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Guest

Sat Feb 09, 2019 12:45 pm   



Could some electronics guru here help clarify the following.
Small signal S parameter amalysis is based on small signal
levels and a linearized cirucuit, with a DC operating point(bias) condition.
Large signal S parameter extends this scheme to high power
operating conditions of non-linear devices, where the
assumptions of small signal do not hold. Large signal
S parameter scheme is based on harmonic balance, which
involves analyzing the signals in the frequency domain.
i.e., Forier transforms.
Both schemes use a 2 port network, with the signal entering
at the inpit("from") port and coming out at the output("to")
port.
With these in mind, what about oscillators ? These are
one port networks, with a 2 port component (amplifier)
in it. So are large and small signal S parameters
applicable to oscillators ? Amplifiers are ripe for
large signal S parameters. For that matter, are the S
parameters quoted for older RF|micrwave transistors
small or karge signal S parameters ?

All hints/suggestions are welcome. Thanks in advance.

Gerhard Hoffmann
Guest

Sat Feb 09, 2019 1:45 pm   



Am 09.02.19 um 12:36 schrieb dakupoto_at_gmail.com:
Quote:
Could some electronics guru here help clarify the following.
Small signal S parameter amalysis is based on small signal
levels and a linearized cirucuit, with a DC operating point(bias) condition.
Large signal S parameter extends this scheme to high power
operating conditions of non-linear devices, where the
assumptions of small signal do not hold. Large signal
S parameter scheme is based on harmonic balance, which
involves analyzing the signals in the frequency domain.
i.e., Forier transforms.
Both schemes use a 2 port network, with the signal entering
at the inpit("from") port and coming out at the output("to")
port.
With these in mind, what about oscillators ? These are
one port networks, with a 2 port component (amplifier)
in it. So are large and small signal S parameters
applicable to oscillators ? Amplifiers are ripe for
large signal S parameters. For that matter, are the S
parameters quoted for older RF|micrwave transistors
small or karge signal S parameters ?

All hints/suggestions are welcome. Thanks in advance.


Yes. It's currently Gospel that large signal s-parameters are
required for oscillator design. Oscillators are inherently
nonlinear since there must be some limiting / gain control
or the amplitude would collapse or explode otherwise.

I don't see that so extreme. I got the the point where the
crystal phase noise is all that matters without HB.


In the Agilent world, look for x-parameters.

Here are some papers from Rohde; he is a mass publisher
so it will be redundant.
There is more interesting material on the synergy microwave web site.

Older s-parameters should be small signal, esp. when there is
only bias given and no levels.

I'm just trying to determine myself if I could use harmonic
balance to simulate the noise behavior of a chopper amplifier
or if that is too non-linear. I'm still struggling with
importing spice models.

cheers,
Gerhard

<
https://depositonce.tu-berlin.de/bitstream/11303/1306/1/Dokument_16.pdf >

<
https://www.unibw.de/technische-informatik/mitarbeiter/professoren/large-signal-oszillator-noise-analysis-then-and-today-2.pdf
>

< https://synergymwave.com/articles/2013/04/full_article.pdf >

<
https://www.mes.tu-darmstadt.de/media/mikroelektronische_systeme/pdf_3/ewme2010/proceedings/sessionvii/hartnagel_slides.pdf
>

Phil Hobbs
Guest

Sat Feb 09, 2019 2:45 pm   



On 2/9/19 6:36 AM, dakupoto_at_gmail.com wrote:
Quote:
Could some electronics guru here help clarify the following.
Small signal S parameter amalysis is based on small signal
levels and a linearized cirucuit, with a DC operating point(bias) condition.
Large signal S parameter extends this scheme to high power
operating conditions of non-linear devices, where the
assumptions of small signal do not hold. Large signal
S parameter scheme is based on harmonic balance, which
involves analyzing the signals in the frequency domain.
i.e., Forier transforms.
Both schemes use a 2 port network, with the signal entering
at the inpit("from") port and coming out at the output("to")
port.
With these in mind, what about oscillators ? These are
one port networks, with a 2 port component (amplifier)
in it. So are large and small signal S parameters
applicable to oscillators ? Amplifiers are ripe for
large signal S parameters. For that matter, are the S
parameters quoted for older RF|micrwave transistors
small or karge signal S parameters ?

All hints/suggestions are welcome. Thanks in advance.


The first thing an oscillator has to do is to start up. It's initially
in the small signal condition, so the resonator + small signal S params
have to be unstable. So you can't ignore them.

Gerhard knows more RF than I do, so I'll let him carry on. ;)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

Winfield Hill
Guest

Sat Feb 09, 2019 3:45 pm   



Phil Hobbs wrote...
Quote:

On 2/9/19 6:36 AM, dakupoto_at_gmail.com wrote:

Small signal S parameter analysis is based on small
signal levels and a linearized circuit, with a DC
operating point(bias) condition. ...

The first thing an oscillator has to do is to start up.
It's initially in the small signal condition ...


I'd just like to add that small-signal analysis can be
very useful in large-signal situations. For example,
I'm working on designing high-voltage amplifiers with
power MOSFETs. These are capable of fast slewing and
high power levels, with excursions of hundreds of volts,
and high currents into capacitive loads. At first it
appeared that small-signal measurements and analysis
would not be so useful. But then I realized that when
the circuit was non-linear, slewing, delivering current,
I'd use the appropriate analysis, i = C dV/dt, etc.,
but after it was done slewing, it'd be the steady-state
condition that was most important, and most of my effort
went into solving the equations for that, and using them
to make the design rock solid. I made sure the amplifier
would then be operating class-A. This scheme worked well,
and I created a simple inexpensive design for a 1200-volt
DC power amplifier that has a -3dB bandwidth of 1 MHz.
It's gratifying to see the amplifier perform well, fast,
powerful, yet stable, with low measured phase shifts at
1MHz and beyond, so that with a transducer, it can work
well in a wideband servo. Small-signal analysis rocks!

BTW, at these frequencies, I wasn't using s-parameters.


--
Thanks,
- Win


Guest

Sat Feb 09, 2019 4:45 pm   



Phil Hobbs <pcdhSpamMeSenseless_at_electrooptical.net> wrote in
news:JcqdnTH2ovEHUcPBnZ2dnUU7-eednZ2d_at_supernews.com:

Quote:
On 2/9/19 6:36 AM, dakupoto_at_gmail.com wrote:
Could some electronics guru here help clarify the following.
Small signal S parameter amalysis is based on small signal
levels and a linearized cirucuit, with a DC operating point(bias)
condition. Large signal S parameter extends this scheme to high
power operating conditions of non-linear devices, where the
assumptions of small signal do not hold. Large signal
S parameter scheme is based on harmonic balance, which
involves analyzing the signals in the frequency domain.
i.e., Forier transforms.
Both schemes use a 2 port network, with the signal entering
at the inpit("from") port and coming out at the output("to")
port.
With these in mind, what about oscillators ? These are
one port networks, with a 2 port component (amplifier)
in it. So are large and small signal S parameters
applicable to oscillators ? Amplifiers are ripe for
large signal S parameters. For that matter, are the S
parameters quoted for older RF|micrwave transistors
small or karge signal S parameters ?

All hints/suggestions are welcome. Thanks in advance.


The first thing an oscillator has to do is to start up. It's
initially in the small signal condition, so the resonator + small
signal S params have to be unstable. So you can't ignore them.

Gerhard knows more RF than I do, so I'll let him carry on. ;)

Cheers

Phil Hobbs


In switch mode power supply design and use, this is known as "slow
start" of "hard start". If one punches the start of some
oscillators too hard the initial swing does not start and the
oscillator 'latches up' and the circuit start fails. In many cases
that input needs to be dampened or led or lagged to achieve a "soft
start" condition that ensures that the oscillator always starts.


Guest

Sat Feb 09, 2019 5:45 pm   



On Sat, 9 Feb 2019 03:36:06 -0800 (PST), dakupoto_at_gmail.com wrote:

Quote:
Could some electronics guru here help clarify the following.
Small signal S parameter amalysis is based on small signal
levels and a linearized cirucuit, with a DC operating point(bias) condition.
Large signal S parameter extends this scheme to high power
operating conditions of non-linear devices, where the
assumptions of small signal do not hold. Large signal
S parameter scheme is based on harmonic balance, which
involves analyzing the signals in the frequency domain.
i.e., Forier transforms.
Both schemes use a 2 port network, with the signal entering
at the inpit("from") port and coming out at the output("to")
port.
With these in mind, what about oscillators ? These are
one port networks, with a 2 port component (amplifier)
in it. So are large and small signal S parameters
applicable to oscillators ?


Think about the Barkhausen criterion, the total loop gain must be
larger than 1 and the total phase around the loop must be correct.

At oscillator startup, there is always some amplifier input related
white thermal noise. The amplifier amplifies the noise G times. This
noise is them coupled back to the input via the frequency selective
network with quality Q with correct phase, thus a narrow band noise
with bandwidth f/Q is connected back to amplifier input. The noise is
amplified nearly to G times and then running again through the filter
and having f/Q bandwidth at amplifier input. During next iteration
the signal is amplified up to G and filtered again to f/Q and so on.

This continues, until the signal amplitude is limited by the available
voltage swing.

The small signal s-parameters are initially critical, since the
Barkhausen criterions must be satisfied from thermal noise levels up
to limiting.

John Larkin
Guest

Sat Feb 09, 2019 6:45 pm   



On Sat, 09 Feb 2019 17:52:12 +0200, upsidedown_at_downunder.com wrote:

Quote:
On Sat, 9 Feb 2019 03:36:06 -0800 (PST), dakupoto_at_gmail.com wrote:

Could some electronics guru here help clarify the following.
Small signal S parameter amalysis is based on small signal
levels and a linearized cirucuit, with a DC operating point(bias) condition.
Large signal S parameter extends this scheme to high power
operating conditions of non-linear devices, where the
assumptions of small signal do not hold. Large signal
S parameter scheme is based on harmonic balance, which
involves analyzing the signals in the frequency domain.
i.e., Forier transforms.
Both schemes use a 2 port network, with the signal entering
at the inpit("from") port and coming out at the output("to")
port.
With these in mind, what about oscillators ? These are
one port networks, with a 2 port component (amplifier)
in it. So are large and small signal S parameters
applicable to oscillators ?

Think about the Barkhausen criterion, the total loop gain must be
larger than 1 and the total phase around the loop must be correct.

At oscillator startup, there is always some amplifier input related
white thermal noise. The amplifier amplifies the noise G times. This
noise is them coupled back to the input via the frequency selective
network with quality Q with correct phase, thus a narrow band noise
with bandwidth f/Q is connected back to amplifier input. The noise is
amplified nearly to G times and then running again through the filter
and having f/Q bandwidth at amplifier input. During next iteration
the signal is amplified up to G and filtered again to f/Q and so on.

This continues, until the signal amplitude is limited by the available
voltage swing.

The small signal s-parameters are initially critical, since the
Barkhausen criterions must be satisfied from thermal noise levels up
to limiting.


If the amp's transfer function has the right (ie, wrong) shape you can
make an oscillator that will run but not start.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

Phil Hobbs
Guest

Sat Feb 09, 2019 7:45 pm   



On 2/9/19 9:29 AM, Winfield Hill wrote:
Quote:
Phil Hobbs wrote...

On 2/9/19 6:36 AM, dakupoto_at_gmail.com wrote:

Small signal S parameter analysis is based on small
signal levels and a linearized circuit, with a DC
operating point(bias) condition. ...

The first thing an oscillator has to do is to start up.
It's initially in the small signal condition ...

I'd just like to add that small-signal analysis can be
very useful in large-signal situations. For example,
I'm working on designing high-voltage amplifiers with
power MOSFETs. These are capable of fast slewing and
high power levels, with excursions of hundreds of volts,
and high currents into capacitive loads. At first it
appeared that small-signal measurements and analysis
would not be so useful. But then I realized that when
the circuit was non-linear, slewing, delivering current,
I'd use the appropriate analysis, i = C dV/dt, etc.,
but after it was done slewing, it'd be the steady-state
condition that was most important, and most of my effort
went into solving the equations for that, and using them
to make the design rock solid. I made sure the amplifier
would then be operating class-A. This scheme worked well,
and I created a simple inexpensive design for a 1200-volt
DC power amplifier that has a -3dB bandwidth of 1 MHz.
It's gratifying to see the amplifier perform well, fast,
powerful, yet stable, with low measured phase shifts at
1MHz and beyond, so that with a transducer, it can work
well in a wideband servo. Small-signal analysis rocks!

BTW, at these frequencies, I wasn't using s-parameters.


Yup. The math isn't hard, and (when both approaches apply) one formula
has more information than a week's worth of simulations.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com


Guest

Sat Feb 09, 2019 7:45 pm   



On Sat, 09 Feb 2019 09:22:56 -0800, John Larkin
<jjlarkin_at_highlandtechnology.com> wrote:

Quote:
On Sat, 09 Feb 2019 17:52:12 +0200, upsidedown_at_downunder.com wrote:

On Sat, 9 Feb 2019 03:36:06 -0800 (PST), dakupoto_at_gmail.com wrote:

Could some electronics guru here help clarify the following.
Small signal S parameter amalysis is based on small signal
levels and a linearized cirucuit, with a DC operating point(bias) condition.
Large signal S parameter extends this scheme to high power
operating conditions of non-linear devices, where the
assumptions of small signal do not hold. Large signal
S parameter scheme is based on harmonic balance, which
involves analyzing the signals in the frequency domain.
i.e., Forier transforms.
Both schemes use a 2 port network, with the signal entering
at the inpit("from") port and coming out at the output("to")
port.
With these in mind, what about oscillators ? These are
one port networks, with a 2 port component (amplifier)
in it. So are large and small signal S parameters
applicable to oscillators ?

Think about the Barkhausen criterion, the total loop gain must be
larger than 1 and the total phase around the loop must be correct.

At oscillator startup, there is always some amplifier input related
white thermal noise. The amplifier amplifies the noise G times. This
noise is them coupled back to the input via the frequency selective
network with quality Q with correct phase, thus a narrow band noise
with bandwidth f/Q is connected back to amplifier input. The noise is
amplified nearly to G times and then running again through the filter
and having f/Q bandwidth at amplifier input. During next iteration
the signal is amplified up to G and filtered again to f/Q and so on.

This continues, until the signal amplitude is limited by the available
voltage swing.

The small signal s-parameters are initially critical, since the
Barkhausen criterions must be satisfied from thermal noise levels up
to limiting.

If the amp's transfer function has the right (ie, wrong) shape you can
make an oscillator that will run but not start.


Biasing the amplifier into class-C and the oscillator will not
automatically start. Once started the amplification in class C will
kick the resonator once each cycle.

In practice, such oscillators may start by quickly applying the
operating voltage, which allows some collector current to flow
momentarily. You may end up with an oscillator, which starts nicely
when battery powered but not when mains powered through linear power
supply with big electrolytes Smile. With such power supply, the voltage
may start too slowly to initiate the initial cycle.


Guest

Mon Feb 11, 2019 12:45 pm   



On Saturday, February 9, 2019 at 7:50:43 AM UTC-5, Phil Hobbs wrote:
Quote:
On 2/9/19 6:36 AM, dakupoto_at_gmail.com wrote:
Could some electronics guru here help clarify the following.
Small signal S parameter amalysis is based on small signal
levels and a linearized cirucuit, with a DC operating point(bias) condition.
Large signal S parameter extends this scheme to high power
operating conditions of non-linear devices, where the
assumptions of small signal do not hold. Large signal
S parameter scheme is based on harmonic balance, which
involves analyzing the signals in the frequency domain.
i.e., Forier transforms.
Both schemes use a 2 port network, with the signal entering
at the inpit("from") port and coming out at the output("to")
port.
With these in mind, what about oscillators ? These are
one port networks, with a 2 port component (amplifier)
in it. So are large and small signal S parameters
applicable to oscillators ? Amplifiers are ripe for
large signal S parameters. For that matter, are the S
parameters quoted for older RF|micrwave transistors
small or karge signal S parameters ?

All hints/suggestions are welcome. Thanks in advance.


The first thing an oscillator has to do is to start up. It's initially
in the small signal condition, so the resonator + small signal S params
have to be unstable. So you can't ignore them.

Gerhard knows more RF than I do, so I'll let him carry on. ;)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com


It depends on the type of oscillator one is looking at.
A differential oscillator, by its very nature, does not need any transistor biasing, and so it does not matter
if the S parameters are used or not.
In addition, for the new breed of transistors(e/g/.
HFA3134 from Renessas Semiconductor) the datasheet DOES NOT list ANY S parameters. With a fT of 8 GHz, it
would work very well in the RF - microwave frequency range.


Guest

Mon Feb 11, 2019 12:45 pm   



On Saturday, February 9, 2019 at 7:31:54 AM UTC-5, Gerhard Hoffmann wrote:
Quote:
Am 09.02.19 um 12:36 schrieb dakupoto_at_gmail.com:
Could some electronics guru here help clarify the following.
Small signal S parameter amalysis is based on small signal
levels and a linearized cirucuit, with a DC operating point(bias) condition.
Large signal S parameter extends this scheme to high power
operating conditions of non-linear devices, where the
assumptions of small signal do not hold. Large signal
S parameter scheme is based on harmonic balance, which
involves analyzing the signals in the frequency domain.
i.e., Forier transforms.
Both schemes use a 2 port network, with the signal entering
at the inpit("from") port and coming out at the output("to")
port.
With these in mind, what about oscillators ? These are
one port networks, with a 2 port component (amplifier)
in it. So are large and small signal S parameters
applicable to oscillators ? Amplifiers are ripe for
large signal S parameters. For that matter, are the S
parameters quoted for older RF|micrwave transistors
small or karge signal S parameters ?

All hints/suggestions are welcome. Thanks in advance.


Yes. It's currently Gospel that large signal s-parameters are
required for oscillator design. Oscillators are inherently
nonlinear since there must be some limiting / gain control
or the amplitude would collapse or explode otherwise.

I don't see that so extreme. I got the the point where the
crystal phase noise is all that matters without HB.


In the Agilent world, look for x-parameters.

Here are some papers from Rohde; he is a mass publisher
so it will be redundant.
There is more interesting material on the synergy microwave web site.

Older s-parameters should be small signal, esp. when there is
only bias given and no levels.

I'm just trying to determine myself if I could use harmonic
balance to simulate the noise behavior of a chopper amplifier
or if that is too non-linear. I'm still struggling with
importing spice models.

cheers,
Gerhard


https://depositonce.tu-berlin.de/bitstream/11303/1306/1/Dokument_16.pdf


https://www.unibw.de/technische-informatik/mitarbeiter/professoren/large-signal-oszillator-noise-analysis-then-and-today-2.pdf


https://synergymwave.com/articles/2013/04/full_article.pdf


https://www.mes.tu-darmstadt.de/media/mikroelektronische_systeme/pdf_3/ewme2010/proceedings/sessionvii/hartnagel_slides.pdf


It certainly is the Gospel to use large signal S
parameters, but things are changing rapidly. A new
breed of bi-junction transistors(e.g., HFA3134 -
Renesas Semiconductor) with a transition frequency
of 8 GHz(well in the RF/microwave range) DOES NOY
require the use of S parameters at all. The easily
downloadable data sheet does not contain any S parameters. I have used it to SPICE simulate common emitter/base feedback/negative resistance oscillators
upto 2 GHz. No issues at all.

My design scheme is simple.
1. AS a real-world oscillator cannot be expedted to
dump all the signal energy at the design frequency, define a set of tolerances (e.g., 5%) on the first
n (3 - 4) harmonics.
2. Compute passive component values e.g., for a common
emiiter feedback oscillator, with a simple C program
(to remove silly calculation errors) and then SPICE
simulate it with transientr analysis.
3. Fourier transform transient analysis output, and
compute power spectrun and check if the frequencies
corresponding to the first n(3 - 4) highest peaks fall
within the predefined tolerances. If not, adjust
resonator component values and iterate through the
above steps till tolerances ae satisfied - convergence.
If yes, task is complete.

I do have a copy of Rohde's 2005 book on microwave
oscillator design, but suffers from the same
problem as books on this topic by others(Grebennikov,
Ludwig Bretchko, Pozar etc.,) hundreds of pages of
theory.

We do have ADS at work, but most of us think that
the learning curve is very steep, and the results are
very non-intuitive.

Thank you very much for the URLs _ I will definitely
look through them.

Phil Hobbs
Guest

Mon Feb 11, 2019 4:45 pm   



On 2/11/19 6:44 AM, dakupoto_at_gmail.com wrote:
Quote:
On Saturday, February 9, 2019 at 7:50:43 AM UTC-5, Phil Hobbs wrote:
On 2/9/19 6:36 AM, dakupoto_at_gmail.com wrote:
Could some electronics guru here help clarify the following.
Small signal S parameter amalysis is based on small signal
levels and a linearized cirucuit, with a DC operating point(bias) condition.
Large signal S parameter extends this scheme to high power
operating conditions of non-linear devices, where the
assumptions of small signal do not hold. Large signal
S parameter scheme is based on harmonic balance, which
involves analyzing the signals in the frequency domain.
i.e., Forier transforms.
Both schemes use a 2 port network, with the signal entering
at the inpit("from") port and coming out at the output("to")
port.
With these in mind, what about oscillators ? These are
one port networks, with a 2 port component (amplifier)
in it. So are large and small signal S parameters
applicable to oscillators ? Amplifiers are ripe for
large signal S parameters. For that matter, are the S
parameters quoted for older RF|micrwave transistors
small or karge signal S parameters ?

All hints/suggestions are welcome. Thanks in advance.


The first thing an oscillator has to do is to start up. It's initially
in the small signal condition, so the resonator + small signal S params
have to be unstable. So you can't ignore them.

Gerhard knows more RF than I do, so I'll let him carry on. ;)


It depends on the type of oscillator one is looking at.
A differential oscillator, by its very nature, does not need any transistor biasing, and so it does not matter
if the S parameters are used or not.
In addition, for the new breed of transistors(e/g/.
HFA3134 from Renessas Semiconductor) the datasheet DOES NOT list ANY S parameters. With a fT of 8 GHz, it
would work very well in the RF - microwave frequency range.


Sure. It has a super-detailed SPICE model for both the device and the
package parasitics, which is going to be more useful than S parameters.
You can generate S parameters from the model, but going the other way is
a lot more complicated.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

John Larkin
Guest

Mon Feb 11, 2019 5:45 pm   



On Sat, 09 Feb 2019 20:26:30 +0200, upsidedown_at_downunder.com wrote:

Quote:
On Sat, 09 Feb 2019 09:22:56 -0800, John Larkin
jjlarkin_at_highlandtechnology.com> wrote:

On Sat, 09 Feb 2019 17:52:12 +0200, upsidedown_at_downunder.com wrote:

On Sat, 9 Feb 2019 03:36:06 -0800 (PST), dakupoto_at_gmail.com wrote:

Could some electronics guru here help clarify the following.
Small signal S parameter amalysis is based on small signal
levels and a linearized cirucuit, with a DC operating point(bias) condition.
Large signal S parameter extends this scheme to high power
operating conditions of non-linear devices, where the
assumptions of small signal do not hold. Large signal
S parameter scheme is based on harmonic balance, which
involves analyzing the signals in the frequency domain.
i.e., Forier transforms.
Both schemes use a 2 port network, with the signal entering
at the inpit("from") port and coming out at the output("to")
port.
With these in mind, what about oscillators ? These are
one port networks, with a 2 port component (amplifier)
in it. So are large and small signal S parameters
applicable to oscillators ?

Think about the Barkhausen criterion, the total loop gain must be
larger than 1 and the total phase around the loop must be correct.

At oscillator startup, there is always some amplifier input related
white thermal noise. The amplifier amplifies the noise G times. This
noise is them coupled back to the input via the frequency selective
network with quality Q with correct phase, thus a narrow band noise
with bandwidth f/Q is connected back to amplifier input. The noise is
amplified nearly to G times and then running again through the filter
and having f/Q bandwidth at amplifier input. During next iteration
the signal is amplified up to G and filtered again to f/Q and so on.

This continues, until the signal amplitude is limited by the available
voltage swing.

The small signal s-parameters are initially critical, since the
Barkhausen criterions must be satisfied from thermal noise levels up
to limiting.

If the amp's transfer function has the right (ie, wrong) shape you can
make an oscillator that will run but not start.

Biasing the amplifier into class-C and the oscillator will not
automatically start. Once started the amplification in class C will
kick the resonator once each cycle.

In practice, such oscillators may start by quickly applying the
operating voltage, which allows some collector current to flow
momentarily. You may end up with an oscillator, which starts nicely
when battery powered but not when mains powered through linear power
supply with big electrolytes Smile. With such power supply, the voltage
may start too slowly to initiate the initial cycle.


Instant-start oscillators are fun.

https://www.dropbox.com/s/0pldde09649579k/Burst_2.jpg?dl=0

The challenge is to make every cycle, including the first one, exactly
periodic.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

John Larkin
Guest

Mon Feb 11, 2019 7:45 pm   



On Mon, 11 Feb 2019 10:30:48 -0500, Phil Hobbs
<pcdhSpamMeSenseless_at_electrooptical.net> wrote:

Quote:
On 2/11/19 6:44 AM, dakupoto_at_gmail.com wrote:
On Saturday, February 9, 2019 at 7:50:43 AM UTC-5, Phil Hobbs wrote:
On 2/9/19 6:36 AM, dakupoto_at_gmail.com wrote:
Could some electronics guru here help clarify the following.
Small signal S parameter amalysis is based on small signal
levels and a linearized cirucuit, with a DC operating point(bias) condition.
Large signal S parameter extends this scheme to high power
operating conditions of non-linear devices, where the
assumptions of small signal do not hold. Large signal
S parameter scheme is based on harmonic balance, which
involves analyzing the signals in the frequency domain.
i.e., Forier transforms.
Both schemes use a 2 port network, with the signal entering
at the inpit("from") port and coming out at the output("to")
port.
With these in mind, what about oscillators ? These are
one port networks, with a 2 port component (amplifier)
in it. So are large and small signal S parameters
applicable to oscillators ? Amplifiers are ripe for
large signal S parameters. For that matter, are the S
parameters quoted for older RF|micrwave transistors
small or karge signal S parameters ?

All hints/suggestions are welcome. Thanks in advance.


The first thing an oscillator has to do is to start up. It's initially
in the small signal condition, so the resonator + small signal S params
have to be unstable. So you can't ignore them.

Gerhard knows more RF than I do, so I'll let him carry on. ;)


It depends on the type of oscillator one is looking at.
A differential oscillator, by its very nature, does not need any transistor biasing, and so it does not matter
if the S parameters are used or not.
In addition, for the new breed of transistors(e/g/.
HFA3134 from Renessas Semiconductor) the datasheet DOES NOT list ANY S parameters. With a fT of 8 GHz, it
would work very well in the RF - microwave frequency range.


Sure. It has a super-detailed SPICE model for both the device and the
package parasitics, which is going to be more useful than S parameters.
You can generate S parameters from the model, but going the other way is
a lot more complicated.

Cheers

Phil Hobbs


Anything really interesting is going to be nonlinear, so may as well
Spice.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

Gerhard Hoffmann
Guest

Mon Feb 11, 2019 8:45 pm   



Am 11.02.19 um 19:06 schrieb John Larkin:
Quote:
On Mon, 11 Feb 2019 10:30:48 -0500, Phil Hobbs
pcdhSpamMeSenseless_at_electrooptical.net> wrote:

On 2/11/19 6:44 AM, dakupoto_at_gmail.com wrote:
On Saturday, February 9, 2019 at 7:50:43 AM UTC-5, Phil Hobbs wrote:
On 2/9/19 6:36 AM, dakupoto_at_gmail.com wrote:
Could some electronics guru here help clarify the following.
Small signal S parameter amalysis is based on small signal
levels and a linearized cirucuit, with a DC operating point(bias) condition.
Large signal S parameter extends this scheme to high power
operating conditions of non-linear devices, where the
assumptions of small signal do not hold. Large signal
S parameter scheme is based on harmonic balance, which
involves analyzing the signals in the frequency domain.
i.e., Forier transforms.
Both schemes use a 2 port network, with the signal entering
at the inpit("from") port and coming out at the output("to")
port.
With these in mind, what about oscillators ? These are
one port networks, with a 2 port component (amplifier)
in it. So are large and small signal S parameters
applicable to oscillators ? Amplifiers are ripe for
large signal S parameters. For that matter, are the S
parameters quoted for older RF|micrwave transistors
small or karge signal S parameters ?

All hints/suggestions are welcome. Thanks in advance.


The first thing an oscillator has to do is to start up. It's initially
in the small signal condition, so the resonator + small signal S params
have to be unstable. So you can't ignore them.

Gerhard knows more RF than I do, so I'll let him carry on. ;)


It depends on the type of oscillator one is looking at.
A differential oscillator, by its very nature, does not need any transistor biasing, and so it does not matter
if the S parameters are used or not.
In addition, for the new breed of transistors(e/g/.
HFA3134 from Renessas Semiconductor) the datasheet DOES NOT list ANY S parameters. With a fT of 8 GHz, it
would work very well in the RF - microwave frequency range.


Sure. It has a super-detailed SPICE model for both the device and the
package parasitics, which is going to be more useful than S parameters.
You can generate S parameters from the model, but going the other way is
a lot more complicated.

Cheers

Phil Hobbs

Anything really interesting is going to be nonlinear, so may as well
Spice.


Unfortunately, nonlinear analysis in Spice is quite meagre.
You just get transient analysis and that's it. OK, add FFT from
the post processor.

For noise and frequency response analysis, the circuit is linearized
around the operating point, so it is small signal only by definition.

No nonlinear noise, no harmonic balance, no large signal frequency response.

I would not get very far determining the noise characteristics of my
chopper amplifiers. How could it linearize the circuit in the presence
of the chopp clock and the continuous switching?

How do I determine the noise level of an amplifier that is near
compression? That is the normal case in the sustaining amplifier
of an oscillator.

How could I see the jitter induced by noise or self heating?
Transient simulation is noise free.

How do I simulate a SRD frequency multiplier? Cannot. There
is no concept of carrier lifetime in Spice. No PIN diodes.
Oh, 1N4007 is a PIN diode. (the others in the series aren't)

cheers,
Gerhard

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