| 摘要 |
PURPOSE:To eliminate defects due to the dispersion of characteristics of a differential amplifier, by increasing the width of change of a control voltage of the differential amplifier near zero sound volume (vicinity of maximum value of control voltage). CONSTITUTION:In response to the selecting operation of a sound volume up key 1 or a sound volume down key 2, a key decoder 3 gives an output to a control circuit 10, calls out a counter data memory 9 and outputs count number information of a counter 5 to the control circuit 10. The control circuit responds a sound volume up or down signal and activates one-up/down circuit 4 or a 16-up/ down circuit 11 according to the count number information. That is, for the up signal, when the information count number is 0, the 16-up/down circuit 11 is activated, when the information count is >=16 and less than the maximum value, the 1-up/down circuit 4 is activated. For the down signal, when the information count number is 16, the 16-up/down circuit 11 is activated and when the count number is >=17, the 1-up/down circuit 4 is activated. |
