| 摘要 |
PURPOSE:To realize a miniature and low-cost automatic gain control circuit with enhanced reliability by dividing the pilot level signal of the feedback circuit via the resistance varying proportionally to the feedback circuit resistance and thus obtaining the monitor output. CONSTITUTION:When the input pilot signal has the level fluctuation, the pilot signal is separated into the output use and the detector circuit use through hybrid circuit H. And only the pilot signal is extracted from the signal for the detector circuit use through BPF and is made to pass through detector circuit DET in order to vary level adjusting resistance ADJ1. Thus, an automatic gain control is carried out. Input voltage VIN changes to VIN' (=kVIN), and output voltage VB of BPF changes to VB'(=VB-DV). And in this instant, resistance R1 of ADJ1 changes to R1'. As a result, Eq. (1) is satisfied. While the input voltage changes from VIN to VIN', and the resistance value of level adjusting variable resistance ADJ2 (featuring the same contents as ADJ1) changes from R4 to R4' (=R1'). Furthermore, the monitor output voltage changes from VM to VM'. In this case, Eq. (2) is obtained. According to Eq. (2), it is known that voltage VM' reproduces the change of VIN without imparing the linearity. |
