ELTI goes Green
Doherty Efficiency Benefit
doherty

Energy efficiency has »top-priority« nowadays everywhere.

Broadcast network operators run to reduce power consumption and increase overall efficiency is pushing us, solution providers, to new research and development activities.

As RF amplifiers are most attractive element for energy saving, today various approaches are available for efficiency improvement, but there are only few truly useful for implementation in broadcasting equipment. The one from those advanced technologies is based on an invention developed by W. H. Doherty back in 1936. His basic idea was to separate the amplification by using a main and peak amplifier. Peak amplifier is not operating until the main amplifier approaches its saturation point. Required headroom for main amplifier is very low and the reached efficiency with a Doherty amplifier can be between 12 to 14 % better than classic class A/B amplifier.

Further development of course bring some “sub-concepts”, ie. Three-way, Four-way Doherty but seems that Two-way Doherty illustrated seems to be the best compromise between minimizing the amplifier complexity and efficiency gain.

doherty_pic

Doherty Efficiency Benefits:

  • Easy for practical implementation and production,
  • Little additional costs for bigger energy savings during lifetime,
  • Known and proven concept from mobile-base stations,
  • Easy Digital pre-correction possible,

The key disadvantage of this concept is the limited operating bandwidth limitation that requires the VHF or UHF bands to be segmented, but this field is still subject of further development.

However this technology is actually a fact, since technology which application is already field-proven in mobile base stations become also a demand in DTT transmitter technology. The Doherty concept makes it “real” to improve the efficiency of a broadcast equipment with COFDM modulation from an average 20 % in the past to 38 % and thereby offering energy savings close to magical 50 %.