Thursday, February 14, 2013

What is Darlington Pair?

This is two transistors connected together so that the amplified current from the first is amplified further by the second transistor. 

This gives the Darlington pair a very high current gain such as 10000. 

Darlington pairs are sold as complete packages containing the two transistors. 

They have three leads (B, C and E) which are equivalent to the leads of a standard individual transistor.

Static RAM Vs Dynamic RAM


The difference between the two Logic Styles are:
  • TTL circuits utilize BJTs while CMOS circuits utilize FETs.
  • CMOS allows a much higher density of logic functions in a single chip compared to TTL.
  • TTL circuits consumes more power compared to CMOS circuits at rest.
  •  CMOS chips are a lot more susceptible to static discharge compared to TTL chips
  • Propagation delay is more in CMOS compared to TTL
  • Switching Speed is More for TTL compared to CMOS.
  • CMOS devices are cheaper than TTL Devices. 
  • The Power Supply requirement for TTL is  3 to 15V, small fluctuations are tolerated.
  • The Power Supply requirement for CMOS is  5V ±0.25V, it must be very smooth, a regulated supply.
  • TTL Can handle only less frequency compared to CMOS.
Why CMOS is Slower compared to TTL?

Since TTL has very little parasitic capacitance, the time delay is very small, & TTL is faster.

MOSFETs, based on voltage operations, have much greater capacitances, the charging & discharging of which consumes time (Ref: RC time constant), hence CMOS is slower.

An Introduction to Digital Logic Families

What is a Logic Family?

In Digital Designs, our primary aim is to create an Integrated Circuit (IC).
A Circuit configuration or arrangement of the circuit elements in a special manner will result in a particular Logic Family.

What are the advantages of creating different Logic Families?

Electrical Characteristics of the  IC will be identical. In other words, the different parameters like Noise Margin, Fan In, Fan Out etc will be identical.
Different ICs belonging to the same logic families will be compatible with each other.

Some Characteristics we consider for the selection of a particular Logic Family are:
  • Supply voltage range 
  • Speed of response 
  • Power dissipation 
  • Input and output logic levels 
  • Current sourcing and sinking capability
  • Fan-out 
  • Noise margin
The basic Classification of the Logic Families are as follows:
  • Bipolar Devices
  • MOS Devices
  • Hybrid Devices
 Bipolar Families:
  1. Diode Logic (DL)
  2. Resistor Transistor Logic (RTL)
  3. Diode Transistor Logic (DTL)
  4. Transistor- Transistor Logic (TTL)
  5. Emitter Coupled Logic (ECL) or Current Mode Logic (CML)
  6. Integrated Injection Logic (IIL)
MOS Families:
  1. P-MOS Family
  2. N-MOS Family
  3. Complementary-MOS Family 
    1.  Standard C-MOS
    2. Clocked C-MOS 
    3. Bi-CMOS
    4. Pseudo N-MOS
    5. C-MOS Domino Logic
    6. Pass Transistor Logic
 Hybrid Family:
  1. Bi-CMOS Family
Diode Logic 
In DL (diode logic), only Diode and Resistors are used for implementing a particular Logic.Remember that the Diode conducts only when it is Forward Biased.

Disadvantages of Diode Logic
  • Diode Logic suffers from voltage degradation from one stage to the next.
  • Diode Logic only permits OR and AND functions.
Resistor Transistor Logic
In RTL (resistor transistor logic), all the logic are implemented using resistors and transistors. One basic thing about the transistor (NPN), is that HIGH at input causes output to be LOW (i.e. like a inverter). In the case of PNP transistor, the LOW at input causes output to be HIGH.
RTL Circuit
  • Less number of Transistors

  • High Power Dissipation
  • Low Fan In
Diode Transistor Logic
In DTL (Diode transistor logic), all the logic is implemented using diodes and transistors.

DTL Logic
  • Propagation Delay is Larger
Transistor Tansistor Logic
In Transistor Transistor logic or just TTL, logic gates are built only around transistors.
TTL Logic has the following sub-families:
  • Standard TTL.
  • High Speed TTL
  • Low Power TTL.
  • Schhottky TTL.
  • Low Power Schottky TTL
  • Advanced Schottky TTL
  • Advanced Low Power Schottky TTL
  • Fast Schottky
Emitter Coupled Logic
The main specialty of ECL is that it is operating in Active Region than the Saturation Region. That is the reason for its high speed operation. As you can see in the figure, the Emitters of the Transistors Q1 and Q2 are coupled together.
Emitter Coupled Pair

  • Large Silicon Area
  • Large Power Consumption

Monday, February 11, 2013

Advanced Digital Audio Codecs

DTS standards
DTS (Digital Theater Sound) is a digital sound coding standard created by Universal. Compared with the Dolby Digital standard, DTS uses four times less compression and digitises sound at 20 bits instead of 16. Therefore, DTS's sound quality is theoretically higher, at the cost of a higher bit rate. To be able to play DTS-encoded media, you need a certified DTS decoder.

DTS falls into four different categories:

DTS 6, the most commonly used 5.1 standard, which can encode six-channel sound with less compression than the Dolby Digital standard. The first five channels are used for the satellite speakers, while the last is reserved for the subwoofer. These devices are normally identified by the presence of this logo:
DTS ES (Digital Theater Sound Extended Surround), 6.1 standard which uses an additional rear channel (rear central). DTS ES uses less compression than Dolby Digital EX.
The DTS ES standard has two variants:
o DTS ES Matrix, which has a seventh channel interpolated with the primary channels. This is called "virtualisation".
o DTS ES Discrete has an seventh independent channel.

DTS 24/96 represents an audio format used for storing high-definition music with several channels. This format is primarily used in DVD Audio, or audio tracks which accompany video DVDs. The name comes from the fact that the tracks are recorded in 24 bits at 96 kHz. It may be in either stereo or 5.1.
DTS Neo:6 is a format for upmixing (virtualising) from a stereo sound source.
Image Courtesy:

Dolby Digital
Dolby Digital and DTS are six-channel digital surround sound systems and are currently the standard in major motion pictures, music, and digital television.

They both use the 5.1 speaker format The format consists of three speakers across the front and two speakers in the rear. The .1 is a sixth channel called an LFE that is sent to a subwoofer.

Dolby Digital uses the AC-3 file format, which any Dolby Digital Decoder can decoder to produce 5.1 audio. Dolby Digitalis the technical name for Dolby's multi-channel digital sound coding technique, more commonly referred to as Dolby 5.1.

A six-channel sound coding process (one channel each for front, left, center, right surround, left surround and a sub-woofer) originally created by Dolby for theaters, AC-3 was subsequently adapted for home use and is now steadily becoming the most common sound format for DVD.

The difference between Dolby Digital (AC-3) and DTS is:
Both systems are great but statistics for reference only..

• DTS seems to provide a deeper and tighter low frequency presence
• DTS allows the sound to breath - transparency
• AC-3 seems to leave the impression that something is missing from the mix.
• At lower bit-rates AC-3 starts to sound like MP3's encoded at 96kbps (artifacts)

Sunday, February 10, 2013

An Introduction to Digital Audio

What is sound? 
Sound is vibrations in the air; that is, a series of rising and falling pressures in the air, deviating from the average, which is represented by atmospheric pressure. The simplest way to create a sound is to make an object vibrate.

In this manner, a violin makes a sound when the bow makes its strikes vibrate, and a piano sounds a note when a key is struck, because a hammer struck a string and made it vibrate.

Speakers are generally used to reproduce these sounds. They are a membrane connected to an electromagnet; as an electrical current travels in front of and behind the magnet very rapidly, it causes vibrations in the air in front of it, and that vibration is sound! This is how sound waves are produced; they can be represented in a diagram as changes in air pressure (or in the electricity level of the magnet) as a function of time.

A sonogram, on the other hand, depicts sound frequencies as a function of time. It should be noted that a sonogram shows fundamental frequency, on top of which higher frequencies, called harmonics, are superimposed. This is what allows us to distinguish between different sources of sound: low notes have low frequencies, while high notes have higher frequencies.
Sound as an input and output to the Computer
Sound sampling To play sound on a computer, it must be converted into a digital format, as this is the only kind of information computers can work with. 
A computer program intersperses small samples of the sound (which amount to differences in pressure) at specific intervals of time. This is called sampling or digitising sound. 
The period of time between two samples is called the sampling rate. As reproducing audio which sounds continuous to the ear requires samples at least once every few 100,000ths of a second, it is more practical to go by the number of samples per second, expressed in Hertz (Hz). 
Here are a few examples of common sampling rates, and what sound quality they correspond to:
Sampling rate -Sound quality 
44,100 Hz -CD quality 
22,000 Hz -Radio quality 
8,000 Hz -Telephone quality 
The sampling rate of an audio CD, for example, is not arbitrary. In fact, it follows from Shannon's theorem. 
Sampling frequency must be high enough to preserve the form of the signal. 
The Nyquist-Shannon theorem stipulates that the sampling rate must be equal to or greater than twice the maximum frequency contained in the signal. 
Our ears can hear sounds up to about 20,000 Hz. Therefore, for a satisfactory level of sound quality, the sampling rate must be at least on the order of 40,000 Hz. 
There are several standardized sampling rates in use:
• 32 kHz: for digital FM radio (band-limited to 15 kHz)
• 44.1 kHz: for professional audio and compact discs
• 48 kHz: for professional digital multitrack recording, and consumer recording equipment (like DAT or MiniDisc)

A computer works with bits, so the number of possible values that the sample could have must be determined. This is done by setting the number of bits on which the sample values are encoded.

• With 8-bit coding, there are 28 (= 256) possible values.
• With 16-bit coding, there are 216 (= 65536) possible values. 
The second option clearly offers higher sound fidelity, but at the cost of using more computer memory. 
Finally, stereo sound requires two channels, with sound recorded individually on each one. One channel is fed into the left speaker, while the other is broadcast from the right speaker. 
In computer processing, a sound is therefore represented by several parameters:
• The sampling rate
• The number of bits in a sample
• The number of channels (one for mono, two for stereo, and four for quadrophonic sound
Memory required for storing a sound file 
It is easy to calculate what size an uncompressed audio sequence will be. By knowing how many bits are used to code the sample, you know its size (as the sample size is the number of bits) 
To find out the size of a channel, all you need to know is the sample rate, and thus the number of samples per second, and from that the amount of space taken up by one second of music.

Image Courtesy :

Saturday, February 09, 2013

Short Notes on Bipolar transistors

NPN Transistor

Placing P-type semiconductor between two N-type semiconductor is NPN transistor

It operates by a small current flow from the emitter to base.current will not  flow from the emitter to the collector until a small voltage (at least 0.7 volts) is applied to the base.

Collector current is much larger than the base current.


 PNP Transistor

 Placing N-type semiconductor between two P-type semiconductor is PNP transistor.

Its operation is same as NPN but reversed.The voltage relations also reversed.So to turn on the device both the collector and base must be negative.

PNP symbol


 Transistors are used as amplifiers to increase the input signals in TV ,stereo and others applications.It is often called as linear electronics since it contains direct relation with the input and output signal.

If the base is given with the power,it gets biased.It switch on the transistor.An increase or decrease in the input signals makes an increase and decrease in the output signal but with the signal inverse.Frequency remains the same.


The measure of amplification is the gain.

For example, if the input signal has an amplitude of 0.2 volts, and the output signal has an amplitude of 10 volts, then:
Power gain =current gain x voltage gain.


Transistors can also be used for switching in case of digital circuits.Digital circuits needs switch on and off.

When the voltage is below 0.6v no current flows through the circuit.when transistor is not conducting ,it is said to be cut-off.

When the base voltage is about 0.85 volts, sufficient base current flows to turn the transistor fully on. The collector voltage drops to approximately half a volt because of the voltage drop across the collector resistor. A transistor which is conducting the maximum current is said to be in saturation.

Transistor Application






Hardwork Can Never Ever Fails..
Best Luck..

Friday, February 08, 2013

3D View of PN Junction

P Type and N Type Materials- Before forming the Junction

P and N type Materials Brought together
Recombination Started (Gold Balls- Recombination)
Depletion Region Formed
(From the article: 'Education in Three Dimensions: Using Virtual Reality in Education for Illustrating Spatial Relationships' by ALLPORT, Christopher, SINES, Paul, SCHREINER, Brandon & DAS, Biswajit)

What are MEMS?

Think if we can integrate a GPS System on every Parcel we are sending via Courier or Post. It will be very easy for us to track the current location of the Parcel and the Handling of the Parcel. But, the system should be small like a Chip, and it should be of least cost. Don't forget that the GPS System has a Processor and an Antenna to receive the signals from the Satellite. How can we integrate the entire system inside a Small Chip? Here comes the application of MEMS.

MEMS is an emerging technology in which Microscopic Machines are developed by the tools and techniques that were developed for the Integrated Circuit (IC)ndustry.

MEMS structure

Micro-Electro Mechanical systems (MEMS) is a technology that combines computers with tiny mechanical devices such as sensors, valves, gears, mirrors, and actuators embedded in semiconductor chips. 

These machines are built on standard silicon wafers.

MEMS are made up of components between 1 to 100 micrometres in size (i.e. 0.001 to 0.1 mm), and MEMS devices generally range in size from 20 micrometres (20 millionths of a metre) to a millimetre (i.e. 0.02 to 1.0 mm).

They usually consist of a Central Unit that processes data (the microprocessor) and several components that interact with the outside such as Microsensors.

Components of MEMS

What are the Advantages of MEMS?

By utilizing this technology, it is possible to integrate both Microelectronic circuits and Mechanical structures on the same chip, enabling monolithic integration while reducing the microsystem size and cost considerably.

What are the Applications of MEMS? 

This technology has an enormous number of application areas, including 

  • Automotive Eg. Accelerometers for airbag systems, Roll-over detection systems, etc.
  • Biomedical Eg.Neural prosthesis devices like hearing and visual aids, Smart drug delivery systems, On Chip body fluid analysis systems, Microsurgery tools, Pacemakers
  • Telecommunication Eg. Micromirrors for fiber optic switching for fast internet,Smart Antennas
  • Household appliances pressure sensors for water level detection, frost sensors for refrigerators
  • Consumer Applications DLP projectors, i-phone,
  • Defense applications Eg. Low cost night vision, Smart munitions

Image Courtesy

Sunday, February 03, 2013

How Electric fan work

An electric fan is an electric motor with some fan blades attached to its rotating shaft. As the motor spins, the fan blades rotate. Each blade is angled a bit, and as the inclined plane of the blade moves through the air, it forces the air ahead of it forward. Each blade does this on a continuous basis, and the result is a moving air stream. The fan is taking air from the area behind itself and blowing it out the front. The fan generates a movement of air, causing the warm, less dense air to rise, and the cool, dense air to descend, thus creating a feeling of coolness in the air.