| 摘要 |
PURPOSE:To obtain a logarithmic amplifier circuit having an illumination detecting function to a temperature change, by separating the illumination light into signals of each color and giving the logarithmic compression and then the differential amplification those separated signals. CONSTITUTION:The illumination light is separated into each color by filters 17 and 18. These separated colors are supplied to a differential amplifier 32 via temperature compensation registers 27 and 28 after undergoing the photoelectric conversion by photodiodes 14 and 15 and then the logarithmic compression by logarithmic amplifier 23 and 24 respectively. Therefore a signal output is obtained at an output terminal 23 according to the ratio of signal quantity of each color. Here the output of amplifiers 23 and 24 are turned into differential outputs by the amplifier 32. Thus the reverse saturation current components of diodes 19 and 20 which affect the temperature characteritics of amplifiers 23 and 24 are offset. The temperature characteristics of resistors 27 and 28 are set at kT/q (k: Boltzman constant; T: absolute temperature; q: characteristics for offset of electron charge amount). In such a constitution, a logarithmic amplifier circuit can attain its desired purpose.
|
