US Patent 7899335 Optical transmitter circuit

A light emitting element driving differential switch (2) includes first and second transistors (M1, M2). A third transistor (M3) is connected as an auxiliary switch in parallel to the first transistor (M1) whose drain is connected to a light emitting element (1). A third switch driving signal (IN3) is input to the third transistor (M3) to turn ON the third transistor (M3) at a slightly earlier point in time than when complementary switch driving signals (IN1, IN2) are input to the first and second transistors (M1, M2) to drive the first and second transistors (M1, M2). This improves the rising characteristics of the output from the light emitting element having a high power level.