The present invention relates to a semiconductor integrated circuit device, and to a technique suitable for use in an SCFL circuit comprised of GaAs FETs, for example.
A differential amplifier circuit called an SCFL (Source Coupled FET logic) circuit (hereinafter called merely "SCFL circuit") inclusive of both analog and digital circuits is widely used in a semiconductor integrated circuit device for light transmission, which is used with GaAs FETs (GaAs Field-Effect-Transistors and hereinafter called merely "GaAs FETs"). FIG. 2 basically shows the configuration of the SCFL circuit.
The SCFL circuit comprises a differential amplifier section and a source follower section. As shown in FIG. 2, the conventional source follower section is constructed in the form of two FETs per stage, i.e., comprises FETs Q21, Q22, Q23 and Q24 supplied with a signal from the differential amplifier section and FETs Q25, Q26, Q27 and Q28 for constant current, all of which are different in gate length from each other. Such an SCFL circuit has been disclosed in Japanese Patent Application Laid-Open Publication No. 62-188280, for example.