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PSpice ABM prob

Discussion in 'CAD' started by Active8, Sep 7, 2003.

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  1. Active8

    Active8 Guest

    hi:

    i'm feeding an ABM expr part [ EXP1=acos(V(%IN)) ] with a 1Vpp sine
    wave. i get errors saying my input is invalid (i.e., >1). something's
    wrong here. my input is 2 1Vpp sines multiplied which is 1Vpp (probe
    output doesn't even come close to the reported error values) and then
    fed to the acos() part.

    i see the acos function isn't even listed as an ABM math function in the
    PSpice ref, but PSpice hasn't choked on it.

    i also can't figure how to get the Average value of a sine wave. not
    doable with an ABM expression, is it?

    TIA,
    mike
     
  2. Make a little integrator. I think pspice allows "time" as a variable, so
    you can divide the integrated value by time.

    Kevin Aylward

    http://www.anasoft.co.uk
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
     
  3. Active8

    Active8 Guest

    i have to "tweak" by .6 ... .7*Vmultout when over once. that's not
    right. 1*1=1 from the mult.

    mike
     
  4. Jim Thompson

    Jim Thompson Guest

    On Sun, 07 Sep 2003 20:10:58 GMT, Active8

    [snip]
    [snip]

    Congratulations! You've found a bug in PSpice. Looks like *both*
    ASIN and ACOS are defective.

    CHARLIE???

    ...Jim Thompson
     
  5. Active8

    Active8 Guest

    why do you say that? are those functions messing with you?

    no. it's telling me the output of the multiplier is 1.2xxx, rather the
    input to the acos function is to high. but as i said, the output of the
    mult, when probed, never shows anything over 1. maybe a little over, but
    not 1.2xxx or even the 1.4xxx i remember seeing on one run.

    i can't figure out how the ABM integral works thank's to lame docs. the
    integrator part *and* the STD function both return 0V DC for an input
    sin/cos which goes from 0V to 1V.

    mike
     
  6. Jim Thompson

    Jim Thompson Guest

    I ran ACOS with just a single-sine input... crashed PSpice v9.2.3 :)

    Reduced amplitude until it ran... 0.6V peak... output was absurd, but
    *was* centered on 1.57 which smells like 1.57 radians = 90°.

    Further testing reveals a cumulative problem. Works right up to input
    amplitude of 0.99. Amplitude of 1.0 locks up PSpice, trying a smaller
    value then crashes PSpice.

    ...Jim Thompson
     
  7. Active8

    Active8 Guest

    thought about that.

    i can't figure out how the ABM integral works thank's to lame docs. the
    integrator part *and* the SDT function both return 0V DC for an input
    sin/cos which goes from 0V to 1V.


    thanks,
    mike
     
  8. Active8

    Active8 Guest

    that's what i got for a DC input... .99V max. the error for 1VDC says
    the acos input is 1.001

    that .6V sin wave seems to work here. returns a value in radians for the
    given input. acos(.595) = .933, acos(-.593) = 2.2, acos(0) = 1.5708...
    why we can't input 1V is beyond me.

    mike
     
  9. Jim Thompson

    Jim Thompson Guest

    On Sun, 07 Sep 2003 22:44:17 GMT, Active8

    [snip]
    I have reported the problem to PSpice support.

    ...Jim Thompson
     
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