TCXO Clipped Sine Wave
 

Hi folks,
I would have to ask a clarification regard to the TCXO.
They are found with output TTL, HCMOS and CLIPPED SINE WAVE.
It is just with respect to this last type that I would want to have
elucidations on when it is convenient to employ it, which the advantages and
the disadvantages and which the extension of spectral harmonicas.
In synthesis, from the plan point of view, which are the motivations that
they make to incline towards a Clipped oscillator?

Anticipated thanks.

73's de IK6GQC Rocco

From: Mario Bros on Jul 17, 4:34 pm

Hi folks,
I would have to ask a clarification regard to the TCXO.
They are found with output TTL, HCMOS and CLIPPED SINE WAVE.
It is just with respect to this last type that I would want to have
elucidations on when it is convenient to employ it, which the advantages and
the disadvantages and which the extension of spectral harmonicas.

The TTL and HCMOS outputs will have (generally) square waves
which are rich in odd harmonic content. Clipped sine waves
have less overall harmonics...but the harmonic content depends
on the amount of clipping (presumably off the peak of the sine).


In synthesis, from the plan point of view, which are the motivations that
they make to incline towards a Clipped oscillator?

Depends entirely on the designer's choice. If this is a
purchased TCXO unit then a clipped sinewave output would
probably come through a buffer stage directly from the
internal oscillator output...which resembles a clipped
sine wave. For the purchased unit, having that output is
a convenience to the customer.

TTL and HCMOS outputs would be made from internal digital
devices, again a customer convenience to allow easy interface
to external TTL or HCMOS circuitry.

bit bit

The clipped sinewave is the simplest output for a TCXO, it's usually just a
capacitor connected between the emitter of the oscillator and the output pin.
You have to be careful what you connect to it, it's possible to throw the temp
compensation out of tolerance. Most CMOS PLL chips have a reference frequency
input that handles it well. If you're rolling your own PLL from SSI or MSI
chips, you probable want to build up a buffer to make the clipped sinewave into
TTL or HCMOS levels, or pay extra for a TCXO with the needed circuit built in.




On Sun, 17 Jul 2005 20:34:25 GMT, "Mario Bros" wrote:

Hi folks,
I would have to ask a clarification regard to the TCXO.
They are found with output TTL, HCMOS and CLIPPED SINE WAVE.
It is just with respect to this last type that I would want to have
elucidations on when it is convenient to employ it, which the advantages and
the disadvantages and which the extension of spectral harmonicas.
In synthesis, from the plan point of view, which are the motivations that
they make to incline towards a Clipped oscillator?

Anticipated thanks.

73's de IK6GQC Rocco

Thanks for the answers.
I have one TCXO 40Mhz 1Vp-p 10K//15pf Clipped Sine Wave.
My idea is of:
1) to gain 40Mhz Sine Wave through buffer with resonant circuit come
to an agreement for 2nd the IF (40.455)
2) to gain 20Mhz with a divisor x2 for the 16F877
3) ..and last.. to gain before 120Mhz (40x3) and then 480Mhz with
helical filter for clock the AD9954.
Thoughts are possible? It is one bad solutions??
Thank you again.



ha scritto nel messaggio
...
The clipped sinewave is the simplest output for a TCXO, it's usually just
a
capacitor connected between the emitter of the oscillator and the output
pin.
You have to be careful what you connect to it, it's possible to throw the
temp
compensation out of tolerance. Most CMOS PLL chips have a reference
frequency
input that handles it well. If you're rolling your own PLL from SSI or MSI
chips, you probable want to build up a buffer to make the clipped sinewave
into
TTL or HCMOS levels, or pay extra for a TCXO with the needed circuit built
in.




On Sun, 17 Jul 2005 20:34:25 GMT, "Mario Bros" wrote:

Hi folks,
I would have to ask a clarification regard to the TCXO.
They are found with output TTL, HCMOS and CLIPPED SINE WAVE.
It is just with respect to this last type that I would want to have
elucidations on when it is convenient to employ it, which the advantages
and
the disadvantages and which the extension of spectral harmonicas.
In synthesis, from the plan point of view, which are the motivations that
they make to incline towards a Clipped oscillator?

Anticipated thanks.

73's de IK6GQC Rocco

It all sounds possible to me. It is not very different from some of
the schemes we use commercially to generate internal frequencies (in
spectral analysis equipment). Your idea of good filtering at 480MHz
(and also, I hope, at 120MHz) is a good one, to keep out other
combinations of multiplication. The one other thing I would be careful
about is the phase noise of the oscillator. The AD9954 should be
capable of very good phase noise performance, but you MUST feed it a
clean reference to keep the output clean. I have recently tested some
TCXOs which are very stable and accurate, but whose phase noise is not
as good as I would really like. It is important to feed the oscillator
from a very clean supply, but that alone is not a guarantee of good
phase noise. See http://www.techlib.com/electronics/finesse.html for a
nice idea to make a very clean supply for circuits that draw
essentially constant current.

Cheers,
Tom

Hi Tom,
Thanks for the councils. An alternative could be an oscillator (480 Mhz)
with 1/4 coax resonator and IC
PLL TSA5511 I2C Bus clocked by 40Mhz/10 (4mhz)...
I must think to us...

Ciao IK6GQC Rocco

"K7ITM" ha scritto nel messaggio
oups.com...
It all sounds possible to me. It is not very different from some of
the schemes we use commercially to generate internal frequencies (in
spectral analysis equipment). Your idea of good filtering at 480MHz
(and also, I hope, at 120MHz) is a good one, to keep out other
combinations of multiplication. The one other thing I would be careful
about is the phase noise of the oscillator. The AD9954 should be
capable of very good phase noise performance, but you MUST feed it a
clean reference to keep the output clean. I have recently tested some
TCXOs which are very stable and accurate, but whose phase noise is not
as good as I would really like. It is important to feed the oscillator
from a very clean supply, but that alone is not a guarantee of good
phase noise. See http://www.techlib.com/electronics/finesse.html for a
nice idea to make a very clean supply for circuits that draw
essentially constant current.

Cheers,
Tom

Hi Rocco,

I would use the multiplication. Within the loop bandwidth of the PLL,
the phase noise will be determined by the crystal oscillator used as a
reference PLUS the noise contributed by the PLL chip itself (the phase
comparator and loop filter/amplifier), and outside the loop bandwidth,
it will be determined by the VCO used in the PLL. The important
thing, whether you use a PLL or multiplication, is to start with a
reference which has low phase noise. In fact, your TCXO may have good
phase noise...I don't know...I only know that some I've tested have not
been as clean as I'd like. But I'm also setting pretty high standards
for what I'm doing.

If I were in your shoes, I would build the multiplier system just as
you first described, and use the TCXO you have, and if it proves to be
too noisy (phase noise), then look for a better oscillator. If you can
make even a crude measurement of the oscillator's phase noise before
you start, that would be good, too, just to know where you are
starting. My comment in my earlier posting was just to make you aware
to look at phase noise, not to change the basic way you are going about
it.

Cheers,
Tom

Hi Tom,
my TCXO is GTXO-531 GOLLEDGE-UK product.

The parameters:
Clipped Sine Wave 1.0V p-p

Test Load 10k//10pF

Phase noise ):
-135dbc/Hz max

To this point I have 2 possible ways:

1) TCXO+HelicalFilter480Mhz+BFR96 Buffer+HelicalFilter480Mhz

2) TCXO+Ampli-Multiplier x3(120 Mhz)+Ampli-Multiplier x4(480Mhz)+Helical
Filter480Mhz

Also here, perhaps it is the case to make some test.
But, to the first impact, what you tasks?

73's de IK6GQC Rocco

"K7ITM" ha scritto nel messaggio
ups.com...
Hi Rocco,

I would use the multiplication. Within the loop bandwidth of the PLL,
the phase noise will be determined by the crystal oscillator used as a
reference PLUS the noise contributed by the PLL chip itself (the phase
comparator and loop filter/amplifier), and outside the loop bandwidth,
it will be determined by the VCO used in the PLL. The important
thing, whether you use a PLL or multiplication, is to start with a
reference which has low phase noise. In fact, your TCXO may have good
phase noise...I don't know...I only know that some I've tested have not
been as clean as I'd like. But I'm also setting pretty high standards
for what I'm doing.

If I were in your shoes, I would build the multiplier system just as
you first described, and use the TCXO you have, and if it proves to be
too noisy (phase noise), then look for a better oscillator. If you can
make even a crude measurement of the oscillator's phase noise before
you start, that would be good, too, just to know where you are
starting. My comment in my earlier posting was just to make you aware
to look at phase noise, not to change the basic way you are going about
it.

Cheers,
Tom

Hi Rocco,

The specified phase noise seems respectable to me. The ones I've been
looking at have some very nice characteristics that I need, but phase
noise about -115dBc/Hz at 1kHz offset.

Though it might look like more work, I would use (2). If I used (1),
I would have a buffer amplifier from the oscillator, driving something
to generate rich harmonics...since you need an even harmonic, use an
assymetrical harmonic generator. Square waves, for example, have
extremely low even-order harmonics ("theoretically" zero). But with
(2), you can use a square wave to get the 3rd harmonic, and not have to
filter much 2nd or 4th, since there is little of either of those in
your square wave. A relatively simple filter at 120MHz will suffice.
Then the 480MHz helical must attenuate only signals 120MHz away, not
signals 40MHz away like in (1).

At least, that is my take on it. There are tradeoffs, always, and
therefore you will see different designs to accomplish the same thing,
and all will work.

Cheers,
Tom

Ok Tom, just the second solution wants more job but creed also I that I am
the better .
Thanks still for the good suggestions.

73's de IK6GQC Rocco




"K7ITM" ha scritto nel messaggio
oups.com...
Hi Rocco,

The specified phase noise seems respectable to me. The ones I've been
looking at have some very nice characteristics that I need, but phase
noise about -115dBc/Hz at 1kHz offset.

Though it might look like more work, I would use (2). If I used (1),
I would have a buffer amplifier from the oscillator, driving something
to generate rich harmonics...since you need an even harmonic, use an
assymetrical harmonic generator. Square waves, for example, have
extremely low even-order harmonics ("theoretically" zero). But with
(2), you can use a square wave to get the 3rd harmonic, and not have to
filter much 2nd or 4th, since there is little of either of those in
your square wave. A relatively simple filter at 120MHz will suffice.
Then the 480MHz helical must attenuate only signals 120MHz away, not
signals 40MHz away like in (1).

At least, that is my take on it. There are tradeoffs, always, and
therefore you will see different designs to accomplish the same thing,
and all will work.

Cheers,
Tom