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Figure 1: Basic NPN common collector circuit (neglecting biasing details).. In electronics, a common collector amplifier (also known as an emitter follower) is one of three basic single-stage bipolar junction transistor (BJT) amplifier topologies, typically used as a voltage buffer.
Figure 2: Small-signal model for calculating various parameters; Thévenin voltage source as signal. For the case when the common-base circuit is used as a voltage amplifier, the circuit is shown in Figure 2. The output resistance is large, at least R C || r O, the value which arises with low source impedance (R S ≪ r E).
Figure 2: Adding an emitter resistor decreases gain, but increases linearity and stability. Common-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. The gain is a strong function of both temperature and bias current, and so the actual gain is somewhat ...
Full hybrid-pi model. The full model introduces the virtual terminal, B′, so that the base spreading resistance, r bb, (the bulk resistance between the base contact and the active region of the base under the emitter) and r b′e (representing the base current required to make up for recombination of minority carriers in the base region) can be represented separately.
[1] [2] [3] The Widlar circuit may be used with bipolar transistors, MOS transistors, and even vacuum tubes. An example application is the 741 operational amplifier, [4] and Widlar used the circuit as a part in many designs. [5] This circuit is named after its inventor, Bob Widlar, and was patented in 1967. [6] [7]
Both types of BJT function by letting a small current input to the base control an amplified output from the collector. The result is that the BJT makes a good switch that is controlled by its base input. The BJT also makes a good amplifier, since it can multiply a weak input signal to about 100 times its original strength.
A translinear circuit is a circuit that carries out its function using the translinear principle. These are current-mode circuits that can be made using transistors that obey an exponential current-voltage characteristic—this includes bipolar junction transistors (BJTs) and CMOS transistors in weak inversion.
Darlington Transistor (NPN-type) In electronics, a Darlington configuration (commonly called as a Darlington pair) is a circuit consisting of two bipolar transistors with the emitter of one transistor connected to the base of the other, such that the current amplified by the first transistor is amplified further by the second one. [1]