Analog Integrated Circuit Design, 2nd Edition

In the early electronic years, the majority of microcircuits were realized using bipolar-junction transistors (BJTs). However, in the late 1970s, microcircuits that used MOS transistors began to dominate the industry. Presently, the need for digital circuitry in nearly every modern integrated circuit has made CMOS devices and processing domiant, but bipolar devices remain important for many high-performance analog circuits. Modern bipolar–CMOS (BiCMOS) processes permit high performance bipolar devices to be integraed alongside large CMOS digital circuits, a particularly attractive option for mixed analog–digital applications. Thus, it remains important for an analog designer to become familiar with bipolar devices.

8.1   BIPOLAR-JUNCTION TRANSISTORS

Bipolar devices offer some inherent advantages over CMOS devices, particularly when a combination of high-frequency operation, high-gain, and/or high breakdown voltage are required. For example, in order to operate at very high speeds, modern CMOS technologies employ very thin gate dielectrics which breakdown under voltages exceeding 1–2 Volts, whereas bipolar devices can be engineered to combine high-speed operation and relatively high breakdown voltages, making them naturally suited to high-voltage radio-frequency circuits. Moreover, since BJTs can tolerate larger voltage signal swings than short gate-length MOS transistors, they ...