Operational Amplifier

OPAMP

 

The operational amplifier is arguably the most useful single device in analog electronic circuitry. With only a handful of external components, it can be made to perform a wide variety of analog signal processing tasks. It is also quite affordable, most general-purpose amplifiers selling for under a dollar apiece. Modern designs have been engineered with durability in mind as well: several "op-amps" are manufactured that can sustain direct short-circuits on their outputs without damage.

The Operational Amplifier is probably the most versatile Integrated Circuit available. It is very cheap especially keeping in mind the fact that it contains several hundred components. The most common Op-Amp is the 741 and it is used in many circuits.

The OP AMP is a ‘Linear Amplifier’ with an amazing variety of uses. Its main purpose is to amplify (increase) a weak signal - a little like a Darlington Pair.

The OP-AMP has two inputs, INVERTING ( - ) and NON-INVERTING (+), and one output.

Working in 2 ways

1. An inverting amplifier. Leg two is the input and the output is always reversed.

In an inverting amplifier the voltage enters the 741 chip through leg two and comes out of the 741 chip at leg six.If the polarity is positive going into the chip, it negative by the time it comes out through leg six.The polarity has been ‘inverted’.

GAIN (AV) = -R2 / R1

2. A non-inverting amplifier. Leg three is the input and the output is not reversed.

In a non-inverting amplifier the voltage enters the 741 chip through leg three and leaves the 741 chip through leg six. This time if it is positive going into the 741 then it is still positive coming out. Polarity remains the same.

GAIN (AV) = 1+(R2 / R1)

OPAMP AS COMPARATOR

However, this time the 741 is used as a comparator and not an amplifier. The difference between the two is small but significant. Even if used as a comparator the 741 still detects weak signals so that they can be recognised more easily. It is important to understand these circuits as they very regularly appear in examinations.

A ‘comparator’ is an circuit that compares two input voltages. One voltage is called the reference voltage (Vref) and the other is called the input voltage (Vin).When Vin rises above or falls below Vref the output changes polarity (+ becomes -).

Positive is sometimes called HIGH. Negative is sometimes called LOW

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Thin Film Transistor

TFT

The TFTs in active-matrix LCD act as simple ON/OFF switches, at different speeds which depend on the refresh rate of the LCD, for example 60Hz. Figure 1 shows a simple structure of TFT, it consists of three terminals: the gate, the source and the drain. 

Figure 1. A simple Thin-Film-Transistor (TFT) structure

Why TFT

 

In TFT technology, a separate miniscule transistor works for each pixel on the display. As the transistors are so tiny, the charge required to operate it is very small too. This way, the display gets refreshed several times per second, ensuring great visual clarity.

In Passive Matrix LCD monitors that were in use before TFT, fast moving images could not be represented with adequate clarity. For instance, a body in motion from point A to point B would disappear between the two rest points. TFT could meet this challenge as each pixel is backed up with a transistor, and thus track the body throughout the screen. Thus TFT monitors are ideal for games, video displays and everything involving multimedia.

Working 

In a simple TFT, for example N-channel TFT, a positive voltage is applied on the gate in order to switch it ON; the insulation layer can be considered as the dielectric layer in a capacitor, hence negative charges are induced on the semiconductor channel, which is the region between source and drain; these negative charges create a electrons flow from source to drain to make the channel conductive. When a negative voltage is applied on the gate, electrons are depleted in the channel, hence almost no current is present. The ON current depends on different parameters, for example channel width, channel length, gate voltage and the threshold voltage of the TFT.

When the TFT is switched ON, a data voltage is applied on the source, the drain with the LC load capacitance will charge up to the voltage with same amplitude, i.e. transferring the data voltage from the data line to the pixel electrode. When switched OFF, no current in the channel, and data voltage cannot be transferred.

The first TFT for LCD was made of Cd-Se semiconductor thin films, however this is not compatible with normal process. In spite AMLCD with Cd-Se has a better performance, its commercialization is still not success.

While a P-channel TFT can be switched ON by applying a negative voltage on the gate, and can be switched OFF by a positive voltage on the gate.

 TFTs can be formed by three different silicons, they are: crystalline silicon, poly-silicon and amorphous silicon; and in practical manufacturing, poly-silicon can also be processed under low and high temperature, i.e. Low-Temperature Poly-Silicon (LTPS) which can be built on common low-cost glasses, and High Temperature Poly-Silicon (HTPS) which needs quartz plate.  

Since the crystalline Si owns higher mobility, it could integrate more peripheral electronics, hence higher pixel-density-required devices, like projection light valves, usually use crystalline Si.  

Amorphous silicon is widely used in LCD monitor and TV because of its easy manufacturing on large glass substrates, but it has a lower mobility; however during manufacturing, the a-Si is formed by using SiH4, the hydrogen enters into the silicon film, and can improve the loosen Si-lattice in a-Si, thus enhance its performance. The a-Si can therefore be also referred as a-Si:H. The normal electron mobility of a-Si:H is ~0.3-1 cm2/Vsec, compared with c-Si’s >500 cm2/Vsec, it is quite small. But for AMLCD’s TFT’s switch, it is enough. On the other hand, its hole mobility is very low, therefore only N-channel TFT can be practically used. Another drawback of a-Si is its high photoconductivity, which cause the undesirable photo-leakage current in the OFF state. To avoid it, a cover layer is used to shield it from ambient and backlight.

Poly-Si can be used to make both P-channel and N-channel TFTs. Because of its relatively high mobility, both row and column drivers can be integrated on the glass, even D/A converters, DC/DC converters and (micro)processors can be integrated too, which significantly cut the cost from external driver and other devices’ chips. However the off current of Poly-Si is much higher than a-Si, i.e. the OFF state is not stable because of the charge on the pixel capacitor cannot be maintained. In order to decrease the OFF current, a dual gate structure and a lightly doped drain (LDD) were proposed. Both methods can effectively lower the OFF current.

Figure 2 shows a typical pixel structure of AMLCD. It is worth to note that a storage capacitor is connected in parallel to pixel capacitor in order to retain the charge at OFF state, and decrease the voltage dependence and leakage current in the LC capacitance, hence the control of RMS voltage on the pixel is easier.

Figure 2. A TFT AMLCD's pixel layout (color-filter substrate is not shown).

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RF based REMOTE CONTROL

Introduction:-
                  The rf transmitter a gadget that disseminates radio waves with the help of an antenna. A rf transmitter consists of an oscillator that changes electrical power in to a reasonable frequency. There is also an amplifier for audio frequency (AF) and radio frequency (RF). A modulator regulates the signal information on to the transmitter for dispersion. The rf transmitter has an important component that makes its working possible; this is the antenna that transmits an electromagnetic signal for many types of communication. rf transmitter works together with rf receivers. There must be rf receivers on the other end for transmitters to play their role. Communication by use of these systems is possible for radios, cell phones, televisions, walkie –talkies and other electronics used for the purpose of broadcasting. It is possible to find both rf receivers and transmitters in one device. A good example of such technology is used in mobile phones where one can receive and call using one gadget. Currently communication does not rely on analogue mode but uses digital technology thus eliminating the need for complex wiring system to do the connections that carry information.

For an example: We will be using ASK (Amplitude Shift Keying) based Tx/Rx(transmitter/receiver) pair operating at 433 MHz. The transmitter module accepts serial data at a maximum of XX baud rate. It can be directly interfaced with a microcontroller or can be used in remote control applications with the help of encoder/decoder ICs.

RF transmitter module:-

RF transmitter module

RF receiver module:-

RF Receiver module

Working:-

The encoder IC takes in parallel data which is to be transmitted, packages it into serial format and then transmits it with the help of the RF transmitter module. At the receiver end the decoder IC receives the signal via the RF receiver module, decodes the serial data and reproduces the original data in the parallel format.In order to control say a dc motor, we require 2 bits of information (switching it on/off) while we need 4 bits of information to control 2 motors. HT12E and HT12D are 4 channel encoder/decoder ICs directly compatible with the specified RF module.In order to drive motors, we would need to connect a suitable motor driver at the output of the decoder IC. The motor driver circuit can consist of a relay, transistorized H-Bridge or motor driver ICs like the L293D, L298 etc. 

Block Diagram:-

Application:-


                 Rf transmitter enables you to make use of your television, radio, phone and other communication hand held devices. Rf receivers are installed in these devices in factory to make them respond to any signal send. A rf transmitter may interfere with other communication services. This means that you should take precaution by seeking from the relevant authorities about the mode of frequency to use when installing your communication system. Rf receivers are capable of receiving broadcast information from a rf transmitter in different patterns like a single beam or broadcast system. You cannot however tell the difference when you are listening from your radio or watching TV. Rf receivers function hand by hand with transmitters so none can be on its own. Communication is hence a two-way traffic and some communication models are accommodating the receiving and transmitting factors in one equipment. These functions perform well by the energy from electricity or solar. The major important thing in a communication system is to send and receive feedback. Modern times have included the aspect of time in the instruments of passing information no matter how far you are located. This would however be impossible if it was not for transmitters and receivers.

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What is RFID

 
RFID stands for Radio-Frequency IDentification. The acronym refers to small electronic devices that consist of a small chip and an antenna. The chip typically is capable of carrying 2,000 bytes of data or less.
The RFID device serves the same purpose as a bar code or a magnetic strip on the back of a credit card or ATM card; it provides a unique identifier for that object. And, just as a bar code or magnetic strip must be scanned to get the information, the RFID device must be scanned to retrieve the identifying information. 

Working

A Radio-Frequency IDentification system has three parts:

• A scanning antenna
• A transceiver with a decoder to interpret the data
• A transponder - the RFID tag - that has been programmed with information.

The scanning antenna puts out radio-frequency signals in a relatively short range. The RF radiation does two things:

• It provides a means of communicating with the transponder (the RFID tag) AND
• It provides the RFID tag with the energy to communicate (in the case of passive RFID tags).

This is an absolutely key part of the technology; RFID tags do not need to contain batteries, and can therefore remain usable for very long periods of time (maybe decades). The scanning antennas can be permanently affixed to a surface; handheld antennas are also available. They can take whatever shape you need; for example, you could build them into a door frame to accept data from persons or objects passing through.
When an RFID tag passes through the field of the scanning antenna, it detects the activation signal from the antenna. That "wakes up" the RFID chip, and it transmits the information on its microchip to be picked up by the scanning antenna.

In addition, the RFID tag may be of one of two types. Active RFID tags have their own power source; the advantage of these tags is that the reader can be much farther away and still get the signal. Even though some of these devices are built to have up to a 10 year life span, they have limited life spans. Passive RFID tags, however, do not require batteries, and can be much smaller and have a virtually unlimited life span.
RFID tags can be read in a wide variety of circumstances, where barcodes or other optically read technologies are useless.

• The tag need not be on the surface of the object (and is therefore not subject to wear)
• The read time is typically less than 100 milliseconds
• Large numbers of tags can be read at once rather than item by item. 

Passive RFID vs. Active RFID

Passive RFID tags operate using power from the RFID transceiver. Passive tags are small and inexpensive, but do not have good range.
Active RFID tags are powered, usually by a battery. Active tags are larger and more expensive, but offer a much better identification range.
RFID tags store data, which is typically used for authentication. Passive tags typically store between 32 and 128 bits of data; Active tags can store up to 1MB of data.
Passive tags are Read-Only; Active tags are typically rewritable.

Applications

Please click at one of the applications below to read how Rotil Communications B.V. applied these techniques successfully at previous projects.

• Vehicle start interruption
• Access control and identification
• Petrol stations
• Working hours registration system

Other possibilities to apply the RFID technique are for example:

Vehicle identification

Every vehicle will carry a transponder. Through the unique id number in the transponder it will be easy to ‘recognise’ the vehicle. This can expanded with the registration of technical vehicle information such as temperature, GPS location.

Logistic processes

Every container, box or crate has a transponder fitted to it. With each step in the process, the transponder is being read and the operation is saved in the central database. By this is, it will be very easy to find out which steps in the production process has already been made.

Service and maintenance

All products, devices or vehicles will get a transponder. The service or maintenance mechanic scans this transponder for each maintenance. The software on a computer, which is connected to a central database, enables him to register for example the product details, customer number, maintenance tasks, date/time. Now it will be much easier to find out which maintenance or service has been provided to a certain product/vehicle with just a click. This will be very (cost) efficient.

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