Doherty Solid-State Power Amps for ATSC .0 & OFDM

SOUTHWICK, MASS.-Hitachi Kokusai Electric Comark LLC has a long standing history in the broadcast TV market. Comark started more than 40 years ago manufacturing RF components for UHF transmitters and branched out to design and deliver full TV transmission systems. Hitachi-Comark has been involved in many innovations that have revolutionized the market. It is the only transmitter manufacturer to win multiple technical Emmy awards including for the Klystrode tube transmitter and for Digital Modular Adaptive Precorrection (DAP).

Over the last 18-24 months Hitachi-Comark has been preparing for the upcoming FCC spectrum auction and UHF channel re-pack with a full portfolio of equipment and services. For DTV transmitters, Hitachi-Comark and its sister organization Hitachi Kokusai Linear have introduced two highly efficient Doherty solid state UHF transmitter designs; PARALLAX and E-Compact. These solid state technologies perfectly complement the company's market leading DCX Paragon MSDC-IOT transmitters.

So why is there an industry wide push towards Doherty? The answer is two-fold. First, Doherty amplifiers are more efficient than Class AB amplifiers. Doherty achieves higher efficiency by using LDMOS devices biased in both Class AB (carrier amp) and Class C (peaking amp). The Class AB device amplifies the average power level and the Class C device amplifies just the peaks of the digital waveform. Driving the Class AB device higher towards saturation improves efficiency; having the Class C complements the power amplifier with ample peak power capability to avoid signal compression and other non-linear distortions.

PA module from Hitachi Kokusai Electric Comark's Parallax transmitter

LINK:	http://www.tvtechnology.com/equipment/0005/doherty-solidstate-power-am...
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