
Principles of Analog Electronics
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13.1.2 Current Source
An ideal DC current source has an innite inner resistance (Section 4.5.3 in
Chapter 4). This is one of the reasons why the current source can be used in place
of a real emitter resistor since it satises the request of an equivalent high resis-
tance value. This resistance being an equivalent and not a real one, no power
dissipation problems arise. Furthermore, this DC source can provide the bias cur-
rent so that the Q-point can be correctly located in the middle of the BJT’s forward
active region. This current bias method (see “Observation” in Section 11.4.1.5 of
Chapter 11) is especia ...