Revision of Circuits and Electronics - Dependent Sources and Amplifiers (Lecture 8)

 Video:- http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-002-circuits-and-electronics-spring-2007/video-lectures/lecture-8/

Lecture Notes:- http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-002-circuits-and-electronics-spring-2007/lecture-notes/

Dependent sources can be linear or nonlinear.

A dependent source needs to have its voltage or current controlled by some other variable. A diamond symbol with a current through it  is a dependent current source. A 2 port device has a control port and an output port.

VCCS  - (Voltage Controlled Current Source) Current at the output port is a function of voltage at the input port.

First, an example with the independent source is done resulting in a result of V=IR.

The dependent source example is an abstracted view of the actual circuit. Node method is also used but probably not really necessary. The general result is still V=IR but I=K/V is used.

 The other types of dependent sources are CCVS, VCVS  and CCCS.

 In another dependent source example, v_O needs to be found as a function of v_IN.  The circuit is different from the previous one as there is an input voltage and a supply voltage V_S.

The drawing is simplified and the node method is used to find v_O.

v_O versus v_I curve can be plotted  for the dependent source example.

 When superposition theorem is used with dependent sources, all dependent sources are left in the circuit. Then, solve for one independent source at a time.

Why amplify? Signal amplification is the key to both analog and digital processing.  Amplification helps to make a signal larger but it can also aid in the process of tolerating noise during communication.

 Amplification is fundamental for the digital domain as well.  It is needed to make a digital device meet the static discipline. The minimum amplification needed is  (V_OH - V_OL)/(V_IH-V_IL)

An amplifier is a 3 ported device.  The power port is not often shown. All ports share a common reference point called ground.

How do we build one? It's already been done! It is the VCCS in the second dependent source example.

Where's the amplification? From the plot of v_O versus v_I ,  there is a region where there is gain.

But what happens in the region when v_O is more than 0 and when it is  less than zero?  . When v_O   is more than zero, the VCCS consumes power. When it is less than zero, the VCCS supplies power.

If VCCS consumes power, there is saturation at some point.