# Determining h parmaters of bjt practically

so i know that h11 is defined as v1/i1 when v2=0 and so on...but the thing is how do i do it practically...my professor told me that v1,i1,v2,i2 in h parameter equations are instantaneous values of current and voltage of ac in a bjt. he even wrote that to get h11, you have to set v2 of ac=0. but since, the lecture was a recorded one, i cudnt get it cleared.i have the following doubts-
1) how can v2 of ac be set to zero....if at all, say in ce config, i short the c and e terminals that is replace load resistance by a short circuit, how is it practically possible...
2) for h12, i will have to set i1=0 ie. in ce config, i will have to set i base as zero. which means i collector=0. which means that i2=0 which means h12 is infinity. not possible!!
3) he told me to set v2=0, we use a capacitor... and for i1=0 we use an inductor at the base side...didnt get it.
4)on further reading on the net, i read that ib is kept constant so that i1 becomes zero..

i am all confused.pls help me asap

h-parameter are only used for small-signal analysis and designing a amplifier circuits. And don't forget that all h parameters are AC parameter.
So 0V means 0V ac voltage at given point. v2 = 0 V means that the collector AC voltage is 0V (Collector is short via large capacitor to ground).
Capacitor is a short for AC signal and coil is a open circuit for AC.
http://www.dtic.mil/dtic/tr/fulltext/u2/658138.pdf
But don't worry too much, in real world we don't use h-parameters to design an amplifier. Only EE students are forced by their mad professors to use it.

NascentOxygen
Staff Emeritus