Method and arrangement for digital transmission using am emitters

• US 20030148743A1
• Filed: 01/29/2003
• Published: 08/07/2003
• Est. Priority Date: 05/30/2001
• Status: Active Grant

• Current Assignee: Deutsche Telekom AG
• Original Assignee: Deutsche Telekom AG
• Inventors: Rudolph, Dietmar
• Granted Patent: US 7,406,131 B2
• Time in Patent Office: Days
• US Class Current: 455/91
• CPC Class Codes: H04H 20/49 for AM stereophonic broadcast systems

Abstract

During digital transmission using existing non-linear AM emitters, spurious emissions occur as a result of the non-linear distortions, in turn causing inner band disturbances and also disturbing adjacent channels, as out-of-band radiation. Non-linear distortions are especially critical for digital multiple carrier signals (e.g., OFDM) which are recommended by the ITU with the DRM system for the AM area. In order to avoid the non-linear distortions, the end step of the AM emitter is operated in the linear mode, thus ensuring the ITU spectrum mask. The relatively low efficiency of the emitter during the linear operation can be improved by tracking the distribution voltage of the emitter end step according to the drive. To this end, the envelope of the complex modulated data signal is scanned, and said signal controls the distribution voltage for the emitter end step by means of the modulator operating as a switched-mode power supply unit.

Claims

1. A method for digital transmission using AM transmitters in which, due to the non-linear operating mode during digital transmission, non-linear distortions arise which result in inband interference and the out-of-band and spurious emissions,

wherein

the output stage of the AM transmitter is operated in the linear mode;

the linear mode is operated in conjunction with a correction of the supply voltage of the transmitter output stage as a function of the instantaneous drive in order to improve the efficiency;

the modulator of the AM transmitter operates as a switched-mode power supply unit and delivers the corrected supply voltage for the transmitter output stage;

the envelope of the complex modulated data signal is scanned, and this signal controls the correction of the supply voltage for the transmitter output stage;

the time constant during the scanning of the envelope is such that it is possible to immediately follow a rise in the envelope;

the time constant during the scanning of the envelope can be equal for the rise and decay of the envelope; and

the complex modulated data signal, subsequent to scanning its envelope, is delayed in such a manner that the correction of the supply voltage is effective in the meantime, thus preventing even short-duration overdrives of the transmitter output stage.

2. The method as recited in claim 1,

wherein the modulator operating as a switched-mode power supply unit can also be a pulse duration modulator or a pulse step modulator;

and

in the case of AM transmitters with class B push-pull modulators, a replacement with one of these modulators has to be carried out.

3. An arrangement for digital transmission using AM transmitters in which the transmitter output stage is operated in the linear mode to avoid non-linear distortions and whose supply voltage is corrected by the complex modulated data signal as a function of the drive in order to improve the efficiency,

wherein an amplitude detector (1) which scans the envelope of the complex modulated data signal is connected upstream of the modulator (5 and 6) operating as a switched-mode power supply unit;

and

a delay stage (2) for the complex modulated data signal is installed upstream of the high-frequency preamplifier stages (3) in the signal path to the transmitter output stage (4).