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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.
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.
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 ...
The transistor continuously monitors V diff and adjusts its emitter voltage to equal V in minus the mostly constant V BE (approximately one diode forward voltage drop) by passing the collector current through the emitter resistor R E. As a result, the output voltage follows the input voltage variations from V BE up to V +; hence the name ...
In bipolar transistors, as the junction temperature increases the V be drop (voltage drop from base to emitter) decreases. In the two previous circuits, a decrease in V be will cause an increase in voltage across the emitter resistor, which in turn will cause an increase in collector current drawn through the load. The end result is that the ...
Examples are imperfect voltage followers (emitter, source, cathode follower, etc.) and amplifiers with series negative feedback (emitter degeneration), whose input impedance is moderately increased. The op-amp non-inverting amplifier is a typical circuit with series negative feedback based on the Miller theorem, where the op-amp differential ...
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].
The current replication ratio may be altered by scaling the transistors, or by the insertion of degeneration resistors in series with the emitters, as was the case with the LH0002. To ensure correct mirroring, T1 and T2 (as well as the opposite pair T3 and T4) must be placed on the die in close proximity or, in case of discrete devices, mounted ...