The following text is an English translation of THIS technical chapter in Hindi.
CHAPTER 1
CATHODE RAY OSCILLATOR AND FUNCTION GENERATOR
Introduction
In the field of electronics, observation of different signals is important. The Cathode Ray Oscillator was invented for this purpose. It is used to measure various parameters of a signal (like – frequency, time and voltage). Earlier, the Cathode Ray Oscillator was used in the measurement process, but later the Digital Storage Oscilloscope was invented, which could measure different parameters of a signal very easily. Digital Storage Oscilloscope is small-sized and very light weight. It is used in community labs, radar systems and research centres.
Different types of signals are generated with the help of a Function Generator, which generates signals of different frequencies. It is mainly used in electronic labs.
1.1] CATHODE RAY OSCILLOSCOPE
A device that displays the characteristics of a signal (like amplitude, frequency etc.) relative to time is called a Cathode Ray Oscilloscope. In short it is also called a CRO. In fact CRO is an ultra-high speed X-Y plotter which makes use of a cathode ray tube. It has an electron gun that generates and directs cathode rays towards a phosphor coated screen. This produces a spot of light on the screen. The shape of the signal appears as the dot moves on the screen with ultra-high speed.Shapeof signals – from very low frequency to very high frequency – is distinctly visible through CRO. Cathode Ray Oscilloscope is used more often in electronics laboratories.
1.1.1) Block Diagram of Cathode Ray Oscilloscope
Different devices are used in a Cathode Ray Oscilloscope as shown in Illustration 1.1 –
Illustration 1.1 – Block Diagram of a Cathode Ray Oscilloscope
Description of apparatus shown in this diagram is as follows –
1) Cathode Ray Tube–It is also called the heart of a CRO. An electron gun inside it generates an electron mass, which strikes a phosphor coated screen and produces a spot of light through which the shape of a signal ismade visible.
2) Vertical Amplifier – The strength of the input signal received by a CRO is not enough. The task of increasing the strength of the input signal is performed by a Vertical Amplifier.By means of an assigned Gainon a Vertical Amplifier, the required bandwidth of the signal can be easily achieved.
3) Delay Line – The Delay Line is used to delay the signal in the vertical section of a CRO.If the Delay Line is not used, a part of the signal is not received in the output. That is why the signal strikes the vertical deflection plates with a delay.
4) Trigger Circuit – It is necessary for the horizontal and vertical signal to start together at the same time. For this purpose a circuit is used which is called the Trigger Circuit. The Trigger Circuit converts the input signal into a trigger pulse which is used in synchronization.
5) Time Base Generator – A Time Base Generator is used to produce saw-tooth voltage through which the beam is deflected in the horizontal section. Values are assigned to the saw-tooth voltage during the beam deflection process.
6) Horizontal Amplifier – The saw-tooth voltage produced by the Time Base Generator has amplitude of low strength. That is why a Horizontal Amplifier is used to amplify the saw-tooth voltage before striking the horizontal deflection plates.
1.1.2) Applications of Cathode Ray Oscilloscope
CRO has various applications, some of which are as follows –
1) It is used for measuring AC and DC supply current and voltage values. It is also used for measuring a signal’s Peak to Peak value, mean square root value, turnover time etc.
2) CRO is used in labs to calculate the mean relationship between the frequency, turnover time etc. of two signals.
3) It can be used in radar for estimating the position of a target.
4) CRO is useful in radio broadcast for inspecting various parameters of RF, IF and AF.
5) In the field of healthcare CRO is used for computing the heart rate graph.
6) In the industrial field CRO is used for inspecting the B-H curve, P-V curve and other graphs.
7) It is used forestimating modulation characteristics of broadcast lines.
8) It is used for testing inductance, capacitance etc.
1.2] DIGITAL STORAGE OSCILLOSCOPE
The Digital Storage Oscilloscope was designed to overcome various shortcomings of theCathode Ray Oscilloscope. In a Digital Storage Oscilloscope, the signal is displayed in the digital form and stored in the memory. These kind of Oscilloscopes use a conventional cathode ray tube which further brings down the overall operating cost. To start it, a low voltage is applied. Once the signal inside it is converted into a digital form it can be easily analysed on a computer.
1.2.1) Block Diagram of Digital Storage Oscilloscope
A Digital Storage Oscilloscopemakes use of various instruments which are shown in Illustration 1.2.
Illustration 1.1 – Block Diagram of a Digital Storage Oscilloscope
Description of blocks in this diagram is as follows –
1) Input Attenuator – In a Digital Storage Oscilloscope, the input signal first strikes the Input Attenuator. The Input Attenuator removes unwanted signal from the input signal and the required signal is sent to the Vertical Amplifier.
2) Vertical Amplifier – It performs the task of increasing the strength of the input signal. By means of an assigned Gain on a Vertical Amplifier, the required Bandwidth of the signal can be easily achieved.
3) Analogue to Digital Converter – To convert analogue signals to digital signals the Analogue to Digital Converter is used. The output of the Vertical Amplifier strikes the Analogue to Digital Converter.
4) Memory – Output of the Analogue to Digital Converter is stored in the memory in the digital form. The digital output is always in binary form. Values stored in the memory are used whenever required.
5) Trigger Circuit – The Trigger Circuit is used to ensure that the horizontal and vertical signals start at the same time. The input signal is converted into a trigger pulse with the help of a Trigger Circuit.
6) Cathode Ray Tube – The Digital Storage Oscilloscope makes use of a simple kind of Cathode Ray Tube. An electron gun inside it generates an electron mass, which strikes a phosphor coated screen and produces a magical dot/spot of lightthrough which the shape of a signal is made visible. It does not use receptor types of Cathode Ray Tubes.
1.2.2) Features of Digital Storage Oscilloscope
Digital Storage Oscilloscope is an advanced technology of CRO and thus has many merits. Some of the major ones are as follows –
1) Pretrigger View – Pretrigger View of a Digital Storage Oscilloscope displays thestate of the signals before the trigger input is applied; that is the statebefore synchronization of the signals. In case any fault arises in the Mode of Operation, then by observing 25%, 50%, and 75% of the Mode of Operation in the Pretrigger View the faults can be detected.
2) Channel Difference – Value of Channel Difference depends on the position of the Reference Cursor. When the Reference Cursor is active, then the mean Channel Difference between Channel A and Channel B iscalculated on that point where the Reference Cursor level is considered zero.
3) Channel Add – Similar to Channel Difference, the Channel Add also depends on the position of the Reference Cursor. It is used for adding channels.
4) Channel Inversion – Through this the input signal given to the channel is displayed in an inverted (reverse) order.
5) X-Y Function – Once the X-Y Function is active, the X-Y Function window screen opens up on which the data is displayed.
6)Trigger Coupling – The Digital Storage Oscilloscope also includesTrigger Coupling facility which is used for AC and DC coupling.
1.2.3) Advantages of Digital Storage Oscilloscope
Advantages of Digital Storage Oscilloscope are as follows –
1) It is easy to operate and has more strength/capacity.
2) Its storage time is infinite.
3) It is possible to calculate the cursor in a Digital Storage Oscilloscope.
4) Signal characteristics are displayed on the screen in analogue form therefore frequency, amplitude and minimum valueare easy to calculate.
5) It can display the X-Y curve, B-H curve and P-V curve.
6) Pretrigger View displays the signal as it was before the trigger was applied.
7) It is possible to store the output signal.
8) The display is big and bright which makes calculation easy.
9) Memory can be storedin one or two dimensional arrays.
1.2.4) Applications of Digital Storage Oscilloscope
Applications of Digital Storage Oscilloscope are as follows –
1) It is possible to calculate DC and AC parameters like current, voltage etc.
2) To calculate various parameters of alternating current like mean square root, turnover time etc.
3) To calculate frequency, turnover time, — and — of periodic and non-periodic signals.
4) It can calculate fleeting/momentary parameters of a signal like – overshoot, acceleration time and deceleration time.
5) Addition, subtraction, calculus and integration of signals is possible.
6) It can be used to calculate slow changing parameters, such as morning temperature.
7) Different operations like – Fast Fourier Transform, Discrete Fourier Transform, and Inverse Fourier Transform can be executed.
8) Inductance, capacitance and resistance can also be calculated with a Digital Storage Oscilloscope.
9) Parameters of the transmission line such as modulation, SWR etc. can be tested.
10) It can also calculate the B-H curve, P-V curve, Hysteresis Loop etc.
1.3] DIFFERENCES BETWEEN CATHODE RAY OSCILLOSCOPE AND DIGITAL STORAGE OSCILLOSCOPE
Differences between Cathode Ray Oscilloscope and Digital Storage Oscilloscope given in Chart 1.1 are as follows –
| S. No. | Cathode Ray Oscilloscope (CRO) | Digital Storage Oscilloscope (DSO) |
| 1. | It cannot store signals. | It can store signals. |
| 2. | It does not use AC to DC converters. | It uses AC to DC converters. |
| 3. | Display screen in smaller and not so bright. | Display screen in bigger and brighter. |
| 4. | B-H curve cannot be obtained. | B-H curve can be obtained. |
| 5. | Big in size and heavy weight. | Small in size and light weight. |
| 6. | It does not have a Pretrigger View. | It has a Pretrigger View. |
| 7. | Channel Difference and Channel Add is not possible. | Channel Difference and Channel Add is possible. |
1.4] FUNCTION GENERATOR
The device through which different signals are generated is called a Function Generator. It can control the frequency of the generated signals up to the required range. A Function Generator is mainly used in labs.
Various parts of a Function Generator are shown in Illustration 1.3.
Illustration 1.1 – Block Diagram of a Function Generator
A Function Generator is used to transmit signals with very low frequencies. Normally, capacitance of the capacitor of an LC and RC circuit is converted to control the frequencies. However, to control the frequencies in a Function Generator, the amplitude of the current is converted by an Integrator. A Function Generator can produce signals with frequencies ranging from 0.01Hz to 100kHz. As shown in Illustration 1.3, the frequencies of the signals are controlled by Upper Constant Current Source and Lower Constant Current Source.Output of these two current sources strikes the integrator. The output from the integrator increases exponentially relative to time.
Output from the integrator is applied to the voltage comparator, which changes the position of the circuit due to which the Upper Constant Current Source is switched off and the Lower Constant Current Source is switched on. The Lower Constant Current Source supplies current to the integrator in the opposite direction. Output from the integrator decreases exponentially relative to time and at a particular point, the Upper Constant Current Source is switched on again by the comparator. In this way, a Function Generator produces signals of different frequencies.
1.4.1) Features of a Function Generator
1) Its FrequencyRange is from 0.01Hz to 100kHz.
2) It can generate signals of different kinds such as sine signal, sawtooth signal etc.
3) In Low Frequency Range its accuracy is ±1%.
4) Value of distortion in a sine signal is less than 1%.
5) DC offset adjustment ranges from -5V to + 5V.
6) — of — signal source can be locked.
1.4.2) Specifications of a Function Generator
Specifications of a Function Generator are given in Chart 1.2
Chart 1.2 – Specifications of a Function Generator
| S. No. | Parameter | Value |
| 1. | Frequency Range | 0.01Hz to 100kHz |
| 2. | Frequency Stability | 0.05% |
| 3. | Distortion | – 55dB Below 50 kHz – 40dB Above 50 kHz |
| 4. | Output Amplitude | 10 VP-P |
| 5. | Output Impedance | 50 Ω |
| 6. | Output Signal | Sine, square, triangular, ramp etc. |
PRACTICE QUESTIONS
- Choose the correct option for the following questions –
1) It is a part of Cathode Ray Oscilloscope –
(a) Vertical Amplifier (b) Delay Line
(c) Trigger Circuit (d) All of the above
Answer) a b c d
2) The substance coated on the screen of a Cathode Ray Oscilloscope is –
(a) Sodium (b) Magnesium
(c) Phosphorous (d) None of the above
Answer) a b cd
3) Which component of a CRO helps in obtaining the bandwidth range –
(a) Delay Line (b) Vertical Amplifier
(c) Trigger Circuit (d) None of the above
Answer) a b c d
4) Which part of a CRO helps in starting the horizontal and vertical signal at the start time –
(a) Delay Line (b) Vertical Amplifier
(c) Horizontal Amplifier (d) Trigger Circuit
Answer) a b c d
5) CRO is used for measuring –
(a) DC value (b) AC value
(c) AC and DC values (d) None of the above
Answer) a b cd
6) This is part of a Digital Storage Oscilloscope –
(a) Attenuator (b) Vertical Amplifier
(c) Cathode Ray Tube (d) All of the above
Answer) a b c d
7) Channel Difference in a Digital Storage Oscilloscope depends upon the-
(a) Reference Cursor (b) Vertical Amplifier
(c) Horizontal Amplifier (d) None of the above
Answer) a b cd
8) Storage time available in a Digital Storage Oscilloscope is –
(a) Zero (b) Infinite
(c) Changeable (d) None of the above
Answer) a bcd
9) Which curve can be obtained using a Digital Storage Oscilloscope –
(a) X-Y curve (b) B-H curve
(c) P-V curve (d) All of the above
Answer) a b cd
10) Digital Storage Oscilloscope stores memory in which order –
(a) 1 dimensional array (b) 2 dimensional array
(c) 3 dimensional array (d) Both (a) and (b)
Answer) a b c d
11) It is a fleeting parameter of a signal –
(a) Overshoot (b) Acceleration Time
(c) Deceleration Time (d) All of the above
Answer) a b c d
12) Another name for a CRO is –
(a) X-Y printer (b) X-Y plotter
(c) X-Y monitor (d) None of the above
Answer) a bcd
13) ____ voltage is used for beam deflection in the horizontal part of a CRO –
(a) Horizontal (b) Wave
(c) Sawtooth (d) None of the above
Answer) a b cd
14) CRO is used in –
(a) Radar (b) Radio broadcasting
(c) Both (a) and (b) (d) Astronomical testing
Answer) a bcd
15) Advantage of a is –
(a) Pretrigger View (b) Channel Difference
(c) X-Y function (d) All of the above
Answer) a b cd
16) What is called the heart of a CRO –
(a) Delay Line (b) Cathode Ray Tube
(c) Attenuator (d) Trigger Circuit
Answer) a bcd
17) ___ is used for generating sawtooth voltage –
(a) Delay Line (b) Cathode Ray Tube
(c) Time Base Generator (d) Trigger Circuit
Answer) a b cd
18) A device that generates different kinds of signals is called ______ –
(a) Cathode Ray Oscilloscope (b) Digital Storage Oscilloscope
(c) Function Generator (d) Cathode Ray Tube
Answer) a b cd
19) ____ frequency is produced with the help of a Function Generator –
(a) 0.01kHz to 100kHz (b) 1Hz to 100Hz
(c) 1kHz to 100kHz (d) 0.01Hz to 100kHz
Answer) a b cd
20) Value of distortion for a sine signal is –
(a) More than 1% (b) More than 2%
(c) Less than 1% (d) 1% to 2%
Answer) a b cd
21) DC offset is adjusted in within ____ values –
(a) -1V to +1V (b) -2V to +2V
(c) -3V to +3V (c) -5V to +5V
Answer) a b cd
22) Frequency stability of a Function Generator is –
(a) 5% (b) 10%
(c) 0.05% (c) 0.08%
Answer) a b cd
23) Output impedance of a Function Generator is –
(a) 5Ω (b) 50 Ω
(c) 500 Ω (d) 5000 Ω
Answer) a bcd
24) A Function Generator gives which kind of output signal –
(a) Sine (b) Square
(c) Triangular (d) All of the above
Answer) a b cd
25) Output amplitude of a Function Generator is –
(a) 5 VP-P (b) 10 VP-P
(c) 15 VP-P (d) 20 VP-P
Answer) a bcd
- Match the following –
1) Match Table 1 with Table 2 –
| Table 1 | Table 2 |
| (a) CRO screen | (i) Oscilloscope with storage capacity |
| (b) DSO | (ii) Upper constant current source |
| (c) Function Generator | (iii) Oscilloscope without storage capacity |
| (d) CRO | (iv) Phosphor |
Answer) a(iv), b(i), c(ii), d(iii)
2) Match Table 1 with Table 2 –
| Table 1 | Table 2 |
| (a) Frequency stability | (i) 10 VP-P |
| (b) Frequency range | (ii) 50 Ω |
| (c) Output impedance | (iii) Sine, square, triangular, ramp etc. |
| (d) Output amplitude | (iv) 0.05% |
| (e) Output signal | (v) 0.01Hz to 100kHz |
Answer) a(iv), b(v), c(ii), d(i), e(iii)
- True or False –
1) CRO is used for measuring various parameters of a signal (like amplitude, frequency, voltage etc.)
Answer) True
2) Function Generator is used to produce different kind of signals.
Answer) True
3) Function Generator comes with an ultra-high speed X-Y plotter.
Answer) False
4) Cathode Ray Tube is called the heart of a CRO.
Answer) True
5) Function Generator calculates the position of a target in radar.
Answer) True
6) In a Digital Storage Oscilloscope the storage time is infinite.
Answer) True
7) Digital Storage Oscilloscope has more strength.
Answer) True
8) Values of fleeting parameters cannot be measured by a Digital Storage Oscilloscope.
Answer) False
9) Cathode Ray Oscilloscope has storage capacity.
Answer) False
10) B-H curve cannot be obtained by a Cathode Ray Oscilloscope.
Answer) False
- Fill in the blanks –
1) _____ generates signals with frequency range of 0.01Hz to 100kHz.
Answer) Function Generator
2) The screen of a CRO is coated with _____.
Answer) Phosphor
3) In a Cathode Ray Tube, electrons are generated by a _____.
Answer) Electron gun
4) A part of the signal is not obtained in a CRO if _____ is not used.
Answer) Delay Line
5) A _____ circuit in a CRO starts the horizontal and vertical signal at the same time.
Answer) Trigger
6) A _____ generator is used to produce sawtooth voltage.
Answer) Time Base
7) A Digital Storage Oscilloscope is used to obtain _____ loop.
Answer) Hysteresis
8) A Digital Storage Oscilloscope has a _____ view.
Answer) Pretrigger
- Briefly answer the following questions –
1) Define a Cathode Ray Oscilloscope.
Answer) A device that displays the characteristics of a signal (like amplitude, frequency etc.) relative to time is called a Cathode Ray Oscilloscope.
2) What is called the heart of a CRO?
Answer) A Cathode Ray Tube is called the heart of a CRO.
3) What is the use of a Delay Line in a CRO?
Answer) Delay Line is used to delay the signal n the vertical part of a CRO.
4) What is the use of a CRO in the field of healthcare?
Answer) In the field of healthcare, CRO is used for computing the heart rate graph.
5) Write two advantages of a Digital Storage Oscilloscope.
Answer) Two advantages of a Digital Storage Oscilloscope are – (i) Pretrigger View (ii) Channel Difference.
6) Which graphs are displayed with the help of a Digital Storage Oscilloscope?
Answer) Graphs displayed with the help of a Digital Storage Oscilloscope are the X-Y curve, B-H curve, and P-V curve.
7) What is a Function Generator?
Answer) Adevice that generates different kinds of signals is called a Function Generator.
- Answer the following questions in detail –
1) What are the applications of aCathode Ray Oscilloscope?
2) Describe the Digital Storage Oscilloscope.
3) Write the advantages of a Digital Storage Oscilloscope.
5) Write the differences between a Cathode Ray Oscilloscope and a Digital Storage Oscilloscope.
6) Describe the Function Generator.
7) Write the advantages of a Function Generator.
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