnitude different. It requires the =
=20
> solution of huge partial differential equation systems, not ordinary=20
> differential equations. It also needs data. One sensor to measure=20
> temperature, pressure, humidity etc every cubic mile is also a huge numbe=
r =20
> sensors. A wasp farting in china could cause a hurricane in Iceland. Ther=
e =20
> are just too many unknowns in climate simulations. ASICs are pretty well =
=20
> defined.
The "wasp farting in China" is better known as the "butterfly in Brazil" an=
d is a problem with weather simulations, rather than climate simulations.
The climate is essentially a mechanism for transporting heat from the equat=
or to the poles. The weather - which does a lot of the work - is chaotic, b=
ut its fluctuations are constrained by thermodynamics.
The biggest unknown in the picture is that a lot of heat is shifted by ocea=
n currents which do meander around a bit over periods of years - decades wi=
th the Atlantic Multidecadal Oscillation. The Argo buoys are collecting dat=
a on the ocean currents - both the surface currents and the deep return cur=
rents - but there are so far only about 3600 of them. The program started a=
round 2000, and the number of papers being published per year on the result=
s crept up to about 120 in 2009, then leapt to about 220 in 2010, creeping =
on up to about 280 in 2013.
http://www.argo.ucsd.edu/http://en.wikipedia.org/wiki/Argo_%28oceanography%29
--=20
Bill Sloman, Sydney
Reply by Kevin Aylward●May 17, 20142014-05-17
>wrote in message news:r9len996m7e1rbmk9hn3av20f1ccon0obu@4ax.com...
>
>>Use a resistor (noise source) followed by 10-100 sections of
>>amplifiers and band pass filters to simulate an oscillator startup.
>>Probing through these stages and you get a view how the oscillator
>>starts.
>
>>This can not be done on regular Spice. Resisters only generate noise in AC
>>simulations. There are some Spices with Transient noise extensions, but
>>this
>>still wont allow you to see what might happen in the real world regarding
>>noise.
>If your simulating tool is that stupid that it can't simulate a -174
>dBm/Hz insertion into each stage why use it ??
The transient and ac response in spice handles 100 of filters no problem,
you just can't feed it with a resistor to generate time based noise. If you
want time based noise, you would have to set up a PWL (piece wise linear
source) to model random noise. LTSpice will let you feed in a wav file, so
it that is loaded with Lady Ga Ga, it should be a reasonable approximation
to random noise. Why you would think Lady Ga Ga would be useful for analog
design is a certainly mystery though.
If your car can't go 200 mph, why use it?
>>The issue is that Spice is temperamental as to when it will start on its
>>own
>>due to numerical noise or needs a kick start.
>I am fully aware that any garden variety simulation package is not
>capable of handling the feedback situation correctly.
I have no idea what you are saying here.
Spice does AC and non-linear Transient analyses in enough detail to reliably
design oscillators in the virtual world, so as such it handles "the feedback
situation" fine.
However, to analyse phase noise, you need a steady state simulator i.e. PSS
and PSS Noise, as available in packages such as Cadence Spectre R.F. This
also costs lot of money. NGSpice has a developmental Periodic Steady State
option, but there are no cheap useable phase noise analysis programs in the
known universe.
>I just asked, how multiple in series non-feedback stages would behave.
Its not really a useful question. Oscillator design manages perfectly well
without modelling start-up under noise conditions.
>Sure you can do all kinds of simulations, but do these have anything
>to do with the real physical world (as in the climate change debate) ?
Yes. Spice simulations for analog ASIC design and development are,
essentially, nuts on, and indispensible. Billions and billions of real world
chips of 10,000s of different types, with 10,000s of transistors per asic,
have been designed purely in the virtual world, in simulation. Period.
Climate debate is several orders of magnitude different. It requires the
solution of huge partial differential equation systems, not ordinary
differential equations. It also needs data. One sensor to measure
temperature, pressure, humidity etc every cubic mile is also a huge number
sensors. A wasp farting in china could cause a hurricane in Iceland. There
are just too many unknowns in climate simulations. ASICs are pretty well
defined.
Kevin Aylward B.Sc.
www.kevinaylward.co.uk
www.anasoft.co.uk
Reply by ●May 17, 20142014-05-17
On Sat, 17 May 2014 04:05:24 -0500, "Tim Williams"
<tmoranwms@charter.net> wrote:
><upsidedown@downunder.com> wrote in message
>news:s65en99hfero6ircom5endqg8moamup96m@4ax.com...
>> This was of course a problems when using computers initially designed
>> in the 1950's to 1970s that did not support denormalized floating
>> point values. With the IEEE floating point standard, anything designed
>> after about after 1980 supports denorms.
>>
>> Even with IEEE floats/doubles, even adding a billion times a very
>> small value to a huge value does not change the result a bit. Thus, it
>> is still critical how the equations are evaluated. A mathematical
>> statement that looks very sensible, might not work properly on a
>> computer, so an alternative mathematical formula may have to be used
>> to work around the computer limitations.
>
>SPICE was a glimmer in some student's eye back in the 50s; it has more to
>do with the RELTOL parameter than the numerical stability of the
>underlying datatypes. By about twelve orders of magnitude.
>
>Was SPICE ever even developed on a platform that didn't support IEEE? I
>don't even know what they used. Something PDP?
>
SPICE? Perhaps not but there were other circuit simulators that did
run on computers without IEEE floats. Of course, there are other uses
for floats, too. ;-)
Reply by ●May 17, 20142014-05-17
On Sat, 17 May 2014 13:13:32 +0100, "Kevin Aylward"
<ExtractkevinRemove@kevinaylward.co.uk> wrote:
>>wrote in message news:73aen9h43rhohnjj85vcd4okdb9sktgd62@4ax.com...
>>>
>>>> This is not how an oscillator functions. An oscillator is not amplified
>>> >noise.
>>
>>>Oscillators build up from noise, though, and they do amplify the close-in
>>>noise very strongly.
>>
>>They do, but it is not necessary. A pulse exciting the tank will start the
>>oscillation, independent of noise.
>>
>>A pendulum clock does not start because of noise.
>
>>If you buy a pendulum clock and the transport company very hardly
>>slams it on your floor (power on transient) it might quite well start
>>ticking.
>
>>Use a resistor (noise source) followed by 10-100 sections of
>>amplifiers and band pass filters to simulate an oscillator startup.
>>Probing through these stages and you get a view how the oscillator
>>starts.
>
>This can not be done on regular Spice. Resisters only generate noise in AC
>simulations. There are some Spices with Transient noise extensions, but this
>still wont allow you to see what might happen in the real world regarding
>noise.
If your simulating tool is that stupid that it can't simulate a -174
dBm/Hz insertion into each stage why use it ??
>The issue is that Spice is temperamental as to when it will start on its own
>due to numerical noise or needs a kick start.
I am fully aware that any garden variety simulation package is not
capable of handling the feedback situation correctly.
I just asked, how multiple in series non-feedback stages would behave.
Sure you can do all kinds of simulations, but do these have anything
to do with the real physical world (as in the climate change debate) ?
Reply by Kevin Aylward●May 17, 20142014-05-17
>wrote in message news:73aen9h43rhohnjj85vcd4okdb9sktgd62@4ax.com...
>>
>>> This is not how an oscillator functions. An oscillator is not amplified
>> >noise.
>
>>Oscillators build up from noise, though, and they do amplify the close-in
>>noise very strongly.
>
>They do, but it is not necessary. A pulse exciting the tank will start the
>oscillation, independent of noise.
>
>A pendulum clock does not start because of noise.
>If you buy a pendulum clock and the transport company very hardly
>slams it on your floor (power on transient) it might quite well start
>ticking.
>Use a resistor (noise source) followed by 10-100 sections of
>amplifiers and band pass filters to simulate an oscillator startup.
>Probing through these stages and you get a view how the oscillator
>starts.
This can not be done on regular Spice. Resisters only generate noise in AC
simulations. There are some Spices with Transient noise extensions, but this
still wont allow you to see what might happen in the real world regarding
noise.
The issue is that Spice is temperamental as to when it will start on its own
due to numerical noise or needs a kick start. The Colpitts oscillator in my
SuperSpice examples, just starts on its own. In contrast, its often been
impossible getting Cadence PSS to start an oscillator when it has specific
functions in it to do so. It doesn't even allow you to have any time
changing sources on the schematic in PSS runs to start it.
So, there would probably be no realistic way to isolate start-up due to
transient noise and start-up due to, that's what it does without noise.
Noise is in the nV region. I wager in the majority of cases, moving bias
conditions on power up, overwhelmingly start up a real oscillator. In fact,
some oscillators won't start up at all on power on. Those ones also need a
lax removal man. Even with a slow PS, a real system has so many bits and
bobs like PORs and devices that there are going to be transient mV/ma
floating about that will break the symmetry from a 0=0 loop response.
Kevin Aylward B.Sc.
www.kevinaylward.co.uk
www.anasoft.co.uk - SuperSpice
Reply by ●May 17, 20142014-05-17
On Sat, 17 May 2014 09:55:10 +0100, "Kevin Aylward"
<ExtractkevinRemove@kevinaylward.co.uk> wrote:
>>"Phil Hobbs" wrote in message
>>news:7tydnQENnKRyquvOnZ2dnUVZ_rWdnZ2d@supernews.com...
>
>>
>>> >When first switched on, the amplifier input related thermal noise is
>>> amplified, Part of it is going to the frequency sensitive network,
>>>> which attenuates the lowest and highest frequencies, leaving a broad
>>>> peak around the resonant frequency.
>>
>>> If this were necessary, than Spice simulations would have problems as
>>> they don't have noise!
>
>>They do, actually, just like all other numerical simulators. It comes from
>>roundoff.
>
>You missed my bit about "numerical noise" then ?
>
>>
>>> This is not how an oscillator functions. An oscillator is not amplified
>> >noise.
>
>>Oscillators build up from noise, though, and they do amplify the close-in
>>noise very strongly.
>
>They do, but it is not necessary. A pulse exciting the tank will start the
>oscillation, independent of noise.
>
>A pendulum clock does not start because of noise.
If you buy a pendulum clock and the transport company very hardly
slams it on your floor (power on transient) it might quite well start
ticking.
Use a resistor (noise source) followed by 10-100 sections of
amplifiers and band pass filters to simulate an oscillator startup.
Probing through these stages and you get a view how the oscillator
starts.
Reply by Tim Williams●May 17, 20142014-05-17
<upsidedown@downunder.com> wrote in message
news:s65en99hfero6ircom5endqg8moamup96m@4ax.com...
> This was of course a problems when using computers initially designed
> in the 1950's to 1970s that did not support denormalized floating
> point values. With the IEEE floating point standard, anything designed
> after about after 1980 supports denorms.
>
> Even with IEEE floats/doubles, even adding a billion times a very
> small value to a huge value does not change the result a bit. Thus, it
> is still critical how the equations are evaluated. A mathematical
> statement that looks very sensible, might not work properly on a
> computer, so an alternative mathematical formula may have to be used
> to work around the computer limitations.
SPICE was a glimmer in some student's eye back in the 50s; it has more to
do with the RELTOL parameter than the numerical stability of the
underlying datatypes. By about twelve orders of magnitude.
Was SPICE ever even developed on a platform that didn't support IEEE? I
don't even know what they used. Something PDP?
Tim
--
Seven Transistor Labs
Electrical Engineering Consultation
Website: http://seventransistorlabs.com
Reply by Kevin Aylward●May 17, 20142014-05-17
>"Phil Hobbs" wrote in message
>news:7tydnQENnKRyquvOnZ2dnUVZ_rWdnZ2d@supernews.com...
>
>> >When first switched on, the amplifier input related thermal noise is
>> amplified, Part of it is going to the frequency sensitive network,
>>> which attenuates the lowest and highest frequencies, leaving a broad
>>> peak around the resonant frequency.
>
>> If this were necessary, than Spice simulations would have problems as
>> they don't have noise!
>They do, actually, just like all other numerical simulators. It comes from
>roundoff.
You missed my bit about "numerical noise" then ?
>
>> This is not how an oscillator functions. An oscillator is not amplified
> >noise.
>Oscillators build up from noise, though, and they do amplify the close-in
>noise very strongly.
They do, but it is not necessary. A pulse exciting the tank will start the
oscillation, independent of noise.
A pendulum clock does not start because of noise.
Well....
Although the paper correctly points out non-linear capacitors, implying non
linear time constants, as a cause of up conversion of low frequency noise,
it incorrectly states/implies that "pumping" action of the oscillator also
generates up conversion noise. Simple mixing does not produce phase noise,
which is what usually matters, despite the creation of up converted
amplitude noise.
Unfortunately that paper perpetuates the myth as to the value of the
Hajimiri- Lee ISF method. The HL method is wrong, and is completely useless
with regard to up conversion, producing errors easily at the 50 dBc level.
Its 1/f up conversion formula is wrong. Period.
This is all shown here:
http://www.kevinaylward.co.uk/ee/phasenoise/phasenoise.html
In particular:
http://www.kevinaylward.co.uk/ee/phasenoise/LTV.xht
Shows why the HL ISF theory is wrong in a manner much more accessible than
A.Dimre's highly mathematical paper I reference.
http://www.kevinaylward.co.uk/ee/phasenoise/OrthogonalPerturbation.xht
Directly demonstrates the invalidity of orthogonal perturbation (hitting the
tank at peaks and zero x-ings for those more mathematically challenged)
parroted in the lec 22 paper.
http://www.kevinaylward.co.uk/ee/phasenoise/PhaseNoiseOscillators.xht
Shows in more detail why HL is wrong, and what is the correct mechanism for
up-conversion of phase noise.
A. Dimir trashed the HL paper pretty much immediately it came out. Its
pretty stunning why such a flawed, unusable approach is still being taught
in universities.
I summarise:
"The HL-LTV method can be shown to be valid for spherical chickens in a
vacuum"
>Oscillators will work without any noise at all. If the system is
>> unstable, any initial DC condition that does not sit at a
>> metastable/unstable equilibrium point will ensure that signals start
>> changing in such a way as to head toward amplifier limiting. This may
>> result in either steady state or chaotic oscillations.
>Not necessarily. There has to be some nonzero signal in the band where the
>oscillator is unstable.
Ho...mm humm... ok to be precise, if the initial DC condition is sitting in
the already mentioned unstable oscillator system at such a point that it can
transverses to the designated limit cycle. Sure, the system might be
unstable for various DC points, but actually sit at a point that is locally
stable.
"Band" implies frequency. Frequency is irrelevant. Instability has nothing
to do with frequency. A chaotic oscillator has no fixed frequency. Only in
the pathological sense that an impulse may be analysed as a continuous
spectrum is it arguable that there is a frequency in the band where the
oscillator is unstable. Even then, this is still dubious for chaotic
oscillators.
>
>> Usually a clean (power on) startup pulse will excite the tank, and it is
>> this ringing that generates the oscillation build-up, just as it does in
> >the real world.
>Sometimes. It's easily possible that the power-up transient is smooth
>enough that its spectrum dies away to well below device noise in the
>relevant band.
Possible, but clutching at straws me thinks.
>Good oscillators are designed so that that is the case, because otherwise
>their supply rejection would stink.
Sure, precision oscillators need need very good PSRR. Mine have 100db @
150mv drop out :-)
You walked into that one...
http://www.rakon.com/products/families/ocxo-ocso - Mercury
Note, a one transistor oscillator has 10,000 supporting transistors...LDO,
LNBG, Function Generators, Constant power circuits, limiters, LN dividers
etc....
Good oscillators are also designed to start as fast as possible.
>
> This bit about noise starting up the circuit is often quoted in the
> books, and er... ah...somewhat mindlessly repeated, but is very dubious.
>
> Theoretically numerical noise could start a simulation, and sometimes
> does, but it is not necessary.
>Arbitrarily sharp power-up steps kickstart the oscillation in simulation,
>maybe, but building up from noise will occur very often in real life,
This missies the point being made. An unstable system is an unstable system.
Noise has nothing to do with it. An oscillator in not amplified noise
despite that fact that it may well amplifier noise.
Kevin Aylward B.Sc.
www.kevinaylward.co.uk
www.anasoft.co.uk - SuperSpice
Reply by ●May 17, 20142014-05-17
On Fri, 16 May 2014 17:19:41 -0500, "Tim Williams"
<tmoranwms@charter.net> wrote:
>"Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message
>news:7tydnQENnKRyquvOnZ2dnUVZ_rWdnZ2d@supernews.com...
>>> If this were necessary, than Spice simulations would have problems as
>>> they don't have noise!
>>
>> They do, actually, just like all other numerical simulators. It comes
>> from roundoff.
>
>It is necessary, and a problem, from time to time.
>
>But this is also *because of* roundoff.
>
>If the derivatives are close enough to zero, they'll be approximated *to
>zero*, the timestep cranks up to max and the simulation skims along,
>blissfully unaware of its own instability.
>
>Tim
This was of course a problems when using computers initially designed
in the 1950's to 1970s that did not support denormalized floating
point values. With the IEEE floating point standard, anything designed
after about after 1980 supports denorms.
Even with IEEE floats/doubles, even adding a billion times a very
small value to a huge value does not change the result a bit. Thus, it
is still critical how the equations are evaluated. A mathematical
statement that looks very sensible, might not work properly on a
computer, so an alternative mathematical formula may have to be used
to work around the computer limitations.