Astable Multivibrator/ Square wave generator circuit/ Oscillator/ Diwali lightning circuitry using 555 Timer i/c

It is the simplest oscillator circuit which has various applications with most important application is producing an hardware delay in the circuitry.
for further requirement of details about the circuitry drop me a mail at sumit.gogna@ymail.com

RESISTIVE TOUCH SCREEN

TOUCH SCREEN

A touch screen is an electronic visual display that can detect the presence and location of a touch within the display area.

ADVANTAGES WITH TOUCH SCREENS

•      Eliminates the need of keyboard input.

•      Device becomes cheaper and lighter.

Quicker to navigate/ speed of correct selection is increased.

    

TYPES OF TOUCH SCREENS

•      There are several types of touch screen such as   resistive, capacitive, surface acoustic wave, optical imaging, strain gauge and so on.

•      The most commonly used types are the resistive and capacitive.

RESISTIVE TOUCH SCREEN

Resistive touch screen basically have two layer i.e. X-layer and Y- layer with both having resistances connected in perpendicular fashion to each other. As a result of this resistance pattern there exists a specific value of output voltage at specific points on the touch screen. These are read as the values of x and y respectively. Now these x and y values makes a sort of matrix and thus can be used to define n number of switches.

RESISTIVE TOUCH SCREEN PRINCIPLE

•      This layer has resistance network from right to left.

Now if we supply voltage across right and left sides of this layer then there will be specific value of voltage for each row, which can be taken across any of the two remaining sides and ground.

4-Wire Resistive Touch Screen

These are the least expensive and most commonly used types of resistive touch screens. Conductive bus bars with silver ink are implanted at the opposite edges of a screen layer.

The principle of operation is such that, as shown in Figure if one side of a layer is connected to +V and the other side to ground, a potential gradient results on the screen layer, and the voltage at any point on this layer becomes directly proportional to the distance from the +V side.

In a 4-wire touch screen two measurements are made one after the other one to determine the X and Y co-ordinates of the point touched by the user. Figure shows how the X co-ordinate can be determined. Here, the right and left hand sides of the top layer can be connected to +V

and ground respectively. The bottom layer can then be used to sense and measure the voltage at the point touched by the user. An A/D converter is used to convert this analogue voltage to digital and then determine the X co-ordinate.

Similarly, Figure shows how the Y co-ordinate can be determined. Here, the upper and lower sides of the bottom layer can be connected to +V and ground respectively. The top layer can then be used to sense and measure the voltage at the point touched by the user. Again, an A/D is used to convert the voltage to digital and then to determine the Y coordinate.

TOUCH ORIENTED DATA ACQUISITION ROBOT

This is the video of a "Touch oriented wireless data acquisition robot".The project has a transmitter section and a receiver section  and  transmitter consists of a temperature sensor i.e LM 35 which senses the temperature of the surrounding and gives an analog output which converted into digital form by the microcontroller and displays it on the  LCD also the converted digital signals are given to the RF transceiver which sends it to the receiver unit.
The transmitter unit is also a mobile one and its steering logic input is given through the touch screen at the receiver again by using the transceiver module. so in short the transceiver works in a half duplex manner.

MMIC(MONOLITHIC MICROWAVE INTEGRATED CIRCUITS)

Progress in GaAs material processing and device development in 1970s has led to the feasibility of the monolithic microwave integrated circuit, where active components required for a given circuit can be grown or implanted in the substrate.

The substrate of an mmic is a semiconductor material and accomadate fabrication of active devices. GaAs is probably the most common substrate for mmic but silicon, silicon-on-sapphire and indium phosphide are also used.

Transmission line and other conductors are usually made with gold metallization. To improve adhesive of the gold to the substrate a thin layer of chromium or titanium is generally deposited first. These metals are relatively lossy,so the gold layer must be made at least several skin depths thick to reduce attenuation.

Designing an mmic requires extensive use of CAD software, for circuit design and optimization as well as mask generation. Careful consideration must be given in the circuit design to allow for component variations and tolerance and the fact that circuit trimming after fabrication will be difficult or impossible. Thus effects such as transmission line discontinuities, bias n/w, spurious coupling and package resonance must be taken into account.

After circuit design has been finalized, the masks can be generated one or more mask are generally required for each processing step. Processing begins by forming an active layer in the semiconductor substrate for the necessary active devices. This can be done by ion implantation or by epitaxial techniques. Then active areas are isolated by etching or additional implantation, leaving mesas for the active devices.

Next ohmic contacts are made to the active devices area by allowing a gold layer onto the substrate. FET gates are then formed with titanium/platinum/gold compound deposited b/w the source and the drain.

At this time, the active devices processing is complete and intermediate test are taken.  If it meets specifications, the next step is to deposit the first layer of metallization for contacts, transmission lines, inductors and other conducting areas then resistors are formed by depositing resistive field and dielectric film req. for capacitors. A second layer of materialization completes the formation of capacitors and overlays are deposited. A second layer of materialization completes.

The final processing steps involve bottom or backside of substrate. First it is lapped to the req. thickness, then via holes are formed by etching and plating. Via holes provide ground connections to the circuitry on the top side of the substrate and provide a heat dissipation path from the active devices to the ground plane. After the processing has been completed, the individual circuits can be cut from the wafer and tested.       

MESFET (Metal Semiconductor Field Effect Transistors)

They consists of a conducting channel positioned between a source and drain contact region.

The carrier flow from source to drain is controlled by schottky metal gate. The control is obtained by varying the depletion layer width underneath the metal contact which modulates the thickness of the conducting channel & thereby the current b/w source & drain.

The key advantage of the MESFET is the higher mobility of the carriers in the channel as compared to the MOSFET. Since the carriers in the inversion layer of a MOSFET have a workfunction, which extends into the oxide their mobility also referred to as surface mobility is less than half of the mobility of bulk material. As the depletion region separates the carrier from the surface their mobility is close to that of bulk material.  The higher mobility leads to a higher current , transconductance and transit frequency of the device.

The disadvantages of the MESFET structure is the presence of the schottky metal gate. It limits the forward bias voltage on the gate to the turn on voltage of the schottky diode. This turn ON voltage is 0.7V for GaAS schottky diode. The threshold voltage therefore must be lower than this turn ON voltage. As a result it is more difficult to fabricate circuits containing a large no. of enhancement mode MESFET.

The high transient frequency of the MESFET makes it particularly of interest for microwave circuits. While the advantage of the MESFET provides a superior microwave amplifier or circuit, the limitation of the diode turn ON is easily terminated. Typically depletion mode devices are used since they provide a larger current  and larger transconductance and the circuit contains only a few transistors, so that threshold control is not a limiting factor. The buried channel also yields a better noise performance as trapping and releases of carriers into and from surface states and defect is eliminated.They consists of a conducting channel positioned between a source and drain contact region.

The carrie flow from source to drain is controlled by schottky metal gate. The control is obtained by varying the depletion layer width underneath the metal contact which modulates the thickness of the conducting channel & thereby the current b/w source & drain.

The key advantage of the MESFET is the higher mobility of the carriers in the channel as compared to the MOSFET. Since the carriers in the inversion layer of a MOSFET have a workfunction, which extends into the oxide their mobility also referred to as surface mobility is less than half of the mobility of bulk material. As the depletion region separates the carrier from the surface their mobility is close to that of bulk material.  The higher mobility leads to a higher current , transconductance and transit frequency of the device.

The disadvantages of the MESFET structure is the presence of the schottky metal gate. It limits the forward bias volage on the gate to the turn on voltage of the schottky diode. This turn ON voltage is 0.7V for GaAS schottky diode. The threshold voltage therefore must be lower than this turn ON voltage. As a result it is more difficult to fabricate circuits containing a large no. of enhancement mode MESFET.

The high transient frequency of the MESFET makes it particularly of interest for microwave circuits. While the advantage of the MESFET provides a superior microwave amplifier or circuit, the limitation of the diode turn ON is easily terminated. Typically depletion mode devices are used since they provide a larger current  and larger transconductance and the circuit contains only a few transistors, so that threshold control is not a limiting factor. The buried channel also yields a better noise performance as trapping and releases of carriers into and from surface states and defect is eliminated. 

HIGH FREQUENCY ISSUES

There are a number of physical effects that are negligible at lower frequencies becomes increasingly important at higher frequencies. Two of these effects are the skin effect and radiation effect.

SKIN EFFECT

The skin effect is caused by the finite penetration depth of an electromagnetic field into conducting material . this effect is a function of frequency and is given by

Therefore  decreases with the increase in frequency and so the electromagnetic fields are confined to regions increasingly near the surface as the frequency increases.  This results in themicrowave currents flowing exclusively along the surface of the conductor, significantly increasing the effective resistance of metallic interconnects.

RADIATION LOSS

For conductors and other components of comparable size to the signal wavelengths ,standing waves caused by reflection of the electromagnetic waves from the boundry of the component can greatly enhance the radiation of electromagnetic energy. These standing waves can be easily established either intentionally or unintentionally  

LTE TECHNOLOGY

LTE ( Long Term Evolution) or 4G LTE, is a standard for wireless communication of high-speed data for mobile phones and data terminals. It is based on the GSM/EDGE and UMTS/HSPA network technologies,
increasing the capacity and speed using new modulation techniques.The world's first publicly available LTE
service was launched by TeliaSonera in Oslo and Stockholm on 14 December 2009. LTE is the natural upgrade path for carriers with GSM/UMTS networks, but even CDMA holdouts such as Verizon Wireless, who launched the first large-scale LTE network in North America in 2010.


 LTE is anticipated to become the first truly global mobile phone standard, although the use of different frequency bands in different countries will mean that only multi-band phones will be able to utilize LTE in all countries where it is supported.

LTE is a standard for wireless data communications technology and an evolution of the GSM/UMTS standards. The goal of LTE was to increase the capacity and speed of wireless data networks using new
DSP (digital signal processing) techniques and modulations that were developed around the turn of the millennium. A further goal was the redesign and simplification of the network architecture to an IP-based system with significantly reduced transfer latency compared to the 3G architecture. The LTE wireless interface is incompatible with 2G and3G networks, so that it must be operated on a separate wireless
spectrum.

LTE was first proposed by NTT DoCoMo of Japan in 2004, and studies on the new standard officially commenced in 2005. In May 2007, the LTE/SAE Trial Initiative (LSTI) alliance was founded as a global collaboration between vendors and operators with the goal of verifying and promoting the new standard in order to ensure the global introduction of the technology as quickly as possible. The LTE standard was finalized in December 2008, and the first publicly available LTE service was launched by TeliaSonera in Oslo and Stockholm on December 14, 2009 as a data connection with a USB modem

The LTE specification provides downlink peak rates of 300 Mbit/s, uplink peak rates of 75 Mbit/s and QoS provisions permitting a transfer latency of less than 5 ms in the radio access network. LTE has the ability to manage fast-moving mobiles and supports multi-cast and broadcast streams. LTE supports scalable carrier bandwidths, from 1.4 MHz to 20 MHz and supports both frequency division duplexing (FDD) and time-division duplexing (TDD). The IP-based network architecture, called the Evolved Packet Core (EPC) and designed to replace the GPRS Core Network, supports seamless handovers for both voice and data to cell towers with older network technology such as GSM, UMTS and CDMA2000.[16] The simpler architecture results in lower operating costs.

Frequency bands

The LTE standard can be used with many different frequency bands. In North America, 700/ 800 and 1700/
1900 MHz are planned to be used; 800, 1800, 2600 MHz in Europe; 1800 and 2600 MHz in Asia; and 1800 MHz in Australia. As a result, phones from one country may not work in other countries. Users will need a multi-band capable phone for roaming internationally.