1. Digital Parts of Receivers and Transmitters Vilmos Rösner

2. Digital Parts of Receivers Digital Parts of Transmitters Special Application: Bandpass Filter

3. DEM out f0 Antenna output: U(t)=A(t)exp(j(tω(t)+φ(t))) modulation-> information Problem: receiver selectivity

4. Superheterodyne Receiver (Edwin Armstrong 1918) new problem: image rejection DEM out IF f0 f 0

5. Frequency Ranges DEM IFRFIFBBRF IFBB radio frequencyintermediate frequencybaseband ~100MHz... ~GHz~10MHz~kHz..MHz generally: F RF : F IF ≈ 10..3 problem with tuning linearity, images... problem with image rejection →solution: multiple conversion (IF) If it is possible, one of the standard intermediate frequencies should be used.

6. Digital Output, Position of the ADC digital IF receiver “software radio” modem

7. Digital IF Receiver Components Analog to Digital Converter (ADC) Digital Mixer (multiplier) Digital Oscillator (NCO Numerically Controlled Oscillator) Digital Filter DDC outin DDC ADC FILTER

8. NCO FTW PACC LUT address data bus set f clk N f out =FTW * fClk / 2^N Intersil HSP45102, HSP45116A optionally complex output other accessories (sweep, modulation, dither) NCO+DAC≈ Direct Digital Syntheser (DDS)

9. Digital Filter / FIR http://www.digitalfilter.com

10. FIR Filter Coeffitients, Window Functions rectangular window: effect of increasing taps (order) other window side lobe level stop band attenuation main lobe width roll-off (slope) http://en.wikipedia.org/wiki/Window_function

11. FIR Filter Design windowing method: coefs=(ift of ideal response) * window Further methods (e.g. Parks-McClellan)

12. Digital Filter / IIR better resource utilization as in FIRs oscillations may occour→not recommended http://www.bores.com/courses/intro/iir/

13. Digital Filter/ CIC (C ascaded Integrator-Comb) mentioned as FIR filter, but it has a feedback part stable there is not multiplier: easy to realize http://www.us.design-reuse.com/articles/article10028.html

14. Decimation if the signal is in a limited narrow band, we can skip samples without losing information 0 +Fsa/2-Fsa/2 0+Fsb/2-Fsb/2 t 1/Fsa ignored samples t 1/Fsb limited band Fs=Fsa Fs=Fsb=Fsa/2

15. Decimation 0 +Fsa/2 0+Fsb/2-Fsb/2 0 +Fsa/2 stop band pass band -Fsa/2 CIC (lpf) Fs DEC Fs/DEC the decimation causes spectrum overlapping, therefore the decimation usually happens at the output of a low pass filter using Mth order CIC and M factor decimation (M=4)

16. Functional Block Diagram of DDCs

17. inout f0FsBB f0Fs f0 CIC DDC FIR The FIR filter is realized with several (1..16) multiplier → we can use more taps at larger decimation

18. Example inout CIC DEC=16 FIR TAPS=16 64MHz4MHz inout CIC DEC=32 FIR TAPS=32 64MHz2MHz Two different settings of the same DDC The decimation plays the similar role as down conversion in the analog techique

19. DDC FIR Filter Limits

20. ADC usually faster ADC -> worse SNR

21. quantization noise, SDFR 0Fs/2Fs Signal Spour 0Fs/2Fs SDFR baseband sampling: if the signal has a large and low frequency part, the overtones are in the used band IF sampling: the overtones can evade the used band, where filters can attenuate them http://www.beis.de/Elektronik/DeltaSigma/DeltaSigma.html

22. Advantages of Digital IF easy to reproduce thermal stability flexibility the output signal can be better as at BB sampling accurate IQ output

23. (analogue complex sampling) IF CH I ADC CH Q AAF IAMP I splitter AAF QAMP Q "sin""cos" 0+Fs/2 SignalAlias -Fs/2 0+Fs/2 Signal -Fs/2 0+Fs/2 SignalAlias -Fs/2 real sampling ideal complex sampling unbalanced complex sampling alias rejection It is possible sampling the IQ signal on baseband, and there are dual ADCs for IQ sampling applications, but these systems have finite rejection to the fs/2 alias because of the analogue gain and phase differences and crosstalk between the two analogue paths.

24. Digital Upconverters f0FsBB f0Fs 0 out in INT DUC DAC fFs

25. Interpolation inverse operation of decimation zero padding or repeating is applicable we have to use LPF to remove unwanted overtones

26. Functional Block Diagram of a DUC

27. Special Application: Bandpass Filter ADC CIC PFIR MIX CH1 CH2 CH3 FPGAFPGA GC5016/DDC CH0 CIC PFIR CH1 CH2 CH3 GC5016/DUC CH0 MIX DAC