EMI UNIT-3,JNTUA R13

1. By
Dr. G.N. Kodanda Ramaiah /
P. Siva Nagendra Reddy

2. SIGNAL GENERATOR
A signal generator is an electronic device that
generates repeating or non-repeating electronic
signals in either the analog or the digital domain.
It is generally used in designing, testing,
troubleshooting, and repairing electronic or
electroacoustic devices, though it often has artistic
uses as well.

3. STANDARD SIGNAL GENERATOR
 A standard signal generator produces known and controllable
voltages. It is used as power source for the measurement of
gain, signal to noise ratio (SN), bandwidth standing wave ratio
and other properties.
 It is extensively used in the measuring of radio receivers and
transmitter instrument is provided with a means of modulating
the carrier frequency, which is indicated by the dial setting on
the front panel.
 The modulation is indicated by a meter. The output signal can
be Amplitude Modulated (AM) or Frequency Modulated
(FM).
 Modulation may be done by a sine wave, Square, rectangular,
or a pulse wave. The elements of a conventional signal
generator

4. STANDARD SIGNAL GENERATOR

5. The carrier frequency is generated by a very stable RF
oscillator using an LC tank circuit, having a constant
output over any frequency range.
The frequency of oscillations is indicated by the frequency
range control and the venire dial setting.
AM is provided by an internal sine wave generator or
from an external source.

6. DIFFERENCE BETWEEN A SIGNAL
GENERATOR AND AN OSCILLATOR
Signal generators are the sources of electrical signals
used for the purpose of testing and
Operating different kinds of electrical equipment. A signal
generator provides different types of waveforms such as
sine, triangular, square, pulse etc., whereas an oscillator
provides only sinusoidal signal at the output.

7. Types:
 The AF oscillators are divided into two types. They are
as follows.
1. Fixed frequency AF oscillator
2. Variable frequency AF oscillator.

8. Fixed Frequency AF Oscillator
 Many instrument circuits contain oscillator as one of its integral parts to
provide output signal within the specified fixed audio frequency range. This
specified audio frequency range can be 1 kHz signal or 400 Hz signal.
 The 1 kHz frequency signal is used to execute a bridge circuit and 400 Hz
frequency signal is used for audio testing. A fixed frequency AF oscillator
employs an iron core transformer. Due to this a positive feedback is
obtained through the inductive coupling placed between the primary
winding and secondary winding of the transformer and hence fixed
frequency oscillations are generated.

9. Variable Frequency AF Oscillator
 It is a general purpose oscillator used in laboratory. It
generates oscillations within the entire audio frequency
range i.e. from 2O Hz to 20 kHz. This oscillator provides
a pure, constant sine wave output throughout this AF
range.
 The examples of variable AF oscillators used in laboratory
are RC feedback oscillator, beat frequency oscillator.

10. FUNCTION GENERATOR
 A function generator is usually a piece of electronic test
equipment or software used to generate different types of
electrical waveforms over a wide range of frequencies. Some
of the most common waveforms produced by the function
generator are the sine, square, triangular and sawtooth shapes.

11.  A function generator is usually a piece of electronic test
equipment or software used to generate different types of
electrical waveforms over a wide range of frequencies.
11

12. Function Generator used to generate
various kind of waveform like………
1) Triangular Wave
2) Sine Wave
3) Square Wave
4) Saw tooth Wave etc…
12

13. Triangle wave
 Simple function generators usually generate triangular waveform whose
frequency can be controlled smoothly as well as in steps.
 This triangular wave is used as the basis for all of its other outputs. The
triangular wave is generated by repeatedly charging and discharging
a capacitor from a constant current source.
 This produces a linearly ascending or descending voltage ramp. As the
output voltage reaches upper and lower limits, the charging and
discharging is reversed using a comparator, producing the linear triangle
wave.
 By varying the current and the size of the capacitor, different
frequencies may be obtained.
13

14. 14
Integrator circuit to produce the Triangle wave
In this circuit capacitor is used as a feedback element.
The circuit connection is shown in figure.
Procedure:

15.  As before the negative feedback of the op-amp ensures that the
inverting input will be held at 0 volts(virtual ground).
 If the input voltage is exactly 0 volts there will be no current
through the resistor.
 Therefore no charging of the capacitor , and there output voltage
will be not change.
 We cannot guarantee what voltage will be at output with respect
to ground in this condition but we can say that output voltage is
constant.
 If we apply a constant positive voltage to the input, the op-amp
output will not fall negative at a linear rate, in attempt to
produced the changing voltage across the capacitor necessary to
maintain the current established by the voltage difference across
the resistor. A constant negative voltage at the input result in
linear, rising voltage at the output. The output voltage rate of
15

16. 16

18. 18
SQUARE WAVE GENERATOR
Fig. Multivibrator

19. 19
 This ‘+ ve’ voltage drives the output of operational amplifier into ‘+ ve’
saturation voltage (+Vsat).
 When the + Vsat is fed back to the inverting terminal (2) through the
resistor R, the capacitor C gets charged and the potential of the right
side plate of the capacitor gradually rises (or) the V2 value rises.
 When V2 becomes slightly more than V1, the input becomes ‘–ve'
and immediately this ‘–ve’ voltage drives the output of the
operational amplifier in to ‘–ve’ saturation voltage (- Vsat).
 First the inverting terminal (2) is at zero potential and the input at the non-
inverting terminal (3) has some potential V1. This occurs due to the power
supply of the operational amplifier. The potential difference between the
two input terminals is Vi= V1-0 = V1.

20.  Now the capacitor discharges gradually. When V2 becomes less than V1
and (V1 – V2) becomes ‘+ve’ and the output drives to +Vsat. The same
process is repeated and the output of the operational amplifier swings
between two saturation voltages i.e. between + Vsat and - Vsat. The
output Eo of the operational amplifier is square wave.
20

21. 21
SINE WAVE GENERATOR
 Sine wave can be generated from triangular wave using Resistor-diode
shaping Network.
Procedure:
• While the diodes are reverse-biased neither
shunt branch conducts, and Vo = V, i.e., the output voltage
follows the ramp.
• Suppose V1 < V2 is 0.5 volt. Then when the input voltage
reaches 0.5 volt D1 begins to conduct. The output voltage is
given by
Vo= 0.5 + (V-0.5)(R1/(1+R1))
and setting Vo = 0.866 when V=1 requires R1 = 2.73W.
Similarly set Vo = 1 volt when V = 1.5V (with V2 = 0.866 volt)
calculate. Note that D1 is conducting in this interval. Calculate R2= 0.42W

22. 22

23. 23

24. RANDOM NOISE GENERATOR

25.  The spectrum of random noise covers all frequencies the lower density
spectrum tells us how the energy of the signal is distributed in
frequency, but it does not specify the signal uniquely nor does it tell us
very much about how the amplitude of the signal varies with time.
 The spectrum does not specify the signal uniquely because it contains
no phase information. The method of generating noise is usually to use
a semi conductor noise which delivers frequencies in a band roughly
extending from 80 – 220 KHz.
 The output from the noise diode is amplified and heterodyned down to
audio frequency band by means of a balanced symmetrical modulator.
 The filter arrangement controls the bandwidth and supplies an output
signal in three spectrum choices, white noise, pink noise and Usasi
noise.

26. From the Fig 4.2 it is seen that white noise is flat from
20Hz to 20 KHz and has upper cutoff frequency of 50 kHz
with a cutoff slope of -12 dbs/ octave.
Pink noise is so called because the lower frequencies have
larger amplitude, similar to red light. Pink noise has a
voltage spectrum which is inversely proportional to the
square root of frequency and is used in band analysis.
Usasi noise ranging simulates the energy distribution of
speech and music frequencies and is used for testing audio
amplifiers and loud speakers.

27. White noise:
 Noise containing many frequencies with equal
intensities.
Pink Noise:
 Pink noise or 1⁄f noise is a signal or process with a frequency
spectrum such that the power spectral density (energy or power
per frequency interval) is inversely proportional to the
frequency of the signal. In pink noise, each octave
(halving/doubling in frequency) carries an equal amount of
noise energy.

29. Sweep Generator
 It provides a sinusoidal output voltage whose frequency
varies smoothly and continuously over an entire
frequency band, usually at an audio rate.
 The process of frequency modulation may be
accomplished electronically or mechanically.
 It is done electronically by using the modulating
voltage to vary the reactance of the oscillator tank
circuit component, and mechanically by means of a
motor driven capacitor, as provided for in a modern
laboratory type signal generator.

31. The frequency sweeper provides a variable
modulating voltage which causes the capacitance of
the master oscillator to vary.
A representative sweep rate could be of the order of
20 sweeps/second. A manual control allows
independent adjustment of the oscillator resonant
frequency.
The frequency sweeper provides a synchronization to
drive the horizontal deflection plates of the CRO.
Thus the amplitude of the response of a test device
will be locked and displayed on the screen.

32.  To identify a frequency interval, a marker generator provides half sinusoidal
waveforms at any frequency within the sweep range.
 The marker voltage can be added to the sweep voltage of the CRO during
alternate cycles of the sweep voltage, and appears superimposed on the
response curve.
 The automatic level control circuit is a closed loop feedback system which
monitors the RF level at some point in the measurement system.
 This circuit holds the power delivered to the load or test circuit constant and
independent of frequency and impedance changes.
 A constant power level prevents any source mismatch and also provides a
constant readout calibration with frequency.

33. SQUARE AND PULSE GENERATOR:
 These generators are used as measuring devices in
combination with a CRO.
They provide both quantitative and qualitative
information of the system under test.
They are made use of in transient response testing of
amplifiers.
The fundamental difference between a pulse generator and
a square wave generator is in the duty cycle

35. Requirements of a Pulse
1. The pulse should have minimum distortion, so that any
distortion, in the display is solely due to the circuit under test.
2. The basic characteristics of the pulse are rise time, overshoot,
ringing, sag, and undershoot.
3. The pulse should have sufficient maximum amplitude, if
appreciable output power is required by the test circuit, e.g. for
magnetic core memory. At the same time, the attenuation range
should be adequate to produce small amplitude pulses to
prevent over driving of some test circuit.
4. The range of frequency control of the pulse repetition rate
(PRR) should meet the needs of the experiment. For example, a
repetition frequency of 100 MHz is required for testing fast
circuits. Other generators have a pulse-burst feature
which allows a train of pulses rather than a continuous
output.

36. 5. Some pulse generators can be triggered by an externally applied trigger
signal; conversely, pulse generators can be used to produce trigger signals,
when this output is passed through a differentiator circuit.
6. The output impedance of the pulse generator is another important
consideration. In a fast pulse system, the generator should be matched to the
cable and the cable to the test circuit. A mismatch would cause energy to be
reflected back to the generator by the test circuit, and this may be re-
reflected by the generator, causing distortion of the pulses.
7. DC coupling of the output circuit is needed, when dc bias level is to be
maintained.

38. WAVE ANALYZERS
 A wave analyzer is an instrument designed to measure
relative amplitude of signal frequency components in a
complex waveform .basically a wave instruments acts as a
frequency selective voltmeter which is tuned to the
frequency of one signal while rejecting all other signal
component

39. BASIC WAVE ANALYZER
39

40. Wave Analyzer
 A harmonic distortion analyzer measures the total harmonic content in a
waveform.
 Any complex waveform is made up of a fundamental and its harmonics.
 Wave analyzer is used to measure the amplitude of each harmonic or
fundamental frequency individually.
 Wave analyzers are also referred to as frequency selective voltmeters, carrier
frequency voltmeters, and selective level voltmeters.
 The instrument is tuned to the frequency of one component whose amplitude is
measured.
 Some wave analyzers have the automatic frequency control which tunes to
the signal automatically.

41.  The analyzer consists of a primary detector, which is a simple
LC circuit.
 The LC circuit is adjusted for resonance at the frequency of
the particular harmonic component to be measured.
 It passes only the frequency to which it is tuned and provides a
high attenuation to all other frequencies.
 The full wave rectifier is used to get the average value of the
input signal.
 The indicating device is a simple dc voltmeter that is
calibrated to read the peak value of the sinusoidal input
voltage.
Working process for wave analyzer

42. Application of wave analyzer
1. Electrical measurements
2. Sound measurements
3. Vibration measurements.

43. 43
FREQUENCY SELECTIVE
WAVE ANALYSER

44. Working :
 In a Frequency Wave Analyzer, the complex wave to be analyzed is passed
through an adjustable attenuator which serves as a range multiplier and
permits a large range of signal amplitudes to be analyzed without loading
the amplifier.
 The output of the attenuator is then fed to a selective amplifier, which
amplifies the selected frequency. The driver amplifier applies the attenuated
input signal to a High-Q active filter. This High-Q filter is a low pass filter
which allows the frequency which is selected to pass and reject all others.
 The magnitude of this selected frequency is indicated by the meter and the
filter section identifies the frequency of the component. The filter circuit
consists of a cascaded RC resonant circuit and amplifiers.

45.  For selecting the frequency range, the capacitors generally used
are of the closed tolerance polystyrene type and the resistances
used are precision potentiometers. The capacitors are used for
range changing and the potentiometer is used to change the
frequency within the selected pass-band.
 The selected signal output from the final amplifier stage is
applied to the meter circuit and to an unturned buffer amplifier.
The main function of the buffer amplifier is to drive output
devices, such as recorders or electronics counters.

47. HETERODYNE WAVE ANALYSER
47

48. RF Heterodyne wave analyzer

49. Applications of Heterodyne Wave
Analyzer
 They are primarily used in electrical, sounds, and vibration
measurements.
 In industries, there are heavy machineries which produce a lot
of sound and vibrations. It is very important to determine the
amount of sound and vibrations because if it exceeds the
permissible level it would create a number of problems. The
source of noise and vibrations is first identified by wave
analyzer and then it is reduced by further circuitry.
 A fine spectrum analysis with the wave analyzer shows various
discrete frequencies and resonances that can be related to the
motion of machines.

50. Distortion analyzer
 Distortion analyzer measures the total harmonic power
present in the test wave rather than the distortion caused
by each component.
 The simplest method is to suppress the fundamental
frequency by means of a high pass filter whose cut
off frequency is a little above the fundamental
frequency.
 This high pass allows only the harmonics to pass and the
total harmonic distortion can then be measured.

51. Resonance Bridge

52. Wien’s Bridge Method
 The bridge is balanced for the fundamental frequency.
The fundamental energy is dissipated in the bridge
circuit elements. Only the harmonic components reach the
output terminals .The harmonic distortion output can
then be measured with a meter. For balance at the
fundamental frequency
 C1=C2=C, R1=R2=R, R3=2R4.

54. Bridged T-Network Method

56. Spectrum Analyzers
 The most common way of observing signals is to display
them on an oscilloscope with time as the X-axis (i.e.
amplitude of the signal versus time).
 This is the time domain. It is also useful to display signals
in the frequency domain. The providing this
frequency domain view is the spectrum analyzer.
 A spectrum analyzer provides a calibrated graphical display
on its CRT, with frequency on the horizontal axis and
amplitude (voltage) on the vertical axis.

58. Basic Spectrum Analyzer Using Swept Receiver
Design
 Referring to the block diagram of fig. 4.2, the saw tooth
generator provides the saw tooth voltage which drives the
horizontal axis element of the scope and this saw tooth voltage is
the frequency controlled element of the voltage tuned oscillator.
 As the oscillator sweeps from fmin to fmax of its frequency band
at a linear recurring rate, it beats with the frequency component
of the input signal and produce an IF, whenever a frequency
component is met during its sweep.
 The frequency component and voltage tuned oscillator frequency
beats together to produce a difference frequency, i.e. The IF
corresponding to the component is amplified and detected if
necessary and then applied to the vertical plates of the CRO,
producing a display of amplitude versus frequency.

62. Types of spectrum analyzers
The two types of spectrum analyzers are,
1. Filter Bank Spectrum analyzer.
2. Super heterodyne Spectrum analyzer.

63. Filter Bank Spectrum analyzer

64. Super hetero dyne Spectrum
analyzer
 The modern spectrum analyzers use a narrow band super
heterodyne receiver.
 Super heterodyne is nothing but mixing of frequencies in
the super above audio range.
 The functional block diagram of super heterodyne
spectrum analyzer or RF spectrum analyzer as shown in
the Figure 7.2

66. Digital Fourier analyzer
 A spectrum analyzer, which uses computer algorithm
and an analog to digital conversion phenomenon and
produces spectrum of a signal applied at its input is
known as digital Fourier or digital FFT or digital
spectrum analyzer.

67. Principle
 When the analog signal to be analyzed is applied, the A/D
converter digitizes the analog signal (i.e., converts the
analog signal into digital signal).
 The digitized signal, which is nothing but the set of digital
numbers indicating the amplitude of the analog signal as a
function of time is stored in the memory of the digital
computer.
 From the stored digitized data, the spectrum of the signal
is computed by means of computer algorithm.

68.  The block arrangement of a digital Fourier analyzer is illustrated in
the figure above fig 5.
 The analog signal to be ana1ysed is applied to the low pass filter,
which passes only low frequency signals and rejects high pass
spurious signals.
 This filter section is used mainly, to prevent aliasing. The output of
low pass filter is given to the attenuator.
 The attenuator is a voltage dividing network whose function is to set
the input signal to the level of the A/D converter.
 The use of attenuator prevents the converter from overloading. The
function of A/D converter is to convert the samples of analog data
into digital i.e. ., to digitize the analog signal.
 When the output of A/D converter is applied to the digital computer,
the computer analyzes the digitized data and adjusts the attenuator
setting accordingly in order to obtain the maximum output from the
inverter without any overloading.
 As soon as the entire analog signal is sampled and digitized by the
A/D converter) computer performs calculations on the data
according to the programmed algorithm and the calculated spectral
components are stored in the memory of the computer.

70. Advantages
1. The use of computer avoids most of the hardware
circuitry such as electronic switches.
Filters and PLLs. The use of less hardware reduces the
cost of the analyzer.
2. More mathematical calculations can be carried-out
on the spectral display.
3. The rate of sampling analog signal can be modified in
order to obtain better spectral display.

71. Difference between wave analyzer and harmonic distortion analyzer
Wave analyzer Harmonic distortion analyzer
1. These are designed to measure the
relative amplitude of each harmonic or
fundamental components separately.
2.They indicate the amplitude of single
frequency component
3.These are tuned to measure amplitude of one
frequency component with in a range of 10Hz
to 40MHz
4.These are also known as frequency selective
voltmeters, selective level voltmeters, carrier
frequency voltmeters
5. These are used with a set of tuned filters and
a voltmeter.
6. Wave analyzers provide very high frequency
resolution.
7.These can be used for electrical
measurements, sound ,vibration ,noise
measurement in industries
1. These are designed to measure the total
harmonic content present in a distorted
or complex wave form.
2. They do not indicate the amplitude of single
frequency component
3.These can be operated with in a band of 5Hz
to 1 MHz frequency
4.It is general know as distortion analyzer
5. These can be used along with a frequency
generator.
6. They measure quantitative harmonic
distortions very accurately.
7.These can be used to measure frequency
stability and spectral purity of signal sources

72. DEPARTMENT OF ECE,
KUPPAM ENGINEERING COLLEGE,KUPPAM.

73. DEPARTMENT OF ECE,
KUPPAM ENGINEERING COLLEGE,KUPPAM.