[SI-LIST] Re: Creating Pseudo Random Bit Sequence (PRBS) stimuli for Hspice


>
>
>Hi! I used the utility written by Mentor(java utility)
>to create a PWL source for PRBS -10 pattern. I copied
>the PWL in my main circuit but when I run the sim it
>gives me error: "piecewise source   0:v_1a1   not
>increasing in time"
>Can somebody help me as to where I am making a
>mistake?
>The PWL source statement is:
>V_1a1 x_1a1 0 PWL (.......)
>Thanks in advance.
>Bob

I ran the Mentor utility to create a PRBS7 pattern
(127 bits long with 5ns bits) and included it in a simple
Hspice deck. It ran fine. (sample deck at end of this message).

Then I created a PRBS10 pattern as you did and attempted to run
it. I saw the same error message.

Troubleshooting shows that the problem is the commas embedded in the
time values > 1000ns. Hspice interprets the commas the same as a space.

So the spice snippet "1,000n 1.0 1,000.001n 1.0" parses out as:
1 000n 1.0 1 000.001n 1.0 . This creates the "not increasing in time"
error since .001n is < 1.0 which makes time march backwards (not a nice 
thing in Hspice land).

Sounds like the author (Weston Beal) needs to make a minor tweek to the code
to make it work reliably for Hspice syntax. Perhaps the commas are Ok
in other simulators ??

-Ray Anderson
Sun Microsystems


------------------sample spice deck follows--------------------

Test Circuit to Illustrate PWL Use

R1 1 2 50       * Rseries
L 2 3 60p       *  
C 3 0 5p        *
R 3 0 50        * Rload





* PRBS7 127 bit pattern generated by Java Utility
V1 1 0 PWL( 0.0n 1.0
+  10n 1.0  10.001n 0.0  15n 0.0  15.001n 1.0  30n 1.0  30.001n 0.0
+  35n 0.0  35.001n 1.0  40n 1.0  40.001n 0.0  50n 0.0  50.001n 1.0
+  55n 1.0  55.001n 0.0  60n 0.0  60.001n 1.0  70n 1.0  70.001n 0.0
+  85n 0.0  85.001n 1.0  95n 1.0  95.001n 0.0  100n 0.0  100.001n 1.0
+  120n 1.0  120.001n 0.0  125n 0.0  125.001n 1.0  135n 1.0  135.001n 0.0
+  140n 0.0  140.001n 1.0  145n 1.0  145.001n 0.0  150n 0.0  150.001n 1.0
+  160n 1.0  160.001n 0.0  165n 0.0  165.001n 1.0  175n 1.0  175.001n 0.0
+  185n 0.0  185.001n 1.0  190n 1.0  190.001n 0.0  200n 0.0  200.001n 1.0
+  205n 1.0  205.001n 0.0  220n 0.0  220.001n 1.0  235n 1.0  235.001n 0.0
+  255n 0.0  255.001n 1.0  260n 1.0  260.001n 0.0  265n 0.0  265.001n 1.0
+  290n 1.0  290.001n 0.0  300n 0.0  300.001n 1.0  305n 1.0  305.001n 0.0
+  310n 0.0  310.001n 1.0  315n 1.0  315.001n 0.0  320n 0.0  320.001n 1.0
+  335n 1.0  335.001n 0.0  345n 0.0  345.001n 1.0  355n 1.0  355.001n 0.0
+  360n 0.0  360.001n 1.0  365n 1.0  365.001n 0.0  380n 0.0  380.001n 1.0
+  385n 1.0  385.001n 0.0  395n 0.0  395.001n 1.0  415n 1.0  415.001n 0.0
+  430n 0.0  430.001n 1.0  435n 1.0  435.001n 0.0  440n 0.0  440.001n 1.0
+  445n 1.0  445.001n 0.0  465n 0.0  465.001n 1.0  475n 1.0  475.001n 0.0
+  500n 0.0  500.001n 1.0  505n 1.0  505.001n 0.0  535n 0.0  535.001n 1.0
+  570n 1.0  570.001n 0.0  575n 0.0  575.001n 1.0  580n 1.0  580.001n 0.0
+  585n 0.0  585.001n 1.0  590n 1.0  590.001n 0.0  595n 0.0  595.001n 1.0
+  600n 1.0  600.001n 0.0  610n 0.0  610.001n 1.0  620n 1.0  620.001n 0.0
+  630n 0.0  630.001n 1.0  635n 1.0 )

.tran 1ns 650ns
.option  post=1

.END


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