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# psrr simulation for op amp

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#### puyeng

##### Newbie level 5
psrr simulation

i've been doing the PSRR simulation with definition: PSRR- = Av(vss=0)/Ass(vin=0)
it means that when i measure Av, i put ac signal at i/p +ve of unity gain op amp, and when i measure Ass, i put ac signal at the vss. is that the correct way of doing it?
what is the value of the frequency when people say 'psrr at high frequency'?is it at GBW of the open loop op amp? what psrr value at GBW is considered high?
i need to improve the psrr of my op amp, but since it is most influenced by Av, i could not just implement the technique right away.

looking forward to the answers. thanks

psrr opamp

Your measurement approach should be correct. In general, 100kHz is the high freq. psrr, it does not have direct relationship between GBW. Certainly, PSRR could be improved by increasing Av.

psrr simulation

That is correct

relationship psrr gain

PSRR includes PSRR+ and PSRR-, your measurement is PSRR-. However, generally PSRR+ is not enough, so it should be considered carefully.

simulating psrr in op-amp

Hi,

1.you need not measure by applying ac signal at both input and vss.u can do at oneshot by connecting the OPAMP in unity gain configuration,and applying the ac signal only at the supply.in that case ur PSRR-=1/Ass.

2.depending on the application,u need to check at what frequency u should ensure the PSRR.For example if ur circuit is taking the supply from dc-dc converter ,which is coming at 200kHz,u have to ensure the PSRR at 200khz and noway related to GBW.

3.you can improve the PSRR by increasing the gain of the OPAMP.

i hope it helps.

simulate psrr

Hi friends,

Actually i am designing a voltage regultor which converts the voltage from 1.8V to 1.5V. This 1.5V supply is given to the ring oscillator. Some one told me that i need to measure the PSRR at the frequency of oscillator, that is 300MHz. Is it right? Because at that high frequency PSRR is very low.

Kumar

pssr simulation

sivankumar said:
Hi friends,

Actually i am designing a voltage regultor which converts the voltage from 1.8V to 1.5V. This 1.5V supply is given to the ring oscillator. Some one told me that i need to measure the PSRR at the frequency of oscillator, that is 300MHz. Is it right? Because at that high frequency PSRR is very low.

Kumar

For PSRR you need to worry about the supply ripple frequency and not the load current frequency. To provide better supply at 300MHz the load regulation of the LDO must be good at that frequency. You can add a 0Vdc, 1Vac voltage source at the output, run a ac analysis and check for the output impedance of the LDO. But 300MHz load regulation is normally helped only by the output decaps.

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