You can measure the transient loading change by conecting a resistor and a transsitor and control the switch on/off of the transistor to make the load changes.
PSRR is defined as dVout/dVDD, so when u change VDD, you observe the change in Vout and the PSRR can then be calculated, it's the simplest method
You can measure the transient loading change by conecting a resistor and a transsitor and control the switch on/off of the transistor to make the load changes.
Since the PSRR of LDO is as high as 80dB. This to say, input voltage should change 10V to make output change 1mV. Thus, this way is not realizable. How do you think about it ?
So you can inject input ripples with say 100mV and measure the output ripple and you can calculate the PSRR, in a simple method. Also, you can vary the frequency to obtain the PSRR vs frequency plot.
An spectrum analyzer can do the job. Other method consists of decoupling the the DC component of the output ripple and amplify it through a low noise amplifier.
Yes, use low noise amp is good idea.
I haven't got a low noise amp but I know that PSRR curve look like Gain curve so I did like bellow step:
[1] I change VIN and measure Vout --> I got PSRR @ DC(f=1K) then I also got PSRR ~ 80dB @ 1KHz if my LDO has BW=1K (approximation)
[2] I change f=10KHz then I got PSRR ~ 60dB (with 60dB you can see on Osc). PSRR roll-off qickly @ BW frequency.