Radio communication system having current control circuit

摘要

In a radio communication system, a predetermined bias voltage is applied to the base of a transistor in a high-frequency amplifier circuit immediately before the transistor makes its normal operation. When a high-frequency input signal is received under a weak electric field, a control circuit generates a control voltage Cc of a high level so that the high-frequency amplifier circuit can operate with its large amplification factor. This control voltage is supplied to the base of the transistor through a diode and a resistor in a current control circuit to be added to the predetermined bias voltage to increase the base current so that the high-frequency amplifier circuit operates with a large amplification factor. On the other hand, when the input signal is received under a strong electric field, the control circuit supplies a control voltage of a low level to the base of the transistor so that the high-frequency amplifier circuit operates with a small amplification factor.