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How does Spice calculate Current Noise?

How does Spice calculate Current Noise?

I know it takes V(ONOISE) and refers it to the input _current_ noise, but _how_ is that calculation done?

Thanks! ...Jim Thompson

-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

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| 1962 |

I'm looking for work... see my website.

Reply to
Jim Thompson
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Well, in LTspice I often plot things like 'V(Q1)*inoise/v(onoise)', which g ives Q1's contribution to the input-referred noise, which in my stuff is no rmally a current.

In a noise simulation, everything is linearized ahead of time, so Zin is a known function of frequency. You can express the simulated noise as either a current or as a voltage, but to separate the contributions of device nois e voltages and currents, you have to use actual algebra. ;)

Cheers

Phil Hobbs

(Back from a jaunt to Coney Island and preparing for another to the Catskil ls tomorrow)

Reply to
Phil Hobbs

I can do Algebra in PSpice ;-)

What's the (set of) equation(s)?

If I can measure Zin (I can), is it magnitude, or how is it handled? ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 

             I'm looking for work... see my website.
Reply to
Jim Thompson

I rarely leave the house on holidays... I despise crowds. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 

             I'm looking for work... see my website.
Reply to
Jim Thompson

It wasn't crowded, just enough people for a buzz. The only wait we had was ~10 minutes for a rooftop table in a beach bar. I really like Coney Island

--I'd like it more if it didn't have certain zones whose music is way too l oud, but you can easily avoid those.

Cheers

Phil Hobbs

Reply to
Phil Hobbs

Figured it out:

Do a normal .NOISE, but step in VAC and IAC ...

.ac DEC 101 10 100Meg .noise V([OUTL],[OUTR]) V_VAC .STEP PARAM PASS LIST 1 2

Step 1 selects source as VAC, Step 2 selects source as IAC

V([OUTL],[OUTR]) because it's a differential stage

In Probe get V(INOISE) from V(INOISE)@1

then INOISE:

I(INOISE) = V(ONOISE)@2/(V(OUTL,OUTR)@2/I(IMZ)@2/I(IMZ)@2)

IMZ is measuring the input current thus providing the transimpedance gain needed to calculate I(INOISE).

Thus I can get both V(INOISE) and I(INOISE) on a single display, and watch current noise go up as voltage noise goes down, thus can quickly find an optimum for the problem at hand. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 

             I'm looking for work... see my website.
Reply to
Jim Thompson

Introverts Unite!

Quietly.

In your own homes.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com 

I'm looking for work -- see my website!
Reply to
Tim Wescott

Trypo, should be:

I(INOISE) = V(ONOISE)@2/V(OUTL,OUTR)@2*I(IMZ)@2 ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 

             I'm looking for work... see my website.
Reply to
Jim Thompson

For PSpice Macro users...

.ac DEC 101 10 100Meg .noise V(A,B) V_VAC .STEP PARAM PASS LIST 1 2

(Step 1 selects source as VAC, Step 2 selects source as IAC)

VNOISE = V(INOISE)@1

INOISE(A,B) = V(ONOISE)@2/V(A,B)@2*I(IMZIN)@2

Where V(A,B) is the reference output ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 

             I'm looking for work... see my website.
Reply to
Jim Thompson

Dyslexics of the world, untie!

Reply to
Tom Del Rosso

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