| 摘要 |
PURPOSE:To control easily the wide-range setting of a gain in a digital value by using the photodetecting element of a photocoupler as the variable resistance part of a gain adjusting mechanism and controlling a supply current to its light emittng element to a specific value according to a digital control signal corresponding to a desired gain. CONSTITUTION:An input voltage Vf is inputted from an A/D converter 3 to a voltage- current converte 4; when the scale of its output voltage is 0-Vfs and its input is in n-bit binary form, a quantization value Df corresponding to digital data required to obtain the voltage Vf is Vf(Vfs/2n)<-1>. The digital data corresponding to the quantization value Df is written in respective address of a read-only memory 2 which uses digital value of each desired gain G as an address signal. Then, when a digital value corresponding to the desired gain G is inputted as a digital control signal to the read-only memory 2, the output of the desired gain G is obtained from output terminal OUT. Namely, the Rf (resistance value) of the photodetecting element (photoconductive element) of the photocoupler 5 corresponding to each gain G is found and then the input voltage Vf to the voltage-current converter 4 by which a resistance value Rf is to be obtained by actual measurement is found, obtaining the quantization value Df corresponding to data to be written in the read-only memory 2. |
