To understand the concept of frrequency synthesizer

1. FREQUENCY SYNTHESIZERS
By
Siva kumar.S
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2.  One is free running generators-output
tuned continuously either electrically
(or)mechanically.
 Second is frequency generator with
frequency synthesize technique
 Synthesis:clock and to derive the wide
frequency range in steps from the output
of an oscillator
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Two Types of frequency generator:

3. Advantages of frequency synthesizer:
 Arbitrarily selectable
 Output is stable
 Accurate Frequency
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Disadvantages of free running generator:
Poor stability
Accuracy is poor

4. Direct synthesis
Indirect synthesis
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Methods of Frequency
Synthesizer:

5.  It use a technique of directly deriving the output
frequency from the referency frequency
 It uses frequency dividers,multipliers,mixers And
bandpass filters
 This method produces more accurate and stable
output

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Direct Synthesis:

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Block diagram:
Reference oscillator
10Mhz Mixer
13 MHz
1Mhz 7Mhz
2Mhz
3Mhz
3Mhz
4Mhz
Basic action in Direct synthesis
÷10
×2
×3
×4
13 Mhz
Bandpass
filter
~

7.  Due to swithching frequencies,phase
continuity is lost
 The method is very prone to spurious
signals in the output
 It suffers from wideband phase noise
 Due to a lot of hardware the circuit is
expensive
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Disadvantage of direct synthesis :

8.  The output frequency is given to VCO
 The programmable divider is a logic element
and it divides the frequency by integer
 The phase detector provides an analog output
 The crystal oscillator in frequency range of
1MHZ to 10MHZ
 F0=N.Fr
 Where
F0-desired output frequency
Fr-reference frequency applied to phase
detector
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Indirect frequency synthesis:

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Block diagram:
output
Frequency programming
Fref Fref
Control voltage
Basic Action in Indirect synthesis
Programmable
divider
Phase
detector
Loop filter
VCO
Reference
frequency source

10.  It can be used master oscillator in transmitter and
local oscillator in receiver
 It is used to detect accurately the frequencies from
remote
 The effective microwave spectrum for a
communication.so, the receiver bandwidth is reduced
 It is used in automatic space systems
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Applications:

11. THANKYOU FOR YOUR
ATTENTION
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