ABSTRACT
Fundamental to the design of bipolar circuits is establishing the bias currents and voltages at which the subcircuits of the design are to operate. This of course determines the small-signal parameters of transistors meant to be operated as small-signal linear devices and the dc voltage levels used in direct-coupled circuits, such as op amps. The subcircuits that perform biasing include current sources, voltage references, and level shifters. Typically, it is desired that BJT circuit design be robust and independent of a variety of external conditions that can affect circuit performance. These factors include variations in supply voltages, in temperature, and process parameters. Desires to improve on these issues have led to many refinements and developments based upon simple ideas and basic building blocks. We present in this section some of the fundamental biasing building blocks that are used in bipolar integrated circuit technology and the refinements of them that have evolved over time.
