| 摘要 |
PURPOSE:To prevent the carrier leakage of a balanced modulation circuit by providing a switch means to a clamp circuit, producing the same voltage drop as the forward voltage drop when a switching element is turned on so as to input a reference voltage to the balanced modulation circuit. CONSTITUTION:When a clamp pulse VCP given to a terminal 4 is at L level, a switching transistor (Tr) Q21 of the clamp circuit 1 is turned on and a current I3 flows to a resistor R1. In this case, a voltage difference between the reference voltage Vr of a reference voltage point 18 and a collector-emitter voltage VCE of the TrQ21 is converted by Trs Q26, Q6 and outputted at a terminal 6. A switch circuit 30 provided to the circuit 1 consists of a Tr Q30 having the equal characteristic as the Tr Q21 and resistors R31, R30 equal to resistors R1, R21 and one terminal of the resistor R31 is connected to a ground Vg, then a current I4 flowing to the resistor R31 is equal to a current I3, the voltage difference between the voltage Vr and the VCE of the TrQ30 is converted by Trs Q24, Q8, and an output voltage to the terminal 5 is equal to the voltage at the terminal 6. Thus, the supply voltage to the balanced modulation circuit 2 is equal and carrier leakage is prevented. |
