CASCODE TYPE SEPP OUTPUT CIRCUIT

PURPOSE:To prevent the unstable operation of oscillation or the like, by connecting a capacitor, where the impedance in the high frequency band is low, between respective collectors of the first and the second NPN and PNP transistors which are connected in series. CONSTITUTION:A capacitor C where the impedance in the high frequency band is low is connected between respective collectors of the first and the second NPN and PNP transistors (TR) Q1 and Q2 in a cascode type SEPP output circuit. When a large input signal is supplied, one of TRs Q3 and Q4 becomes the saturation state but the other is operated in the linear operation region. Collectors of TRs Q1 and Q2 are connected to emitters of TRs Q3 and Q4, which are operated in the linear operation region, directly or through the capacitor C. Consequently, collectors of TRs Q1 and Q2 are always grounded in AC, and oscillation or the like is prevented even for the large input.