Electronic Devices and Amplifier Circuits with MATLAB Computing, Second Edition
Emphasizing operational amplifiers and integrated devices used in digital circuits, this text presents a thorough discussion of state-of-the-art electronic devices.
TABLE OF CONTENTS Electronic Devices and Amplifier Circuits with MATLAB Computing, Second Edition
Chapter 7: Pulse Circuits and Waveform Generators
This chapter is an introduction to several pulsed circuits and waveform generators also known as relaxation oscillators. These circuits are part of a family of circuits that include differentiators, integrators, clipping and clamping circuits, pulse-timing and delay circuits, logic circuits, and switching circuits. In this chapter we discuss the three types of multivibrators, the 555 Timer, and the Schmitt trigger. Sinusoidal oscillators are discussed in Chapter 10.
7.1 Astable (Free-Running) Multivibrators
An astable or free-running multivibrator, shown in Figure 7.1, is essentially a digital clock which has two momentarily stable states which alternate continuously thus producing square pulses as shown in Figure 7.2. We have assumed that all devices in the circuit of Figure 7.1 are identical.
Figure 7.1: Astable multivibrator
Figure 7.2: Output waveforms of the astable multivibrator
Let us now consider Output 1 and assume that the time ON T 1 and time OFF T 2 are equal and the period is T as shown in Figure 7.3.
Figure 7.3: Waveform showing period T and times ON and OFF for the multivibrator circuit of Figure 7.1
If in Figure 7.3 T 1=T 2, the pulse repetition frequency f is given by
where R B and C are as shown in Figure 7.1.
7.2 The 555 Timer
The 555 Timer circuit is a widely used IC for generating waveforms. A simplified diagram is shown in Figure 7.4.
Figure 7.4: Simplified circuit for the 555 Timer
We observe that this IC includes...
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