Introduction To Wordless Wednesdays

7 08 2008

The more eagle-eyed of you will have noticed that yesterday’s post was a little different from the usual offerings here on Textual Relations. After some recent feedback, Mr President discontinued Wiki-Wednesday. When he thought of his options for its replacement, he decided he still wanted Wednesday posts to fit with the ebb and flow of the week. Wednesday is hump day, after all.

When he started Wiki-Wednesday, he liked the idea of a “lighter” post. His content could be rather dry and serious at times and Wednesdays are dour days enough as it is. What good could come of yet more depressing stuff to encounter every Wednesday? Naturally whatever replaced the Wiki-Wednesdays would have to conform to this.

Wiki-Wednesday had actually failed to do so. In the end “random” topics only meant that the content was often dry and dull, and only rarely interesting. So what did this blog lack that could fulfill this criteria? What could be added that be “uplifting”?

The answer was simple. Textual Relations needed visual stimulation.

Every Wednesday there will be a new photograph to raise your spirits.





Leechblock Is A Lifesaver

5 08 2008

Facebook is a great thing. It is also incredibly distracting. Nor is it the only site that seems to leech time away like there is no tomorrow. YouTube. Discussion forums. Wikipedia. There is a distraction around every corner of the web ready to suck you in and make you lose track of time. This is not a minor issue either, time is the most valuable commodity any of us possess yet we waste it.

Does this sound familiar? You get a block of time to catch up on things that you need to do, whether it’s household tasks or something for work. Say a weekend which you have already earmarked to do tasks which you didn’t have time for during the week. It starts well, you wake up late (it is the weekend after all), make some coffee or tea.

You sit down in front of your computer. Check your mail. Decide to “pop into” Facebook to check your messages Before you know it, four hours have passed, and all the stuff you’d planned to do can’t be done because it is getting late. There is hardly much time left in the day and you kick yourself for falling into the trap of teh internetz.

We’ve all done it. Well salvation is here. Leechblock is willpower in a bottle*.

*Note, it’s not actually in a bottle because fluids and computers don’t mix.





Wonderful WordPress Saves The Day

25 07 2008

Thanks to WordPress, having an active social life need not stop you blogging. Without the ease with which he was able to pre-publish today’s blog post, you might have had to all do without his pearls of wisdom. Quite how you would have managed nobody knows.

Fear not, though, for here is today’s post. It’s as if he’s in two places at the same time. Which hopefully won’t cause damage to the spacetime continuum or anything like that.

After the recent slump in reader participation Mr President is concerned that you might all be losing interest in his littler corner of the internet. Despite not being one to bow to public pressure he is a man of the people, and wants you to be happy.

With that in mind he’d like some feedback. What would you like to see more of? What do you like about the blog? Is there anything at all you’d like to see less of?





Apple And WordPress Sitting In A Tree…

22 07 2008

Just in case you needed another good reason to get an iPhone or an iPod touch (Mr President wants both) those lovely folk at WordPress have given you one. If you have a WordPress blog, chances are you’ve seen this already, but for those who haven’t, you’re about to get very excited. In fact you might want to put a newspaper down to take care of the mess you might leave on the floor.

Ready? WordPress now has an app for the iPhone and iPod touch! Blog while you’re out and about. Next time you see something you think would make good blog material, just sit down with your swanky new Apple gadgetry and post it. Never again will you have to think “That’ll make a good blog post. Better remember to write about that.”

It’s one small step for WordPress…one giant leap for Blog-kind. Sort of.





What’s With All The Spam?

17 07 2008


Spam (no, not that kind of spam, the other one) has been the bane of almost all Internet users since its inception. The inception of the Internet, that is, not spam. Although those are practically the same thing. Every single one of you reading this now (yeah, all three of you) will have encountered spam before, in fact you probably encountered it today.

Of course this shouldn’t surprise us. Every time we invent something it’s simply a matter of time before a shrewd business sees a way to make money out of it. Some might even say (and Mr President would be one of these) that this is the way things should be in a Capitalist society. It is, after all, this behaviour that has made us such a great species.

Thanks to spam filters getting better at catching it, it’s not as instrusive as it used to be, but that really only poses the question why it still exists. If spam is not seen by a human it serves no purpose, so why bother with spambots at all? Not only does it not work as a means of advertising but it is now purely an annoyance. What good does that do?

Given its impotency, the rising amount Mr President receives is baffling. Whether it is via email or blog comments, not a day goes by when he isn’t accosted by a number next to the “spam” counter. He could ignore it but the problem with trusting the spam filters is that over-automisation leads to some important things slipping through the cracks.

What about you, have you noticed an increase in your spam counts? What do you do?





Google Make Backing Up Easier

10 07 2008

It has been said before but it bears repeating. Tech posts on Textual Relations are quite the rarity, but they’re a lot like buses. When you get one, all too often you get another hot on its heels. This is no different. After the truly “fascinating” Wiki-Wednesday yesterday all about Field-effect transistors, today’s post has a disctinctly technological flavour. Non-geeks should really look away now.

Ever had a hard disk failure? Ok, that one was too easy, so how about this; presumably you had a backup, right? What do you mean “no”? Well, you’re not alone, as a survey conducted in 2006 showed that 62 percent of computer users back up less than once a month, and an amazing 23 percent have never even performed a backup.

To be fair, Mr President once lost some data (although he managed to recover most of it later using recovery software) due to not having a backup. After suffering a harrowing experience like that (you don’t know just how bad data loss is until you’ve suffered it) you might think he’d learn his lesson and do regular backups, right? Wrong.

Why? Well, probably the same reason most people fail to do regular backups. It’s just too much hassle for a minute risk. You need to run some software, then have a stack of blank DVDs or buy external hard drives, and after all of that your data is still at risk, as those backup mediums are no less susceptible to data loss. Why bother?

That’s where the Google Docs List Uploader comes in. Ok, so some people are not all that enamoured with Google, preferring to back Microsoft, a company that hasn’t done much of note since 1998 (does anyone else find Office 2007 far less user friendly?) yet that shouldn’t take away from the fact that Google are great at backing up.

With Google Docs and the List Uploader backing up is quick and easy.





Wiki-Wednesday – Field-effect transistor

9 07 2008

Field-effect transistor

From Wikipedia, the free encyclopedia

High-power N-channel field-effect transistor

The field-effect transistor (FET) is a type of transistor that relies on an electric field to control the shape and hence the conductivity of a ‘channel’ in a semiconductor material. The concept of the field effect transistor predates the bipolar junction transistor (BJT), though it was not physically implemented until after BJTs, due to the limitations of semiconductor materials and relative ease of manufacturing BJTs compared to FETs at the time.

Terminals

All FETs except J-FETs have four terminals, which are known as the gate, drain, source and body/base/bulk/substrate. Compare these to the terms used for BJTs: base, collector and emitter. BJTs and J-FETs have no body terminal.

Cross Section of an n-type MOSFET

The names of the terminals refer to their functions. The gate terminal may be thought of as controlling the opening and closing of a physical gate. This gate permits electrons to flow through or blocks their passage by creating or eliminating a channel between the source and drain. Electrons flow from the source terminal towards the drain terminal if influenced by an applied voltage. The body simply refers to the bulk of the semiconductor in which the gate, source and drain lie. Usually the body terminal is connected to the highest or lowest voltage within the circuit, depending on type. The body terminal and the source terminal are sometimes connected together since the source is also sometimes connected to the highest or lowest voltage within the circuit, however there are several uses of FETs which do not have such a configuration, such as transmission gates and cascode circuits.

Composition

The FET can be constructed from a number of semiconductors, silicon being by far the most common. Most FETs are made with conventional bulk semiconductor processing techniques, using the single crystal semiconductor wafer as the active region, or channel.

Among the more unusual body materials are amorphous silicon, polycrystalline silicon or other amorphous semiconductors in thin-film transistors or organic field effect transistors that are based on organic semiconductors and often apply organic gate insulators and electrodes.

Types of field-effect transistors

Depletion-type FETs under typical voltages. JFET, poly-silicon MOSFET, double-gate MOSFET, metal-gate MOSFET, MESFET.  depletion ,  electrons ,  holes ,  metal ,  insulator . Top=source, bottom=drain, left=gate, right=bulk. Voltages that lead to channel formation are not shown

Depletion-type FETs under typical voltages. JFET, poly-silicon MOSFET, double-gate MOSFET, metal-gate MOSFET, MESFET. depletion , electrons , holes , metal , insulator . Top=source, bottom=drain, left=gate, right=bulk. Voltages that lead to channel formation are not shown

The channel of a FET (explained below) is doped to produce either an N-type semiconductor or a P-type semiconductor. The drain and source may be doped of opposite type to the channel, in the case of enhancement mode FETs, or doped of similar type to the channel as in depletion mode FETs. Field-effect transistors are also distinguished by the method of insulation between channel and gate. Types of FETs are:

  • The MOSFET (Metal–Oxide–Semiconductor Field-Effect Transistor) utilizes an insulator (typically SiO2) between the gate and the body .
  • The JFET (Junction Field-Effect Transistor) uses a reverse biased p-n junction to separate the gate from the body.
  • The MESFET (Metal–Semiconductor Field-Effect Transistor) substitutes the p-n junction of the JFET with a Schottky barrier; used in GaAs and other III-V semiconductor materials.
  • Using bandgap engineering in a ternary semiconductor like AlGaAs gives a HEMT (High Electron Mobility Transistor), also called an HFET (heterostructure FET). The fully depleted wide-band-gap material forms the isolation between gate and body.
  • The MODFET (Modulation-Doped Field Effect Transistor) uses a quantum well structure formed by graded doping of the active region.
  • The IGBT (Insulated-Gate Bipolar Transistor) is a device for power control. It has a structure akin to a MOSFET coupled with a bipolar-like main conduction channel. These are commonly used for the 200-3000 V drain-to-source voltage range of operation. Power MOSFETs are still the device of choice for drain-to-source voltages of 1 to 200 V.
  • The FREDFET(Fast Reverse or Fast Recovery Epitaxial Diode FET) is a specialized FET designed to provide a very fast recovery (turn-off) of the body diode.
  • The DNAFET is a specialized FET that acts as a biosensor, by using a gate made of single-strand DNA molecules to detect matching DNA strands.

FET operation

The FET controls the flow of electrons (or electron holes) from the source to drain by affecting the size and shape of a “conductive channel” created and influenced by voltage (or lack of voltage) applied across the gate and source terminals. (For ease of discussion, this assumes body and source are connected). This conductive channel is the “stream” through which electrons flow from source to drain.

Consider an n-channel “depletion-mode” device. A negative gate-to-source voltage causes a depletion region to expand in width and encroach on the channel from the sides, narrowing the channel. If the depletion region expands to completely close the channel, the resistance of the channel from source to drain becomes large, and the FET is effectively turned off like a switch. Likewise a positive gate-to-source voltage increases the channel size and allows electrons to flow easily.

Now consider an n-channel “enhancement-mode” device. A positive gate-to-source voltage is necessary to create a conductive channel, since one does not exist naturally within the transistor. The positive voltage attracts free-floating electrons within the body towards the gate, forming a conductive channel. But first, enough electrons must be attracted near the gate to counter the dopant ions added to the body of the FET; this forms a region free of mobile carriers called a depletion region, and the phenomenon is referred to as the threshold voltage of the FET. Further gate-to-source voltage increase will attract even more electrons towards the gate which are able to create a conductive channel from source to drain; this process is called inversion.

For either enhancement- or depletion-mode devices, at drain-to-source voltages much less than gate-to-source voltages, changing the gate voltage will alter the channel resistance, and drain current will be proportional to drain voltage (referenced to source voltage). In this mode the FET operates like a variable resistor and the FET is said to be operating in a linear mode or ohmic mode.

If drain-to-source voltage is increased, this creates a significant asymmetrical change in the shape of the channel due to a gradient of voltage potential from source to drain. The shape of the inversion region becomes “pinched-off” near the drain end of the channel. If drain-to-source voltage is increased further, the pinch-off point of the channel begins to move away from the drain towards the source. The FET is said to be in saturation mode; some authors refer to it as active mode, for a better analogy with bipolar transistor operating regions. The saturation mode, or the region between ohmic and saturation, is used when amplification is needed. The in-between region is sometimes considered to be part of the ohmic or linear region, even where drain current is not approximately linear with drain voltage.

Even though the conductive channel formed by gate-to-source voltage no longer connects source to drain during saturation mode, carriers are not blocked from flowing. Considering again an n-channel device, a depletion region exists in the p-type body, surrounding the conductive channel and drain and source regions. The electrons which comprise the channel are free to move out of the channel through the depletion region if attracted to the drain by drain-to-source voltage. The depletion region is free of carriers and has a resistance similar to silicon. Any increase of the drain-to-source voltage will increase the distance from drain to the pinch-off point, increasing resistance due to the depletion region proportionally to the applied drain-to-source voltage. This proportional change causes the drain-to-source current to remain relatively fixed independent of changes to the drain-to-source voltage and quite unlike the linear mode operation. Thus in saturation mode, the FET behaves as a constant-current source rather than as a resistor and can be used most effectively as a voltage amplifier. In this case, the gate-to-source voltage determines the level of constant current through the channel.

Uses

The most commonly used FET is the MOSFET. The CMOS (complementary-symmetry metal oxide semiconductor) process technology is the basis for modern digital integrated circuits. This process technology uses an arrangement where the (usually “enhancement-mode”) p-channel MOSFET and n-channel MOSFET are connected in series such that when one is on, the other is off.

The fragile insulating layer of the MOSFET between the gate and channel makes it vulnerable to electrostatic damage during handling. This is not usually a problem after the device has been installed.

In FETs electrons can flow in either direction through the channel when operated in the linear mode, and the naming convention of drain terminal and source terminal is somewhat arbitrary, as the devices are typically (but not always) built symmetrically from source to drain. This makes FETs suitable for switching analog signals between paths (multiplexing). With this concept, one can construct a solid-state mixing board, for example.