Heck of a way to run an oscillator?

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) ?

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.  ;-)

>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 

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

Kevin Aylward wrote:
> 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/