Ngspice - Propagation delay of cmos full adder

vlsi
1

Good day!
I am attaching the code of full adder and simulation results. Please do have a look and let me know my mistakes.

.param psu = 0.9V
.param len = 16n
.param wpmos=100n wnmos=50n
vsupply vdd 0 {psu}
vgnd vss 0 0V
*Inputs to transistors
vina va vss PULSE(0 {psu} 2NS 2NS 2NS 60NS 120NS)
vinb vb vss PULSE(0 {psu} 2NS 2NS 2NS 80NS 160NS)
vinc vc vss PULSE(0 {psu} 2NS 2NS 2NS 90NS 200NS)

*Function for sum
Mpb vbbar vb vdd vdd pmos l={len} w={wpmos} ; pmos
Mnb vbbar vb vss vss nmos l={len} w={wnmos} ; nmos

Mpa vabar va vdd vdd pmos l={len} w={wpmos} ; pmos
Mna vabar va vss vss nmos l={len} w={wnmos} ; nmos

Mpc vcbar vc vdd vdd pmos l={len} w={wpmos} ; pmos
Mnc vcbar vc vss vss nmos l={len} w={wnmos} ; nmos
******************MOSFETs drain gate source body
*sum inputs(a b c)
Mp1 vdr1 va vdd vdd pmos l={len} w={wpmos} ; pmos
Mp2 vdr2 vabar vdd vdd pmos l={len} w={wpmos} ; pmos

Mp3 vdr3 va vdd vdd pmos l={len} w={wpmos} ; pmos
Mp4 vdr4 vabar vdd vdd pmos l={len} w={wpmos} ; pmos

Mp5 vdr5 vbbar vdr1 vdd pmos l={len} w={wpmos} ; pmos
Mp6 vdr6 vb vdr2 vdd pmos l={len} w={wpmos} ; pmos
Mp7 vdr7 vb vdr3 vdd pmos l={len} w={wpmos} ; pmos
Mp8 vdr8 vbbar vdr4 vdd pmos l={len} w={wpmos} ; pmos

Mp9 vout vc vdr5 vdd pmos l={len} w={wpmos} ; pmos
Mp10 vout vc vdr6 vdd pmos l={len} w={wpmos} ; pmos
Mp11 vout vcbar vdr7 vdd pmos l={len} w={wpmos} ; pmos
Mp12 vout vcbar vdr8 vdd pmos l={len} w={wpmos} ; pmos

Mn1 vout va vdr9 vss nmos l={len} w={wnmos} ; nmos
Mn2 vout vbbar vdr9 vss nmos l={len} w={wnmos} ; nmos
Mn3 vout vc vdr9 vss nmos l={len} w={wnmos} ; nmos

Mn4 vdr9 vabar vdr10 vss nmos l={len} w={wnmos} ; nmos
Mn5 vdr9 vb vdr10 vss nmos l={len} w={wnmos} ; nmos
Mn6 vdr9 vc vdr10 vss nmos l={len} w={wnmos} ; nmos

Mn7 vdr10 va vdr11 vss nmos l={len} w={wnmos} ; nmos
Mn8 vdr10 vb vdr11 vss nmos l={len} w={wnmos} ; nmos
Mn9 vdr10 vcbar vdr11 vss nmos l={len} w={wnmos} ; nmos

Mn10 vdr11 vabar vss vss nmos l={len} w={wnmos} ; nmos
Mn11 vdr11 vbbar vss vss nmos l={len} w={wnmos} ; nmos
Mn12 vdr11 vcbar vss vss nmos l={len} w={wnmos} ; nmos

*carry inputs(a b c)
Mp11a vdr1c vabar vdd vdd pmos l={len} w={wpmos} ; pmos
Mp21 vdr2c vbbar vdd vdd pmos l={len} w={wpmos} ; pmos
Mp31 vdr3c vcbar vdd vdd pmos l={len} w={wpmos} ; pmos
Mp41 voutc vbbar vdr1c vdd pmos l={len} w={wpmos} ; pmos
Mp51 voutc vcbar vdr2c vdd pmos l={len} w={wpmos} ; pmos
Mp61 voutc vabar vdr3c vdd pmos l={len} w={wpmos} ; pmos

Mn11a voutc vabar vdr4c vss nmos l={len} w={wnmos} ; nmos
Mn21 voutc vbbar vdr4c vss nmos l={len} w={wnmos} ; nmos
Mn31 vdr4c vbbar vdr5c vss nmos l={len} w={wnmos} ; nmos
Mn41 vdr4c vcbar vdr5c vss nmos l={len} w={wnmos} ; nmos
Mn51 vdr5c vcbar vss vss nmos l={len} w={wnmos} ; nmos
Mn61 vdr5c vabar vss vss nmos l={len} w={wnmos} ; nmos

Cload1 vout vss1 200f
vdc1 vss1 vss dc 0V

Cload2 voutc vss2 200f
vdc2 vss2 vss dc 0V

.options method=gear reltol=0.1m
.tran 0.1n 200n 0 0.1n
.save all @vsupply[p]

.control
run

*delay for sum
meas tran t1 TRIG va VAL=0.45 rise=1 TARG vout VAL=0.45 rise=1
meas tran t2 TRIG va VAL=0.45 fall=1 TARG vout VAL=0.45 fall=1

meas tran t3 TRIG vb VAL=0.45 rise=1 TARG vout VAL=0.45 rise=1
meas tran t4 TRIG vb VAL=0.45 fall=1 TARG vout VAL=0.45 fall=1

meas tran t5 TRIG vc VAL=0.45 rise=1 TARG vout VAL=0.45 rise=1
meas tran t6 TRIG vc VAL=0.45 fall=1 TARG vout VAL=0.45 fall=1

let delaya = (t1+t2)/2
let delayb = (t3+t4)/2
let delayc = (t5+t6)/2

*delay for carry
meas tran t7 TRIG va VAL=0.45 rise=1 TARG voutc VAL=0.45 rise=1
meas tran t8 TRIG va VAL=0.45 fall=1 TARG voutc VAL=0.45 fall=1

meas tran t9 TRIG vb VAL=0.45 rise=1 TARG voutc VAL=0.45 rise=1
meas tran t10 TRIG vb VAL=0.45 fall=1 TARG voutc VAL=0.45 fall=1

meas tran t11 TRIG vc VAL=0.45 rise=1 TARG voutc VAL=0.45 rise=1
meas tran t12 TRIG vc VAL=0.45 fall=1 TARG voutc VAL=0.45 fall=1

let delayd = (t7+t8)/2
let delaye = (t9+t10)/2
let delayf = (t11+t12)/2

set filetype = ascii
write output.raw v(va) v(vout)
plot v(va) v(vb) v(vc)
plot v(vout) v(voutc)
print delaya delayb delayc delayd delaye delayf
.endc
.End

Finally
Delay for sum= delaya+delayb+delayc/3
Delay for carry= delayd+delaye+delayf/3

Delay for sum= 7.1666ns
Delay for carry= 5.6366ns

image

2

Hello Aarchi,
Please let me know what are the issues u are getting ? In code or in output?

3

Thanku ma’am for your reply. Ma’am what is the concept behind finding the delay.
I have taken the average of total delay
Is that correct?
And also
Is the code that I have used to find out the delay correct?

4

Delay or propagation delay is the time taken by the output to change its state corresponding to the change in input state.
For finding the delay of the sum, you can use the maximum propagation delay which is the longest delay between an input changing value and the output changing value.
Smita