PURPOSE:To simplify a circuit constitution, to reduce a power consumption, and to increase an emitter current in a low level. CONSTITUTION:When the base input of an emitter follower transistor Q3 is in the low level, the transistor Q1 of a differential gate is turned on, and the transistor Q2 of the differential gate is turned off. At that time, when the base input of the transistor Q1 is defined as V1E, the potential of a common emitter contact CE is defined as (V1E-VF). Therefore, the emitter voltage of a transistor Q4 is defined as (V1E-2VF), and then currents I4 passing through the transistor Q4 are defined as (V1E-2V1)/REF. On the other hand, when the transistor Q1 of the differential gate is turned off, and the transistor Q2 of the differential gate is turned on, the input of the emitter follower transistor Q3 is turned in a high level, and the potential VCE of the common emitter contact CE is defined as (VR-VF) for the transistor Q2 is turned on. Therefore, the currents I4 passing through the transistor Q4 are defined as (VR-2VF)/REF.
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