NEED help for NAND simulation in spice

[yzzrlzc]

Xand 1 2 3 NAND2
V1 1 0 DC 5
V2 2 0 PULSE(0 5 0 0 0 5n 20n)
.tran 1ns 300ns

*NAND subcircuit
***********************************
.subckt NAND2 A B out
M1000 out A VDD VDD pfet w=10u l=1u
+ ad=30p pd=22u as=30p ps=32u
M1001 VDD B out VDD pfet w=10u l=1u
+ ad=0p pd=0u as=0p ps=0u
M1002 a_n52_6# A Gnd Gnd nfet w=10u l=1u
+ ad=30p pd=22u as=15p ps=16u
M1003 out B a_n52_6# Gnd nfet w=10u l=1u
+ ad=15p pd=16u as=0p ps=0u
C0 B gnd 3.4fF
C1 VDD gnd 49.4fF
******rail voltage***************
VDD VDD 0 DC 5V
Vgnd Gnd 0 DC 0
.ends NAND2
**********************************
.MODEL nfet NMOS ( .....)
.MODEL pfet NMOS ( .....)
.end

I cant get a correct output for node3(out in subcircuit)
can someone tell me what is wrong with it ?
do i need to make VDD and VGnd global?

 

[keith1200rs]

do i need to make VDD and VGnd global?

Yes. Otherwise the ground & vdd within the subcircuit will not connect outside the subcircuit.

Keith

 

[yzzrlzc]

my problem is not the global command
my problem is that I typed " plot 1" to show the result, while the right way to do it is " plot v(1)" anyway, rly appreciate your help

 

[keith1200rs]

I didn't spot that you had put the power source within the subcircuit. Normally the power source would be outside the subcircuit and the connections would have to be global.

Keith

 

[yzzrlzc]

i am sorry i am just a beginner
so using .global command should be as follows:

.global VDD
.global Vgnd
VDD VDD 0 DC 5
Vgnd Gnd 0 DC 0

.Xand 1 2 3 NAND2
.........
.subckt. nand2 A B out
(.......)
.ends
.model nfet/pfet NMOS/PMOS
(.......)

right???

 

[keith1200rs]

I would normally expect something like this:

.GLOBAL VDD! GND!
Vsupply VDD! 0 DC 5

Xand 1 2 3 NAND2
...

.subckt. nand2 A B out
M1000 out A VDD! VDD! pfet w=10u l=1u
+ ad=30p pd=22u as=30p ps=32u
M1002 a_n52_6# A GND! GND! nfet w=10u l=1u
+ ad=30p pd=22u as=15p ps=16u
...
.ends

. model ...

.end

You don't need to connect GND! to node zero in Hspice - it is treated as node zero. Other simulators may need a zero volt source to node zero (such as my simulator!).

I don't think you need the exclamation mark in Hspice, but it is common. I am not sure why, but it may be due to the digital libraries really coming from Cadence. I am not sure if it means it is global in Cadence without needing the GLOBAL statement. Anyway try it without the ! and see what happens.

Keith.

 

[yzzrlzc]

rly rly rly appreciate your help

sorry for replying late

 

[keith1200rs]

Re: VDD VDD 0 DC 5

I forgot to mention - it is best not to give a node and voltage source the same name. Even if the simulator doesn't get confused, you might!

Keith

 

[yzzrlzc]

ok

but actually, i always use it this way.