D/A CONVERTER AND SEMICONDUCTOR INTEGRATED CIRCUIT USING THE SAME

摘要

In a current-driven D/A converter, a 1-LSB current source (1) and a 2-LSB current source (2) are current sources of binary codes each weighted by 1/2, and a 4-LSB current source (3) is one of a multiple number of current sources each having the same structure of a thermometer code design. Each of first circuits (A1,A2,A4) of the respective current sources (1,2,3), which decides a constant current value, comprises a cascode connection of MOS transistors, where L = L3 and W = W3, having a common gate terminal. Each of second circuits (B1,B2,B4) of the respective current sources (1,2,3), which establishes a high output impedance, comprises a cascode connection of MOS transistors, where L = L4 and W = W4, having a common gate terminal, and is cascade-connected to a respective one of the first circuits (A1,A2,A4). Therefore, the structure area can be further reduced, while the current characteristics of the current sources can be further uniformed so that the linearity of D/A conversion characteristic can be improved.