| 摘要 |
PURPOSE:To avoid the occurrence of detection errors, by performing the sampling and detection corresponding to the period of background light. CONSTITUTION:When a first timing pulse is applied from a timing circuit 6a, a first switch 6b is turned On only for the width of said timing pulse. Based on this action, a first detecting circuit 6d performs the a sample and hold operation of a voltage corresponding to the level of the background light at this time. When the next timing pulse is generated by the timing circuit 6a after the specified time, a light beam irradiating means is started, and a second switch 6c is concurrently opened. As a result, the sample and hold operation of the voltage corresponding to the level of the sum of the background light and the signal light is performed by a second detecting circuit 6e. The outputs of the first and second detecting circuits 6d and 6e are compared in a comparing circuit 6f, and the signal light component is taken out. |
