High-precision MOS current mirror

Matching accuracies of current mirrors using SIMOX technology are discussed. The variation in matching errors has been both qualitatively and quantitatively analysed for MOS current mirrors. Matching errors at low operating currents are dominated by variations in threshold voltage and are inversely proportional to the drain current. In high-current operations, however, they are not dependent on drain current and are dominated by variations in channel length and width. Using 10 ¿m-channel-length devices, matching error less than 0.6% with 100 ¿A drain current is obtained without any compensation circuits. MOS current mirrors have been found to present greater advantages for low-current operation, such as higher matching accuracy and a smaller pattern area than similar bipolar current mirrors.