Communication Systems, 5e

Transcription

1 Communiation Systems, 5e Chapter 7: Analog Communiation Systems A. Brue Carlson Paul B. Crilly 010 The Mraw-Hill Companies

2 Chapter 7: Analog Communiation Systems Reeiver blok diagram design Image requeny bands that may ause spurious responses (more ilter requirements) Signal Multiplexing Frequeny division (FDM) and Time division (TDM) Phase-Lok Loops (PLL) 010 The Mraw-Hill Companies

3 Objetives Reeiver blok diagram design Image requeny bands that may ause spurious responses (more ilter requirements) Signal Multiplexing Frequeny division (FDM) and Time division (TDM) Phase-Lok Loops (PLL) 3

4 Tuned RF Reeiver (TRF) RF ampliier + demodulator All gain is aomplished with RF ampliier For the produt detetor TRF, seletivity and station seletion is aomplished via a tuned RF ampliier Crystal radio is lassi TRF Diret to digital implementation, otherwise not typial Antenna Put ADC here x () t Tunable BPF RF Amp Demod Amp x() t 010 The Mraw-Hill Companies

5 Superheterodyne Reeiver (Superhet) Copyright The Mraw-Hill Companies, In. Permission required or reprodution or display. Figure RF: Radio Frequeny : Intermediate Frequeny 5

6 Superheterodyne Input bandpass signal at heterodyned (or beat ) down to an intermediate requeny beore detetion. Tuning done via hanging the loal osillator Adjaent hannels are rejeted via a seletive BPF in the stage The stage additional stage o gain the RF ampliier is not required to supply all the gain better stability 010 The Mraw-Hill Companies

7 Superhet reeiver waveorms Copyright The Mraw-Hill Companies, In. Permission required or reprodution or display. Figure 7.1- Image RF Filter Pass entire tuning band Filter Deine signal bandwidth 7

8 Why the Superhetrodyne vs the Tuned RF Easier to design a seletive BPF with ixed requeny or adjaent hannel rejetion versus a tunable ilter Speial ilters or bandwidths! Examples: SAW, rystal ilters stages o gain versus 1 stage o gain inherently more stable (i.e. it is diiulty to design a high gain, stable RF amp) 010 The Mraw-Hill Companies

9 Superhet Reeiver Intermediate Frequeny Typially at a known ixed requeny, Usually where a bandpass ilter sets the predemodulation signal bandwidth Common requenies ( ) Television reeivers: 30 MHz to 900 MHz FM radio reeivers: 5.5 MHz, 10.7 MHz, 98 MHz. In double onversion superheterodyne reeivers, oten a irst intermediate requeny o 1.6 MHz is used ollowed by a seond intermediate requeny o 470 khz. AM radio reeivers: 455 khz, 460 khz, 465 khz, 470 khz, 475 khz, 480 khz Satellite uplink downlink equipment 70 MHz, Downink irst Terrestrial mirowave equipment 50 MHz, 70 MHz Radar 30 MHz RF Test Equipment MHz, 160 MHz, 1.4 MHz 9

10 High and Low Side s Low Side Loal Osillator ( < RF) image image image High Side Loal Osillator (>RF) image image image 10

11 Image Bands Mixed to The image bands will mix to the bands with one exeption, omplex mixing/proessing Image bands should be iltered out prior to mixing Bandpass iltering For a square wave mixing, multiple images bands exist and must be iltered t os t os3 t os t 11

12 AM and FM Radio Parameters AM FM Carrier Frequeny khz MHz Carrier Spaing 10 khz 00 khz Intermediate Frequeny 455 khz 10.7 MHz Bandwidth 6-10 khz khz Audio Bandwidth 3-5 khz 15 khz High Side khz MHz Tuning Ratio.06:1 1.0:1 Low Side khz MHz Tuning Ratio 13.47:1 1.6:1 C C RF tuning High Side C Low Side C Image Spetrum ' C ' C C ' C ' C C 1

13 Nonlinear Mixing Produts nd and 3 rd harmonis may be generated and appear in the or baseband strips o a reeiver The ollowing images may also our Harmoni Produts C11 C1 C13 C14 C15 C16 C17 C18 C C1 C C3 C4 C5 C6 C7 C8 C

14 @ 500 khz F/RF Band: Low Side mixing Example 7.1-1a 4.0 to 4.5 MHz 3.5 to 4.0 MHz 3 rd harmoni present in (mixer more likely) (@ 10.5 to 1 MHz) Draw Piture! They help. 1 st Image Band: 3.0 to 3.5 MHz 3 rd Image Band Low: 10.0 to 11.5 MHz 3 rd Image Band High: 11 to 1.5 MHz 14

15 Example 500 khz F/RF Band: 4.0 to 4.5 MHz High Side Mixing 4.5 to 5.0 MHz 3 rd harmoni present in (mixer more likely) (13.5 to 15 MHz) Draw Piture! They help. 1 st Image Band: 3.5 to 4.0 MHz 3 rd Image Band Low: 13.0 to 14.5 MHz 3 rd Image Band High: 14 to 15.5 MHz 15

16 Diret onversion reeiver Copyright The Mraw-Hill Companies, In. Permission required or reprodution or display. Figure y x i t A os t A os i t A os t A os t os t y 1 A A 1 t os t os i os 1 t t os 1 t t y LPF A A i 1 t os t os t 16

17 Diret onversion reeiver with opposite sideband rejetion Copyright The Mraw-Hill Companies, In. Permission required or reprodution or display. Figure Canellation o lower sideband requenies! Equivalent to Complex Mixing and iltering 17

18 Image Rejetion Diret Conversion y y sin os x i t A os t A os i t A os 1t A os t sin t i t A t A os t os t y 1 y os 1 y t sin t sin t A A A A i sin LPF 1 A A i sin LPF 90 1 t os t os t i oslpf 1 t os t os t t y sum t A os t 1 y di i t A os t 18

19 Double onversion reeiver Copyright The Mraw-Hill Companies, In. Permission required or reprodution or display. Figure Dual Conversion Superhet, typially using a high side s 19

20 RFID Reeiver Downonversion ISM Band Downonversion (90-98 MHz) Only mixing and ilters shown High-side Los Synthesizer provides enter requeny seletion ilter sets bandwidth LPF or ADC anti-aliasing Convert to s/4 or post- ADC omplex proessing Fs > 4 x max 0

21 Casaded ain Multiple the gain (loss) o eah stage together I gain in db, add the gains (in db) and subtrat the losses (in db) db db db db db db predemod RF 1stMixer 1 ndmixer I the mixers have loss instead o gain (passive mixers) db db L db db L db db predemod RF 1stMixer 1 ndmixer 1

22 Noise Figure The noise igure is a measure o the additional noise that is added by any iruit element. Eetive additional input noise xt y t F SNR SNR in out P Sin P Sin N N in in N amp F SNR SNR in in amp 1 out N N N in N N amp in

23 Casaded Noise Figure The noise igure is a measure o the additional noise that is added by any iruit element. Eetive additional input noise xt yt F SNR SNR in out 1 P Sin P Sin 1 N N in in N amp1 N amp SNR N in amp in in Namp N amp 1 F SNR out 1 N in N N N amp in N F 1 N N amp1 1 amp 1 F 1 1 F1 1 F 1 F1 in 1 Nin 1 1 N 3

24 Basi Reeiver x t Bandpass Filter Ampliier Bandpass Filter Lowpass Filter x PreD t Demod x M t Pr ed Tuning os 1 t RF Filter removes images Low Noise Ampliier Mixer to BPF sets the system BW Mixer to baseband Baseband LPF to remove mixing produts db db db db db db db RF BPF LNA 1stMixer BPF ndmixer os t LPF F Pr ed F RF BPF RF BPF F F RF BPF ndmixer Amp 1stMixer 1 1 1stMixer Amp BPF F 1stMixer RF BPF 1 RF BPF Amp Amp F RF BPF LPF 1 1stMixer F BPF Amp BPF 1 1stMixer ndmixer 4

25 Thermal Noise Power Modeled as additive white aussian noise (AWN) N T B Where N is the noise power κ is Boltzmann s onstant T is absolute temperature in degrees Kelvin B is the bandwidth in Hertz 8.6 dbw / K Hz T 0 90K IEEE re N 0 0 T 1.38e e 1 N 0 04 dbw / Hz 174 dbm / Hz 5

26 Reeiver Operating Charateristis Sensitivity minimum input value Dynami Range usable signal range Seletivity ilter out adjaent noise and intererene Adjaent Channel Intererene (ACI) Rejetion Building a perormane diagram or a sotware radio Antenna to the Input o the ADC 6

27 FM Radio Design Diagram FM reeiver 00 khz BW 1-bit ADC with 10-bit perormane Multiple signal environment SOI detetion threshold 7

28 Sanning spetrum analyzer Copyright The Mraw-Hill Companies, In. Permission required or reprodution or display. a) blok diagram (b) amplitude response Figure

29 Spetrum Analyzer Considerations Resolution Bandwidth The bandwidth o the signal power measurement Adjustable with orresponding noise power hange Filter setting Video Bandwidth The ilter prior to displaying the san Baseband ilter setting Sweep time must support the ilters! Move slow enough or the ilter time onstant Most automatially set the RB, VB and sweep time 9

30 Multiplexing Combining multiple signals into a wider bandwidth system or transmission Typially multiplex in time or requeny TDM time division multiplexing FDM requeny division multiplexing For time multiplexing, PAM sampling, bandwidth based on PAM pulse periods For requeny multiplexing, bandwidth is the sum o all the multiplexed elements plus their guard bands 30

31 Frequeny-Division Multiplexing (FDM) Stallings, Wireless Communiations & Networks, Seond Edition, 005 Pearson Eduation, In. ISBN:

32 Time-Division Multiplexing (TDM) Stallings, Wireless Communiations & Networks, Seond Edition, 005 Pearson Eduation, In. ISBN:

33 FDM transmitter Copyright The Mraw-Hill Companies, In. Permission required or reprodution or display. Figure 7.-1 uard Bands: allow or ilter transition bands Transmitter Reeiver 33

34 FDM reeiver Copyright The Mraw-Hill Companies, In. Permission required or reprodution or display. uard Bands: allow or reeiver ilter transition bands Cross Talk: unwanted energy rom adjaent FDM hannels Figure 7.- Post-De-FDM Baseband Bandwidths: Signal Passband + both guard bands 34

35 FDMA satellite repeater system Copyright The Mraw-Hill Companies, In. Permission required or reprodution or display. Figure 7.-3 Nominally 36 MHz BW Links 336 to 900 Voie Channels or 4 groups 1.5 MHz/group 35