| 摘要 |
PURPOSE:To more easily and surely transmit data by inserting a current value detecting circuit to a switching circuit and providing a comparing circuit and a control circuit and measuring the line DC current of the switching circuit only to calculate the AC transmission loss automatically and adjusting the transmission level most suitably. CONSTITUTION:The level adjusting circuit consists of a current value detecting circuit 8 inserted to the switching circuit, an A/D converter 9, the comparing circuit 10, and the control circuit 11. With respect to a cable used as a line 1, the AC transmission loss and the DC resistance are proportional to each other though there is a slight difference by the line diameter. Consequently, the AC transmission loss is estimated if the DC resistance value of the line is found. The DC current of the line 1 of the switching circuit is detected by the current value detecting circuit 8 and is converted to a digital value by the A/D converter 9 to calculate the AC transmission loss of the line by the comparing circuit 10, and a control signal is issued from a control circuit 11 so that this transmission loss is compensated, thus obtaining the simple level adjusting circuit which controls automatically the gain of a variable gain circuit 5. |
