| 摘要 |
PROBLEM TO BE SOLVED: To provide a variable gain amplifier with a large variable gain range, less distortion, and less noises. SOLUTION: A gm variable differential amplifier 104 to execute the control of the gain by a bias current is used as a unit amplifier (VGA)102 constituting the variable gain amplifier 100. A large variable gain range can be obtained by connecting a plurality of stages of the gm variable differential amplifiers in series. Signals are attenuated by providing an attenuator 101 at least on the input side of the initial stage VGA1. By this, it prevents amplitude distortion from occurring in each VGA. A capacitance voltage dividing attenuator 101 which does not generate noises is used as an attenuator in order to reduce noises. A fixed gain amplifier 103 is provided at the final stage in order to obtain the desired whole gain if required in the variable gain amplifier 100. If the variable gain amplifier is used for the variable gain amplifier for controlling transmission output of a Polar loop transmitter, an excellent transmission output control function can be realized without causing large degradation of distortion characteristics and noise characteristics. COPYRIGHT: (C)2004,JPO
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