Question on PSRR Measurement

[suria3]

.extract ac label=

Hi guys,

I have a question here on exact method of PSRR measurement. When i referred to Philip Allen book on the method of PSRR measurement of a opamp, it is stated that the opamp is put in the unity configuration, so the closed loop gain is 1. The PSRR definition in general is given as PSRR=[Vout/Vin]/[Vout/Vsupply]. So since the opamp gain is 1, then the PSRR=Vsupply/Vout=PSR. My question here is, when i measured the opamp in the open loop configuration and I measured the PSRR of the opamp at 10kHz with the same concept as PSRR=[Vout/Vin]/[Vout/Vsupply], i'm not getting the same result, which means the transient suppresion from supply to output not same as measurent from AC simulation. Why?? It only gives same result of AC and transient when the opamp in the unity configuration. Does it mean that the opamp gain not helping in PSRR? Please explain about this confusion.

Suria.

 

[eric.hanyq]

Actually,Vout=Add/(1+Av) Vdd~Add/Av Vdd =Vdd/PSRR.Av is the large the better!!
If it was as you said,maybe your setting is wrong or coincidental .....

 

[gafsos]

.EXTRACT AC LABEL = PSRR_min FILE=PSRR.aex MAX(Vdb(VBG))
.EXTRACT AC LABEL = PSRR_dc FILE=PSRR.aex yval(Vdb(VBG),1)
.EXTRACT AC LABEL = PSRR_min_freq FILE=PSRR.aex XMAX(Vdb(VBG))