V03 Carrier Effects in RF Semiconductor

In 1971 Dr. Ohsaki joined OKI Research Laboratory and engaged in R&D of very high speed wireless data transmission by 20GHz band amiming 500Mbps per CH, system data rate more than 8Gbps. In his research activity, he found two very important findings of carrier effects in FR semiconductor.

The first one is an invention of today's Hetero-Junction to generate high density free electrons at an interface of i-Ge (i-GaAs) and n-GaAs (n-GaP) of compound semiconductor crystals. By this structure, ultra high speed transistors of bipolar and FET are realized. So far wave guides were used in microwave systems with very large physical size and weight. Such microwave systems could be integrated on a tinny semiconducto chip by Hetero-Juction structure. RF Amp, LO, and Mixer were integrated on a GaAs chip of a few square mm. Today his invented structure is so widely used in cellular phone, TV, and satellite communication and many others.

The second one is minority carrier effect of PN junction when it is switched from forward to reverse and application to very high spped high power direct phase modulation. The minority carrier works as a variable resistance (not reactance), and hence orthogonal component of modulated microwave is dramatically decreased, and QPSK(Multi-PAM) modulation & de-modulation by low bit error rate is achieved. And PIN junction for more effective application of minority carriers was proposed. A special driving circuit for modulation was developed too. Before his invention, SBD or varactor diode were used, but power handling capability was very small and modulation loss was large, -2 to -3 dB. On the other hand, the loss by his method was less tahn -0.5 dB. Today his invention is still used in satellite communication and rader system.

Category:

Science & Technology

Tags:

• Dr.
• Ohsaki
• GaAs
• compound
• Hetero-Junction
• free
• electron
• minority
• carrier
• QPSK
• PAM
• resistance
• Cellular
• phone
• microwave
• MIC