Colpitts oscillators

[Vladimir Vassilevsky]

There are very few good RF books and IMHO the best
are from the ham radio community. I could recommend a some really good
ones but except for the ARRL Handbook the ones here aren't in English.

The design of the high stability and low noise oscillators is the
special sort of knowledge, and there are quite many books about that.
This stuff is covered well in the professional books on the frequency
synthesizers.

SPICE and theoretical approaches are fine but at the end of the day
you'll have to fire up the old Weller and experiment. Find out the
boundaries, stability ranges etc. I found that transistor models for
SPICE aren't the cat's meouw when you approach the UHF range and above.

The SPICE model of transistor is OK, but it has somewhat 50 or so
parameters. Of course, most of those parameters are not even specified
by the manufacturers. There is also other problem with SPICE simulation
of RF: damn slow. The timestep is determined by the carrier frequency,
and the duration of a run is determined by the modulation.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

 

[Joerg]

You must be much younger than you appear.

What's wrong with just getting a higher-level education, such that you
can make _informed_ decisions, rather than just a couple of years of job
training and basket-weaving?

Nothing wrong with that. But isn't that supposed to be complete at the
end of high school? There is an alarming number of "kids" in our area
who haven't made up their minds while pushing 30 (!).

 

[Joerg]

The design of the high stability and low noise oscillators is the
special sort of knowledge, and there are quite many books about that.
This stuff is covered well in the professional books on the frequency
synthesizers.

Ok, there is indeed another good one here on the shelf and it's in
English: Rohde's "Communications Receivers", McGraw-Hill. Top notch
stuff. If he just hadn't picked that ugly bonbon-green for the cover.

The SPICE model of transistor is OK, but it has somewhat 50 or so
parameters. Of course, most of those parameters are not even specified
by the manufacturers. There is also other problem with SPICE simulation
of RF: damn slow. The timestep is determined by the carrier frequency,
and the duration of a run is determined by the modulation.

Yup. I remember a guy who smoked out a Pentium doing that.

 

[Joel Koltner]

Ok, there is indeed another good one here on the shelf and it's in English:
Rohde's "Communications Receivers", McGraw-Hill. Top notch stuff. If he just
hadn't picked that ugly bonbon-green for the cover.

Is that an older edition of
http://www.amazon.com/Communication...=sr_1_1?ie=UTF8&s=books&qid=1199833388&sr=1-1 ?
Because I don't see any green on the cover there...

---Joel

 

[Joerg]

Is that an older edition of
http://www.amazon.com/Communication...=sr_1_1?ie=UTF8&s=books&qid=1199833388&sr=1-1 ?
Because I don't see any green on the cover there...

---Joel

Mine is this one:
http://www.amazon.com/Communication...=sr_1_1?ie=UTF8&s=books&qid=1199834179&sr=1-1

Different Co-Author and 1988 edition. I never keep the dust covers,
maybe that had a different color. Chapter 7 goes into great detail about
spectral purity of oscillators including amplitude stabilization.

 

[Rich Grise]

Nothing wrong with that. But isn't that supposed to be complete at the
end of high school? There is an alarming number of "kids" in our area
who haven't made up their minds while pushing 30 (!).

Well, I can only speak for myself, of course, but my college experience
was even worse than grade school, when it comes to being surrounded by
belligerent assholes.

After two quarters of the same crap I'd just endured for the past 12
years, I decided, "**** this shit", and dropped out (which was
surprisingly easy - the gal put "not going" on the form, and I was
free), and joined the US Air Force.

That's where I got a _REAL_ education, that actually had a tangible
relationship to real life.

Thanks!
Rich

 

[Joerg]

Well, I can only speak for myself, of course, but my college experience
was even worse than grade school, when it comes to being surrounded by
belligerent assholes.

After two quarters of the same crap I'd just endured for the past 12
years, I decided, "**** this shit", and dropped out (which was
surprisingly easy - the gal put "not going" on the form, and I was
free), and joined the US Air Force.

That's where I got a _REAL_ education, that actually had a tangible
relationship to real life.

Mine was in the army. The drill sergeant said, or rather, hollered:
"ATTEEEENSHUNN! As civilians you came, as men you will leave! Now lemme
tell you about some of the ground rules and what happens if you don't
...." Then came the tough stuff, but you've undoubtedly gone through that
as well.

 

[Richard The Dreaded Libertarian]

I think that was already a given at the time they wrote it, so no one thought
specifically to write it down.

Well, if it isn't written down,it isn't in the Constitution.

And attitudes like yours are PRECISELY why the Constitution is needed.

Are you a universal healthcare supporter, Rich?

No. I am committed to opposing socialism in any guise.

When people start going down
the path of "universal healthcare is socialism!" -- which, to a certain
extent, sure, it is

Yes, the extent 100%.


-- I like to point out to them how much other socialism

we've had in this country for many decades if not centuries...

OK, so you're saying that, since 90% of the government is fucked up and
we're putting up with it, that we should **** up the rest of it and make
people suck it up and submit to the socialists?

Two wrongs piled on top of each other don't make a right.

Do you really want the USA to follow the path of the Soviet Union, which,
BTW, destroyed itself by going down the socialist primrose path?

Do you really, really _LIKE_ having 1/3 of your income taken away from
you so some "elected" authority can hand it over to people who don't
deserve it? To people who are too stupid, lazy, or negilgent to see to
their own well-being?

That's the thing about Liberty - it has a really scary side - when you're
free, you have to make your own decisions and bear the consequences
yourself.

I saw snippets of that commie M.Moore's flick "Sicko". The clip that stood
out in my mind was the idiot who cut off two of his fingers on a table
saw, and couldn't afford to get them sewed back on. Apparently, according
to that commie, you should take food from your family's mouths to pay this
asshole to save him from the consequences of his own negligence?

Man, back in the old days, when we had to walk 50 miles uphill both ways
through 20 feet of snow and all we had was clay tablets, "Freedom"
actually meant something. I was very young when my Dad taught me NOT TO
CUT OFF MY OWN FINGERS ON A TABLE SAW!!

I have absolutely no patience for communists, socialists, parasites, or
their sympathizers.

If you want socialist medicine, move to one of the socialist countries,
and good luck.

Thanks,
Rich

 

[Joel Koltner]

Mine is this one:

....

Thanks Joerg.

Surprising how many people have written books on receiver design... I can
definitely see the attraction.

 

[Joel Koltner]

Hi Rich,

Well, if it isn't written down,it isn't in the Constitution.
And attitudes like yours are PRECISELY why the Constitution is needed.

That was meant to be a joke, son!

OK, so you're saying that, since 90% of the government is fucked up and
we're putting up with it, that we should **** up the rest of it and make
people suck it up and submit to the socialists?

I'm saying that there's ample evidence that the nation's citizens support a
certain level of socialism in this country, and while universal health care is
a pretty heavyweight addition to that level, I'm not at all surprised that
having it is such a popular "request" these days. The heathcare system *is*
pretty screwed up in this country, and while I can't say I've studied the
problem enough to know what the *best* response is, it's easy to point to,
e.g., Europe and say, "see, look, they have it and it solves a certain problem
and they haven't totally self-destructed... maybe that's not such a bad idea?"

Do you really, really _LIKE_ having 1/3 of your income taken away from
you so some "elected" authority can hand it over to people who don't
deserve it? To people who are too stupid, lazy, or negilgent to see to
their own well-being?

How to distribute taxes only to "deserving" people or causes is an impossible
problem, since obviously in any reasonably sized group of people you'll never
have agreement on who deserves it, how lazy or negligent is "too" lazy or
negligent, how much people are stupid based on their genetics vs. the effort
they make at life, etc.

I saw snippets of that commie M.Moore's flick "Sicko". The clip that stood
out in my mind was the idiot who cut off two of his fingers on a table
saw, and couldn't afford to get them sewed back on. Apparently, according
to that commie, you should take food from your family's mouths to pay this
asshole to save him from the consequences of his own negligence?

Umm... if you watch that scene again, I think you'll find that the guy paid
MUCH more to have one finger re-attached in the U.S. than he would have paying
100% of the bill in Europe (no tax subsidies whatsoever). So even if you
don't think the taxpayers should be paying to re-attach peoples' fingers,
hopefully you'd agree that it still demonstrates a problem in our current
healthcare system as I previously mentioned.

I was very young when my Dad taught me NOT TO
CUT OFF MY OWN FINGERS ON A TABLE SAW!!

It's not like the guy *meant* to saw off his fingers. I mean, sure, he
was pretty negligent, but ALL OF US have been neglient at times when it comes
to "safety" and usually you get lucky and there's no harm done, but sometimes
you don't...

---Joel

 

[Joerg]

Joel Koltner wrote:

[...]

I'm saying that there's ample evidence that the nation's citizens support a
certain level of socialism in this country, and while universal health care is
a pretty heavyweight addition to that level, I'm not at all surprised that
having it is such a popular "request" these days. The heathcare system *is*
pretty screwed up in this country, ...

Good point. Our current health system is facing two major issues:

a. It is hyper-inflationary.

b. Once you or a family member have the slightest pre-existing
condition, took anti-depressants many moons ago or whatever, you become
a pariah. De-facto uninsurable even if you have the money. Unless you
are lucky to have an employer with a group plan, a dwindling species at
least among small business operators.

[...]

 

[Jim Thompson]

Joel Koltner wrote:

[...]

I'm saying that there's ample evidence that the nation's citizens support a
certain level of socialism in this country, and while universal health care is
a pretty heavyweight addition to that level, I'm not at all surprised that
having it is such a popular "request" these days. The heathcare system *is*
pretty screwed up in this country, ...

Good point. Our current health system is facing two major issues:

a. It is hyper-inflationary.

b. Once you or a family member have the slightest pre-existing
condition, took anti-depressants many moons ago or whatever, you become
a pariah. De-facto uninsurable even if you have the money. Unless you
are lucky to have an employer with a group plan, a dwindling species at
least among small business operators.

[...]

Or live long enough ;-) My tab for the hip replacement... $156

...Jim Thompson

 

[Joerg]

Joel Koltner wrote:

[...]

I'm saying that there's ample evidence that the nation's citizens support a
certain level of socialism in this country, and while universal health care is
a pretty heavyweight addition to that level, I'm not at all surprised that
having it is such a popular "request" these days. The heathcare system *is*
pretty screwed up in this country, ...

Good point. Our current health system is facing two major issues:

a. It is hyper-inflationary.

b. Once you or a family member have the slightest pre-existing
condition, took anti-depressants many moons ago or whatever, you become
a pariah. De-facto uninsurable even if you have the money. Unless you
are lucky to have an employer with a group plan, a dwindling species at
least among small business operators.

[...]

Or live long enough ;-) My tab for the hip replacement... $156

Would Medicare alone have covered it or did your extra coverage kick in?

Problem with the uninsured is that that's the group they seem to pummel
with super-high billing, maybe to offset the paltry or non-existent
profits when having to treat Medicare patients. Probably hoping that one
of the bills sticks, where they find someone who has some money and
where they can send the goons out to get it. A friend just received the
bill for a simple MRI. Well north of $2k :-(

 

[Jim Thompson]

Joel Koltner wrote:

[...]

I'm saying that there's ample evidence that the nation's citizens support a
certain level of socialism in this country, and while universal health care is
a pretty heavyweight addition to that level, I'm not at all surprised that
having it is such a popular "request" these days. The heathcare system *is*
pretty screwed up in this country, ...

Good point. Our current health system is facing two major issues:

a. It is hyper-inflationary.

b. Once you or a family member have the slightest pre-existing
condition, took anti-depressants many moons ago or whatever, you become
a pariah. De-facto uninsurable even if you have the money. Unless you
are lucky to have an employer with a group plan, a dwindling species at
least among small business operators.

[...]

Or live long enough ;-) My tab for the hip replacement... $156

Would Medicare alone have covered it or did your extra coverage kick in?

Problem with the uninsured is that that's the group they seem to pummel
with super-high billing, maybe to offset the paltry or non-existent
profits when having to treat Medicare patients. Probably hoping that one
of the bills sticks, where they find someone who has some money and
where they can send the goons out to get it. A friend just received the
bill for a simple MRI. Well north of $2k :-(

What troubles me... it was such a high tab, >$80K total.

Yet the Medicare and Mutual of Omaha reports are fishy... I can't
figure out who paid what.

I only know of the $156 because a testing lab sent me a separate bill
labeled "Not covered by Medicare... tests repeated in less than one
year"

...Jim Thompson

 

[Joerg]

On Tue, 08 Jan 2008 18:15:09 -0800, Joerg

Joel Koltner wrote:

[...]

I'm saying that there's ample evidence that the nation's citizens support a
certain level of socialism in this country, and while universal health care is
a pretty heavyweight addition to that level, I'm not at all surprised that
having it is such a popular "request" these days. The heathcare system *is*
pretty screwed up in this country, ...
Good point. Our current health system is facing two major issues:

a. It is hyper-inflationary.

b. Once you or a family member have the slightest pre-existing
condition, took anti-depressants many moons ago or whatever, you become
a pariah. De-facto uninsurable even if you have the money. Unless you
are lucky to have an employer with a group plan, a dwindling species at
least among small business operators.

[...]
Or live long enough ;-) My tab for the hip replacement... $156

Would Medicare alone have covered it or did your extra coverage kick in?

Problem with the uninsured is that that's the group they seem to pummel
with super-high billing, maybe to offset the paltry or non-existent
profits when having to treat Medicare patients. Probably hoping that one
of the bills sticks, where they find someone who has some money and
where they can send the goons out to get it. A friend just received the
bill for a simple MRI. Well north of $2k :-(

What troubles me... it was such a high tab, >$80K total.

Might be the usual inflated bill where Medicare then pays 10% or so and
they call it quits.

Yet the Medicare and Mutual of Omaha reports are fishy... I can't
figure out who paid what.

That is exactly the third problem, lack of transparency. How can a
patient be expected to be frugal when they don't even know what stuff
costs? And don't try to ask up front because the information can be
total bogus. I did that and the bill was three (!) times what had been
quoted. Of course, while a contractor would have the license board
breathing down his neck this behavior is considered perfectly fine in
the medical world. I lodged a formal complaint with the state and the

 

[Robert Baer]

I've did some troubleshooting of a common-collector 3rd-hamornic crystal
Colpitts oscillator this weekend, discovering that my emitter inductor (used
to force harmonic operation) was too big, thereby sometimes allowing
oscillation at the fundamental rather than the harmonic. In tracking this
down, I re-read the relevant sections of Matthys's "Crystal Oscillator
Circuits" and Hayward's "Radio Frequency Design." The two of them have
somewhat different focuses, but I find it interesting that when it comes to
the two capacitors in the "Colpitts network" Matthys says, "There is no
requirement for any specific ratio of C1 [the base-emitter cap] to C2
[emitter-ground cap]." While arguably an entirely true statement, in contrast
Hayward spends plenty of time discussing the ratio, even going so far as to
create a graph of the oscillator's loop gain and phase as a function of one
capacitor's value vs. the other, with the intent of letting you choose a gain
that's not too much bigger than one so as try to minimize output waveform
distortion.

Anyone have some thoughts on this? I have a suspicion that Hayward addresses
the topic because he's trying hard to keep the transistor in small-signal
(active) mode as much as possible, where Matthys right off-the-bat says that
you can expect your transistor to be off ~80% of the time, saturated ~10% of
the time, and operating actively ~10% of the time.

Matthys also suggests that the C2 (base-emitter) cap should generally be
"between 40-70pF," whereas Hayward likes 100pF (and generally prefers larger
caps... which I suspect reflects his emphasis on oscillators down at HF
whereas Matthys often wanders into VHF territory).

I'm interested in whether those of you who design such oscillators tend to do
it more from heuristic techniques (I have another book which suggests very
heuristical approaches, e.g., "make the ratio of C2:C1 about 4:1") and expect
to do a bit of tweaking on a bench vs. simulating the entire thing in SPICE
first and expecting that it'll work just ducky on a bench. Also... when
you're looking at a Colpitts oscillator, what do you tend to "see?" The most
"natural" representation to *me* of the various configurations are:

Common base: Transistor thought of as a gain=1 emitter follower, and you're
chasing loop gain. Hayward uses this point of analysis (and points out that
it is, of course, an arbitrary choice.) I can see it readily as a negative
resistance too.
Common collector: Transistor thought of as a negative resistance, and with a
few quick network transformations you're back to an RLC network where the
transistor's negative R cancels our the load R. (Plastonek takes this
approach. Matthys does loop gain analysis with just a bit of hand-waving
thrown in. Hayward points out that all the topologies are really the same,
you're just shifting the ground reference around...)
Common emitter: Classic loop gain approach, with transistor base being a
resistive load and the collector being a current source driving a pi network.
Everyone seems to do it this way, since it's perhaps the most intuitively
obvious topology and it's easy to analyze.

I also find it interestingly the Hayward's book -- aimed at hams -- seems to
have one of the most comprehensive discussions of all this. The Art of
Electronics only has a page on it!

---Joel

I have never seen much less heard of either of those authors,but from
your description, i would most prefer Hayward because of the C1/C2
analysis is more instructive - probably allows one to go to the
"extreme" of tha "class C" operation previously mentioned.
How about a common emitter, grounded collector design running at
minimum distortion with maximum (transistor) temp stability and taking
the output via a lo-Z tap on a resonant LC tank at the collector?
Totally load independent...

 

[Richard Henry]

message My tab for the hip replacement... $156

Socialist weenie.

 

[Michael A. Terrell]

Nothing wrong with that. But isn't that supposed to be complete at the
end of high school? There is an alarming number of "kids" in our area
who haven't made up their minds while pushing 30 (!).

I knew I would work in electronics when I was in Jr. High School,
back in the mid '60s. I figured I might as well, since I was already
repairing car radios and phonographs, after school.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[T]

Joel Koltner wrote:

[...]

I'm saying that there's ample evidence that the nation's citizens support a
certain level of socialism in this country, and while universal health care is
a pretty heavyweight addition to that level, I'm not at all surprised that
having it is such a popular "request" these days. The heathcare system *is*
pretty screwed up in this country, ...

Good point. Our current health system is facing two major issues:

a. It is hyper-inflationary.

b. Once you or a family member have the slightest pre-existing
condition, took anti-depressants many moons ago or whatever, you become
a pariah. De-facto uninsurable even if you have the money. Unless you
are lucky to have an employer with a group plan, a dwindling species at
least among small business operators.

[...]

I had my eyes opened to the root of the probelm a few years ago. Part of
it is becuase you have so many different insurers now, doctors are
forced to use a billing company if they expect to be paid.

So now you have two layers making money, the insurance companies and the
billing companies.

Two layers of absolute greed.

 

[MooseFET]

I've did some troubleshooting of a common-collector 3rd-hamornic crystal
Colpitts oscillator this weekend, discovering that my emitter inductor (used
to force harmonic operation) was too big, thereby sometimes allowing
oscillation at the fundamental rather than the harmonic. In tracking this
down, I re-read the relevant sections of Matthys's "Crystal Oscillator
Circuits" and Hayward's "Radio Frequency Design." The two of them have
somewhat different focuses, but I find it interesting that when it comes to
the two capacitors in the "Colpitts network" Matthys says, "There is no
requirement for any specific ratio of C1 [the base-emitter cap] to C2
[emitter-ground cap]." While arguably an entirely true statement, in contrast
Hayward spends plenty of time discussing the ratio, even going so far as to
create a graph of the oscillator's loop gain and phase as a function of one
capacitor's value vs. the other, with the intent of letting you choose a gain
that's not too much bigger than one so as try to minimize output waveform
distortion.

Anyone have some thoughts on this? I have a suspicion that Hayward addresses
the topic because he's trying hard to keep the transistor in small-signal
(active) mode as much as possible, where Matthys right off-the-bat says that
you can expect your transistor to be off ~80% of the time, saturated ~10% of
the time, and operating actively ~10% of the time.

Matthys also suggests that the C2 (base-emitter) cap should generally be
"between 40-70pF," whereas Hayward likes 100pF (and generally prefers larger
caps... which I suspect reflects his emphasis on oscillators down at HF
whereas Matthys often wanders into VHF territory).

I'm interested in whether those of you who design such oscillators tend to do
it more from heuristic techniques (I have another book which suggests very
heuristical approaches, e.g., "make the ratio of C2:C1 about 4:1") and expect
to do a bit of tweaking on a bench vs. simulating the entire thing in SPICE
first and expecting that it'll work just ducky on a bench. Also... when
you're looking at a Colpitts oscillator, what do you tend to "see?" The most
"natural" representation to *me* of the various configurations are:

Common base: Transistor thought of as a gain=1 emitter follower, and you're
chasing loop gain. Hayward uses this point of analysis (and points out that
it is, of course, an arbitrary choice.) I can see it readily as a negative
resistance too.
Common collector: Transistor thought of as a negative resistance, and with a
few quick network transformations you're back to an RLC network where the
transistor's negative R cancels our the load R. (Plastonek takes this
approach. Matthys does loop gain analysis with just a bit of hand-waving
thrown in. Hayward points out that all the topologies are really the same,
you're just shifting the ground reference around...)
Common emitter: Classic loop gain approach, with transistor base being a
resistive load and the collector being a current source driving a pi network.
Everyone seems to do it this way, since it's perhaps the most intuitively
obvious topology and it's easy to analyze.

I also find it interestingly the Hayward's book -- aimed at hams -- seems to
have one of the most comprehensive discussions of all this. The Art of
Electronics only has a page on it!

---Joel

I have never seen much less heard of either of those authors,but from
your description, i would most prefer Hayward because of the C1/C2
analysis is more instructive - probably allows one to go to the
"extreme" of tha "class C" operation previously mentioned.
How about a common emitter, grounded collector design running at
minimum distortion with maximum (transistor) temp stability and taking
the output via a lo-Z tap on a resonant LC tank at the collector?
Totally load independent...

It is not totally independent but fairly good.

You can also frequency multiply in the collector section. This makes
the operating frequency even more load independent. The impedance
between the emitter and base at the harmonic is very low so anything
that transfers back sees nearly a dead short. It works best if the
oscillator is "gm reduction" or AGC controlled and doesn't bottom.