| 摘要 |
PURPOSE:To suppress an event that an output is saturated by applying logarithmic compression to the input at an excess input. CONSTITUTION:The amplifier circuit is provided with a photodiode 12 converting an optical signal into an electric signal and an amplifier circuit 11 whose input terminal connects to the photodiode 12 and amplifying an optical current. A log diode 13 is connected in parallel with a feedback resistor Rf of the amplifier circuit 11 and the optical signal obtained at the photodiode 12 is linearly amplified up to a required level and the input signal is logarithmically compressed and then amplified at an excess input. Since only the feedback resistor Rf is active till the input voltage reaches a forward drop voltage of the log diode 13, the optical current is amplified linearly and when the voltage reaches the forward drop voltage, the optical current is logarithmically compressed and amplified. Thus, the optical signal is linearly amplified without effect of illuminance up to a signal level required for the photoelectric sensor and a saturated output is suppressed. |
