Page 173 - Concise Encyclopedia of Robotics

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resistor
_
+ V cc Integrated Circuit
Output
V ee
Input

Integrated circuit—Fig 1

used with pulse modulation. An analog multiplexer can also be used in
reverse; then it works as a demultiplexer.
Like an op amp, a comparator IC has two inputs. The device compares
the voltages at the two inputs (called A and B). If the input at A is signifi-
cantly greater than the input at B, the output is about +5 V. This is logic
1, or high. If the input at A is not greater than the input at B, the output
voltage is about +2 V. This is designated as logic 0, or low. Comparators
are employed to actuate, or trigger, other devices such as relays and elec-
tronic switching circuits.They have various applications in robotic systems.

Digital ICs
Digital integrated circuits consist of gates that perform logical operations
at high speeds. There are several different technologies, each with unique
characteristics. Digital-logic technology can employ bipolar and/or
metal-oxide semiconductor devices.
In transistor-transistor logic (TTL), arrays of bipolar transistors, some
with multiple emitters, operate on DC pulses. A TTL gate is illustrated in
Fig.2.The transistors are either cut off or saturated;there is no “in between.”
Because of this,TTL circuitry is comparatively immune to extraneous noise.
Another bipolar-transistor logic form is known as emitter-coupled
logic (ECL). In ECL, the transistors are not operated at saturation, as they
are with TTL. This increases the speed of operation of ECL compared
with TTL. However, noise pulses have a greater effect in ECL, because

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