| 摘要 |
PROBLEM TO BE SOLVED: To provide optimum power efficiency in accordance with transmission output voltage by compensating impedance to match it in accordance with transmission output power which is set. SOLUTION: A high frequency transmission signal outputted from a voltage control oscillator 1 is amplified by a transmission buffer amplifier 2 and is amplified to specified output power by a transmission power amplifier 3. The characteristic of the transmission power amplifier 3 is to shift the maximum point of a frequency characteristic curve against efficiency to a frequency low area by increasing capacity to an output side. When a transmission circuit outputs the power of 5w, an output power change-over switch 11 is connected to a bias voltage 13-side at the time of 5w and bias voltage for 5w time is supplied to the transmission power amplifier 3. Bias voltage for 5w time is supplied to a variable capacitive element 15. The variable capacitive element 15 shows fine capacity and it does not affect the frequency characteristic curve against efficiency. Thus, the curve shows a maximum value with a specified frequency. Consequently, transmission output power is switched and power efficiency is raised to a maximum.
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