PREAMPLIFIER

摘要

PROBLEM TO BE SOLVED: To prevent the band from decreasing even when the source voltage is lowered by providing a transistor(TR) whose emitter is grounded, whose collector is connected through a resistance to a power source and that has a voltage amplifying action and connecting a current source between the collector of the TR and the power source. SOLUTION: Even when the power source voltage Vcc is lowered, the collector current Ic of the TR Q2 can be set not to change by varying the current I1 of the current source I1. The band ft of the preamplifier is represented as ft=(Vcc-2Vbe+Rc1*I1)/(8π*Ci*Rf*kT/q). Therefore, the band ft can be prevented from decreasing by increasing resistance Rc1*I1 by the amount equivalent to the lowered amount of the source voltage Vcc without decreasing feedback resistance Rf1 or input capacity Ci including the parasitic capacity of an input part. Specially, when the current is set to satisfy Vcc-2Vbe<