Abstract
During the last two decades, new digital modu- lation systems have appeared in the audio broadcasting. Such broadcasting systems require new transmitters' con- cepts to enable the transmission of digitally modulated sig- nals. Moreover, the selected modulation schemes (e.g. or- thogonal frequency division multiplexing) require a high lin- earitypowerstage,whichtypicallyexhibitslowecienc ydue to high peak-to-average power ratio of the modulated signal. One of the promising transmitter concepts is the Kahn enve- lope elimination and restoration technique, where the origi- nal Cartesian in-phase and quadrature baseband signals are transformed to the envelope and phase signals. The main ad- vantageofthistechniqueisanabilitytoemploysuitabletypes of highly ecient amplitude modulation transmitters for en- velope amplification, while the phase modulated carrier is produced by an additional phase modulator. The substantial drawback of envelope elimination and restoration is non- ideal recombination of linearly distorted amplitude signal and phase modulated carrier at the output power stage. The aim of this paper is twofold. Firstly, to analyze the eect oftheenvelopeandphasesignalsbandwidthlimitationonthe modulated signal in-channel distortion and out-of-channel emission. Secondly, to present the performance results as a reference for transmitter designers to properly set the en- velope and phase paths to reach required in-channel signal quality and suppress out-of-channel products.
Highlights
New radio broadcasting standards operating in the LW, MW, and switching amplifier (SW) broadcasting bands, such as Digital Radio Mondiale (DRM) [1] and HD Radio [2], are mainly based on the orthogonal frequency division multiplexing (OFDM) modulation scheme
Utilizing the envelope elimination and restoration (EER) modulation method proposed by Kahn in 1952 [9], it is possible to design a switching transmitter convenient for digital broadcasting (e.g. DRM 30), which is still based on the pulse width modulation (PWM) technique applied to the transmitter envelope signal processing path
It can be concluded that the modulated signal out-of-band emissions are very much alike in the band up to the cut-off frequency, the spectrum regrowth is more sensitive to the phase path cut-off frequency at the frequencies greater or equal to the cut-off frequency
Summary
New radio broadcasting standards operating in the LW, MW, and SW broadcasting bands, such as Digital Radio Mondiale (DRM) [1] and HD Radio [2], are mainly based on the orthogonal frequency division multiplexing (OFDM) modulation scheme. The implementation of such new OFDM based schemes caused the new high-power transmitter designs to evolve during the past two decades. The amplitude (envelope) signal controls the power supply voltage of the phase signal power amplifier. As a switching mode power amplifier can be used in the power supply block as well, the overall transmitter efficiency achieves very good values
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