How ac analysis works

Hi,
Can any body tell how ac analysis in Cadence or some other tools work,

Meaning do the tool find the operating points of the devices and then perform the ac analysis.
I want to know about the tools internal working.

On a similar note do anybody has some notes/docs on the internal operation of the tool for various analysis.

Thanks
Shaikh Sarfraz

shaikhsarfraz said:

Hi,
Can any body tell how ac analysis in Cadence or some other tools work,

Meaning do the tool find the operating points of the devices and then perform the ac analysis.
I want to know about the tools internal working.

On a similar note do anybody has some notes/docs on the internal operation of the tool for various analysis.

Thanks
Shaikh Sarfraz

Click to expand...

tools just solve differential equation

Hi,
I also know that the tool solves the differential equations.

My question is can I get some information on the Algorithms used for the analysis.
Algorithms start with some assumptions or calculation like finding the operating points or some stuff like that, so I want to know the step by step procedure which the tools do to converge to a particular solution.

Thanks
Shaikh Sarfraz

DC simulation get the OP point, there linearize the components
around it, form Jacobian matrix and solve the equations with Newton-Ralphson.
So AC simulation is really small-signal. For large signal, you will then
need to run TRAN.

if you remember while doiing ac analysis you need to give the ac magnitude or acm, the default value for acm is 0. so what the tool does is it simulates your circuit at this given acm and with varying frequency according to the range of frequency already supplied by you. for e.g say you have given your range as 0 - 1 GHZ and acm = 1 Volt. then now your simulation is run starting from 0Hz acm=1 to 1Ghz acm=1, and the response you get as plot as your output.

shaikhsarfraz said:

Hi,
Can any body tell how ac analysis in Cadence or some other tools work,

Meaning do the tool find the operating points of the devices and then perform the ac analysis.
I want to know about the tools internal working.

On a similar note do anybody has some notes/docs on the internal operation of the tool for various analysis.

Thanks
Shaikh Sarfraz

Click to expand...

Hi,
I think you understod my question in the wrong way.
My question is how the Simulators internally works.
Doesn't mean that how to set up for simulations.

Thanks
Shaikh Sarfraz

AC analysis is a frequency-domain analysis. phasor analysis is the underlying mathematical technique, it computes the small-signal sinusiodal steady-state response of the circuit. I think you can refer to Kenneth S. Kundert 's "The designer's guide to spice and spectre".

Another advice: if you just want to use the EDA tools for your design, you need not to step in so deeper. Simulation methods and algorithms are a huge work and there are a large group of people and companies worked for it incluing Sysnopsis, Cadence, Mentor, Agilent, Ansys, etc....