Analog circuit cells

Establishing bias currents and voltages for building blocks comprising an overall design is fundamental to the design of bipolar integrated circuits. These building blocks include single-stage and differential amplifiers, output stages, etc. Biasing often has a direct relationship to electrical characteristics, such as gain, signal-swing, slew-rate, etc., of the individual building blocks and hence to the overall design. Biasing circuits include current sources, voltage references, and level-shifters. Most often, it is desirable that the integrated circuit design be robust and independent of a variety of external factors that can affect circuit performance. These factors include variations in process parameters, supply voltage, and temperature. Efforts to improve the performance of current sources and voltage references have led to many refinements and developments that have started from simple beginnings. This section presents some of the fundamental current sources and voltage references used for biasing in bipolar integrated circuit technologies and refinements of these circuits that have evolved over time.