Basic BJT Circuits

A bipolar junction transistor (BJT) is a three-terminal semiconductor electronic device, designed to serve, in its active mode, as a current-controlled current source. Physically, a BJT consists of two overlapping p–n junctions: Base–emitter and base–collector. Hence, there are two types of BJT transistors: NPN and PNP. Depending on its biasing, a BJT may inadvertently be in modes other than active mode, such as saturation and cutoff modes, which are useful for digital electronics applications. ADS DC simulation is a powerful tool to study the transistor’s modes and curves. Applications of active mode BJT transistors range from current driving and power amplification to small-signal linear voltage amplification. Another important ADS feature further developed in this chapter is equations, used as a post-processing tool for analyzing data display simulation results. A new simulation mode featured in this chapter is the harmonic balance simulation, used to assess, in a quantitative manner, distortion effects in linear amplifiers.