here the PPT on the Frequency Synthesized Signal Generator or we can also called it basic RF Signal Sources.

1. MAKE IN INDIA
Frequency Synthesized Signal Generator

2. Desh Deepak
Shaur ya Jai n
Var un Kumar
Pankaj Pandey
Fr equency Synt hes i zed
Si gnal Gener at or

3. About Frequency Synthesized Signal Generator
Frequency Synthesizers are basically RF signal sources with
variable output frequencies which are directly derived and
generated from a precise reference frequency (internal or
external) with no additional frequency error. The ideal output
signal is a single spectrum line with no other unwanted
frequencies. This can't be realized in practice and all RF-signals
have a so-called spectral purity. This is a combination of
harmonics, non-harmonics (discrete spurious), SSB phase noise,
noise floor and residual FM

4. Frequency Synthesized Signal
Generator

5. Met hods of Fr equency
Synt hes i s
1. Indirect Method (Phase locked Loop)
2. Direct Synthesis
I ndi r ect Met hod
component of indirect method
1. Voltage controlled Oscillator (VCO)
2.The Programmable Divider
3.The Phase Detector
4.The Phase reference
5. The Loop filter

6. Voltage controlled Oscillator (VCO)
It is the source of the output frequency and has the ability
to be tuned electronically usually by applying a variable
voltage.
Some oscillators are electronically tuned using a current
especially in the higher frequencies , but for the general
discussion of the indirect synthesizer the signal source
will be considered as a Voltage controlled device

7. Programmable Divider
It is a logic element that divides a frequency of the VCO by
an integer that can be entered via programmable switches a
microprocessor or the other method.
Phase Detector
It provides an analog output that is a function of the phase
angle between the two inputs which in the case of a
frequency synthesizer is the reference source and the output
of the programmable divider.

8. Reference Source
It is a very accurate and stable frequency source which is
typically a quartz crystal oscillator. The accuracy of entire
synthesizer is dependent on the accuracy of the reference
source
The crystal oscillator operates in the region of 1-10 MHz and
that frequency is divided down using digital counters to
provide the necessary clock and reference frequencies for
the synthesizer
Loop Filter
It is an analog filter and is required to assure stable and noise
free operations of the synthesizer.

9. Working of the PLL
The programmable divider divides the frequency of the VCO
by N. The output frequency of the programmable divider is
fv/N or fr/N
fv- desired frequency of the VCO
fr- reference frequency applied to the Phase detector
N- integer entered in to the programmable divider
The output of the programmable divider is fed to the phase
detector and compared to the phase of the reference
frequency.

10. If output of the phase detector were returned to the VCO, any
variation in the phase could be corrected so that the frequency
of the VCO would be exactly N times the reference frequency.
However the phase determination can be made only once in
each reference frequency period, and thus the frequency of the
VCO can only be corrected at this rate, this would cause the
frequency of VCO to be modulated and creates spurious
sidebands called the reference side bands, in such a fashion as to
make the VCO output useless for precision measurements.
A filter is inserted between the phase detector and the VCO so
that the periodic frequency changes are smoothed and then the
frequency modulation is reduced .

11. Block Diagram of PLL

12. Disadvantages
1. It is not capable of removing all the side band energy and
something must retain. The sideband level required for the
critical testing is very low and can make the PLL
synthesizer practically unsuitable.
2. The loop filter affects the frequency slewing the
characteristics of the synthesizer
3. When it is necessary to change the frequency of the signal
generator by large amount the time required for the
change can be long.

13. DIRECT SYNTHESIS METHOD
In this method a single 18 MHz reference frequency is used
which is divided, mixed multiplied, to provide 10 outputs in
100KHz steps from 2 to 2.9 MHz, as well as 16 MHz
output.
Rather than stabilizing the frequency of VCO by comparing
the phase of fraction of the VCO’s frequency to reference
frequency, this method generates the desired frequency from
reference frequency.
A selected frequency from the 2 to 2.9 MHz set is heterodyned
with 18 MHz reference, and the sum is filtered to produce
10 selectable frequencies from 20 to 20.9 MHz in 100 KHz
steps

14. Block diagram of Direct Synthesis

15. This frequency is divided by 10 and mixed with 16MHz and so
on.
It can be seen from the block diagram that the circuit is
repeated for each switch, and the repeated circuit are
required whenever decade is added.
Although the synthesizer circuits appear complex and
expensive, each decade is identical with the previous decade.
Because there are no low frequency circuits, the frequency
can be changed practically instantaneously in addition
because the entire synthesizer operates from a single
frequency source ,the close-in frequency spectrum can be
quite pure without any undesired modulation

16. APPLICATIONS
They are found in many modern devices, including
 radio receivers
mobile telephones
Radiotelephones
Walkie-talkies
satellite receivers
GPS systems, etc.

17.  A frequency synthesizer can combine
frequency multiplication, frequency division, and
frequency mixing (the frequency mixing process generates
sum and difference frequencies) operations to produce the
desired output signal.

19. DONATE