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Monday, 9 December 2019

Flemings Right Hand Rule for Generators

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Flemings Right Hand Rule can be used to find out the direction of induced e.m.f. in a conductor undergoing generation of emf. Fig shows the method of positioning right hand with fingers at right angles to each other. Flemings Right hand rule says that keeping the first finger, second finger and the thumb of right hand at right angles to each other similar to be three axis, if the first finger points out in the direction of magnetic field, the thumb in the direction of motion of conductor, then the second finger points out the direction of induced e.m.f.
(a) Method of positing Right Hand
(b) Direction of Induced EMF
As seen from above, for an e.m.f. to be produced in a conductor there should be a flux and motion between the conductor and the flux. Here the conductor of length 'l' meter is placed in a magnetic field of Φ Wb in A square metres so that the flux density

B = Φ/A Wb/m2 or testla.

The conductor is rotated about the axis with a velocity of 'v' m/sec. According to Faradays Laws of Electromagnetic induction, the e.m.f. induced in the conductor is given by

e = Rate of change of flux linkages
= B.l.v Volts

This value is maximum since the direction of motion is at right angle to the direction of flux. If the conductor were to move parallel to the direction of flux, then the conductor does not cut the lines of force i.e.. no flux linkage. Therefore, no e.m.f. will be induced in the conductor. Hence when the conductor is made to rotate about an axis it moves from parallel to the magnetic flux to perpendicular position. Therefore, the induced e.m.f. would also vary from zero to maximum.

Consider a position between zero angle to the direction of flux to perpendicular position wherein the direction of motion at any instant makes an angle of θo with respect to the direction of flux.
The component of voltage induced perpendicular to the direction of flux at any instant is equal to v sinθ. This will be true since when the conductor moves parallel to the direction of flux θ = 0 and sin 0o = 0. When the conductor moves perpendicular to the direction of flux θ = 90°. Hence re-writing the equation of e.m.f. as

e = B.l.v sin θ volts

Where e = e.m.f. induced in the conductor (Volts)
B = Flux density (Wb/m2)
l = length of the conductor (m)
θ = Angle of incidence between the direction of flux and the direction of motion about an axis

If the coil has N number of turns, then the e.m.f. induced at any instant is given by

e = 2N.B.l.v.sin θ, Since a coil contains two sides.


RS232 Parameters, Start and Stop Bits

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RS232

RS232 (Recommended Standard 232) is the standard developed by EIA (Electronic Industry Association) in the year 1960 for the serial communications of data. This standard is a widely used standard, the PC consist of two RS232 ports Com1 and Com2.  Rs232 is used to connect a DTE (Data Terminal Equipment) to a DCE (Data Communications Equipment). For E.g. ., DTE is pc, printer and DCE is Physical interface. In RS232, data are transmitted serially and Provides full duplex Communication.

RS232 Parameters

When two devices want to communicate, the sender sends data as character by Character. The character is corresponds to a bit. The number of characters is called data bits. The data is appended with one start bit at prefix and stop bit in the suffix. The receiver decodes the data using start and stops bits and receives it. This type of communication is called an asynchoronous communication, because no clock is used. Parity bit is also appended to the data to be sent in order to achieve error correction. For two devices to communicate through RS232 the communication parameters should set in both systems. They are Data bits, data rate, start bit, stop bit, parity bit, flow control.

Data rate

• Data rate is the rate at which the data communication takes place.

• The PC supports various data rates such as, 50,150,300,600,1200,2400,4800,19200,38400,57600 and 115200 bps.

• The oscillator in the RS232 circuitry operates at 1.845 MHZ.

• It is divided by 1600 to obtain 115200 data.

Data bits

• Data bits is the Number of of bits transmitted for each character.
• The character can have 5 or 6 or 7 or 8 bits.
• If ASCII character is send, the number of bits is 7.

Start bits

• Start bit is the bit that is prefixed to the data in order to identify the beginning of the character.

Stop bits

• These bits are appended to the data bits to identify the end of character.
• If the data bits are 7 or 8, one stop bit is appended.
• If the data bits are 5 or 6, two stop bits are appended.

Parity

• Parity bits are appended to the character for error checking.
• The parity can be even or odd.
• For even parity, the parity will make the total no. of bits even.
• For odd parity, the parity will make the total no. of bits odd.

Flow control

• Flow control can be defined as a protocol to stop/resume data transmission. It is also known as hand shaking protocol.

• For Hardware handshaking, two signals are used:

• RTS-REQUEST TO SEND

• CTS-Clear To Send

• The software handshaking is known as XON/XOFF.

RS232 Connector Configurations

• RS232 specifies two types of connectors:

25-pin connector
9-pin connector

• Only few pins are used in 25-pin connector.

• Important pins are 2 (Transmit), 3 (Receive) 7 (Signal Ground)

• RS232 uses unbalanced transmission and is susceptible to noise.


For the 25-pin Connector

Pin Number
Function (Abbreviation)
1
Chassis Ground
2
Transmit Data (TXD)
3
Receive Data (RXD)
4
Request To Send (RTS)
5
Clear To Send (CTS)
6
Data Set Ready (DSR)
7
Signal Ground (GND)
8
Carrier Detect (CD)
20
Data Terminal Ready (DTR)
22
Ring Indicator (RI)

For the 9-pin Connector

Pin Number
Function (Abbreviation)
1
Carrier Detect (CD)
2
Receive Data (RXD)
3
Transmit Data (TXD)
4
Data Terminal Ready (DTR)
5
Signal Ground (GND)
6
Data Set Ready (DSR)
7
Request To Send (RTS)
8
Clear To Send (CTS)
9
Ring Indicator (RI)




Saturday, 7 December 2019

Working of Simple Loop DC Generator

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Working Principle of Simple Loop DC Generator

For the purpose of study, a single loop generator is taken. In figure, the single loop generator having a coil with two sides connected to a commutator to which two brushes slide.


The coil is placed in between two permanent magnet in such a way that it can rotate about its axis cutting the flux produced by the permanent magnet.

Five distinct positions of the coil are chosen for the purpose of study. in Fig, the coil side ‘ab' and 'cd' rotate between the north pole and the south pole of a permanent magnet. Assuming the initial position of the coil sides moving parallel to the direction of flux as shown in Fig, no linking of the flux takes place as it does not cut the flux. Hence, no e.m.f. is induced in the conductor.
Conductor moving Parallel to the Direction of Flux
Rotating the conductor by 90o clockwise, the conductor travels along the path of a circle and takes a position as shown in Fig. The conductor coil sides 'ab' moves down perpendicular to the flux while the coil side 'cd' moves upwards again perpendicular to the flux. Maximum e.m.f. is induced in the coil and since the sides of the coil arc connected in series, the total e.m.f. is the sum of the e.m.f. of each side of the coil.
Conductor moving at Right Angle to the Direction of Flux
If external circuit is complete, the current, in the coil will be in the direction 'b' to 'a' in coil side 'ab’ and 'd' to 'c' in coil side 'cd'. Since the coil sides 'ab' and 'cd' are connected in series, the total e.m.f. is the sum of the e.m.f. induced in each coil side and the direction will be from 'dcba'. Again rotating the coil by another 900 (i.e., 180° from initial position), the coil occupies a position as shown in Fig. The conductor coil sides 'ab' and 'cd' moves parallel to the magnetic flux. Since it does not cut the magnetic flux, no e.m.f. is induced in it. Hence, the e.m.f. which was maximum in the previous position drops down to zero.
Conductor moving Parallel to the Direction of Flux
If the position of the coil sides 'ab’ and 'cd' are moved by rotating it further by 90o (i.e., 270° from initial position), it occupies a place as shown in Fig. The coil sides having rotated by 90° and the motion of the coil side 'all' is upwards perpendicular to the magnetic flux while the coil side 'cd' is downwards perpendicular to the magnetic flux. The e.m.f. induced in the coil sides are maximum but since the direction of motion of the conductors are opposite to that shown in Fig, the sign of the maximum e.m.f. induced and the resultant current is also opposite. The direction of current is from 'a' to 'b' in conductor 'ab' and similar from 'c' to 'd' in conductor 'cd'.
Figure
Rotating the coil sides by another 90° (i.e., 360° from the initial position) bringing the conductors to the position shown in Fig, the coil travels parallel to the flux and as such no e.m.f. is induced in it. This position also refers to the initial position. The e.m.f. which was negative maximum would drop down to zero. It should be noted that since the conductor moves in the path of a circle and the change in the magnitude of e.m.f. also is smooth following sine law. Since the e.m.f. has a positive quantity and a negative quantity, the e.m.f. is said to alternate from a positive to negative quantity. Therefore, it is called alternating e.m.f. or alternating current. If a graphical representation of the e.m.f. produced in the coil is shown, it would resemble as shown in Fig.

The representation at each stage of rotation of conductor is shown in Fig below.

From the above, it is seen that the e.m.f. produced within the coil is alternating in nature and to convert to direct current a commutator is used. A commutator is a device by which current flows in single direction in the external circuit. The- simplest commutator for the above two pole generator is split ring and is represented in Fig. With the use of commutator the negative portion of the induced e.m.f. is converted into positive such that the current in the external circuit is in single direction. In Fig, two distinct positions of the conductor representing the positions shown in Fig and are shown with an external circuit. Note carefully the flow of current from the coil to the external circuit even though the current in coil side 'ab' and 'cd' change for every 180° rotation of the conductor. The graphical representation of e.m.f. in the external circuit is shown in Fig.

Such unidirectional current is called direct current in short d.c. A generator which gives d.c. in the external circuit is called d.c. generator. Necessarily it uses a commutator.

FUNCTIONS OF SPLIT RING AND COMMUTATOR:

When the coil rotates, the e.m.f. induced in the conductor is of alternating in nature. The current in the conductor coil is the result of the e.m.f. produced in the conductor. Since the coil rotates, there should be a method of drawing the current for the external circuit from a rotating coil to, a stationary terminal. There are three methods of achieving this object. They are :

a. By using a split ring when the generator is of two pole
b. By using a commutator when the generator is of multipole
c. By using a slip ring

The split ring and commutator are used in case the current in the external circuit should, be uni-directional, and slip ring is used when the current in the external circuit has to be alternating. Fig. (a) shows a split ring while Fig (b) shows the commutator. In both the cases, two or four carbon brushes slide over it collecting the current from the rotating conductor. Commutators are used for d.c. machine as well as repulsion motors.
(a) Commutator
(b) Split Ring
A commutator consists of number of bars, an equal number of mica segments, and an iron core consisting of two end rims and a connecting shell on which the bars and mica segments are placed. Towards the bottom, the bars are partly cut out on both sides in the shape of a V for holding the commutator together by rings. Mica segments are used between bars to prevent adjacent bars from touching. The armature windings are connected to the commutator segments to enable the e.m.f. generated to be collected to a stationary terminal. Fig. shows the commutator assembly.
Commutator Assembly


Friday, 6 December 2019

Classification of DC Generators

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CLASSIFICATION OF DC GENERATORS

D.C Generators are classified depending on the type of connections made. If the field coils are connected in parallel to armature, it is called shunt generator. If the field coils are excited separately, it is said to be separately excited generator, and if the field coils are connected in series to armature it is known as series generator. There are two combinations possible viz shunt and series and if both are used, then it is said to be compound generator. In compound generator two combinations are possible

(a) Short shunt compound generator. and
(b) Long shunt compound generator.

The generator classification tree is given below.
Separately Excited DC Generator :

When the field winding is excited by a separated d.c. current, it is called separately excited DC generator. In this case the field current can be varied through a variable resistance connected in series to the battery circuit.  The Load is connected directly across the armature. The polarity of the generated e.m.f. depends on the direction of rotation of the shaft and the polarity of battery source. The connection diagram is shown in Figure.

D.C. Shunt Generator :

On the shunt generator the current for the magnetization of the field is tapped from the armature itse1f. The shunt field is connected in parallel to the armature. As such the shunt winding has to take full voltage of the armature and so it consists of thin wire of many turns. The sum of the load current and shunt field current is the armature current. The connection diagram is shown in Figure.



D.C. Series Generator :

In the case of a series generator, the field winding is connected in series to armature and the current in the armature, series field and the line are same. Since the voltage drop iii the series field should be as least as possible and also be capable of taking full load current, the field winding consists of less number of turns with thick wire. The total current is the same as that of series field or the armature. The connection diagram is shown in Figure.


D.C. Compound Generator :

D.C Compound generators are of two types

(a) Long shunt compound generator and
(b) Short shunt compound generator.

The difference between the two lies in the connection of the shunt winding.

Long Shunt Compound Generator :

Compound generator utilise both the shunt field and the series field. In the long shunt compound generator, the shunt field is connected parallel to the line as shown in Figure. The line current distribution is again a combination of shunt generator and series generator. In this case the armature current is equal to series field current but the line current is the sum of armature current and shunt field current.

Short Shunt Compound Generator :

When the shunt field is connected across the armature of a series generator, it is termed as short shunt compound generator. As in the shunt generator, the shunt field is impressed with armature voltage and series field takes the line current. The line current is the sum of armature current and the shunt field current. The connection diagram is shown in Figure.



Monday, 2 December 2019

Micromachined Antennas

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Micromachine is a technique used in an antenna or a system for improving the performance of the system. The performance improvement includes increasing the gain, bandwidth, efficiency etc.  In other words, we can say that by using a micromachine technique, we can improve the radiation intensity of the antenna. We know that the surface waves will affect the radiation (fringing waves) of an antenna (since it will affect the major and minor lobes). By using micromachine technique, we can reduce the surface waves. Thus the major lobe and minor lobe levels can be increased.   

Micromachine

First we are considering a substrate over which we are creating a cavity. i.e., the removal of some portion of substrate for  providing the patch over the substrate. Micromachine are of two types.

(i) Surface micromachining

Surface micromachining means removal of portion (small) of substrate from the surface of the substrate for producing the pitch.

(ii) Bulk micromachining

Bulk micromachining means bulk amount of substrate can be removed from the substrate. In order to remove the substrate portion, we use the etching process. etching process is of two types.


Dry etching:

In dry etching, an evacuated chamber is used. In the evacuated chamber, the plasma is generated and this plasma is used to remove the silicon substrate.

Wet etching:

In wet etching, a durable mask is used. The region of the substrate which need to be etched is unmasked and all other portions are masked, where we have to undergo chemical reactions.


GaAs ( Gallium Arsenic) Substrate:
ɛr = 12.9

Thickness = 350 μm
Patch length = 1.21 mm
Patch width = 1.91 mm

The permittivity of the substrate determine the performance. The synthesised permitivity can be obtained as


Where,  ɛr_ syntheff is the effective synthesized permittivity and can be obtained as:
Where, K0 is the free space wave number and β is the propagation constant.


The effective synthesized permittivity can be obtained as:



From the graph, it is clear that as the microstrip width increases, the permittivity decreases. As permittivity increases, the performance also increases. Hence, in order to improve the permittivity, we must select the width of the microstrip as very small.

Micromachined slotline Antenna:

The micromachined slotline antenna can be easily integrated with 2 or 3 terminal active devices.
There are mainly 2 types of slot ring antenna.

(i) With trenches
(ii) Without trenches

GaAs FET activated by DC bias.

For fixed resonant frequency, a trenched one is having larger size than the untrenched. So there will be a higher radiation efficiency for the trenched one. E - plane and H - plane radiation power is about 1 to 2 dB higher for trenched.

Gate is used for control of flow of charge carriers from source to drain (S to D). The amount of fringing can be calculated by the applied voltage. Depending upon our requirement, we can increase the cavity by changing the DC applied voltage.




By applying the voltage, the capacitor can be trenched. For backside trenching, anisotropic etchant (KOH) is used. By doing like this, 550 tapered edges are produced. For slot line, isotropic etchant CP4 is used (mixture of nitric acid, hydrofluoric acid and water).

Microelectro mechanical system antenna:

The micro electro mechanical system antenna is used when a single antenna is used for a range of frequencies. This can be applied in telecommunication systems, radars etc. Since a single antenna is used for the entire system, we can reduce the size and cost of the system. This can be achieved by using micro electro mechanical switches or capacitors in antenna. The capacitors used here are cantilever type capacitors and fixed beam type capacitors.



The substrate used is glass type (ɛr = 400). The sputtering is done at 100/3000 A0. The seed layer is Ti/Au.



Friday, 29 November 2019

Difference between Static Ram and Dynamic Ram

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STATIC RAM (SRAM)

A static RAM essentially contains an array of flip-flops, one for each stored bit. Data written into a flip-flop remains stored as long as a d.c. power is maintained. The memory capacity of a static RAM varies from 64 bits to 1 Mega bit.

Static RAM cell: The logic diagram of a static RAM cell is shown in Fig. 4.5. The cell (or a group of cells) is selected by HIGH values on the ROW and COLUMN lines. The input data bit (1 or 0) is written into the cell by setting the flip-flop for a 1 and resetting the flip-flop for a 0 when the READ/ WRITE’ line is LOW (i.e., write). When the READ/ WRITE’ line is HIGH, the flip-flop is unaffected. It means that the stored bit (data) is gated to the data out line.

The flip-flop in static memory cell can be constructed using Bipolar Junction Transistor (BJT) and MOSFETs that are shown in Fig respectively.
(a) Using Bipolar Transistor
(b) Using MOS Transistor
In a bipolar static RAM cell shown in Fig (a), two BJTs Q1 and Q2, are cross-coupled to form a flip-flop. Here, each transistor has three emitters, namely Row Select input, Column Select input, and Write input. To select the cell, both the row and column select lines must be held HIGH. When selected, a data bit can be stored in the cell (Write operation) or the content of the cell can be read (Read operation). If either row or column select line is LOW, then the memory cell is disabled.
In a MOS stalk RAM cell shown in Fig, Q1 and Q2 act like switches while Q3 and Q4 acts as active load resistors. The transistor Q1 conducts and Q2 is cut off or vice versa. As a static RAM uses a flip-flop as the basic memory cell, it consists of thousands of flip-flops.

DYNAMIC RAM (DRAM):

The Dynamic Random Access Memory (DRAM) is the lowest cost, highest density random access memory available. Nowadays, computers use DRAM for main memory storage with the memory sizes ranging from 16 to 256 Mega bytes.

Data are stored as charge on every capacitor, which must be recharged or refreshed thousands of times every second in order to retain the stored charge. These memory devices make use of an integrated MOS capacitor as basic memory cell instead of a flip-flop. The disadvantage is that the MOS capacitor cannot hold the stored charge over an extended period of time and it has to be refreshed every few milliseconds. This requires more circuitry and complicates the design problem. Static RAMs are simpler than dynamic RAMs.


A typical dynamic RAM cell consisting of a single MOSFET and a capacitor is shown in Figure. A dynamic RAM consists of an array of such memory cells. In this type of cell, the transistor acts as a switch. The memory cell also requires MOSFETs for READ and WRITE, gating to operated the cell. Data input is connected for storage by a WRITE control signal.

The dynamic RAM offers reduced power consumption and huge storage capacity in a single memory chip.

ADVANTAGES OF DRAM OVER SRAM :

Advantages of DRAM over SRAM :

• DRAMs, due to their simple cell structure have 4 times the density of SRAMs. This permits 4 times the memory of SRAMs on a board of the same size.

• The cost of DRAMs for each bit of storage is nearly one-fifth that of SRAMs.

• DRAMs have lower power consumption as compared to SRAMs. So, smaller and cheaper power supplied can be used for DRAMs and also the cost of the overall system can be reduced.

• Because of their high capacity and low power consumption, DRAMs are used in the main internal memory of most personal computers.

Disadvantages of DRAM over SRAM :

• DRAMs are slower in speed and more complex as compared to SRAMs.

• DRAMs require refreshing operation after regular intervals, whereas SRAMs do not require any refreshing.

• DRAMs can not be used where only a small amount of memory, typically less than 64kB and high speed is required.

Difference between Static Ram and Dynamic Ram in tabular form:

Static RAM

Dynamic RAM

1. Stored data is retained as long as power is ON.
1. Stored data gets lost and refreshing is needed.
2. Stored data do not change with time.
2. Stored data changes with time.
3. Consumes more power.
3. Consumes less power.
4. Expensive.
4. Economical.
5. Construction is complex.
5. Construction is simple.
6. Low packing density.
6. High packing density.
7. No refreshing is required and hence the operation is easy.
7. Refreshing is needed with additional memory circuitry and hence complicates the operation.
8. No maintenance is required.
8. Maintenance is required.



Thursday, 28 November 2019

ROM Working, Types and Application

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Working Principle of ROM

Though the current ROMs do not make use of diode matrix but it will help in understanding the working of ROM. The principle on which ROM is based can be explained with the help of Figure which shows storage in a diode ROM. A storage cell is capable of storing a 1 or a 0. A ROM can be formed from a matrix of diodes and such memories are called diode matrix ROM.
Storage in a Diode ROM
A storage cell in the diode matrix is located at each intersection of a row line and column line. For storing a 0 the diode is not connected and for storing a 1 the diode is connected at the intersection of row line and column line as shown in Figure. These coupling binary cells are normally fixed at the time of manufacture and cannot be altered later. These ROMs are either made as per users requirement or are available in standard form for special purposes such as binary-to-gray code conversion for determining the squares of numbers etc.

For explaining the working of diode matrix ROM let us consider a memory which can store eight words each of 4 bits and any one of these words can be read whenever required. The connections for such a ROM are shown in Figure. The words to be stored from location 0 to 7 are given in Table - 1.

For addressing or accessing eight locations we need eight lines or we may use a three line to eight line decoder and we will have only three address lines. This decoder is made inside the ROM and with the three input address line we can access any of the eight locations by assigning proper input address signal. The address signal required for accessing any location from 0 - 7 is shown in Table - 2 and is called look up table for ROM.


Table – 1, Location or Address and Words to be Stored

Location or Address
0
1
2
3
4
5
6
7
Word to be stored
0011
1100
1010
0101
0111
0000
1111
0001

Table – 2, Binary Address or Input Signal and Stored Word

Address A2 A1 A0
000
001
010
011
100
101
110
111
Stored word D2 D1 D0
0011
1100
1010
0101
0111
0000
1111
0001

In Figure, we have shown the use of three to eight line decoder. We may extend the capacity of such memories. In general, a ROM with capacity to store in words for n bits is known as m x n ROM and is represented as shown in Figure.

Working : Let us see how the circuit of ROM (Figure) works. The address of location which we wish to read is given as input signal to the decoder say we wish to read the contents of 5th location so we give input 101 to the decoder and decoder will activate the line corresponding to 5th row. As no diode is connected between 5th row line and 1, 2, 3 and 4th column line so all the outputs will be 0s, i.e., the output word will be 0000 and this is what we expect. Now let us examine what happens when 011 is the address signal, this signal will make the decoder to activate line corresponding to 3rd row line. As no diode is connected between this row line and first column line the output D3 will be a 0, at the junction of row line 3 and column line 2, a diode is connected, so D2 will be a 1. Similarly D1 will be a 0 and D0 will be a 1. Hence the word at the output D3 D2 D1 D0 will be 0101 as we should have.

Types of ROM in Digital Electronics

Depending upon the methodology of programming, crusing and reprogramming information into ROMs, these are classified as

1. Mask-Programmed ROM (MROM)
2. Programmable ROM (PROM)
3. Erasable Programmable ROM (EPROM)
4. Electrically Erasable Programmable ROM (EEPROM)
5. Flash ROM.

• MROMs are permanently programmed by the manufacturer during the fabrication process by using a custom designed mask as per the system design specification. These are non-programmable ROMs.

• In case of PROMs, the programming is done by the customer with the help of a special gadget called PROM programmer. These are one time programmable ROMs.

• An EPROM can be erased and reprogrammed as many times as desired. Once programmed, it is non-volatile, i.e., it holds the stored data indefinitely.

• The stored information can however be erased by exposing the chip to ultra-violet (UV) radiation through a transparent window on the top of the chip meant for the purpose. These EPROMs are referred to as UVEPROMs.

• EEPROMs, also called EAPROMs (Electrically Alterable PROMs) can be erased and programmed by the application of controlled electric pulses the IC. EEPROM is a rugged, low power low density semiconductor device and it occupies less space. The cost is higher as compared to EPROMs.

• The flash memory combines the low cost and high density features of EPROM and in-circuit electrical erasability of EEPROM without compromising on the high speed access of both.

Differences between EPROM and UVEPROM

S. No.
EEPROM
UVEPROM
1
Erasure and programming is done with electrical pulses.
Erasure and programming is done with ultra violet light.
2
Erasure and reprogramming is possible when the EEPROM is still in the circuit.
Erasure and reprogramming should be done by taking out the UVEPROM chip from the circuit.
3
Easy to construct
Difficult to construct.
4
The voltage on the floating gate permits the storage.
The photocurrent from the insulated gate structure permits the storage.
5
Speed of operation is more.
Speed of operation is less.
6
Shorter time of erasure.
Longer time of erasure.
7
Ability to erase and write individual bytes
Ability to erase and write memory array.
8
Low density
High density.
9
Expensive
Economical.
10
Suitable for field and remote control applications.
Suitable for experimental projects, product development and college labs.


Applications of ROM in Digital Electronics

Some of the applications of ROM in Digital Electronics are

1. ROMs are used for a variety of tasks within a digital system. They can be used as a direct substitute for any random logic of AND, OR and NOR gates.

2. ROMs are used to store bootstrap program that loads operating system program available in secondary memory and language interpreters in personal and business computers and to store, monitor or control programs in microcomputer and microprocessor based systems like electronic games, electronic cash registers, electronic scales and microcomputer controlled automobile fuel injection.

3. A very significant application of MOS ROM is for character generation. This includes display control for moving billboards and LED arrays.

4. They can also be used for code conversion, e.g., ASCII to EBCDIC conversion.

5. A ROM and a DAC can be used to generate sine waves, saw-tooth waves, triangular waves and square waves.

6. A ROM can be used to implement any or a set of logic expressions and is therefore used in the design of combinational circuits.