Transistor OP - how to? What is the criteria?

[CAMALEAO]

Hi all. Noob here. How do you check a transistor for the operation point and what are the best values to look for? Someone told me things like your vds>vdsat and all that but didn't understand why.
What are the criteria to check the different points of operation of a transistor using its characteristics: vis, nth, vis, vdsat, vov? What rule of thumb for each value? Which ones we have check against the other parameters?

Thank you very much in advance.

 

[KlausST]

Hi,

You, or better say: your application has requirements.
You need to specify them.

Is it a low frequency switching application (saturated), where low R_ds_on is required?
Or is it a high frequency application (non saturated), where low capacitance is required?

Klaus

 

[CAMALEAO]

HM, good point actually. It is low frequency.

 

[KlausST]

Hi,

Low frequency audio, or low frequency switching?
No complete informations, no circuit?

Klaus

 

[CAMALEAO]

Thanks for your comment. Appreciate it.

Basically it applies to any circuit I think. Current mirrors, amplifiers, iDACs, namdgap circuits, etc.

How do we access the transistor operating point? What is, as a rule of thum - of course will depend on the type of circuit, but as a rule of thumb how do we assess the transistor OP in terms of which value against the other (vis, vis, vgs-vth, vov, vdsat) is ok, all right, good.

Do you know what I mean?