Quantcast

Semiconductor Galore

The world has been a very different place since the invention of the humble transistor.  There are many pages where you can read about the invention and history but I’m not prepared to give a history lesson.  A transistor has two uses: amplification and switching.  They also come in many varieties, sizes and flavours (Bipolars, FETs, MOSFETs).  A transistor is made from semi-conductive materials such as germanium and silicon.

Out of all the elements in the periodic table, why are germanium and silicon semi-conductive?  The answer lies in the chemistry and physics (electronics is applied physics!).  The two elements I have mentioned belong in Group IV of the periodic table.  This means that they have a valency of 4, meaning they can form 4 bonds due to a half-filled outer electron shell.  Their outer electron shells can only hold 8 electrons.  So, in order for them to be “happy”,they want that gap filled.  This gap can be filled in the process called doping.  This is where we introduce either an N or P type element.  An N type is the result of doping the semiconductor with a Group V element, whereas a P type is doping with a Group III element.  The effect of this is that the N type has additional negative carriers (electrons) making it conductive whereas P type has holes (a gap in the electron shell) which we also treat as particles, oddly enough, which are positive carriers.

If we were to join a section of P type with a section of N type, we would get a diode (see badly drawn figure 3).  Figure 1 is a typical diode; Figure 2 is the electrical symbol for completeness’ sake.  I’m talking loosely here— it is not as simple as taking a lump of both materials and slapping them together.  A diode is a passive component where electrical current is allowed to flow one way and not the other.  A one-way street for electrons, if you like.  What actually happens is that, in the realm of physics, depending on whether the diode is forward-biased (when the positive voltage is connected to the anode (the red +)) or reverse-biased (when the positive voltage is connected to the cathode (the blue -)).  With forward bias, you simply get current flowing through (which has a typical voltage drop of 0.7V); in the reverse bias, you get a depletion region in the PN junction, which prevents current flow.

Now, if we were to get two diodes and slap them back to back, we would get a transistor (Fig 4).  Fig 5 shows the NPN layout, and, unsurprisingly, this is called an NPN transistor.  PNP transistors also exist, with a P region either side of the N region.  The process for producing these semiconductor materials is very complex which is why no two transistors are exactly the same—thus, though we have to design circuits around this property, it can be exploited in many useful ways. I have also greatly exaggerated the P region in Fig 5. as it is very very very thin (that is, measurable in nanometers to microns) in the real thing.  The PN junction is the basic building block for pretty much all semiconductor components such as LEDs, all transistors, and diodes, Solar Cells and ICs (Integrated Circuits).

Fig. 6 shows the electrical symbol for a NPN bipolar transistor.  Bipolar transistors are used mainly for amplification, due to the fact they are relatively slow at switching.  It takes a typical bipolar 300ns to switch on and 1300ns to swtich off whereas FETs take ~50ns to switch on and off making them much more faster. The transistor has three connections labelled B, C and E.  These are the base, collector and emitter. Depending on how these three are wired up, determines which one of three main types of amplifiers you have: common collector, emitter follower or common base.

The reason bipolars make great amplifiers is because a small base current will cause a much larger emitter-collector current to flow.  This amplification is known as the amplifier’s gain, which has the symbol β (beta) or hfe. The beta of a typical transistor such as the BC337 ranges from 60 to 630. The large variance is due to the complex manufacturing process.  If we had a transistor with a beta of 200, and we fed 10mA through the base, we would get 200x10mA through the collector, which is 2A. This is particularly useful when we want large currents to be controlled by integrated circuits which can only pass a small amount of current.  DC or AC (and even both superimposed) can be fed through the base.

Even though a gain of 600 is pretty large, what if we require a higher gain?  First of all, there are some applications where we deal with very small signals— for example the radio receivers in our mobiles.  Typically the received signal is less than a microvolt.  To put this into perspective, a microvolt is 1*10^-6V (for those who do not understand standard engineering notation or scientific notation, it is 0.000001V).  This is why poorly-designed antennas such as the one in the iPhone 4 will drop your call if you hold the device “incorrectly”.  A microvolt is a tiny amount of voltage and too small to be used for anything in general elctronics so it must be amplified.  Usually a signal will go through several stages of amplification to get the desired required result, but the same result can be gained with a super-beta transistor which is also known as a Darlington configuration.

The gain of this configuration is beta^2.  So in the previous example the beta value was 200, in this new configuration the beta value is 200^2 which equals 40000.  If you think about it, that’s absolutely insane—mind you don’t blow the transistor by applying too much base current!

Transistors can be found in almost anything that runs on electricity, quietly doing their jobs so we can live much easier lives.  Did you know that each pixel on your TFT (Thin Film Transistor) monitor has a transistor on it?  Incredible, if you ask me.

This entry was posted in Electronics, Engineering, Physics and tagged , , . Bookmark the permalink. Post a comment or leave a trackback: Trackback URL.

5 Comments

  1. Posted 10/04/2013 at 4:42 AM | Permalink

    After i strolling path along with my buddy I became entice by this high end brand. Exactly like the our omega, Cartier and then for any several other luxurious manufacturer on the planet. And also my buddy informs me that it is not just my personal aspiration and also substantially more individuals worldwide. Additional people today employ a aspiration One day they’re going to person this high-class An individual. Not just quite producer them selves and the standing up that will patterns.

    However, you that it’s a nighttime fantasy in my opinion and much more widespread consumers. Consequently, the 1st time it is extremely stressful may own this specific top end until eventually my spouse and i have the Look-alike Cartier Designer watches. Your entire day My partner and i investigate net, I have found an internet acquiring, i discover this particular notice is indeed design and style and chic. As well as the astonishing would it be offers a amount of sequence, you might select the shade you need along with virtually any Processing Cartier Watches their very own exclusive styling. The fashion type together with refreshing type pushes you to amazing inside it. Probably the most vital are these claims merely from the inexpensive observing. Therefore, it may be undoubtedly to select the idea. Ahead of My spouse and i get this Look-alike Cartier Designer watches, Irrrve never at any time buy one factor on the net; because of the fact My spouse and i estimate that online purchasing just isn’t protected. Look-alike Cartier Wrist watches, My spouse and i stage I became incorrect. The online buying is basically comfort and ease for the lure and we are in a position to select the actual pleasant just one.

    Copy Cartier Wrist watches make my personal dream becoming reality by just it really is kind trend as well as high-end. This kind of Look-alike Cartier Wrist watches is definitely well-designed along with confuse, you will see reality fashion within it and you will probably delight in the good high quality. Once the discover seriously isn’t just use intended for seeing the time, your Look-alike Cartier Wrist watches using the staff of fashion styling, that may provide the clean fashion you may want for this fashion globe. Plus the work inside to line of Duplicate Cartier Watches, many people can easily see your efficiency onto it. The specific Replicate Cartier Wrist watches goes pertaining to a great deal of a very long time; you are able to understand the file beyond the standing on that. In a lot of view creating business, the particular Copy Cartier Wrist watches is becoming the primary onto it. and its larger recognition is in fact analyze their very best in order to meet individuals need, together with achieve their unique magnificent fantasy.

    I suppose I became lucky to obtain this opportunity to personal this kind of high end Replica Cartier Watches in this affordable. But it surely might be sincere for all; many people may possibly private your thing along with top quality Copy Cartier Timepieces, much like all of us personal this specific high-class.

    mens watches on sale|

  2. Posted 06/07/2014 at 2:08 AM | Permalink

    I see a lot of interesting content on your
    page. You have to spend a lot of time writing, i know
    how to save you a lot of work, there is a tool that creates unique, SEO friendly articles in couple
    of seconds, just type in google – laranita’s free content source

  3. Posted 25/09/2014 at 2:16 AM | Permalink

    Thank you forr thhe good writeup. It actually used to be a entertainment account it.Glance
    complex to more delivered agreeable from you! By the way, how
    caan we communicate?

  4. Posted 30/09/2014 at 5:49 PM | Permalink

    At this time it appears like Movable Type is the best blogging platform
    out there right now. (from what I’ve read) Is that what you’re using
    on your blog?

  5. Posted 17/12/2014 at 8:07 AM | Permalink

    It’s imperative that yolur potential clients get to know and trust you, and one of
    the best ways to do this is to let them experience some
    of your magic – at no charge. Millions of pelple are logging into these websites at all hours of the day and night, and
    you have the opportunity to be able to reach out to these people,
    andd end up having a loot of them added to your
    customer base. Contact your local associations
    (the ones that you have already targeted), in addition to libraries and industry associations and get scheduled
    to speak at their meetings. Look for ways to increase
    the value of the product or service you offer.

Post a Comment

Your email is never published nor shared. Required fields are marked *

*
*

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>

  • Welcome to TechRant…

    We are a group of techies from emerging students to full blown professionals who are enthusiastic about technology related subjects. Everyone has opinions and feelings about things, sometimes stronger than others. On TechRant, we will be sharing those opinions, and have a good ol' rant! We may also do non ranting type articles, like news, reviews, tutorials, tips and tricks, how-tos and even the odd interview.

  • Authors

  • Categories

  • Archives