| 摘要 |
PURPOSE:To design a circuit which causes no malfunction even in case PLL control is executed by using an output of an encoder, and a direction is discriminated from two outputs which are shifted by 90 degrees by constituting a titled circuit so that a duty ratio of an output of a sqaure wave is not varied beyond 50% even at a high temperature. CONSTITUTION:An optical output from a light emitting element 1 is intermitted by a slit plate 3 and its light quantity is varied like a triangular wave. When it is photodetected by photodetector 2, a photodetecting output of an approximate sine wave is obtained. In order to make it to a sqaure wave, it is necessary to determine a suitable threshold level and to compare it with the pohtodetecting output. In this case, a temperature compensating diode 5 is connected to a comparator 4. In case an ambient temperature rises and reaches 100 deg.C, the photodetecting output is reduced by 20%, but the forward voltage of the temperature compensating diode 5 by which the threshold level is determined is varied by about -2mv/ deg.C, therefore, it is reduced by 28%. The drop of the photodetecting output is offset relatively, and as for the output, it is possible to make the duty ratio to about 50%. |
