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Subject: PLL Detected ReceiversSec: D

SUBMITTED TO:

SYED ARBAB MOHD SYED ARBAB MOHD SHIHABSHIHAB

NAME & ID of Group Members:

(1)(1)Azimel BakiAzimel Baki 10-16493-210-16493-2(2)(2)Tonmoy BaruaTonmoy Barua 10-16953-210-16953-2

Phased Locked Loop (PLL)Phased Locked Loop (PLL)

• PLL initially locks to the IF frequency

• After locking, voltage controlled oscillator (VCO) would track frequency changes in the input signal by maintaining a phase error

• The PLL input is a deviated FM and the VCO natural frequency is equal to the IF center frequency

• The correction voltage produced at the output of the phase comparator is proportional to the frequency deviation that is equal to the demodulated information signal

Phase-Locked LoopPhase-Locked Loop

• The PLL is the basis of practically all modern frequency synthesizer design.

• The block diagram of a simple PLL:

PhasePhaseDetectorDetector

LPFLPFLoopLoop

AmplifierAmplifier VCOVCOffrr ffoo

VVpp

Operation of PLLOperation of PLL

Initially, the PLL is unlocked, i.e., the VCO is at the free-running frequency, fo.

Since fo is probably not the same as the reference frequency, fr, the phase detector will generate an error/control voltage, Vp.

Vp is filtered, amplified, and applied to the VCO to change its frequency so that fo = fr. The PLL will then remain in phase lock.

PLL applications (I)PLL applications (I) FM demodulation• PLL tracks variation in frequency

• also used in Frequency-shift keying - where mark/space ratio changes, not f

AM detection• if input is sinusoidal, then PLL can demodulate signal from

carrier

PLL applications (ii)PLL applications (ii) Frequency synchronization and signal

conditioning• a poor oscillator can be locked to good

reference signal - e.g. color TV• remove out-of-range interference, i.e. phase

jitter Synchronization for control• e.g. motor speed - required for many

applications• e.g. CD player

FM ReceiversFM Receivers

• FM receivers, like AM receivers, utilize the super heterodyne principle, but they operate at much higher frequencies (88 - 108 MHz).

• A limiter is often used to ensure the received signal is constant in amplitude before it enters the discriminator or detector.

Block Diagram of FM ReceiverBlock Diagram of FM Receiver

FM DemodulatorsFM Demodulators

• The FM demodulators must convert frequency variations of the input signal into amplitude variations at the output.

• The Foster-Seeley discriminator and its variant, the ratio detector are commonly found in older receivers. They are based on the principle of slope detection using resonant circuits.

PLL FM DetectorPLL FM Detector

PhasePhase

DetectorDetector

LPFLPFDemodulatedDemodulated

outputoutput

VCOVCO

FM IFFM IF

SignalSignal

S-curve Characteristics of FM DetectorsS-curve Characteristics of FM Detectors

ffIFIF

ffii

vvoo

EEmm

AdvantageAdvantage

Good frequency accuracy and stability over time and temperature and easy of tuning across multiple channels.

THANKTHANK

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