PLL OSCILLATION CIRCUIT, POLAR TRANSMITTING CIRCUIT, AND COMMUNICATION DEVICE

摘要

Provided is a PLL oscillation circuit that can reduce the variability of modulation sensitivity of a VCO 101 and obtain a desired output amplitude quickly with high precision. An amplitude detector 103 detects an output amplitude of the VCO 101. An amplitude controller 105 controls a current value of a variable current source 109 so as to have an output amplitude of the VCO 101 detected by the amplitude detector 103 to be a desired amplitude. A LPF 108 is connected between the amplitude controller 105 and the variable current source 109. A switch 107 connects or disconnects the LPF 108 between the amplitude controller 105 and the variable current source 109. The amplitude controller 105 is connected to the variable current source 109 through either the LPF 108 or the switching switch 107.