Transmitters and Receivers Generalized Transmitter Generalized Receiver The Superheterodyne Receiver Minimum Sampling frequency
Transmitters and Receivers Generalized Transmitter Generalized Receiver The Superheterodyne Receiver Minimum Sampling frequency
Generalized Transmitter Transmitter generate the modulated signal at the frequency fc from the message signal m(t) Any type of modulated signal can be represented by ■ v(t)=Refz(t)e v(t)=V(t)cos(2πft+θt) v(t)=x.(t)cos(2πft)-x,(t)sin(2πft) (h9呢9mp災YPR8 Is function of m(t)
Generalized Transmitter ◼ Transmitter generate the modulated signal at the frequency fc from the message signal m(t) ◼ Any type of modulated signal can be represented by ◼ ◼ where complex envelope ◼ Is function of m(t) 2 ( ) Re{ ( ) } ( ) ( )cos(2 ( )) ( ) ( )cos(2 ) ( )sin(2 ) c j f t c c c s c v t z t e v t V t f t t v t x t f t x t f t = = + = − ( ) ( ) ( ) ( ) ( ) j t c s z t V t e x t jx t = = +
Complex envelope Type of Mapping Corresponding Quadrature modulation modulation z(m(t)) (t) x(t) AM A.[1+m(t] A.1+m(t)] 0 DSB A.m(t) A.m(t) 0 PM Lekmr) A cos(km(t)) 4 sin(km(t)) FM e m A.cos(k,['m(r)dr)Asin(k,fm()dr) SSB A.[m(t)±jm(t)] Am(t)） ±jAm(t)
Complex envelope ( ) ( ) [1 ( )] ( ) [ ( ) ( )] p t f c c jk m t c jk m d c c A m t A m t A e A e A m t jm t − + [1 ( )] ( ) cos( ( )) cos( ( ) ) ( ) c c c p t c f c A m t A m t A k m t A k m d A m t − + 0 0 sin( ( )) sin( ( ) ) ( ) c p t c f c A k m t A k m d jA m t − Type of modulation AM DSB PM FM SSB Mapping z(m(t)) Corresponding Quadrature modulation xc (t) xs (t)
Complex envelope Type of Mapping Corresponding Amplitude and phase modulation modulation z(m(t)) V(t) 0(t) AM A,1+m(t)] A.1+m) 0, m(t)>-1 180°，m(t)0 180°，m(t)<0 PM A.e。mo) A k,m(t) FM A kimr)dr SSB A.[m(t)±jm(t)] AVm2()+m2(0 an'±m m(t)
Complex envelope 2 2 1 ( ) ( ) ( ) ( ) c c c c c A m t A m t A A A m t m t + + 1 0, ( ) 1 180 , ( ) 1 0, ( ) 0 180 , ( ) 0 ( ) ( ) ( ) tan [ ] ( ) p t f m t m t m t m t k m t k m d m t m t − − − − Type of modulation AM DSB PM FM SSB Mapping z(m(t)) Corresponding Amplitude and phase modulation V(t) (t) ( ) ( ) [1 ( )] ( ) [ ( ) ( )] p t f c c jk m t c jk m d c c A m t A m t A e A e A m t jm t − +
Generalized Transmitter ■Two canonical form AM-PM generation technique Quadrature generation technique Choice is up to designer Maximize performance Minimize cost Based upon the available device and circuits
Generalized Transmitter ◼ Two canonical form ◼ AM-PM generation technique ◼ Quadrature generation technique ◼ Choice is up to designer ◼ Maximize performance ◼ Minimize cost ◼ Based upon the available device and circuits
AM-PM generation technique Generalized transmitter using AM-PM generation technique u(t)=V(t)cos(2πft+θt) V() Baseband circuits m(t) V(t),0( from m(t) 0(t) Phase Maybe nonlinear modulator cos(2πft+0(t) Analog or Digital Osc. f=fc
AM-PM generation technique ◼ Generalized transmitter using AM-PM generation technique Baseband circuits V(t), (t) from m(t) Maybe nonlinear Osc. f=fc Phase modulator m(t) V(t) (t) cos(2 ( )) c f t t + ( ) ( )cos(2 ( )) u t V t f t t = + c Analog or Digital
Quadrature generation technique Generalized transmitter using Quadrature generation technique Analog or Digital u(t)=x.(t)cos(2πft)-x,(t)sin(2πft) Baseband circuits (t) m(t) x(t),x (t) from m(t) x(t) Maybe nonlinear sin(2πft) Osc. -90° f=fc cos(2πfCt) Phase shift
Quadrature generation technique ◼ Generalized transmitter using Quadrature generation technique Baseband circuits xc (t), xs (t) from m(t) Maybe nonlinear Osc. f=fc -90 Phase shift m(t) xc (t) xs (t) cos(2 ) c f t ( ) ( )cos(2 ) ( )sin(2 ) u t x t f t x t f t = − c c s c Analog or Digital sin(2 ) c f t
Generalized Receiver Extracting the source information from received modulated signal ■Corrupted by noise Often it is a replica of the message signal Two main classes of receiver TRF(Tuned Radio Frequency) -Not popular because hard to design and implement Superhetrodyne Most receiver uses this technique
Generalized Receiver ◼ Extracting the source information from received modulated signal ◼ Corrupted by noise ◼ Often it is a replica of the message signal ◼ Two main classes of receiver ◼ TRF(Tuned Radio Frequency) ◼ Not popular because hard to design and implement ◼ Superhetrodyne ◼ Most receiver uses this technique
Superhetrodyne Receiver RF signal is down converted to IF(intermediate frequency)band Information is detected from IF signal RF RF amp. f fIF =fc-fLo IF amp. input H1(f) H2() LO,fio Baseband Baseband IF output Detector output amp
Superhetrodyne Receiver ◼ RF signal is down converted to IF(intermediate frequency) band ◼ Information is detected from IF signal RF amp. H1(f) LO, fLO IF amp. H2(f) Detector Baseband amp. RF input Baseband IF output output fc fIF =fc -fLO
Superhetrodyne Receiver ■IQ detector IF signal v(t)=Re[=(t)e2] =xe(t)cos(2πfirt)-x,(t)sin(2πfirt) x.(t) LPF x,() LPF sin(2πfrt) Osc. -90° f-fie cos(2πfiFl) Phase shift
Superhetrodyne Receiver ◼ IQ detector Osc. f=fIF -90 cos(2 ) f t IF Phase shift sin(2 ) IF f t IF signal 2 ( ) Re[ ( ) ] ( ) cos(2 ) ( ) sin(2 ) IF j f t IF c IF s IF v t z t e x t f t x t f t = = − LPF LPF ( ) c x t( ) s x t