The ILD3/ ILQ3 are optically coupled isolated pairs employing GaAs infrared LEDs and silicon NPN phototransistors. Signal information, including a DC level, can be transmitted by the drive while maintaining a high degree of electrical isolation between input and output. The ILD3/ ILQ3 are especially designed for driving medium-speed logic and can be used to eliminate troublesome ground loop and noise problems. Also these couplers can be used to replace relays and transformers in many digital interface applications such as CTR modulation. The ILD3 has two isolated channels in a single DIP package and the ILQ3 has four isolated channels per package.