How to measure psrr of LDO?

[freeray]

how to measure psrr

hi,all.
Can anybody suggest me how to measure psrr of LDO?
Could anybody suggest the ways and the required instruments I need to use? Thanks a lot.

 

[benslama ahmed]

ldo psrr simulation

hi
set the ac value of the supply to 1
run ac simulation
and show the output of the LDO
this link may be help you

regards

 

[saro_k_82]

psrr ldo

The method described above is the easiest suggestion.
You could also do a xf analysis specifying the output node. You could get the PSRR, Ground rejection and output impedance of the LDO against frequency in one run.

 

[svraj]

ldo psrr

PSRR shows how the LDO output varies in accordance with power supply noise.

You will need either HSpice or Cadence to run your simulation.

For Cadence:
Place a vdc source at the power supply net. Set ac=1 for this along with its DC value.
Run AC analysis.
Use the direct plot drop down menu (Results) and click on AC dB20
Go to your schematic and click on the LDO output.
Hit Escape and u will be able to view the PSRR waveform.

For Spice:
At the power supply include ac=1
Run .ac simulation
Since PSRR = Vsupply/Vout in dB, Set a .print command as follows:
.print ac par '(20*log10((v(vsupply))/(v(vout))))'

Hope this helps!

Regards,
svraj

 

[imar]

psrr simmulation in ldo

For Cadence:
Place a vdc source at the power supply net. Set ac=1 for this along with its DC value.
Run AC analysis.
Use the direct plot drop down menu (Results) and click on AC dB20
Go to your schematic and click on the LDO output.
Hit Escape and u will be able to view the PSRR waveform.
svraj

that is the way to measure the PSRR of your LDO.
i have yet designed a LDO and i used this way to measure it.