A FULLY DIFFERENTIAL CMOS LINE DRIVER FOR ISDN

A CMOS differential buffer amplifier for ISDN applications is reported. The chip operates from a single 5-V power supply and can deliver a 6-V 80-kHz signal into a load of 100 Ω and/or 300 pF with a THD of about 0.25%. The amplifier's main feature is its PSRR, which remains practically constant at - 75 dB from dc to several hundred kilohertz for both positive and negative supplies with the common-mode voltage generated on chip. In an inverting configuration with a gain of 1.5. the 1% setting time for step input is less than 500 ns for a step of 1.5 V and less than 1 μs for a set of 6 V (for both cases, the output load is 100 f2 and 300 pF). By using relatively small devices for the output stage, the amplifier occupies an area of only 1400 mil2 in a 2-μm double-poly single-metal n-well CMOS technology. 0018-9200/90/0400-0546$01.00 © 1990 IEEE