| 摘要 |
<p>PURPOSE:To detect stably the existence of a magnetic tape by driving a photodiode by AC and using a detector as an AC coupled amplifier to attain detection. CONSTITUTION:The titled device is provided with a square wave oscillator 11 to be oscillated at 50% duty ratio, a buffer amplifier 12 executing switching operation to receive the output of the oscillator 11 and driving a photodiode 1 and a limiting resistor 2 limiting current in a half period of a period making current flow into the photodiode 1. In addition, a phototransistor 4 receiving an optical output from the photodiode 1 and converting the output into an electric signal, its load resistance 6, capacitor 13 coupling the output with AC, amplifier 14 with hysteresis, detector 15 detecting the existence of the signal of the output pulse string, and a controller 18 receiving the detected output 16 and various controllig inputs 17 supplied from other parts of the device and applying a control output 19 to other parts are also included in the device.</p> |
