 However, because the relationship between input and output for a transistor is not linear across its full operating range, the transistor amplifier only approximates linear operation.For low distortion, the transistor must be biased so the output signal swing does not drive the transistor into a region of extremely nonlinear operation.For a bipolar junction transistor amplifier, this requirement means that the transistor must stay in the active mode, and avoid cut-off or saturation.