Search results
Results From The WOW.Com Content Network
In the bipolar transistor example, it is the ratio of the output current to the input current, both measured in amperes. In the case of other devices, the gain will have a value in SI units. Such is the case with the operational transconductance amplifier , which has an open-loop gain ( transconductance ) in siemens ( mhos ), because the gain ...
No physical current source is ideal. For example, no physical current source can operate when applied to an open circuit. There are two characteristics that define a current source in real life. One is its internal resistance and the other is its compliance voltage. The compliance voltage is the maximum voltage that the current source can ...
Current gain in the common emitter circuit is obtained from the base and the collector circuit currents. Because a very small change in base current produces a large change in collector current, the current gain (β) is always greater than unity for the common-emitter circuit, a typical value is about 50.
Another useful characteristic is the common-base current gain, α F. The common-base current gain is approximately the gain of current from emitter to collector in the forward-active region. This ratio usually has a value close to unity; between 0.980 and 0.998. It is less than unity due to recombination of charge carriers as they cross the ...
A Darlington pair behaves like a single transistor, meaning it has one base, collector, and emitter. It typically creates a high current gain (approximately the product of the gains of the two transistors, because their β values multiply together). A general relation between the compound current gain and the individual gains is given by:
For a typical current of 10 mA, g m ≈ 385 mS. The input impedance is the current gain (β) divided by the transconductance. The output (collector) conductance is determined by the Early voltage and is proportional to the collector current. For most transistors in linear operation it is well below 100 μS.
Large output resistance is a desirable attribute of a current source because favorable current division sends most of the current to the load. The current gain is very nearly unity as long as R S ≫ r E. An alternative analysis technique is based upon two-port networks. For example, in an application like this one where current is the output ...
For a current buffer, if the current is transferred unchanged (the current gain β i is 1), the amplifier is again a unity gain buffer; this time known as a current follower because the output current follows or tracks the input current. As an example, consider a Norton source (current I A, parallel resistance R A) driving a resistor load R L.