| 摘要 |
PURPOSE:To prevent malfunction such as abnormal oscillation by retarding the leading of operation of a high frequency power amplifier after application of a transmission power switch more than the operating leading time of an antenna switch for switching transmission/reception in the high frequency power amplifier. CONSTITUTION:The control circuit is so devised that a signal is inputted to a large power amplifier section 4 of the high frequency power amplifier with a delay over 10-15ms from the operating lead time of a coaxial relay. For example, an electrolytic capacitor 16 is placed between a reference voltage input section of a comparator and ground so as to retard the leading time of a reference voltage. The delay time in this case depends on a resistor 19 and a capacitance of the electrolytic capacitor 16 when a reference voltage circuit 18 is formed as shown in Fig. Although the electric charge in the electrolytic capacitor 16 is not discharged quickly depending on the constitution of a reference voltage circuit and the effect of delay might not be enhanced, when the circuit is constituted effectively, this method is very effective for the protection of the high frequency transistors with the simple circuit constitution. |
