Negative PSRR in two stage opamp

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

Reply to
lionelgreenstreet
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schrieb im Newsbeitrag news: snipped-for-privacy@59g2000hsb.googlegroups.com...

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

Reply to
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

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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

Reply to
lionelgreenstreet

schrieb im Newsbeitrag news: snipped-for-privacy@c58g2000hsc.googlegroups.com...

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

Reply to
Helmut Sennewald

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