June 2010
Intermediate to advanced
721 pages
21h 32m
English
A voltage-controlled oscillator (VCO) is one in which the frequency of oscillations varies as a function of voltage. The same circuit is also called a voltage-to-frequency converter (VFC) because a given voltage gives rise to a specific frequency. An astable multivibrator is used as voltage-controlled oscillator [see Fig. 7.13(a)]. A comparison of this with the circuit shown in Fig. 7.1 shows that here the two resistors R and R are returned to a separate source VBB rather than to VCC.
When Q1 is OFF and Q2 is ON, C1 charges. When Q1 is ON, the charge on C1 decays with a time constant τ1 = RC1 as shown in Fig. 7.13(b). As a result, the voltage at the base of Q2, VB2 varies with time, ...
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