| 摘要 |
PURPOSE:To vary the gain, by connecting in parallel two differential couples which have common load and different gain, forming an amplifying circuit by connecting these parallel connected differential couples in series with the third differential couple, and selecting one of the parallel connected differential couples by controlling the third differential couple. CONSTITUTION:Transistors 25, 28 form the first differential couple, transistors 26, 27 form the second differential couple, and the gain of the first and the second differential couples is different each other. The output ratio of the output terminals 3, 4, that is to say, the ratio of gain of the burst signal and the chroma signal is decided depending upon the ratio of resistors 34-37 of the emitter side of transistors 25-28. Moreover, the third differential couple consisting of transistors 29, 30 controls the first and the second differential couples by the burst gate signal 20, makes the second differential couple an operation status in case the signal 20 is non-signal, and makes the first differential couple an operation status when the signal is input. |
