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LECTURE NOTES EC6401 – ELECTRONIC CIRCUITS - II SEMESTER: IV / ECE
Prepared by: T. SIVA KUMAR AP / ECE. SYLLABUS
EC6401
ELECTRONIC CIRCUITS II
LTPC 3 00 3
OBJECTIVES: To understand the advantages and method of analysis of feedback amplifiers. To understand the analysis and design of LC and RC oscillators, amplifiers, multivibrators, and time base generators. UNIT I FEEDBACK AMPLIFIERS 9 General Feedback Structure – Properties of negative feedback – Basic Feedback Topologies – Feedback amplifiers – Series – Shunt, Series – Series, Shunt – Shunt and Shunt – Series Feedback – Determining the Loop Gain – Stability Problem – Nyquist Plot – Effect of feedback on amplifier poles – Frequency Compensation. UNIT II OSCILLATORS 9 Classification, Barkhausen Criterion - Mechanism for start of oscillation and stabilization of amplitude, General form of an Oscillator, Analysis of LC oscillators - Hartley, Colpitts,Clapp, Franklin, Armstrong, Tuned collector oscillators, RC oscillators - phase shift –Wienbridge - Twin-T Oscillators, Frequency range of RC and LC Oscillators, Quartz Crystal Construction, Electrical equivalent circuit of Crystal, Miller and Pierce Crystal oscillators, frequency stability of oscillators. UNIT III TUNED AMPLIFIERS 9 Coil losses, unloaded and loaded Q of tank circuits, small signal tuned amplifiers - Analysis of capacitor coupled single tuned amplifier – double tuned amplifier - effect of cascading single tuned and double tuned amplifiers on bandwidth – Stagger tuned amplifiers – large signal tuned amplifiers – Class C tuned amplifier – Efficiency and applications of Class C tuned amplifier - Stability of tuned amplifiers – Neutralization - Hazeltine neutralization method. UNIT IV WAVE SHAPING AND MULTIVIBRATOR CIRCUITS 9 RC & RL Integrator and Differentiator circuits – Storage, Delay and Calculation of Transistor Switching Times – Speed-up Capaitor - Diode clippers, Diode comparator - Clampers. Collector coupled and Emitter coupled Astable multivibrator – Monostable multivibrator - Bistable multivibrators - Triggering methods for Bigtable multivibrators - Schmitt trigger circuit UNIT V BLOCKING OSCILLATORS AND TIMEBASE GENERATORS 9 UJT saw tooth waveform generator, Pulse transformers – equivalent circuit – response - applications, Blocking Oscillator – Free running blocking oscillator - Astable Blocking Oscillators with base timing – Push-pull Astable blocking oscillator with emitter timing, Frequency control using core saturation, Triggered blocking oscillator – Monostable blocking oscillator with base timing – Monostable blocking oscillator with emitter timing, Time base circuits - Voltage-Time base circuit, Current-Time base circuit – Linearization through adjustment of driving waveform. TOTAL: 45 PERIODS TEXT BOOK: 1. Sedra and Smith, “Micro Electronic Circuits”; Sixth Edition, Oxford University Press, 2011. REFERENCES: 1. Robert L. Boylestad and Louis Nasheresky, “Electronic Devices and Circuit Theory”, 10 th Edition,
Pearson Education / PHI, 2008 2. David A. Bell, “Electronic Devices and Circuits”, Fifth Edition, Oxford University Press, 2008. 3. Millman J. and Taub H., “Pulse Digital and Switching Waveforms”, TMH, 2000. 4. Millman and Halkias. C., Integrated Electronics, TMH, 2007.
Block diagram
UJT A Unijunction transistor is a three terminal semiconductor switching device.this device has a unique characteristics that when it is triggered , the emitter current increases regeneratively until is limited by emitter power supply the unijunction transistor can be employed in a variety of applications switching pulse generator saw tooth generator etc.
Construction
It consists of an N type silicon bar with an electrical connection on each end the leads to these connection are called base leads. Base 1 B1 Base 2 B2 the bar between the two bases nearer to B2 than B1. A pn junction is formed between a p type emitter and Bar.the lead to the junction is called emitter lead E. Operation
The device has normally B2 positive w.r.t B1 If voltage VBB is applied between B2 and B1 with emitter open. Voltage gradient is established along the n type bar since emitter is located nearer to B2 more than half of VBB appears between the emitter and B1. the voltage V1 between emitter and B1 establishes a reverse bias on the pn junction and the emitter current is cut off. A small leakage current flows from B2 to emitter due to minority carriers If a positive voltage is applied at the emitter the pn junction will remain reverse biased so long as the input voltage is less than V1 if the input voltage to the emitter exceeds V1 the pn junction becomes forward biased. under these conditions holes are injected from the p type material into the n type bar these holes are repelled by positive B2 terminal and they are attracted towards B1 terminal of the bar. This accumulation of holes in the emitter to B1 region results in the degrees of resistance in this section of the bar the internal voltage drop from emitter to b1 is decreased hence emitter current Ie increases as more holes are injected a condition of saturation will eventually be reached at this point a emitter current limited by emitter power supply only the devices is in on state. If a negative pulse is applied to the emitter, the pn junction is reverse biased and the emitter current is cut off. The device is said to be off state. Characteristics of UJT
The curve between Emitter voltage Ve and emitter current Ie of a UJT at a given voltage Vbb between the bases this is known as emitter characteristic of UJT Initially in the cut off region as Ve increases from zero ,slight leakage current flows from terminal B2 to the emitter the current is due to the minority carriers in the reverse biased diode . Above a certain value of Ve forward Ie begins to flow , increasing until the peak voltage Vp and current Ip are reached at point P. After the peak point P an attempt to increase Ve is followed by a sudden increases in emitter current Ie with decrease in Ve is a negative resistance portion of the curve The negative portion of the curve lasts until the valley point V is reached with valley point voltage Vv.and valley point current Iv after the valley point the device is driven to saturation the difference Vp-Vv is a measure of a switching efficiency of UJT fall of Vbb decreases Advantages of UJT It is a Low cost device It has excellent characteristics It is a low-power absorbing device under normal operating conditions
TRANSFORMER EQUIVALENT CIRCUIT: The influences of a transformer’s parameters can best be understood by considering the equivalent circuit in below. This circuit shows a typical output pulse waveform. Assuming that this output pulse is the result of injecting an ideal rectangular input pulse, one can see that a number of parameters are distorted. Overshoot, droop, back swing, rise time, etc. appear as unwanted signal distortion on the output pulse. Assuming the pulse transformer is properly matched and the source is delivering an ideal rectangular pulse, the transformer should have low values of leakage inductance and distributed capacitance while having a high open circuit inductance. This will limit the deterioration of the pulse shape. Also, the fact that the source will never produce an ideal rectangular pulse adds to the problems of distortion.
