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.
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.
Does a negative 50-ohm resistor make as much noise as a regular 50 ohm resistor?
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.
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
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?)
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.
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
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.
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.
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?
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.
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:
I want to simulate jitter in a LC oscillator, and of course an
oscillator always has some nonlinear amplitude limiting mechanism.
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:
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.
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
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
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.
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.
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
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/ >
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:
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/ >
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
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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