AUTOMATIC GAIN CONTROL LOOP AND GAIN CONTROL METHOD

PROBLEM TO BE SOLVED: To reduce the substrate area and the production cost by preparing a constitution such that plural signal processing units receive the signals from a variable gain amplifier and every signal processing unit produces a feedback control signal. SOLUTION: The output signals received through an antenna are supplied to a demodulator 82, via a mixer and demodulated there. For the case of QSPK, the demodulator 82 produces the in-phase and quadri-phase signals via two output terminals. The LPF 86 and 88 eliminate the high-frequency component signals which are inputted from the demodulator 82. Both the in-phase and quadri-phase signals are balanced with each other by the dual-mode variable gain attenuators 90, 96 and 104, so that the same amplitude and phase delay are secured between both signals. The output signals of the attenuators are converted into digital signals by A/D converters 124 to 134 and then supplied to the signal processing units 76, 78 and 80. The attenuators receive the feedback signals from the signal processing units and control the attenuation of these signals.