A Low-Voltage High-Drive Differential Amplifier For ISDN Applications

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 Vpp 80 kHz signal into a load of 100 ohm and/or 300 pF with a THD of about 0.25 %. The circuit main feature is its PSRR which remain practically constant from de to several hundred kHz around - 75 dB for both positive and negative supplies with the common mode voltage generated ou chip. The step response at 1 % for the same loading conditions is less than 500 nsec for a step of + 1.5V and less than 1 ¿sec for a step of ++6V. By using relatively small devices at the output the amplifier occupies an area of only 1720 square mils in a 2.5 ¿m n-well CMOS technology.