A low-power class-AB BiCMOS opamp using `pseudo-pnp´ transistors

A low-power Class AB BiCMOS operational amplifier is discussed. Low power is achieved through Class-AB architecture, as well as through a structure called pseudo-PNP. The pseudo-PNP structure, along with an appropriate level-shifting arrangement, has the advantages of high transconductance per unit of bias current and zero input bias current as compared to either a PMOS or a lateral-PNP transistor. The application, advantages and tradeoffs of this structure as input devices and current-mirrors, are explained. A Class-AB operational amplifier using pseudo-PNP is proposed. For 0.8-μm BiCMOS technology, this shows a gain of 73.8 dB, a unity gain bandwidth of 49 MHz, and a settling time of 98 ns for a 2.5 V step at a quiescent power of 12 mW