cadence transient and pss simulation

Thread Starter

bbilgic

Joined Jan 27, 2021
7
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.
 

Papabravo

Joined Feb 24, 2006
19,561
What are you referring to when you say you want to "analyze distortion". What properties to the part are you trying to understand?
 

Danko

Joined Nov 22, 2017
1,487
Spurious-Free Dynamic Range (SFDR)

1660656148081.png
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:

1660656331711.png
Given RMS voltages, you can calculate SFDR with the following equation:

1660656424026.png
 

Papabravo

Joined Feb 24, 2006
19,561
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.
 
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