( ESNUG 389 Item 11 ) -------------------------------------------- [03/06/02]
From: Mouli Gopalakrishnan <cgopalak@csee.usf.edu>
Subject: Can't Get Static Leakage Power Of A NAND Gate In NanoSim/PowerMill
Hi John,
I have a question regarding measurement of static leakage power using
NanoSim (formerly EPIC's PowerMill tool.) I wasn't satisfied with the
Synopsys tech support's answer. :(
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 do this using HSPICE by printing out VGS values and determining if each
transistor is ON/OFF and measuring the instantaneous power at that time if
it is OFF. This is time consuming and tedious and I wish there is a way by
which a tool like NanoSim could help me. :(
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.
- Mouli Gopalakrishnan
University of South Florida Tampa, FLA
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