READ AMPLIFIER CIRCUIT AND SEMICONDUCTOR INTEGRATED CIRCUIT

PROBLEM TO BE SOLVED: To reduce the parasitic capacitance to be connected to each emitter and the noise caused by the base resistance of the transistors for a cascade connection by plurally dividing the cascade connected transistors and connecting a few transistors for a head bias to each emitter. SOLUTION: The collectors of five transistors are connected to the emitter of an upper stage cascade connection transistor Q1. The parasitic capacitance associated with the emitter of the transistor Q1 is 5×Cb and the parasitic capacitance associated with the emitters of lower stage cascade connection transistors Q11 to Q15 becomes 5×CA. Noises generated by the base resistances of the transistors Q1 and the transistors Q11 to Q15 are equal and set to Vn. If the sizes of the transistors Q11 to Q15 and head bias transistors Qb1 to Qb10 are the same and parasitic capacitances of the emitters are CA=Cb, the noise in the read amplifier is reduced to an approximately 1/2 value and the noise reduction effect is obtained at a higher frequency band.