Technology:
Mitsubishi Electric
developed an amplifier made of gallium nitride semiconductor for mobile phone base stations of the 2.14 GHz band. The new amplifier has a structure that gallium
nitride is formed on the silicon substrate, and the production cost is about
one thirtieth of that of the convention chip. It has an output of 170 W with
currently world’s highest power conversion efficiency of 70%. If it is put into
practical use, a unit complete with this amplifier and a power circuit will be
30% smaller than the existing unit. The company wishes to upgrade the new
amplifier to make it effective for the 2.5 GHz band in 2013.
The new
semiconductor sandwiches a buffer of a micrometer size between the silicon substrate
and the gallium nitride layer. Because silicon and gallium nitride have
different crystal structures, distortion is generated from the gallium nitride
layer. The company decreased the distortion that affects the performance of a
transistor and improved the performance by devising the higher harmonic wave
processing circuit. Two kinds of amplifiers exist. One is made of silicon
alone, and the other is made of either a silicon substrate or a silicon carbide
substrate with gallium nitride on it. An amplifier made entirely of silicone
has an output of 150 W with power conversion efficiency of 58%, while an
amplifier made of silicon substrate or a silicon carbide substrate with gallium
nitride on it has an output of 200 W with power conversion efficiency of 68%.
Because the latter is much higher in performance than the former, a technology
to produce the latter at a lower cost has been desired.
Mitsubishi Electric’s
newly-developed amplifier made of gallium nitride semiconductor 
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