How do you decide on DC operating point?

[surno]

Hi,, all~

I have a basic question. How do you desice dc operating point?
I have been decided operating point small overdrive voltage. Is it OK? And Vds is decied Vds=vdsat+0.1(or 0.2)V.
Please tell me your method to decide dc operating point. Thanks~

 

[A.Anand Srinivasan]

Re: The basic question

what is the circuit for which you want to decide a DC operating point....

assuming that you are talking about a amplifier the selection of the DC operating point or Q point should be in the middle of the loadline so that the circuit is stable through signal swing.... if you decide on Vds=Vdsat+0.1V or 0.2V it might not be the right point so you better find the DC point graphically....

 

[surno]

The basic question

Thank you, A.Anand Srinivasan

How can I find the DC point graphically? I don't understand your advice. Tell me more detail~

 

[A.Anand Srinivasan]

Re: The basic question

if you have the datasheet of the MOSFET you are using then take the desired values of x(Vgs) and y(Id)... now mark your required value of Vgs when Id=0 and required value of Id when Vgs=0.... now join these two points and you will get a line called the load line... take the midpoint of this line as your operating point and bias accordingly....

Regards

 

[psmon]

The basic question

How much current can you burn under the specifications? This determines the DC operating pt.

 

[hazemafify]

The basic question

What the simulation tool you use?

 

[iamxo]

Re: The basic question

the DC operating point should be in your input voltage range. and it should maximize the input voltage swing, just like what is said above, it should be best at the middle of the input voltage range.

 

[test_123]

The basic question

in hspice, you can use .op to get circuit DC operation point