Display Devices and Signal Generators
Recall Cathode Ray Oscilloscope (CRO) and the advantages of CRO
A cathode ray oscilloscope (CRO) is a type of electronic test instrument used to display and analyse various electrical signals. It works by using an electron beam to produce a visual representation of an electrical signal on a screen.
The main advantages of CRO are:
- Real-time analysis: CROs can display electrical signals in real-time, making them useful for analysing signals that change rapidly over time. This makes them ideal for diagnosing problems in electronic circuits, detecting glitches, and measuring the frequency and amplitude of signals.
- High sensitivity: CROs are highly sensitive and can detect even very small changes in an electrical signal. This makes them useful for detecting noise and other disturbances in circuits.
- Versatility: CROs can be used to measure a wide range of electrical signals, including AC and DC voltages, current, frequency, and phase. They can also be used to measure the time delay between signals.
- Easy to use: CROs are relatively simple to operate and can be used by technicians and engineers with minimal training. They also have a user-friendly interface that allows for quick and easy adjustments to the display settings.
- Provides visual representation: CROs provide a visual representation of an electrical signal, allowing users to see the shape, frequency, and amplitude of the signal. This makes it easier to identify problems and to make adjustments to the circuit.
A graticule is a pattern of grid lines or markings on a display, such as the screen of a cathode ray oscilloscope (CRO), that is used to aid in measurements or observations. The graticule is typically etched onto the surface of the display or is a part of a transparent overlay placed on the display.
In a CRO, the graticule is a pattern of horizontal and vertical lines that divide the screen into a grid of squares. This allows the user to measure the amplitude and time period of the signal being displayed, as well as to make other measurements such as phase shift, rise time, and fall time.
The graticule lines are typically labelled with numeric values or other symbols to indicate the units of measurement. For example, the horizontal graticule lines might be labelled in units of time (such as milliseconds or microseconds), while the vertical lines might be labelled in units of voltage (such as volts or millivolts).
Graticules are also used in other types of displays, such as microscopes and telescopes, to aid in measurements or observations of specimens or objects.
The cathode ray tube (CRT) in a CRO is the heart of the instrument. It consists of an electron gun that produces a beam of electrons, and an anode that accelerates and focuses the beam onto the face of the tube. The face of the tube is coated with a fluorescent material that glows when struck by the electron beam.
The principle of operation of a CRT is based on the interaction of electric and magnetic fields. The electron gun produces a beam of electrons, which is accelerated by the anode towards the face of the tube. The beam is deflected by electric fields, which are created by the deflecting plates. The beam is also deflected by magnetic fields, which are created by the deflection coils.
The various parts of a CRT include:
- Electron gun: The electron gun produces a beam of electrons.
- Anode: The anode accelerates and focuses the beam onto the face of the tube.
- Deflecting plates: The deflecting plates create electric fields that deflect the electron beam.
- Deflection coils: The deflection coils create magnetic fields that deflect the electron beam.
- Fluorescent screen: The face of the tube is coated with a fluorescent material that glows when struck by the electron beam.
The deflection sensitivity of a CRO is defined as the change in the vertical deflection of the electron beam per unit change in the input signal voltage. It is given by the expression:
Sensitivity = ΔY/ΔV
where ΔY is the change in the vertical deflection of the electron beam and ΔV is the change in the input signal voltage.
The deflection sensitivity can be expressed in terms of the deflection voltage Vd, the deflection angle θ, and the length of the deflecting plates L. The deflection voltage Vd is given by:
Vd = Vm sin(ωt)
where Vm is the peak amplitude of the input voltage and ω is the angular frequency of the input voltage.
The deflection angle θ is given by:
θ = (Vd/E)L
where E is the electric field strength between the deflecting plates.
A parallax error is a type of measurement error that occurs when the position of an object appears to be different depending on the angle or position from which it is viewed. In other words, it is an error that arises when the observer’s position is not directly aligned with the measurement being taken.
A common example of parallax error is when reading the level of liquid in a graduated cylinder or measuring the length of an object with a ruler. If the observer’s eye is not directly aligned with the scale or the object being measured, the measurement may appear to be different than the actual value.
Parallax errors can be minimised by taking measurements from a position that is directly aligned with the object being measured, or by using instruments that are designed to compensate for parallax errors, such as digital vernier callipers.
In some cases, parallax errors can lead to significant measurement errors, particularly in scientific experiments or engineering applications where precise measurements are required. Therefore, it is important to be aware of parallax errors and to take steps to minimise them whenever possible.
The bandwidth of a response is defined as the range of frequencies over which the response is accurate. The rise-time of a response is the time it takes for the output to rise from 10% to 90% of its final value.
There is a relationship between the bandwidth and rise-time of a response. The rise-time is related to the bandwidth by the equation:
Rise-time = 0.35/Bandwidth
Bandwidth and rise-time are two key parameters used to characterise the response of a system or device to an input signal. They are related in that a system’s bandwidth and rise-time are inversely proportional to each other.
The bandwidth of a system is defined as the range of frequencies over which the system can transmit or process signals with minimal distortion. It is typically measured as the difference between the upper and lower frequencies at which the system’s response drops to a specified level, such as -3dB.
The rise-time of a system is defined as the time it takes for the system’s output to rise from a specified percentage of the final value to the final value, typically 10% to 90% of the final value. The rise-time is an indication of how quickly the system responds to changes in the input signal.
In general, a system with a wider bandwidth will have a faster rise-time, and vice versa. This is because a wider bandwidth allows the system to respond more quickly to changes in the input signal, resulting in a faster rise-time. Conversely, a narrower bandwidth will cause the system to respond more slowly, resulting in a slower rise-time.
A Lissajous pattern is a complex curve that is generated by the intersection of two perpendicular sine waves of different frequencies, phases, and amplitudes. These patterns are named after Jules Antoine Lissajous, a French mathematician who discovered them in the mid-19th century.
In a Lissajous pattern, one of the sine waves is plotted along the X-axis, while the other is plotted along the Y-axis. As the two sine waves are plotted, their intersection creates a complex curve that can take on a wide variety of shapes, depending on the relative frequency, phase, and amplitude of the two sine waves.
Lissajous patterns are commonly used in physics and engineering to study the behaviour of oscillating systems, such as pendulums, springs, and electrical circuits. By analysing the shape and movement of the Lissajous pattern, engineers and scientists can gain insights into the properties of these systems, such as their frequency, damping, and resonant frequencies.
Lissajous patterns are also used in entertainment and art, particularly in the creation of light displays and laser shows. By projecting Lissajous patterns onto a screen or surface, artists can create complex and visually appealing displays that are synchronised with music or other sound sources.
The Lissajous pattern depends on the relative frequencies and phases of the two input signals. There are several different types of Lissajous patterns, depending on the relationship between the frequencies and phases of the two signals:
- When the two signals have the same frequency and phase, the Lissajous pattern is a straight line at 45 degrees to the x-axis.
- When the two signals have the same frequency but are out of phase, the Lissajous pattern is an ellipse.
- When the two signals have different frequencies and are in phase, the Lissajous pattern is a series of vertical lines.
- When the two signals have different frequencies and are out of phase, the Lissajous pattern is a complex pattern that depends on the relative frequencies and phases of the two signals.
The frequency and phase angle of the two signals can be determined from the Lissajous pattern. The frequency ratio of the two signals can be calculated from the shape of the pattern. For example, if the pattern is a vertical line, the frequency ratio is 1:2. If the pattern is an ellipse, the frequency ratio is the ratio of the major and minor axes.
The phase angle can be determined by measuring the horizontal and vertical distances between points on the Lissajous pattern and using trigonometric functions to calculate the phase angle. For example, the phase angle θ can be calculated as:
θ = arctan((Δy/Δx)/m)
where Δy is the vertical distance between two points on the pattern, Δx is the horizontal distance between the same two points, and m is the slope of the pattern.
Special CROs are designed to meet specific measurement requirements. Some examples of special CROs include multi-input CROs, sampling CROs, and storage CROs.
Multi-input CROs are used to measure multiple signals simultaneously. They have two or more input channels, which can be displayed on the screen simultaneously. There are several types of multi-input CROs, including:
- Dual-trace CROs: These CROs have two input channels, which can be displayed on the screen separately or overlaid.
- Dual-beam CROs: These CROs have two electron beams, which can be used to display two input signals simultaneously.
- Multiple-trace CROs: These CROs have more than two input channels, which can be displayed on the screen simultaneously.
Sampling CROs are used to measure high-frequency signals. They use a technique called sampling to capture and display the waveform of the signal. The signal is sampled at a high rate, and the samples are then displayed on the screen.
Storage CROs are used to capture and display waveforms that change slowly over time. They have a built-in storage device, such as a CRT or digital memory, which can store the waveform for a period of time. The waveform can then be displayed on the screen for further analysis. Storage CROs are often used in applications such as radar and television.
A sweep frequency generator is an electronic device used to generate a varying frequency signal. The device produces a linear or logarithmic varying frequency signal, which is used to test and measure the frequency response of electronic circuits and devices.
The sweep frequency generator generates a continuous wave (CW) signal, which is then passed through a sweep circuit that varies the frequency of the signal over a specified range. The sweep circuit typically consists of a voltage-controlled oscillator (VCO) and a sweep generator. The sweep generator generates a voltage signal that is used to control the VCO frequency. As the voltage signal varies, the frequency of the VCO changes, resulting in a varying frequency output signal.
The output signal of the sweep frequency generator can be used to measure the frequency response of electronic circuits and devices. The signal is fed into the device under test, and the response of the device is measured using a detector or spectrum analyzer.
Sweep errors refer to errors that can occur in a sweep frequency generator, which can affect the accuracy of the measured frequency response. There are several types of sweep errors, including:
- Nonlinear sweep: This occurs when the frequency sweep is not linear, resulting in inaccurate frequency measurements.
- Sweep distortion: This occurs when the amplitude of the output signal varies during the frequency sweep, resulting in inaccurate amplitude measurements.
- Sweep jitter: This occurs when the frequency sweep is not stable, resulting in fluctuations in the output signal frequency.
- Sweep non repeatability: This occurs when the sweep frequency generator does not produce the same output signal for each sweep, resulting in inconsistent measurements.
- Sweep leakage: This occurs when the sweep frequency generator output signal leaks into other measurement channels, resulting in cross-talk and inaccurate measurements.
It is important to calibrate and test the sweep frequency generator to ensure accurate and reliable frequency measurements.
A pulse generator is a device or circuit that generates electrical pulses or square wave signals with specific characteristics. The primary purpose of a pulse generator is to produce well-defined pulses of desired amplitude, duration, frequency, and shape.
The working of a pulse generator typically involves the following components:
- Oscillator: The pulse generator contains an oscillator circuit that generates a continuous waveform. This waveform can be a sinusoidal wave or a square wave, depending on the specific type of pulse generator.
- Timing Circuit: The timing circuit determines the duration or width of the pulses generated by the pulse generator. It typically consists of capacitors, resistors, and timing components that control the charging and discharging of the capacitors.
- Pulse Shaping Circuit: The pulse shaping circuit is responsible for shaping the waveform of the pulses generated by the pulse generator. It can include components such as diodes, transistors, and operational amplifiers to modify the pulse characteristics.
- Amplitude Control Circuit: The amplitude control circuit allows the user to adjust the amplitude or voltage level of the generated pulses. It may include variable resistors, voltage dividers, or amplification stages to achieve the desired amplitude.
The function of a pulse generator is to provide precise and controlled pulses for various applications, including:
- Timing and synchronization: Pulse generators are used in digital systems, communication systems, and instrumentation to provide precise timing and synchronization signals.
- Testing and measurement: Pulse generators are used in laboratories and testing environments to simulate and test electronic circuits, components, and systems. They can generate pulses with specific characteristics to evaluate the performance and behavior of the tested devices.
- Signal generation: Pulse generators are used to generate signals for various applications such as data transmission, pulse-width modulation (PWM), pulse position modulation (PPM), and pulse code modulation (PCM).
- Triggering and control: Pulse generators are often used as trigger sources for other devices or circuits. They can initiate specific actions or events based on the timing and characteristics of the generated pulses.
Overall, pulse generators are versatile tools in electronics and are essential for generating precise and controlled pulses for a wide range of applications, including timing, testing, measurement, and signal generation.
Pulse and square wave generators have a wide range of applications in electronics and electrical engineering. Some of the common application areas of pulse and square wave generators include:
- Timing circuits: Pulse and square wave generators are commonly used to generate clock signals and timing circuits in electronic systems.
- Digital circuits: Pulse and square wave generators are used to simulate digital signals in electronic circuits and devices.
- Communication systems: Pulse and square wave generators are used to generate modulation signals in communication systems, such as amplitude modulation (AM) and frequency modulation (FM) signals.
- Test and measurement: Pulse and square wave generators are used to test and measure the performance of electronic circuits and devices, such as signal transmission and reception.
- Medical equipment: Pulse and square wave generators are used in medical equipment, such as electrocardiography (ECG) machines and ultrasound equipment, to generate electrical signals for diagnostic and therapeutic purposes.