| 摘要 |
PURPOSE:To perform high-precision control with a small-sized device by setting variably the reference voltage of an A/D converter, which is provided in the preceding stage of a balanced modulator, with a voltage varying means to control the modulated wave output level of the balanced modulator. CONSTITUTION:Two systems of amplitude frequency information are outputted from an ROM21 on the basis of transmission data supplied from an input terminal 20. These two systems of outputs are converted by D/A converters 22 and 23 to obtain signals I and Q. Magnitudes of signals I and Q are controlled by the variable reference voltage outputted from a reference voltage generating circuit 27. An orthogonal modulating circuit 24 multiplies a carrier wave from a carrier input terminal 30 and the signal I in a multiplier 28 and multiplies a carrier wave, which is obtained by shifting said carrier wave in phase by 90 deg. in a phase shifter 31, and the signal Q in a multiplier 29 and outputs multiplication results. Outputs of the orthogoanl modulating circuit 24 are added by an adder 25 to drive a transmission output amplifier 26. Thus, the reference voltage is varied in the small-sized device to perform high-precision output control of a good frequency characteristic.
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