My Circuit Study

LED 7 segment display driver circuit

2013-07-31T11:57:00.000-07:00

7 segment display.

Seven segment display is a device that can display decimal numbers and are widely used in electronic clocks, electronic meters, digital display panels and a hand full of applications where numerical data is is displayed. The idea of seven segment display is very old and they are in the scenario from early nineteenth century. Seven segment display have seven segments which can be individually controlled (ON/OFF) to display the desired number. Numbers from 0 to 9 can be displayed using various combinations of the segments and in addition to this the hexadecimal letters A to F can be also displayed using a seven segment display. The seven elements (segments) are arranged in the form of a square shaped “8″ which is slightly inclined to the right. The slight inclination to the right is given to improve the readability.Some seven segment displays have an additional dot element which can be used for indicating decimal points. The segments may be based on incandescent bulbs, fluorescent lamps, LCD or LED. Here in this article we give stress to the LED seven segment display.

In an LED 7 segment display, as the name indicates the 7 segments plus the dot segment are based on LEDs. When power is given to a particular segment, it glows and the desired digit can be displayed by powering the suitable combination of LEDs. LED seven segment displays are of two types, common cathode and common anode. In a common cathode display, the cathode of all LED segments are tied together as one common cathode pin and the anode terminals are left alone as input pins. In this scheme the common cathode is always connected to ground and the control signals (active high) are applied to the inputs (anode terminals) .In common anode type display, the anodes of LED segments are tied together as one common anode and the cathode terminals are left alone as input. In this configuration the common anode is always connected to a suitable positive voltage and the control signals (active low) are applied to the inputs (cathode terminals). Pin out and image of a seven segment display is shown in the figure below.

Basic LED 7 segment display driver system.

The block diagram of a basic LED seven segment display system that can display a given input in numerical form is shown Above .

The decoder block converts the given input signal into an 8 line code corresponding to the ‘a’ to ‘g’ segments and the decimal point which controls the segments to display the desired number. For example if the line corresponding to ‘f ‘and ‘e’ are activated then segments f and e of the display glows indicating a “1″. If the input quantity is an analogue signal then it must be converter into digital format using an ADC before applying to the decoder. If the input signal is digital then there is no need for the ADC and the decoder alone will convert the particular input code into the 8 line code compatible to the seven segment LED display. The purpose of the driver stage is to provide the necessary current drive in order to drive the LED seven segment display. If the decoder stage is powerful enough to drive the display, then the driver stage is not required. A typical 7 segment display driver stage consists of an array (8 nos ) transistor or FET based switches. For example consider the line ‘a’ . The “a” output of the decoder is connected to the input terminal (base/gate) of the corresponding switching element inside the driver stage. The same line is buffered by the switching element and is available as output line ‘a’ of the driver. This output is connected to the corresponding ‘a’ element of the display. The driver can be arranged in sinking or sourcing mode.

Sinking and sourcing digital outputs.

A sinking digital output keeps the particular output low by using a transistor and thus makes a path for the load current to flow to the ground. Here the current flows from the load to the respective output terminal. In sourcing mode the the particular output is held high using a transistor the output line itself provides the necessary current for energizing the load. Here the current flows from the output terminal to the load.

In case of the sinking digital output the current comes from the external power supply V+ , passes through the load, and the internal transistor conducts it to the ground. For a sourcing digital output the current comes from the digital circuits own power supply V+, then conducted by the transistor , passes through the load and then to the external ground.

Seven segment decoder / driver.

Seven segment decoder / driver is a digital circuit that can decode a digital input to the seven segment format and simultaneously drive a 7 segment LED display using the decoded information. What that will be displayed on the 7 segment display is the numerical equivalent of the input data. For example a BCD to seven segment decoder driver can decode a 4 line BCD ( binary coded decimal) to 8 line seven segment format and can drive the display using this information. For example, if the input BCD code is 0001, the display output will be 1 , for 0010 the display output will be 2 and so on. The circuit diagram shown below is of a BCD to seven segment decoder / driver using 7446 IC.

7446 is a BCD to 7 segment display driver IC with active low outputs. The IC is stand alone and requires no external components other than the LED current limiting resistors. All output of the IC have complete ripple blanking and requires no external driver transistors. There is also a built in lamp test function which can be used to test the LED segments. Pin 5 of the IC is the ripple blanking input (RBI) and pin 4 is the ripple blanking output (RBO). Pin 3 is the lamp test (LT) input pin. When the RBI and RBO pins are held high and the lamp test (LT) input pin 3 is held low all LED segment output goes high. The display used here must be a common anode type because the IC has active low outputs.

Digital thermometer using 8051

2013-07-31T11:27:00.001-07:00

Digital thermometer using 8051

Thermometer using 8051.

This article is about a simple 0-100°C digital thermometer with 1°C resolution using 8051. The circuit is based on LM35 analog temperature sensor, ADC0804 and AT89S51 microcontroller. LM35 is an analogue temperature sensor IC which can measure a temperature range of -55 to 150°C. Its output voltage varies 10mV per °C change in temperature.

For example, if the temperature is 32°C, the output voltage will be 32 x 10mV = 320mV. ADC 0804 is used to convert the analogue output voltage of the LM35 to a proportional 8 bit digital value suitable for the microcontroller. The microcontroller accepts the output of ADC, performs necessary manipulations on it and displays it numerically on a 2 digit seven segment LED display.

Out put of the LM35 is connected to the +Vin (pin 6) of the ADC0804. Resistor R13 and preset R14 is used to provide an external reference voltage of 1.28V to the Vref/2 pin ( pin 9) of the ADC0804 and with this reference voltage, the step size of the ADC will be 10mV and span will be 0-1 V. This means that for a 10mV input the digital out of ADC will be 1 (1 in decimal also), for 20mV it will be 10 (2 in decimal), for 30mV it will be 11 (3 in decimal) and so on. The microcontroller accepts this data and puts it on the seven segment display.

Circuit diagram.

Digital out of the ADC (D0 to D7) are connected to P1 (P1.0 to P1.7) of the microcontroller. This is the line through which the microcontroller accepts data from the ADC. The control pins CS, RD, WR and INTR are connected to P3.7, P3.6, P3.5 and P3.4 of the microcontroller. This is the data path through which the microcontroller sends chip select (CS), read (RD) write (WR) signals to the ADC and receives INTR signal from the ADC. Data lines (a to h) of the multiplexed seven segment display are interfaced to P0 (P0.0 to P0.7) of the microcontroller. Activation signals for the segment driver transistors Q1 and Q2 are available from P3.2 and P3.1 pins of the microcontroller.

Before attempting this circuit go through these articles Voltmeter using 8051 , Interfacing ADC to 8051 , Interfacing seven segment display to 8051.

Program.

ORG 00H

MOV P1,#11111111B // initializes P1 as input port

MOV P0,#00000000B // initializes P0 as output port

MOV P3,#00000000B // initializes P3 as output port

MOV DPTR,#LABEL // loads the address of "LABEL" to DPTR

MAIN: MOV R4,#250D // loads register R4 with 250D

CLR P3.7 // makes Cs=0

SETB P3.6 // makes RD high

CLR P3.5 // makes WR low

SETB P3.5 // low to high pulse to WR for starting conversion

WAIT: JB P3.4,WAIT // polls until INTR=0

CLR P3.7 // ensures CS=0

CLR P3.6 // high to low pulse to RD for reading the data from ADC

MOV A,P1 // moves the digital output of ADC to accumulator A

MOV B,#10D // load B with 10D

DIV AB // divides the content of A with that in B

MOV R6,A // moves the quotient to R6

MOV R7,B // moves the remainder to R7

DLOOP:SETB P3.2 // sets P3.2 which activates LED segment 1

MOV A,R6 // moves the quotient to A

ACALL DISPLAY // calls DISPLAY subroutine

MOV P0,A // moves the content of A to P0

ACALL DELAY // calls the DELAY subroutine

CLR A // clears A

MOV A,R7 // moves the remainder to A

CLR P3.2 // deactivates LED segment 1

SETB P3.1 // activates LED segment 2

ACALL DISPLAY

MOV P0,A

ACALL DELAY

CLR A

CLR P3.1 // deactivates LED segment 2

DJNZ R4,DLOOP // repeats the loop "DLOOP" until R4=0

SJMP MAIN // jumps back to the main loop

DELAY: MOV R3,#255D // produces around 0.8mS delay

LABEL1: DJNZ R3,LABEL1

RET

DISPLAY: MOVC A,@A+DPTR // converts A's content to corresponding digit drive pattern

RET

LABEL: DB 3FH // LUT (look up table) starts here

DB 06H

DB 5BH

DB 4FH

DB 66H

DB 6DH

DB 7DH

DB 07H

DB 7FH

DB 6FH

END

The Junction field Effect transistor (JFET)

2013-07-30T11:36:00.004-07:00

The Junction Field Effect Transistor (JFET)

Bipolar junction transistors have low input impedance, small high-frequency gain and are non-linear when |VCE| < 2 V. The input impedance is naturally restricted by the forwardbiased base-emitter junction. There are always problems due to the main charge carriers passing through the region where the majority carriers are of opposite polarity.

The junction field effect transistor (JFET) overcomes some of the problems of the bipolar junction transistor. JFETs come in two types: N-channel and P-channel.

The designation refers to the polarity of the majority charge carriers in the bar of semiconductor that connects the drain terminal D to the source terminal S. Since the channel is formed from a single-polarity (unipolar) material, its resistance is a function only of the geometry of the conducting volume and the conductivity of the material. The JFET operates with all PN junctions reverse-biased so as to obtain a high input impedance into the gate.

1. Principles of Operation

An N-channel JFET with DC bias voltage applied. Just as for a simple

diode, the depletion region grows as the reverse bias across the PN junction is increased, thereby constricting the cross section of the conducting N-channel material and increasing the resistance of the channel. The major current ID in the channel is caused by the applied voltage between the drain and source, VDS, and is controlled by the applied voltage between the gate and source, VGS.

N−Channel P−Channel

Basic geometry and circuit symbols of JFETS.

The JFET has two distinct modes of operation: the variable-resistance mode, and the

pinch-off mode. In the variable-resistance mode the JFET behaves like a resistor whose value is controlled by VGS. In the pinch-off mode, the channel has been heavily constricted with most of the drain-source voltage drop occuring along the narrow and therefore high-resistance part of the channel near the depletion regions.

The characteristic curves of a typical JFET . At small values of VDS (in the range of a few tenths of a volt), the curves of constant VGS show a linear relationship between VDS and ID. This is the variable-resistance region of the graph. As VDS increases, each of the curves of constant VGS enters a region of nearly constant ID

This is the pinch-off region, where the JFET can be used as a linear voltage and current

amplifier. At VGS = 0 the current through the JFET reaches a maximum known as IDSS,

the current from Drain to Source with the gate Shorted to the source. If VGS goes positive for this N-channel JFET, the PN junction becomes conducting and the JFET becomes just a forward-biased diode.

The Common Emitter Amplifier : Mycircuitstudy

2013-07-30T11:28:00.002-07:00

The Common Emitter Amplifier

The common emitter configuration is the most versatile of the three. It has low input

impedance, moderate output impedance, voltage gain and current gain. The input and

output are often capacitively coupled. Before performing an AC analysis we will discuss DC biasing.

1. DC Biasing

DC biasing is setting up a circuit to operate a transistor at a desired operating point on its characteristic curve. Three bias networks for the common emitter amplifier are shown in the only path for DC bias current into the base is through RB. VCC is a power supply voltage which is generally greater than 10 V such that VPN can be ignored.

The DC voltage at the collector should be large enough to provide at least a 2 V drop between collector and emitter and clearly must be less than VCC. In the absence of other circuit requirements, a convenient algebraic choice for VC is VCC/2. DC circuit analysis results in the following relative sizes of the two resistors: RB = 2hFERC.

Although the circuit works reasonably well, the fact that hFE is quite variable among

samples leads to a bad design. A well-designed circuit should have an operating point that is less dependent on this parameter. shows a network with the base-biasing resistor connected to the collector instead of VCC. RF acts as a negative feedback resistor since it feeds the collector current back into the base. Analysis gives

RF = hFERC.

Therefore a change in hFE has only half the effect of the previous design.

A more common bias stabilization technique employs a series resistor between the emitter and ground. This circuit has about the same sensitivity to changes in hFE as the previous

circuit.

Bias circuits for the common emitter amplifier.

A further improvement can be made by introducing a second base-bias resistor as shown in figure . The bias voltage is determined almost entirely by the two bias resistors.

These biasing methods can also be used for the common collector and common base configurations.

2. Approximate AC Model

The circuit is the basic common emitter amplifier using the simplest biasing method. Because it is constant, the power supply voltage VCC is an AC ground indistinguishable from the normal ground of the circuit. We can therefore relocate the upper end of RB and RC to the common ground line .

The transistor symbol is ideal and hie is shown explicitly as the input impedance and hence iS = iB.

3.The Basic CE Amplifier

We can now use the AC equivalent circuit to calculate the AC voltage gain between the base and collector. The base voltage is developed across the input resistor hie and vB = hieiB.

The collector voltage can be similarity expressed as the voltage drop across the resistor RC: 0 − vC = RChfeiB. Eliminating iB, we can write the amplifier voltage transfer function

between the base and collector .

a) Basic CE amplifier and b) AC equivalent circuit drawn using an ideal transistor

symbol with hie shown explicitly.

The minus sign indicates that the voltage signal at the collector is 180o out of phase with

the signal at the base. The input impedance to this amplifier circuit is just the parallel combination of RB and hie, and since hie is usually much smaller than RB, the input impedance generally reduces to just the input impedance of the transistor itself, namely, hie.

The circuit output impedance is the collector resistance RC.

The high-frequency operation of the common emitter amplifier is limited by the parasitic

capacitance between the collector and base. This capacitance provides a path by which

the large and inverted signal at the collector drives a feedback current into the base. The base-to-collector voltage gain of this amplifier looks like a low-pass filter.

Basic of Bipolar Junction Transistors : Mycircuitstudy

2013-07-30T11:20:00.001-07:00

Transistor Circuits

The circuits we have encountered so far are passive and dissipate power. Even a transformer that is capable of giving a voltage gain to a circuit is not an active element. Active elements in a circuit increase the power by controlling or modulating the flow of energy or power from an additional power supply into the circuit.

Transistors are active circuit elements and are typically made from silicon or germanium

and come in two types. The bipolar transistor controls the current by varying the number

of charge carriers. The field effect transistor (FET) varies the current by varying the shape of the conducting volume.

Before starting we will define some notation. The voltages that are with respect to

ground are indicated by a single subscript. Voltages with repeated letters are power supply voltages. And voltages between two terminals are indicated by a double subscript.

1. Bipolar Junction Transistors

By placing two PN junctions together we can create a bipolar transistor. In a PNP transistor the majority charge carriers are holes and germanium is favoured for these devices. Silicon is best for NPN transistors where the majority charge carriers are electrons. The thin and lightly doped central region is known as the base (B) and has majority charge carriers of opposite polarity to those in the surrounding material. The two outer regions are known as the emitter (E) and the collector (C). Under the proper operating conditions the emitter will emit or inject majority charge carriers into the base region, and because the base is very thin, most will ultimately reach the collector.

The emitter is highly doped to reduce resistance. The collector is lightly doped to reduce the junction capacitance of the collector-base junction.

The schematic circuit symbols for bipolar transistors . The arrows on the schematic symbols indicate the direction of both IB and IC. The collector is usually

at a higher voltage than the emitter. The emitter-base junction is forward biased while the collector-base junction is reversed biased.

Basic of Diode Circuits : Mycircuitstudy

2013-07-30T11:15:00.002-07:00

Diode Circuits

So far we have only considered passive circuit elements. Now we will consider our first reactive circuit element, the diode. Hopefully things will start to get a little more interesting.

Along with the diode there is the transistor, which will be discussed in future lectures.

These circuit elements are commonly made from a semiconductor basic material. Semiconductors along with the passive circuit elements are often integrated onto a single electronics chip. If a hundred or so transistors are on a chip it is referred to as an integrated circuit or IC. Large-scale integrated circuits, LSI, contain thousands of transistors.

And today even very-large-scale integrated circuits, VLSI, exist, with hundreds of thousands of transistors.

Now lets talk physics.

1 . Energy Levels

The physical principles of semiconductor devices can be understood by considering quantum energy levels in the material. I will just give a sketchy view here and define some terminology.

Valance electrons are the electrons outside the closed shells of an atom. In silicon and

germanium there are four valence electrons, arsenic has five and gallium three. The large number of valance electrons favour these elements as semiconductors.

To sustain an electric current, a material must have charge carriers that are free to move. There is some probability that an atom may eject a valence electron which is then free to move in the material. The conductivity of a material is thus a function of the number of free charge carriers per unit volume. Based on these probability densities it is common to divide materials into three categories: conductors, semiconductors and insulators.

In crystals atoms interact and bind by sharing valence electrons. The wave function is

no longer associated with a single atom but extends over the entire crystal. One effect of the interaction between the atoms is that the otherwise degenerate energy levels split into closely spaced levels. Since the number of atoms is large, it is common to refer to this set of levels as a continuous energy band.

In solid materials there usually exist a valance band which is an energy region where

the states are filled or partially filled by valence electrons. The conduction band is defined to be the lowest unfilled energy band. So our three materials can be characterized by their band structure. An insulator has the valence and conduction band well separated.

semiconductor has the valence band close to the conduction band – separated by about a1 eV gap. Conductors on the other hand have the conduction and valence bands overlapping.

The interesting property of a semiconductor is that thermally excited electrons can move

from the valence band to the conduction band and conduct current. Silicon and germanium have thermally excited electrons at room temperature and hence their common use in diodesand transistors.

When an electron has been excited into the conduction band, the hole left behind in the

valence band is also free to move through the crystal. A quantum mechanical treatment of this effect puts the hole on an approximately equal footing with the electron. Temperaturecauses the thermal generation of electron-hole pairs. One of the components of the pair will add a little to the majority charge carriers. The other component of the electron-hole pair will become the minority charge carrier. Minority charge carriers limit ideal performance and increase with increasing temperature.

A common method for generating even more charge carriers in a semiconductor is by

doping. That is, replacing a few atoms of the base material with atoms of a different element.

These impurities will contribute an excess electron or hole which is loosely bound and hence can be excited into the conduction band by thermal energy. In N-type semiconductors the majority of free charge carriers are negative, while in a P-type semiconductor the majority are positive.

Basic of Inductance : Mycircuitstudy

2013-07-30T11:14:00.000-07:00

Inductance

Faraday’s law applied to an inductor states that a changing current induces a back EMF

that opposes the change. Or

V = VA − VB = LdI/dt

Where V is the voltage across the inductor and L is the inductance measured in henry (H).

The more common units encountered in circuits are μH and mH.

The inductance will tend to smooth sudden changes in current just as the capacitance

smoothes sudden changes in voltage. Of course, if the current is constant there will be no induced EMF. So unlike the capacitor which behaves like an open-circuit in DC circuits, an inductor behaves like a short-circuit in DC circuits.

Applications using inductors are less common than those using capacitors, but inductors are very common in high frequency circuits. We will again skip over the unpleasantness – that non-ideal inductors have some resistance and some capacitance.

Inductors are never pure inductances because there is always some resistance in

and some capacitance between the coil windings.

When choosing an inductor(occasionally called a choke) for a specific application, it is necessary to considerthe value of the inductance, the DC resistance of the coil, the current-carryingcapacity of the coil windings, the breakdown voltage between the coil and theframe, and the frequency range in which the coil is designed to operate. To obtain a very high inductance it is necessary to have a coil of many turns.

The inductance can be further increased by winding the coil on a closed-loop iron or

ferrite core. To obtain as pure an inductance as possible, the DC resistance of

the windings should be reduced to a minimum. This can be done by increasing

the wire size, which of course, increases the size of the choke. The size of the wire

also determines the current-handling capacity of the choke since the work done

in forcing a current through a resistance is converted to heat in the resistance.

Magnetic losses in an iron core also account for some heating, and this heating

restricts any choke to a certain safe operating current. The windings of the coil

must be insulated from the frame as well as from each other. Heavier insulation,

which necessarily makes the choke more bulky, is used in applications where

there will be a high voltage between the frame and the winding. The losses

sustained in the iron core increases as the frequency increases. Large inductors,

rated in henries, are used principally in power applications. The frequency in

these circuits is relatively low, generally 60 Hz or low multiples thereof. In highfrequency

circuits, such as those found in FM radios and television sets, very

small inductors (of the order of microhenries) are frequently used.

Basic Of Capacitance

2013-07-30T11:02:00.001-07:00

Capacitance

The fundamental property of a capacitor is that it can store charge and hence electric field energy. The capacitance C between two appropriate surfaces is defined by

V =Q/C

where V is the potential difference between the surfaces and Q is the magnitude of the charge distributed on either surface.

In terms of current, I = dQ/dt implies

In electronics we take I = ID (displacement current). In other words, the current flowing

from or to the capacitor is taken to be equal to the displacement current through the

capacitor. You should be able to show that capacitors add linearly when placed in parallel.

There are four principle functions of a capacitor in a circuit.

1. Since Q and E can be stored a capacitor can be used as a (non-ideal) source of I and V .

2. Since a capacitor passes AC current but not DC current it can be used to connect

parts of a circuit that must operate at different DC voltage levels.

3. A capacitor and resistor in series will limit current and hence smooth sharp edges in

voltage signals.

4. Charging or discharging a capacitor with a constant current results in the capacitor

having a voltage signal with a constant slope, ie. dV/dt = I/C = constant if I is a

constant.

Some capacitors (electrolytic) are asymmetric devices with a polarity that must be

hooked-up in a definite way. You will learn this in the lab. The SI unit for capacitance

is farad (F). The capacitance in a circuit is typically measured in μF or pF. Non-ideal circuits will have stray capacitance, leakage currents and inductive coupling at high frequency.

Although important in real circuit design we will slip over these nasties at this point.

Capacitors can be obtained in various tolerance ratings from ±20% to ±0.5%.

Because of dimensional changes, capacitors have a high temperature dependence

of capacitance. A capacitor does not hold a charge indefinitely because the dielectric

is never a perfect insulator. Capacitors are rated for leakage, the conduction

through the dielectric, by the leakage resistance-capacitance product in MΩ· μF.

High temperature increases leakage.

Direct Currents Circuits

2013-07-30T10:42:00.007-07:00

Direct Current Circuits

These lectures follow the traditional review of direct current circuits, with emphasis on two terminal networks and equivalent circuits. The idea is to bring you up to speed for what is to come. The course will get less quantitative as we go along. In fact, you will probably find the course gets easier as we go.

1.1 Basic Concepts

Direct current (DC) circuit analysis deals with constant currents and voltages, while alternating current (AC) circuit analysis deals with time-varying voltage and current signals whose time average values are zero. Circuits with time-average values of non-zero are also important and will be mentioned briefly in the section on filters. The DC circuit components considered in this course are the constant voltage source, constant current source, and resistor. Electronics also deals with charge Q, electric E and magnetic B fields, as well as, potential V . We will not be concerned with a detailed description of these quantities but will use approximation methods when dealing with them. Hence electronics can be considered as a more practical approach to these subjects.

1.1.1 Current

The fundamental quantity in electronics is charge and at its basic level is due to the charge properties of the fundamental particles of matter. For all intensive purposes it is the electron (or lack of electrons) that matter. The role of the proton charge is negligible.

The aggregate motion of charges is called current I

I =dq/dt

where dq is the amount of positive charge crossing a specified surface in a time dt. Be aware that the charges in motion are actually negative electrons. Thus the electrons move in the opposite direction to the current flow.

The SI unit for current is the ampere (A). For most electronic circuits the ampere is a

rather large unit so the mA unit is more common.

1.1.2 Potential Difference

It is often more convenient to consider the electrostatic potential V rather than electric

field E as the motivating influence for the flow of electric charge. The generalized vector

properties of E are usually unimportant. The change in potential dV across a distance d_r in an electric field is

dV = −E · d_r.

A positive charge will move from a higher to a lower potential. The potential is also

referred to as the potential difference or, incorrectly, as just voltage:

V = V21 = V2 − V1 = _ V2V1 dV.

Remember that current flowing in a conductor is due to a potential difference between

its ends. Electrons move from a point of less positive potential to more positive potential

and the current flows in the opposite direction.

The SI unit of potential difference is the volt (V).

1.1.3 Resistance and Ohm’s Law

For most materials V ∝ I; V = RI, where V = V2−V1 is the voltage across the object, I is the current through the object, and R is a proportionality constant called the resistance of the object. Resistance is a function of the material and shape of the object, and has SI units of ohms (Ω). It is more common to find units of kΩ and MΩ. The inverse of resistivity is conductivity.

Resistor tolerances can be as bad as ±20% for general-purpose resistors to ±0.1%

for ultra-precision resistors. Only wire-wound resistors are capable of ultraprecision

applications. The concept of current through and potential across are key to the understanding of and sounding intelligent about electronics.

Now comes the most useful visual tool of this course.

1.2 The Schematic Diagram

The schematic diagram consists of idealized circuit elements each of which represents some property of the actual circuit. shows some common circuit elements encountered

in DC circuits. A two-terminal network is a circuit that has only two points of interest, say

A and B.

1.2.1 Electromotive Force (EMF)

Charge can flow in a material under the influence of an external electric field. Eventually

the internal field due to the repositioned charge cancels the external electric field resulting in zero current flow. To maintain a potential drop (and flow of charge) requires an external energy source, ie. EMF (battery, power supply, signal generator, etc.). We will deal with two types of EMFs:

The ideal voltage source is able to maintain a constant voltage regardless of the current

it must put out (I →∞ is possible).

The ideal current source is able to maintain a constant current regardless of the voltage

needed (V →∞ is possible).

Because a battery cannot produce an infinite amount of current, a model for the behavior of a battery is to put an internal resistance in series with an ideal voltage source (zero resistance). Real-life EMFs can always be approximated with ideal EMFs and appropriate combinations of other circuit elements.

1.2.2 Ground

A voltage must always be measured relative to some reference point. It is proper to speak of the voltage across an electrical component but we often speak of voltage at a point. It is then assumed that the reference voltage point is ground. Under strict definition, ground is the body of the earth. It is an infinite electrical sink.

It can accept or supply any reasonable amount of charge without changing its electrical

characteristics. It is common, but not always necessary, to connect some part of the circuit to earth or ground, which is taken, for convenience and by convention, to be at zero volts. Frequently, a common (or reference) connection of the metal chassis of the instrument suffices. Sometimes there is a common reference voltage that is not at 0 V. Figure 1.2 show some common ways of depicting grounds on a circuit diagram.

When neither a ground nor any other voltage reference is shown explicitly on a schematic diagram, it is useful for purposes of discussion to adopt the convention that the bottom line on a circuit is at zero potential.

Application of PLL : Frequency Demodulation

2013-07-27T08:25:00.000-07:00

FM demodulation or detection can be directly achieved using the PLL circuit. If

the PLL center frequency is selected or designed at the FM carrier frequency, the filtered or output voltage of the circuit is the desired demodulated voltage, varying in value proportional to the variation of the signal frequency. The PLL circuit thus operates as a complete intermediate-frequency (IF) strip, limiter, and demodulator as used in FM receivers.

One popular PLL , The 565 contains a phase detector, amplifier, and voltage-controlled oscillator, which are only partially connected internally. An external resistor and capacitor, R1 and C1, are used to set the free-running or center frequency of the VCO. Another external capacitor, C2, is used to set the low-pass filter passband, and the VCO output must be connected back as input to the phase detector to close the PLL loop. The 565 typically uses two power supplies, V_ and V.

The signal at pin 4 is a 136.36-kHz square wave. An input within the lock range of

181.8 kHz will result in the output at pin 7 varying around its dc voltage level set

with input signal at fo. the output at pin 7 as a function of the input signal frequency. The dc voltage at pin 7 is linearly related to the input signal

frequency within the frequency range fL _ 181.8 kHz around the center frequency

136.36 kHz. The output voltage is the demodulated signal that varies with frequency within the operating range specified.

Basic Phase Locked Loop Operation

2013-07-27T08:11:00.002-07:00

BASIC PHASE LOCKED LOOP OPERATION

The basic operation of a PLL circuit can be explained using the circuit . We will first consider the operation of the various circuits in the phaselocked

loop when the loop is operating in lock (the input signal frequency and the

VCO frequency are the same). When the input signal frequency is the same as that

from the VCO to the comparator, the voltage, Vd, taken as output is the value needed to hold the VCO in lock with the input signal. The VCO then provides output of a fixed-amplitude square-wave signal at the frequency of the input. Best operation is obtained if the VCO center frequency, fo, is set with the dc bias voltage midway in its linear operating range. The amplifier allows this adjustment in dc voltage from that obtained as output of the filter circuit. When the loop is in lock, the two signals to the comparator are of the same frequency, although not necessarily in phase. A fixed phase difference between the two signals to the comparator results in a fixed dc voltage to the VCO. Changes in the input signal frequency then result in change in the dc voltage to the VCO. Within a capture-and-lock frequency range, the dc voltage will drive the VCO frequency to match that of the input.

While the loop is trying to achieve lock, the output of the phase comparator contains frequency components at the sum and difference of the signals compared. A lowpass filter passes only the lower-frequency component of the signal so that the loop can obtain lock between input and VCO signals.

Owing to the limited operating range of the VCO and the feedback connection of

the PLL circuit, there are two important frequency bands specified for a PLL. The

capture range of a PLL is the frequency range centered about the VCO free-running frequency, fo, over which the loop can acquire lock with the input signal.

Once the PLL has achieved capture, it can maintain lock with the input signal over a somewhat wider frequency range called the lock range.

Conduction in solids Part- 2: basic electronics

2013-07-18T20:52:00.000-07:00

Conventional Currents and electron flow

In the early years of electrical experimentation it was believed that a positive charge represented an increased amount of electricity an that a negative charge was a reduced quantity. Consequently current was assumed to flow from positive to negative charge . This is convention that remains in use today even though current is now known to be movement of electrons from negative to positive.

Current flow from positive to negative is referred to as the conventional current direction.

Electron flow from the negative to positive is known as the direction of electron flow.

It is important to understand both electron flow and conventional current direction . The operation of electronic devices is explained in terms of the electron movement. However , every graphic symbol used to represent an electronic device has an arrowhead which indicates conventional current direction.

Consequently electronic circuits are most easily explained by using current flow from positive to negative.

Conduction in Solids Part - 1 : Basic electronics

2013-07-18T20:50:00.002-07:00

CONDUCTION IN SOLIDS

ELECTRON MOTION AND HOLE TRANSFER

Conduction occurs in any material when an applied voltage causes electrons in the material to move in a particular direction . This may be due to one or both of two processes : electron motion and hole transfer . In electron motion free electrons in the condition band are moved under the influence of the applied electric field thus creating an electric current . Since electrons have a negative charge , they are repelled from the negative terminal of the applied voltage and attracted toward the positive terminal . Hole transfer involves electrons which are still attached to atoms ( Those in the valence band ).

If some of the electron positions in the valence shell of an atom are not occupied by electrons, there are holes where electrons could exist . when sufficient energy is applied, an electron may be made to jump from one atom to a hole in another atom . When it jumps the electron leaves a hole behind it. And consequently the hole has moved in a direction opposite to that of the electron .

Holes may be thought of as positively charged particles and as such they move through an electric field in a direction opposite to that of electrons. Or positive particles are attracted toward the negative terminal of an applied voltage . where there are few free electrons it is more convenient to think of hole movement than of electrons jumping from atom to atom.

Since the flow of electric current is constituted by the movement of electrons and holes electrons and holes are referred to as charge carriers . Each time a hole moves ,an electron must be supplied with enough energy to enable it to escape from its atom . Free electrons can be moved with less application of energy than the holes because they are already disconnected from their atoms. For this reason , electrons have greater mobility than holes.

Introduction Chapter 1 : basic electronics

2013-07-18T20:48:00.001-07:00

INTRODUCTION

An electronic device controls the movement of electrons. The Study of electronic devices requires a basic understanding of the relationship between electrons and the other components of an atom. The movement of electrons within a solid and the bonding forces between atoms can then be investigated . this leads to a knowledge of the differences between conductors , insulators and semiconductors and to an understanding of p-Type and n-Type semiconductor materials. Junctions of p-Type and n-Type material (pn- junction) are basic to all but a very few semiconductors devices . forces act upon electrons that are adjacent to a pn – Junction , and these forces are altered by the presence of an external bias voltage.

1-1 ATOMIC THEORY

THE ATOM

The Atom can be thought of as consisting of a central nucleus surrounded by orbiting electrons . It may be compared to a planet with orbiting satellites. Just are satellites are held in orbit by the attractive force of gravity due to the mass of the planet so each electrons is held in orbit by an electrostatic force of attraction between it and the nucleus.

Each electron has a negative electrical charge of 1.602*10(-19) Coulombs ©. And Some particles within the nucleus have a positive charge of the same magnitude. Because opposite charge attract, a force of attraction exists between the oppositely charged electron and nucleus . Compared to the mass of the nucleus , electrons are relatively tiny particles of almost negligible mass . In fact they can be considered to be little particles of negative having no mass at all.

The nucleus of an atom is largely a cluster of two types of particles protons, and neutrons. Protons have a positive electrical charge , equal in magnitude (But opposite in polarity) to the negative charge on an electron . A neutron has no charge at all. Protons and neutrons each have masses about 1800 times the mass of an electron . for a given atom,the number of protons in the nucleus normally equals the number of orbiting electrons.

Because the protons and orbital electrons are equal in number and equal and opposite in charge , they neutralize eah other electrically . For this reason , ll atoms are normally electrically neutral. If an atom loses an electron , It has lost some negative charge. Consequently, it becomes positively charged and is referred to as a positive ion. Similarly if an atom gains an additional electron, it becomes negatively charged and is termed a negative ion.

The number of protons in an atom is referred to as atomic number of the atom. The atomic weight is approximately equal to the total number of protons and neutrons in the nucleus of the atom . The atom of the semiconductor material silicon has the 14 protons and 14 neutrons in its nucleus , as well as 14 orbital electrons. Therefore the atomic number for silicon is 14 and its atomic weight is approximately 28.

Basic Semiconductor and pn-Junction Theory : Basic electronics

2013-07-18T20:45:00.000-07:00

CHAPTER 1 : Basic Semiconductor and pn-Junction Theory

1-1 : Atomic Theory

a. The Atom

b. Electron orbits and Energy Levels

c. Energy bands

1-2 : Conduction in Solids

a. Electron Motion and Hole transfer

b. Conventional Current and Electron Flow

1-3: Conductors,Semiconductors and insulators

a. Bonding forces between Atoms

b. Energy Bands in Different Materials

1-4 : n-Type and p-Type semiconductors

a. Doping

b. n-Type Material

c. p-type Material

d. Majority and Minority charge carriers

e. Effects of Heat and Light

f. Charge Carrier density

1-5 : Semiconductor Conductivity

a. Drift current

b. Diffusion Current

c. Charge carrier Velocity

d. Conductivity

1-6 : The pn- Junction

a. Junction of p-Type and n-Type

b. Barrier Voltage

c. Depletion Region

d. Summary

1-7: Biased Juctions

a. Reverse-Biased Junction

b. Forward-Biased Junction

c. Junction Temperature Effects

1-8 : Junction Currents and Voltages

a. Shockley Equation

b. Junction Current

c. Junction Voltage

Privacy Policy : My circuit study

2013-07-18T20:35:00.000-07:00

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Disclaimer : my circuit study

2013-07-18T20:32:00.002-07:00

We doesn't Hold any Responsibility for the damage/accidents that you may cause while working with Hazardous ELECTRONIC EQUIPMENTS.

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Techniques used in manufacturing integrated circuits

2013-04-18T07:07:00.000-07:00

In a monolithic integrated circuit all components are fabricated by the diffusion process on a single chip of silicon . Interconnections between components are provided on the surface of the structure and external connecting wires are taken out to terminals. The vast majorityof integrated circuits are monolithic because the diffusion process is the most economicalfor mass production.

Thin Film :

Thin-film integrated circuits are constructed by depositing films of conducting materials on the surface of a glass or ceramic base.
By controlling the width and thickness of the films and by using different materials selected for their resistivity , resistors and conductors are fabricated . capacitors are produced by sandwiching a film of insulating oxide between two conducting films. Inductors are made by depositing metal film in a spiral formation . transistors and diodes are usually tiny discrete componenets connected into the circuit.

Thick-film :
Thick- film integrated circuits are sometimes referred to as printed thin-film Circuits. In this process , silk -screen printing technique are employed to create the desired circuit pattern on a ceramic substrate . The inks used are pastes which have conductive , resistive or dielectric properties. after printing, the circuits are fired at a high temperature in a furnace to fuse the films to the substrate .

INTEGRATED CIRCUITS- definition, types

2013-04-18T06:29:00.002-07:00

TYPES OF IC :

An integrated Circuits (IC) Consists of several interconnected transistors , resistors , and so on, all contained in one all small package with external connecting terminals . the circuit may be entirely self - contained , requiring only input and output connections and a supply voltage . alternatively , a few external componenets may have to be connected to make the circuit operate.

Integrated circuits may be classified in terms of their function as analog or digital. Analog ICs ( Also termed linear ICs ) may be amplifiers , voltage regulators, and so on. digital ICs ( logic gates and counting circuits) contain transistors that are normally either in a switched - off or switched - on state.

The Techniques used in manufacturing integrated circuits provide another method of classification . The major IC manufacturing technique is termed as monolithic . other fabrication techniques are thin - film , thick-film and hybrid.

The Three - Input Adder With Truth table

2013-04-18T06:22:00.003-07:00

It is possible To construct a complete adder without the use of half adders . The circuit has three inputs : A, B and carry C. The Output Carry C' in a serial system is delayed one synchronizing interval T and then becomes the input carry C . From The truth Table we Can verify thet the Boolean expressions for the sum S and the carry C' are given by

By Algebraic manipulation these expressions may be transformed into a number of different forms . In particular it turns out that

These expressions can also be verified from the truth table . The three - input adder is considered

The Free Android Applications for the Electronics & Electrical Engineers

2013-04-06T05:10:00.004-07:00

Go to Android Market( aka Google Play )

1. ElectroDroid

2. EveryCircuit :

EveryCircuit Premium

APPLICATIONS OF P-N JUNCTION DIODES

2013-04-06T00:46:00.002-07:00

P-N JUNCTION DIODES WORKING

2013-04-06T00:43:00.002-07:00

CLICK HERE FOR APPLICATION OF P-N JUNCTION DIODE

P-N JUNCTION DIODES

2013-04-06T00:35:00.003-07:00

What is a P-N junction Diode ?

Definition Of P-N Junction diode?

CLICK HERE FOR HOW P-N JUNCTION DIODE WORKS

STUDY OF DECODER COUNTER IC 74LS90

2013-04-06T00:02:00.001-07:00

Function Description :

The LS90 is a 4 bit ripple type decode counter . it consists of four master / slave flip flops which we alternative connnected to provide a divide by two - section and a divide by five section .

Each station has a separate clock input with initiate state change of the counter on high to low clock transition state changes of the counter output do not occurs simultaneously because a interval ripple delay.

Therefore decoded output signals are subject to decoding spykes and should not be used for clock or strobes. the Qo Output is designed and specified to drive the rated fan-out plus the CPI input of Device