| 摘要 |
PURPOSE:To obtain a wide gain adjustment width, by making the characteristic of output current to the input signal into an operation characteristic nearly similar to DC to adjust the gain of the balanced mixer circuit by the receiving signal strength. CONSTITUTION:Transistors TRs Q6-Q11 constitute balanced mixer circuits respectively, and TRQ12 constitutes the constant-current source for these circuits. The constant-current value is determined by the base potential and resistance R2 and determines the gain of these circuits together with load impedance ZL consisting of capacitor C2 and coil L2. When the receiving signal is small, the automatic gain control signal applied to the base of TRQ4 is small, and these circuits have the gain determined by the constant-current value and impedance ZL. The receiving signal is applied to these circuits as it is. When the receiving signal becomes large and the automatic gain control signal becomes large, the gain of these circuits are lowered, and the input signal amplitude to circuits becomes narrow. When the input signal is larger furthermore, the input signal to these circuits becomes small. |
