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Diagram from Widlar's original patent. A Widlar current source is a modification of the basic two-transistor current mirror that incorporates an emitter degeneration resistor for only the output transistor, enabling the current source to generate low currents using only moderate resistor values.
A typical example of the use of a common-emitter amplifier is shown in Figure 3. Figure 3: Single-ended npn common-emitter amplifier with emitter degeneration. The AC-coupled circuit acts as a level-shifter amplifier. Here, the base–emitter voltage drop is assumed to be 0.65 volts.
The narrowing of the collector does not have a significant effect as the collector is much longer than the base. The emitter–base junction is unchanged because the emitter–base voltage is the same. Base-narrowing has two consequences that affect the current: There is a lesser chance for recombination within the "smaller" base region.
If Q 1 and Q 2 are matched, that is, have substantially the same device properties, and if the mirror output voltage is chosen so the collector-base voltage of Q 2 is also zero, then the V BE-value set by Q 1 results in an emitter current in the matched Q 2 that is the same as the emitter current in Q 1 [citation needed].
As a result, the common emitter resistor R E acts nearly as a current source. The output voltages at the collector load resistors R C1 and R C3 are shifted and buffered to the inverting and non-inverting outputs by the emitter followers T4 and T5 (shaded blue). The output emitter resistors R E4 and R E5 do not exist in all versions of ECL. In ...
In a circuit with a three terminal device, such as a transistor, the current–voltage curve of the collector-emitter current depends on the base current. This is depicted on graphs by a series of (I C –V CE) curves at different base currents. A load line drawn on this graph shows how the base current will affect the operating point of the ...
Using the Smith chart, the normalised impedance may be obtained with appreciable accuracy by plotting the point representing the reflection coefficient treating the Smith chart as a polar diagram and then reading its value directly using the characteristic Smith chart scaling. This technique is a graphical alternative to substituting the values ...
The Wilson current mirror achieves the high output impedance of equation (6) by negative feedback rather than by emitter degeneration as cascoded mirrors or sources with resistor degeneration do. The node impedance of the only internal node of the mirror, the node at the emitter of Q 3 and the collector of Q 2, is quite low. [3]