| 摘要 |
PURPOSE:To attain a voltage indicating the reception signal intensity and the tuning state in an AM broadcast receiver, by outputting a signal changed in response to an input signal level over the input level range before and after an AGC operating start point. CONSTITUTION:An AGC voltage increases with an increase in the input signal, a base potential of a Q12 is increased and when the potential is equal to a voltage applied to a terminal V5, a part of a current I2 flows to the Q12, the operating current of differential transistors Q9, Q10 is reduced, the gain of an IF amplifier section is lowered with applied IF-AGC. When the input signal further increases, the AGC voltage is gradually increased, the base potential of a Q7 is equal to that of a Q8, and then, when a part of a current I1 flows to the Q7, the operating current of a mixer stage is reduced, the conversion gain is lowered to become equal to the application of the mixer AGC. Thus, the signal intensity indicating circuit where the output is changed over the input signal level range before and after the operating level of AGC is obtained. |
