| 摘要 |
PROBLEM TO BE SOLVED: To provide a signal amplifier circuit capable of preventing it from breaking by blocking the excessive broadcast signals. SOLUTION: A signal amplifier circuit 50 is constituted of: an amplifier 7 constituted by connecting amplifier devices 71 to 74 in four stages; a GC6 which adjusts the attenuation quantity of a transmission signal by using a control signal inputted to an adjustment control terminal 6a from a CPU and outputs the obtained transmission signal to the amplifier 7; and an RF switch 4a(4) which switches the transmission signal inputted to an input terminal 4a1 to one of a passing contact 4a2 which passes the transmission signal to the GC6 and a non-passing contact 4a3 which does not pass the transmission signal to the GC6 by using the control signal inputted to a switching control terminal 4c from the CPU. When the power is turned on or during the arbitrary initialization processing period of the signal amplifier circuit 50, a pull-down resistor 5d is connected with the adjustment control terminal 6a so that the attenuation quantity of the transmission signal to be outputted from the GC6 to the amplifier 7 becomes maximum, and a pull-down resistor 5c is connected with the switching control terminal 4c so that the RF switch 4a(4) is switched to the non-passing contact 4a3. COPYRIGHT: (C)2005,JPO&NCIPI
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