# FM

```3. Frequency Modulation and De-Modulation using PLL
Objectives:
1. To construct and study the Frequency Modulation technique.
2. To examine the time displays of an FM signal.
3. To examine the frequency deviations for various modulating signal voltages.
4. To measure the percentage of modulation, and total power in frequency
modulation.
5. To investigate the use FM demodulation using PLL.
Pre-Lab Work:
1. Basic theory of Frequency Modulation techniques. Time and Frequency
analysis of AM waves.
2. Basic theory of PLL FM demodulation.
3. Understanding the circuit diagrams of FM generation and detection.
4. Understanding the data sheets of components used in the experiment.
6. Computer simulations (Multisim / pSpice) are performed and the objectives are
obtained prior to the hardware experiment.
Equipment and Components:
1.
2.
3.
4.
5.
6.
Signal generator
CRO
IC XR-2206, LM 565
Resistors
Capacitors.
Connecting wires &probes
Basic Theory:
Modulation is concerned with changing some characteristics of a high frequency
carrier wave in accordance with the amplitude of the modulating signal to be transmitted.
Frequency modulation is a system in which the frequency of the carrier is varied in
accordance with the amplitude variations of the message signal; whereas the amplitude
of the carrier remains unaltered. In FM the information is being carried by the carrier in
its frequency variations and not in amplitude. This is a great advantage in FM because
the noise generally affects the amplitudes of the waveform.
The mathematical representation of FM is given by
t
sFM (t)  Ac cos ct  2 k f  m( ) d 


where c(t )  Ac cos ct is RF carrier signal, m(t ) is modulating signal and k f
is
frequency modulation sensitivity constant. For a single-tone modulating signal, the FM
wave is represented by
sFM (t )  Ac cos ct   f sin 2 f mt 
where  f 
f
Am
m
f
is called frequency m odulation index, and where again
f
f  k f Am is known as frequency deviation. The bandwidth required to propagate
an FM wave according to the Carson’s rule is represented by B.WFM  2(f  k f )
Hz. The circuit diagram of Frequency Modulation is shown in Fig.1.
Frequency De modulation:
Frequency demodulation is the process that enables one to extract the original
modulating from the frequency m odulated wave. This can be achieved by a system
which has a transfer characteristics just inverse of voltage controlled oscillator
(VCO). In other words a frequency demodulator produces an output voltage whose
instantaneous frequency of input FM signal. There are various kinds of FM
dem odulation techniques are available. In this experim ent PLL based Frequency
dem odulation technique is used and the circuit is shown in Fig 2.
Circuit Diagram:
Fig.1 Circuit diagram of Frequency Modulation
Fig.2 Circuit diagram of FM Demodulation
Procedure:
Frequency Modulation.
1. Connect the Frequency Modulation circuit diagram shown in Fig.1.
2. Measure the frequency of the carrier signal at the FM output terminal with the
modulating signal is zero and plot the same on graph.
3. Apply the modulating signal of 500HZ with 1Vp-p.
4. Observe the modulated wave on the C.R.O & plot the same on graph.
5. Find the modulation index by measuring minimum and maximum frequency
deviations from the carrier frequency using CRO.
6. Determine the bandwidth of FM wave
7. Repeat the steps 5 and 6 by changing the amplitude and /or frequency of the
modulating Signal.
FM Demodulation:
8. Now wire the circuit as per the FM demodulation circuit shown in Fig.2.
9. Initially lock the VCO of PLL to the carrier frequency of FM wave.
10. Now apply the modulated signal as an input to demodulator circuit and compare
the demodulated signal with the input modulating signal & also draw the same on
the graph.
11. Observe the demodulated output for changing the amplitude and /or frequency of
the modulating Signal.
Observations:
S.No
Am
fc
fm
f max
Volts
Hz
Hz
Hz
1
2
Model Wave Forms:
f min
Hz
Freq.
Deviation
f
Modulation
index
Precautions:
1. Connections should be made carefully.
2. The components must be identified properly before giving the circuit connections.
3. The components must be properly doped into the bread board.
Results:
Viva Questions:
XR-2206
...the analog plus
Monolithic
Function Generator
company TM
February 2008-8
FEATURES
APPLICATIONS
Waveform Generation
Low-Sine Wave Distortion, 0.5%, Typical
Excellent Temperature Stability, 20ppm/°C, Typ.
Sweep Generation
Wide Sweep Range, 2000:1, Typical
AM/FM Generation
Low-Supply Sensitivity, 0.01%V, Typ.
V/F Conversion
Linear Amplitude Modulation
FSK Generation
TTL Compatible FSK Controls
Phase-Locked Loops (VCO)
Wide Supply Range, 10V to 26V
Adjustable Duty Cycle, 1% TO 99%
GENERAL DESCRIPTION
The circuit is ideally suited for communications,
instrumentation, and function generator applications
requiring sinusoidal tone, AM, FM, or FSK generation. It
has a typical drift specification of 20ppm/°C. The oscillator
frequency can be linearly swept over a 2000:1 frequency
range with an external control voltage, while maintaining
low distortion.
The XR-2206 is a monolithic function generator
integrated circuit capable of producing high quality sine,
square, triangle, ramp, and pulse waveforms of
high-stability and accuracy. The output waveforms can be
both amplitude and frequency modulated by an external
voltage. Frequency of operation can be selected
externally over a range of 0.01Hz to more than 1MHz.
ORDERING INFORMATION
Part No.
Package
Operating
Temperature Range
XR-2206P
–40°C to +85°C
XR-2206CP
0°C to +70°C
XR-2206D
16 Lead 300 Mil JEDEC SOIC
0°C to +70°C
Rev. 1.04
2008
EXAR Corporation, 48720 Kato Road, Fremont, CA 94538 (510) 668-7000 (510) 668-7017
1
XR-2206
TC1
5
TC2
6
TR1
7
TR2
8
FSKI
9
AMSI
1
Timing
Capacitor
Timing
Resistors
VCC
GND
BIAS
4
12
10
11 SYNCO
VCO
Current
Switches
Multiplier
And Sine
Shaper
WAVEA1 13
WAVEA2 14
SYMA1 15
SYMA2 16
Figure 1. XR-2206 Block Diagram
Rev. 1.04
2
+1
2
STO
3
MO
XR-2206
AMSI
STO
MO
VCC
TC1
TC2
TR1
TR2
1
16
2
15
3
14
4
13
5
12
6
11
7
10
8
9
SYMA2
SYMA1
WAVEA2
WAVEA1
GND
SYNCO
BIAS
FSKI
AMSI
STO
MO
VCC
TC1
TC2
TR1
TR2
1
16
2
15
3
14
4
13
5
12
6
11
7
10
8
9
SYMA2
SYMA1
WAVEA2
WAVEA1
GND
SYNCO
BIAS
FSKI
PIN DESCRIPTION
Pin #
Symbol
Type
Description
1
AMSI
I
Amplitude Modulating Signal Input.
2
STO
O
Sine or Triangle Wave Output.
3
MO
O
Multiplier Output.
4
VCC
5
TC1
I
Timing Capacitor Input.
6
TC2
I
Timing Capacitor Input.
7
TR1
O
Timing Resistor 1 Output.
8
TR2
O
Timing Resistor 2 Output.
9
FSKI
I
Frequency Shift Keying Input.
10
BIAS
O
Internal Voltage Reference.
O
Sync Output. This output is a open collector and needs a pull up resistor to VCC.
Positive Power Supply.
11
SYNCO
12
GND
13
WAVEA1
I
14
WAVEA2
I
15
SYMA1
I
16
SYMA2
I
Ground pin.
Rev. 1.04
3
XR-2206
DC ELECTRICAL CHARACTERISTICS
Test Conditions: Test Circuit of Figure 2 Vcc = 12V, TA = 25°C, C = 0.01F, R1 = 100k, R2 = 10k, R3 = 25k
Unless Otherwise Specified. S1 open for triangle, closed for sine wave.
XR-2206P
Parameters
Min.
Typ.
XR-2206CP/D
Max.
Min.
Typ.
Max.
Units
Conditions
General Characteristics
Single Supply Voltage
10
26
10
26
V
Split-Supply Voltage
+5
+13
+5
+13
V
20
mA
Supply Current
12
17
14
R1 10k
Oscillator Section
Max. Operating Frequency
0.5
Lowest Practical Frequency
1
0.5
0.01
1
MHz
0.01
Hz
C = 1000pF, R1 = 1k
C = 50F, R1 = 2M
Frequency Accuracy
+1
+4
+2
% of fo
Temperature Stability
Frequency
+10
+50
+20
ppm/°C 0°C TA 70°C
R1 = R2 = 20k
Sine Wave Amplitude Stability2
4800
4800
ppm/°C
Supply Sensitivity
0.01
0.01
%/V
2000:1
fH = fL
2
%
fL = 1kHz, fH = 10kHz
Sweep Range
0.1
1000:1 2000:1
fo = 1/R1C
VLOW = 10V, VHIGH = 20V,
R1 = R2 = 20k
fH @ R1 = 1k
fL @ R1 = 2M
Sweep Linearity
10:1 Sweep
2
1000:1 Sweep
8
8
%
fL = 100Hz, fH = 100kHz
FM Distortion
0.1
0.1
%
+10% Deviation
Figure 5
Recommended Timing Components
Timing Capacitor: C
Timing Resistors: R1 & R2
Triangle Sine Wave
0.001
100
0.001
100
F
1
2000
1
2000
k
Output1
Figure 3
Triangle Amplitude
Sine Wave Amplitude
160
40
60
80
160
mV/k
Figure 2, S1 Open
60
mV/k
Figure 2, S1 Closed
Max. Output Swing
6
6
Vp-p
Output Impedance
600
600
Triangle Linearity
1
1
%
Amplitude Stability
0.5
0.5
dB
For 1000:1 Sweep
%
R1 = 30k
%
See Figure 7 and Figure 8
Sine Wave Distortion
2.5
0.4
2.5
1.0
0.5
1.5
Notes
1 Output amplitude is directly proportional to the resistance, R , on Pin 3. See Figure 3.
3
2 For maximum amplitude stability, R should be a positive temperature coefficient resistor.
3
Bold face parameters are covered by production test and guaranteed over operating temperature range.
Rev. 1.04
4
XR-2206
DC ELECTRICAL CHARACTERISTICS (CONT’D)
XR-2206P
Parameters
Min.
Typ.
50
100
XR-2206CP/D
Max.
Min.
Typ.
Max.
Units
50
100
k
Conditions
Amplitude Modulation
Input Impedance
Modulation Range
100
100
%
Carrier Suppression
55
55
dB
Linearity
2
2
%
For 95% modulation
Amplitude
12
12
Vp-p
Measured at Pin 11.
Rise Time
250
250
ns
CL = 10pF
Fall Time
50
50
ns
CL = 10pF
Saturation Voltage
0.2
0.4
0.2
0.6
V
IL = 2mA
Leakage Current
0.1
20
0.1
100
A
VCC = 26V
Square-Wave Output
FSK Keying Level (Pin 9)
0.8
1.4
2.4
0.8
1.4
2.4
V
See section on circuit controls
Reference Bypass Voltage
2.9
3.1
3.3
2.5
3
3.5
V
Measured at Pin 10.
Notes
1 Output amplitude is directly proportional to the resistance, R , on Pin 3. See Figure 3.
3
2 For maximum amplitude stability, R should be a positive temperature coefficient resistor.
3
Bold face parameters are covered by production test and guaranteed over operating temperature range.
Specifications are subject to change without notice
ABSOLUTE MAXIMUM RATINGS
Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26V
Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . 750mW
Derate Above 25°C . . . . . . . . . . . . . . . . . . . . . . 5mW/°C
Total Timing Current . . . . . . . . . . . . . . . . . . . . . . . . 6mA
Storage Temperature . . . . . . . . . . . . -65°C to +150°C
SYSTEM DESCRIPTION
terminals to ground. With two timing pins, two discrete
output frequencies can be independently produced for
FSK generation applications by using the FSK input
control pin. This input controls the current switches which
select one of the timing resistor currents, and routes it to
the VCO.
The XR-2206 is comprised of four functional blocks; a
voltage-controlled oscillator (VCO), an analog multiplier
and sine-shaper; a unity gain buffer amplifier; and a set of
current switches.
The VCO produces an output frequency proportional to
an input current, which is set by a resistor from the timing
Rev. 1.04
5
LM565/LM565C
Phase Locked Loop
General Description
The LM565 and LM565C are general purpose phase locked
loops containing a stable, highly linear voltage controlled oscillator for low distortion FM demodulation, and a double balanced phase detector with good carrier suppression. The
VCO frequency is set with an external resistor and capacitor,
and a tuning range of 10:1 can be obtained with the same
capacitor. The characteristics of the closed loop
system — bandwidth, response speed, capture and pull in
range — may be adjusted over a wide range with an external
resistor and capacitor. The loop may be broken between the
VCO and the phase detector for insertion of a digital frequency divider to obtain frequency multiplication.
The LM565H is specified for operation over the −55˚C to
+125˚C military temperature range. The LM565CN is specified for operation over the 0˚C to +70˚C temperature range.
Features
n 200 ppm/˚C frequency stability of the VCO
n Power supply range of ± 5 to ± 12 volts with 100 ppm/%
typical
n 0.2% linearity of demodulated output
n Linear triangle wave with in phase zero crossings
available
n TTL and DTL compatible phase detector input and
square wave output
n Adjustable hold in range from ± 1% to > ± 60%
Applications
n
n
n
n
n
n
n
n
n
n
n
Data and tape synchronization
Modems
FSK demodulation
FM demodulation
Frequency synthesizer
Tone decoding
Frequency multiplication and division
SCA demodulators
Signal regeneration
Coherent demodulators
Connection Diagrams
Metal Can Package
Dual-in-Line Package
DS007853-2
Order Number LM565H
See NS Package Number H10C
DS007853
DS007853-3
Order Number LM565CN
See NS Package Number N14A
www.national.com
LM565/LM565C Phase Locked Loop
May 1999
Absolute Maximum Ratings (Note 1)
Operating Temperature Range
LM565H
LM565CN
Storage Temperature Range
(Soldering, 10 sec.)
If Military/Aerospace specified devices are required,
Distributors for availability and specifications.
± 12V
1400 mW
± 1V
Supply Voltage
Power Dissipation (Note 2)
Differential Input Voltage
−55˚C to +125˚C
0˚C to +70˚C
−65˚C to +150˚C
260˚C
Electrical Characteristics
AC Test Circuit, TA = 25˚C, VCC = ± 6V
Parameter
LM565
Conditions
Min
Power Supply Current
Input Impedance (Pins 2, 3)
VCO Maximum Operating
Frequency
VCO Free-Running Frequency
−4V < V2, V3 < 0V
Co = 2.7 pF
Co = 1.5 nF
Ro = 20 kΩ
fo = 10 kHz
Max
8.0
12.5
7
10
300
500
−10
0
Operating Frequency
Temperature Coefficient
LM565C
Typ
+10
Min
Triangle Wave Output Voltage
2
Triangle Wave Output Linearity
1.0
2.4
3
5.4
45
50
Output Impedance (Pin 4)
500
kHz
−30
0
Square Wave Rise Time
2
0.6
VCO Sensitivity
fo = 10 kHz
Demodulated Output Voltage
(Pin 7)
± 10% Frequency Deviation
Total Harmonic Distortion
± 10% Frequency Deviation
Output Impedance (Pin 7)
4.25
Output Offset Voltage
|V7 − V6|
Temperature Drift of |V7 − V6|
AM Rejection
30
Phase Detector Sensitivity KD
1.5
%/V
2.4
3
Vp-p
%
Vp-p
40
50
kΩ
60
20
1
0.6
300
400
0.2
0.75
200
3.5
DC Level (Pin 7)
0.2
5.4
6600
250
ppm/˚C
4.7
50
Output Current Sink (Pin 4)
4.75
30
100
4.0
%
ns
50
ns
1
mA
6600
Hz/V
300
450
0.2
1.5
3.5
4.5
%
0.5
20
Square Wave Fall Time
+30
5
55
mA
250
5
Square Wave Duty Cycle
12.5
−200
0.1
4.7
8.0
Units
kΩ
0.2
Square Wave Output Level
Max
5
−100
Frequency Drift with
Supply Voltage
Typ
mVp-p
%
kΩ
4.5
5.0
V
50
200
mV
500
500
40
40
µV/˚C
dB
0.68
0.68