Hi, I want to analyze distortion in a single outpu opamp. First, I fed the circuit with a single tone signal and used transient simulation - measurement/spectrum tool to get frequency response. Then I tried PSS analysis. I got different results i.e. SFDR was different, output magnitude was different, harmonic magnitudes were different. I wonder: Should we trust transient analysis? Is PSS for switching or and oscillating circuits like switched cap, PLL, oscillator? Thank you.

 

What are you referring to when you say you want to "analyze distortion". What properties to the part are you trying to understand?

 

I want to measure SFDR, THD

 

Spurious-Free Dynamic Range (SFDR)


To measure the SFDR of a signal generator, a tone is generated at a given frequency.
A spectrum analyzer is then used to measure the amplitude of the fundamental tone
and the amplitude of the next highest tone. Typically, this is one of the harmonics.

Using decibels, it is easy to calculate SFDR:


Given RMS voltages, you can calculate SFDR with the following equation:

 

So, when you do a simulation of the opamp you can select a single frequency tone and do an FFT on the output then, compare the fundamental magnitude with the magnitude of the spur.