Environmental Engineering Reference
In-Depth Information
and, the return ratio with respect to the critical parameter
is
The fundamental difference with the previous case is that instead of
factor
which introduces open loop gain reduction, we have
now factor
which can be simply made greater than one. Moreover,
asymptotic gain,
is unchanged, while forward gain,
is further
reduced. Indeed, resistance
in (6.2) is now replaced by the parallel
between
itself and the resistance seen at node X of transistor T3 (i.e.,
It is apparent that since the circuit now exhibits
a higher open loop gain and a lower forward gain, the closed loop gain,
tends to be more close to Of course, the improved topology provides
also advantages in terms of input resistance, increased by the greater loop
gain
and in terms of output resistance, which is reduced both for the greater loop
gain and for the lower open loop output impedance provided by voltage
buffer T3
6.2 SHUNT-SERIES AMPLIFIER
While the series-shunt feedback circuit well behaves as a voltage
amplifier, the shunt-series configuration, whose AC schematic diagram is
depicted in Fig. 6.12, is best suited for implementing a current amplifier. In
the subject circuit, the current on node X of transistor T2, equal to the output
signal current,
(approximately equal for BJT's), is sampled by the
