
Ampliers: Basic BJT Congurations
421
This equation can be rewritten as
A
i
i
i
i
i
i
A
i
l
e
b
io iBJT
==
A
iBJT
i
i
iBJT
e
b
def
For the BJT’s current, i
b
+
i
c
=
i
e
, and we replace the i
c
value with that
from Equation II C.E. ihih
bfeb oe ce e
. But vv
ce
, so
ihihRi i
bfeb oe EL
from which
+=+hi hR i11
fe
eE
.
So we nally write
A
i
i
h
hR
iBJT
e
b
fe
oe EL
==
+
1
1
We can compare this result with the one obtained in Section 11.6.2.2, which is
in agreement with the expressions reported in Table 11.5, that is,
fc fe
=− +
1
and
oc oe
.
α
i,o
io
l
e
i
i
=
From the output current divider equation
i
R
i
l
E
e
=
+
, therefore,
α
io
E
R