Page 93 - Understanding Automotive Electronics

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3 ELECTRONICS FUNDAMENTALS

At the same time, the difference voltage v is transmitted on a subcarrier:
D

v D = v R – v L

The right-channel voltage can be separated from the sum and difference
voltages using the circuit of Figure 3.5. Replacing voltages V and V by v and
a b S
V , respectively, yields an output:
D
– R f
v o = ------- v R +( v L + v R – v L )
R

=  – 2R f
----------- v R
 R 
A simple extension of this circuit permits similar separation of the left-channel
voltage.

Analog Computers

Analog computers, like The op amp is the basic building block for analog computers. Analog
those used to simulate computers are used to simulate the behavior of other systems. Virtually any
the performance of auto- system that can be described in a block diagram using standard building blocks
motive systems, are con- can be duplicated on an analog computer. If a control system designer is
structed with building an automotive speed controller and does not want to waste a lot of
operational amplifiers. time and money testing prototypes on a real car, he or she can program the
analog computer to simulate the car’s speed electronically. By varying amplifier
gains, frequency responses, and resistor, capacitor, and inductor values, system
parameters can be varied to study their effect on system performance. Such
system studies help to determine the parts needed for a system before any
hardware is built.
The main problem with analog circuits and analog computers is that their
performance changes with changes in temperature, supply voltage, signal levels,
and noise levels. While most of these problems are eliminated when digital
circuits are used, analog computers are much more cost effective when dealing
with relatively simple systems. However, analog computers have effectively been
replaced in all practical applications by a corresponding digital computer.

DIGITAL CIRCUITS
Binary circuits can oper- Digital circuits, including digital computers, are formed from binary
ate in only one of two circuits. Binary digital circuits are circuits whose output can be only one of two
states (on or off). different states. Each state is indicated by a particular voltage or current level.
An example of a simple binary digital system is a door-open indicator on a car.
When a car door is opened, a light comes on. When it is closed, the light goes

80 UNDERSTANDING AUTOMOTIVE ELECTRONICS