Master Degree in Electronic Engineering

Master Degree in Electronic Engineering Analog and telecommunication electronic course (ATLCE-01NWM) Miniproject: Baseband signal transmission techniques Name: LI. XINRUI E-mail: s219989@studenti.polito.it 1 Monday, June 08, 2015

Syllabus Introduction of technique of baseband signal transmission - the definition of baseband signal - typical techniques are applied to transmitted signal - The role of modulation technology in signal transmission theory. Linear- modulation -amplitude modulation (AM) - DSB-SC modulation - SSB-SC modulation - VSB-SC modulation Demodulation - AM demodulation envelope detection coherent demodulation - DSB-SC demodulation - SSB-SC demodulation - VSB-SC demodulation 2 Monday, June 08, 2015

Syllabus Non linear modulation - frequency modulation (FM) direct FM indirect FM - phase modulation (PM) Demodulation - FM demodulation slope discriminator phase discriminator ratio discriminator PLL discriminator - PM demodulation the applications of modulation techniques - BeiDou Navigation Satellite System - AM decoder (NE567) - stereo FM transmitter - LM1596 Balanced Modulator-Demodulator - advanced technology Software Defined Ratio 3 Monday, June 08, 2015

Theme : baseband signal transmission Introduction of technique of baseband signal transmission Recently, there are dramatically evolutions of information techniques, such as cellphone, computer and network etc, along with the development of technology. Particularly, in the electronic and wireless transmission fields, for instance, the speed of network is much higher than before. Even though, the most popular way to transmit baseband signal is based on the digital technique, such as, improving the channel transmission or develop the digital elements, I would like to study the analog signal transmission in the free space according to the analog techniques. The following graph illustrates the basic architecture of baseband transmission between receiver and transmitter. 4 Monday, June 08, 2015

The modulation and demodulation techniques are applied to baseband signal transmission What are not shown in the picture Filter amplifier 5 Monday, June 08, 2015

Definition for baseband signal A signal is baseband if it has a very narrow frequency range, i.e. a spectral magnitude that is nonzero only for frequencies in the vicinity of the origin (termed f = 0) and negligible elsewhere. Compared with RF signal, it has rather low frequency. Baseband signals always represent basic information voice image audio.etc 6 Monday, June 08, 2015

Typical techniques are applied to transmitted signal baseband transmission applied to computer inner parallel buses, most Local Area Network such as, Ethernet and Token Ring Benefits: convenient for short transmission; low attenuation ; high speed transmission low error probability no need of M-DeM cells Drawback: not suitable for long transmission since it has many AC components 7 Monday, June 08, 2015

Typical techniques are applied to transmitted signal Pass-band transmission Passband transmission technique is related to transmitting signal directly inner channels and based on the modulation and demodulation technologies. Benefits: high radiation capability capability for long-distance transmission Drawback: low speed, high error probability 8 Monday, June 08, 2015

Typical techniques are applied to transmitted signal broadband transmission Broadband transmissions are divided into multiple bands or channels by multiplexers using a multiplexing scheme such as frequency-division multiplexing (FDM). Benefits: high bandwidth (>128Kbps typical) high speed Drawback: strict requirements complex structure 9 Monday, June 08, 2015

Linear modulation Amplitude Modulation (AM) Definition: the amplitude of a high frequency sine wave (usually at a radio frequency) is varied in direct proportion to that of a modulating signal AM radio transmitter system 10 Monday, June 08, 2015

Linear modulation Mathematic model m(t) modulating signal A 0 is additional DC component X c (t) = cos (ω c t) called carrier s AM (t) called AM signal or modulated signal Mathematic expression: From the spectrum : Center frequency at ω=±ω C AM bandwidth: 2B m (2f H ) 11 Monday, June 08, 2015

Linear modulation AM parameters: Power p AM No DC component for m(t) <m(t)> t =0 <cos 2 (ω c t)> t =< 1 2 cos 2ω ct + 1 2 > t=1/2 finally, P AM =A 02 /2+ <m 2 (t)> t /2 =P C + P S with carrier power P C and sideband power P S Modulation efficiency ή AM definition: ή AM =Ps/P AM =<m 2 (t)> t /(A 02 +<m 2 (t)> t ) < 1 always! 12 Monday, June 08, 2015

Linear modulation Modulation index m : Modulation index m is defined as the maximum changes of modulated signal marked as ΔV AM (t) max also could be expressed with (V M -V m )/(V M +V m ) m= (V M -V m )/(V M +V m ) or ΔV AM (t) max Interpolation of m: m=1 is called full-modulated; m>1 is called overmodulated. general case : 0<m<1 13 Monday, June 08, 2015

Linear modulation Example of voice signal modulation: Human voice : Frequency range from 300 to 20,000 hertz 14 Monday, June 08, 2015

Linear modulation DSB-SC modulation: Mathematic expression: Notation: m(t)=v m cos(ω m t) called modulating signal V c cos( c t)=x c (t) called carrier 15 Monday, June 08, 2015

Linear modulation DSB-SC modulation: Spectrum analysis: no carrier component amplitude attenuation 1/2 What about DSB-SC in time domain? 16 Monday, June 08, 2015

Linear modulation DSB-SC modulation: In time domain m(t)=0 Parameters analysis: power P DSB =<m 2 (t)> t /2 is the same as AM ME ή DSB =100% improve the modulation efficiency 17 Monday, June 08, 2015

Linear modulation SSB-SC modulation: Basic idea: since both sidebands carry the same information, we can only keep one sideband (upper or lower)component to save resource expression in time domain: How can we create the SSB-SC signal? 1. using a sideband filter, which can be HPF or LPF HPF or LPF can be applied to remove one of the sideband, leaving only either the upper sideband (USB) or the lower sideband (LSB) according to which sideband we want to keep. Assuming both sidebands are symmetric, no information is lost in the process and the effective power output is greater than in normal AM. method model Where H SSB (ω) is the transfer function of sideband filter 18 Monday, June 08, 2015

Linear modulation SSB-SC modulation: Requirements: need a dramatic cut-off characteristic at f cut-off LPF Lower sideband Benefit: rather easy way to create SSB Drawbacks: difficult to make such kinds of filters (very steep filter) HPF upper sideband 19 Monday, June 08, 2015

Linear modulation SSB-SC modulation: How to create SSB-SC signal 2. Phase-shift method Parameter analysis: bandwidth Notation: H h (ω) is the transfer function of Hilbert transform filter, which translates all the components coming from m(t) with phase shift - 90 o Drawbacks: big problem for obtaining such kinds filters with a strict -90 o phase shift. BW SSB = 1 2 BW DSB=B m =f H Power modulation efficiency ή SSB =100% 20 Monday, June 08, 2015

Linear modulation VSB-SC modulation: VSB-SC is called Vestigial Sideband suppression carrier. The idea is designing a kind of filter called VSB filter to filter one sideband and keeps a little part of the other one Requirement: H VSB (ω+ω C )+H VSB (ω-ω C )=constant for ω <=ω H. This is derived from VSB demodulation techniques. H VSB (ω) is reciprocal around carrier frequency ω c 21 Monday, June 08, 2015

Linear modulation VSB-SC modulation: Expression: 2 cases according to SSB-SC principle Benefits: we could make VSB filter without the strict requirement like SSB However we still have some requirement. Now, let s have a look at the demodulation techniques 22 Monday, June 08, 2015

demodulation AM demodulation envelope detection coherent demodulation DSB-SC demodulation SSB-SC demodulation VSB-SC demodulation 1. envelope detection Detector: rectifier and a LPF Diode rectifier condition :1/ω c <<RC<<1/ω H Output: m o (t)=a 0 +m(t) No distortion when A 0 >= m(t) max 23 Monday, June 08, 2015

1. envelope detection demodulation Bridge circuit with diodes rectifying circuit process of envelop detection 24 Monday, June 08, 2015

demodulation 2. coherent demodulation applying the mixer with inputs s AM (t) and x c (t) can recover the modulating signal m(t). Output: m o (t) = 1/2[A o +m(t)]. PLL applied reference signal. stable frequency component ω called 25 Monday, June 08, 2015

demodulation DSB-SC demodulation Only coherent demodulation method can be used, since the DSB envelope is not corresponding with the shape of m(t) The structure is the same as AM one. From the LPF, we can get m o (t)= 1 2 m(t) 26 Monday, June 08, 2015

demodulation SSB-SC demodulation With the same factor as DSB-SC, the coherent demodulation is also applied for SSB-SC demodulation process with the same principle circuit The output from mixer is The output from LPF is m o (t) = 1 4 m(t) 27 Monday, June 08, 2015

demodulation VSB-SC demodulation Coherent technique is applied: Output from the multiplier Spectrum domain: From LPF we get: 28 Monday, June 08, 2015

demodulation VSB-SC demodulation From above equation, we can conclude that in order to get the modulating signal m (t) without distortion from VSB-SC signal, we have H VSB (ω+ω C )+H VSB (ω-ω C )=constant for ω <=ω H Up to now, we have analyzed some kinds of the linear modulation and demodulation techniques Comparison among these AM, DSB-SC, SSB-SC, VSB-SC 29 Monday, June 08, 2015

Comparison chart Modulation type Demodulation methods benefits drawbacks AM Envelope detector and coherent demodulation Simple structure for demodulation process; envelope detection can be applied; Low modulation efficiency; Large band is occupied DSB-SC Coherent demodulation No carrier power; High modulation efficiency Large band is occupied SSB-SC Coherent demodulation No carrier power; High modulation efficiency; Few band occupied; Difficult to realize steep sideband filter; VSB-SC Coherent demodulation No carrier power; High modulation efficiency; Few band occupied; Strict condition limited 30 Monday, June 08, 2015

Non-linear modulation Non-linear modulation Frequency modulation (FM): frequency variation of carrier Δω c is proportional to modulating signal m(t). Phase modulation (PM): phase variation of carrier ΔΦ is proportional to modulating signal m(t). Frequency modulation (FM): encoding information in a carrier wave by varying the instantaneous frequency of the wave and keep the amplitude constant. 31 Monday, June 08, 2015

FM modulation Instantaneous phase and frequency introduction: a(t) Am cos (t) is called the total phase (t) t Relationship between phase and frequency t ω t ω Non-linear modulation dt 0 0 t d (t) dt ω c called instantaneous radius and φ 0 called initial phase. t instantaneous phase: t ω t d t 0 x m (t) is called transmitted signal. sinusoidal carrier: x c (t) = A c cos (2πf c t) 0 32 Monday, June 08, 2015

FM modulation Non-linear modulation f(τ) is the instantaneous frequency of local oscillator and f Δ is the frequency deviation, which represents the maximum shift away from f c in one direction, assuming x m (t) is limited to the range ±1 namely, x m (t)=sin(2πf m t). expression for y(t) simplifies to Modulation index: Δf is the maximum deviation of the instantaneous frequency f m : highest frequency component 33 Monday, June 08, 2015

FM modulation Non-linear modulation When h<<1, narrowband FM otherwise wideband FM. The realization of FM circuit 1. Direct FM modulation circuit FM circuit with var-diode Crystal oscillator FM circuit Reactance tube FM circuit 2. Indirect FM modulation circuit Direct FM modulation circuit Basic idea: control the output frequency for resonance circuit with modulating signal m (t) f r = 1 2π LC 34 Monday, June 08, 2015

Direct modulation FM circuit with var-diode Non-linear modulation Basic steps: 1. Integrating m(t) 2. phase modulation Finally, we get the resonance frequency ( x ) 1 LC j u ( t) c(1 ) V V Crystal oscillator FM circuit D 2 (1 x ) 2 c Q Using m(t) controls resonance frequency 35 Monday, June 08, 2015

Direct modulation Non-linear modulation Reactance tube FM circuit Reactance tube which is the same as var-diode is also voltage control device Modulating signal M(t) Indirect FM modulation circuit First, do the integration for modulating signal m(t) and after that do the phase modulation. 36 Monday, June 08, 2015

indirect modulation Non-linear modulation output Carrier in M(t) Integrator isolation resistors: R 1,R 2 and R 3 Three capacitors: short circuit for high frequency and open circuit for modulating signal m(t) 37 Monday, June 08, 2015

Non-linear modulation PM modulation Analysis: phase Φ is the integration of angle frequency ω technique is quite similar with FM modulation PM modulation using modulating signal m(t) controls the phase of carrier, thus the carrier phase variation ΔΦ is proportional to m(t). The expression is : u U cos ω t k u (t) Δ instantaneous phase: k p :proportion coefficient, (t)called instantaneous phase shift. p PM cm c p Ω (t) ω t k u (t) ω t Δ (t) c p Ω c p instantaneous frequency: d ( t) du ( t) ( t) c kp c p( t) dt dt with du ( t) p( t) kp dt 38 Monday, June 08, 2015

Non-linear modulation PM modulation Modulation index :m p Δ p t max maximum phase shift bandwidth: 2(m p + 1)f M with f M =ω m /2π PM circuits correspond to the FM circuits. when doing FM, we get PM as well. 39 Monday, June 08, 2015

demodulation FM demodulation FM demodulation process is called frequency detector or discriminator 1. Modifying FM to AM or pulses with different duty cycle 2. Applying AM demodulation methods Fig. basic principle for FM demodulation process 40 Monday, June 08, 2015

demodulation FM demodulation Discriminator transconductance : CONSTANT 1. Slope discriminator Circuit : double loop detuning frequency discriminator f 1 <f c f 2 >f c When f c -f 1 =f 2 -f c 41 Monday, June 08, 2015

FM demodulation demodulation 2. Phase discriminator Phase discriminator is based on the phase-frequency curve for resonance circuit to change the FM signal to AM signal. Another idea is using steep filter to transfer FM to AM basic circuit equivalent circuit Output voltage : K d called voltage transmission coefficient 42 Monday, June 08, 2015

FM demodulation demodulation 3. Ratio discriminator Clipping to avoid the parasitic signal Ratio discriminator has both discrimination function and clipping function 43 Monday, June 08, 2015

FM demodulation demodulation 4. PLL-discriminator Recalling the behavior of PLL, we can use certain region F p =F po +KM(t) there is full F p spectrum in the lock range marked with L and V C (t) is proportional to M(t) 44 Monday, June 08, 2015

The applications of modulation techniques BeiDou Navigation Satellite System I-Q demodulation 45 Monday, June 08, 2015

The applications of modulation techniques AM decoder: NE567 IC 46 Monday, June 08, 2015

The applications of modulation techniques AM decoder: NE567 IC Configuration PLL cell 47 Monday, June 08, 2015

The applications of modulation techniques stereo FM transmitter: Rohm BA1404 maximum voltage <3V battery can be used 7805 Regulator with a couple of 1N4001 diodes can drive this IC reducing supply voltage to about 2.8 V 48 Monday, June 08, 2015

The applications of modulation techniques LM1596/LM1496 Balanced Modulator-Demodulator Applications: suppressed- carrier modulation, AM, syn-detection, FM or PM detection. 49 Monday, June 08, 2015

The applications of modulation techniques LM1596/LM1496 Balanced Modulator-Demodulator 50 Monday, June 08, 2015

The applications of modulation techniques Advanced technique-software Defined Radio (SDR) Software structure instead of hardware components (e.g. mixer filter amplifier modulator,etc.) Based on computers or embedded systems Benefits: Increasing capacity Reducing interference to others Software defined antenna 51 Monday, June 08, 2015

summary Modulation techniques: Linear-modulation: AM modulation: DSB-SC modulation SSB-SC modulation VSB-SC modulation Non-linear modulation: FM modulation: PM modulation Demodulation techniques: Envelope detection Coherent demodulation FM/PM demodulation circuits Case study: BDS, GPS, NE567,LM1596/LM1496,SDR 52 Monday, June 08, 2015

Reference materials 1. <<Fundamentals of Telecommunications>>, published by John Wiley & Sons, 1999. 2. <<High frequency electrons>> published by Chen He. 3. Datasheet of LM1596/LM1496 Balanced Modulator-Demodulator. 4. Datasheet of IC SI4730 based on broadcast AM/FM/SW/LW radio receiver. 5. 0http://www.allaboutcircuits.com/vol_3/chpt_9/6.html 6. http://www.radio-electronics.com/info/rf-technology-design/amamplitude-modulation/what-is-am-tutorial.php 7. http://en.wikipedia.org/wiki/frequency_modulation 53 Monday, June 08, 2015

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