| 摘要 |
PURPOSE:To attain excellent power efficiency by constituting the power amplifier that a single operation where output current is applied from a low voltage power supply and a cascode operation where the current is applied from a high voltage power supply are changed over depending on the signal power. CONSTITUTION:When a signal power is small, a load current flows from the 2nd power supply 23 having a low voltage via the 2nd power TR28 and when the signal power is increased, the load current flows from the 1st power supply 13 having a high voltage via the 1st power TR18 and the 2nd power TR28 being in saturated state. Thus, the power efficiency is kept excellent over a wide dynamic range of the signal power. Thus, a small heat sink is enough and power TRs with less collector loss is enough for the application because the power TRs are operated in cascode at a large output current. |
