SARVAJANIK COLLEGE

OF

ENGINEEING & TECNOLOGY

TOPIC APPLICTIONS OF PLL

FM DEMODULATION

FSK DEMODULATOR

NAME ENROLLMENTNOJARIWALA SIDDHARTH R. 140423109005VASAVA CHIRAG M. 140423109014

SUB NAME :- ANALOG ELECTRONICS

Internal Block Diagram of IC 565

The LM565 is a general purpose

phase locked loop(PLL) containing a

stable, highly linear voltage controlled

oscillator(VCO) and a double balanced

phase detector with good carrier

suppression.

• PLL – Phase Locked Loops

• It is two type – linear and Nonlinear

• It is use in TV , FM Demodulation , FSK Demodulation Motor speed control

, etc.

• PLL ICS :- 560,561,562,564,565 & 567

INRODUCTION OF PLL

APPLICATION OF PLL

1. Frequency multiplication/division.

2. Frequency translation

3. AM detection

4. FM detection

5. FSK demodulation

FM DEMODULATION USING PLL

Circuit Diagram

of

FM Demodulation

The operation of FM demodulation using PLL

The FM signal is applied to PLL.

As the PLL is locked to the FM signal, the VCO start tracking instantaneous frequency in the input FM signal.

The error voltage produced at the output of the error amplifier is directly proportional to the frequency deviation.

Thus the ac component of the error voltage represents the modulating signal.

Demodulation FM output is obtained at the output of the error amplifier.

Advantage of using PLL for FM demodulation

PLL ensures a high degree of linearity between the instantaneous input frequency and VCO control voltage which is the output of error amplifier.

The bandwidth of the incoming FM signal can be much wider than that of the low-pass which is restricted to the baseband.

The control voltage signal of the VCO has bandwidth of the modulating signal.

FSK DEMODULATOR USING PLL

OPRATION OF FSK DEMODULATOR USING PLL

The capacitor coupling at the i/p is used for removing the dc level in the i/p FSK signal.

As we apply the FSK signal at the i/p, the loop gets locked to the i/p frequency and the VCO

tracks the i/p frequency between the two frequencies Fh and Fl. A corresponding dc shift will be

produced at the o/p.

The three stage RC low pass filter is used for removing the carrier component from the o/p.

R1 & C1 are decide the free running frequency of VCO .

VOC Control voltage is produced which is given by:

Vc1 = Fh – F0

K

Where, F0 = Free running VCO frequency &

K = V to f transfer coefficient of VCO.

When the i/p frequency is FL the control voltage is given by:

Vc2 = F0 – FL

K

Where, Vc2 is i/p side capacitor

These voltages are compared whit the reference voltage by the external comparator to produce a

digital signal.

ANY QUESTION

?

THE END

Thank..u