Politecnico di Torino ICT School Lesson A1 A1 Telecommunication Electronics Radio systems architecture» Basic radio systems» Image rejection» Digital and SW radio» Functional units Basic radio systems architectures Heterodyne The image problem Image rejection techniques Digital radio Sotware deined radio Transmitter block diagram Heterodyne Direct synthesis Identiication o unctional modules Description o unctional modules this lessons next lessons 03/05/2007 1 TLCE A1 2007 DDC 03/05/2007 2 TLCE A1 2007 DDC Example IC or GPS + Galileo Elementary receiver ANT. DEMD. Input ilter (narrowband, variable F) Filter, ampliier, and demodulator must operate at variable requency. Sept 2006 Tuning shits the resonant requency A o the ilter. world s irst Galileoready receiver or mass market consumer electronics. A 03/05/2007 3 TLCE A1 2007 DDC 03/05/2007 4 TLCE A1 2007 DDC The heterodyne receiver Not so new Wideband input ilter a channel i = a o Filter and ampliier (narrowband, ixed requency i ) DEMD. Armstrong original drawing 1 MHz RF to 100 khz (D. Marsh Direct conversion receivers. edn europe, ct.2000) i = a o a The input signal is shited to a ixed requency i = a o. Tuning shits the requency o the local oscillator Reginald Fessenden (1901) rom the Greek heteros (other) and dynamis (orce). (http//www.antiqueradios.com/superhet/) 03/05/2007 5 TLCE A1 2007 DDC 03/05/2007 6 TLCE A1 2007 DDC Page 1 2007 DDC 1
TLCE A1 03/05/2007 Receiver architectures The image requency Heterodyne receivers The image problem Dual conversion receivers Complex mixer & I/Q processing Digital receivers Sotware Deined Radio Examples Wideband input ilter i = a o a1 + a2 i i a1 a2 channel i = a1 o = a2 o Filter and ampliier (ixed requency i ) DEMD. All input signals at a = o ± i are shited to the requency F a1 = o i and a2 = o + o are both shited to the requency i 03/05/2007 7 TLCE A1 2007 DDC 03/05/2007 8 TLCE A1 2007 DDC Complete spectrum Complete spectrum The mixer generates sum and dierence beats Sum beats can be easily iltered good RF (1) olded to The mixer generates sum and dierence beats Sum beats can be easily iltered image (2) also olded to GD L 2L L IMAGE 2L LRF1 RF1 RF1+L RF2L RF2 RF2+L DF BEATS SUM BEATS DF BEATS SUM BEATS 03/05/2007 9 TLCE A1 2007 DDC 03/05/2007 10 TLCE A1 2007 DDC Complete spectrum Handling images The mixer generates sum and dierence beats Sum beats can be easily iltered good RF (1) and image (2) olded to Same requency, the image cannot be iltered (at ) The image could come rom Nearby transmitter ther channels ther radio system GD L IMAGE 2L Can be stronger than the useul signal, and cause Intererence (high noise) Blocking (drive LNA/mixer into saturation) LRF1 RF2L DF BEATS RF1 RF2 RF1+L RF2+L SUM BEATS Mandatory to reduce the power o images Filters Image rejection mixers Zero architectures 03/05/2007 11 TLCE A1 2007 DDC 03/05/2007 12 TLCE A1 2007 DDC Page 2 2007 DDC 2
Remove the image by iltering Remove the image by iltering i A passband ilter beore the mixer can remove the image a1b. i A passband ilter beore the mixer can remove the image a1b. i1 = o1 a1 a1 1 a1b i1 = o1 a1 a1 1 a1b i i i i i1 = o1 a1 a1 1 a1b i1 = o1 a1 a1 1 a1b With high, the image a1b is more ar away, and the ilter can be less steep. 03/05/2007 13 TLCE A1 2007 DDC 03/05/2007 14 TLCE A1 2007 DDC Example o image requency RF Input channel 2.5 GHz channel 1 MHz L requency 2.5 GHz + 1 MHz = 2,501 MHz Image at 2.502 GHz Q o RF image removal ilter 2,500/2 = 1250!!! channel 10 MHz L requency 2.5 GHz + 10 MHz = 2,510 MHz Image at 2.52 GHz Q o RF image removal ilter 2,500/20 = 125 Wideband noise, removed by RF IR ilter Adjacent channels, rejected by ilter Noise and ilters ilter must have tightly controlled transer unction Diicult to get high Q ilters at high a 03/05/2007 15 TLCE A1 2007 DDC 03/05/2007 16 TLCE A1 2007 DDC Filters in the heterodyne receiver Filters in the heterodyne receiver 1 channel I = o 1 1 channel I = o 1 1, 2 RF input ilter Removes image requency 2 DEMD. 1, 2 DEMD. ilter Removes adjacent channels (narrowband, ixed requency i ) 1 2 i = o 1 03/05/2007 17 TLCE A1 2007 DDC 03/05/2007 18 TLCE A1 2007 DDC Page 3 2007 DDC 3
Filters in the heterodyne receiver Filters in the heterodyne receiver 1 channel I = o 1 1 channel I = o 1 1, 2 RF input ilter Removes image requency 2 DEMD. ilter Removes adjacent channels (narrowband, ixed requency i ) 1, 2 RF input ilter Removes image requency 2 DEMD. ilter Removes adjacent channels (narrowband, ixed requency i ) i = o 1 2 1 i = o 1 2 1 03/05/2007 19 TLCE A1 2007 DDC 03/05/2007 20 TLCE A1 2007 DDC Problems with high requency Receiver architectures B B i1 = a o1 i2 = o2 i1 i1 o2 i1b i Q = /B With high, a given bandwidth B needs high Q (or ilter) Heterodyne receivers The image problem Dual conversion receivers Complex mixer & I/Q processing Digital receivers Sotware Deined Radio Examples The channel is moved to a lower requency with a second beat rom i1 to i2. Since i2 is lower, the same bandwidth B can be achieved with lower Q 03/05/2007 21 TLCE A1 2007 DDC 03/05/2007 22 TLCE A1 2007 DDC Dualconversion heterodyne receiver Dualconversion heterodyne receiver DEM. DEM. Wideband LNA + ilter 1 1 ilter +Ampli. 2 2 ilter +Ampli. Wideband LNA + ilter 1 1 ilter +Ampli. 2 2 ilter +Ampli. i1 = a 2 a 1 First requency translation to a high (1) Removes image requency Simple RF and ilters i1 = a 2 a 1 Second requency translation to a low (2) Simple channel ilter (2) Usually 2 is ixed; tuning is achieved by shiting 1 i2 2 i1 03/05/2007 23 TLCE A1 2007 DDC 03/05/2007 24 TLCE A1 2007 DDC Page 4 2007 DDC 4
First requency conversion Second requency conversion RF spectrum Band o interest F RF spectrum F = F RF F L1 Signal o interest GHz mult. by local oscillator no. 1 multiply by local oscillator 2 L1 L2 spectrum F = F RF F L1 Signal o interest Baseband spectrum Low F BB = F F L2 Baseband spectrum Zero (Z) F BB = F F L2 (Adapted rom Spectrum digital radio products) 03/05/2007 25 TLCE A1 2007 DDC 03/05/2007 26 TLCE A1 2007 DDC Beneits o dualconversion receivers RF IR ilter removes images BW and Q related with 1st requency High wide IR ilter (image is 2 x away) First (High) reduce noise and ar channels Second (low) urter noise rejection Remove adjacent channels (narrowband ilter) Usually L2 is ixed; tuning is achieved by shiting L1 Problems o dualconversion receivers Need good bandpass ilters at Expensive & bulky Diicult to shape the passband Filter technologies LC Mechanical resonators» SAW, Ceramic, Quartz Another solution Image rejection mixer No ilter Needs or matched mixers and ampliiers 03/05/2007 27 TLCE A1 2007 DDC 03/05/2007 28 TLCE A1 2007 DDC Mechanical ilters Receiver architectures Surace Acoustic Waves (SAW) Heterodyne receivers The image problem Dual conversion receivers Complex mixer & I/Q processing Digital receivers Sotware Deined Radio Examples Quartz lattice ilters 03/05/2007 29 TLCE A1 2007 DDC 03/05/2007 30 TLCE A1 2007 DDC Page 5 2007 DDC 5
TLCE A1 03/05/2007 Complex mixers SSB Single Side Band (SSB) mixer Werner s ormulae sen a x sen b = ½ (cos(ab) cos(a+b)) A sen a x cos b = ½ (sen(ab) + sen(a+b)) cos a x cos b = ½ (cos(ab) + cos(a+b)) B Single Side Band beat A + B = cos(ab) nly dierence product term No sum term RF Filter and LNA + DEMD. In T chain generation o SSB signals Need RF wideband phase shit 03/05/2007 31 TLCE A1 2007 DDC 03/05/2007 32 TLCE A1 2007 DDC Complex mixers image rejection Image rejection mixer 1 Werner s ormulae sen a x sen b = ½ (cos(ab) cos(a+b)) A sen a x cos b = ½ (sen(ab) + sen(a+b)) image good cos a x cos b = ½ (cos(ab) + cos(a+b)) B Single Side Band beat A + B = cos(ab) RF1 L L RF2 RF2 L RF1 The same technique is used in Image rejection mixer Dierence beats No image components No need or ilter (but needs phase shiters) 03/05/2007 33 TLCE A1 2007 DDC 03/05/2007 34 TLCE A1 2007 DDC Image rejection mixer 1 Image rejection mixer 1 image good image good x Cos(L) RF1 L L RF2 RF2 x Sin(L) L RF1 x Cos(L) RF1 L L RF2 x Sin(L) RF2 L RF1 Sen(RF1 L) Sen(L RF2) Cos(RF1 L) Cos(L RF2) Sen(RF1 L) Sen(L RF2) Cos(RF1 L) Cos(L RF2) Sen(RF1 L) Sen(L RF2) 03/05/2007 35 TLCE A1 2007 DDC 03/05/2007 36 TLCE A1 2007 DDC Page 6 2007 DDC 6
TLCE A1 03/05/2007 Image rejection mixer 2 Hartely image rejection Sin(RF1, RF2) Cos(RF1L)+Cos(LRF2) Sen(RF1 L) Sen(L RF2) + = Sen(RF1 L) Sen(L RF2) 2Sen(RF1 L) Sin(L) Cos(L) Sen( )+Sen( ) + Sen(RF1L) Requires tight matching o mixer transer unction Gain Phase rotation phase shit (narrowband) Sen(RF1L)Sen(LRF2) No RF2 in 03/05/2007 37 TLCE A1 2007 DDC 03/05/2007 38 TLCE A1 2007 DDC Complete receiver with image rejection mixer Receiver with image reject mixer RF Filter and LNA + DEMD. Image rejection mixer phase shit (narrowband) L phase shit with digital tecniques 03/05/2007 39 TLCE A1 2007 DDC 03/05/2007 40 TLCE A1 2007 DDC Weaver image rejection Beneits o image rejection mixers No need or complex RF and bandpass ilters But Based on canceling A A = 0 i A = A Needs balanced ampliier + mixer channels» Same gain» Same phase shit» Good analog technology Complex mixer 03/05/2007 41 TLCE A1 2007 DDC 03/05/2007 42 TLCE A1 2007 DDC Page 7 2007 DDC 7
TLCE A1 03/05/2007 IQ demodulation IQ channels V V C S = V cosωt = V senωt cos Vc V Vs sen 1 1 Ampli. The signal is decomposed in I and Q components, at 2 or at demodulator Q channel I channel 2 Ampli. V Q DEM. V I V V The demodulator can compute V and V 03/05/2007 43 TLCE A1 2007 DDC 03/05/2007 44 TLCE A1 2007 DDC Zero (low) receiver Conventional vs Z a Input ilter and LNA (variable F) Low pass ilter DEMD. a Bandpass ilter i = a o i = 0 = a1 Received signal at a directly moved to baseband Lowpass ilter in channel a = a Lowpass ilter i = 0 03/05/2007 45 TLCE A1 2007 DDC 03/05/2007 46 TLCE A1 2007 DDC Beneits o zero Z with IQ channels Bandpass ilters replaced by Lowpass Better control o shape and bandwidth Fully digital ilter Suitable or SC (less external components) But set becomes a problem (DC is a signal) L to RF and RF to L leakage (DC beat)» Double balanced mixer Image is the inverted spectrum» Separate I/Q channels RF Ampli. The signal is decomposed in I and Q components directly at RF Q channel I channel V Q DEM. V I baseband Ampliier & demod. V V 03/05/2007 47 TLCE A1 2007 DDC 03/05/2007 48 TLCE A1 2007 DDC Page 8 2007 DDC 8
Example o Z with IQ channels Receiver architectures Commercial device (receiver channel) Heterodyne receivers The image problem Dual conversion receivers Complex mixer & I/Q processing Digital receivers Sotware Deined Radio Examples LPF Z architecture 03/05/2007 49 TLCE A1 2007 DDC 03/05/2007 50 TLCE A1 2007 DDC First step towards digital radio Digital baseband processing Wideband ilter channel ilter and Ampliier (ixed F) DEMD. Analog Demodulator Many applications use directly digital data conversion ater demodulation. out Antenna RF (GHz) 1st conversion Digital algorithms Error correction Compression Encryption Equalization (MHz) 2nd conversion Base band (khz) Analog Baseband demodulation Digital From Spectrum digital radio products 03/05/2007 51 TLCE A1 2007 DDC 03/05/2007 52 TLCE A1 2007 DDC More digital 2 Digital demodulation channel Antenna Analog Digital DEMD. RF (GHz) 1st conversion (MHz) 2nd conversion baseband (khz) Baseband demodulation Wideband ilter ilter and Ampliier (ixed F) Digital demodulator The digital demodulator can use complex algorithms The same HW support dierent types o modulation The converter must operate at high requency Advantages Proprietary demodulation schemes in sotware Improved noise immunity and robustness Easier multiplexing o various orms o inormation (e.g., voice, data, video) 03/05/2007 53 TLCE A1 2007 DDC 03/05/2007 54 TLCE A1 2007 DDC Page 9 2007 DDC 9
More digital 3 How many bits do we need? (digital) channel DEMD. RF signals have wide dynamic (µv V) Nonlinearity distorsion, intermodulation, Two approaches Many bits /12, 14, ) high power & cost AGC with analog or digital control loop Wideban LNA and ilter (variable F) ilter and demodulator (all digital) riable Gain Ampliier (VGA) The digital ilter increases the computational load, but allows to modiy the parameters in the SW PRC. Gain control 03/05/2007 55 TLCE A1 2007 DDC 03/05/2007 56 TLCE A1 2007 DDC Digital processing Digitization Antenna Analog Digital signal o interest other signals noise RF (GHz) 1st conversion (MHz) 2nd conversion baseband (khz) Baseband demodulation (ater antialias ilter) Additional advantages Precision, conigurable tuning Lower cost Smaller size Requires a) Fast s (up to 100 Msamples/sec) b) Hardware digital down converters c) Fast DSP s or baseband processing Digitized 2 s sampling rate s 0 s 2 s 03/05/2007 57 TLCE A1 2007 DDC 03/05/2007 58 TLCE A1 2007 DDC IQ digitization versampling, iltering and decimation Digitized Baseband (Inphase component) I signal o interest other spectral components (useless) 2 s s 0 s 2 s Digitized NC (centered on signal o interest) NC Baseband (inphase) I 2 NC Baseband (quadrature) Q 2 NC I I s Nyquist rate Filtering, resampling at lower rate 2 s and decimate (get rid o redundant samples) s 03/05/2007 59 TLCE A1 2007 DDC 03/05/2007 60 TLCE A1 2007 DDC Page 10 2007 DDC 10
Mixing and sampling Nyquist sampling A mixer shits the input signal requency Sampling can be seen as product o the signal with a sequence o δ. The spectrum o a δ is a sequence o δ F S = 1/T S The product o input signal with the undamental requency o the δ stream corresponds to the mixing operation S/H DEMD. Local oscillator 03/05/2007 61 TLCE A1 2007 DDC 03/05/2007 62 TLCE A1 2007 DDC Nyquist sampling Subsampling and olding F S = 1/T S F S 2F S 3F S 4F S From Critical techniques or High Speed converters Pentek 03/05/2007 63 TLCE A1 2007 DDC 03/05/2007 64 TLCE A1 2007 DDC Frequency translation by subsampling Frequency translation by subsampling F S = 1/T S F S 2F S 3F S 4F S F S = 1/T S F S 2F S 3F S 4F S Sampling rate Useul signal Bandpass ilter Useul signal 03/05/2007 65 TLCE A1 2007 DDC 03/05/2007 66 TLCE A1 2007 DDC Page 11 2007 DDC 11
Frequency translation by subsampling Frequency translation by subsampling F S = 1/T S F S 2F S 3F S 4F S F S = 1/T S F S 2F S 3F S 4F S Sampled signal Translated signal Lowpass ilter 03/05/2007 67 TLCE A1 2007 DDC 03/05/2007 68 TLCE A1 2007 DDC Subsampling and sampling jitter Receiver architectures Sampling rate depends on signal bandwidth Subsampling receivers use less power Sampling jitter depends on carrier Amplitude error = (time jitter) x (slew rate) Slew rate = V x ω(carrier) Phase error in I/Q chains Sampling jitter is a critical parameter Need or highspeed (low jitter) Sample/Hold circuits Heterodyne receivers The image problem Dual conversion receivers Complex mixer & I/Q processing Digital receivers Sotware Deined Radio Examples 03/05/2007 69 TLCE A1 2007 DDC 03/05/2007 70 TLCE A1 2007 DDC SDR Sotware Deined Radio Digital RF processing key parameters Speed Noise&Dynamic range Linearity Sampling jitter Numeric unction perormed by DSP or EPLD (programmable) Analog Digital Antenna RF (GHz) 1st conversion (MHz) 2nd conversion baseband (khz) Baseband demodulation DEMD. Analog components LNA, ilter µp, DSP 2006 Commercial SC available (2.5 GHz) Z architectures 03/05/2007 71 TLCE A1 2007 DDC 03/05/2007 72 TLCE A1 2007 DDC Page 12 2007 DDC 12
I/Q sotware deined radio Direct sampling IQ SDR Input ampliier (LNA) Q channel I channel V Q V I DEMD. V, V RF Analog components ilter LNA DEMD. DSP BANDPASS Signal decomposed in IQ components, ed to the digital demodulator Universal radio HW Can change requency, modulation, application (GSM, GPS, UMTS, ) = RF + processing Bandpass ilter 03/05/2007 73 TLCE A1 2007 DDC 03/05/2007 74 TLCE A1 2007 DDC Z I/Q Receiver architectures Analog components ilter LNA DEMD. DSP LWPASS Heterodyne receivers The image problem Dual conversion receivers Complex mixer & I/Q processing Digital receivers Sotware Deined Radio Examples Universal radio HW Can change requency, modulation, application (GSM, GPS, UMTS, ) = RF Baseband proc. Lowpass ilter 03/05/2007 75 TLCE A1 2007 DDC 03/05/2007 76 TLCE A1 2007 DDC Positioning R single conversion Positioning R dual conversion IEEE JSSC, VL. 33, N. 12, DECEMBER 1998 Thomas H. Lee, A 115mW, 0.5 m CMS GPS Receiver with Wide DynamicRange Active Filters (same paper) 03/05/2007 77 TLCE A1 2007 DDC 03/05/2007 78 TLCE A1 2007 DDC Page 13 2007 DDC 13
Positioning Receivers I/Q Z Positioning R image reject mixer (same paper) 03/05/2007 79 TLCE A1 2007 DDC 03/05/2007 80 TLCE A1 2007 DDC Positioning Receivers Last IC ilter Complete R RF input ampliier Image reject mixer Mixer II PLL synthetizer converter 03/05/2007 81 TLCE A1 2007 DDC 03/05/2007 82 TLCE A1 2007 DDC The transmitter chain Complete RT structure Conventional Generate carrier Modulate Filter and Ampliy (PA) Reverse heterodyne receiver chain Generate baseband modulated signal Filter and translate to RF Filter and ampliy (PA) Next Direct generation o RF (high speed DAC) Filter and ampliy 03/05/2007 83 TLCE A1 2007 DDC 03/05/2007 84 TLCE A1 2007 DDC Page 14 2007 DDC 14
TLCE A1 03/05/2007 Details o receiver I/Q chain I/Q transmitter structure Section o the receiver chain ilters, ampliiers, PLL, mixer converters Numeric demodulator Signal low Section o the transmission chain D/A converters, ampliiers, ilters PLL, mixer, Signal low 03/05/2007 85 TLCE A1 2007 DDC 03/05/2007 86 TLCE A1 2007 DDC Example o Z transceiver Example o true SDR analog parts LPF Z architecture 03/05/2007 87 TLCE A1 2007 DDC IEEE JSSC, Vol. 40, No. 12, DEC 2005 AllDigital PLL and Transmitter or Mobile Phones. 03/05/2007 88 TLCE A1 2007 DDC Reerence block diagram Basic blocks o RT (next lessons) ANTENNA RF 0,9/2GHz 100 MHz Low Noise Ampliier 900MHz/2GHz PLL DDS Power Ampliier 900MHz/2GHz BASEBAND MIED R channel I/Q I/Q scillators and synthesizers T channel DIGITAL TRANSDUCERS I/Q R channel DEM. µp, DSP, memory,.. CNTRL D/A MD. D/A I/Q T channel D/A User Interace Mike, Earph., Display, Keys LNA (Low Noise Ampliiers) PA (Power Ampliier) MIER AGC, RSSI (Received Signal Strength Indicator) PLL (Phase Lock Loops) or DDS (Direct Digital Synthesizers) and D/A converters Signal conditioning (antialias ilters, S/H) (Filters, tuned circuit, Digital processing) 03/05/2007 89 TLCE A1 2007 DDC 03/05/2007 90 TLCE A1 2007 DDC Page 15 2007 DDC 15
TLCE A1 03/05/2007 Lesson A1 Lesson A1 inal test Basic radio systems architectures Heterodyne The image problem Image rejection techniques Digital radio Sotware deined radio Transmitter block diagram Heterodyne Direct synthesis Identiication o unctional modules Description o unctional modules this lessons next lessons Which are the beneits o heterodyne receivers? Explain the image requency problem. Which ilter is used or channel separation? Why some receivers use dual conversion? Which techniques are used or image rejection? What do AGC and VGA mean? Describe the architecture o a SW radio. Which is the minimum sampling rate (Fs) or a signal with 2.5 GHz carrier, and a bandwidth o 2 MHz? 03/05/2007 91 TLCE A1 2007 DDC 03/05/2007 92 TLCE A1 2007 DDC Next lesson (A2) Transistor ampliiers Basic circuit, Linear transistor model, Biasing Small signal analysis, Frequency response Design o ampliiers Speciications, Design sequence Lab experience 1 Transistor ampliier, small signal (linear model) Lab experience 2 Transistor ampliier, large signal (nonlinear model) Text reerence Transistor circuits 1.1, 1.2 03/05/2007 93 TLCE A1 2007 DDC Page 16 2007 DDC 16