| 摘要 |
PURPOSE:To predetermine an arbitrary current value in a digital manner by a method wherein a plurality of current driving circuits are provided and their current values are made to conform to binary relations and a plurality of the current driving circuits are individually turned ON and OFF. CONSTITUTION:A light emitting device 1 converts a current into a light and current switching transistors 3a and 3b drive the light emitting device 1. (n) current driving transistors 41-4n are so provided as to have the sizes or current values of those transistors roughly conform to binary relations. Switches 91-9n are switches for turning ON and OFF current mirror transistors 71-7n respectively and a current value ID applied to the current switching transistors 3a and 3b, i.e., a current for driving the light emitting device 1, can be changed in a digital manner. For instance, if a current applied to the current driving transistor 41 is denoted by I, a current applied to the transistor 42 is 2I, a current applied to the transistor 43 is 4I and so on. The current value ID applied to the transistors 3a and 3b, therefore, can be predetermined by an arbotrary value. |
