| 摘要 |
PROBLEM TO BE SOLVED: To provide an RF output power amplifier (PA) of a cellular telephone with an increased average power efficiency.SOLUTION: The PA 8 includes first and second Class AB amplifier circuits 109, 110. If the cellular telephone is to operate in a high power operating mode, then the first amplifier 109 drives a PA output terminal. Power transistors in the first amplifier are biased by Vbias2 so as to optimize efficiency and linearity at high output power. If the cellular telephone is to operate in a low power operating mode, then the second amplifier 110 drives the output terminal. Power transistors in the second amplifier are biased by Vbias3, 4 so as to optimize efficiency and linearity at low output power. By sizing the power transistors in the amplifiers appropriately, emitter current densities are maintained substantially equal so that PA power gain is the same in the two operating modes. |
