| 摘要 |
PURPOSE:To obtain a photometric apparatus which can measure the low luminance by logarithmically compressing/converting photo currents obtained by a photoelectric converting element and accumulating the currents in a capacitor. CONSTITUTION:When a MOS transistor Q1 is driven in an area where a sub threshold current flows, a photo current IP output from a photodiode (photoelectric conversion element) P1 becomes a logarithmically compressed current and accumulated in a capacitor C1. The load of the capacitor C1 is reset by a transistor Q4. A transistor Q3 performs the integral control of the capacitor C1. Accordingly, an integrated value of the photo current IP is logarithmically compressed to be a voltage VO at a connecting point between a source of a transistor Q2 and the capacitor C1. The dynamic range is made wide because of the logarithmic compression. Moreover, since the voltage accumulated in the capacitor C1 or photometric value is calculated, it becomes possible to measure the low luminance. A narrow spot can be measured with good accuracy. |
