research group
Radiating Tomorrow's Technology
Prof. Zhang
Useful Info.
Teaching Courses:

1) Engineering Electromagnetics (EE208)

2) Antenna and Wave Progpagation (EE315)

3) Microwave Engineering (EE425)

4) Fundamental of Analog Electronic Technology (EE201)


Interesting Comments Regarding Transistors and Amplifiers

1) Question: Is a transistor really an amplifying element? Is it an active or passive device? Are there amplifying elements? Is it possible to amplify energy at all?

It is well known that the transistor is an active element used to build amplifiers. But I thinkthis is not true. The transistor is not active but passive element; the only thing that a transistor can do is to dissipate energy. So, it is not amplifying but attenuating element. It is just a resistor (non-linear, electrically controlled but still a resistor) that decreases the current.

The true amplification is impossible; so there are no real amplifiers. The so-called "amplification" is just an illusion, a clever trick and the "amplifier" is just a "magic box" where we see a bigger output power but this is not the amplified small input power. This is else's power.

In analog electronics, we implement such an "amplification" in the possibly most paradoxical, absurd and silly way - to obtain output power bigger than the input one, we get a big power source and then throw away a part of it (from zero up to the whole power). In comparison, in energetics, they can't afford to do it..
Am I right?

Good Answer: If one uses a small external magnetic field to excite a ferro-magnetic material one finds one is able to produce magnetic fields some 10,000 stronger within the material itself. This is the basis upon which all transformers etc work in that we rely or exploit the high induction that is available within the material.

Here we are not amplifying anything but rather exploiting or controlling the material properties and if we do same for wood nothing will happen.

In the same vein we have studied, designed and used smart manufacturing techniques to allow semiconductors to have similar properties whereby we may utilise smaller amounts of power / energy to control large amounts of power / energy flow through the device itself. We may also do same with hydraulic systems.

Cyril you appear to confuse the use of the term AMPLIFY and incorrectly use it as the ability to generate power rather than the ability to control the flow of power which forms the basis of Derek's use of the system boundary.?

This is why using it in the context of applying power to the gate of a transistor will suddenly allow huge amounts of power out is impossible as you have said.

Where is this power going to come from? From inside the device! Impossible as you correctly state.

However, if we attach a source of power then we may use the transistor to control the flow of power through itself (not from within itself). Furthermore, through smart design and manufacturing techniques we only need small amounts of power to control the flow of substantially larger amounts of power through the device.

Thus the use of the term amplification as the ability to control the flow of power and its use as the ability to generate power are not the same as the latter defies the laws of physics.

Thus you are quite correct and I fully agree that AMPLIFICATION does not mean that one can somehow create or generate power but this was never the intention.

And the ILLUSION as you correctly note is that it appears as if the device amplifies power from within itself whereas in reality it is only controlling the flow of power through itself.

As far as passive and active devices go an active device is meant to define one in which the flow of power may be controlled. As such a resistor is passive and a transistor classed as active.

Thus a transistor as an active element may used to control the flow of substantially larger amounts of power through itself and in doing so allow amplification of the control signal. All the transistor is doing is controlling the flow of power between the source and load based on its input control signal. The amplifier used for a radio being one such example.




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