Wish you all Very Happy New Year

Size: px

Start display at page:

Download "Wish you all Very Happy New Year"

Lizbeth Grant
5 years ago
Views:

1 Wish you all Very Happy New Year Course: Basic Electronics (EC21101) Course Instructors: Prof. Goutam Saha (Sec. 2), Prof. Shailendra K. Varshney (Sec. 1), Prof. Sudip Nag (Sec. 3 ), Prof. Debashish Sen (Sec. 4) MON(10:00-10:55), WED(08:00-08:55), WED(09:00-09:55), THURS(10:00-10:55) Contact skvarshney@ece.iitkgp.ernet.in basicelectronicst@gmail.com

2 Course Breakup Mid-Semester Examination : 30 Marks End-Semester Examination: 50 Marks TA: 20 Marks Two class Tests (14 marks) Tutorial (3 marks) Attendance and interaction in class (3 marks) Mid Semester Examination: Feb End-Semester Examination: April 2016

3 Course contents Signal, noise, system, RL, RC filter circuit etc., Intrinsic, extrinsic semiconductor, drift & diffusion current, p-n junction, forward bias/ reverse bias, I-V equation (without proof), diode model (ideal, piece wise linear etc), Zener diode characteristics; half wave, full wave rectifier, bridge rectifier, ripple, Zener diode circuit (voltage ref, regulation), filter, clipper, clamper, multi diode circuit BJT Basics, alpha-beta relation, I-V equation with different regions, DC circuit analysis, common emitter circuit with and without emitter resistor, BJT amplifier, load line, Q point, small signal equivalent circuit, common emitter amplifier (gain, input resistance, output resistance).

4 Course contents MOSFET basic structure, IV equation (no proof) with different regions, depletion mode, enhancement mode, channel length modulation, DC circuit analysis, common source circuit with and without source resistor MOSFET amplifier, load line, Q point, small signal equivalent circuit, common source amplifier (gain, input resistance, output resistance). OPAMP basic, virtual ground, ideal properties, inverting, non inverting, buffer, differential amplifier, CMRR (all these with ideal and non ideal OPAMP gain), integrator, differentiator. Digital electronics- number system, Digital gates (symbol, truth table), universal gate, sum of product, product of sum, Karnaugh map, RS/D/T Flip Flop.

5 References Donald A Neamen, Electronic Circuits- Analysis and Design Text book Sedra and Smith, Microelectronics Text book (some portion). Raza Vi, Fundamentals of Microelectronics, Reference book Milliman and Halikas, Microelectronics, Reference book

6 What is signal? Function that provides information about the behavior or attributes of some phenomenon -audio, video, speech, image, medical, muscial etc.

7 Brown, red, orange: 12x10 3 Ω

8 Filter Circuits Low pass (RC, RL) High Pass (CR, LR)

9 Filters as Integrator and Differentiator

10 Semiconductor physics

semiconductors) p-type Group III elements B, Al, (acceptor) holes:

11 n-type Extrinsic semiconductors Group V elements P, As, Sb (donor) free electrons: majority (adding impurities to intrinsic semiconductors) p-type Group III elements B, Al, (acceptor) holes: majority Rough sketch of bandgap for n-type Rough sketch of bandgap for n-type

12 Carrier Transport Drift Movement caused by electric field Diffusion Flow caused by concentration gradient (due to non homogenous distribution)

13 Transport of free carriers in semiconductors Drift e - Random motion of carriers in semiconductors with and without field o Thermal motion of an individual electron random scattering (lattice vibration, impurities, other electrons, and defects) o no net motion of group of n electrons/cm 3 over any period of time J n

14 Diffusion Flow from region of high concentration to low concentration - concentration gradient Charge carriers in absence of electric field move toward region of low concentration More nonuniform the concentration, the larger the current

15 n : carrier concentration at given point along x Concentration gradient If each carrier has charge q, and the semiconductor has cross-section area A D n : diffusion constant (cm 2 /s) D n = 34 cm 2 /s (for electrons); D p =12 cm 2 /s (for holes) Current density (electrons) Current density (holes)

16 With both electron and hole gradients present, the total current density is Consider a situation as shown in figure below. Suppose the electron concentration is N at x=0 and falls linearly to zero at x=l. Determine the diffusion current.

17 L d is constant Make an analysis of both gradient profiles (linear and exponential) Exercise At what value of x does the current density drops to 1% of its maximum value?

18 Now, we can FINALLY write down the TOTAL current in a semiconductor: For electrons: J N = J N,drift + J N,diff = qnµ n ε + qd N dn dx For holes: J P = J P,drift + J P,diff = qpµ p ε qd P dp dx And TOTAL current:

19 Under equilibrium, or open circuit conditions, total current must always be zero J drift = -J diffusion J N = qnµ ε + qd n N dn dx = 0 Leads to the Einstein Relationship: D = µ kt q This is very, very important because it connects diffusivity with mobility, which we already know how to look up

20 pn junction Simplest semiconductor device Flow of current freely when p region has external positive voltage (forward bias) No current in reverse bias mode This asymmetry in current flows makes pn junction diodes useful as rectifier. Biased pn junction can be used Voltage variable capacitors Photocells Light emittters

21 What are we going to study.. No external connections Terminals are open p-type n-type A pn junction employs following doping levels, N a =10 16 cm -3, N d = cm -3. Calculate the electron and hole concentrations on the two sides. electrons holes

22 Evolution of junction with time t = t =t t = E in Junction reaches equilibrium once the electric field is strong enough to stop diffusion

23 Forward bias E A E in V f

24 Diode characteristics

25 No biasing p-region holes flow Reverse bias Bound charges electrons flow n-region p-region n-region E in E A V R

26 Peak Reverse Voltage (Peak Inverse Voltage): Voltage that may be applied to the junction without causing junction breakdown

27 Effect of temperature I s and V T are temperature dependent Diode characteristics will change with temperature Greater be the temperature, lower be the forward voltage required for the conduction of current. For Si, 2mV/ C

28 Breakdown in Diodes Zener breakdown Avalance breakdown

29 Zener breakdown Dominant for heavily doped (>10 18 cm -3 ) Depletion region becomes narrower Tunneling of carriers across the region Breakdown at a few volts (typically < 5 V)

30 Zener diodes Diodes operated under Zener breakdown effect Can be used as voltage regulator

31 Avalanche breakdown More lightly doped junctions (< cm -3 ) Wider depletion region, electrons accelerated across it gain enough kinetic energy to create additional EHPs by breaking the covalent bonds Impact ionization and carrier multiplication V R > 7V Most common breakdown V BR ε 2 CR ε s 2qN if V BR >> V 0 V BR decreases with increasing N (=N A or N D ) V BR decreases with decreasing E G

32 Diodes in DC circuit Voltage and current designation Ideal I D -V D characteristics Forward bias Reverse bias

34 Half-wave Rectifiers

36 Full Wave Bridge Rectifier with Capacitor Filter

38 Diode as Clipper Also known as Diode limiter Wave shaping circuit that clips or slice certain portion of a input waveform Positive clipper Negative clipper Biased Positive clipper Biased negative clipper

39 Positive clipper Courtesy: circuitstoday.com

40 Courtesy: circuitstoday.com Negative clipper

41 Courtesy: circuitstoday.com Biased Positive Clipper

42 Courtesy: circuitstoday.com Biased Negative Clipper

44 Different clipping circuits

50 Diode as Clamper A clamping circuit is used to place either the positive or negative peak of a signal at a desired level. The dc component is simply added or subtracted to/from the input signal. The clamper is also referred to as an IC restorer and ac signal level shifter.

Intrinsic Semiconductor

Intrinsic Semiconductor Semiconductors Crystalline solid materials whose resistivities are values between those of conductors and insulators. Good electrical characteristics and feasible fabrication technology are some reasons