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5th April 2011, 20:34 #1
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 Apr 2011
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Amplifier Linearity measurement in CADENCE (using the calculator)
Hi all,
[Thank you note]
This is my first post so I just wanted to thank you all for all the stuff you have put up here, it has helped me a lot and I hope I can at least give back as much as I learned...
[Serious Stuff]
So I am designing a linear low frequency amplifier and I am looking for an expression to measure the gain compression (the amount that the gain drops as the output approaches saturation) for a specified output voltage swing AS A NUMBER
Again... I already know how to see it on a plot, but I need the calculator to give me a NUMBER.
To see it on the curve, I plot Vin vs. Vout, looks something like this:
_/``
i deriv() it to see a waveform like this:
_/``\_
the middle is where we are getting gain and it obviously drops as the output goes toward VDD or GND. I then measure how much the gain "compresses" near the voltage swing limits I am looking for.
Some notes:
1
I am not sure that using the "compression" function in the calculator is a good idea cuz I am not working high frequency, not running PSS, just a simple vin/vout sould do the trick
2
Some dude told me to use THD. I dont think he is correct... THD is calculated for a given frequency, right? I dont think it appropriately demonstrates the linearity for lowfrequency amplifiers (no carrier). But then, I'm pretty sure that THD and compressionpoint are related, i'm confused...
So what do you guys think?Last edited by Mamdos; 5th April 2011 at 20:39. Reason: typo

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