| 摘要 |
PURPOSE:To improve temp. characteristics, by a method wherein two diodes having different wavelength sensitivity characteristics and two kinds of transistors for applying logarithmic compression to the detection signals of said diodes are mounted and the number ratio of two transistors is adjusted to make the current densities of both of them almost same. CONSTITUTION:In a system utilizing the proportional relation between the logarithmic value of the shortcircuit current ratio ISC1/ISC2 of photodiodes PD-1, 2 and an incident light wavelength or color temp. value and the logarithmic characteristic of IC-VBE characteristics of plural transistors Q1, Q2, the output voltage V0' of an amplifier OP-3 is represented by formula (wherein q: electron charge, K: Boltzmann constant, T: absolute temp., M: parallel number of transistors). When circumferential temp. changes between -20-60 deg.C in a state detecting color temp. of 3,200 deg.K, output variation caused by the first item of the formula comes to zero when M is 4 and a temp. characteristic is improved. |
