Tài liệu INTRODUCTION TO ELECTRONIC ENGINEERING- P7 doc

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Introduction to Electronic Engineering

120

Electronic Circuits

a.

b.

c.

d.

e.

f.

Fig. 2.50

a.

Sine wave generators. Fig. 2.51,a shows a sine wave generator built as the Wien bridge. Thanks to

the feedbacks, while the supply voltage is applied, this circuit generates the oscillations shown in Fig.

2.51,b with a period defined as

T = 2RC,

where R = R1 = R2, C = C1 = C2, and R3 = 2R4. For instance, if R = 10 k and C = 10 nF, then f = 1,6

kHz, T = 0,628 ms.

2

Uout

a. b.

C1

R2 C2

R1

R4

R3

Fig. 2.51

average

amplitude

T

rms

peak-to-peak

t

Fig. 2.52 represents the circuits that convert a sinusoidal input signal to the pulsating output voltage.

They are called precision rectifiers because the rectified diodes are included into the feedback loops.

The second op amp in Fig. 2.52,b inserts the missed alternation to the rectified pulse chain.

Push-pull amplifiers. When a transistor is biased for the class B mode of operation, it clips off half a

cycle of the input signal. To reduce distortion, two transistors are used in push-pull arrangement that is

the pair of identical transistors connected so that the signal can be introduced across. Fig. 2.53,a shows

a way to connect a class B transistors by linking an npn emitter follower to pnp emitter follower. The

load is connected to the emitters of the transistors, which operate as repeaters.

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