Compact class-AB follower for wideband closed loop line drivers

A wideband and compact class-AB follower is presented. A fast local feedback loop provides class-AB operation and decreases the output impedance even at high frequency, thus providing line driving capability. Both CMOS and BiCMOS versions in a 0.35 μm BiCMOS technology are discussed. The proposed follower bandwidth exceeds 1 GHz, with relatively low power consumption and it is suitable as output stage of closed loop amplifiers. The BiCMOS follower version has been integrated in a fully differential operational amplifier. According to simulations line driver THD is smaller than -70 dB when the input is a 0.5 Vpp sinusoid at frequencies below 10 MHz; and smaller than -50 dB THD at 100 MHz. Measurement results of a transimpedance amplifier (TIA) including the operational amplifier are presented as well.