LECTURE 5-6. RECEIVERS OF RADIO AND TV BROADCASTING SYSTEMS 1. 2. 3. 4. GENERAL INFORMATION ABOUT RECEIVERS OF RADIO AND TV BROADCASTING SYSTEMS MAIN TYPES OF BROADCASTING RECEIVERS RECEIVER NOISE FACTOR AND SENSITIVITY (SENSEPTIBLITY) MAIN ELEMENTS OF RECEIVERS 5. SOFTWARE DEFINED RADIO (SDR) 1. GENERAL INFORMATION ABOUT RECEIVERS OF RADIO AND TV BROADCASTING SYSTEMS RS Sound and (or) image transducer RS+ interference TX RX Оконечное устройство Interference The general block diagram of radio channel of the broadcast and TV systems A sound or image, is transformed in voltage or current, modulates a high-frequency carrier. As a result the output radio signal (RS) of TX can be amplitude, phase or frequency modulated U t U t cos t t t t 0 Interference. At propagation radio signal in free space and feed lines it take place distortions, which are conditioned: •by irregularity of propagation medium; •by the artificial and natural restriction ; •by internal noises of antenna and receiver and its imperfection Radio receiver (RX) intended for transformation input signals with the purpose of extraction of useful information. RX must contain units, necessary for realization of the followings operations: •selection from all of aggregate of electric vibrations, pointed in aerial the external electromagnetic fields, signal from a necessary radio transmitter; • amplfication of high-frequency signals; • demodulation signals; •strengthening of prorectifying signal. 0 The radio receivers is designed to extraction of useful signals received from the receiving antenna, its amplification and conversion to the form required for the normal operation of terminals (loudspeaker, monitor, etc.) By apointment: radio broadcasting, TV broadcasting, communication, navigation, radiolocation, radio control, etc. By type of signal: wireless analog or digital By the method of signal processing: - with filter processing; - with correlation-filter processing. By frequency band: LF, MF, SF, VHF, UHF, SHF, et cetera The main functions of radio receivers: the selectivity (separation of the useful signal); amplification (to the level required for normal working terminal); conversion (to increase selectivity and stable amplification); automatic gain control (for widening dynamic rang) ; demodulation (selection of modulation law) or measure the signal parameters. Sensitivity - the minimum power or voltage at the input RX, which provide a given quality of signal processing Peak (noise-limited) sensitivity - the minimum power Psmin or voltage Uc min at the receiver input at which the SNR at the output of the linear part RX equal to one (Ps / Pn = 1 or Uc / Un = 1); Real (actual or threshold) sensitivity - minimum power or voltage at the receiver input at which the predetermined reception quality (given the SNR at the output of the linear part RX). At wavelength > 1 m, when the resonans circuits RX can be considered as systems with lumped parameters, the sensitivity is taken in units of voltage - microvolts or millivolts Uc min. If <1 m - in terms of power Pc min. Real sensitivity radio receiver is in the range of 50 ... 300 μV, depending on the quality class. Sensitivity of satellite TV receiver can be -14 -15 up 10 ... 10 W. For broadcast receivers with ferrite antenna uses the concept of sensitivity in field strength. It has a value from 0.3 to 5 mV/m. 2. MAIN TYPES OF BROADCASTING RECEIVERS Block diagram of the receiver of direct amplification Frequency Converter . The block diagram of a superheterodyne receiver f p УВЧ Uc f СМ p U гр УНЧ f г= f р Гетеродин Block diagram of direct conversion receivers SDR RX Parameters of the radio receivers Frequency range - the entire band of frequencies, which can receive signals Dynamic range RX describes its ability to receive signals without distortion f f max f min Pвых D,дБ=10 lg(Pinmax/Pin min) Selectivity: by the frequency (on the next channel, the image channel) by the waveform, by the polarization B PПвх / PПвых B,дБ 10lg PПвх 10lg PПвых 50...70дБ у B зерк 4f ПЧ 1 Q fc 2 Quantitative estimation of noises Пn y 2 f df 0 0 y f П 0,7 1 1 2RCf 2 1 2RC a П0,7 2 П0,7 f 0 2 2 П0,7 П02,7 f 2 df П 2 0,7 0 df П02,7 f 2 2 П0, 7 dx 1 x 1 arctg 2 x a a 2a 2 Thermal (heat) noise Stored energy 1 C 4 RÏ 1 Ý Ñ U 2n 2 n 1 Э kT 2 U n2 1 k T 4kTRÏ C n Nyquist formula k 1,38 1023 Shot noise Power rating (nominal power) Рш 0 Ðn 0 kTÏ U 2n R RL Рn 0 4R n N0 I n2sn 2eI0 Пn I0 Shottky formula – noise power at matched load U 2n Рn 2Rs RL Un2т 4kTRПn Рn 0 Пn 3. RECEIVER NOISE FACTOR (figure, ratio) ( Pc / PШ )in ( Pc / PШ )out INPUT. UNIT nRX LNA ( Ps / Pn )in ( Рs / Рn )out nRX nIN IFA Detector G nLNA 1 n 1 nIFA 1 MIX ... n d 1/ K шIN IN pIN К рIN К рIN K рLNA К рIN К рLNA К рMIX nRX nLNA If КрIN ≈1 nRX 1 TRX / T0 RX RX LNA MIX MIX К рLNA IFA К рLNA К рMIX ... K pIN 1 nMIX 1 nIFA 1 ... К рLNA К рLNA K рMIX nRX TRX / T0 1 RX 1 TRX TLNA Т MIX Т IFA ... К рLNA К рLNA К рMIX Pn kTRX Пn kT0 Пn RX kT0 Пn (nRX 1) NOISE OF RECEIVER ANTENNA * * Ta Ta TL 1 a Т Т sky Тatmosphere Т ground 5 T 3 30 0.1 250o 60o K Ta 60 0.9 290 0.1 54 29 83o K 83 T a a a 0.25 T0 290 RECEIVERS SENCITIVITY Noise power output Рn _ out Рn _ ant К р Рn K p ; Power output noise, converted to the input Pn kTПn kT0 Пn RX kT0 Пn (nшRX 1) RX TRX / T0 nшRX 1 → Рna nш RX 1 U U 4kTa Ra n kT0 a n ; 2 Rа Rin 4 Ra 4 Ra 2 nа 2 nа R =Ra s Un2т 4kTRПn RL=Rin Nyquist formula U n2 4 KTRn Pn Rн KTn 2( Rs RL ) 4R T0 3000 K k =1,38·10-23 W/Hz grad Рnout kT0 а n К р kT0n К рRX nRX 1 kT0n К рRX nRX а 1; a Ta / T0 Рs min kT0 Пn nnRX 1 а kT0 Пn ( RX а ) kПn (Т RX Т а ) 4. MAIN ELEMENTS OF RECEIVERS Low-nose amplifier Wf exp d f lf Ps ( n ) RXin Ps ( n ) AWf Balanced frequency converter Demodulators (detectors) Uout KАМ U — AM Uout KFМ f — FM Uout KPМ — PM Amplitude detectors Сbl >> С F D Uintm С HF RF F LF RL U LFout Demodulation of ASK signal а б в Demodulation of PM signal Phase detector VD1 Uout 1 R C Us/2 U0 kdUd1 0,5 Us 9 0 0 Us/2 kdUd2 Рис.16.13 -0,5 U d1= U 0 + Us /2; U d2= U0 - Us /2. U out К дU 0 1 m 2 2m cos 1 m 2 2m cos Us/U0 = m m << 1 m=1 120 60 Uout R C VD2 30 Uout 2 КдUs cos Uout 2 КдU s cos sin 2 2 Synchronous detector Output voltage phase detector for in-phase input and reference signals Uout 2 КдUs φ =0 is proportional to the input signal Us, and the phase detector is converted in the synchronous detector. These detectors, due to their high linearity, are widely used in analog TV for demodulation of the image signals and in digital TV for demodulating PSK signals. -1 Рис.16.1 4 150 180 Frequency detector Correlated detector ucd( ) filter x u2(t) u1(t) Var. time delay u1(t- ) z ( ) u1 (t )u2 (t )dt ( Ps / Pn )out (2 / 1 2 )Kcompr Kcompr fin / fout fin / Пout PSmin kT0 fin (nnRX 1) Kcompr compression expansion BHF LNA MIX PreIFA f IF= |f1 – fs | Bmirr 4 f IF 1 Q f s AGC BIF BD Matched filter –Main IFA KuIFA 2 _ X BLF (BDP) АD LFA PD ADC UinDET PSмin К рBHF Main IFA D S P f2 f1 FS PD 90 Block diagram of the analog – digital receiver o ADC DAC nnRX n 1 nnIFA 1 n 1 nnLNA nIF ... nADC К рLNA К рувчK рIF К р( beforADC ) nnADC PnADC For ADC U 2 Rin 12Rin n шАЦП 1 L=8 U max ADCin 7.5 10 3 2 12 75 4 1021 106 ADC AD9260 1.69 10 7 L=16 2L 1 N U max PD U U 2 2 N 2L 1 U 2UmахADCout / N 2 *1 / 255 0.0075V 7.5mV Rin 75 L For K p nnADC PnADC U 2 U 2 1 1 Pn 0 К рADC 12RinkT0 Пn 12RinkT0 Пn n2 1107ПВ2 If only ADC have not affected on RX noise factor D N N , or D 20 lg [dB] 6L 2 2 FT , MHz nnADC 1 D, dB 3 10 5 2 21 12 75 4 10 10 6 200 The twentieth century saw the explosion of hardware defined radio (HDR) as a means of communicating all forms of audible; visual, and machine-generated information over vast distances. Most radios are hardware defined with little or no software control; they are fixed in function for mostly consumer items for broadcast reception. They have a short life and are designed to be discarded and replaced. Software defined radio (SDR) uses programmable digital devices to perform the signal processing necessary to transmit and receive baseband information at radio frequency. Devices such as digital signal processors (DSPs) and field programmable gate arrays (FPGAs) use software to provide them with the required signal processing functionality. This technology offers greater flexibility and potentially longer product life, since the radio can be upgraded very cost effectively with software. Software Defined Radio (SDR) SDR equipment - these are elements of the wireless network which operating modes and parameters can be changed or expanded after the elements are made using the software. Modulated signal u(t ) A(t ) cos[0t (t )] can to present by sum of two quadrature component u(t ) [ A(t ) cos (t )]cos0t [ A(t ) sin (t )]sin 0t Ac cos0t As sin 0t I cos0t Q sin 0t. A(t ) Ac2 As2 As Ac (t ) arctg I 2 Q2 Q arctg I Zero IF Quadrature Product Detector One cycle Sine Wave at Sampled Frequency Fo