Institutional Repository | Satya Wacana Christian University: Penelitian Sistem Audio Stereo dengan Media Transmisi Jala-Jala Listrik
EXPERIMENT #7: FREQUENCY MODULATION
INTRODUCTION:
Frequency modulation, or FM, is an important method of impressing information on a carrier. It has
many advantages over AM. First, since FM only changes the frequency, and not the amplitude of the
carrier wave, FM receivers can be built to ignore amplitude (voltage) changes. This is important,
because most external noise is in the form of voltage variations that are "added" to the carrier wave as
it makes its way from transmitter to receiver. An AM receiver directly responds to these with the
familiar sounds of static interference; an FM receiver ignores the amplitude changes, almost
eliminating the effect of the noise.
Second, it is much easier to design systems to reproduce high-fidelity sound using FM. "High-fidelity"
means accurate signal reproduction, with a minimum of distortion. The reproduced information signal
is a very close replica of the original in an FM system. It's difficult to build hi-fi AM receivers, partly
due to the inherent nonlinear distortion created in a conventional AM diode detector, and also partly
due to the limited transmission bandwidth (8 kHz) allotted for AM broadcast.
These advantages do come at a price; that price is increased bandwidth. A typical FM broadcast station
uses up to 75 kHz of signal deviation (the peak frequency change), which results in a typical bandwidth
of 150 to 200 kHz. Because of the high bandwidth requirements, FM broadcasting is done in the VHF
band between 88 and 108 MHz. FM receivers and detectors are slightly more complex than those for
AM; and the higher frequencies used for FM (VHF) complicate overall transmitter and receiver design.
The circuitry in this lab operates on a carrier frequency of 100 kHz, which is in the VLF band. At such
a low carrier frequency, the frequency deviation needs to be limited so that the available bandwidth is
not used up. FM systems with limited deviation are very commonly used where the highest fidelity is
not needed. Voice-only communication systems in the amateur, business, and government radio
services are typical "narrowband" FM applications. Most narrowband FM communications occurs in the
VHF and UHF bands, where the reduced bandwidth requirement allows more stations to share the
available range of radio frequencies.
CIRCUIT ANALYSIS:
This experiment is in two parts, an FM modulator and an FM detector. The circuitry is designed to
operate in the VLF band at a carrier frequency of 100 kHz. The voltage-controlled-oscillator (VCO)
section of an LM565 PLL is used to create the FM waveform, and a second LM565 phase-locked-loop
(PLL) operates as the FM detector.
FM Modulator
Figure 1 illustrates the FM modulator circuit. It's based on the LM565 phase-locked loop (PLL). Only
the VCO section of the IC is used.
Lab 7: Frequency Modulation - Rev B:10032002
© 2002 Tom A. Wheeler
7-1
Vcc (+15 V)
2
R3
10K
3
7
R4
4.7K
+
AF Input
R6
VCON
REF
VOUT
TCAP
VCC-
C2
0.001 uF
VCC+
IN
1
R5
10K
9
IN
TRES
U1
8
R1
2.2 K
R2
4.7K
VIN
10
C1
0.1 uF
6
4
5
FM Output (Square Wave)
LM565
C3
10 uF
1K
C4
0.01 uF
Figure 1: FM Modulator Employing the LM565
The frequency produced by the LM565 VCO is expressed by the following equation:
(1)
f =
2.4(Vcc − Vc )
RtCtVcc
Where: Rt = The timing resistance on pin 8,
Ct = The timing capacitance on pin 9,
Vcc = The power supply voltage,
Vc = The control voltage on pin 7.
The intelligence enters the circuit through C3, a DC block, and is superimposed on the control voltage.
This causes the DC control voltage at pin 7 of the VCO to rise and fall with the intelligence signal.
Lab 7: Frequency Modulation - Rev B:10032002
© 2002 Tom A. Wheeler
7-2
AC
Information
Signal
Vaverage
t
LM565
Pin 7
Voltage
Notice that the audio signal is now riding on top of a DC level. Potentiometer R3 sets this DC level,
which controls the carrier center frequency. As the DC voltage rises, the VCO frequency decreases
in direct proportion to the amount of rise. The voltage "rise" is actually the same thing as the
amplitude of the information. Thus, positive information causes negative carrier frequency change or
deviation. The opposite effect happens on the negative peak of the intelligence; when the control
voltage falls, the VCO frequency increases. In other words, frequency modulation occurs.
Considerable amounts of RF signal from the VCO may “leak” out of pin 7 of the LM565. Components
R6 and C4 form a low-pass filter to prevent this RF energy from passing back to the audio input.
Modulator Sensitivity
The amount of frequency deviation produced in the VCO is directly proportional to the amplitude of the
information signal. The amount of deviation can be predicted by using the following equation:
(2) δ = VmK 0
Where: K0 is the modulator sensitivity, in Hz/Volt.
Vm = the peak information signal amplitude.
δ = the deviation or peak frequency swing.
For example, if Vm=1/2 volt peak, and K0 = 50 kHz / Volt, then the amount of deviation produced will
be:
δ = VmK 0 = (0.5V )(50 KHz / V ) = 25KHz
This would probably be too much deviation, since the carrier frequency is only 100 kHz! Therefore, the
deviation in the experiment will be limited to 10 kHz.
Lab 7: Frequency Modulation - Rev B:10032002
© 2002 Tom A. Wheeler
7-3
Finding the Modulator Sensitivity
The constant of the modulator in the experiment can be easily derived by differentiating equation (1)
with respect to Vc (recall that the control voltage Vc is the sum of the information signal, Vm(t) and
the average DC control voltage):
(3) K 0 =
dF
− 2.4
(Hz/V)
=
dVc RtCtVcc
This derivative is negative, indicating that positive intelligence voltage decreases the oscillator
frequency.
FM Detector:
Figure 2 shows the FM detector. It's based on the NE565 phase-locked-loop. The loop is set to free-run
at 100 kHz by C104 and the series combination of R107 and R106. Pot R106 allows adjustment of the
free-running frequency, which should be the same as the carrier or center frequency of the FM
transmitter.
R103
R102
R101
+15 V
4.7K
4.7K
C102
0.1 uF
R104
10K
10 Ohms
R106
10K
C101
0.1 uF
VCO Free Run
Adjustment
R105
10K
R107
1K
10
3
4
C103
FM INPUT
0.1 uF
5
8
V+
IN 1
R T
U101
IN 2
LM565
VCO OUT
CTRL
VLTG
7
C105
47 pF
PD VCO IN
V1
R109
R110
10K
10K
C110
+
2
AF OUT
10 uF
R108
47K
C T
9
C104
470 pF
C106
47 pF
C107
150 pF
C108
.0022
C109
.001 uF
Figure 2: FM Detector using the LM565 PLL
The FM signal is coupled into the number 1 reference input of the phase detector (pin 2) through C103.
Since the PLL is operating from a single supply, resistors R102 and R103 are used as a voltage divider
to split the power supply in half. Approximately 7.5 volts appears at the junction of R102 and R103
when the circuit is working properly. C102 is an RF bypass for the bias point, and R104 and R105 serve
to isolate the two phase detector inputs (since signal should only be introduced into one input at a
time.)
Lab 7: Frequency Modulation - Rev B:10032002
© 2002 Tom A. Wheeler
7-4
The VCO control voltage of the loop on pin 7 of the 565 contains two componenents. One is a DC level
corresponding to the "average" frequency going into the PLL from the FM modulator, and the other is
an AC level that is actually the detected information signal. This AC signal arises because of the PLL's
self-correcting action; as the transmitter deviates up or down in frequency, the PLL attempts to force
the VCO to follow this frequency exactly by varying its control voltage. Thus, the control voltage is a
copy of the original information signal.
Components C106, C107, and R108 form the loop filter, which sets up the loop operating parameters
(capture range, damping ratio, natural frequency) appropriately for demodulation of an FM signal.
The signal at pin 7 of the 565 contains some carrier frequency in addition to the AC and DC levels just
discussed; components R109, C108, R110, and C109 form a low-pass filter to remove any traces of
100 kHz carrier signal. The final output is AC coupled by C110, leaving only demodulated information
at the output.
Lab 7: Frequency Modulation - Rev B:10032002
© 2002 Tom A. Wheeler
7-5
LABORATORY PROCEDURE:
In this experiment you'll have two circuits to build. It is suggested that they be built on separate
breadboards, if possible.
Important: You must use proper RF grounding techniques for this experiment to work properly.
Use only one bus for ground, and keep all wires and leads as short as possible.
1. Build the circuit of Figure 1. Don't connect anything to the AF INPUT yet.
2. Connect a frequency counter and scope to the FM OUTPUT of the circuit, and adjust R3 until a 100
kHz carrier wave is obtained. The waveshape from the VCO circuit will be a square wave.
3. Calculate K0, the modulator sensitivity, by using equation (3).
4. Now connect a signal generator to the AF INPUT. Adjust it for 5 kHz frequency, and correct peak
voltage for 10 kHz deviation. (Use the result from step 3).
5. Connect scope channel 1 to the AF INPUT, and scope channel 2 to the FM OUTPUT. Trigger off
scope channel 1. Adjust the controls appropriately. Record the oscilloscope graph: FM Output vs AF
INPUT. Can you see the frequency deviation taking place? Why or why not?
6. Using the Agilent 54622D’s spectrum analyzer feature, look at the spectrum being displayed on
channel 1. Record this spectrum. Calculate the theoretical spectrum and compare the results.
TIP: To get the best picture of the FM signal on the ‘54622D, the following settings are
suggested:
Timebase: 100 µS/div (or 2 MSample/s)
Span: 100 kHz
Center Frequency: 100 kHz
Window: HANNING
You’ll also find it very helpful to take a spectral picture in the unmodulated condition in order
to measure Vc(unmodulated). You’ll need this value to calculate the theoretical spectrum.
7. Build the circuit of Figure 2. Keep component lead lengths as short as possible.
8. Apply power to the demodulator circuit, but don't connect its FM INPUT to anything yet. First,
adjust R106 so that the free-running VCO output on pin 4 of the NE565 PLL is 100 kHz. Use a
frequency counter for this measurement (the frequency counter function of the digital scope is
sufficiently accurate for this adjustment.)
Lab 7: Frequency Modulation - Rev B:10032002
© 2002 Tom A. Wheeler
7-6
9. Now connect the transmitter and receiver circuits together. Don't forget to hook together the
grounds! Connect the scope probes as follows: Channel 1 to the AF INPUT of the FM modulator,
and Channel 2 to the AF OUT of the FM detector. Record the oscilloscope graph: Detected FM
Output vs AF Input.
Note: Make sure the amplitude and frequency of the function generator are set correctly as in step 4.
10. How accurate is the reproduction of the information at the detector, when compared to the original
information (scope channel 1)? Use the subtract feature of the oscilloscope to find out. Set up an
oscilloscope trace that is the difference of channels 1 and 2 (use the math menu). You may need to
scale the channels appropriately to get “null” on equal signals. A system that isn’t creating any
distortion will have an input-output difference signal of zero.
11. Increase the deviation at the modulator (by adjusting the amplitude of the signal generator) until
the detected output just begins to become distorted.
How much deviation could this system support? __________________
Lab 7: Frequency Modulation - Rev B:10032002
© 2002 Tom A. Wheeler
7-7
QUESTIONS (ANSWER IN YOUR THEORY OF OPERATION SECTION)
1. What characteristic of the carrier is varied during Frequency Modulation?
______________________________________________________________________
______________________________________________________________________
2. What controls the amount of deviation in an FM transmitter?
______________________________________________________________________
______________________________________________________________________
3. What did R3 adjust? Why was this important?
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
4. What causes the voltage at pin 7 of the FM demodulator (NE565) to follow the original information
signal?
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
Lab 7: Frequency Modulation - Rev B:10032002
© 2002 Tom A. Wheeler
7-8
LM139-N, LM239-N, LM2901-N, LM3302-N, LM339-N
www.ti.com
SNOSBJ3D – NOVEMBER 1999 – REVISED MARCH 2013
LM139/LM239/LM339/LM2901/LM3302 Low Power Low Offset Voltage Quad Comparators
Check for Samples: LM139-N, LM239-N, LM2901-N, LM3302-N, LM339-N
FEATURES
APPLICATIONS
•
•
•
•
•
•
•
•
•
•
1
2
•
•
•
•
•
•
•
Wide Supply Voltage Range
LM139/139A Series 2 to 36 VDCor ±1 to ±18 VDC
LM2901: 2 to 36 VDCor ±1 to ±18 VDC
LM3302: 2 to 28 VDCor ±1 to ±14 VDC
Very Low Supply Current Drain (0.8 mA) —
Independent of Supply Voltage
Low Input Biasing Current: 25 nA
Low Input Offset Current: ±5 nA
Offset Voltage: ±3 mV
Input Common-Mode Voltage Range Includes
GND
Differential Input Voltage Range Equal to the
Power Supply Voltage
Low Output Saturation Voltage: 250 mV at 4
mA
Output Voltage Compatible with TTL, DTL,
ECL, MOS and CMOS Logic Systems
ADVANTAGES
•
•
•
•
•
•
High Precision Comparators
Reduced VOS Drift Over Temperature
Eliminates Need for Dual Supplies
Allows Sensing Near GND
Compatible with all Forms of Logic
Power Drain Suitable for Battery Operation
Limit Comparators
Simple Analog-to-Digital Converters
Pulse, Squarewave and Time Delay Generators
Wide Range VCO; MOS Clock Timers
Multivibrators and High Voltage Digital Logic
Gates
DESCRIPTION
The LM139 series consists of four independent
precision voltage comparators with an offset voltage
specification as low as 2 mV max for all four
comparators. These were designed specifically to
operate from a single power supply over a wide range
of voltages. Operation from split power supplies is
also possible and the low power supply current drain
is independent of the magnitude of the power supply
voltage. These comparators also have a unique
characteristic in that the input common-mode voltage
range includes ground, even though operated from a
single power supply voltage.
The LM139 series was designed to directly interface
with TTL and CMOS. When operated from both plus
and minus power supplies, they will directly interface
with MOS logic— where the low power drain of the
LM339 is a distinct advantage over standard
comparators.
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 1999–2013, Texas Instruments Incorporated
LM139-N, LM239-N, LM2901-N, LM3302-N, LM339-N
SNOSBJ3D – NOVEMBER 1999 – REVISED MARCH 2013
www.ti.com
One-Shot Multivibrator with Input Lock Out
Connection Diagrams
Figure 1. CDIP, SOIC, PDIP Packages – Top View
See Package Numbers J0014A, D0014A, NFF0014A
Figure 2. CLGA Package
See Package Numbers NAD0014B, NAC0014A
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
2
Submit Documentation Feedback
Copyright © 1999–2013, Texas Instruments Incorporated
Product Folder Links: LM139-N LM239-N LM2901-N LM3302-N LM339-N
LM139-N, LM239-N, LM2901-N, LM3302-N, LM339-N
www.ti.com
SNOSBJ3D – NOVEMBER 1999 – REVISED MARCH 2013
Absolute Maximum Ratings (1)
LM139/LM239/LM339
LM139A/LM239A/LM339A
LM3302
LM2901
Supply Voltage, V+
Differential Input Voltage
36 VDC or ±18 VDC
(2)
28 VDC or ±14 VDC
36 VDC
28 VDC
−0.3 VDC to +36 VDC
−0.3 VDC to +28 VDC
50 mA
50 mA
PDIP
1050 mW
1050 mW
Cavity DIP
1190 mW
Input Voltage
Input Current (VIN
INTRODUCTION:
Frequency modulation, or FM, is an important method of impressing information on a carrier. It has
many advantages over AM. First, since FM only changes the frequency, and not the amplitude of the
carrier wave, FM receivers can be built to ignore amplitude (voltage) changes. This is important,
because most external noise is in the form of voltage variations that are "added" to the carrier wave as
it makes its way from transmitter to receiver. An AM receiver directly responds to these with the
familiar sounds of static interference; an FM receiver ignores the amplitude changes, almost
eliminating the effect of the noise.
Second, it is much easier to design systems to reproduce high-fidelity sound using FM. "High-fidelity"
means accurate signal reproduction, with a minimum of distortion. The reproduced information signal
is a very close replica of the original in an FM system. It's difficult to build hi-fi AM receivers, partly
due to the inherent nonlinear distortion created in a conventional AM diode detector, and also partly
due to the limited transmission bandwidth (8 kHz) allotted for AM broadcast.
These advantages do come at a price; that price is increased bandwidth. A typical FM broadcast station
uses up to 75 kHz of signal deviation (the peak frequency change), which results in a typical bandwidth
of 150 to 200 kHz. Because of the high bandwidth requirements, FM broadcasting is done in the VHF
band between 88 and 108 MHz. FM receivers and detectors are slightly more complex than those for
AM; and the higher frequencies used for FM (VHF) complicate overall transmitter and receiver design.
The circuitry in this lab operates on a carrier frequency of 100 kHz, which is in the VLF band. At such
a low carrier frequency, the frequency deviation needs to be limited so that the available bandwidth is
not used up. FM systems with limited deviation are very commonly used where the highest fidelity is
not needed. Voice-only communication systems in the amateur, business, and government radio
services are typical "narrowband" FM applications. Most narrowband FM communications occurs in the
VHF and UHF bands, where the reduced bandwidth requirement allows more stations to share the
available range of radio frequencies.
CIRCUIT ANALYSIS:
This experiment is in two parts, an FM modulator and an FM detector. The circuitry is designed to
operate in the VLF band at a carrier frequency of 100 kHz. The voltage-controlled-oscillator (VCO)
section of an LM565 PLL is used to create the FM waveform, and a second LM565 phase-locked-loop
(PLL) operates as the FM detector.
FM Modulator
Figure 1 illustrates the FM modulator circuit. It's based on the LM565 phase-locked loop (PLL). Only
the VCO section of the IC is used.
Lab 7: Frequency Modulation - Rev B:10032002
© 2002 Tom A. Wheeler
7-1
Vcc (+15 V)
2
R3
10K
3
7
R4
4.7K
+
AF Input
R6
VCON
REF
VOUT
TCAP
VCC-
C2
0.001 uF
VCC+
IN
1
R5
10K
9
IN
TRES
U1
8
R1
2.2 K
R2
4.7K
VIN
10
C1
0.1 uF
6
4
5
FM Output (Square Wave)
LM565
C3
10 uF
1K
C4
0.01 uF
Figure 1: FM Modulator Employing the LM565
The frequency produced by the LM565 VCO is expressed by the following equation:
(1)
f =
2.4(Vcc − Vc )
RtCtVcc
Where: Rt = The timing resistance on pin 8,
Ct = The timing capacitance on pin 9,
Vcc = The power supply voltage,
Vc = The control voltage on pin 7.
The intelligence enters the circuit through C3, a DC block, and is superimposed on the control voltage.
This causes the DC control voltage at pin 7 of the VCO to rise and fall with the intelligence signal.
Lab 7: Frequency Modulation - Rev B:10032002
© 2002 Tom A. Wheeler
7-2
AC
Information
Signal
Vaverage
t
LM565
Pin 7
Voltage
Notice that the audio signal is now riding on top of a DC level. Potentiometer R3 sets this DC level,
which controls the carrier center frequency. As the DC voltage rises, the VCO frequency decreases
in direct proportion to the amount of rise. The voltage "rise" is actually the same thing as the
amplitude of the information. Thus, positive information causes negative carrier frequency change or
deviation. The opposite effect happens on the negative peak of the intelligence; when the control
voltage falls, the VCO frequency increases. In other words, frequency modulation occurs.
Considerable amounts of RF signal from the VCO may “leak” out of pin 7 of the LM565. Components
R6 and C4 form a low-pass filter to prevent this RF energy from passing back to the audio input.
Modulator Sensitivity
The amount of frequency deviation produced in the VCO is directly proportional to the amplitude of the
information signal. The amount of deviation can be predicted by using the following equation:
(2) δ = VmK 0
Where: K0 is the modulator sensitivity, in Hz/Volt.
Vm = the peak information signal amplitude.
δ = the deviation or peak frequency swing.
For example, if Vm=1/2 volt peak, and K0 = 50 kHz / Volt, then the amount of deviation produced will
be:
δ = VmK 0 = (0.5V )(50 KHz / V ) = 25KHz
This would probably be too much deviation, since the carrier frequency is only 100 kHz! Therefore, the
deviation in the experiment will be limited to 10 kHz.
Lab 7: Frequency Modulation - Rev B:10032002
© 2002 Tom A. Wheeler
7-3
Finding the Modulator Sensitivity
The constant of the modulator in the experiment can be easily derived by differentiating equation (1)
with respect to Vc (recall that the control voltage Vc is the sum of the information signal, Vm(t) and
the average DC control voltage):
(3) K 0 =
dF
− 2.4
(Hz/V)
=
dVc RtCtVcc
This derivative is negative, indicating that positive intelligence voltage decreases the oscillator
frequency.
FM Detector:
Figure 2 shows the FM detector. It's based on the NE565 phase-locked-loop. The loop is set to free-run
at 100 kHz by C104 and the series combination of R107 and R106. Pot R106 allows adjustment of the
free-running frequency, which should be the same as the carrier or center frequency of the FM
transmitter.
R103
R102
R101
+15 V
4.7K
4.7K
C102
0.1 uF
R104
10K
10 Ohms
R106
10K
C101
0.1 uF
VCO Free Run
Adjustment
R105
10K
R107
1K
10
3
4
C103
FM INPUT
0.1 uF
5
8
V+
IN 1
R T
U101
IN 2
LM565
VCO OUT
CTRL
VLTG
7
C105
47 pF
PD VCO IN
V1
R109
R110
10K
10K
C110
+
2
AF OUT
10 uF
R108
47K
C T
9
C104
470 pF
C106
47 pF
C107
150 pF
C108
.0022
C109
.001 uF
Figure 2: FM Detector using the LM565 PLL
The FM signal is coupled into the number 1 reference input of the phase detector (pin 2) through C103.
Since the PLL is operating from a single supply, resistors R102 and R103 are used as a voltage divider
to split the power supply in half. Approximately 7.5 volts appears at the junction of R102 and R103
when the circuit is working properly. C102 is an RF bypass for the bias point, and R104 and R105 serve
to isolate the two phase detector inputs (since signal should only be introduced into one input at a
time.)
Lab 7: Frequency Modulation - Rev B:10032002
© 2002 Tom A. Wheeler
7-4
The VCO control voltage of the loop on pin 7 of the 565 contains two componenents. One is a DC level
corresponding to the "average" frequency going into the PLL from the FM modulator, and the other is
an AC level that is actually the detected information signal. This AC signal arises because of the PLL's
self-correcting action; as the transmitter deviates up or down in frequency, the PLL attempts to force
the VCO to follow this frequency exactly by varying its control voltage. Thus, the control voltage is a
copy of the original information signal.
Components C106, C107, and R108 form the loop filter, which sets up the loop operating parameters
(capture range, damping ratio, natural frequency) appropriately for demodulation of an FM signal.
The signal at pin 7 of the 565 contains some carrier frequency in addition to the AC and DC levels just
discussed; components R109, C108, R110, and C109 form a low-pass filter to remove any traces of
100 kHz carrier signal. The final output is AC coupled by C110, leaving only demodulated information
at the output.
Lab 7: Frequency Modulation - Rev B:10032002
© 2002 Tom A. Wheeler
7-5
LABORATORY PROCEDURE:
In this experiment you'll have two circuits to build. It is suggested that they be built on separate
breadboards, if possible.
Important: You must use proper RF grounding techniques for this experiment to work properly.
Use only one bus for ground, and keep all wires and leads as short as possible.
1. Build the circuit of Figure 1. Don't connect anything to the AF INPUT yet.
2. Connect a frequency counter and scope to the FM OUTPUT of the circuit, and adjust R3 until a 100
kHz carrier wave is obtained. The waveshape from the VCO circuit will be a square wave.
3. Calculate K0, the modulator sensitivity, by using equation (3).
4. Now connect a signal generator to the AF INPUT. Adjust it for 5 kHz frequency, and correct peak
voltage for 10 kHz deviation. (Use the result from step 3).
5. Connect scope channel 1 to the AF INPUT, and scope channel 2 to the FM OUTPUT. Trigger off
scope channel 1. Adjust the controls appropriately. Record the oscilloscope graph: FM Output vs AF
INPUT. Can you see the frequency deviation taking place? Why or why not?
6. Using the Agilent 54622D’s spectrum analyzer feature, look at the spectrum being displayed on
channel 1. Record this spectrum. Calculate the theoretical spectrum and compare the results.
TIP: To get the best picture of the FM signal on the ‘54622D, the following settings are
suggested:
Timebase: 100 µS/div (or 2 MSample/s)
Span: 100 kHz
Center Frequency: 100 kHz
Window: HANNING
You’ll also find it very helpful to take a spectral picture in the unmodulated condition in order
to measure Vc(unmodulated). You’ll need this value to calculate the theoretical spectrum.
7. Build the circuit of Figure 2. Keep component lead lengths as short as possible.
8. Apply power to the demodulator circuit, but don't connect its FM INPUT to anything yet. First,
adjust R106 so that the free-running VCO output on pin 4 of the NE565 PLL is 100 kHz. Use a
frequency counter for this measurement (the frequency counter function of the digital scope is
sufficiently accurate for this adjustment.)
Lab 7: Frequency Modulation - Rev B:10032002
© 2002 Tom A. Wheeler
7-6
9. Now connect the transmitter and receiver circuits together. Don't forget to hook together the
grounds! Connect the scope probes as follows: Channel 1 to the AF INPUT of the FM modulator,
and Channel 2 to the AF OUT of the FM detector. Record the oscilloscope graph: Detected FM
Output vs AF Input.
Note: Make sure the amplitude and frequency of the function generator are set correctly as in step 4.
10. How accurate is the reproduction of the information at the detector, when compared to the original
information (scope channel 1)? Use the subtract feature of the oscilloscope to find out. Set up an
oscilloscope trace that is the difference of channels 1 and 2 (use the math menu). You may need to
scale the channels appropriately to get “null” on equal signals. A system that isn’t creating any
distortion will have an input-output difference signal of zero.
11. Increase the deviation at the modulator (by adjusting the amplitude of the signal generator) until
the detected output just begins to become distorted.
How much deviation could this system support? __________________
Lab 7: Frequency Modulation - Rev B:10032002
© 2002 Tom A. Wheeler
7-7
QUESTIONS (ANSWER IN YOUR THEORY OF OPERATION SECTION)
1. What characteristic of the carrier is varied during Frequency Modulation?
______________________________________________________________________
______________________________________________________________________
2. What controls the amount of deviation in an FM transmitter?
______________________________________________________________________
______________________________________________________________________
3. What did R3 adjust? Why was this important?
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
4. What causes the voltage at pin 7 of the FM demodulator (NE565) to follow the original information
signal?
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
Lab 7: Frequency Modulation - Rev B:10032002
© 2002 Tom A. Wheeler
7-8
LM139-N, LM239-N, LM2901-N, LM3302-N, LM339-N
www.ti.com
SNOSBJ3D – NOVEMBER 1999 – REVISED MARCH 2013
LM139/LM239/LM339/LM2901/LM3302 Low Power Low Offset Voltage Quad Comparators
Check for Samples: LM139-N, LM239-N, LM2901-N, LM3302-N, LM339-N
FEATURES
APPLICATIONS
•
•
•
•
•
•
•
•
•
•
1
2
•
•
•
•
•
•
•
Wide Supply Voltage Range
LM139/139A Series 2 to 36 VDCor ±1 to ±18 VDC
LM2901: 2 to 36 VDCor ±1 to ±18 VDC
LM3302: 2 to 28 VDCor ±1 to ±14 VDC
Very Low Supply Current Drain (0.8 mA) —
Independent of Supply Voltage
Low Input Biasing Current: 25 nA
Low Input Offset Current: ±5 nA
Offset Voltage: ±3 mV
Input Common-Mode Voltage Range Includes
GND
Differential Input Voltage Range Equal to the
Power Supply Voltage
Low Output Saturation Voltage: 250 mV at 4
mA
Output Voltage Compatible with TTL, DTL,
ECL, MOS and CMOS Logic Systems
ADVANTAGES
•
•
•
•
•
•
High Precision Comparators
Reduced VOS Drift Over Temperature
Eliminates Need for Dual Supplies
Allows Sensing Near GND
Compatible with all Forms of Logic
Power Drain Suitable for Battery Operation
Limit Comparators
Simple Analog-to-Digital Converters
Pulse, Squarewave and Time Delay Generators
Wide Range VCO; MOS Clock Timers
Multivibrators and High Voltage Digital Logic
Gates
DESCRIPTION
The LM139 series consists of four independent
precision voltage comparators with an offset voltage
specification as low as 2 mV max for all four
comparators. These were designed specifically to
operate from a single power supply over a wide range
of voltages. Operation from split power supplies is
also possible and the low power supply current drain
is independent of the magnitude of the power supply
voltage. These comparators also have a unique
characteristic in that the input common-mode voltage
range includes ground, even though operated from a
single power supply voltage.
The LM139 series was designed to directly interface
with TTL and CMOS. When operated from both plus
and minus power supplies, they will directly interface
with MOS logic— where the low power drain of the
LM339 is a distinct advantage over standard
comparators.
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 1999–2013, Texas Instruments Incorporated
LM139-N, LM239-N, LM2901-N, LM3302-N, LM339-N
SNOSBJ3D – NOVEMBER 1999 – REVISED MARCH 2013
www.ti.com
One-Shot Multivibrator with Input Lock Out
Connection Diagrams
Figure 1. CDIP, SOIC, PDIP Packages – Top View
See Package Numbers J0014A, D0014A, NFF0014A
Figure 2. CLGA Package
See Package Numbers NAD0014B, NAC0014A
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
2
Submit Documentation Feedback
Copyright © 1999–2013, Texas Instruments Incorporated
Product Folder Links: LM139-N LM239-N LM2901-N LM3302-N LM339-N
LM139-N, LM239-N, LM2901-N, LM3302-N, LM339-N
www.ti.com
SNOSBJ3D – NOVEMBER 1999 – REVISED MARCH 2013
Absolute Maximum Ratings (1)
LM139/LM239/LM339
LM139A/LM239A/LM339A
LM3302
LM2901
Supply Voltage, V+
Differential Input Voltage
36 VDC or ±18 VDC
(2)
28 VDC or ±14 VDC
36 VDC
28 VDC
−0.3 VDC to +36 VDC
−0.3 VDC to +28 VDC
50 mA
50 mA
PDIP
1050 mW
1050 mW
Cavity DIP
1190 mW
Input Voltage
Input Current (VIN