OPERATIONAL AMPLIFIER, ACTIVE FILTER EQUIPPED WITH IT, AND DATA TRANSMISSION SYSTEM

摘要

PROBLEM TO BE SOLVED: To provide an operational amplifier capable of relaxing limitation on a frequency band of an active filter usable depending on the band, and to provide the active filter and a data transmission system. SOLUTION: The operational amplifier comprises a common emitter differential amplifier circuit 11 including a first transistor Q11 and a second transistor Q12 having base terminals as a differential input and emitters connected commonly and delivering an output signal from the collector of the second transistor Q12, and an emitter earth amplification stage 12 being driven with the collector output from the common emitter differential amplifier circuit 11 wherein the emitter earth amplification stage 12 comprises a series circuit 121 of two capacitor elements C11 and C12 connected between the collector and base of a transistor Q15, and a resistor element R11 connected between the joint of the capacitor elements in the series circuit 121 and the ground potential. COPYRIGHT: (C)2005,JPO&NCIPI