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Engineering and Construction
Pages 4 (1004 words)
Name of student: Course Code: Instructor: Date of submission: FM demodulation using CD 4046 CMOS Phase-Locked Loop (PLL) integrated circuit. Introduction FM is obtained by the variation of the frequency components of the modulating signal voltage through a Voltage Controlled Oscillator so that the output varies according to the input signal.FM demodulation is the reverse process of modulation where the Voltage Controlled Oscillator is locked to the incoming modulated FM signal by the Phase-Locked Loop to recover the original input signal.
The PLL has a voltage-controlled oscillator, a phase detector, and a low pass filter connected in a feedback loop. The input voltage determines the frequency of oscillation at the output of the VCO (Sedra 1998). This fosc is equal to the intermediate frequency fi required to be 470 kHz in this case. The circuit is built on a proto board according to the block diagram shown fig1 bellow; The components required are; CD 4046 CMOS Phase-Lock Loop (PLL) integrated circuit Resistors of values; 1k, 10k, 18k (2). Capacitors of values; 0.1?F, 0.01?F, 3900pF and, Breadboard. The actual circuit is realized according to the circuit shown in fig 2 bellow. The circuit components in the PLL providing a centre frequency of 470 kHz are determined according to the equation, fosc = 1/2пRC. Therefore 470000Hz*2п = 1/RC and taking R = 100K then 1/C =470000* 2п*100000= 3.386pF and the preferred value is 3400nf. ...
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