**Experimental Determination of Hybrid Parameters:**

Determination of hybrid parameters of a general linear circuit has already been discussed. For determination of hybrid parameters for a CE transistor, consider the circuits given in Fig. 11.8. The rms values will be considered in discussion. Volt-ampere equations for a CE transistor are as given below :

For measurement of h_{ie} and h_{fe }parameters, output is ac short circuited [Fig. 11.8 (a)] by making capacitance C_{2} deliberately large. The result is that the changing component of collector current flows through C_{2} instead of R_{C} and ac voltage developed across C_{2} is zero i.e., V_{ce} = 0. Here it should be clarified that setting V_{ce} = 0 does not mean that the dc collector-emitter voltage, V_{CE} is zero. It simply means that ac output is short circuited.

Substituting V_{ce} = 0 in Eqs. (11.10) and (11.11), we have

Thus from Eqs. (11.12) and (11.13) h parameters h_{ie} and h_{fe} can be determined. It is to be noted here that I_{b} and I_{c} are ac rms base and collector currents respectively. Also V_{be} is the ac rms value of base-emitter voltage.

For measuring hybrid parameters h_{oe} and h_{re} the input is ac open circuited, a signal generator is applied across the output and a large inductor L is connected in series with R_{B}, as illustrated in Fig. 11.8 (b). The inductor L, having dc resistance very small, does not disturb the operating point but does not allow flow of ac current through R_{B}. Furthermore, a voltmeter of high input impedance is used to measure base-emitter voltage V_{be} and hence there are no paths connected to the base with any appreciable ac current. Thus base is effectively ac open circuited i.e., I_{b} = 0.

Substituting I_{b} = 0 in Eqs. (11.10) and (11.11), we have

Thus by measurement of V_{be}, V_{ce} and l_{c}, the hybrid parameters h_{re} and h_{oe} can be determined.