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Conversely, a current source provides a constant current, as long as the impedance of the load is sufficiently lower than the current source's parallel impedance (which is preferably very high and ideally infinite). In the case of transistor current sources, impedances of a few megohms (at low frequencies) are typical. Because power is current ...
It can also be used to model a more realistic current source (since ideal current sources do not exist). The circuit topology covered here is one that appears in many monolithic ICs. It is a Widlar mirror without an emitter degeneration resistor in the follower (output) transistor. This topology can only be done in an IC, as the matching has to ...
Current mode logic (CML), or source-coupled logic (SCL), is a digital design style used both for logic gates and for board-level digital signaling of digital data.. The basic principle of CML is that current from a constant current generator is steered between two alternate paths depending on whether a logic zero or logic one is being represented.
The "long-tail" current source (R E) sets the total current flowing through the two legs of the pair. The input voltage controls the current flowing through the transistors by sharing it between the two legs, steering it all to one side when not near the switching point.
This is the only first order source of mismatch in the three-transistor Wilson current mirror [8] Second, at high currents the current gain, β, of transistors decreases and the relation of collector current to base-emitter voltage deviates from = (). The severity of these effects depends on the collector voltage.
The use of electronic constant current sources and large-area, sustained-beta output transistors delays the onset of clipping, but does not change the pattern. An increase in idle currents allows a proportional increase in current handling, [ 18 ] however, high idle currents invariably increase power consumption and heatsinking requirements.
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. [1] [2] [3]
During the Off-state, the current in this equation is the load current. In the On-state the current is the difference between the switch current (or source current) and the load current. The duration of time (dT) is defined by the duty cycle and by the switching frequency. For the on-state: = =
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