A HIGH-LINEARITY 50-OMEGA CMOS DIFFERENTIAL DRIVER FOR ISDN APPLICATIONS

A CMOS differential line-driver amplifier that uses positive feedback in the input stage to give transconductance multiplication and pole-zero doublet insertion is reported. The gain-bandwidth product at 60 kHz is 30 MHz and the unity-gain frequency is 2.7 MHz. The circuit operates from a single 5-V power supply and can achieve a total harmonic distortion (THD) of -78 dB for a 6-V(pp) differential output signal at 40 kHz and for a load of 100-OMEGA and/or 150 pF. For the same measuring condition but with a load of 50-OMEGA and/or 150 pF, the THD is -73 dB. A power supply rejection of more than 76 dB up to 150 kHz is obtained. The chip occupies an area of 1200 mil2 in a 1.5-mu-m CMOS technology and dissipates 20 mW.