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about fully differential opamp simulation in hspice

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lhlbluesky

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differential op amp

how to simulate the fully differential opamp in hspice? how to write the input stimilus in netlist?

i write:(vdd=3.3)
V1 vin+ 0 1.65 ac 1
V2 vin- 0 1.65 ac -1

it is wrong.

and i use vcvs to couple two ac small signal to the two inputs,
the result is wrong,too.

i want to know, how to write the right stimilus in the netlist?

can anyone help me, or give me some advice, thanks.
 

hspice fully differential

i think if you want to perform ac analysis, you can use of these sources as inputs:
V1 Vin+ 0 dc 1.65 ac 1
V2 Vin- 0 dc 1.65 ac 0
what's your mean about couple two ac small signal?both of Vin+ and Vin- are inputs of your circuit(you must define inputs of dif. opamp i.e gates of transistors with Vin+ and Vin-) thus vcvs is useless!
Good luck
 
fully differential op amp ac simulation

Hi,

A vcvs should actually work.

As an example, consider this

e+ 1 10 0 7 0.5
e- 2 10 7 0 0.5
vic 10 0 dc 0.9v

here 1 and 2 are connected to 2 input nodes i,e (gate of mosfets where differential input is applied)

All the best
 

phase margin opamp hspice differential fully

i haveused the following two methods:

V1 Vin+ 0 dc 1.65 ac 1
V2 Vin- 0 dc 1.65 ac 0

and

e+ 1 10 0 7 0.5
e- 2 10 7 0 0.5
vic 10 0 dc 0.9v
vac 7 0 dc 0 ac 1

but when i check the waveform of vout+ and vout-, i find their amplitude (at low frequency) is different, one is about 80dB, and the other is only 10dB or so, then why, or i was wrong, pls help me again. thanks.
 

full differential hspice

Dear lhlbluesky, i think standard form for ac analysis is first format and i used to this and i think results of these inputs are reliable.
 
fully differential ac simulation hspice

if i used the following inputs:

V1 Vin+ 0 dc 1.65 ac 1
V2 Vin- 0 dc 1.65 ac 0

then, when i check the output results, should i observe the waveform of vout+, vout-,
or (vout+ - vout-), pls?
 

hspice differential op

if you want to watch the differential output, you can use of .param as follows:
.param Vout=par('V(vout+)-V(vout-)').
for example if you want to find UGBW, you can use of Vout+ merely, then find a frequency that Vout+=0.5 or use of differential output and find a frequency that Vout=1.
besides you can use of these commands too:
.MEAS AC PM FIND VP(Vout+) WHEN VM(Vout+)=.5
.MEAS AC FU WHEN VM(Vout+)=0.5
.MEAS AC Gain max v(Vout+)
fist syntax is for phase margin(but you must plus PM with 180) .
second is for UGBW.
third is for gain.
 
fully diff amp need and some .options

if not set it
probe Vout+ and Vout- will =0

.options acout=0

default acount=1
 

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