There are two types of frequency generators: free running generators whose output is tuned continuously mechanically or electrically, and frequency synthesizers. Frequency synthesizers use a reference clock and frequency synthesis techniques to derive a wide frequency range in steps from an oscillator output. There are two methods of frequency synthesis: direct synthesis which directly derives the output frequency from the reference using dividers, multipliers, mixers and filters; and indirect synthesis which uses a voltage controlled oscillator controlled by a phase detector feedback loop including a programmable divider. Frequency synthesizers have advantages over free running generators of arbitrarily selectable, stable and accurate frequencies. Their applications include use as local oscillators in receivers and for accurately detecting frequencies from remote transmitters.

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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