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Microelectronics & Computer Principles

Nov 21, 2014




Microelectronics is a subfield of electronics. Microelectronics, as the name suggests, is related to the study and manufacture, or microfabrication, of electronic components which are very small (usually micrometre-scale or smaller, but not always). These devices are made from semiconductors. Many components of normal electronic design are available in microelectronic equivalent: transistors, capacitors, inductors, resistors, diodes and of course insulators and conductors can all be found in microelectronic devices. Unique wiring techniques such as wire bonding are also often used in microelectronics because of the unusually small size of the components, leads and pads. This technique requires specialized equipment.

Digital integrated circuits (ICs) consist mostly of transistors. Analog circuits commonly contain resistors and capacitors as well. Inductors are used in some high frequency analog circuits, but tend to occupy large chip area if used at low frequencies; gyrators can replace them in many applications. As techniques improve, the scale of microelectronic components continues to decrease. At smaller scales, the relative impact of intrinsic circuit properties such as interconnections may become more significant. These are called parasitic effects, and the goal of the microelectronics design engineer is to find ways to compensate for or to minimize these effects, while always delivering smaller, faster, and cheaper devices

1. Monolithic integrated circuits are usually referred to as _____. a. Silicon chips b. Selenium rectifiers c. Germanium chips d. Hybrids

2. Which type of component is generally not practical for fabrication in an IC? a. Resistors b. Inductors c. Diodes d. Capacitors

3. Which type of IC is used to determine whether voltage levels are the same or not? a. An op amp b. A timer c. A comparator d. A multiplexer/demultiplexer

4. Which of the following statements is true? a. Each LED in a common-anode display requires an active +V input to light b. Each LED in a common-cathode display requires an active ground input to light c. An LCD requires less power to operate than a typical LED multisegment display d. All of the above

5. An electronic device that can be turned on and turned off by a gate pulse is called a _____. a. Bipolar junction transistor b. Silicon-controlled switch c. Silicon-controlled rectifier d. Shockley diode

Advantages of IC technology * Compactness An obvious asset of IC design is economy of space; ICs are far more compact than equivalent circuits made from individual transistors, diodes, capacitors, and resistors. A corollary to this is the fact that far more complex circuits can be built, and kept down to a reasonable size, using ICs as compared with discrete components. Thus, you see notebook computers, also known as laptops, with capabilities more advanced than early computers that took up whole rooms.

* High speed Another corollary to the compactness of ICs is the fact that the interconnections among components are physically tiny, making high switching speeds possible. Electric currents travel fast, but not instantaneously. The less time charge carriers need to get from component X to component Y, in general, the more computations are possible within a given span of time, and the less time is needed for complex operations.

* Low power requirement Another advantage of ICs is that they use less power than equivalent discrete-component circuits. This is especially important if batteries are to be used for operation. Because ICs use so little current, they produce less heat than their discrete component equivalents. This translates into better efficiency. It also minimizes the problems that plague equipment that gets hot with use, such as frequency drift and generation of internal noise.

* Reliability Integrated circuits fail less often, per component-hour of use, than appliances that make use of discrete components. This is mainly a result of the fact that all interconnections are sealed within the IC case, preventing corrosion or the intrusion of dust. The reduced failure rate translates into less downtime, or time during which the equipment is out of service for repairs.

* Ease of maintenance Integrated-circuit technology lowers maintenance costs, mainly because repair procedures are simplified when failures do occur. Many appliances use sockets for ICs, and replacement is simply a matter of finding the faulty IC, unplugging it, and plugging in a new one. Special desoldering equipment is used with appliances having ICs soldered directly to the circuit boards.

* Modular construction Modern IC appliances use modular construction. In this scheme, individual ICs perform defined functions within a circuit board; the circuit board or card, in turn, fits into a socket and has a specific purpose. Computers, programmed with customized software, are used by repair technicians to locate the faulty card in an appliance. The whole card can be pulled and replaced, getting the appliance back to the consumer in the shortest possible time. Then the computer can be used to troubleshoot the faulty card, getting the card ready for use in the next appliance that happens to come along with a failure in the same card.

Modular construction can theoretically be used with discrete-component design. But this is rarely done. When a device is sophisticated enough to need modular construction, IC design is usually needed to keep the size within reason.

6. The channel of JFET is between the _____. a. Input and output b. Drain and source c. Gate and drain d. Gate and source

7. To produce tin film resistors, which of the following materials is the most widely used? a. Titanium b. Tantalum c. Nichrome d. Chromium cermets

8. As the input voltage varies within specified limits, the zener diode maintains a nearly constant output voltage across its terminal. This is called _____. a. Auto regulation b. Specific regulation c. Line regulation d. Load regulation

9. The BEST choice electronic device to turn a device at a particular voltage is a/an _____. a. SCR b. SCS c. DIAC d. PUT

10. _____ is a kind of oscilloscope which consist of narrowband if filter and a local oscillator (receiver) capable of showing transmitter carriers, spacing, harmonics and sidebands. a. Polygraph b. Harmonics analyzer c. Spectrum analyzer d. Computerized tomography

Limitations of IC technology * Inductors impractical While some components are easy to fabricate onto chips, other components defy the IC manufacturing process. Inductances, except for extremely low values, are one such bugaboo. Devices using ICs must generally be designed to work without inductors. Fortunately, resistance-capacitance (RC) circuits are capable of doing most things that inductance- capacitance (LC) circuits can do.

* Mega-power impossible The small size and low current consumption of ICs comes with a flip side. This is the fact that high-power amplifiers cannot, in general, be fabricated onto semiconductor chips. High power necessitates a certain minimum physical bulk, because such amplifiers always generate large amounts of heat. This isnt a serious drawback. Power transistors and vacuum tubes are available to perform high-power tasks. Integrated circuits are no different than anything else: theyre good at some things, and not so good at others.

11. Which of the following are UJT terminals? a. Emitter b. Base c. Base2 d. Gate i. B, C and D only ii. A, B, and C only iii. A, B and D only iv. All of the above

12. Type of semiconductor diode varies its internal capacitance as the voltage applied to its terminals varies. a. A zener diode b. A varactor diode c. A silicon-controlled rectifier d. A tunnel diode

13. Alkaline cells are: a. Are cheaper than zinc-carbon cells b. Are generally better in radios than zinc-carbon cells c. Have higher voltages than zinc-carbon cells d. Have shorter shelf lives than zinc-carbon cells

14. Which type of digital IC is least susceptible to noise? a. Transistor-transistor logic b. Base-coupled logic c. Emitter-coupled logic d. N-channel-coupled logic

15. In magnetic video tape: a. The video tracks are parallel to the edges b. The video tracks are diagonal c. The video tracks are perpendicular to the edges d. The video tracks can be oriented at any angle

Component density The number of elements per chip in an IC is called the component density. There has been a steady increase in the number of components that can be fabricated on a single chip. Of course there is an absolute limit on the component density that can be attained; it is imposed by the atomic structure of the semiconductor material. A logic gate will never be devised that is smaller than an individual atom. Technology hasnt bumped up against that barrier yet.

* MSI In medium-scale integration (MSI), there are 10 to 100 gates per chip. This allows for considerable miniaturization, but it is not a high level of component density, relatively speaking. An advantage of MSI (in a few applications) is that fairly large currents can be carried by the individual gates. Both bipolar and MOS technologies can be adapted to MSI.

* LSI In large-scale integration (LSI), there are 100 to 1000 gates per semiconductor chip. This is an order of magnitude (a factor of 10) more dense than MSI. Electronic wristwatches, single-chip calculators, and small microcomputers are examples of devices using LSI ICs. They can be 10 times more sophisticated than MSI devices.

* VLSI Very-large-scale integration (VLSI) devices have from 1,000 to 10,000 components per chip. This is an order of magnitude more dense than LSI. Complex microcomputers, and peripheral circuits such as memory storage ICs, are made using