LOGARITHMIC AMPLIFIER, SENSOR CELL OF AFORESAID LOGARITHMIC AMPLIFIER, AND METHOD FOR DETERMINING SIGNAL INTENSITY OF SIGNAL GENERATED BY AFORESAID LOGARITHMIC AMPLIFIER

摘要

PROBLEM TO BE SOLVED: To obtain a logarithmic amplifier which has low power consumption by making output current almost zero when a signal is not applied to a differential input of a detection cell. SOLUTION: A detector cell of a logarithmic amplifier has a pair of differential inputs and a pair of differential outputs to which an input signal V0 is applied and consists of transistors Q4 to Q6. A resistor RB is connected between the bases of adjacent transistors and forms a voltage divider of the signal V0 . The emitters of the three transistors are connected to a power supply and supplies current ID of a prescribed value. The collectors of the transistors Q4 and Q6 are connected and form a pair of differential inputs 71 and 73 together with the collector of the transistor Q5. An emitter area of the transistor Q5 is in proportion to emitter areas of the transistors Q4 and Q6 so that current I1 flowing through a 1st differential output may be equal to current I2 flowing through a 2nd differential output. A differential amplifier 70 compares the current I1 with the current I2 and generates output current Iout that is in proportion to the difference between the current I1 and I2 . A load resistor R1 and 38 is connected to an output of the differential amplifier and converts the current Iout into an output voltage signal VRSSI.