Analog and Telecommunication Electronics

Transcription

1 Politecnico di Torino - ICT School Analog and Telecommunication Electronics B1 - Radio systems architecture» Basic radio systems» Image rejection» Digital and SW radio» Functional units 19/03/ ATLCE - B DDC

2 Lesson B1: radio system architectures Basic radio systems architectures Heterodyne receivers The image problem & image rejection techniques Heterodyne transmitters Direct synthesis (PLL lesson group) Digital radio, sotware deined radio Identiication o unctional modules this lecture Description o unctional modules next lectures Reerences Slides with notes 19/03/ ATLCE - B DDC

3 Expectations rom a radio receiver ANTENNA The input signal Va (rom the antenna) contains the wanted signal (usually quite weak), plus many types o noise and intererences. Va Vu Va RADIO RECEIVER Vu The receiver ouput signal Vu should be a copy o the original modulation, without noise and/or distortion. 19/03/ ATLCE - B DDC

4 Elementary receiver ANT. Va DEMOD. Vu Input ilter (narrowband, variable F) Filter, ampliier, and demodulator must operate at variable requency. A B Tuning shits the resonant requency A o the ilter (e.g. rom A to B ) 19/03/ ATLCE - B DDC

5 The crystal receiver Antenna and input ilter Crystal demodulator Tuning changes the C o a resonant circuit Vu From 19/03/ ATLCE - B DDC

6 Beats I we multiply two sine signals, the output is sum and dierence beats Werner s ormulae. a This is the RF signal -: we are interested in O O X IF Fo - Fa Fa Fo Fa + Fo Dierence beat Local Oscillator Sum beat 19/03/ ATLCE - B DDC

7 The heterodyne receiver a IF channel i = a - o Va Wideband input ilter O O X Filter and ampliier (narrowband, ixed requency i ) DEMOD. Vu i = a - o a O The input signal is shited to a ixed requency i = a - o. Tuning shits the requency O o the local oscillator 19/03/ ATLCE - B DDC

8 Not so new Armstrong original drawing: 1 MHz RF to 100 khz IF (D. Marsh: Direct conversion receivers. edn europe, Oct.2000) Reginald Fessenden (1901): rom the Greek heteros (other) and dynamis (orce). (rom 19/03/ ATLCE - B DDC

9 Beneits o heterodyne receivers Channel isolation achieved by ixed-requency IF ilter No need or tunable narrowband ilter Tuning achieved by shiting the LO requency Possible to cover wide requency range Ampliiers and demodulator operate at ixed IF Narrowband circuits more easy to design and test But Fi = Fo Fa or Fb Fo both Fa and Fb enter the IF chain image requency problem 19/03/ ATLCE - B DDC

10 The image requency The mixer generates sum and dierence beats Sum beats can be easily iltered good (RFa) and image (RFb) both olded to IF -: Same requency: cannot be separated by IF ilters IF GOOD LO IMAGE 2LO LO-RFa RFb-LO RFa RFb RFa+LO RFb+LO SUM BEATS 19/03/ ATLCE - B DDC

11 Image removal with RF ilter The RF bandpass ilter allows good channels to go through to the mixer, but blocks the images. IF GOOD RF + Other cannles IF LO IMAGE (o GOOD RF) The IF band-pass ilter keeps only one channel IF 19/03/ ATLCE - B DDC

12 Filters in the heterodyne receiver 1 IF channel I = o 1 1, 2 RF input ilter: Removes image requency 2 O O X DEMOD. Vu IF ilter: Removes adjacent channels (narrowband, ixed requency i ) i = o O Same eect as narrowband RF ilter 19/03/ ATLCE - B DDC

13 Noise and IF ilters Adjacent channels, rejected by IF ilter Good chalnnel; can go through RF and IF ilter Outband signals, wideband noise and image, removed by RF IR ilter 19/03/ ATLCE - B DDC

14 Lesson B1: radio system architectures Heterodyne receivers The image problem Dual conversion receivers Complex mixer & I/Q processing Digital receivers Sotware Deined Radio Examples 19/03/ ATLCE - B DDC

15 Remove the image by RF iltering i1 = o1 a a O1 b1 i1 A passband ilter beore the mixer can remove the image b1. i2 i2 i2 = o2 a a O2 b2 With high IF, the image b2 is more ar away, and the ilter can be less steep. 19/03/ ATLCE - B DDC

16 high or low IF requency? B i1 i1 i1 = o1 a1 a1 o1 b1 B i2 = o2 a1 a1 o2 b1 i2 Q = /B With high IF, a given bandwidth B needs high Q (or IF ilter) The IF 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 19/03/ ATLCE - B DDC

17 Dual-conversion heterodyne receiver Va X X DEM. Wideband LNA + ilter O1 IF1 ilter +Ampli. O2 IF2 ilter +Ampli. i1 = a O1 a O1 High irst IF (IF1) easy image removal Low second IF (IF2) Simple channel ilter Tuning by shiting O1 or O2 i1 i2 = i1 O2 O2 i1b IF1 image risk on IF2 ( i1b )! 19/03/ ATLCE - B DDC

18 Mechanical ilters Quartz lattice ilters Combination o high-q resonators Surace Acoustic Waves (SAW) 19/03/ ATLCE - B DDC

19 Complex mixers: SSB & image reject Werner s ormulae: sin a x sin b = ½ (cos(a-b) - cos(a+b)) A sin a x cos b = ½ (sin(a-b) + sin(a+b)) cos a x cos b = ½ (cos(a-b) + cos(a+b)) B -: Single Side Band beat: A + B = cos(a-b) No ilter Only dierence product term No sum term In TX chain: generation o SSB signals : - Image rejection mixer No need or image RF ilter (but needs phase shiters) 19/03/ ATLCE - B DDC

20 I/Q mixer in receivers Only dierence (or sum) beat here O X RF Filter and LNA /2 /2 X + DEMOD. The Q signal can be generated directly by LO Vu Need RF π/2 wideband phase shit 19/03/ ATLCE - B DDC

21 Single Side Band (SSB) transmitter Vb LO /2 a X IFi + IFt B /2 X IFq Output Filter and Power Ampliier B V U a The spectrum o Vb is translated to Fa to build a SSB signal. O = a B 19/03/ ATLCE - B DDC

22 Image rejection mixer RF1 LO LO RF2 image IF IF good x Cos(LO) x Sin(LO) RF2 LO RF1 /2 Sin(RF1 LO) -Sin(LO RF2) : Cos(RF1 LO) Cos(LO RF2) Sin(RF1 LO) Sin(LO RF2) + 2Sin(RF1 LO) 19/03/ ATLCE - B DDC

23 Hartley image rejection Sin(RF1, RF2) Cos(RF1-LO)+Cos(LO-RF2) O X Sin(LO) /2 Sin( )+Sin( ) /2 Cos(LO) X + Sin(RF1-LO) : - Sin(RF1-LO)-Sin(LO-RF2) IF π/2 phase shit (narrowband) No RF2 in IF 19/03/ ATLCE - B DDC

24 Receiver with image rejection mixer O X RF Filter and LNA /2 X + /2 DEMOD. Vu Image rejection mixer IF π/2 phase shit (narrowband) LO phase shit with digital techniques 19/03/ ATLCE - B DDC

25 Receiver with image reject mixer 19/03/ ATLCE - B DDC

26 Weaver image rejection Complex mixer 19/03/ ATLCE - B DDC

27 : I-Q channels Va X O1 IF1 Ampliier V O /2 X X V Q V I Q channel I channel DEM. V V cos V Q V V Q V IF2 Ampliier cos t V I sin V I V sen t 19/03/ ATLCE - B DDC

28 Zero- IF (or low-if) receiver a Va Input ilter and LNA (variable F) O O X Low pass ilter DEMOD. Vu i = 0 O = a1 Received signal at a directly moved to baseband Lowpass ilter in IF channel 19/03/ ATLCE - B DDC

29 ZIF with I-Q channels Q channel Va RF Ampli. O /2 X X I channel V Q DEM. & IMAGE REJECT V V V I The signal is decomposed in I and Q components directly at RF. baseband Ampliier & demod. Image rejection by I/Q processing 19/03/ ATLCE - B DDC

30 ZIF beneits an problems Beneits Low-pass IF ilters,» more easy to build inside Ics Not new (homodyne) Problems Requires I/Q processing or image rejection» Second mixer DC errors overlapped with signals» Use dierential structures to get low DC errors» Careull matching o various branches» Expensive with discrete components, good or ICs 19/03/ ATLCE - B DDC

31 Example o ZIF with I-Q channels Commercial device (receiver channel) LPF: ZIF architecture 19/03/ ATLCE - B DDC

32 Lesson B1: radio system architectures Heterodyne receivers The image problem Dual conversion receivers Complex mixer & I/Q processing Digital receivers Sotware Deined Radio Examples 19/03/ ATLCE - B DDC

33 First step towards digital radio IF channel A/D conversion ater demodulation. Va Wideband ilter O X IF ilter and Ampliier (ixed F) DEMOD. Analog Demodulator A/D out Many applications use directly digital data 19/03/ ATLCE - B DDC

34 More digital - 2 IF channel Va O X A/D DEMOD. Vu Wideband ilter IF ilter and Ampliier (ixed F) Digital demodulator The digital demodulator can use complex algorithms The same HW support dierent types o modulation The A/D converter must operate at high requency 19/03/ ATLCE - B DDC

35 More digital - 3 IF (digital) channel Va O X A/D DEMOD. Vu Wideban LNA and ilter (variable F) IF ilter and demodulator (all digital) The digital IF ilter increases the computational load, but allows to modiy the IF parameters in the SW 19/03/ ATLCE - B DDC

36 Mixing and sampling A mixer shits the input signal requency Sampling can be seen as product o the signal with a sequence o δ. O X The spectrum o a δ is a sequence o δ The product o input signal with the undamental requency o the δ stream corresponds to the mixing operation Va S/H A/D DEMOD. O Local oscillator 19/03/ ATLCE - B DDC

37 Heterodyne requency translation B1 Dierence beat: IF signal Local Oscillator LO1 LO1 RF signal B1 Sum beat IF bandpass ilter 19/03/ ATLCE - B DDC

38 Nyquist sampling and reconstruction Sampling rate F S = 1/T S Signal Spectrum S F S 2F S 3F S 4F S Anti-aliasing input ilter F S -S F S F S + S 4F S S Anti-aliasing reconstruction (output) ilter Aliases caused by sampling 19/03/ ATLCE - B DDC

39 Frequency translation by sampling Sampling rate RF signal S > 2 B1 F S 2F S 3F S B1 4F S Reconstruction ilter Sampled signal S - 3F S 5F S -S S - F S S 19/03/ ATLCE - B DDC

40 Subsampling and spectrum olding Sampling rate F S = 1/T S F S 2F S 3F S 4F S RF signal S S - 3F S 5F S -S S - F S 19/03/ ATLCE - B DDC

41 Single signal subsampling and olding 0 F S F S /2 3F S /2 2F S F S 2F S 0 F S /2 3F S /2 19/03/ ATLCE - B DDC

42 Subsampling and olding Unwanted Out-o-Band Signals RF ilter From: Critical techniques or High Speed A/D converters - Pentek 19/03/ ATLCE - B DDC

43 Folding with spurious and noise Sampling rate F S = 1/T S F S 2F S 3F S 4F S Useul signal Outband spurious and noise Folding overlaps spurious and noise in baseband UNUSABLE! 19/03/ ATLCE - B DDC

44 Subsampling and iltering F S = 1/T S F S 2F S 3F S 4F S Useul signal Bandpass ilter Translated signal Lowpass ilter OK 19/03/ ATLCE - B DDC

45 Which sampling rate? Sampling rate Feasible RF ilter Multichannel RF signal Too narrow ilter > 2 B1 F S 2F S 3F S Baseband signal (still multichannel) Channel ilter (Digital) 19/03/ ATLCE - B DDC

46 Subsampling and sampling jitter 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 low jitter sampling clock high-speed Sample/Hold circuits (low aperture jitter) 19/03/ ATLCE - B DDC

47 Oversampling, iltering and decimation A: Complete input signal signal o interest other spectral components (useless) B: Useul input signal Nyquist rate Filtering, resampling at lower rate s 2 s C: Signal ater decimation s and decimate (get rid o redundant samples) 19/03/ ATLCE - B DDC

48 Digital downconversion (GSM receiver) A B C 19/03/ ATLCE - B DDC

49 How many bits do we need? RF signals have wide dynamic (µv V) Nonlinearity distortion, intermodulation, Two approaches: Many bits /12, 14, high power & cost AGC with analog or digital control loop Variable Gain Ampliier (VGA) Vu O X A/D PROC. Gain control 19/03/ ATLCE - B DDC

50 SDR: Sotware Deined Radio IF sampling X A/D O RF (under)sampling DEMOD. μp, DSP A/D DEMOD. Analog: LNA, ilter O μp, DSP Numeric unctions: DSP or EPLD 19/03/ ATLCE - B DDC

51 Direct sampling I-Q SDR RF A/D /2 O DEMOD. Analog components - ilter -LNA A/D DSP: BANDPASS O = RF + IF IF processing Bandpass ilter Universal radio HW: Can change requency, modulation, application (GSM, GPS, UMTS, ) 19/03/ ATLCE - B DDC

52 ZIF I/Q Va A/D /2 O DEMOD. Analog components - ilter -LNA A/D DSP: LOWPASS O = RF Baseband proc. Lowpass ilter Universal radio HW: Can change requency, modulation, application (GSM, GPS, UMTS, ) 19/03/ ATLCE - B DDC

53 Lesson B1: radio system architectures Heterodyne receivers The image problem Dual conversion receivers Complex mixer & I/Q processing Digital receivers Sotware Deined Radio Examples 19/03/ ATLCE - B DDC

54 Positioning RX dual conversion Single requency conversion Double requency conversion IEEE JSSC, VOL. 33, NO. 12, Dec Thomas H. Lee: A 115-mW, 0.5- m CMOS GPS Receiver with Wide Dynamic-Range Active Filters 19/03/ ATLCE - B DDC

55 Positioning Receivers I/Q ZIF (same paper) 19/03/ ATLCE - B DDC

56 Positioning RX image reject mixer 19/03/ ATLCE - B DDC

57 IF ilter Complete RX Image reject mixer Mixer II RF input ampliier PLL synthetizer A/D converter 19/03/ ATLCE - B DDC

58 The transmitter chain 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) Digital correction o PA nonlinearity 19/03/ ATLCE - B DDC

59 Complete RTX structure 19/03/ ATLCE - B DDC

60 Details o receiver I/Q chain Section o the receiver chain: - ilters, ampliiers, PLL, mixer - A/D converters - Numeric demodulator Signal low 19/03/ ATLCE - B DDC

61 I/Q transmitter structure Section o the transmission chain: - D/A converters, - ampliiers, ilters - PLL, mixer, Signal low 19/03/ ATLCE - B DDC

62 Example o ZIF transceiver LPF : ZIF architecture 19/03/ ATLCE - B DDC

63 Reerence block diagram ANTENNA Low Noise Ampliier 900MHz/2GHz IF RX channel I/Q RX channel X X A/D DEM. X A/D PLL DDS O O I/Q I/Q µp, DSP, memory,.. CONTROL X Oscillators and synthesizers X X D/A D/A MOD. RF: 0,9/2GHz Power Ampliier 900MHz/2GHz BASEBAND IF TX channel DIGITAL I/Q TX channel User Interace A/D D/A IF: 100 MHz MIXED A/D TRANSDUCERS Mike, Earph., Display, Keys 19/03/ ATLCE - B DDC

64 Lesson B1 inal test Which are the beneits o heterodyne receivers? Explain the image requency problem. Which ilter is used or channel separation? -: Why do 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. - : Draw the block diagram o a receiver with digital I/Q processing or image cancelation. Which is the minimum sampling rate (Fs) or a signal with 2.5 GHz carrier, and a bandwidth o 2 MHz? 19/03/ ATLCE - B DDC