| 摘要 |
PURPOSE: An output limiting circuit in a radio system is provided to minimize a delay while maintaining each circuit characteristic by constructing one circuit for an automatic gain control circuit and a level control circuit by using an automatic gain control loop which operates the automatic gain control before limiting an output signal level and operates the automatic level control circuit to limit the output signal level. CONSTITUTION: An automatic gain control unit(310) includes an input terminal coupler(C1), the first voltage variable attenuator(311), a power amplifier(312), the first diode(313), the first subtracter(314), the second diode(315), the second voltage variable attenuator(316) and an output terminal coupler(C2). The first diode(313) receives a signal coupled by the input terminal coupler(C1) and generates Vdet1, a DC voltage. The second diode(315) receives a signal coupled by the output terminal coupler(C2) and generates Vdt2, a DC voltage. The first subtracter(314) applies a difference Vout1 between the Vdt1 and Vdet2 to the first voltage variable attenuator(311). The first voltage variable attenuator(311) receives the Vout1, changes an insertion loss value and maintains a gain of an RF system containing the power amplifier(312) to be constant by repeating the closed loop. The second voltage variable attenuator(316) is to have a constant insertion loss value, and this is possible if the Vout2 voltage value is constant. An automatic level control unit(320) includes the third diode(321), the second subtracter(322), the fourth diode(323) and an integrator(324). An operation time point of the automatic level control unit(320) is determined by the fixed voltage of Vref1, and the minimum voltage is generated which is determined by Vref2 of the minimum voltage fixing circuit before the level controlling operation time point.
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