Digital Electronics: Ee-303 & Cse-303

Digital Electronics EE-303 & CSE-303

APPLICATIONS OF SUMMING AMPLIFIER 1. As Averaging Amplifier 2. As Subtractor As Averaging Amplifier  by using proper i/p & feedback resister a summing amplifier can be design to provide an o/p voltage that is equal to the average of i/p voltages

The Conditions must satisfy  all i/p resister either R1, R2 & so on must be in equal value  the ratio of any i/p resister to the feedback resister is equal to the no. of i/p ckts

APPLICATIONS OF SUMMING AMPLIFIER As Averaging Amplifier

 all resisters are in equal value (3kΩ)  as the ratio of any input resister to the feedback resister = 3kΩ/ 1kΩ  the o/p voltage is given by as

APPLICATIONS OF SUMMING AMPLIFIER As Subtractor Amplifier

 used to provide an o/p voltage equal to the difference of two voltages

 as v1 applied to standard i/p having unity gain  o/p for inverting will be equal to -v1  this o/p is applied to the summing amplifier along with v2  the o/p from 2nd op-amp is as Vout = - (VA + VB) = - ( - V1 + V2 ) = V1 - V2

APPLICATIONS OF SUMMING AMPLIFIER As Subtractor Amplifier

 if the ckt is to act as a subtractor, the i/p inverting amplifier must have unity gain, otherwise the o/p will not be proportional to the true difference b/w V1 and V2

COMPARATOR  an op-amp ckt without -ve feedback  having advantages of very high open-loop voltage gain  a very small difference voltage b/w two inputs drives the amplifier to saturation  operates in non-linear mode

COMPARATOR  can be perform the functions like

As a square wave generator As a zero-crossing detector As a level detector As a square wave generator a comparator may use to produce a square wave o/p from a sine wave  the gain of comparator is equal to Aol  the difference voltage b/w input will causes the o/p to go to one of the voltage extrems ( + Vsat or - Vsat ) when the i/p signal goes +ve, the o/p jumps to about +ve v, and when the i/p goes -ve, the o/p jumps to about -ve v. The o/p changes rapidly from -ve to +ve and vice-versa. This change is so rapid that we get square wave o/p for a sine wave input

COMPARATOR As a square wave generator

when the i/p signal goes +ve, the o/p jumps to about +13 v, and when the i/p goes -13 v, the o/p jumps to about -13 v. The o/p changes rapidly from -13 v to +13 v and vice-versa. This change is so rapid that we get square wave o/p for a sine wave input

COMPARATOR As a Zero-Crossing Detector

 when one i/p point is connected to ground, known as zero-crossing detector  o/p changes occurred only when i/o crosses 0v

 when i/p signal is +ve going, o/p is driven to +ve max: value (i.e + Vsat = +13 v)  when i/p crosses the zero axis and begins to go -ve, the o/p is driven to -ve max: (i.e -Vsat = -13v)

COMPARATOR As a Level Detector  used to compare a signal amplitude to a fixed d.c level (reference voltage)  the zero-crossing detector ckt may can be modify to construct level detector  can be done by connecting a fixed reference voltage Vref to the inverting Battery reference

i/p Voltage divider reference

IDEAL & REAL SWITCHES what is a switch……? In electronics, a switch is an electrical component which can break an electrical circuit, interrupting the current or diverting it from one conductor to another. With the passage of time, the term switch has spread to a variety of digital active devices such as transistors and logic gates whose function is to change their output state between two logic levels or connect different signal lines

IDEAL & REAL SWITCHES Ideal Switch  having zero resistance when closed  having infinite resistance when open  can be switch from one state to the other in zero time

IDEAL & REAL SWITCHES Ideal Switch

IDEAL & REAL SWITCHES Real Switch  having small but non zero resistance when closed  having large but finite resistance when open  requires short but non-zero time to change from one state to other  having non zero resistance RON when closed and non infinite resistance ROFF when open

IDEAL & REAL SWITCHES Real Switch

switch closed

switch open

voltage division b/w R and RON

SIGNAL What is a signal….?  any nonverbal action or gesture that encodes a message  in electronics, a signal is an electric current or electromagnetic field used to convey data from one place to another

Analog

Some thing that is continues……… A set of specific points of data with all other points in between

Digital Some thing that is discrete……… A set of specific points of data with no other points in between

Features of a signal Amplitude: the value of the signal at any point on the wave. It is equal to the vertical distance from a given point

SIGNAL Features of a signal Cycle: the completion of one full pattern

Period: the amount of time in seconds, a signal needs to complete one cycle denote by T

SIGNAL Features of a signal Frequency: the No. of periods in one second

Phase: the position of waveform relative to time zero

SIGNAL Types of a signal Periodic: completes a pattern within a measurable time frame, and repeats that pattern over identical subsequent periods

Aperiodic: changes constantly without exhibiting a pattern or cycle that repeats over time

PULSE FUNDAMENTALS  a +ve voltage pulse is a change in voltage from low to high and high to low  amplitude changes from one level to another in zero time

An ideal pulse

 Real pulse can not change the level instantaneously  tr is the total time for leading edge to change from 10% of amplitude to 90%  tf is the total time for trailing edge to fall from 90% to 10% of its amplitude Real pulse

SQUARE WAVE AND RECTANGULAR WAVEFORM Square Wave

 a periodic waveform  a series of recurring pulse  just have two values, 0 V and +VS. There are no intermediate values  having

instantaneous transitions between two levels

SQUARE WAVE AND RECTANGULAR WAVEFORM

Square Waveform it repeats the same pattern of values at regular intervals the period T is the time b/w repetitions, that is the time required to complete one cycle  used to synchronize logic operations  used in waveshaping applications to produce other periodic waveforms  the period T of a square wave is also called the Pulse Repetition Time (PRT)  while the frequency is referred as Pulse Repetition Frequency (PRF) with unit pulse per second (PPS)

SQUARE WAVE AND RECTANGULAR WAVEFORM Rectangular Waveform characterized by flat maximum and minimum levels  fast-rising and fast-falling edges  having squared-off corners  Because of the squared corners, also called a square waveform  the ratio of the total time is high during one cycle(period) to period OR  the ratio of time high to the total period is called as percent

DUTY CYCLE, expressed

SQUARE WAVE AND RECTANGULAR WAVEFORM Rectangular Waveform

Periodic rectangular waveform

Aperiodic rectangular waveform

DESIGN OF WAVESHAPING CIRCUIT  alteration of a waveform to produce a new waveform having specific characteristics is called waveshaping  it can be described as a function that takes the original signal x as input, and produces a new output signal y. This function is called the transfer function as

y = f(x) Alteration have two view points  The Time Domain  The Frequency Domain Time Domain  In general, the change in signal amplitude with respect to time.  phase and frequency are not explicitly measured The Frequency Domain  the max: amplitude change with respect to frequency

DESIGN OF WAVESHAPING CIRCUIT Time Domain  a waveform is a voltage or current whose values change in a prescribed way with the passage of time  new waveform generates by applying the original waveform to various kinds kinds of electronic ckts  as original waveform changes with time, it creates new time-varying voltages Example  o/p of square wave generator is connected with RC ckt  capacitor charges & discharge during each cycle and thus produces an altered waveform  the prediction of new waveform can be occurs due to the voltage across a capacitor changes with time

DESIGN OF WAVESHAPING CIRCUIT The Frequency Domain  as every periodic waveform is a sum of sine waves  the frequency, phase angle & amplitudes of those sine waves determine the shape of the waveform  the wave shaping is an altering the frequency content of a waveform Example  filtering, where sinewaves having certain frequencies are suppressed  thus changing the frequency contents & therefore the shape of a waveform  the new frequency can be added to a given waveform to alter its shape In digital electronic the wave shaping is studied in time domain

DESIGN OF WAVESHAPING CIRCUIT Multivibrator  an electronic ckt used to implement a variety of simple two-state systems like Oscillators, Timers & Flip-Flops Three types of multivibrator ckts  Astable  Monostable  Bistable

Astable  ckt is not stable in either states  continuously oscillates from one state to another  having zero stable states  o/p continuously alternates b/w low and high  square or rectangular waveform generator, also called free-running

DESIGN OF WAVESHAPING CIRCUIT Multivibrator Astable  very simple astable multivibrator is an inverter with the output fed directly back to the input  When the input is 0, the output switches to 1. That 1 output gets fed back to the input as a 1. When the input is 1, the output switches to 0. That 0 output gets fed back to the input as a 0, and the cycle repeats itself  resulting a high frequency (several megahertz)

DESIGN OF WAVESHAPING CIRCUIT Multivibrator Astable  a two-state device which is not stable in either state  If start with point A high, then that high voltage charges the capacitor  after a time characteristic of the time constant RC will reach the threshold for switching A low and B high  the charging process will reverse until the transition back to the original state occurs

DESIGN OF WAVESHAPING CIRCUIT Multivibrator Astable  suppose with voltage comparator  max: +ve and –ve o/p of comparator are  capacitor charges & discharges continuously  the voltage fedback to the non-inverting i/p is  and where as

β = R1/ (R1 + R2)

 when capacitor charges or discharges to one of these levels & o/p switches state

DESIGN OF WAVESHAPING CIRCUIT Multivibrator Astable the period of o/p square wave is

where as

DESIGN OF WAVESHAPING CIRCUIT Multivibrator Monostable  having one stable state  produces a pulse of pre-determined width in response to a trigger i/p  o/p width is determined by resistance & capacitance values in an RC n/w  usefull for creating a timing period of fixed duration to some external events  also called one-shoot or single shoot  application, eliminating switch bounce

DESIGN OF WAVESHAPING CIRCUIT Multivibrator Monostable  a re-triggerable monostable accept new trigger i/p while the o/p pulse produced by previous trigger is still in progress  new trigger initiates a new timing cycle, so pulse is extened  a non-retriggerable monostable ignores any new trigger that occurs while a pulse o/p is in progress

DESIGN OF WAVESHAPING CIRCUIT Three State Logic/ Tri State Logic  allows o/p ports to have a value of logical 0,1 or Hi-Z  Hi-Z puts the pin in a high impedance state  allows multiple ckts to share the same o/p lines or bus  implements in various families of digital ICs like 7400  also used in the data and address bus lines of microprocessor  the third state Hi-Z removes the device’s influence from the rest of ckt  if more than one device is electrically connected, putting an o/p into the HiZ state is often used to prevent short ckts

DESIGN OF WAVESHAPING CIRCUIT CMOS Logic  a newer technology, based on the use of complementary MOS transistors to perform logic functions with almost no current required  use P-type and N-type MOSFET  speed the switching of capacitive loads  extremely small power consumption  having capability to operate at high voltage resulting in improved noise immunity  CMOS technology has been used to construct small, medium and large scale ICS