The definition of load-line

[RFbeginner]

Who can explian the The definition of load-line in detailes? It is a very important concept in Crips book.
Thanks in advance.

 

[chviswanadh]

Load is the output impedance of any circuit which it can drive(typically it is the next stage input impedance).

 

[madengr]

We'll the slope of the load line dpends on you load resistance. I think it's -1/R but you'll have to draw it out. Anyway if you plot the load line over the IV curves the point is to adjust the load (to change the slope) and drive level (length of line) until the left end hits the point of maximum current (until it rolls off the knee) and the right end hits maximum VDS at which gate-drain breakdown is the limiting factor. This gets you maximum power. Of course the point your load line expands about is the quiescent bias point so you have to change this as well.

All this assume no reactive components (at which point your load like turns into an oval), or nonlinearites and harmonics that bend the line.

Use a simulator to plot the dynamic load line (ids and vds) over the IV curves and you can get a good feel about what's going on. Microwave Office does this easily and you can tune drive, load, and bias point in real time. Very cool.