EE477Assignment

EE477Assignment - Q1: What are the advantages of MOSFET...

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Q1: What are the advantages of MOSFET over BJT? (name at least 3) In BiCMOS technology both BJT and MOS are used in the design. What strength in BJT makes BiCMOS design favorable? Q1: (part A) What are the advantages of MOSFET over BJT? (name at least 3) Answer: Following are the advantages of MOSFET over BJT: a) MOSFET allowed for the development of digital CMOS logic, with p- and n- channel MOSFETS as building blocks. CMOS Logic reduces power consumption as compared to BJT, because idealy no current flows except when the input to logic changes causing the switching current to flow from source to drain. b) As the power consumption in MOSFETS is much smaller than BJT, the heat generation in th MOSFET based digital integrated circuits is also lesser. Thus allowing greater integration of transistors in a smaller chip. c) MOSFETs have the advantage of not suffering from thermal runaway as BJTs do. d) MOSFETs occupy a relatively smaller silicon area and its fabrication used to involve fewer processing steps. It also has a relatively simple operation as compared to BJT. e) MOSFETS has the advantage of requiring very small switching current. For digital switching DC current does not flow through the gate due to the insulation of oxide layer between gate and channel. The oxide layer between channel and gate isolate a MOSFET in one logic stage from earlier and later stages, due to which single MOSFET can have a high fan out capacity. BJTs do not have such a high fan-out capacity. Q1 (part B) In BiCMOS technology both BJT and MOS are used in the design. What strength in BJT makes BiCMOS design favorable? Answer: Bipolar Junction Transistors have significantly larger current-driving as compared to CMOS. In the CMOS digital integrated circuits, the signal propagation delay due to large interconnect capacitances is a major performance limiting factor. The speed of the system depends on the current-driving capability of CMOS gates that drive large capacitive loads. The CMOS based arrangements for current driving require larger silicon area. BJTs on the other hand have more current driving capability and can overcome such speed bottlenecks using less silicon area. This is the strength of BJT which makes it useful for BiCMOS logic circuits where it is used for high on-chip or of-chip drive capability.
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Q2: Voltage scaling is considered as one of the most important means of power reduction in modern VLSI design. The following table from ITRS shows the power supply voltage scales down with the downscaling of technology, however, the maximum power dissipation increases. How do you explain this trend? Answer: The above table shows the trend of increasing maximum power dissipation per chip.
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The explanation of this trend is provided as follows. According to table, with the technological advancement
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This note was uploaded on 07/21/2010 for the course EE- 477 taught by Professor Shahinnazarian during the Spring '09 term at USC.

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EE477Assignment - Q1: What are the advantages of MOSFET...

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