| 摘要 |
PURPOSE:To perform stably sound switch operation by applying A/D conversion while referencing a logarithmic table prepared in an ROM or an RAM of a CPU to expand the dynamic range of logarithmic transformation. CONSTITUTION:In obtaining the dynamic range of, e.g., 60dB, resistors R1, R2 are selected as values to obtain 30dB. In outputting 1dB from the CPU5 to a ladder resistor 14, when an output voltage of a detecting rectifier circuit 18 is 1V or over, an output of comparators 16, 17 goes to an H level, and when the output voltage is smaller than 1V, the output of the comparator 16 only goes to an L level. Thus, the output of the comparators 16, 17 is observed by the CPU15, a signal is subject to A/D conversion while the output of the circuit 18 and the output A of the ladder resistor 14 are compared by the comparator 16 when the level of a CH1 is larger, and a numeral 30 is added in the CPU15, allowing to expand the dynamic range to 60dB. |
