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 16 Lead 300 Mil PDIP –40°C to +85°C XR-2206CP 16 Lead 300 Mil PDIP 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 16 Lead PDIP, CDIP (0.300”) 1 16 2 15 3 14 4 13 5 12 6 11 7 10 8 9 SYMA2 SYMA1 WAVEA2 WAVEA1 GND SYNCO BIAS FSKI 16 Lead SOIC (Jedec, 0.300”) 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 Wave Form Adjust Input 1. 14 WAVEA2 I Wave Form Adjust Input 2. 15 SYMA1 I Wave Symetry Adjust 1. 16 SYMA2 I Wave Symetry Adjust 2. 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 Without Adjustment 2.5 With Adjustment 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 Telemetry receivers Signal regeneration Coherent demodulators Connection Diagrams Metal Can Package Dual-in-Line Package DS007853-2 Order Number LM565H See NS Package Number H10C © 1999 National Semiconductor Corporation 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 Lead Temperature (Soldering, 10 sec.) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ 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 V/radian Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit is given, however, the typical value is a good indication of device performance. Note 2: The maximum junction temperature of the LM565 and LM565C is +150˚C. For operation at elevated temperatures, devices in the TO-5 package must be derated based on a thermal resistance of +150˚C/W junction to ambient or +45˚C/W junction to case. Thermal resistance of the dual-in-line package is +85˚C/W. www.national.com 2