Negative PSRR in two stage opamp

[[email protected]]

I have problems to simulate negative psrr in two stage opamp...
If i consider an ac Vss in series with a dc VSS, if opamp is
configured as buffer with V+ to ground, i should have Vout/Vss=1/
Psrr-, so Psrr-=Vss/Vout.....is this right?
I've simulated this configuration in spice with dc VSS=2V and ac
Vss=0.1V, so psrr- should be Vss(=0.1V)/Vout...
My problem is bode plot of Vss/Vout: arg[Vss/Vout] has higher values
at higher frequency and this is not possible: what's wrong? Using the
same method with psrr+ i have the right bode plot, so i think i've
done some error in plotting....Can you help me?
Thanks in advance

 

[Helmut Sennewald]

I have problems to simulate negative psrr in two stage opamp...
If i consider an ac Vss in series with a dc VSS, if opamp is
configured as buffer with V+ to ground, i should have Vout/Vss=1/
Psrr-, so Psrr-=Vss/Vout.....is this right?
I've simulated this configuration in spice with dc VSS=2V and ac
Vss=0.1V, so psrr- should be Vss(=0.1V)/Vout...
My problem is bode plot of Vss/Vout: arg[Vss/Vout] has higher values
at higher frequency and this is not possible: what's wrong? Using the
same method with psrr+ i have the right bode plot, so i think i've
done some error in plotting....Can you help me?
Thanks in advance

Hello,

Is there any comment in the model that the PSRR is modeled?
If not, the simulation will be useless.
Please show the model text.

Best regards,
Helmut

 

[[email protected]]

thanks for the answer...
i don't have opamp macromodel because i've done the same two stage
opamp used in this link:
users.ece.gatech.edu/~pallen/Academic/ECE_6412/Spring_2003/L180-
PSRR-2UP.pdf
I've tried to use the same method to calculate positive psrr and
negative psrr, but for negtive prss i have obtained this picture
http://img262.imageshack.us/img262/5314/sdgsdfgru0.jpg
i don't understand the picture, because phase shoud descrease as
frequency increases and not the contrary....
For positive psrr using the same method i have a correct bode plot...
What's wrong?
thanks

 

[Helmut Sennewald]

thanks for the answer...
i don't have opamp macromodel because i've done the same two stage
opamp used in this link:
users.ece.gatech.edu/~pallen/Academic/ECE_6412/Spring_2003/L180-
PSRR-2UP.pdf
I've tried to use the same method to calculate positive psrr and
negative psrr, but for negtive prss i have obtained this picture
http://img262.imageshack.us/img262/5314/sdgsdfgru0.jpg
i don't understand the picture, because phase shoud descrease as
frequency increases and not the contrary....
For positive psrr using the same method i have a correct bode plot...
What's wrong?
thanks

Hello,

This may be just a question how you have polarized your AC-source in series
with the supply voltage source.

Taking care of phase in a PSSR simulation is nonsense in my opinion.

Best regards,
Helmut