7.7 Operating Point Selection

• We are often interested in amplifying time-varying signals.
• Because the amplifier turns off for input voltages less than VT, it is important to add an appropriate DC offset voltage to the time-varying input signal so that the amplifier remains in the saturation region for the entire range of input voltage variation.
• This input DC offset voltage defines the operating point of the amplifier.
• The DC offset must be chosen carefully, for if it is too large, the amplifier will be pushed into the triode region, and if it is too low, the amplifier will slide into the cutoff region.
• The input offset voltage is also called the input bias voltage or the input operating voltage
• The corresponding output voltage and the output current define the output operating point of the amplifier.
• Valid range for operating point under the saturation discipline: