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CD4000 models - earthed pins

Discussion in 'CAD' started by The Captain, Jul 17, 2003.

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  1. The Captain

    The Captain Guest

    Does anyone know how to handle pins in a PSpice A/D circuit using
    CD4000 series IC models.

    My specific problem is with the CD4013 dual D type flip flop connected
    as a divide by two circuit. I am using + and - 5V supplies, specified
    in param as CD4000_VSS = -5V and CD4000_VDD = +10V. However, the S
    and R pins need to be connected to circuit earth or equivalent, which,
    in this case, is the -5V VSS level, as specified in param.

    How do I go about making this connection? I've tried connecting the S
    and R pins to a -5V VDC voltage source, but this simply doesn't work -
    Q output is near zero volts for all CK inputs.

    I'd appreciate any help, as this is holding up a fairly important
    project and it's an awkward thing to have to explain to investors!

    Regards

    John Fortier
     
  2. Does anyone know how to handle pins in a PSpice A/D circuit using
    I'm not a Pspice user, but a quick look at the Reference and User guides
    suggests it is not that far removed from Xspice, at least in some of the
    concepts. The S and R pins will almost certainly be 'digital', and as such
    you will need to connect them either to a 'digital ground', or 'digital
    power' - connecting them to analogue nodes (either normal ground or a power
    source) will probably make the simulator automatically introduce special
    a-to-d or d-to-a blocks in order to convert them, but whether they come out
    as 'low' or 'high' could be hit or miss (and will depend on the 'I/O model'
    referenced in the CD4013 model, apparently called 'IO_4000B', which likely
    'defines' the transition levels from low to high etc.). Find the appropriate
    D_GND or D_PWR symbols (or whatever they are called), and hook them in
    instead. This will also apply to the Vdd and Vss - the CD4013 model says
    they are optional, so if I were you I'd leave them out to see if it works
    with out them first!

    Hope that might be of some use.... (there are several sections in the User
    Guide about digital and mixed analog/digital simulation, but they are hardly
    a quick read!)

    Tim
     
  3. Ah ha...

    ....I now see where this is coming from - the 'Creating Custom Digital Power
    Supplies' section in the User Guide? (I didn't immediately see where the
    'odd' arithmetic with Vdd came from!) So R and S still need to be connected
    to digital nodes, but you'll have to make sure that you reset all the params
    properly so that all CD4000 chips 'see' the modified power supply (there
    appear to be quite a few things to consider which I can't comment on due to
    not being a Pspice user). It might be a good idea to see if you can get your
    circuit working with 0 - 5V supplies first perhaps, _then_ try modifying to
    +/-5V?

    Tim
     
  4. Jim Thompson

    Jim Thompson Guest

    [snip]

    There is apparently a way to configure a CD4000 Power Block for what
    you need, but since I haven't used a CD4000 since I was a kid ;-) I'd
    just build ideal EVALUE interfaces into and out of the CD4000.

    For example

    Einto4000 node1 0 Value {V(%IN+,%IN-)/2-2.5}

    Eoutof4000 node2 0 Value {V(%IN+,%IN-)*2-5}

    ...Jim Thompson
     
  5. The Captain

    The Captain Guest


    Thanks, everyone. The problem is now solved.

    John
     
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