| 摘要 |
PURPOSE:To prevent the deterioration of an open-loop gain by providing a band limit circuit in an open-loop circuit comprising 1st and 2nd subscribers, a quadrature modulator, a power amplifier, an attenuator and quadrature demodulator, demodulating the output of the power amplifier and feeding back it as the form of a base band signal. CONSTITUTION:A signal inputted from a terminal 101 is inputted to a subtractor 110 and a signal inputted from a terminal 102 is inputted to a subtractor 115.A part of the output of an amplifier 140 is atteneated by an atteneator 145 and inputted to the quadrature demodulator 135. The quadrature demodulator 135 receives the output of a sinusoidal wave generator 131 through a phase shifter 132, demodulates the output of the attenuator 145 to obtain the 1st and 2nd base band signals. The 1st and 2nd base band signals are inputted respectively to the subtractors 110 and 115. The phase change DELTAtheta of the phase shifter 132 is controlled so as to cancel the phase change by a delay DELTAtau from the output of the quadrature modulator 130 to the input of the quadrature demodulator 135. Thus, even if the transmission frequency is changed, the deterioration of the open-loop gain and the deterioration of the distortion improving characteristic are avoided.
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