ABSTRACT
CMOS is preferred for most applications because of its low standby dissipation, high packing density, rail-to-rail voltage swing, and excellent speed. However, because bipolar circuitry still outperforms CMOS in terms of offchip data rates, bipolar-CMOS (BiCMOS) logic was developed in an attempt to achieve the advantages of both types of logic gates. At the present time, high-performance BiCMOS circuits have been developed based on Si and SiGe technology and are widely used.1-15
A number of different versions of BiCMOS logic gates are available9-15; however, they all share the salient features of the inverter shown in Figure 11.1. The two important design features of this circuit are 1) CMOS-type logic circuitry and 2) a totem-pole output formed using two npn bipolar transistors. The CMOS logic circuitry provides low standby power dissipation while the bipolar transistors at the output provide superior performance with highly capacitive loads. In fact, the packing density of BiCMOS can be excellent because the relatively large bipolar transistors are only needed to drive the output connections; thus, BiCMOS integrated circuits are really just CMOS on the inside.
