In a hybrid model of a transistor h_r (h₁₂) is defined as:

Concept:

Small signal equivalent hybrid π model of BJT at low frequency

here,

rbb = Base spreading resistance

rbe = resistance between base and emitter.

h parameter equations for BJT

vi = hie ib + hre vce  ...........(1)

ic = hfe ib + hoe vce .............(2)

From equation (1)

\(h_{ie} = \frac{v_{i}}{i_{b}} \bigg\rvert_{v_{ce}=0}\)

hi = input resistance with output shorted (Ω)

hr = Reverse voltage gain with input open (V)

hf = Forward current gain with output shorted

ho = Output conductance with input open