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# Explanation Needed on Linear and Nonlinear Simulation

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#### avins_1234

##### Member level 3
Hello,

I have these doubts

I want to know what is the difference between

1) Linear and Non Linear Simulation

They say linear simulators analyze ckts in frequency domain without application of any drive level (biasing or applying voltages). What does this statement mean ?

2) Secondly, Is non linear simulation (the one finds voltages and current at nodes) same as harmonic balance ? Please explain ?

3)Thirdly, what is the meaning of

Linearized Harmonic Balance

Transient Simulation

Time domain Simulators

APLAC

HSPICE

SPICE

Cheers,

I think the following book can help you on some specific area, specially chapter one
Nonlinear Microwave and RF Circuits, Stephan Mass

Regards,
Avs

OK, I'll try to answer some of your questions:

1) Linear and Non Linear Simulation
They say linear simulators analyze ckts in frequency domain without application of any drive level (biasing or applying voltages). What does this statement mean ?

In frequency domain analyses (ac analyses) the circuit is automatically linearized around the operating point, which is determined by dc bias conditions. That is exactly the same you are doing if you apply the classical small signal ac calculations (for example, using 1/wC as capacitive impedance, ...)

2) Secondly, Is non linear simulation (the one finds voltages and current at nodes) same as harmonic balance ?

Each time domain simulation that calculates node voltages and currents as a function of time considers any non-linearities of the circuit.

3)Thirdly, what is the meaning of
Linearized Harmonic Balance

That is a special approach based on the fundamental frequency only and, thus, allows ac analyses also for non-linear circuits.

Transient Simulation
Time domain Simulators

See 2) above

APLAC HSPICE

Simulation packages (programs)

SPICE

A simulation algorithm (kernel) that is used in many commercial simulation programs
_______________
Regards
LvW

The linear simulation assumes that the transfer function of your circuit is linear. This means it can be defined by the following parameters, function of the frequency only:

input impedance
output impedance
forward gain (from input to output)
reverse gain (from output to input)

These parameters are extracted for a fixed biasing. Changing the biasing the parameters will change.

Due to the linearity if you double or triplicate the input also the output will doble or triplicate. In real word this is true under some conditions f.i. if the level is low enough not to drive the circuit into compression. For instance using the linear analysis you can design an LNA in which you have to check inpout and output matching networks, gain, isolation.
If you need, instead, to know the behaviour of a circuit close to compression or circuits like oscillators or limiters you will need a non-linear simulator.

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