• Re: noise question

    From Phil Hobbs@21:1/5 to All on Mon Jul 15 14:46:51 2024
    john larkin <jlarkin_highland_tech> wrote:
    Does a negative 50-ohm resistor make as much noise as a regular 50 ohm resistor?

    I'd sorta guess the current noise to be the same, and maybe the
    open-circuit voltage noise is infinite.

    I could Spice that, at least the current noise, if Spice handles it
    right. LT Spice noise analysis is kind of weird.



    Alas, it doesn’t have imaginary noise.

    There’s no general formula, because a negative resistance can’t exist in thermodynamic equilibrium. You have to figure it out from the actual
    circuit.

    When it’s just an LTspice spherical-cow resistor, I don’t know what happens in a .noise simulation.

    Cheers

    Phil Hobbs

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

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  • From Bill Sloman@21:1/5 to john larkin on Tue Jul 16 00:49:10 2024
    On 16/07/2024 12:30 am, john larkin wrote:
    Does a negative 50-ohm resistor make as much noise as a regular 50 ohm resistor?

    I'd sorta guess the current noise to be the same, and maybe the
    open-circuit voltage noise is infinite.

    I could Spice that, at least the current noise, if Spice handles it
    right. LT Spice noise analysis is kind of weird.

    A negative resistance is an active circuit, and you have to add up the
    noise contribution from all the real components in the actual circuit.

    Imagining that you could treat a negative resistance as if it were an
    isolated component is a trifle unrealistic.

    --
    Bill Sloman, Sydney



    --
    This email has been checked for viruses by Norton antivirus software. www.norton.com

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  • From john larkin @21:1/5 to All on Mon Jul 15 07:30:43 2024
    Does a negative 50-ohm resistor make as much noise as a regular 50 ohm resistor?

    I'd sorta guess the current noise to be the same, and maybe the
    open-circuit voltage noise is infinite.

    I could Spice that, at least the current noise, if Spice handles it
    right. LT Spice noise analysis is kind of weird.

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  • From Dan Purgert@21:1/5 to john larkin on Mon Jul 15 14:40:44 2024
    On 2024-07-15, john larkin wrote:
    Does a negative 50-ohm resistor make as much noise as a regular 50 ohm resistor?

    Yes, just inverted?

    (also, "negative" resistance?)

    --
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  • From Jeroen Belleman@21:1/5 to john larkin on Mon Jul 15 17:35:08 2024
    On 7/15/24 16:30, john larkin wrote:
    Does a negative 50-ohm resistor make as much noise as a regular 50 ohm resistor?

    I'd sorta guess the current noise to be the same, and maybe the
    open-circuit voltage noise is infinite.

    I could Spice that, at least the current noise, if Spice handles it
    right. LT Spice noise analysis is kind of weird.


    I just tried it: In LTspice the sign doesn't matter,
    only the absolute value. Also, if you put a positive
    resistor in series with negative one, the noise
    voltages add RMS-wise, like you'd expect of independent
    sources.

    In real life, a negative resistor may have more or
    less noise than an actual resistor, depending on the
    low-noise design skills of the designer.

    I think you knew that...

    Jeroen Belleman

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  • From john larkin @21:1/5 to jeroen@nospam.please on Mon Jul 15 09:09:01 2024
    On Mon, 15 Jul 2024 17:35:08 +0200, Jeroen Belleman
    <jeroen@nospam.please> wrote:

    On 7/15/24 16:30, john larkin wrote:
    Does a negative 50-ohm resistor make as much noise as a regular 50 ohm
    resistor?

    I'd sorta guess the current noise to be the same, and maybe the
    open-circuit voltage noise is infinite.

    I could Spice that, at least the current noise, if Spice handles it
    right. LT Spice noise analysis is kind of weird.


    I just tried it: In LTspice the sign doesn't matter,
    only the absolute value. Also, if you put a positive
    resistor in series with negative one, the noise
    voltages add RMS-wise, like you'd expect of independent
    sources.

    Cool. Thanks.


    In real life, a negative resistor may have more or
    less noise than an actual resistor, depending on the
    low-noise design skills of the designer.

    I think you knew that...

    Jeroen Belleman

    Sure, I was considering an ideal neg resistor, without added noise
    from active parts.

    As a college project, I built a 2-terminal negative resistor and
    plugged the negative value into a bunch of equations (voltage
    dividers, RCs, LRCs, things like that) and demonstrated that they
    worked that way in real life. That was fun.

    What I was thinking lately was about making an LC oscillator with very
    low phase noise, namely low jitter in my world. The finite Q of the
    parallel LC is equivalent to a shunt resistor so I'd expect it to have
    the Johnson noise of that equivalent resistance. Then the active stuff
    must look like a negative resistor, which is noisy too.

    LT Spice noise analysis is very limited. I have sometimes added some random-noise BV blocks in series with resistors and such, so I can do
    genuine nonlinear sims with noise. It's actually easier to breadboard.

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  • From john larkin @21:1/5 to All on Mon Jul 15 09:15:45 2024
    On Mon, 15 Jul 2024 14:40:44 -0000 (UTC), Dan Purgert <dan@djph.net>
    wrote:

    On 2024-07-15, john larkin wrote:
    Does a negative 50-ohm resistor make as much noise as a regular 50 ohm
    resistor?

    Yes, just inverted?

    (also, "negative" resistance?)

    Sure. I = -E/R.

    Connect that to a battery, and it charges the battery. Across a
    capacitor, you get an exponentially increasing voltage.

    That works in Spice.

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  • From Jeroen Belleman@21:1/5 to john larkin on Mon Jul 15 19:33:52 2024
    On 7/15/24 18:09, john larkin wrote:
    On Mon, 15 Jul 2024 17:35:08 +0200, Jeroen Belleman
    <jeroen@nospam.please> wrote:

    On 7/15/24 16:30, john larkin wrote:
    Does a negative 50-ohm resistor make as much noise as a regular 50 ohm
    resistor?

    I'd sorta guess the current noise to be the same, and maybe the
    open-circuit voltage noise is infinite.

    I could Spice that, at least the current noise, if Spice handles it
    right. LT Spice noise analysis is kind of weird.


    I just tried it: In LTspice the sign doesn't matter,
    only the absolute value. Also, if you put a positive
    resistor in series with negative one, the noise
    voltages add RMS-wise, like you'd expect of independent
    sources.

    Cool. Thanks.


    In real life, a negative resistor may have more or
    less noise than an actual resistor, depending on the
    low-noise design skills of the designer.

    I think you knew that...

    Jeroen Belleman

    Sure, I was considering an ideal neg resistor, without added noise
    from active parts.

    As a college project, I built a 2-terminal negative resistor and
    plugged the negative value into a bunch of equations (voltage
    dividers, RCs, LRCs, things like that) and demonstrated that they
    worked that way in real life. That was fun.

    What I was thinking lately was about making an LC oscillator with very
    low phase noise, namely low jitter in my world. The finite Q of the
    parallel LC is equivalent to a shunt resistor so I'd expect it to have
    the Johnson noise of that equivalent resistance. Then the active stuff
    must look like a negative resistor, which is noisy too.

    Yes, that's what I'd expect too.


    LT Spice noise analysis is very limited. I have sometimes added some random-noise BV blocks in series with resistors and such, so I can do
    genuine nonlinear sims with noise. It's actually easier to breadboard.


    BTDT. What's with the nonlinear bit? LTspice noise analysis is
    basically an AC analysis, no?

    Jeroen Belleman

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  • From john larkin @21:1/5 to jeroen@nospam.please on Mon Jul 15 11:04:38 2024
    On Mon, 15 Jul 2024 19:33:52 +0200, Jeroen Belleman
    <jeroen@nospam.please> wrote:

    On 7/15/24 18:09, john larkin wrote:
    On Mon, 15 Jul 2024 17:35:08 +0200, Jeroen Belleman
    <jeroen@nospam.please> wrote:

    On 7/15/24 16:30, john larkin wrote:
    Does a negative 50-ohm resistor make as much noise as a regular 50 ohm >>>> resistor?

    I'd sorta guess the current noise to be the same, and maybe the
    open-circuit voltage noise is infinite.

    I could Spice that, at least the current noise, if Spice handles it
    right. LT Spice noise analysis is kind of weird.


    I just tried it: In LTspice the sign doesn't matter,
    only the absolute value. Also, if you put a positive
    resistor in series with negative one, the noise
    voltages add RMS-wise, like you'd expect of independent
    sources.

    Cool. Thanks.


    In real life, a negative resistor may have more or
    less noise than an actual resistor, depending on the
    low-noise design skills of the designer.

    I think you knew that...

    Jeroen Belleman

    Sure, I was considering an ideal neg resistor, without added noise
    from active parts.

    As a college project, I built a 2-terminal negative resistor and
    plugged the negative value into a bunch of equations (voltage
    dividers, RCs, LRCs, things like that) and demonstrated that they
    worked that way in real life. That was fun.

    What I was thinking lately was about making an LC oscillator with very
    low phase noise, namely low jitter in my world. The finite Q of the
    parallel LC is equivalent to a shunt resistor so I'd expect it to have
    the Johnson noise of that equivalent resistance. Then the active stuff
    must look like a negative resistor, which is noisy too.

    Yes, that's what I'd expect too.


    LT Spice noise analysis is very limited. I have sometimes added some
    random-noise BV blocks in series with resistors and such, so I can do
    genuine nonlinear sims with noise. It's actually easier to breadboard.


    BTDT. What's with the nonlinear bit? LTspice noise analysis is
    basically an AC analysis, no?

    Jeroen Belleman

    LT Spice noise analysis is weird. You need one signal source, even if
    you don't use it. And you can only probe one node. It must be entirely
    linear.

    I want to simulate jitter in a LC oscillator, and of course an
    oscillator always has some nonlinear amplitude limiting mechanism.

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  • From Jeroen Belleman@21:1/5 to john larkin on Mon Jul 15 22:25:29 2024
    On 7/15/24 20:04, john larkin wrote:
    On Mon, 15 Jul 2024 19:33:52 +0200, Jeroen Belleman
    <jeroen@nospam.please> wrote:

    On 7/15/24 18:09, john larkin wrote:
    On Mon, 15 Jul 2024 17:35:08 +0200, Jeroen Belleman
    <jeroen@nospam.please> wrote:

    On 7/15/24 16:30, john larkin wrote:
    Does a negative 50-ohm resistor make as much noise as a regular 50 ohm >>>>> resistor?

    I'd sorta guess the current noise to be the same, and maybe the
    open-circuit voltage noise is infinite.

    I could Spice that, at least the current noise, if Spice handles it
    right. LT Spice noise analysis is kind of weird.


    I just tried it: In LTspice the sign doesn't matter,
    only the absolute value. Also, if you put a positive
    resistor in series with negative one, the noise
    voltages add RMS-wise, like you'd expect of independent
    sources.

    Cool. Thanks.


    In real life, a negative resistor may have more or
    less noise than an actual resistor, depending on the
    low-noise design skills of the designer.

    I think you knew that...

    Jeroen Belleman

    Sure, I was considering an ideal neg resistor, without added noise
    from active parts.

    As a college project, I built a 2-terminal negative resistor and
    plugged the negative value into a bunch of equations (voltage
    dividers, RCs, LRCs, things like that) and demonstrated that they
    worked that way in real life. That was fun.

    What I was thinking lately was about making an LC oscillator with very
    low phase noise, namely low jitter in my world. The finite Q of the
    parallel LC is equivalent to a shunt resistor so I'd expect it to have
    the Johnson noise of that equivalent resistance. Then the active stuff
    must look like a negative resistor, which is noisy too.

    Yes, that's what I'd expect too.


    LT Spice noise analysis is very limited. I have sometimes added some
    random-noise BV blocks in series with resistors and such, so I can do
    genuine nonlinear sims with noise. It's actually easier to breadboard.


    BTDT. What's with the nonlinear bit? LTspice noise analysis is
    basically an AC analysis, no?

    Jeroen Belleman

    LT Spice noise analysis is weird. You need one signal source, even if
    you don't use it. And you can only probe one node. It must be entirely linear.

    You can probe *components*, rather than nodes, to see how much each
    contributes to the output noise.


    I want to simulate jitter in a LC oscillator, and of course an
    oscillator always has some nonlinear amplitude limiting mechanism.


    I think I'd open the loop somewhere and treat the thing as an
    amplifier. I dabbled with the conversion between voltage noise
    and oscillator jitter, but the details have faded somewhat.

    Jeroen Belleman

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  • From Phil Hobbs@21:1/5 to All on Mon Jul 15 21:06:35 2024
    john larkin <jlarkin_highland_tech> wrote:
    On Mon, 15 Jul 2024 19:33:52 +0200, Jeroen Belleman
    <jeroen@nospam.please> wrote:

    On 7/15/24 18:09, john larkin wrote:
    On Mon, 15 Jul 2024 17:35:08 +0200, Jeroen Belleman
    <jeroen@nospam.please> wrote:

    On 7/15/24 16:30, john larkin wrote:
    Does a negative 50-ohm resistor make as much noise as a regular 50 ohm >>>>> resistor?

    I'd sorta guess the current noise to be the same, and maybe the
    open-circuit voltage noise is infinite.

    I could Spice that, at least the current noise, if Spice handles it
    right. LT Spice noise analysis is kind of weird.


    I just tried it: In LTspice the sign doesn't matter,
    only the absolute value. Also, if you put a positive
    resistor in series with negative one, the noise
    voltages add RMS-wise, like you'd expect of independent
    sources.

    Cool. Thanks.


    In real life, a negative resistor may have more or
    less noise than an actual resistor, depending on the
    low-noise design skills of the designer.

    I think you knew that...

    Jeroen Belleman

    Sure, I was considering an ideal neg resistor, without added noise
    from active parts.

    As a college project, I built a 2-terminal negative resistor and
    plugged the negative value into a bunch of equations (voltage
    dividers, RCs, LRCs, things like that) and demonstrated that they
    worked that way in real life. That was fun.

    What I was thinking lately was about making an LC oscillator with very
    low phase noise, namely low jitter in my world. The finite Q of the
    parallel LC is equivalent to a shunt resistor so I'd expect it to have
    the Johnson noise of that equivalent resistance. Then the active stuff
    must look like a negative resistor, which is noisy too.

    Yes, that's what I'd expect too.


    LT Spice noise analysis is very limited. I have sometimes added some
    random-noise BV blocks in series with resistors and such, so I can do
    genuine nonlinear sims with noise. It's actually easier to breadboard.


    BTDT. What's with the nonlinear bit? LTspice noise analysis is
    basically an AC analysis, no?

    Jeroen Belleman

    LT Spice noise analysis is weird. You need one signal source, even if
    you don't use it. And you can only probe one node. It must be entirely linear.

    I want to simulate jitter in a LC oscillator, and of course an
    oscillator always has some nonlinear amplitude limiting mechanism.



    LTspice has time domain noise sources. They’re actually deterministic, of course, but you can use a big time offset to fix that.

    The scaling iirc 1 sample per second, so you wind up using

    noise(1e8*time+2e9)

    and stuff like that.

    Cheers

    Phil Hobbs

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

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  • From Gerhard Hoffmann@21:1/5 to All on Tue Jul 16 01:40:29 2024
    Am 15.07.24 um 20:04 schrieb john larkin:
    On Mon, 15 Jul 2024 19:33:52 +0200, Jeroen Belleman
    <jeroen@nospam.please> wrote:

    On 7/15/24 18:09, john larkin wrote:
    On Mon, 15 Jul 2024 17:35:08 +0200, Jeroen Belleman
    <jeroen@nospam.please> wrote:

    On 7/15/24 16:30, john larkin wrote:
    Does a negative 50-ohm resistor make as much noise as a regular 50 ohm >>>>> resistor?

    I'd sorta guess the current noise to be the same, and maybe the
    open-circuit voltage noise is infinite.

    I could Spice that, at least the current noise, if Spice handles it
    right. LT Spice noise analysis is kind of weird.


    I just tried it: In LTspice the sign doesn't matter,
    only the absolute value. Also, if you put a positive
    resistor in series with negative one, the noise
    voltages add RMS-wise, like you'd expect of independent
    sources.

    Cool. Thanks.


    In real life, a negative resistor may have more or
    less noise than an actual resistor, depending on the
    low-noise design skills of the designer.

    I think you knew that...

    Jeroen Belleman

    Sure, I was considering an ideal neg resistor, without added noise
    from active parts.

    As a college project, I built a 2-terminal negative resistor and
    plugged the negative value into a bunch of equations (voltage
    dividers, RCs, LRCs, things like that) and demonstrated that they
    worked that way in real life. That was fun.

    What I was thinking lately was about making an LC oscillator with very
    low phase noise, namely low jitter in my world. The finite Q of the
    parallel LC is equivalent to a shunt resistor so I'd expect it to have
    the Johnson noise of that equivalent resistance. Then the active stuff
    must look like a negative resistor, which is noisy too.

    Yes, that's what I'd expect too.


    LT Spice noise analysis is very limited. I have sometimes added some
    random-noise BV blocks in series with resistors and such, so I can do
    genuine nonlinear sims with noise. It's actually easier to breadboard.


    BTDT. What's with the nonlinear bit? LTspice noise analysis is
    basically an AC analysis, no?

    What irritates me is, that I need to edit .noise and .ac commands if I
    want to see noise and some gains; I want want both at the same time.
    The way it's now is clumsy.

    LT Spice noise analysis is weird. You need one signal source, even if
    you don't use it. And you can only probe one node. It must be entirely linear.

    At least, that seems to work.
    < https://www.flickr.com/photos/137684711@N07/51974219045/in/album-72157662535945536/lightbox/
    >

    I want to simulate jitter in a LC oscillator, and of course an
    oscillator always has some nonlinear amplitude limiting mechanism.

    If you want nonlinear noise, you need Keysight's Advanced Design System
    or such. Be prepared to a 5 or 6 digit price tag, depending on options.
    The keyword is harmonic balance simulator.

    cheers, Gerhard

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  • From Bill Sloman@21:1/5 to john larkin on Tue Jul 16 13:24:03 2024
    On 16/07/2024 4:04 am, john larkin wrote:
    On Mon, 15 Jul 2024 19:33:52 +0200, Jeroen Belleman
    <jeroen@nospam.please> wrote:
    On 7/15/24 18:09, john larkin wrote:
    On Mon, 15 Jul 2024 17:35:08 +0200, Jeroen Belleman
    <jeroen@nospam.please> wrote:
    On 7/15/24 16:30, john larkin wrote:

    <snip>

    I want to simulate jitter in a LC oscillator, and of course an
    oscillator always has some nonlinear amplitude limiting mechanism.

    I've done a couple of LC oscillators using an asymmetric current mirror
    as the amplitude-controlling mechanism. That stays linear as long as the amplitude is stable, and it only gets very slightly non-linear while it
    is getting the amplitude back to where it ought to be.

    As a jitter source it should be innocuous.

    I've also simulated a Wein Bridge with an Analog Devices AD734 as the gain-adjusting device, which is essentially the same idea (but with a linearised current mirror) and Spice suggests that it introduces less distortion than the usual gain-adjusting mechanisms.

    Use two of them and you can control frequency (over a limited range) as
    well as amplitude. I've never found an application for that.

    --
    Bill Sloman, Sydney



    --
    This email has been checked for viruses by Norton antivirus software. www.norton.com

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  • From Phil Hobbs@21:1/5 to Gerhard Hoffmann on Tue Jul 16 03:29:19 2024
    Gerhard Hoffmann <dk4xp@arcor.de> wrote:
    Am 15.07.24 um 20:04 schrieb john larkin:
    On Mon, 15 Jul 2024 19:33:52 +0200, Jeroen Belleman
    <jeroen@nospam.please> wrote:

    On 7/15/24 18:09, john larkin wrote:
    On Mon, 15 Jul 2024 17:35:08 +0200, Jeroen Belleman
    <jeroen@nospam.please> wrote:

    On 7/15/24 16:30, john larkin wrote:

    <sniiip>

    If you want nonlinear noise, you need Keysight's Advanced Design System
    or such. Be prepared to a 5 or 6 digit price tag, depending on options.
    The keyword is harmonic balance simulator.




    Nah. The LTspice noise() and white() functions give you time-domain noise, with uniform or Gaussian amplitude statistics, and are good enough for many things.

    If you want separate voltage and current noise contributions, you can use a voltage controlled current source.

    To keep the complexity down, you need to do a little analysis to figure out what the dominant noise sources are going to be, so that you can just model those.

    Cheers

    Phil Hobbs






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

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  • From Phil Hobbs@21:1/5 to Phil Hobbs on Tue Jul 16 03:30:52 2024
    Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
    Gerhard Hoffmann <dk4xp@arcor.de> wrote:
    Am 15.07.24 um 20:04 schrieb john larkin:
    On Mon, 15 Jul 2024 19:33:52 +0200, Jeroen Belleman
    <jeroen@nospam.please> wrote:

    On 7/15/24 18:09, john larkin wrote:
    On Mon, 15 Jul 2024 17:35:08 +0200, Jeroen Belleman
    <jeroen@nospam.please> wrote:

    On 7/15/24 16:30, john larkin wrote:

    <sniiip>

    If you want nonlinear noise, you need Keysight's Advanced Design System
    or such. Be prepared to a 5 or 6 digit price tag, depending on options.
    The keyword is harmonic balance simulator.




    Nah. The LTspice

    random()

    and white() functions give you-domain noise,
    with uniform or Gaussian amplitude statistics, and are good enough for many things.

    If you want separate voltage and current noise contributions, you can use a voltage controlled current source.

    To keep the complexity down, you need to do a little analysis to figure out what the dominant noise sources are going to be, so that you can just model those.

    Cheers

    Phil Hobbs









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

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  • From Jan Panteltje@21:1/5 to All on Tue Jul 16 05:42:51 2024
    On a sunny day (Mon, 15 Jul 2024 09:15:45 -0700) it happened john larkin <jlarkin_highland_tech> wrote in <ikia9jhlgdclsb40267f6potnk6hec6ue9@4ax.com>:

    On Mon, 15 Jul 2024 14:40:44 -0000 (UTC), Dan Purgert <dan@djph.net>
    wrote:

    On 2024-07-15, john larkin wrote:
    Does a negative 50-ohm resistor make as much noise as a regular 50 ohm
    resistor?

    Yes, just inverted?

    (also, "negative" resistance?)

    Sure. I = -E/R.

    Connect that to a battery, and it charges the battery. Across a
    capacitor, you get an exponentially increasing voltage.

    That works in Spice.

    I was thinking about this last night (so beware)
    The only 2 pole negative resistors I know about are tunnel diodes.

    For 50 Ohms if you could bias one so an increase of 50 mV leads to a 1 mA decrease in current that would be -50 Ohms?
    No idea if the curve allows that,
    And then measure the noise with some of your super test equipment.
    If 500 Ohms divide by 10

    No idea if this makes sense, have not had my hands on tunnel diodes for many decades.
    Those were still on ebay some years ago,
    Got some UJTs to make nice stable pulse generators....

    For what it is worth mamaticians!

    EL Tee Spice, ..mostly use salt, pepper and Chili.
    Oh and sugar...
    oops the list is longer

    Too much of Spice is . too much not good 4 U

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  • From Dan Purgert@21:1/5 to john larkin on Tue Jul 16 09:13:53 2024
    On 2024-07-15, john larkin wrote:
    On Mon, 15 Jul 2024 14:40:44 -0000 (UTC), Dan Purgert <dan@djph.net>
    wrote:

    On 2024-07-15, john larkin wrote:
    Does a negative 50-ohm resistor make as much noise as a regular 50 ohm
    resistor?

    Yes, just inverted?

    (also, "negative" resistance?)

    Sure. I = -E/R.

    Isn't that negative voltage, as written?

    I should probably have more coffee before trying to figure this out


    --
    |_|O|_|
    |_|_|O| Github: https://github.com/dpurgert
    |O|O|O| PGP: DDAB 23FB 19FA 7D85 1CC1 E067 6D65 70E5 4CE7 2860

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  • From Gerhard Hoffmann@21:1/5 to All on Tue Jul 16 11:52:47 2024
    Am 16.07.24 um 05:29 schrieb Phil Hobbs:
    Gerhard Hoffmann <dk4xp@arcor.de> wrote:
    Am 15.07.24 um 20:04 schrieb john larkin:
    On Mon, 15 Jul 2024 19:33:52 +0200, Jeroen Belleman
    <jeroen@nospam.please> wrote:

    On 7/15/24 18:09, john larkin wrote:
    On Mon, 15 Jul 2024 17:35:08 +0200, Jeroen Belleman
    <jeroen@nospam.please> wrote:

    On 7/15/24 16:30, john larkin wrote:

    <sniiip>

    If you want nonlinear noise, you need Keysight's Advanced Design System
    or such. Be prepared to a 5 or 6 digit price tag, depending on options.
    The keyword is harmonic balance simulator.




    Nah. The LTspice noise() and white() functions give you time-domain noise, with uniform or Gaussian amplitude statistics, and are good enough for many things.

    If you want separate voltage and current noise contributions, you can use a voltage controlled current source.

    To keep the complexity down, you need to do a little analysis to figure out what the dominant noise sources are going to be, so that you can just model those.

    That assumes that oscillators are mostly linear, but they aren't.
    Switching on a really linear oscillator would imply an explosion
    soon after power on.So there must be a large scale non-linearity
    to limit the growth.

    There are even proposals that say that there is an optimum point
    in the cycle to inject all the feedback for best phase noise.

    < https://people.engr.tamu.edu/spalermo/ecen620/general_pn_theory_hajimiri_jssc_1998.pdf
    >
    (and books on it)

    Our ex-regular Kevin Aylward, WardenOf The King's Ale
    < https://www.kevinaylward.co.uk/ > has written fiercely
    against that but people like Rubiola and U.L.Rohde seem to buy it.

    interesting: < https://rubiola.org/ >


    Cheers

    Gerhard

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  • From Phil Hobbs@21:1/5 to Gerhard Hoffmann on Tue Jul 16 11:25:43 2024
    Gerhard Hoffmann <dk4xp@arcor.de> wrote:
    Am 16.07.24 um 05:29 schrieb Phil Hobbs:
    Gerhard Hoffmann <dk4xp@arcor.de> wrote:
    Am 15.07.24 um 20:04 schrieb john larkin:
    On Mon, 15 Jul 2024 19:33:52 +0200, Jeroen Belleman
    <jeroen@nospam.please> wrote:

    On 7/15/24 18:09, john larkin wrote:
    On Mon, 15 Jul 2024 17:35:08 +0200, Jeroen Belleman
    <jeroen@nospam.please> wrote:

    On 7/15/24 16:30, john larkin wrote:

    <sniiip>

    If you want nonlinear noise, you need Keysight's Advanced Design System
    or such. Be prepared to a 5 or 6 digit price tag, depending on options.
    The keyword is harmonic balance simulator.




    Nah. The LTspice noise() and white() functions give you time-domain noise, >> with uniform or Gaussian amplitude statistics, and are good enough for many >> things.

    If you want separate voltage and current noise contributions, you can use a >> voltage controlled current source.

    To keep the complexity down, you need to do a little analysis to figure out >> what the dominant noise sources are going to be, so that you can just model >> those.

    That assumes that oscillators are mostly linear, but they aren't.

    No, it doesn’t. It’s the normal .tran simulation, not .noise or .ac.

    Switching on a really linear oscillator would imply an explosion
    soon after power on.So there must be a large scale non-linearity
    to limit the growth.

    Try it sometime. It works fine, as long as you scale and offset the
    argument reasonably thoughtfully, to get the right bandwidth and enough independent runs for good statistics.

    Using white() or random() as part of a bv or bi expression will let you
    model the changes in the noise with bias.


    There are even proposals that say that there is an optimum point
    in the cycle to inject all the feedback for best phase noise.

    < https://people.engr.tamu.edu/spalermo/ecen620/general_pn_theory_hajimiri_jssc_1998.pdf
    >
    (and books on it)

    Our ex-regular Kevin Aylward, WardenOf The King's Ale
    < https://www.kevinaylward.co.uk/ > has written fiercely
    against that but people like Rubiola and U.L.Rohde seem to buy it.

    interesting: < https://rubiola.org/ >



    Sure, oscillator theory is fun. Try looking into the math of injection locking, if you like that sort of thing—it’s full of bifurcations and strange attractors and limit cycles and stuff.

    Most of the time I try to be relentlessly practical, but often fail. ;)

    Cheers

    Phil Hobbs



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

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  • From Bill Sloman@21:1/5 to Gerhard Hoffmann on Tue Jul 16 22:22:27 2024
    On 16/07/2024 7:52 pm, Gerhard Hoffmann wrote:
    Am 16.07.24 um 05:29 schrieb Phil Hobbs:
    Gerhard Hoffmann <dk4xp@arcor.de> wrote:
    Am 15.07.24 um 20:04 schrieb john larkin:
    On Mon, 15 Jul 2024 19:33:52 +0200, Jeroen Belleman
    <jeroen@nospam.please> wrote:

    On 7/15/24 18:09, john larkin wrote:
    On Mon, 15 Jul 2024 17:35:08 +0200, Jeroen Belleman
    <jeroen@nospam.please> wrote:

    On 7/15/24 16:30, john larkin wrote:

    <snip>

    That assumes that oscillators are mostly linear, but they aren't.

    They can be remarkably close to it, once the amplitude has settled down.

    http://sophia-electronica.com/BillsBaxandall.html

    uses an asymmetric current mirror to control the loop gain, and once
    you've got the amplitude where you want it - that at the right level of asymmetry - the current mirror is pretty linear.

    If you use a AD734 four quadrant multiplier as your gain-setting device
    you can do even better, which is something I've only done in
    simulation,but should work in real life.

    Switching on a really linear oscillator would imply an explosion
    soon after power on.So there must be a large scale non-linearity
    to limit the growth.

    No. You just have to be able to control the gain around the loop to hold
    the amplitude of oscillation at a stable level. Obviously that gain has
    to be changed from time to time, but it doesn't have to changed all that
    much or all that fast.

    There are even proposals that say that there is an optimum point
    in the cycle to inject all the feedback for best phase noise.

    Seems implausible.

    https://people.engr.tamu.edu/spalermo/ecen620/general_pn_theory_hajimiri_jssc_1998.pdf     >
    (and books on it)

    Our ex-regular Kevin Aylward, WardenOf The King's Ale
    https://www.kevinaylward.co.uk/    > has written fiercely
    against that but people like Rubiola and U.L.Rohde seem to buy it.

    interesting:   <  https://rubiola.org/   >

    --
    Bill Sloman, Sydney



    --
    This email has been checked for viruses by Norton antivirus software. www.norton.com

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  • From john larkin @21:1/5 to All on Tue Jul 16 06:57:07 2024
    On Tue, 16 Jul 2024 09:13:53 -0000 (UTC), Dan Purgert <dan@djph.net>
    wrote:

    On 2024-07-15, john larkin wrote:
    On Mon, 15 Jul 2024 14:40:44 -0000 (UTC), Dan Purgert <dan@djph.net>
    wrote:

    On 2024-07-15, john larkin wrote:
    Does a negative 50-ohm resistor make as much noise as a regular 50 ohm >>>> resistor?

    Yes, just inverted?

    (also, "negative" resistance?)

    Sure. I = -E/R.

    Isn't that negative voltage, as written?

    I should probably have more coffee before trying to figure this out

    Having just finished my first cup of Peets, I'm way ahead of you.

    The minus sign just means that the current flows the opposite way from
    what an ordinary resistor would do. A negative resistor doesn't load
    down a signal, it helps it.

    In my case, I have basically a negative resistor across a parellel LC.
    So instead of a ringy thing dying out exponentially, it increases exponentially. That's an oscillator.

    Of course, an exponentially increasing oscillation can't keep
    increasing forever, so something has to limit the swing or else Planet
    Earth will be incinerated. If you Spice the case of paralleled L C -R,
    it swings to teravolts and runs out of floating-point range before we
    are all killed.

    (Of course you have to goose it to get it started.)

    I guess the L C -R can still have a low Q, in which case it would be
    stable. Sure, it doesn't have enough gain to oscillate. I've done
    that.

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  • From john larkin @21:1/5 to All on Tue Jul 16 07:18:12 2024
    On Tue, 16 Jul 2024 06:57:07 -0700, john larkin
    <jlarkin_highland_tech> wrote:

    On Tue, 16 Jul 2024 09:13:53 -0000 (UTC), Dan Purgert <dan@djph.net>
    wrote:

    On 2024-07-15, john larkin wrote:
    On Mon, 15 Jul 2024 14:40:44 -0000 (UTC), Dan Purgert <dan@djph.net>
    wrote:

    On 2024-07-15, john larkin wrote:
    Does a negative 50-ohm resistor make as much noise as a regular 50 ohm >>>>> resistor?

    Yes, just inverted?

    (also, "negative" resistance?)

    Sure. I = -E/R.

    Isn't that negative voltage, as written?

    I should probably have more coffee before trying to figure this out

    Having just finished my first cup of Peets, I'm way ahead of you.

    The minus sign just means that the current flows the opposite way from
    what an ordinary resistor would do. A negative resistor doesn't load
    down a signal, it helps it.

    In my case, I have basically a negative resistor across a parellel LC.
    So instead of a ringy thing dying out exponentially, it increases >exponentially. That's an oscillator.

    Of course, an exponentially increasing oscillation can't keep
    increasing forever, so something has to limit the swing or else Planet
    Earth will be incinerated. If you Spice the case of paralleled L C -R,
    it swings to teravolts and runs out of floating-point range before we
    are all killed.

    (Of course you have to goose it to get it started.)

    I guess the L C -R can still have a low Q, in which case it would be
    stable. Sure, it doesn't have enough gain to oscillate. I've done
    that.


    Probably wrong. Any L C -R will probably oscillate. Need more coffee.

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