In the simple circuit shown in Figure 9.9 (the case shown is for an NPN transistor, but a virtually identical circuit, but with negative supply rails, could be made with a similar PNP transistor), the ...

The classic transistor amplifier circuit then has a pair of resistors in series between supply and ground, forming a potential divider that gives the base its bias.

For circuit designs that use complementarybipolar transistors,you sometimes need to sort the NPNand PNP transistors to have matchingdc-current gains (β). One example of acircuit requiring matching is ...