Output swing & ICMR

[ljy4468]

output swing

Hi everybody?
I'm new in this forum
I have a question about opamp
I designed fully differential folded cascode opamp using hspice
and i want to measure output swing and input range
how can I measure it using Hspice?

please tell me how to do it

thanks
have a good day

 

[kienhuy]

output swing

For output swing, you need to sweep the inputs differentially. For ICMR, you need to sweep both inputs at the same time.

 

[winsonpku]

icmr differential

so if i want to find wether the CMFB can work properly in the output range,then i how i should do?sweep the input common mode voltage and then watch the output voltage wether is the expected value?

For output swing, you need to sweep the inputs differentially. For ICMR, you need to sweep both inputs at the same time.

 

[ljy4468]

how to measure the output swing

thanks for your answer.
but i don't understand what does it mean
for single ended I can measure ICMR with negative
feedback. But how can for fully differential??
DC sweep both input?
Please tell me more easily~

 

[kienhuy]

icmr input

ljy4468,
To sweep the inputs differentially, you need to have a common mode source and differential source at each input. For example, at the positive input, there is Vcm and 0.5*Vac. At the negative input, there is Vcm and a voltage-controlled voltage source with value -0.5*Vac. For your sweep, you simply need to sweep the 0.5*Vac source at the positive input.

winsonpku,
For CMFB, you should also check the stability of the CMFB loop, since you are also interested in the ac characteristics of the CM voltage. See the Gray and Meyer book for a better analysis.

 

[winsonpku]

outp you

for output swing,you should give differentiat sigal.which keinhuy said the most thing.you should set a named vid voltage,and then give 0.5vid and -0.5vid give two input ports,then you just sweep vid.
for differential output,meaure the ICMR is the same as single-ended output.
fully differental amp,you have inn and inp two input ports,then outn and outp two corresponding ports.you must sure that be the relationship between the output ports and input ports.you can increase the inn,then the output node volatge increase is outn,the other is outp.you can sweep any one of the two input ports.
if you want sweep the inn,then you must short outn with inp.then the overlaped region(outn=inn) is the ICMR.
is it clear?

thanks for your answer.
but i don't understand what does it mean
for single ended I can measure ICMR with negative
feedback. But how can for fully differential??
DC sweep both input?
Please tell me more easily~