Dependent Sources

Output of source depends on some other variable. These are of four types depending on the controlling variable and output of the source.

Voltage controlled voltage sources: This is a voltage source whose output can be controlled by changing the controlling voltage $V_{ab}$ (Fig.3.11). This is a voltage amplifier if we consider the VCVS to be a box which takes the input as voltage and then at the output generated the amplified voltage. In the figure, 20 will be the gain of voltge amplifier.

Figure 3.11: Voltage controlled voltage source

Voltage controlled current sources: In case the control variable is voltage and the output of the source is current, it is VCCS. The unit of gain factor (20 in the Fig.3.12) will of siemens. This is transconductance amplifier.

Figure 3.12: Voltage controlled current source

Output current can be modified by changing $V_{ab}$. $\frac{Output\; current}{Input\;voltage}=conductance=\frac{i}{v}$.

Current controlled voltage sources: shown in figure 3.13.

Figure 3.13: Current controlled voltage source

This is a transimpedence amplifier since the ratio of output to input has units of resistance (more general term is impendance). The gain factor for this type of source has units of ohm, measured as $\frac{v_{output}}{i_{input}}$.

Current controlled current sources (Fig.3.14: A current amplifier, the gain is current gain $\frac{i_{output}}{i_{input}}$ (dimensionless, as in voltage amplifier).

Figure 3.14: Current controlled current source