Noise in parallel

P

Paul

Guest
Hi,

I'm having a discussion about placing two noise sources in parallel
such as Johnson noise. I would appreciate it if a EE would please tell
us who is correct? Here is the conversation -->


I wrote:
++++++
Any EE knows that parallel noise sources decreases.

Here is a Spice noise analysis on one single 1N914 diode, full
bandwidth -->
32.324 uV rms

Here is a Spice noise analysis on two 1N914 diodes in parallel, full
bandwidth -->
22.856 uV rms

22.856 uV / 32.324 uV = 0.70709


And here's the noise source of two 1N914 diodes in *series* -->

45.713 ľV rms

45.713 ľV / 32.324 uV = 1.4142

As stated, two noise source in *series* is relative to sqrt(n).

The net noise from noise sources in parallel decreases. The net noise
from noise sources in series increases.
++++++



The other person wrote:
------
if you base your existence on simulation software rather than reality
no wonder you are chasing a stupid idea. Noise does not negate because
of increased samples you moron.

I spent 6 years as a senior geophysicist for Exxon and I know my stuff
when it comes to noise. Seismic data is all about signal and noise and
it is universal in information theory.

Prove it to yourself fool by simply generating random numbers in a
basic program and see that it is impossible to get a noise peak of 100
or -100 if the random number is between 0 and 1 with a -0.5 bias, that
is just so obvious, then run it accumulating a million loops and look
at the highest responses, there will be some greater than 1, some
greater than 10 etc etc.

If there is a coherent signal bias then the signal adds directly to
the n samples but the noise adds to the sqrt of n samples x rms noise.

So PL when you start attacking peoples knowledge you want to do so
with a bit more justification than your 2 sample spice data.

You are the most arrogant and stupid pseudo scientist I have ever
read.

There are a lot of people here that are real scientists that have
given you a hearing and you have proved to be the proverbial
Whackadoo.

Grow up Paul, get a life and do something you can achieve, you will
never qualify as a scientist!!!!


BTW read my original post on noise and see that it mentions the issue
of increased load, that is the real issue!

A spice model if run properly will reflect that the load increases
with resistors in parallel, so too did I. So in my post I said that
diode arrays would not work and so do you. Also in my post I pointed
out your stupidity for if not in parallel then what use is pA currents
for the real World. MORON.

PL F off!!
------


I wrote:
++++++
Resistance decreases when paralleling. I'm recalling when you tried to
show some math on calculating power where you even forgot to write the
voltage, LOL.

I already explained your error, as you forget to include phase angle.
When you include phase angle in addition to amplitude you will clearly
see your error. That is why the Johnson noise equation clearly shows I
am correct -->

Vn = sqrt(4 k T R BW)

R is resistance. When you place two resistors in parallel you get half
the resistance. Do the math, will you.
++++++




The other person wrote:
------
You really are showing yourself to be so stupid.

The issue of noise is an issue of measured noise across a load.

Noise itself does not decrease but measured noise decreases because
the load increases.

If you are going to quote a formula do us the service of understanding
it yourself first.

You argue for me not against me.


read again moron!

I said load increases with resistors in parallel!!.

You laugh when you cannot read or understand apparently.

Paul I know you have never held a science post in your life and that
seems to have come from an incomplete education experience, perhaps
you flunked science. It is fair to say that you have been ridiculed by
many in your life which is why you stupidly attack people.

I can only suggest that you start listening a bit more and go back to
college if you can afford to do so.
------
 
On Thu, 16 Jul 2009 16:43:02 -0700 (PDT), Paul <energymover@gmail.com>
wrote:

Hi,

I'm having a discussion about placing two noise sources in parallel
such as Johnson noise. I would appreciate it if a EE would please tell
us who is correct? Here is the conversation --


I wrote:
++++++
Any EE knows that parallel noise sources decreases.

Here is a Spice noise analysis on one single 1N914 diode, full
bandwidth --
32.324 uV rms

Here is a Spice noise analysis on two 1N914 diodes in parallel, full
bandwidth --
22.856 uV rms

22.856 uV / 32.324 uV = 0.70709


And here's the noise source of two 1N914 diodes in *series* --

45.713 ľV rms

45.713 ľV / 32.324 uV = 1.4142

Were the diodes run at some DC bias current? If so, what was the
current of each individual diode in the above situations?

Diodes don't necessarily behave like resistive noise generators
because diode impedance and noise depend on bias currents.

John
 
On Jul 16, 5:48 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Thu, 16 Jul 2009 16:43:02 -0700 (PDT), Paul <energymo...@gmail.com
wrote:



Hi,

I'm having a discussion about placing two noise sources in parallel
such as Johnson noise. I would appreciate it if a EE would please tell
us who is correct? Here is the conversation --

I wrote:
++++++
Any EE knows that parallel noise sources decreases.

Here is a Spice noise analysis on one single 1N914 diode, full
bandwidth --
32.324 uV rms

Here is a Spice noise analysis on two 1N914 diodes in parallel, full
bandwidth --
22.856 uV rms

22.856 uV / 32.324 uV = 0.70709

And here's the noise source of two 1N914 diodes in *series* --

45.713 ľV rms

45.713 ľV / 32.324 uV = 1.4142

Were the diodes run at some DC bias current? If so, what was the
current of each individual diode in the above situations?

Diodes don't necessarily behave like resistive noise generators
because diode impedance and noise depend on bias currents.

John


Hi,

It was done in LTspice at zero bias, at RT, which I believe is 27C in
LTspice. So the noise is Johnson noise at Rz if we ignore Ct. In this
case, the noise is easily calculated from kTC noise, Vn = sqrt(k T /
C).

So who's correct? He's saying the noise from two noise sources in
parallel increases. I'm saying it decreases.

Regards,
Paul
 
On Thu, 16 Jul 2009 17:58:47 -0700 (PDT), Paul <energymover@gmail.com>
wrote:

On Jul 16, 5:48 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Thu, 16 Jul 2009 16:43:02 -0700 (PDT), Paul <energymo...@gmail.com
wrote:



Hi,

I'm having a discussion about placing two noise sources in parallel
such as Johnson noise. I would appreciate it if a EE would please tell
us who is correct? Here is the conversation --

I wrote:
++++++
Any EE knows that parallel noise sources decreases.

Here is a Spice noise analysis on one single 1N914 diode, full
bandwidth --
32.324 uV rms

Here is a Spice noise analysis on two 1N914 diodes in parallel, full
bandwidth --
22.856 uV rms

22.856 uV / 32.324 uV = 0.70709

And here's the noise source of two 1N914 diodes in *series* --

45.713 ľV rms

45.713 ľV / 32.324 uV = 1.4142

Were the diodes run at some DC bias current? If so, what was the
current of each individual diode in the above situations?

Diodes don't necessarily behave like resistive noise generators
because diode impedance and noise depend on bias currents.

John



Hi,

It was done in LTspice at zero bias, at RT, which I believe is 27C in
LTspice. So the noise is Johnson noise at Rz if we ignore Ct. In this
case, the noise is easily calculated from kTC noise, Vn = sqrt(k T /
C).

So who's correct? He's saying the noise from two noise sources in
parallel increases. I'm saying it decreases.

Regards,
Paul
Given two identical noise sources having identical source impedances,
if the noise voltage of one unloaded source is E, the noise voltage of
the paralleled sources is 0.707 * E.

That can be arrived at several different ways.

But be careful: the default behavior of the diodes that come with LT
Spice is very wrong. But that won't affect the generalization about
paralleling.

John
 
"Paul"

I'm having a discussion about placing two noise sources in parallel
such as Johnson noise. I would appreciate it if a EE would please tell
us who is correct?


** Johnson noise sources implies resistances.

Two resistances in parallel follow a simple rule for computing the
combination.

The noise voltage (Vn) in any given bandwidth is related to that combined
value by the usual formula.

Vn = sq.rt. 4kTBR

Vn is proportinal to the sq.rt. of the combined resistance value - if all
other factors remain the same.



...... Phil
 
On Thu, 16 Jul 2009 19:31:01 -0700 (PDT), Paul <energymover@gmail.com>
wrote:

On Jul 16, 7:11 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Thu, 16 Jul 2009 17:58:47 -0700 (PDT), Paul <energymo...@gmail.com
wrote:



On Jul 16, 5:48 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Thu, 16 Jul 2009 16:43:02 -0700 (PDT), Paul <energymo...@gmail.com
wrote:

Hi,

I'm having a discussion about placing two noise sources in parallel
such as Johnson noise. I would appreciate it if a EE would please tell
us who is correct? Here is the conversation --

I wrote:
++++++
Any EE knows that parallel noise sources decreases.

Here is a Spice noise analysis on one single 1N914 diode, full
bandwidth --
32.324 uV rms

Here is a Spice noise analysis on two 1N914 diodes in parallel, full
bandwidth --
22.856 uV rms

22.856 uV / 32.324 uV = 0.70709

And here's the noise source of two 1N914 diodes in *series* --

45.713 ľV rms

45.713 ľV / 32.324 uV = 1.4142

Were the diodes run at some DC bias current? If so, what was the
current of each individual diode in the above situations?

Diodes don't necessarily behave like resistive noise generators
because diode impedance and noise depend on bias currents.

John

Hi,

It was done in LTspice at zero bias, at RT, which I believe is 27C in
LTspice. So the noise is Johnson noise at Rz if we ignore Ct. In this
case, the noise is easily calculated from kTC noise, Vn = sqrt(k T /
C).

So who's correct? He's saying the noise from two noise sources in
parallel increases. I'm saying it decreases.

Regards,
Paul

Given two identical noise sources having identical source impedances,
if the noise voltage of one unloaded source is E, the noise voltage of
the paralleled sources is 0.707 * E.


Thanks, that's what I was telling the guy, but he kept calling me a
stupid moron among other names.



That can be arrived at several different ways.

But be careful: the default behavior of the diodes that come with LT
Spice is very wrong. But that won't affect the generalization about
paralleling.


What type of behaviors? I haven't seen anything to far off in LTspice
given a good detailed model. The problem is a lot of diode models are
to generalized. Also, the same part # made by different manufactures
are often different. For example the Ge diodes such as the 1N314A vary
so much from manufacture to manufacture that a generalized model is
almost worthless.

One limitation is LTspice is the diode parameters are static. The
parameters in a good microwave Si diode don't change much, but the
1N34A does. The difference in emission coefficient between zero bias
and 10 mA could be significant.

Set up LT Spice to curve-trace its 1N914 model.

John
 
On Jul 16, 7:11 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Thu, 16 Jul 2009 17:58:47 -0700 (PDT), Paul <energymo...@gmail.com
wrote:



On Jul 16, 5:48 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Thu, 16 Jul 2009 16:43:02 -0700 (PDT), Paul <energymo...@gmail.com
wrote:

Hi,

I'm having a discussion about placing two noise sources in parallel
such as Johnson noise. I would appreciate it if a EE would please tell
us who is correct? Here is the conversation --

I wrote:
++++++
Any EE knows that parallel noise sources decreases.

Here is a Spice noise analysis on one single 1N914 diode, full
bandwidth --
32.324 uV rms

Here is a Spice noise analysis on two 1N914 diodes in parallel, full
bandwidth --
22.856 uV rms

22.856 uV / 32.324 uV = 0.70709

And here's the noise source of two 1N914 diodes in *series* --

45.713 ľV rms

45.713 ľV / 32.324 uV = 1.4142

Were the diodes run at some DC bias current? If so, what was the
current of each individual diode in the above situations?

Diodes don't necessarily behave like resistive noise generators
because diode impedance and noise depend on bias currents.

John

Hi,

It was done in LTspice at zero bias, at RT, which I believe is 27C in
LTspice. So the noise is Johnson noise at Rz if we ignore Ct. In this
case, the noise is easily calculated from kTC noise, Vn = sqrt(k T /
C).

So who's correct? He's saying the noise from two noise sources in
parallel increases. I'm saying it decreases.

Regards,
Paul

Given two identical noise sources having identical source impedances,
if the noise voltage of one unloaded source is E, the noise voltage of
the paralleled sources is 0.707 * E.

Thanks, that's what I was telling the guy, but he kept calling me a
stupid moron among other names.



That can be arrived at several different ways.

But be careful: the default behavior of the diodes that come with LT
Spice is very wrong. But that won't affect the generalization about
paralleling.

What type of behaviors? I haven't seen anything to far off in LTspice
given a good detailed model. The problem is a lot of diode models are
to generalized. Also, the same part # made by different manufactures
are often different. For example the Ge diodes such as the 1N314A vary
so much from manufacture to manufacture that a generalized model is
almost worthless.

One limitation is LTspice is the diode parameters are static. The
parameters in a good microwave Si diode don't change much, but the
1N34A does. The difference in emission coefficient between zero bias
and 10 mA could be significant.

That's enough of my rant. :)


Paul
 
"Paul"

( snip mind numbing drivel)

I have not matched LTspice with the full I-V curve of a particular
1N914, but the 1N914 model that comes with LTspice is remarkably close
to a Radio Shack 1N914 diode at zero bias.


** What do you imagine the resistance of an 1N914 the diode is at zero bias
and room temp ?

50k ?

500k ?

50M ?? ?



I'd imagine it's close at higher current levels as well.


** That is so fucking stupid it must have come from a code scribbler .




...... Phil
 
On Fri, 17 Jul 2009 08:28:26 -0700 (PDT), Paul <energymover@gmail.com>
wrote:

On Jul 17, 7:28 am, "Phil Allison" <phi...@tpg.com.au> wrote:
"Paul"

( snip mind numbing drivel)

I have not matched LTspice with the full I-V curve of a particular
1N914, but the 1N914 model that comes with LTspice is remarkably close
to a Radio Shack 1N914 diode at zero bias.

** What do you imagine the resistance of an 1N914 the diode is at zero bias
and room temp ?

  50k ?

  500k ?

  50M  ?? ?

 I'd imagine it's close at higher current levels as well.

** That is so fucking stupid it must have come from a code scribbler .

..... Phil



Zero bias resistance is an important and common parameter in certain
types of diodes. The zero bias resistance of the 1N914 is ~ 8 Mohms,
and varies somewhat from manufacturer to manufacturer.

PL
Here's a PAD5...

ftp://jjlarkin.lmi.net/PAD5.JPG

which hits roughly 1 Tohm.

The 1N914 that comes with LT Spice simulates at about 20M, suggesting
an Is of around 2 nA. I suppose I could actually read the model specs
and see what Is really is...

John
 
On Jul 16, 8:05 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Thu, 16 Jul 2009 19:31:01 -0700 (PDT), Paul <energymo...@gmail.com
wrote:



On Jul 16, 7:11 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Thu, 16 Jul 2009 17:58:47 -0700 (PDT), Paul <energymo...@gmail.com
wrote:

On Jul 16, 5:48 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Thu, 16 Jul 2009 16:43:02 -0700 (PDT), Paul <energymo...@gmail.com
wrote:

Hi,

I'm having a discussion about placing two noise sources in parallel
such as Johnson noise. I would appreciate it if a EE would please tell
us who is correct? Here is the conversation --

I wrote:
++++++
Any EE knows that parallel noise sources decreases.

Here is a Spice noise analysis on one single 1N914 diode, full
bandwidth --
32.324 uV rms

Here is a Spice noise analysis on two 1N914 diodes in parallel, full
bandwidth --
22.856 uV rms

22.856 uV / 32.324 uV = 0.70709

And here's the noise source of two 1N914 diodes in *series* --

45.713 ľV rms

45.713 ľV / 32.324 uV = 1.4142

Were the diodes run at some DC bias current? If so, what was the
current of each individual diode in the above situations?

Diodes don't necessarily behave like resistive noise generators
because diode impedance and noise depend on bias currents.

John

Hi,

It was done in LTspice at zero bias, at RT, which I believe is 27C in
LTspice. So the noise is Johnson noise at Rz if we ignore Ct. In this
case, the noise is easily calculated from kTC noise, Vn = sqrt(k T /
C).

So who's correct? He's saying the noise from two noise sources in
parallel increases. I'm saying it decreases.

Regards,
Paul

Given two identical noise sources having identical source impedances,
if the noise voltage of one unloaded source is E, the noise voltage of
the paralleled sources is 0.707 * E.

Thanks, that's what I was telling the guy, but he kept calling me a
stupid moron among other names.

That can be arrived at several different ways.

But be careful: the default behavior of the diodes that come with LT
Spice is very wrong. But that won't affect the generalization about
paralleling.

What type of behaviors?  I haven't seen anything to far off in LTspice
given a good detailed model. The problem is a lot of diode models are
to generalized. Also, the same part # made by different manufactures
are often different. For example the Ge diodes such as the 1N314A vary
so much from manufacture to manufacture that a generalized model is
almost worthless.

One limitation is LTspice is the diode parameters are static. The
parameters in a good microwave Si diode don't change much, but the
1N34A does. The difference in emission coefficient between zero bias
and 10 mA could be significant.

Set up LT Spice to curve-trace its 1N914 model.

John


The accuracy is limited to the model. LTspice only models fundamental
components. As you know, a real component is modeled using numerous
ideal components. A real diode is complex, and sometimes requires
using multiple diodes just to accurately model one single diode. I've
seen manufactures using two diodes to model ultra low ZBD's that have
unusually high reverse leakage.

I have not matched LTspice with the full I-V curve of a particular
1N914, but the 1N914 model that comes with LTspice is remarkably close
to a Radio Shack 1N914 diode at zero bias. I'd imagine it's close at
higher current levels as well.

Paul
 
On Jul 17, 7:28 am, "Phil Allison" <phi...@tpg.com.au> wrote:
"Paul"

( snip mind numbing drivel)

I have not matched LTspice with the full I-V curve of a particular
1N914, but the 1N914 model that comes with LTspice is remarkably close
to a Radio Shack 1N914 diode at zero bias.

** What do you imagine the resistance of an 1N914 the diode is at zero bias
and room temp ?

  50k ?

  500k ?

  50M  ?? ?

 I'd imagine it's close at higher current levels as well.

** That is so fucking stupid it must have come from a code scribbler .

..... Phil


Zero bias resistance is an important and common parameter in certain
types of diodes. The zero bias resistance of the 1N914 is ~ 8 Mohms,
and varies somewhat from manufacturer to manufacturer.

PL
 
On Jul 17, 9:01 am, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 17 Jul 2009 08:28:26 -0700 (PDT), Paul <energymo...@gmail.com
wrote:



On Jul 17, 7:28 am, "Phil Allison" <phi...@tpg.com.au> wrote:
"Paul"

( snip mind numbing drivel)

I have not matched LTspice with the full I-V curve of a particular
1N914, but the 1N914 model that comes with LTspice is remarkably close
to a Radio Shack 1N914 diode at zero bias.

** What do you imagine the resistance of an 1N914 the diode is at zero bias
and room temp ?

  50k ?

  500k ?

  50M  ?? ?

 I'd imagine it's close at higher current levels as well.

** That is so fucking stupid it must have come from a code scribbler .

..... Phil

Zero bias resistance is an important and common parameter in certain
types of diodes. The zero bias resistance of the 1N914 is ~ 8 Mohms,
and varies somewhat from manufacturer to manufacturer.

PL

Here's a PAD5...

ftp://jjlarkin.lmi.net/PAD5.JPG

which hits roughly 1 Tohm.

The 1N914 that comes with LT Spice simulates at about 20M, suggesting
an Is of around 2 nA. I suppose I could actually read the model specs
and see what Is really is...

John

It depends on the diode model and manufacturer, but I seriously doubt
that diode is a 1N914. My radio shack 1N914 was close to what LTspice
predicts.

Anyhow, the first datasheet I found that shows a Vr vs Ir graph shows
1.5nA @ 10V = 6.7 Gohms. This is not Ro, but a relatively high reverse
voltage, 10V. LTspice stock 1N914 shows 4.0 Gohms @ 10V (reverse
voltage). The problem with modeling this particular 1N914BWS diode is
that as you can see in the graph the diode begins changing
characteristics at ~ 15V Vr, as it begins to slightly breakdown. To
model anything beyond 15V Vr would require multiple diodes in the
model. Although, modeling a diode near Rz is entirely different, as
the common diode characteristic is predictable according to the ideal
diode equation.

See bottom of page 3 -->
http://www.fairchildsemi.com/ds/1N%2F1N4148WS.pdf


Paul
 
On Jul 17, 9:40 am, Paul <energymo...@gmail.com> wrote:
On Jul 17, 9:01 am, John Larkin



jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 17 Jul 2009 08:28:26 -0700 (PDT), Paul <energymo...@gmail.com
wrote:

On Jul 17, 7:28 am, "Phil Allison" <phi...@tpg.com.au> wrote:
"Paul"

( snip mind numbing drivel)

I have not matched LTspice with the full I-V curve of a particular
1N914, but the 1N914 model that comes with LTspice is remarkably close
to a Radio Shack 1N914 diode at zero bias.

** What do you imagine the resistance of an 1N914 the diode is at zero bias
and room temp ?

  50k ?

  500k ?

  50M  ?? ?

 I'd imagine it's close at higher current levels as well.

** That is so fucking stupid it must have come from a code scribbler .

..... Phil

Zero bias resistance is an important and common parameter in certain
types of diodes. The zero bias resistance of the 1N914 is ~ 8 Mohms,
and varies somewhat from manufacturer to manufacturer.

PL

Here's a PAD5...

ftp://jjlarkin.lmi.net/PAD5.JPG

which hits roughly 1 Tohm.

The 1N914 that comes with LT Spice simulates at about 20M, suggesting
an Is of around 2 nA. I suppose I could actually read the model specs
and see what Is really is...

John

It depends on the diode model and manufacturer, but I seriously doubt
that diode is a 1N914.

I'm only saying that *if* the graph suggests a 1N914 diode is ~ 1 Tohm
at Rz.

Paul
 
"Paul"
"Phil Allison"
( snip mind numbing drivel)

I have not matched LTspice with the full I-V curve of a particular
1N914, but the 1N914 model that comes with LTspice is remarkably close
to a Radio Shack 1N914 diode at zero bias.

** What do you imagine the resistance of an 1N914 the diode is at zero
bias
and room temp ?

50k ?

500k ?

50M ?? ?

I'd imagine it's close at higher current levels as well.

** That is so fucking stupid it must have come from a code scribbler .

Zero bias resistance is an important and common parameter in certain
types of diodes. The zero bias resistance of the 1N914 is ~ 8 Mohms,
and varies somewhat from manufacturer to manufacturer.

** Any sane reason for computing the noise voltage of that ??




..... Phil
 
Paul wrote:
Hi,

I'm having a discussion about placing two noise sources in parallel
such as Johnson noise. I would appreciate it if a EE would please tell
us who is correct?
Basically, you are correct. All things being equal of course.

I spent 6 years as a senior geophysicist for Exxon and I know my stuff
when it comes to noise. Seismic data is all about signal and noise and
it is universal in information theory.
Funny he mentions that, I've spent more than 10 years in the marine Seismic
industry designing seimsic data aquisition equiment. Parallel components in
seismic analog front ends are a common technique to lower the noise figure.
Not uncommon in other industries either, but I wouldn't say "every EE
knows", I've found it is one of the lesser known techniques.

Seems he has a bee in his bonet, good luck with that!

Dave.
--
---------------------------------------------
Check out my Electronics Engineering Video Blog & Podcast:
http://www.alternatezone.com/eevblog/
 
On Jul 16, 10:11 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Thu, 16 Jul 2009 17:58:47 -0700 (PDT), Paul <energymo...@gmail.com
wrote:





On Jul 16, 5:48 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Thu, 16 Jul 2009 16:43:02 -0700 (PDT), Paul <energymo...@gmail.com
wrote:

Hi,

I'm having a discussion about placing two noise sources in parallel
such as Johnson noise. I would appreciate it if a EE would please tell
us who is correct? Here is the conversation --

I wrote:
++++++
Any EE knows that parallel noise sources decreases.

Here is a Spice noise analysis on one single 1N914 diode, full
bandwidth --
32.324 uV rms

Here is a Spice noise analysis on two 1N914 diodes in parallel, full
bandwidth --
22.856 uV rms

22.856 uV / 32.324 uV = 0.70709

And here's the noise source of two 1N914 diodes in *series* --

45.713 ľV rms

45.713 ľV / 32.324 uV = 1.4142

Were the diodes run at some DC bias current? If so, what was the
current of each individual diode in the above situations?

Diodes don't necessarily behave like resistive noise generators
because diode impedance and noise depend on bias currents.

John

Hi,

It was done in LTspice at zero bias, at RT, which I believe is 27C in
LTspice. So the noise is Johnson noise at Rz if we ignore Ct. In this
case, the noise is easily calculated from kTC noise, Vn = sqrt(k T /
C).

So who's correct? He's saying the noise from two noise sources in
parallel increases. I'm saying it decreases.

Regards,
Paul

Given two identical noise sources having identical source impedances,
if the noise voltage of one unloaded source is E, the noise voltage of
the paralleled sources is 0.707 * E.

That can be arrived at several different ways.

But be careful: the default behavior of the diodes that come with LT
Spice is very wrong. But that won't affect the generalization about
paralleling.

John- Hide quoted text -

- Show quoted text -
Won't the current noise increase in lock step. Parallel impedances
reduce the thermal voltage noise and increase the thermal current
noise. The thermal noise power is a function of kT.

George H.



George H.
 
On Jul 16, 10:11 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Thu, 16 Jul 2009 17:58:47 -0700 (PDT), Paul <energymo...@gmail.com
wrote:





On Jul 16, 5:48 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Thu, 16 Jul 2009 16:43:02 -0700 (PDT), Paul <energymo...@gmail.com
wrote:

Hi,

I'm having a discussion about placing two noise sources in parallel
such as Johnson noise. I would appreciate it if a EE would please tell
us who is correct? Here is the conversation --

I wrote:
++++++
Any EE knows that parallel noise sources decreases.

Here is a Spice noise analysis on one single 1N914 diode, full
bandwidth --
32.324 uV rms

Here is a Spice noise analysis on two 1N914 diodes in parallel, full
bandwidth --
22.856 uV rms

22.856 uV / 32.324 uV = 0.70709

And here's the noise source of two 1N914 diodes in *series* --

45.713 ľV rms

45.713 ľV / 32.324 uV = 1.4142

Were the diodes run at some DC bias current? If so, what was the
current of each individual diode in the above situations?

Diodes don't necessarily behave like resistive noise generators
because diode impedance and noise depend on bias currents.

John

Hi,

It was done in LTspice at zero bias, at RT, which I believe is 27C in
LTspice. So the noise is Johnson noise at Rz if we ignore Ct. In this
case, the noise is easily calculated from kTC noise, Vn = sqrt(k T /
C).

So who's correct? He's saying the noise from two noise sources in
parallel increases. I'm saying it decreases.

Regards,
Paul

Given two identical noise sources having identical source impedances,
if the noise voltage of one unloaded source is E, the noise voltage of
the paralleled sources is 0.707 * E.

That can be arrived at several different ways.

But be careful: the default behavior of the diodes that come with LT
Spice is very wrong. But that won't affect the generalization about
paralleling.

John- Hide quoted text -

- Show quoted text -
Won't the current noise increase in lock step. Parallel impedances
reduce the thermal voltage noise and increase the thermal current
noise. The thermal noise power is a function of kT.

George H.



George H.
 
On Fri, 17 Jul 2009 20:00:58 -0700 (PDT), George Herold
<ggherold@gmail.com> wrote:

On Jul 16, 10:11 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Thu, 16 Jul 2009 17:58:47 -0700 (PDT), Paul <energymo...@gmail.com
wrote:





On Jul 16, 5:48 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Thu, 16 Jul 2009 16:43:02 -0700 (PDT), Paul <energymo...@gmail.com
wrote:

Hi,

I'm having a discussion about placing two noise sources in parallel
such as Johnson noise. I would appreciate it if a EE would please tell
us who is correct? Here is the conversation --

I wrote:
++++++
Any EE knows that parallel noise sources decreases.

Here is a Spice noise analysis on one single 1N914 diode, full
bandwidth --
32.324 uV rms

Here is a Spice noise analysis on two 1N914 diodes in parallel, full
bandwidth --
22.856 uV rms

22.856 uV / 32.324 uV = 0.70709

And here's the noise source of two 1N914 diodes in *series* --

45.713 ľV rms

45.713 ľV / 32.324 uV = 1.4142

Were the diodes run at some DC bias current? If so, what was the
current of each individual diode in the above situations?

Diodes don't necessarily behave like resistive noise generators
because diode impedance and noise depend on bias currents.

John

Hi,

It was done in LTspice at zero bias, at RT, which I believe is 27C in
LTspice. So the noise is Johnson noise at Rz if we ignore Ct. In this
case, the noise is easily calculated from kTC noise, Vn = sqrt(k T /
C).

So who's correct? He's saying the noise from two noise sources in
parallel increases. I'm saying it decreases.

Regards,
Paul

Given two identical noise sources having identical source impedances,
if the noise voltage of one unloaded source is E, the noise voltage of
the paralleled sources is 0.707 * E.

That can be arrived at several different ways.

But be careful: the default behavior of the diodes that come with LT
Spice is very wrong. But that won't affect the generalization about
paralleling.

John- Hide quoted text -

- Show quoted text -

Won't the current noise increase in lock step. Parallel impedances
reduce the thermal voltage noise and increase the thermal current
noise. The thermal noise power is a function of kT.
You only have current noise if there's a finite-impedance load to have
current into.

If a noise source dumps I amps RMS into a short, adding an identical
noise source in parallel will result in 1.414 * I into the short.

John
 
On Jul 20, 7:54 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 17 Jul 2009 20:00:58 -0700 (PDT), George Herold





ggher...@gmail.com> wrote:
On Jul 16, 10:11 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Thu, 16 Jul 2009 17:58:47 -0700 (PDT), Paul <energymo...@gmail.com
wrote:

On Jul 16, 5:48 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Thu, 16 Jul 2009 16:43:02 -0700 (PDT), Paul <energymo...@gmail.com
wrote:

Hi,

I'm having a discussion about placing two noise sources in parallel
such as Johnson noise. I would appreciate it if a EE would please tell
us who is correct? Here is the conversation --

I wrote:
++++++
Any EE knows that parallel noise sources decreases.

Here is a Spice noise analysis on one single 1N914 diode, full
bandwidth --
32.324 uV rms

Here is a Spice noise analysis on two 1N914 diodes in parallel, full
bandwidth --
22.856 uV rms

22.856 uV / 32.324 uV = 0.70709

And here's the noise source of two 1N914 diodes in *series* --

45.713 ľV rms

45.713 ľV / 32.324 uV = 1.4142

Were the diodes run at some DC bias current? If so, what was the
current of each individual diode in the above situations?

Diodes don't necessarily behave like resistive noise generators
because diode impedance and noise depend on bias currents.

John

Hi,

It was done in LTspice at zero bias, at RT, which I believe is 27C in
LTspice. So the noise is Johnson noise at Rz if we ignore Ct. In this
case, the noise is easily calculated from kTC noise, Vn = sqrt(k T /
C).

So who's correct? He's saying the noise from two noise sources in
parallel increases. I'm saying it decreases.

Regards,
Paul

Given two identical noise sources having identical source impedances,
if the noise voltage of one unloaded source is E, the noise voltage of
the paralleled sources is 0.707 * E.

That can be arrived at several different ways.

But be careful: the default behavior of the diodes that come with LT
Spice is very wrong. But that won't affect the generalization about
paralleling.

John- Hide quoted text -

- Show quoted text -

Won't the current noise increase in lock step.  Parallel impedances
reduce the thermal voltage noise and increase the thermal current
noise.   The thermal noise power is a function of kT.

You only have current noise if there's a finite-impedance load to have
current into.

If a noise source dumps I amps RMS into a short, adding an identical
noise source in parallel will result in 1.414 * I into the short.

John- Hide quoted text -

- Show quoted text -

You only have current noise if there's a finite-impedance load to have
current into.

Photodiode into TIA op-amp. Until the frequency gets high the op-amp
looks like a short. But I can measure lots of current noise.

If a noise source dumps I amps RMS into a short, adding an identical
noise source in parallel will result in 1.414 * I into the short.

Yup, that seems right. Resistors have sqrt(4kTR) of volatge noise and
sqrt(4kT/R) of current noise.

George H.
 

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