Plasma Display - Advantages and Disadvantages

Plasma Display - Its Advantages and Disadvantages

The term "panel" refers to a form of flat panel display that is now extensively utilised for huge television displays. An inert mixture of noble gases is held in many small cells positioned between two glass panels. The cell's gas is electrically converted to plasma, which then excites phosphors to produce light.

When typical gas atoms are stimulated, they release electrons. The atoms become positively charged when the negatively charged electrons are lost, and the gas is said to be ionised. When this process reaches a particular point, the gas transforms into plasma. When an electrical current is transmitted through a gas, a plasma display will light (Zenon or Neon). Hundreds of thousands of microscopic cells are sandwiched between two glass plates to hold the gas.

On both ends of the cells, long electrodes are sand-witched between the glassware plates. Along with the back glass plate, the address electrodes are hidden behind the cells. The figure is a schematic representation of a plasma display.

Figure: Schematic representation of a plasma display

A dielectric substance and magnesium oxide cover the display electrodes (protective layer). This assembly is attached to the front glass plate above the cell. Both sets of electrodes run the length of the screen. The display electrons are placed in horizontal rows and the address electrodes are positioned in vertical columns along with the screen. A simple grid's horizontal and vertical electrodes. The plasma display's microprocessor charges the electrodes that intersect at that cell to ionise the gas in that cell.

When a tiny voltage is applied to the intersecting electrodes, an electric current runs through the gas in the cell. A fast flow of charged particles is created by the current. They use gas toms to imitate the emission of UV photons. The ultraviolet photons emitted interact with phosphor material on the cell's interior wall. When an ultraviolet photon strikes a phosphor atom in a cell, one of the atom's electrons leaps to a higher energy level, causing the atom to heat up.

When an electron returns to its original state, energy is released in the form of a visible light photon, which lights the screen. When colour phosphors in a plasma display are energised, they emit colour light. Each pixel is made up of three subpixel cells with various coloured phosphors (R, G, and B). Their hues combine to produce the panel's overall hue. The control system may adjust the intensity of each subpixel colour by altering the pulse of current flowing through the cells.

Hundreds of distinct red, green, and blue colour combinations may be made with this effect. This allows the control system to generate colours that span the full visible spectrum. Plasma displays are thin and delicate. They're big and heavy, and they need a lot of energy.

Plasma displays have the following advantages:

1. They can provide a higher contrast ratio.

2. It is possible to make a very big, very thin screen.

3. The image is bright and has a broad field of vision.

4. Motion blurs are less evident.

5. Quick reaction time.

Disadvantages of Plasma displays:

1. They use more electricity.

2. A shorter life expectancy

3. The brightness range of the image is smaller.

4. It is ineffective at high elevations.

5. It is necessary to utilise a more costly plasma suitable sensor.

Block Diagram of Cable TV Network

 

CABLE TELEVISION (CABLE TV):

Cable television is a type of CCTV in which users get regular channel television signals over coaxial cables in exchange for a monthly fee. Master Antenna TV (MATV) is needed,  when a common antennal system is utilized to transmit a strong signal to every TV set connected to the system through coaxial cable.

The cable television system is used to broadcast high-quality television signals to a large number of people. Subscribers that pay a charge for this service get access to more TV programming through this arrangement. The cable system might have more active  channels (VHF and UHF) than a receiver can directly select. This necessitates the employment of a unique active converter in the head end.

Cable TV's primary signal source is a constellation of satellites. Satellite transmissions are received using high power parabolic dish antennas. Most communication satellite downlink communications are in the C-band (3700-4200 MHz) frequency range.

Figure: The block diagram of a cable television system

The block diagram of cable tv network is shown above. Dish antenna signals are first transformed into a lower frequency using a Low Noise Block Converter (LNBC). Conventional antennas erected on high-rise buildings receive VHF and UHF terrestrial broadcast transmissions. Local sports and cultural programming might be broadcast through the cable TV network. Cable network also distributes programmes such as popular movies and music that have been already recorded.

The combining network applies signals from numerous TV stations. The LNB converter converts the signal received by the dish antenna into low frequency signals. Similarly, a translator converts the signal received by a UHF antenna into low-frequency impulses. The combining network combines all of the signals and allocates each channel to a different carrier frequency.

Through a broadband distribution amplifier, the outputs of the combining network are routed to a number of trunk lines. The purpose of a distribution amplifier is to boost the signal amplitude to a higher level in order to compensate for distribution system losses. Through co-axial trunk lines, the distribution amplifier's output is sent to the splitter. Signals are carried by trunk cables to the utilization sites, which may be several kilometres away. Feeder amplifiers are installed at various places along the line to compensate for signal attenuation caused by cable loss.

The signal attenuation that happens as a result of cable failure. Multicore coaxial cables are used to distribute signals from splitters to tap-off locations. A splitter is a resistive-inductive device that offers impedance matching and trunk line isolation. Transformer-coupled, capacitive-coupled, or resistive-pad subscriber taps are all possibilities.

They avoid mutual interference by providing separation between receivers on the same line. Normally, taps are positioned on the wall. Wall taps are available with 300 Ω, 75 Ω, or dual outputs. Standing waves will form as a result of poorly terminated lines. Each 75 Ω distribution cable is terminated by a 75 Ω resistor called a terminator to prevent standing waves.

Crystal Oscillators

 

Crystal Oscillators

Due to the variations in temperature, humidity, transistor, and circuit constants, etc. The frequency stability is usually poor in conventional radio frequency oscillators (using LC circuits). Stable oscillations are required in most applications. In such conditions,  a crystal oscillator works great. It has a high level of stability and quality. In a crystal oscillator, a resonant tuned (tank) circuit is made of a piezoelectric crystal.

Piezoelectric effect

The piezoelectric effect is a highly essential feature of quartz crystals. When an AC voltage is applied, it vibrates at the applied voltage's frequency. On the other hand, if mechanically force to vibrate, it produces an ac voltage. The piezoelectric effect may also be found in Rochelle salt and tourmaline, in addition to quartz.

The most resistant are tourmaline, even though it has the least piezoelectric activity. It is also the most costly. It is used at very high frequencies on occasion. The most piezoelectric activity is found in Rochelle salt, but it is mechanically the weakest. They are readily broken. Microphones, headsets, and loudspeakers are all made with Rochelle salts.

Quartz is a compromise between the Rochelle salt's piezoelectric activity and the tourmaline's strength. It is both affordable and abundant in nature. It is mostly utilized in RE oscillators as a crystal.

Characteristics of crystal oscillator

The crystal is appropriately cut and then placed between two metal plates for use in electronics oscillators, as illustrated in the figure. Let's observe what happens when an ac source is linked across the crystal. Because two metal plates separated by a dielectric operate as a capacitor, even when the attached crystal is not vibrating, it is comparable to a capacitance Cm.

Fig: Quartz Crystal Circuit

Mechanical vibrations are built up when an ac voltage is supplied to the crystal. The natural resonance frequency of these Equivalent circuit vibrations is determined by a variety of variables. Dimensions of the crystal, how the surface is orientated about the axis, and how the crystal is placed are some of these considerations. Although the crystal possesses an electric-mechanical resonance, an analogous electrical resonant circuit may be used to simulate it in motion, as illustrated in the figure.

L = 137H, C = 0.0235, and R = 15 K are typical values for 90 kHz. This is equal to a Q of 5500. The mounting capacitance Cm is substantially higher than the capacitance (C = 3.5pF).

When compared to a discrete LC circuit, the crystal's extraordinarily high Q-value is a standout characteristic. The use of crystals may produce Q values of almost 106, whereas a discrete LC circuit seldom exceeds 100. The extraordinarily high Q of a crystal ensures a relatively steady oscillation frequency.

There are two resonant frequencies in the crystal. First, a series resonant frequency fs, inductance L resonates with capacitance C. The series branch exhibits a parallel resonance with capacitance Cm above the frequency fs. Parallel resonant frequency (F_P) is the name given to this frequency. The crystal oscillator has a capacitive reactance above this frequency. Only between the frequencies F_s and F_P do the crystal act as an inductor. If the crystal is utilized as an inductor in the circuit, the oscillation frequency must be between F_s and F_P. The crystal's two frequencies are temperature-dependent. It is feasible to have a frequency drift of less than 1 part in 10¹⁰ by maintaining the crystal in temperature-controlled ovens.

Transistor crystal oscillator

The circuit of a crystal oscillator is shown in the diagram below. In the collector, a tank circuit L1-C1 is installed, and the crystal is installed in the base circuit. Coil L2, which is inductively connected to coil L1, provides feedback. The feedback winding is linked in series with the crystal. The natural frequency of the LC circuit is roughly equivalent to the crystal's natural frequency.

Fig: Crystal Oscillator Circuit

Capacitor C1 will charge when the power is switched on. Oscillations are created as the capacitor discharges. The crystal oscillator produces oscillations as a result of the positive feedback. The frequency of oscillation in the circuit is controlled by the crystal. Because the crystal is connected to the base circuit, it has a far greater impact on the frequency of the circuit than the LC circuit. As a result, the entire circuit oscillates at the crystal's inherent frequency, causing the circuit to create a resonant frequency.

 

Advantages

1. Because the crystal's frequency is independent of temperature, these oscillators have a high degree of frequency stability.

2. It can create high-frequency oscillations.

Disadvantages

1. They are delicate and should only be used in low-power circuits.

2. Oscillation frequency cannot be adjusted significantly.

What is Current and Voltage in Electronics

Current and Voltage in Electronics

In electrical circuits, it is important to keep track of two quantities: voltage and current. Both voltage and current usually change with time. 

What is Voltage (symbol: V, or sometimes E)  

The cost in energy (work done) necessary to shift a unit of positive charge from a more negative position (lower potential) to a more positive location is the voltage between two places (higher potential). It is, in other words, the energy released as a unit charge goes "downhill" from a higher to a lower potential. The potential difference or electromotive force (EMF)  is also referred to as voltage (EMF). The volt is the standard unit of measurement, with voltages given in volts (V), kilovolts (1kV = 10³V), millivolts (1mV = 10^-3V), and microvolts (1µV = 10^-6 V). To transport a coulomb of charge over a potential difference of one volt, a joule of effort is required. (A coulomb is a unit of electric charge that roughly matches the charge of 6 x 10¹⁸ electrons).  The uncommonly used other voltage levels are nanovolts (1nV = 10^-9 V) and megavolts (1MV = 10⁶ V).

What is Current (symbol: I )

Current is the rate of flow of electric charge past a point. The unit of measure is the ampere, or amp, with currents usually expressed in amperes (A), milliamperes (1mA = 10^-3A), microamperes (1µA = 10^-6A), nano-amperes (1nA = 10^-9A), or occasionally picoamperes (1pA = 10^-12A). A current of one ampere equals a flow of one coulomb of charge per second. By convention, current in a circuit is considered to flow from a more positive point to a more negative point, even though the actual electron flow is in the opposite direction.

The rate of flow of electric charge through a location is known as current. Currents are commonly represented in amperes (A),

milliamperes (1mA = 10^-3A),

microamperes (1µA= 10^-6A)

nano-amperes (1nA = 10^-9A), or

picoamperes (1pA = 10^-12A) as the unit of measurement.

A current of one ampere corresponds to a charge flow of one coulomb per second. Even though the real electron movement is in the opposite drection, the current in a circuit is assumed to flow from a more positive point to a more negative point.

Note: Usually voltage in a circuit is referred to as voltage between two points or voltage across two points. Always use the term "current" to describe the flow of electricity through a device or circuit connection.

It's incorrect, or worse, to state anything like "the voltage across a resistor..." We do, however, commonly refer to the voltage at a circuit's point. This is always taken to indicate the voltage between that point and "ground," which appears to be a well-known position in the circuit.

Voltages are formed by working with charges in devices like batteries (electrochemical), generators (magnetic forces), solar cells (photovoltaic conversion of photon energy), and so on. We get currents by connecting elements (active and passive) with voltages.

The oscilloscope is the most valuable electronic tool because it allows one to look at voltages (and sometimes currents) in a circuit as a function of time. it is often termed as the "eye" of an electronic engineer.

Wires, metallic conductors, and the identical voltage on each of them are used to link items in actual circuits (concerning ground). But this isn't technically true in the domain of high frequencies or low impedances. Since wires may be rearranged, an actual circuit does not have to appear exactly like its schematic representation.

Rules about Voltage and Current:       

1. In a circuit, the sum of the currents entering a point equals the sum of the currents out (conservation of charge). Kirchhoff's present law is a term used to describe this. A node is a term used by engineers to describe such a place. As a result, this may deduce the following: The current in a series circuit (a group of two-terminal devices linked end-to-end) remains constant.

2. When two components are connected in parallel, the voltage across them is the same. In other words, the sum of the "voltage drops" from A to B by one path via a circuit equals the sum of the "voltage drops" via any other route between A and B. This is sometimes described as follows: The sum of any closed circuit's voltage is always zero. This is termed referred to as   Kirchhoff's Voltage Law.

3. A circuit device's power consumption (work per unit time) is P = VI.

This is simply (work/charge) x (charge/ time). For V in volts and I in amps, P comes out in watts. Watts are joules per second (IW = IJ/s).

Usually, power is converted to heat, but it can also be converted to mechanical work (motors), radiated energy (lamps, transmitters), or stored energy (batteries, capacitors). Managing the heat load of a complex system (for example, a computer, where several kilowatts of electrical energy are converted to heat with the energetically inconsequential by-product of a few pages of computing output) can be a critical aspect of the process.

We'll have to expand the basic equation P = VI to deal with average power when dealing with regularly variable voltages and currents, but it's correct as a description of instantaneous power as is. Don't call current "amperage," by the way; that's bush-league. When we get to resistance, the word "ohmage" will be treated with the same discretion.

Radio Frequency Bandwidth of the Signal

 

Radio Frequency Bandwidth of the Signal

The frequency range (i.e., bandwidth) required for a given transmission is depend on the bandwidth occupied by the modulation signals itself. For example, a high -fidelity audio- signal which occupies the range 50 Hz to 15 KHz requires a bandwidth of 300 to 3400 Hz for a telephone conservation. If the same carrier has been similarly modulated a more bandwidth signal the modulated wave bandwidth will also increases. However the transmitted signal bandwidth need not be exactly same as the bandwidth of original signal. Also it is necessary to know the bandwidth of modulating signal itself before finding the bandwidth of modulated signal. If the orrginal signals are sinusoidal in nature, the bandwidth is simply the frequency range between the lowest and the highest sine-wave signal. This creates no difficulty. However, if the modulating signals are non-sinusoidal in nature, then much more complexity arises.

                                                                

In the selection of a particular carrier frequency for a given application, there are number of considerations, but most important is the width of the frequency band covered by the signal components. In television broadcasting, where each radio frequencies channel width is 6 MHz, high carrier frequencies must be employed for interference free reception. A similar requirement applies to frequency modulated sound broadcasts. Radio frequency bandwidths covered by different types of signal and the carrier frequencies at which signals are normally transmitted are shown in table

 

Sl No:	Type of Signal	Radio Frequency Transmission Bandwidth	Typical Carrier Frequency Ranges
1	Telegraphy signals	80 Hz – 2 KHz	18 KHz – 30 MHz
2	Telephony signals and AM signals	10 KHz	500 KHz – 30 MHz
3	FM signals	150 KHz	88 MHz – 108 MHz
4	Facsimile signals	6 KHz	500 KHz – 30 MHz
5	Television signals	6 MHz	54 MHz – 216 MHz
6	Radar signals	2 MHz – 10 MHz	200 MHz – 30,000 MHz

.

Radio waves Classification

 

The frequencies, used for radio communication will range from 15 KHz to more than 30000 MHz. The selection of a particular carrier frequency for a particular application depends upon number of factors: From the Electromagnetic -Spectrum which extends through audio frequencies (20 Hz to 15 KHz), radio frequencies (15 KHz to 300,000 MHz), the infra-red region, the visible light region, the ultraviolet region and X-rays, γ-rays, cosmic rays etc., our interest at present for radio communication purposes is specially with radio frequencies and with audio frequencies to some extent. The radio and audio frequency range is subdivided as shown in table below. The wavelength can be find by the using the equation f = c/λ, where c is velocity of light, f is frequency and λ wavelength.

 

Sl No:	Classification	Frequency range
1	Audio frequency, AF	20 – 2500 Hz
2	High Audio Frequency, HAF	2500 – 5000 Hz
3	Very Low Frequency, VLF	10 – 30 KHz
4	Low Frequency, LF	30 – 300 KHz
5	Medium Frequency, MF	300 – 3,000 KHz
6	High Frequency, HF	3,000 – 30,000 KHz (3 – 30 MHz)
7	Very High Frequency, VHF	30 – 300 MHz
8	Ultra High Frequency, UHF	300 – 3,000 MHz
9	Super High Frequency, SHF	3,000 – 30,000 MHz (3 – 30 GHz)
10	Extremely High Frequency, EHF	30 – 300 GHz

 

Note: Frequencies more than about 2000 MHz are generally referred to as micro wave frequencies.

Single Sideband Amplitude Modulation

Single Sideband Amplitude Modulation

The general AM equation shows that when a carrier is amplitude-modulated by a single sine wave, the resulting signal consists of three frequencies — the original carrier frequency, the USB (f_c + f_m) and the LSB (f_c — f_m). Out of this, the carrier itself does not carry any information, and hence the power transmitted in the carrier signal will have no use. The two sidebands carry the same information. We need only one sideband at the receiver for the demodulation of the AM signal. We can improve the efficiency of the transmission by transmitting only one sideband (upper or lower one can be used). The resulting signal is referred to as single sideband SSB. As we know, the power transmitted,

 

P_T = P_CARR (1+ m²/2) = P_CARR + P_CARR m²/2

 

That is about 2/3rd of the power is transmitted by the carrier, which is a wastage. For the highest modulation index (m = 1), the efficiency of transmission is 33%. Under these conditions, 67% of power is transmitted by carrier, and this much power is waste. For values of m < 1, the efficiency is less than 33%. If the carrier is suppressed, only the side band power remains. As this is only P_CARR m²/2 , a 2/3^rd saving is effected at 100% modulation, and even more is saved as depth of modulation is reduced. If one of the sidebands is now also suppressed, the remaining power is P_CARR m²/4 a further saving of 50% can be achieved over the carrier suppressed AM.

 

Single-sideband transmission (SSB) is a method of transmitting signals based on amplitude modulation in which only one sideband is transmitted. Essentially, the carrier and one sideband of an AM signal are removed, leaving only the other sideband. Assuming both sidebands are symmetric, no information is lost in the process. The required signal bandwidth is reduced and, since the final RF amplification is concentrated in a single sideband, effective power output is greater than normal AM. The carrier and removed sideband account for well over half of the power output of an AM transmitter.

 

To decode the signal at the receiving end the original AM mode is synthesized by adding a carrier signal to the lone sideband. The signal can then be demodulated as a standard AM signal. Because the synthesized carrier is locally generated, it of much higher quality than a transmitted one, which contributes to a higher quality received signal. An SSB signal cannot be demodulated by standard AM receivers because of the lack of a reference carrier signal. The major advantages of SSB over normal AM are

 

1. The power saving - Since the carrier is not transmitted, there is a reduction by 50% of the transmitted power. In AM, at 100% modulation, 1/2 of the power is comprised of the carrier; with the remaining (half) power in both sidebands.

 

2. Because in SSB, only one sideband is transmitted, there is a further power reduction by 50%.

 

3. Since SSB has only one sideband, the bandwidth required is only half than that required for normal AM.

AM Modulator Block Diagram

AM Transmitter Block Diagram

Note: Class C RF output amplifier is used in High Level Modulation.

Class B RF linear power amplifier is used in Low Level Modulation.

 

The general block diagram of an AM modulator is shown in the figure. A tuned circuit is used to generate AM. It is probable to create the output current of a class C amplifier relative to the modulating voltage by the application of this voltage in series by means of some of the 'dc' supply voltages for this amplifier.

 

In an AM transmitter, amplitude modulation can be done at any point after the radio frequency source. If the output stage in a transmitter is collector modulated, the system is known as high level modulation. In high level modulation, the power amplification of the RF signal takes place before modulation. If modulation is applied to any other point (base or emitter), the system is known as low level modulation. In low level modulation, the power amplification of the RF signal takes place after modulation.

 

The RF oscillator generates the radio frequency wave for modulation (i.e. the carrier wave). This is generally a crystal oscillator because it can generate highly stable frequency. The oscillator frequency shall not be affected by the loading of the next stages. Hence a buffer amplifier is required at the oscillator output. It will be a class A amplifier. The RF power amplifier raises the power of the RF signal to the required level for modulation. It will be a class-C amplifier.

 

The audio signal to be transmitted is applied to microphone. Microphone will converts sound wave into electrical audio frequency waves. Microphone is an audio transducer. The output signal from the microphone is very small in amplitude. The signal voltage must be raised to the sufficient level before power amplifications. AF pre-amplifier is used for this purpose. It will be a class A amplifier. The power of the AF signal must be raised to the required level before modulation AF power amplifier raises the power of the audio signal to the required level. It will be a class B amplifier.

 

The AM modulating amplifiers will modulate the RF signal by the AF signal from the output of the AF power amplifier. The transmitting antenna radiates the RF power from the output of the modulator into space.