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How do I simulate the fully differential OTA?

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hk2004

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fully differential ota

Hi all,

I am newbie on analog IC design.
How do I simulate the fully differential OTA such as, AC gain and phase margin because there are two outputs.

THx,
HK2004
 

fully differential+simulation

go search for the lecture notes of ee214 from Stanford University.
 
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calcolo slewrate ota fully differential

Thanks for all.

Generall speaking, fully differential amplifier has two input vin+/vin-, two outputs vout+/vout-, . I know the differential mode gain is Adm=(vout+ - vout-)/(vin+ - vin-). But How do I do this in the Cadence ADE? In Cadence analog artist, ac analysis shows the vout+ and vout- has the same response. In the ac response waveform, both vin+ and vin- are the same. So if I do the Adm calculation in the calculator, I will get error of "divid zero" since vin+ and vin- is the same. There are no difference in AC response.
What mistake I make?

thanks,
HK2004
 

ota ac analysis

You should give a 0.5 AC magnitude to +vin and -0.5 to -vin then u can get Adm by just taking vout+ - vout- since denominator is 1. Hope that helps
 

waveform viewer differential mode

Thanks for ccw27's suggestion.

Actually I have set the +0.5v for vin+ and -0.5v for Vin. But in ac reponse, from waveform, the vout+ is identical to vout-. That means there is no differecne betwenn this differential output in ac responce. I know they are oppsite in transisient analysis.

Kindly let me how to plot the fully differential OTA's gain and phase frequency response.

Thanks,
 

ota differential mode gain

I think you could hardly find the diffrence in ac analysis.try transient analyses and prob the diffrence voltage but use small step size in order to reduction in differences cozed by numerical rounding problems....
also u could use a same voltage source as -&+ inputs ....

hope this would help u
 

ota symmetric fully differential

AC responce will be the same in dB, but are you sure you looked at the phase responce. It should be different. Take (Vout+)-(Vout-) and do dB of it and you'll see it is not 0 - of course if you have put non-zero differential input.
 

fully differential ota simulation

sutapanaki is correct. You will see the same amplitude response at Vout+ and Vout- if you use the same structure of both side of your output, but the phase would be 180 degree shift for sure.

One easy way to see diff. response in waveform viewer is by using VCVS. In schematic page, connect your Vout+ and Vout- to In+ and In- of VCVS, respectively. Then put the Out- of VCVS to ground and probe at the Out+ to see diff response.
 

ota simulation cadence pdf

Thanks for all.

Use the VCVS to convert two output singal to one output signal, then dirct plot the magnitude and phase. then get the plot. right? Thanks HK2004
 

ota simmetrico fully differential

To ccw27,

In my cadence evn, no balun in the analogLib. But rfLib has one. Is it the same?
 

fully differential amplifier simulation lecture

There is no problem.
Usually I insert a VDC source with Vdc=0 am=1m into net connected to one of the inputs (to In+ or In- don't care) After that run AC analysis and plot
dB20(Vf(Vout+)-Vf(Vout-))/(Vf(Vin+)-Vf(Vin-))
phase(Vf(Vout+)-Vf(Vout-))/(Vf(Vin+)-Vf(Vin-))

Vout+, Vout-, Vin+ and Vin- are terminals of differential aplifier.
 
characterize differential ota

To ccw27,

In my cadence evn, no balun in the analogLib. But rfLib has one. Is it the same?
Click to expand...

Are you sure? It is called ideal_balun. You should have it. I am not sure if the one is rfLib is the same. Maybe someone can comment on that.

Also reference **broken link removed**

Thanks
 
differential ota

how can we find a slew rate for the fully differential OTA?
if i m using a single stage OTA with out using CMFB ckt then plz tell me the procedure for it

sorry for my poor english..
 

ota balun buy

balun in rfLib isn't the ideal_balun as mentioned earlier. The ideal_balun has been included to analogLib start from IC5 that's why you can't see it in IC4.46.

Anyway, the article pointed by ccw27 shows the method how to make your own ideal balun from 2 transfermers. Please read from it and you will get many useful information.
 

ota differential

tell me if i am correct.we can get the gain from one output and add 3db to it to get the gain of differential output.
 

fully differential ac simulation hspice

avinash said:
tell me if i am correct.we can get the gain from one output and add 3db to it to get the gain of differential output.
Click to expand...

i think you are right.
 

simulating fully differential amplifier

wait.......

Added after 15 minutes:

this can help u.......
 

rflib balun transient simulation problem cadence

thanks..
i will check them..
 

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