Page 213 - DCAP108_DIGITAL_CIRCUITS_AND_LOGIC_DESIGNS

Digital Circuits and Logic Design

Notes to be cut up and individually packaged in tiny cans. Packaging each component and hand
wiring the components into circuits was extremely inefficient. The military sought more
efficient methods of making circuits.
New technologies emerged and integrated circuits were soon developed with various
components (transistors, resistors, and capacitors) formed on the same chip, but interconnection
of the various components still required tedious hand wiring.

In 1959, Jean Hoerni and Robert Noyce developed a new process called planar technology at
Fairchild Semiconductor which enabled them to diffuse various layers onto the surface of a
silicon wafer to make a transistor, leaving a layer of protective oxide on the junctions. This
process allowed metal interconnections to be evaporated onto the flat transistor surface and
replaced the hand wiring. The new process used silicon instead of germanium, and made
commercial production of ICs possible.
The initial resistance to the new IC technology gave way to enormous popularity. By the end
of the 1960s, nearly 90% of all the components manufactured were integrated circuits.

Questions:
1. Explain the brief history of semiconductors.
2. What do you understand by dopants?

Self Assessment

True or False:
6. RAM is the place in a computer where the operating system, application programs, and
data in current use are kept.
(a) True (b) False
7. RAM is a very slow-speed type of memory.
(a) True (b) False
Multiple choice questions:
8. PROM, stands for ....................... .
(a) Personal Read Only Memory (b) Peripheral Read Only Memory
(c) Programmable Read Only Memory (d) None of these

9. Flash memory may be considered as a development of ........................technology.
(a) EEPROM (b) DRAM
(c) EPROM (d) None of these

11.6 Summary

The MOD number of a Johnson counter is twice the number of flip-flops.
• The flip-flop in the lowest-order position is complemented/toggled with every clock pulse
and a flip-flop in any other position is complemented on the next clock pulse provided all
the bits in the lower-order positions are equal to 1.
• The basic types of shift registers are studied, such as Serial-In/Serial-Out, Serial-In/
Parallel-Out, Parallel-In/Serial-Out, Parallel-In/Parallel-Out, bidirectional shift registers.
• Semiconductor memory technology is moving forward apace not only are the sizes
of memories being increased, and the data densities improving, but new forms of
semiconductor memory such as MRAM are being introduced.

208 LOVELY PROFESSIONAL UNIVERSITY