| 摘要 |
PURPOSE:To reduce the current supply ability of an AGC voltage generating circuit while setting an AGC operation start level precisely, by controlling the extent of attenuation of the output signal of an amplifying transistor (TR) through a transistor (TR) and an impedance means. CONSTITUTION:According to a rise in AGC voltage, the collector-emitter saturation resistance rCS of a TRQ1 is reduced to attenuate a received signal to an RF amplification stage, thus performing AGC operation. A voltage drop across a resistance R1 by the base current of the TRQ1 is utilized starting approximately at the point the collector-emitter saturation resistance rCS reaches a minimum value according to a rise in the AGC voltage, thereby turning on a TRQ2. The collector of the TRQ2 is connected to the drain of an amplifying TRF1 through a capacitor C8 in terms of alternating current, so it operates in a saturation region. Therefore, the gain of the RF amplifier decreases as the collector-emitter saturation resistance rCS of the TRQ2 decreases, performing the AGC operation. |
