How does Spice calculate Current Noise?

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)

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

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

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

Introverts Unite!

Quietly.

In your own homes.

Trypo, should be:

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

Dyslexics of the world, untie!