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in parallel with the collector–emitter junction of the transistor. This resistor can thus account for the finite output resistance of a simple current mirror or an actively loaded common-emitter amplifier. In keeping with the model used in SPICE and as discussed above using the resistance becomes:
In a standard two-transistor current mirror, the output impedance would be the dynamic early resistance of the output transistor, the equivalent of which in this case is . The Wilson current mirror has an output impedance that is higher by the factor β 2 {\displaystyle \scriptstyle {\frac {\beta }{2}}} , on the order of 50 times.
In practice, the internal resistance of a battery is dependent on its size, state of charge, chemical properties, age, temperature, and the discharge current. It has an electronic component due to the resistivity of the component materials and an ionic component due to electrochemical factors such as electrolyte conductivity , ion mobility ...
In this type the resistance varies with the applied voltage or current. Negative resistance vs positive resistance: If the I–V curve has a positive slope (increasing to the right) throughout, it represents a positive resistance. An I–V curve that is nonmonotonic (having peaks and valleys) represents a device which has negative resistance.
To keep the output transistor resistance high, V DG ≥ 0 V. [nb 1] (see Baker). [3] That means the lowest output voltage that results in correct mirror behavior, the compliance voltage, is V OUT = V CV = V GS for the output transistor at the output current level with V DG = 0 V, or using the inverse of the f-function, f −1:
One is its internal resistance and the other is its compliance voltage. The compliance voltage is the maximum voltage that the current source can supply to a load. Over a given load range, it is possible for some types of real current sources to exhibit nearly infinite internal resistance.
Figure 1: A version of the Widlar current source using bipolar transistors. Figure 1 is an example Widlar current source using bipolar transistors, where the emitter resistance R 2 is connected to the output transistor Q 2, and has the effect of reducing the current in Q 2 relative to Q 1.
Internal resistance varies with the age of a battery, but for most commercial batteries the internal resistance is on the order of 1 ohm. When there is a current through a cell, the measured e.m.f. is lower than when there is no current delivered by the cell.