Heterodyna odbiornika cyfrowego DRM

• Autorzy: Chaciński H. , Jaros P.

Warianty tytułu

EN

Heterodyne of DRM digital receiver

• Konferencja: Urządzenia i systemy radioelektroniczne (UiSR) ; (2 ; 13-15.06.2007 ; Soczewka k. Płocka, Polska)
• Języki publikacji: PL

Abstrakty

PL

W pracy przedstawiono układ heterodyny odbiornika DRM (Digital Radio Mundiale) zrealizowany w technologii DDS (direct digital synthesis). W technologii DDS sygnał jest wytwarzany technikami cyfrowymi z próbek sygnału odczytywanego z pamięci. Zrealizowano układ heterodyny, wykorzystując scalony układ DDS typu AD9852 wspomagany mikrokontrolerem AVR. Opracowane i zainstalowane na komputerze PC oprogramowanie umożliwia przyjazne sterowanie pracą układu heterodyny. Oprogramowanie składa się z dwóch części: pierwsza część programu steruje transmisją danych i wizualizacją realizowanych nastaw na ekranie monitora komputerowego; drugą część oprogramowania stanowią procedury w asemblerze mikrokontrolera, odbierające dane konfiguracyjne z komputera PC i dokonujące zmian nastaw w układzie generatora zgodnie z preferencjami użytkownika. Zrealizowany układ generatora pracuje w zakresie częstotliwości od kilkudziesięciu kHz do 90 Mhz.

EN

Receiving DRM (Digital Radio Mundiale) digital radio signals impose different requirements on electrical parameters of single receiver blocks than when receiving analogue modulation signals. An example of significantly higher demand being made is a block of local generator called heterodyne. Direct digital synthesis (DDS) has been used in implementation of a digital receiver's heterodyne system. It consists of fixed-shape wave-forms and frequency stabilization by a reference source, most commonly quartz. Taking into consideration the way in which DDS works, one can say that the signal is not exactly generated, but rather computed by digital systems. The system carrying out the DDS digital frequency synthesis consists of digital phase generator (phase accumulator), function generator, digital/analogue converter, and low-pass filter on the output. Phase accumulator consists of a register and an adder. With each reference generator of the clock, the number stored in the B-bit register is increased by a certain constant N. If the register overflows, carry from the bit is ignored and counting starts over again. Such a situation occurs for every stroke of the clock. Samples read from memory are transmitted to the D/A converter and next the signal is filtered by a low-pass filter. Signal frequency depends on tact frequency, size of phase accumulator register and the number N, being a tunable word. Heterodyne system has been implemented using AD9852 type DDS integrated system by AVR microcontroller-aided. The software developed and installed on a PC enables user-friendly control over heterodyne system functioning. The software consists of two parts: the first part controls data transmission and visualization of implemented settings; the second part consists of procedures in microcontroller's assembler, taking configuration data from PC and making changes to settings of the generator system according to user’s preferences. The implemented generator system operates in the frequency range from tens of kHz to 90 MHz. The required frequency range for the operation of a heterodyne, for the purposes of implemented DRM receiver is significantly smaller: from 45.1 MHz to 75.l MHz. This paper contains the results of a study on the composition of harmonic in the signal being generated and the signal amplitude as a function of retune frequency. Advantages of generators with DDS synthesis are substantial. These are: large frequency resolution and ability to quickly change signal frequency, as well as short setting time. Frequency resolution depends on the size of phase accumulator and the frequency standard. Large resolution is easier to be obtained than in case of the PLL technique. A drawback of direct synthesis is the fact that these systems consume significant amount of power, which results from high switching of generator system's constituents. Stability of the DDS-type generator is very high and depends on stability of the reference generator. The possibility of using very stable atomic standards enables us to use these generators in specialist projects. In the DDS technology, the maximum frequency of signal being generated equals half the frequency of reference signal.

Słowa kluczowe

PL

nawigacja; akumulator; słowo przestrajające; heterodyna; Digital Radio Mundiale; DRM; direct digital synthesis; DDS

EN

navigation; DRM (Digital Radio Mundiale); DDS (direct digital synthesis); accumulator; tunable word; heterodyne

• Wydawca: Wojskowa Akademia Techniczna im. Jarosława Dąbrowskiego
• Czasopismo: Biuletyn Wojskowej Akademii Technicznej
• Rocznik: 2007
• Tom: Vol. 56, nr sp.2
• Strony: 49--55
• Opis fizyczny: Bibliogr. 4 poz., tab.

Twórcy

autor

Chaciński H.

autor

Jaros P.

• Politechnika Warszawska, Wydział Elektroniki i Nauk Informacyjnych, Instytut Radioelektroniki, 00-665 Warszawa, ul. Nowowiejska 15/19

Bibliografia

• [1] H. T. Nicholas, H. Samueli, An analysis of the output spectrum of direct digital frequency synthesizers in the presence of phase-accumulator truncation, in Proc. 41st Annual Frequency Control Symp., Ft. Monmouth, NJ, May 1987, USERACOM, 495-502.
• [2] A Technical Tutorial on Digital Signal Synthesis, Analog Device, Iinc. 1999.
• [3] Karta katalogowa: AD9852 CMOS 300 MSPS Complete DDS, Analog Devices, 2006.
• [4] P. Jaros, Heterodyna do zastosowania w odbiorniku radiofonii cyfrowej, praca dyplomowa, Politechnika Warszawska, 2006.