How to simulate the ouput impedance

[ebuddy]

I am new to analog design.

How can I simulate the ouput impedance of an amplifier? Say I have a simple common source amplifier . Don't know what is the best way to change the output voltage and find the change of current.

Thanks for the help.

 

[wonbef]

make input ac short. and do ac analysis.
you can reference TI's materials.

 

[Sadegh.j]

Well, a good idea would be to change the output load and note the output voltage. Do it again with a different load. Then solve a two-equation two-unknown system.

cheers

 

[wpchan05]

I am new to analog design.

How can I simulate the ouput impedance of an amplifier? Say I have a simple common source amplifier . Don't know what is the best way to change the output voltage and find the change of current.

Thanks for the help.

Short the input (not the power supply and the other bias), and place a grounded current source at the output. The voltage across the current source give you the output impedance.

 

[LvW]

Yes ! That´s the easiest and most direct way as it is according to the definition of output impedance !

 

[asuprash]

The procedure is simple...

Short any input voltage source .. and open any input current source...
Apply a voltage between the output terminals and observe the current or
Apply a current between the output terminals and observe the voltage developed
across the terminals...
The Output resistance = ROut= Vapplied/ Iobserved
or Rout = Vobserved/Iapplied

 

[edge_tv]

Becarful with shorting input voltage source and that stuff if you want to simulat your Output res. You still need the Bias for your CS stage, to set the right operating point. So set the Bias, that every thing looks right, put a AC Voltage source to the Output (and only to the Output) run an AC simulation and calculat Vout/Iout (both from the AC voltage source), the simulater ignores the DC voltages but it needs the Voltages to get the right small signal paramters

 

[ashish_chauhan]

If you are using spice ..
then use .tf command.

.tf vout vin

where vout is the o/p node and Vin is input source

This command will give dc small signal gain wrt vin and the small signal output impedence ...

hope this helps.

 

[dkocer]

I would like to ask anotherquestion. How can we choose simulation parameters for any different type antennas?For example, while adding sweep which frequencies we can use for 2.4 GHz antennas?

 

[xinweitang]

you could use a voltage source ac=1 at the output point,

and use an super big inductor connect the other point of the voltage source and ground,

then use ac simulation, see the current in the voltage source.