Phaced lock loop

1. Phase locked loop basics
• PLL stands for 'Phase-Locked Loop' and is basically a closed loop
frequency control system, • which functioning is based on the phase
sensitive detection of phase difference between the input and output
signals of the controlled oscillator (CO)
• The Phase Locked Loop method of frequency synthesis is now the most
commonly used method of producing high frequency oscillations in
modern communications equipment
• PLL circuits are now frequently being used to demodulate FM signals,
making obsolete the Foster-Seerly and radio detectors of the early years.
Other applications for PLL circuits include AM demodulators, FSK
decoders, two-tone decoders and motor speed controls.

3. A basic phase locked loop, PLL,
consists of three basic
elements:
Phase comparator / detector: As
the name implies, this circuit block
within the PLL compares the phase
of two signals and generates a
voltage according to the phase
difference between the two signals.

4. • A PD is a circuit that senses two periodic inputs and produces an output
whose average value is proportional to the difference between the phases of
the inputs
• The input/output characteristic of the PD is ideally a straight line, with a
slope called the “gain” and denoted by KPD

5.  We seek a circuit whose average output is proportional to the input
phase difference.
 An Exclusive-OR (XOR) gate can serve this purpose. It generates
pulses whose width is equal to Δϕ

6. • Loop filter;
• This filter is used to filter the output from the phase comparator in the PLL.
It is used to remove any components of the signals of which the phase is
being compared from the VCO line. It also governs many of the
characteristics of the loop and its stability.
• Voltage controlled oscillator (VCO): The voltage controlled oscillator is the
circuit block that generates the output radio frequency signal. Its frequency
can be controlled and swung over the operational frequency band for the
loop.

7. Negative feedback loop: if the “loop gain” is sufficiently high, the circuit
minimizes the input error.
The PD produces repetitive pulses at its output, modulating the VCO frequency
and generating large sidebands.
Interpose a low-pass filter between the PD and the VCO to suppress
these pulses.

8. An important and unique consequence of phase
locking is that the input and output frequencies
of the PLL are exactly equal.

11. • A voltage-controlled oscillator or VCO is an electronic oscillator whose
oscillation frequency is controlled by a voltage input. The applied input
voltage determines the instantaneous oscillation frequency. Consequently,
modulating signals applied to control input may cause frequency
modulation (FM) or phase modulation (PM).
A VCO may also be part of a phase-locked loop.

12. • What is a PLL?
• Control System Representation
• Parts of a PLL
• Digital frequency control system
• Generate high speed oscillations
• Acquire and track signals
• Radio Frequency Demodulation
• DX-ing
• RF communications

16.  Phase Detector
 Filter
 Voltage Controlled Oscillator
Programmable Counter

17.  Phase Detector
 Acts as comparator
 Produces a voltage proportional to the phase difference
between input and output signal
 Voltage becomes a control signal

18.  Filter
 Determines dynamic characteristics of PLL
 Specify Capture Range (bandwidth)
 Specify Tracking Range
 Receives signal from Phase Detector and filters
accordingly

19. • Voltage Controlled Oscillator
• Set tuning range
• Set noise margin
• Creates low noise clock oscillation

20. • Divider
• Divides the VCO output by the degree of the open loop gain
• Feedback loop allows phase comparison

21. • (mō´dem) :- Short for modulator-demodulator. A modem is adevice or
program that enables a computer to transmit data over, for example,
telephone or cable lines. Computer information is stored digitally,
whereas information transmitted over telephone lines is transmitted in
the form of analog waves. A modem converts between these two forms.