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  1. #1
    Newbie level 5
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    Measurement of static leakage power using NanoSim

    I have a question regarding measurement of static leakage power using NanoSim.

    What I am trying to measure is the static wasted power in a NAND gate (or for that matter any circuit ... I am starting off small). Input is a HSPICE netlist of a NAND gate (4 transistors). Inputs to the NAND gate are 2 dc inputs. Simulation time for some 400 nsec (arbitrary). What I want is the
    leakage power dissipated due to the subthreshold leakage currents flowing through the dc paths.

    I was reading in the documentation NanoSim does measure leakage (wasted) current -- both static and dynamic. I have been trying to use the track_wasted and split_wasted option. According to the docs, it says the split_wasted option splits the wasted currents (powers) into static and dynamic. I tried it out for a simple nand gate. My input is in the form of a SPICE netlist:

    .inc 'TSMC-0.35um.model'
    .global GND

    V_vdd Vdd GND 1V

    *V_a A1 GND PWL (0n 0 49n 0 50n 1 100n 1 101n 0)
    *V_b B1 GND PWL (0n 0 100n 0 101n 1)

    V_a A1 GND dc 0.0
    V_b B1 GND dc 1.0


    * HSPICE file created from nanf201.ext - technology: SCN4M.25.TSMC

    .option scale=0.25u

    m0 O A1 Vdd Vdd CMOSPL w=25 l=2
    + ad=150 pd=62 as=242 ps=132
    m1 Vdd B1 O Vdd CMOSPL w=25 l=2
    + ad=0 pd=0 as=0 ps=0
    m2 a_13_3 A1 GND GND CMOSNL w=21 l=2
    + ad=42 pd=46 as=105 ps=52
    m3 O B1 a_13_3 GND CMOSNL w=21 l=2
    + ad=79 pd=52 as=0 ps=0
    C0 Vdd GND 6.8fF

    ** hspice subcircuit dictionary

    **.measure tran Vdd_pwr avg power from=0ns to=400ns

    .tran .1ns 200n
    .end

    My cfg file:

    report_block_powr total track_power=1 split_wasted=1 *


    When I ran the above circuit, it gives dynamic wasted = 0 W and static wasted = 0 W and % Wasted power = 100%. I understand the dynamic wasted part -- since there is no switching activity, there cant be short circuit currents -- but shouldn't there be some static leakage power ??

    Can someone point out to me, what I am doing wrong -- or is the simulator not capable of getting this value ?? I would really appreciate if someone sheds some light on this for me.

    thanks in advance

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  2. #2
    Newbie level 3
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    Re: Measurement of static leakage power using NanoSim

    The problem could be with the large units used by report_block_powr. The leakage is pretty small number and may be rounded to 0 when higher units are used. Try changing units using
    set_sim_ires=1pA
    set_print_ires=1pA
    in the cfg file.
    I think what might solve your problem with most certainty is using the command
    set_sim_leak
    in the cfg file (no options exist for this command).



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