PGTRB:LASTEST STUDY MATERIALS: PHYSICS: ELECTRONICS.

 PGTRB:LASTEST STUDY MATERIALS: PHYSICS: 

ELECTRONICS.

• The branch of science and engineering which deals with current conduction through vacuum or gas or semiconductor is known as electronics.
• A transistor is formed by sandwiching a thin layer of doped semiconductor between two thick layers of oppositively  doped semiconductor. The resulting semiconductor device is called a junction or bipolar transistor.
• Normal operation of the transistor, the following biasing is necessary.(i) emitter-base junction is always forward biased and  (ii) collector-base junction is reverse biased.
• The input impedance is the ratio of small change in the base-emitter voltage to the corresponding changes in the base current at a constant value of V CE.
• The region left to the saturation point is called saturation region.
• The region between the saturation and cut off is called the active region of the transistor.
• Output admittance is defined as the ratio of the variation in the collector current to the corresponding variation in the collector emitter voltage at constant base current. Its unit is mho.
• There is a phase reversal of 180degree between the input and output voltages in an amplifier using a single transistor.
• The energy of a wave directly proportional to its frequency.
• The audio signal is to be transmitted properly, the audio signal must be superimposed on high frequency wave is called carrier.
• This radio wave transmitted in space through antenna.
• The amplitude modulation is used in radio broadcasting.
• In television transmission frequency modulation is used for sound single and amplitude modulation for picture signal.
• The modulation factor m>1 distortion is produced in the transmitted wave.
• When the frequency of carrier wave is changed in accordance with the intensity of the signal, it is called frequency modulations.
• Frequency modulation gives, noiseless reception. Noise is a form of amplitude variation and a FM receiver will reject such signals.
• The process of recovering the audio signal from the modulated wave is known as demodulation or detection.
• Radio receiver, the selected radio frequency is converted to a fixed lower value called intermediate frequency(IF).
• The AF channel consists of a microphone which converts sound waves into AF electrical signals.
• In the RF channel the high frequency carrier wave is generated by a crystal controlled oscillator.
• The frequency of scanning is about is about 25 frames per second. Hence, due to the persistence of vision the eye receives the picture as a continuous one.
• The word microwave means very short wave. Microwave region is the shortest wavelength regions of the radio spectrum.
• Rader and radio astronomy use microwaves. The property that microwaves travel along straight lines and can be reflected is used in Rader and radio astronomy.
• The OR gate represents the Boolean equation A+B=C.
• The AND gate represents the Boolean equations A*B=C, A.B=C, AB=C.
• The NOT gate is also called an inverter.
• A NOR function is just the reverse of the OR functions.
• By using a NOR gate all the basic gates namely OR, AND, and NOT can be obtained. Hence a NOR gate is referred as universal gate.
• By using NAND gate all the basic gates OR, AND and NOT can be obtained. Hence NAND gate is also known as universal gate. 
• A semiconductor transistor is a three terminal electronic device. There are two types NPN and PNP. The emitter is forward biased. The collector is reverse biased.
• CB, CE, and CC configurations satisfy the condition that the emitter current is the sum of the collector and the base current.
• The CE mode is commonly used due to its high current and power gain.
• The transistor static characteristic curves are drawn to determine the transistor parameters namely input impedance, output admittance and current gain.
• The characteristics of a transistor amplifier is out of phase with the input.
• The gain of a single stage amplifier is a small. Hence cascaded type of amplifiers are used. 
• Two stage RC coupled amplifier is a cascaded amplifier. the mid-frequency gain is independent of frequency, low and high frequency gains are dependent on frequency.
• The frequency range between the lower cutoff and higher cutoff points is band-width.
• The characteristic of an amplifier highly is dependent pm transistor parameters which change due to temperature and electrical power variation.
• A better performance of an amplifier is achieved by feed back principle.
• The feed back may be positive or negative.
• Feed back is done with the help of feed back network. It is usually consists of passive components. The type of feed back can also be obtained by feed back network.
• The gain with negative feed back is reduced. Still it is preferred for overall performance pf an amplifier.
• The gain with the positive  feed back is increased. still it is preferred for overall performance of an amplifier.
• The gain with the positive feed back is increased. The gain can be made equal to infinity. This is the condition for oscillator circuit.
• An oscillator or a waveform generator is an electronic circuit to convert dc power into ac signals.
• Oscillators are classified as harmonic oscillators (sinusoidal waves) and non-harmonic oscillators(square wave, saw tooth etc.,).
• The Hartley oscillator is a harmonic oscillator.
• In radio and TV communications the modulation and demodulation are important.
• In order to get a high performance amplification super heterodyne principle is used in the receiver.
• Iconoscope is a television camera which converts the picture into electrical signals. The mosaic of iconoscope products electrical pulses corresponding to the intensity of the image on it by the process of scanning.
• Scanning is done by an electron beam with synchronising pulses.
• The picture and synchronising pulses are amplitude modulated and the sound is frequency modulated and transmitted through the same antenna.
• Microwaves are very small wave. They are generated by magnetron oscillators.
• Logic gate is an electronic circuit which has one output for one or more inputs. The variables assume either 0 or 1 state. The basic logic gates are OR,AND, and NOT. Universal logic gates are NOR and NAND.
• Integrated circuits are packaged electronic circuits in a single chip. By construction, there are monolithic, film and hybrid ICs and by application there are linear and digital ICs.
• A transistor has two PN junction.
• If emitter current in a transistor is 1 mA, then collector current is nearly 1 mA.
• The most used transistor circuit is CE.
• The input resistance of a transistor is high.
• In RC coupled amplifier voltage gain at mid frequency range decrease.
• RC coupled amplifier is used in voltage amplification.
• For oscillators the feed back required is positive.
• In amplitude modulation which component of the carrier wave is varied in accordance with the intensity of the signal amplitude.
• In TV picture transmission is done by amplitude modulation.
• Magnetron is used for the production of microwaves.