| 摘要 |
<p>PURPOSE: To efficiently correct the parasitic capacitance characteristic of a photodetector such as a phototransistor by switching the impedance to a high impedance when a light emitting diode(LED) is on and switching it to a low impedance when the LED is off. CONSTITUTION: In order to minimize power while using a CMOS micro- processor, variable offset voltage 300 is inserted into the collector of the phototransistor 10. During the OFF time of the LED, parasitic capacitor BCbc can charge selective voltage of Vth -0.5 volt e.g. instead of applied voltage. The offset voltage 300 has two states to be turned to '0' in the on time of the LED and turned to offset in the OFF time of the LED. Since emitter voltage Ve is substantially started by optionally selected voltage, the higher threshold of the CMOS microprocessor can easily be corrected.</p> |
