Biasing taking two power supplies

                                                The loop equation for the loop marked as L is

Example: The bias arrangement given in the figure is to be utilized in common base amplifier. Make the circuit to generate a dc emitter current of 1mA and give the highest possible gain while permiting for a maximum signal swing of ±2V at the collector. Take +10V and -5V power supplies.

Solution:

                As the amplifier is to utilized in common base configuration, thus the circuit will take the shape as given.

                                                                Thus

                                                                                R_B=0

                                Taking the base-emitter junction forward biased , the emitter resistance can be calculated as

                                                                                R_E=(-0.7-(-5))/1m=4.3kW

                So as to permit for ±2V signal swing at the collector, whereas selecting as larger value of R_C as possible, set V_C=+2V, thus -2V signal would not saturate the BJT. Therefore

                                                                                R_C= (10-2)/I_C

                                                                                      = 8/1mA

                                                                                RC = 8kW