RF MICROELECTRONICS BEHZAD RAZAVI

1. RF MICROELECTRONICSBEHZAD RAZAVI 지능형 마이크로웨이브 시스템 연구실 박 종 훈

2. Contents • Ch.3 Modulation and Detection • 3.1 General Considerations • 3.2 Analog Modulation • 3.2.1 Amplitude Modulation • 3.2.2 Phase and Frequency Modulation • 3.3 Digital Modulation • 3.3.1 Basic Concepts • 3.3.2 Binary Modulation • 3.3.3 Quadrature Modulation • 3.4 Power Efficiency of Modulation Schemes • 3.4.1 Constant-and Variable-Envelope Signals • 3.4.2 Spectral Regrowth • 3.5 Noncoherent Detection

3. 3.1 General Considerations • The transmitted waveform in RF communications is usually a high-frequency carrier modulated by the original signal • Reason of modulations • Wired systems - Superior shielding(coaxial lines) • Wireless systems – antenna size(for resonable gain) • Must occur in a certain part of the spectrum • FCC regulations • Allows simpler detection at the receive end

4. 3.1 General Considerations • Base band / Pass band signals • Base band – Nonzero in the vicinity of ω = 0 • E.g. signal generated by a microphone or a video camera • Pass band – Nonzero in a band around a carrier frequency ωc

5. 3.1 General Considerations • Modulation • Converts a baseband signal to a passband counterpart • Pass band signal – • a(t), θ(t) – functions of time • Carrier signal – • Vary its amplitude or phase • ωct + θ(t) – total phase • θ(t) - excess phase • ωct + dθ/dt - total frequency • dθ/dt – excess frequency (frequency deviation)

6. 3.1 General Considerations • Demodulation(Detection) • Inverse of modulation • Extract the original baseband signal with minimum noise, distortion, ISI, etc.

7. 3.1 General Considerations • Important Aspects of Modems • Quality(e.g. SNR) • Attenuation and interference in the channel • Noise at input of the detector • If the modem achieves higher tolerance of noise • Power reduced • providing longer talk time in portable device • Allowing communication over a longer distance • Bandwidth • Spectral efficiency • Power efficiency • Linear amplifier / Nonlinear amplifier

8. 3.1 General Considerations • AWGN(Additive White Gaussian Noise) Channel • Power spectral density = N0/2

9. 3.2 Analog Modulation • 3.2.1 Amplitude Modulation • 3.2.2 Phase and Frequency Modulation

10. 3.2.1 Amplitude Modulation • Modulation • mxBB(t) : baseband signal • m : modulation index

11. 3.2.1 Amplitude Modulation • Demodulation(Envelope detector) • SNR

12. 3.2.1 Amplitude Modulation • Limited use in today’s wireless systems • Except for broadcast radios and the sound in television • Susceptible to noise • Highly linear power amplifier in the transmitter • High SNR at the input

13. 3.2.2 Phase and Frequency Modulation

14. 3.2.2 Phase and Frequency Modulation • Phase Modulation(PM) • Frequency Modulation(FM) • VCO(Voltage Controlled Oscillator)

15. 3.2.2 Phase and Frequency Modulation • Modulator

16. 3.2.2 Phase and Frequency Modulation • Demodulation • Demodulator

17. 3.2.2 Phase and Frequency Modulation • Narrowband FM

18. 3.2.2 Phase and Frequency Modulation • Narrowband FM -> • ωm increase, magnitude of the sidebands decrease • maximum frequency deviation is mAm • Low SNR • Wideband FM • Without the restriction

19. 3.2.2 Phase and Frequency Modulation • Bessel Function Referance – Introduction to Analog & Digital Communications 2nd

20. 3.2.2 Phase and Frequency Modulation • Wideband FM VS Narrow FM

21. 3.2.2 Phase and Frequency Modulation • Bandwidth(BFM) • Containing 98% of the signal power • BFM ≈2(β+1)BBB – Carson’s rule • Preemphasis and Deemphasis • Larger gain at higher freq. -> Amplifying noise at high freq.

22. 3.2.2 Phase and Frequency Modulation • SNR Comparison • Without Preemphasis and deemphasis • With Preemphasis and deemphasis • f1 : -3dB corner frequency of the low pass filter • Typical applications : 10 to 15dB higher than 1st eqn.

23. 3.3 Digital Modulation • ASK, PSK, FSK • Analog parameters • signal quality, spectral efficiency, and power efficiency • Digital parameter • BER(bit error rate) • Average number of erroneous bits observed at the output of the detector divided by the total number of bits received in a unit time

24. 3.3.1 Basic Concepts • Binary and M-ary Signaling • Binary waveform(Digital baseband signal) • bn : ‘bit’ value in the time interval • Multilevel(M-ary signaling) • Bandwidth relaxed • bn : ‘symbol’ value in the time interval

25. 3.3.1 Basic Concepts • Basic Functions ( e.g. FSK ) • Digitally modulated waveforms

26. 3.3.1 Basic Concepts • Signal Constellations

27. 3.3.1 Basic Concepts • Cartesian minimum distance : Relate to the bit error rate

28. 3.3.1 Basic Concepts • Optimum Detection • Since the baseband signal is digital, the detector output must be sampled every bit period to determine the received value • Problem of Noise

29. 3.3.1 Basic Concepts • Solution • Use of filter • Sampling is synchronized such that the peak value of the pulse is sensed, the output SNR is high

30. 3.3.1 Basic Concepts • Noise components that vary significantly in a period of Tb tendto average out

31. 3.3.1 Basic Concepts • Matched Filter • Pulse p(t) that is corrupted by additive white noise, there exists an optimum filter that maximizes the SNR at the sampling instant

32. 3.3.1 Basic Concepts • Maximum value at t = Tb

33. 3.3.1 Basic Concepts • Ep : energy of the signal • P(t) : voltage quantity • Optimum detection of modulated signals • where x(t) = p(t) + n(t). If p(t) is zero outside the interval [0 Tb], then

34. 3.3.1 Basic Concepts • Coherent and Noncoherent Detection • Detection schemes that require phase synchronization

35. 3.3.1 Basic Concepts • This circuit employs two narrowband filters

36. 3.3.1 Basic Concepts • Definition of Bandwidth • Containing 99% signal power

37. 3.3.2 Binary Modulation • BPSK(Binary PSK) • BFSK(Binary FSK) • ASK is rarely used in RF applications

38. 3.3.2 Binary Modulation • PDF for binary data with additive noise

39. 3.3.2 Binary Modulation • BPSK

40. 3.3.2 Binary Modulation • BFSK

41. 3.3.2 Binary Modulation • BPSK VS BFSK • Bit energy in BFSK must be twice that in BPSK • Minimum distance between the points in the constellation is greater in BPSK • BPSK hasa 3-dB advantage over BFSK

42. 3.3.2 Binary Modulation • Quadrature Modulation • To subdivide a binary data stream into pairs of two bits

43. 3.3.2 Binary Modulation • Categories • QPSK(Quadrature Phase Shift Keying) • Offset QPSK(OQPSK) • π/4-QPSK • MSK(Minimum Shift Keying) • GMSK(Gaussian MSK)

44. 3.3.2 Binary Modulation • QPSK • Important drawback of QPSK islarge phase changes

45. 3.3.2 Binary Modulation • OQPSK

46. 3.3.2 Binary Modulation • Phasestep is only ±90˚ • BER and spectrum of OQPSK are identical to those of QPSK • criticaldrawback • It doew not lend itself to differential encoding • Differential encoding plays an important role in noncoherent receivers, the most popular type in today’s RF applications

47. 3.3.2 Binary Modulation

48. 3.3.2 Binary Modulation • Since no two consecutive points are from the same constellation • Maximum phase step is 135˚, 45˚ less than QPSK • BER are identical to those of QPSK

49. 3.3.2 Binary Modulation • MSK • Continuous phase modulation • Rectangular pulse leading to a wide spectrum and presenting difficulties in the design of power amplifiers

50. 3.3.2 Binary Modulation • The smooth phase transition in MSK lower the signal power in the sidelobes of the spectrum • But at the cost of widening the main lobe • Decay proportional to