It is usual to begin the design of a bipolar transistor amplifying stage by choosing a value of mean collector current which enables the required current swing and/or voltage swing to be delivered with an acceptable degree of linearity. The next step is to devise a biasing circuit to give this particular value of mean collector current.
The most obvious way of biasing a bipolar transistor is by the simple circuit of Fig. 6.1 in which a resistor Rb is connected between the base of the transistor and source of steady voltage Vbb. Certainly it is possible by adjustment of Rb and/or Vbb to set the mean collector current at the desired value but such adjustments to individual transistors ...