BiCMOS - Bipolar-CMOS

BiCMOS (Bipolar-CMOS) is a technique for constructing analog and digital logic circuits from both CMOS and Bipolar semiconductor technologies.

Overview

Bipolar transistors have a higher current output per unit input capacitance. CMOS on the other hand is low-power, has wide noise margin and high input impedance. BiCMOS makes use of those excellent current drive characteristics to build buffers that can quickly drive large fanouts. It attempts to provide improved speed over CMOS and lower power dissipation than bipolar by combining both technologies on a single die. BiCMOS fabrication therefore ends up being considerably more expensive due to the increase mask count.

Inverter Example

Main article: inverter#BiCMOS

BiCMOS NOT gate

A simple BiCMOS inverter can be constructed from a pair of MOS transistor and NPN transistors. Each of the MOS transitors are cascaded with an NPN transistor. When the input is HIGH, the NMOS transitor is conducting becoming the base current for the Q₂ NPN transistor causing the discharge current to drop. Conversely when the input is LOW, the PMOS transistor is conducting becoming the base current for the Q₁ NPN transistor, causing the output the increase.

Logic Families/Types

Various types of BiCMOS gates were devised over time to overcome different issues, some of the common ones are listed below: