Page 68 - Understanding Automotive Electronics

2735 | CH 2 Page 55 Tuesday, March 10, 1998 10:55 AM

THE SYSTEMS APPROACH TO CONTROL AND INSTRUMENTATION 2

Figure 2.18
Operational Amplifier
Diagram

FPO

As an example of the signal processing application of the operational
amplifier, consider an instrument using a sensor that has an imperfect response.
For the purpose of illustration, assume that the frequency response H for the
sensor is as shown in Figure 2.19. The output voltage for a fixed-amplitude
input increases linearly with frequency, as shown in the graph. An example of
this type of frequency response is a magnetic angular speed sensor, described in
Chapter 6.
A signal processing circuit that can compensate for the undesirable frequency
response is shown in Figure 2.20. In this circuit, a parallel resistance–capacitance
(R C ) combination is connected in a so-called feedback path from the output to
f
the inverting input. The frequency response for this circuit (H = v /v ) is shown
o s
sp
graphically in Figure 2.21. Also shown in this illustration is the frequency
response for the combination sensor and signal processor. For frequencies
above about 2 Hz, the frequency response (H = v /x) for the combination is
o
flat, as is desired. The characteristics and applications of operational
amplifiers are discussed in greater detail in Chapter 3.

Figure 2.19
Example Sensor
Frequency Response

FPO

UNDERSTANDING AUTOMOTIVE ELECTRONICS 55