Performance of a digital stereo FM modulator with reduced output resolution

Author

Twelves, Sue ; Kikkert, J.

Author_Institution

Dept. of Electr. & Comput. Eng., James Cook Univ. of North Queensland, Townsville, Qld., Australia

Volume

43

Issue

1

fYear

1997

fDate

3/1/1997 12:00:00 AM

Firstpage

104

Lastpage

113

Abstract

A digital stereo FM modulator has been built using a direct digital synthesiser (DDS). The system incorporates a digital stereo generator to provide the modulating signal. The stereo generator was sampled at 228 kHz and interpolation by 2 was carried out to move the unwanted FM sidebands further away from the FM carrier, in order to facilitate filtering. The paper presents the effects of quantisation noise on the system output by reduction in output resolution. Demodulation has been carried out so that the signal to noise and distortion ratios (SINAD) could be measured for all spectral components ⩽53 kHz with different monotone modulation frequencies and varying output resolution. An FM simulation of this process has been developed and the FM spectra produced by it are shown to match the experimental spectra almost exactly. These spectra complied with broadcast standards even with as little as a 6 bit output. The experimental system, with a 10 bit output, gives a SINAD performance which is ⩾77 dB

Keywords

Hi-Fi equipment; demodulation; digital audio broadcasting; direct digital synthesis; filtering theory; frequency modulation; interpolation; modulators; quantisation (signal); 10 bit; 228 kHz; 6 bit; FM carrier; FM sidebands; FM simulation; FM spectra; SINAD; broadcast standards; demodulation; digital stereo FM modulator; digital stereo generator; direct digital synthesiser; experimental spectra; experimental system; filtering; interpolation; modulating signal; monotone modulation frequencies; quantisation noise; reduced output resolution; signal to noise and distortion ratio; spectral components; system output; system performance; Demodulation; Digital modulation; Filtering; Frequency modulation; Interpolation; Noise reduction; Quantization; Signal generators; Signal resolution; Signal synthesis;

fLanguage

English

Journal_Title

Broadcasting, IEEE Transactions on

Publisher

ieee

ISSN

0018-9316

Type

jour

DOI

10.1109/11.566831

Filename

566831