03-01-2013, 10:39 AM
Bicmos Inverter
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Introduction
Bipolar transistors are three terminal devices formed by layering alternate n- and p-type regions. The cross-section of its process is shown in Figure 1.1. The three terminals termed as the emitter, base, and collector corresponds to the n+, p, and n sections (i.e. n+ means heavily or
highly doped region), for an npn transistor. Current flow relies on the motion of electrons from the emitter n+ region to the collector n-type, which is controlled by the p-type base.
BiCMOS
BiCMOS is a VLSI technology that unites Bipolar and CMOS circuits on the same chip to combine the advantages of both logic families. Consiquently, BiCMOS digital gates enjoys both, the low-power, high- input-impedance and wide-noise-margin of CMOS and the high current- driving-capability and high-speed-switching of BJT
Since BiCMOS technology is well suited for implementing
highperformance analog circuits, realization of both analog and digital functions on the same IC chip or 'system on a chip' becomes attainable.
BiCMOS Logic Gates are especially suitable for large capacitive loads
(greater than 0.5 pF or so) or when the logic gate has to drive a number of
other logic gates, requiring large amount of output current.
Modern BiCMOS, invented by intel, was available in the market in 1992 and was eventually used to construct VLSI chips for personal computers3
Advantage of BiCOMOS inverter:
• i) Low power dissipation comparable to CMOS
• ii) Improved speed comparable to TTL or ECL technology
• iii) Large current driving capability comparable to TTL or ECL
• iv) large noise margin similar to TTL technology
Disadvantage BiCOMOS inverter :
i) Highest cost
ii) Large fabrication cycle time up to thirty mask steps are common compared with ten to twenty for bipolar or CMOS.BiCMOS is a complex processing technology that provides both NMOS and PMOS devices, as well as npn and pnp bipolar transistors
• High input impedance logic gates (that require little drive current) are provided by the MOSFETs, and high current drive can be provided from the BJTs due to their high current gain and transconductance.