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An ideal current source generates a current that is independent of the voltage changes across it. An ideal current source is a mathematical model, which real devices can approach very closely. If the current through an ideal current source can be specified independently of any other variable in a circuit, it is called an independent current source.
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.
A resistor (with the current simply proportional to the voltage) would be better, and a current source (with the current fixed, independent of voltage) better yet. A depletion-mode device with gate tied to the opposite supply rail is a much better load than an enhancement-mode device, acting somewhere between a resistor and a current source.
There are three main specifications that characterize a current mirror. The first is the transfer ratio (in the case of a current amplifier) or the output current magnitude (in the case of a constant current source CCS). The second is its AC output resistance, which determines how much the output current varies with the voltage applied to the ...
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.
For values of V GS near zero, the drain-to-source voltage linearization voltage or triode breakpoint is much higher than when V GS levels are near the pinch-off voltage. This means in order to maintain constant resistor behavior for different values of V GS, the maximal linearization value would be set according to the highest value of V GS used.
In textbooks, channel length modulation in active mode usually is described using the Shichman–Hodges model, accurate only for old technology: [2] where = drain current, ′ = technology parameter sometimes called the transconductance coefficient, W, L = MOSFET width and length, = gate-to-source voltage, =threshold voltage, = drain-to-source voltage, =, and λ = channel-length modulation ...
The 2N7000 is housed in a TO92 package, with lead 1 connected as the source, lead 2 as the gate, and lead 3 as the drain. The BS170 has the source and drain leads interchanged. The 2N7002 variant is packaged in a TO-236 surface-mount package. The 2N7000 is an N-channel, enhancement-mode MOSFET used for low-power switching applications. [1]