a common base amplifier) between the transistor's collector and the load. Using a cascode configuration, which inserts a low input impedance current buffer (e.g.This impedance R E of the signal source connected to the base (e.g., by using an emitter follower or some other voltage follower). This refers to the addition of a small resistor between the emitter and the common signal source (e.g., the ground reference or a power supply rail). One common way of alleviating these issues is with emitter degeneration. Other problems associated with the circuit are the low input dynamic range imposed by the small-signal limit there is high distortion if this limit is exceeded and the transistor ceases to behave like its small-signal model. Stability is another problem associated with such high-gain circuits due to any unintentional positive feedback that may be present. The gain is a strong function of both temperature and bias current, and so the actual gain is somewhat unpredictable. Figure 2: Adding an emitter resistor decreases gain, but increases linearity and stabilityĬommon-emitter amplifiers give the amplifier an inverted output and can have a very high gain that may vary widely from one transistor to the next.

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