Transmitters for Digital Terrestrial TV Distribution A comparison of class A and class AB amplifiers

摘要

Within the European DVB Project, a specification on terrestrial DVB has been developed and will probably be fed into the European standardisation process during the second half of 1995. In this specification, a multi-carrier system for terrestrial DVB capable of supporting nation-wide single-frequency-networks (SFN), is described. Due to the various requirements, the system specifies a signal with several thousand carriers, each of which is QPSK, 16QAM or 64QAM modulated. Such a system requires an extremely high linearity of the transmitter amplifiers; this, however, is normally at the expense of high power consumption. Careful design and a sophisticated pre-correction circuitry can nevertheless give excellent results. Test results of transmitter systems for DVB based on tube amplifiers and transistor amplifiers will be presented. Measurement examples are also given for the DVB transmitters with different levels of output power. The level of intermodulation products and the spurious responses are given particular consideration. Examples of trade-offs between linearity and efficiency (i.e. output power / power consumption) are given.