Transceiver rchiecures 김영석 충북대학교전자정보대학 010.9.1 Email: kimys@cbu.ac.kr 전자정보대학김영석 3-1
Conens 3. Modulaion and Deecion 3.1 General Consideraions 3. nalog Modulaion M, PM, FM 3.3 Digial Modulaion BPSK, BFSK, QPSK 5. Transceiver rchiecures 5. Rx rchiecures Heerodyne, Homodyne, Image-Rejec, Digial-IF, Subsampling 5.3 Tx rchiecures Direc-Conversion, i To-sep 전자정보대학김영석 3-
3.1 General Consideraions (Modulaion Definiions (a Baseband Signal: One hose specrum is non-zero in he viciniy of =0 and negligible elsehere (b Passband Signal: one hose specrum is non-zero in a band around a carrier frequency c and negligible elsehere x( = a( cos[ c + θ ( ] Modulaion convers a baseband signal o i s passband counerpar, for ease of ransmission (e.g. anenna size Demodulaion exracs he baseband signal Modulaion/Demodulaion Schemes = Modem Imporan specs of Modems Qualiy: SNR, or bi error rae Bandidh: Specral Efficiency Poer Efficiency 전자정보대학김영석 3-3
3. nalog Modulaion: mpliude Mod. For a baseband signal x b (, he ampliude modulaed signal is x M ( = [1 + m x Can be generaed ih a mixer c BB ( ] cos c Passband signal has ice he bandidh of he baseband signal Demodulaion: mix ih carrier and LPF, or use an envelope deecor 전자정보대학김영석 3-4
3.. Phase and Frequency Modulaion Phase and Frequency are relaed by = dφ / d Phase modulaed signal is expressed as (m=phase mod. Index x ( = cos[ mx ( ] PM c c + BB Frequency modulaed d signal is expressed as x FM ( = c cos[ c + m x BB ( d] 전자정보대학김영석 3-5
Modulaion/Demodulaion Frequency Modulaion can be done by varying he freq. of an OSC ih he baseband signal Frequency Demodulaion can be performed by freq. sensiive ck, commonly by a PLL 전자정보대학김영석 3-6
3.3 Digial Modulaion Mos modern ireless sysems use digial modulaion due o is advanages over analog modulaion Qualiy of RF sysems is evaluaed by BER(bi error rae. Modulaion mehods are compared according o heir probabiliy of error (Pe 전자정보대학김영석 3-7
3.3. Basic conceps Basis funcions: any modulaion scheme can be represened by a se of orhogonal basis funcions T Def. orhogonal: φ ( φ ( d = 0 s E.g. FSK(Frequency shif keying x FSK ( = α 1 φ 1 ( + α φ ( here[ α, α ] = [0 ] for a1and [ 1 c basis funcions φ ( = cos, φ ( = cos 1 1 c 0 m k 0] for a 0 Signal consellaions: modulaed aveforms can be vieed in erms of heir coefficiens and basis funcions Each basis funcions conribues one axis o he plo 전자정보대학김영석 3-8
3.3. Basic conceps Opimum deecion: I can be shon ha he opimum deecor is a correlaor, hich can be buil by a muliplier (mixer folloed by an inegraor (p(=pulse shape Inegraion produces an averaging ha reduces he effecs of he noise 전자정보대학김영석 3-9
Digial Modulaion BPSK(Binary Phase Shif Keying x BPSK ( = c cos( c + φ here φ = 0 or 180 x ( = α cos hereα = + c or c BPSK c P e, BPSK = Q( E N 0 b here E b is he average energy per bi and N0 is he poer specral densiy of he addiive i hie Gaussian noise 전자정보대학김영석 3-10
Digial Modulaion BFSK(Binary Frequency Shif Keying x BPSK ( = α1 cos 1 + α cos here [ α α ] = [0 ] or [ 0] 1 c c P e, BPSK = Q( E N b 0 here E b is he average energy per bi and N0 is he poer specral densiy of he addiive i hie Gaussian noise 전자정보대학김영석 3-11
Digial Modulaion Quadraure Modulaion: basis funcions (a QPSK(Quadraure Phase Shif Keying Send bis ih one symbol QPSK here [ α α ] = [ cos and sin x = α cos + α sin c ( 1 c c ], [- c ],[ - ],[- - ] 1 c c c c c c c c P e, BPSK = here E b Q( E N 0 b is he average energy per bi and N 0 is he poer specral densiy of he addiive hie Gaussian noise problem ih QPSK is he sharp ransiions => OQPSK or π/4- QPSK 전자정보대학김영석 3-1
5. Receiver rchiecures Why no perform Channel Selecion and Demodulaion a he RF? Tuneable Filers are harder o realize Very High Q Channel Selec Filer a f c is needed Q=f c /Δf Ex: IS-54, 30kHz, 900MHz, 60dB enuaion a 45kHz offse, nd -order LC filer Q=10 7 (Impossible Donconvering RF o IF before Channel Selecion using a variable VCO => Use a fixed, lo-q filer (lo f c, same Δf 전자정보대학김영석 3-13
Herero=differen, dyne=mix 5..1 Heerodyne Receivers RF o IF(Inermediae Frequency by Donconversion Mixing High Q Filer is no required Inclusion of LN o loer he Noise Figure 전자정보대학김영석 3-14
Problem of Image Signal and Image are donconvered o he same frequency Ho o suppress he Image: Image-Rejec Filer 전자정보대학김영석 3-15
IF Selecion Trade-off beeen Image Rejecion and Channel Selecion High IF: Beer Image Rejecion Lo IF: Beer Channel Selecion Oher facors: vailabiliy, Physical Size of IF filers High or Lo-side Injecion Lo-side: Minimize LO freq High-side: Reduced Tuning Range for he VCO 전자정보대학김영석 3-16
Dual-IF Topology To Lessen he rade-off beeen Image Rejecion and Channel Selecion, a Dual-IF is used 1 s -mixer convers o a relaively high IF o allo Image Rejecion nd -mixer convers o a lo IF o allo Channel Selecion 전자정보대학김영석 3-17
5.. Homodyne Receivers Homodyne, Direc-Conversion, Zero-IF rchiecure Only LPF is required for channel selecion Topology (a : Double-sideband M (Same informaion on boh sides of he specrum Topology (b (Quaraure Donconversion: FM or PM (Differen informaion on he differen sides of he signal 전자정보대학김영석 3-18
dvanages No Image Filer No IF SW filer Single Chip Rx (IC Drabacks DC Offses I/Q Mismach Even-order Disorion Flicker Noise Homodyne Receivers 전자정보대학김영석 3-19
DC Offses DC Offse Volages resul from Self-mixing due o Poor isolaion beeen LO and RF during donconversion Example: Inpu RF = 1μVrms ( => Mix oupu RF = 30μVrms (30dB LO = 0.63V (0dBm => LO leakage = 0.63mV (60dB Isolaion => Mix oupu DC offse = 10mV (30dB gain => Sauraes he gain sages (50-70dB gain 전자정보대학김영석 3-0
Soluions for DC Offses High Pass Filering o remove DC offses Coding is required o remove he informaion a DC Lo Cuoff Frequency => Large C Wases Specrum Perform Periodic Offse Cancellaion Periodically sample he signal and cancel i Works bes for TDM Sysems Mos common soluion 전자정보대학김영석 3-1
I-Q Mismach Mismach in gain and phase beeen I/Q LO signals => gain and phase error in he received signal consellaion Eg. for QPSK signal RF : x ( = a cos( + bsin( i( here a, b = ± 1 I c Q ε θ LO : v LO, I ( = (1 + cos( c + ε θ vlo, Q ( = (1 sin( c ε θ ε θ IF( afer mixing : xbb, I ( = a(1 + cos b(1 + sin ε θ ε θ xbb, Q ( = a(1 sin + b(1 cos c mpliude mismach < 1dB, phase error < 5deg 전자정보대학김영석 3-
Even-Order Disorion Like 3 rd -order disorion (IP3, nd -order Nonlineariy of mp is problemaic in homodyne To High-freq inerferers generae a lo-freq bea in he presence of even-order disorion => Direc feedhrough from RF o IF (lo- freq bea muliplied by cos LO is ranslaed o high freq: no a problem RF : x ( = cos( + cos( 1 LN oupu : y( = α x( + α x 1 1 ( =... + α 1 cos( 1 Differenial circui opologies ill help suppress nd -order disorion 전자정보대학김영석 3-3
Flicker Noise Donconvered (afer only amplified by LN and mixer lo-freq signals are influenced by 1/f of nex sages Despie all of hese difficulies, homodyne receivers become more common Due o high levels of inegraion Sandard in some applicaions (eg. pagers 전자정보대학김영석 3-4
5..3 Image-Rejec Receivers 90deg phase shif = muliply he specrum by G(=-j*sgn( Eg. sin => -cos (90deg phase shif j sin( = e 1 cos( = e j + j j e 1 j e j 전자정보대학김영석 3-5
Harley rchiecure ssume lo-side injecion i( i( ( cos cos ( x im RF im LO LO RF im im RF RF + = + = sin( sin( sin( sin( ( x im LO im LO RF RF im LO im RF LO RF + = + = cos( cos( ( cos( cos( ( x x im LO im RF LO RF B im LO im RF LO RF C + = = (Image componens cancel ou cos( ( ( ( x x x RF LO RF B C IF = + = 전자정보대학김영석 3-6
Harley rchiecure 90 deg phase shif is replaced ih +45 shif in one pah and -45 shif in he oher 전자정보대학김영석 3-7
Harley rchiecure Gain and phase mismach ill lead o incomplee image rejecion Eg. x LO1 ( = LO sin LO, LO P IRR(Image Rejecion Raio = P x im P sig ( = ( LO ( ε / LO + ε cos( 4 + θ LO + θ In mos RF applicaions, IRR=60-70dB is required For ypical maching in IC, gain mismach=0.-0.6db,.6db, phase imbalance=1-5deg, IRR=30-40dB So, Image Rejec Filer mus sill be used 전자정보대학김영석 3-8
Weaver rchiecure To avoid 90 deg phase shif (problemaic, an alernae image rejec archiecure can be used. Secondary Image problem 전자정보대학김영석 3-9
5..4 Digial-IF Receivers fer iniial donconversion, use DC o digiize he signal and perform second mixing and filering in he digial domain dvanages: No I-Q mismach, maximum flexibiliy 전자정보대학김영석 3-30
5..5 Subsampling Receivers Subsample he RF signal a he Nyquis rae (lo LO Filer he resuling oupu, eliminaing he need for a mixer Meris: simplify he design of he LO Demeris: Noise aliasing (Subsampling by a facor m => Increase he noise poer by a facor m 전자정보대학김영석 3-31
5.3 Transmier rchiecures Tx archiecures are generally much less varied, because noise, inerference rejecion, and band seleciviy are more relaxed. 5.3.1 Direc-conversion Transmier LO pulling: P oupu couples o LO, corruping is oupu by pulling i o a differen frequency pulling i o a differen frequency 전자정보대학김영석 3-3
5.3. To-sep Transmiers P frequency (1+ is differen from LO frequency (1 (no LO pulling 전자정보대학김영석 3-33
References Behzad Razavi, RF Microelecronics, Prenice Hall, Inc, 1998 전자정보대학김영석 3-34