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Measuring Power Consumption of Processor

Discussion in 'Electronic Basics' started by Nilesh Khambekar, Nov 18, 2004.

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  1. Hi,

    question about basics of power measurement...

    In the power equation, we have
    1) static power by = I X Vdd
    [static]
    2) switching power = 0.5 X C X (Vdd^2) X f
    [dynamic]
    3) short circuit power = Q X vdd X f X N
    [dynamic]
    4) leakage power = I(leak) X Vdd
    [static]

    How do we measure these components?

    -For finding static power, we find total current flowing (from voltage
    drop across register). and Multiply it by Supply voltage (core
    voltage). right?

    -How do we measure switching power of processor assuming maximum
    switching activity? we know f and Vdd. What about C ?

    -How do we measure short circuit power ?

    -Can we disable clock to find leakage power component of static power?

    Thanks,
    Nilesh
     
  2. John Larkin

    John Larkin Guest

    1.0, not 0.5. Every clock has two edges.

    John
     
  3. john jardine

    john jardine Guest

    Does not, the bucket fill on the positive edge, using the top FET?. Bucket
    contents dumped on neg edge.
    regards
    john
     
  4. Fred Bartoli

    Fred Bartoli Guest

    Sure, but... 1/2 C V^2 is just the energy stored into the capacitor and
    doesn't account for the energy wasted into the switches.

    For a cap charged from a supply U :

    Wu = U int(i*dt)

    and also U = int(i/C*dt)

    which gives Wu = C U^2.

    So, 1/2 C U^2 dissipated into the CPU at the rising edge, and the same at
    the falling edge.
     
  5. john jardine

    john jardine Guest

    "Fred Bartoli"
    Thanks Fred.
    I'd come in from a simple SMPS 'transfer of energy' POV, assuming zero
    switch losses and neglecting that it needs the averaged work to charge the
    cap (*0.5) and then averaged work to discharge it (*0.5).
    regards
    john
     
  6. Hi,

    Thanks.

    Let me pinpoint my question...
    What is practical procedure to measure these power components ?
    1) How do I get C for finding switching power ?
    2) How do I get I(leak) to meaure short circuit power
    3) How can one measure leakage power

    thanks,
    Nilesh

     
  7. John Larkin

    John Larkin Guest

    Measure the slope of the Icc-versus-Fclock curve. Or look for it on a
    datasheet, where it's sometimes specified. Note that "dynamic power
    capacitance" isn't always real capacitance, as it may include
    significant shoot-through current spikes.
    Short circuit power is zero.
    Measure Icc at zero clock frequency. Multiply by Vcc.

    John
     
  8. Hi,

    Thanks!

    Can you suggest some useful book related to this topic?
    Or some good online references?

    This will help me doing the actual measurements.

    Basically I am CS student having some work experience in embedded systems.

    again thanks,
    Nilesh
     
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