how to simulate PSRR of bandgap v?ltages.

[triquent]

For a bandgap voltage reference(Op-Amp type). how to simulate the PSRR?
I use the following command:
vdd 1 0 dc vd ac 1.0
.ac dec 20 1 1G
.plot vdb(vref)
Is this right? what does dec 20 mean? should I look at vdb(vref) or 'vdb(vdd)-vdb(vref)'?

 

[wee_liang]

dec 20 refers to simulation of 20 points spread out in each decade, (i.e. not linearly)

vdb(vbg) is good enough 'cos it will show the effect of an ac signal (i.e. noise) with magnitude 1 on the overall output.