The transistor in the circuit shown in the figure. is so biased (dc biasing N/W is not shown) that the dc collector current I_C = 1mA. Supply is V_CC = 5V.

The N/W components have following values, R_C = 2$$k\Omega $$,
R_S = $$1.4k\Omega $$,
R_E = $$100\Omega $$.

The transistor has specifications, $$\beta \,\, = \,\,100$$
and base spreading resistance $${r_{bb\,}}^1\, = \,100\Omega $$

$$Assume\,\,{{KT} \over q}\,\, = \,\,25\,mV$$

Evaluate input resistance R_i for two cases. At a frequency of 10 kHz

(a)C_E, the bypass capacitor across R_E is 25 $$\mu F$$
(b)The bypass capacitor C_E is removed leaving R_E unbypassed.

In the cascade amplifier circuit shown below, determine the values of R₁, R₂ and R_L. Such that the quiescent current through the transistors is 1mA and the collector voltage V_c1 = 3V, and V_c2 = 6V. Tke V_BE = 0.7V, Transistor $$\beta $$ to be hifgh and base currents to be negligible.

An Amplifier a has 6 dB gain and 50 $$\Omega $$ input and output impedances. The noise figure of this Amplifier as shown in the figure is 3 dB. A cascade of two such Amplifiers as in the figure will have a noise figure of

Negative feedback in

1. Voltage series configuration
2.Current shunt configuration

(a) increases input impedance
(b) decreases input impedance
(c) increases closed loop gain
(d) leads to ascillation.