How do I find output impedance in my current source?

[ilter]

Dear all,
How do I find output impedance in my current source?
I use hspice. Thanks.

 

[Syukri]

impedance in current source is given by the devices resistance@internal resistance..
What type of current source did u use?
Find the architecture of the current ssource and then u can find the impedance of the device.....

 

[willyboy19]

Put a voltage source at the current source output terminal. Sweep this voltage source and plot the current through this voltage source. The ratio of the voltage versus current gives you the output impedance. This can be done easily in HSPICE.

 

[sunking]

add a ac voltage at the current source output terminal and try

 

[ilter]

Put a voltage source at the current source output terminal. Sweep this voltage source and plot the current through this voltage source. The ratio of the voltage versus current gives you the output impedance. This can be done easily in HSPICE.

I think this is good idea.
But I have a switch.
If I want to see my output impedance, is my switch turn on or off?
How is my bias circuit? Thanks.

 

[vdaniel]

How is the switch connected? You cannot leave the current
source output disconnected.
If it is connected in parallel to the load, then for modelling
you have to open the switch.

 

[surianova]

Dear all,
How do I find output impedance in my current source?
I use hspice. Thanks.

Basically, you just inject a AC current source=1 at that node and sweep across the frequency. Then plot the volatge of that node across frequecy. That voltage is impedance of that node.

v(ac)=i (ac) * output impedance, since i(ac)=1,

v(ac)=output impedance

Hope this help.