13-04-2013, 04:48 PM
STUDY OF VCO AND PLL IC’s
AIM:
i) To observe the applications of VCO-IC 566
ii) To generate the frequency modulated wave by using IC 566
THEORY:
The VCO is a free running Multivibrator and operates at a set frequency fo called free running frequency. This frequency is determined by an external timing capacitor and an external resistor. It can also be shifted to either side by applying a d.c control voltage vc to an appropriate terminal of the IC. The frequency deviation is directly proportional to the dc control voltage and hence it is called a “voltage controlled oscillator” or, in short, VCO.
The output frequency of the VCO can be changed either by R1, C1 or the voltage VC at the modulating input terminal (pin 5). The voltage VC can be varied by connecting a R1R2 circuit. The components R1 and C1 are first selected so that VCO output frequency lies in the centre of the operating frequency range. Now the modulating input voltage is usually varied from 0.75 VCC which can produce a frequency variation of about 10 to 1.
PROCEDURE:
1. The circuit is connected as per the circuit diagram shown in Fig1.
2. Observe the modulating signal on CRO and measure the amplitude and frequency of the signal.
3. Without giving modulating signal, take output at pin 4, we get the carrier wave.
4. Measure the maximum frequency deviation of each step and evaluate the modulating Index.