1. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Analog Modulation (Bilingual Teaching )

2. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Chapter 5 Analog Modulation INTRODUCTION TO MODULATION INTRODUCTION TO MODULATION INTRODUCTION TO MODULATION INTRODUCTION TO MODULATION 5.1 AMPLITUDE MODULATlON 5.1 AMPLITUDE MODULATlON 5.1 AMPLITUDE MODULATlON 5.1 AMPLITUDE MODULATlON 5.2 NOISE IN AM SYSYEMS 5.2 NOISE IN AM SYSYEMS 5.3 ANGLE MODULATlON 5.3 ANGLE MODULATlON 5.4 NOISE IN FM RECIVERS 5.4 NOISE IN FM RECIVERS 5.5 MULTIPLEXING 5.5 MULTIPLEXING 5.6 FM-RADIO AND TV BOADCASTING 5.6 FM-RADIO AND TV BOADCASTING

3. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY THE KEY OF THIS CHAPTER Conventional Characteristic of the Conventional, Double-Sideband Suppressed-Carrier Double-Sideband Suppressed-Carrier, Single-SidebandVestigial-Sideband Single-Sideband and Vestigial-Sideband Amplitude modulation Noise performance of different AM systems

4. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY THE KEY OF THIS CHAPTER FMPM The relationship between FM and PM Implementation of ANGLE modulators and demodulators Noise in FM receivers

5. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY INTRODUCTION TO MODULATION Why Modulation is Used? Using carrier to shape and shift the frequency spectrum enable modulation by which several advantages are obtained: different radio bands can be used for communications wireless communications (smaller antennas ) multiplexing techniques become applicable

6. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Radio Spectrum

7. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY United States Frequency Allocation

8. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY INTRODUCTION TO MODULATION message signal message signal: The analog signal to be transmitted is denote by m(t): A lowpass signal of bandwidth W, The power content of this signal is: carrier signal: m(t) is transmitted through the channel by impressing it on a carrier signal:

9. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY AMPLITUDE MODULATlON Several different ways of amplitude modulating the carrier signal by m(t) : (a) conventional double-sideband AM, (b) double sideband suppressed-carrier AM, (c) single-sideband AM, (d) vestigial-sideband AM. spectral characteristics each way results in different spectral characteristics for the transmitted signal.

10. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Conventional Amplitude Modulation AM modulation model A conventional AM signal in the time domain

11. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Conventional Amplitude Modulation m(t) is constrained to satisfy : overmodulated If the AM signal is overmodulated Spectrum of the AM Signal Spectrum of the AM Signal F +F+F

12. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Conventional Amplitude Modulation

13. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Conventional Amplitude Modulation

14. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Example 5.1.1 Modulating signal m(t) is a sinusoid : Determine the AM signal, its upper and lower sidebands, and its spectrum. Solution ： the AM signal is expressed as modulation index: modulation index:

15. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY so that lower sideband The lower sideband component is: The upper sideband component is :

16. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY The spectrum of the AM signal The power of carrier component is A c 2 / 2 The power of two sideband is A c 2 β/ 4

17. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY The power content of the AM signal is : Conventional Amplitude Modulation

18. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Conventional Amplitude Modulation Since the envelope is slowly varying, the positive and the negative halves of each cycle have almost the same amplitude. integral of is almost zero.

19. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Conventional Amplitude Modulation Note that DSB-SC systems Note that the second component is much smaller than the first component ( ). This shows that the conventional AM systems are far less power efficient than the DSB-SC systems described in next subsection. So So

20. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Conventional Amplitude Modulation Demodulation of Conventional AM Signals rectify the received signal lowpass filter envelope detector output of the envelope detector DC component gain factor gain factor due to the signal demodulator

21. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Double-Sideband Suppressed-Carrier AM DSB-SC AM signal is obtained by

22. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Double-Sideband Suppressed-Carrier AM An example of message, carrier,and DSB-SC modulated signals.

23. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Double-Sideband Suppressed-Carrier AM Spectrum of the DSB-SC AM Signal. The bandwidth 2W The bandwidth occupancy of the amplitude-modulated signal is 2W the channel bandwidth required B c =2W. And it does not contain a carrier component u(t) For this reason, u(t) is called a suppressed-carrier signal.

24. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Double-Sideband Suppressed-Carrier AM

25. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Double-Sideband Suppressed-Carrier AM Power Content of DSB-SC Signals. P m m(t ) P m indicates the power in the message signal m(t )

26. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Double-Sideband Suppressed-Carrier AM Example 5.1.2 The modulating signal DSB-SC signalupperlower DSB-SC signal and its upper and lower sidebands Solution : in the time domain

27. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Taking the Fourier transform The lower sideband of u(t)The upper sideband of u(t)

28. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Spectrum of u(t) lower sideband upper sideband

29. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Demodulation of DSB-SC AM Signals. (X) Modulator v(t) Modulated signal u(t ) A c cos( 2  f c t +  ) Local oscillator LPF (low pass filter) v o (t) suppose the received signal : multiplying r(t) by a locally generated sinusoid: Double-Sideband Suppressed-Carrier AM

30. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Double-Sideband Suppressed-Carrier AM W: Then, we pass the product signal through an ideal lowpass filter with the bandwidth W: Then: Note that m(t) is multiplied by:

31. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Single-Sideband AM DSB-SC B c =2WW A DSB-SC AM signal required a channel bandwidth of B c =2W for transmission, where W is the bandwidth of the message signal. We reduce the bandwidth of the transmitted signal to that of the baseband message signal m(t). the Hilbert transform of m(t) lower sideband upper sideband

32. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Hilbert transform linear filter Hilbert transform may be viewed as a linear filter with impulse response frequency response and frequency response With phase shift 

33. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Single-Sideband AM Generation of a lower single-sideband AM signal Generation of a single- sideband AM signal by filtering one of the sidebands of a DSB- SCAM signal.

34. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Example 5.1.4 the modulating signal is a sinusoid Determine the two possible SSB-AM signals. Solution : The Hilbert transform of m(t) is : Hence, (-) sign USSB signal (+) sign LSSB signal

35. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Single-Sideband AM Demodulation of SSB-AM Signals for the USSB signal : for the USSB signal : passing the signal through an ideal lowpass filter

36. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Vestigial-Sideband AM stringent Sideband filter in an SSB-AM system is stringent Can be relaxed by allowing vestige, which is a portion of the unwanted sideband

37. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Vestigial-Sideband AM A DSB-SC AM signal passing through a sideband filter with the frequency response H(f)

38. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Vestigial-Sideband AM Demodulation of the VSB signal Demodulation of the VSB signal

39. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Vestigial-Sideband AM The lowpass filter frequency range The lowpass filter frequency range VSB-filter characteristic must satisfy : VSB-filter characteristic must satisfy :

40. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Vestigial-Sideband AM

41. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Implementation of AM Modulators and demodulatiors Block diagram of power-law AM modulator Power-Law Modulation generate a product of the m(t) with the carrier

42. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Switching Modulator. passing v o (t) through a bandpass filter with the center frequency f = f c and the bandwidth 2W passing v o (t) through a bandpass filter with the center frequency f = f c and the bandwidth 2W

43. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Balanced Modulator. Balanced Modulator. modulators approximately identical characteristics Care must be taken to select modulators with approximately identical characteristics so that the carrier component cancels out at the summing junction.

44. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Ring Modulator. Ring Modulator. The switching of the diodes is controlled by a square wave of frequency f c,

45. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Demodulation of AM signals Envelope Detector. simple lowpass filter

46. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Demodulation of DSB-SC AM Signals Requires a synchronous demodulator Requires a synchronous demodulator Note that m(t) is multiplied by:

47. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Demodulation of SSB and VSB Signals SSB signal: insert a small carrier component that is transmitted along with the message VSB signal: carrier component that is transmitted along with the message

48. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY  Channel model  Channel model Additive white Gaussian noise (AWGN) communication channel.  Receiver model  Receiver model Ideal band-pass filter followed by an ideal demodulator NOISE IN AM SYSYEMS Channel and Receiver model

49. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY NOISE IN AM SYSYEMS Signal-to-noise ratios power spectral densityw(t) n 0 the front end of the receiver  Let the power spectral density of the noise w(t) be denoted by n 0 /2, n 0 is the average noise power per unit bandwidth measured at the front end of the receiver B c  the band-pass filter having a bandwidth equal to the transmission bandwidth B c Conventional Conventional-AM DSB-SC SSB VSB

50. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY Channel and Receiver model n(t)narrowband noise The filtered noise n(t) as a narrowband noise : the in-phase noise component the quadrature noise component x(t) The filtered signal x(t) available for demodulation is defined by

51. Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY NOISE IN AM SYSYEMS n 0 B c Average noise power is equal to n 0 B c (SNR) c s(t) n(t) (SNR) c = the ratio of the average power of the modulated signal s(t) to the average power of the filtered noise n(t).