Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04H—BROADCAST COMMUNICATION
  • H04H20/00—Arrangements for broadcast or for distribution combined with broadcast
  • H04H20/44—Arrangements characterised by circuits or components specially adapted for broadcast
  • H04H20/46—Arrangements characterised by circuits or components specially adapted for broadcast specially adapted for broadcast systems covered by groups H04H20/53-H04H20/95
  • H04H20/47—Arrangements characterised by circuits or components specially adapted for broadcast specially adapted for broadcast systems covered by groups H04H20/53-H04H20/95 specially adapted for stereophonic broadcast systems
  • H04H20/49—Arrangements characterised by circuits or components specially adapted for broadcast specially adapted for broadcast systems covered by groups H04H20/53-H04H20/95 specially adapted for stereophonic broadcast systems for AM stereophonic broadcast systems

Definitions

• the invention relates to the field of radio transmitters, which are being converted from analog amplitude modulation (AM) to digital modulation in the course of digitization.
• AM analog amplitude modulation
• the AM transmitters work internally in switching mode and therefore have up to a factor of 3 better efficiencies than linear transmitters, which are otherwise usually used for digital transmission, e.g. with DAB (Digital Audio Broadcasting) and DVB (Digital Video Broadcasting). This results in savings in operating costs.
• DAB Digital Audio Broadcasting
• DVB Digital Video Broadcasting
• the broadcasters are easier to convince to switch from analog to digital if there are no large investments in advance.
• the use of a non-linear AM transmitter for digital modulation requires a special mode of operation of the transmitter.
• the modulated digital signal is generated using two mutually orthogonal partial signals (I and Q).
• the I signal (“in phase”) is modulated onto a cosine oscillation with the frequency Ft (carrier frequency).
• the Q signal (“quadrature”) is modulated onto a sine wave of the same frequency Ft.
• the sum of both modulated vibrations results in the complex modulated data signal (cosine 0 - 180 degrees, sine -90 - +90 degrees).
• the modulated I / Q signal is shaped by filters so that it has exactly the prescribed curve shape with the desired bandwidth.
• the modulated I / Q signal must be converted in such a way that the two signals amplitude signal (A signal) and phase-modulated carrier signal (RF-P) are generated, which are suitable for correctly controlling the AM transmitter.
• the modulated I / Q signal with greater power is then again obtained at the output of the AM transmitter.
• the modulated I / Q signal corresponds to a Cartesian representation. This is converted into a polar representation with amplitude and phase.
• the amplitude signal (A signal) is thus obtained for controlling the AM transmitter at the audio input.
• a phase-modulated RF (RF-P signal) is generated from the phase signal (P signal) that initially arises.
• the RF-P signal can also advantageously be obtained directly via the P signal without the intermediate step. This gives you the signals necessary to control the AM transmitter:
• the A signal is fed into the modulator input (audio input) of the AM transmitter and the RF-P signal is used to control the transmitter according to HF.
• the two signals A & RF-P are multiplicatively combined in the transmitter output stage and form the high-frequency digital output signal.
• both the A signal and the RF-P signal receive far larger bandwidths than the digital signal initially had and should also have again at the transmitter output.
• Non-linear distortions are particularly problematic when multicarrier signals, e.g. B. OFDM signals (Orthogonal Frequency Division Multiplexing) to be transmitted.
• multicarrier signals e.g. B. OFDM signals (Orthogonal Frequency Division Multiplexing) to be transmitted.
• the amplitude signal of an AM transmitter operating in this nonlinear mode is limited in amplitude, nonlinear distortions arise which, on the one hand, lead to increased out-of-band radiation and, on the other hand, also cause in-band interference which, due to the mode of operation of the transmitter, can be considerably above the out-of-band radiation.
• the in-band interference reduces the available coverage area, since a signal that is already disturbed can tolerate less interference in the radio channel in order to reach a critical threshold at the receiver.
• the present invention describes a procedure and arrangement for digital transmission with conventional AM transmitters, with which undesired secondary emissions due to nonlinear distortions are largely avoided.
• Nonlinear distortion can be prevented if the transmitter's operating point is shifted so that a linear mode of operation is created.
• the transmitter output stage is controlled with the complex modulated data signal (I / Q signal), as is known from the digital systems DAB and DVB.
• the linear operation of the transmitter is advantageous with regard to the interference emissions. These have spectrally much larger gradients than in the nonlinear mode described above, so that the ITU spectrum mask can be maintained if the transmitter is well balanced. Only the efficiency of the transmitter is very low in linear operation and causes high electricity costs.
• the efficiency with linear operation of the AM transmitter is so bad because the full supply voltage is present at this stage even with a small modulation of the transmitter output stage and power is converted into heat due to the quiescent current of the transmitter output stage.
• An improved efficiency can be achieved in that the supply voltage is not made much larger than the current control of the output stage requires.
• the envelope of the complex modulated data signal is scanned by an amplitude detector (envelope rectifier or peak rectifier) and the supply voltage or anode voltage of the output stage is controlled by means of the modulator operating as a clocked power supply.
• an amplitude detector envelope rectifier or peak rectifier
• the time constant of the envelope detector must be such that an increase in the envelope curve can be followed immediately, so that there is no overdriving with the resulting distortions and interference emissions.
• the time constant for the drop can be chosen just as large as for the increase, since here no "listening impression” must be taken into account. The smaller fall time constant further increases the efficiency of the transmitter.
• PDM Pulse Duration Modulation
• PSM Pulse Step Modulation

Landscapes

• Engineering & Computer Science (AREA)
• Signal Processing (AREA)
• Transmitters (AREA)
• Bipolar Transistors (AREA)

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• 2001
  • 2001-05-30 DE DE10127571A patent/DE10127571A1/de not_active Withdrawn
• 2002
  • 2002-04-10 CN CNB028018788A patent/CN100391132C/zh not_active Expired - Lifetime
  • 2002-04-10 AU AU2002257556A patent/AU2002257556A1/en not_active Abandoned
  • 2002-04-10 US US10/343,356 patent/US7406131B2/en not_active Expired - Lifetime
  • 2002-04-10 AT AT02727296T patent/ATE450941T1/de active
  • 2002-04-10 ES ES02727296T patent/ES2337450T3/es not_active Expired - Lifetime
  • 2002-04-10 JP JP2003501100A patent/JP4164023B2/ja not_active Expired - Lifetime
  • 2002-04-10 EP EP02727296A patent/EP1413075B1/fr not_active Expired - Lifetime
  • 2002-04-10 WO PCT/DE2002/001314 patent/WO2002098028A2/fr active Application Filing
  • 2002-04-10 DE DE50214048T patent/DE50214048D1/de not_active Expired - Lifetime
• 2008
  • 2008-04-03 JP JP2008096812A patent/JP2008182766A/ja not_active Withdrawn

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