Description and function
We can think of an oscilloscope simply as a voltmeter with a graphical display.
A common voltmeter is a pointer or digital display that moves over its dial to give a measurement of the signal voltage. And the oscilloscope is different. An oscilloscope has a screen on which the signal voltage changes over time in a graphical manner, that is, the waveform.
The main differences between an oscilloscope and a voltmeter are:
1. The voltmeter can give the value of the test signal, which is usually the RMS value. But the voltmeter cannot give information about the shape of the signal. Some voltmeters can also measure the peak voltage and frequency of the signal. However, the oscilloscope can display the history of the signal with time by graph.
2. The voltmeter can usually measure only one signal, while the oscilloscope can show two or more signals at the same time.
Display system
The display device of the oscilloscope is the cathode ray tube, abbreviated as CRT, as shown in figure 1. The basis of a cathode ray tube is a system that produces electrons, called an electron gun. The electron gun emits electrons to the screen. The electron emitted by an electron gun is focused to form an electron beam that hits a point in the center of the screen. The inner surface of the screen is coated with fluorescent material so that the dots in the electron beam emit light.
Electrons go through a deflection system on their way from the gun to the screen. Applying a voltage to the deflection system allows the dot to move across the screen. The deflection system consists of a horizontal (X) deflector and a vertical (Y) deflector. This deflection is called electrostatic deflection. A network of horizontal and vertical lines made by etching or etching the inner surface of a screen is called a ruler. The scale is usually 8 in the vertical direction, 10 in the horizontal direction, and each lattice is 1cm. Some lines are further divided into small squares and special lines indicating 0% and 100%. These special lines are used in conjunction with the 10% and 90% rulers to measure the rise time. We'll talk about that later.
As noted above, when bombarded with electrons, the fluorescent material on the CRT glows. When the electron beam is removed, the fluorescent material continues to glow for a short period of time. This time is called afterglow time. The duration of the afterglow varies with the fluorescence substance. The most commonly used fluorescent substance is P31, whose afterglow time is less than one millisecond (ms). However, the afterglow time of fluorescent substance P7 is relatively long, about 300ms, which is very useful for observing slower signals. The P31 material emits green light, while the P7 material glows yellow and green.
The input signal is added to the Y-axis deflector, and the oscilloscope itself makes the electron beam scan along the X-axis. This allows the dot to trace the input signal's waveform on the screen. Such swept signal waveform is called waveform trace.
The control mechanisms affecting the screen include:
- the luminance
The brightness control is used to adjust the brightness of the waveform display. The oscilloscope used as an example in this book USES a circuit that automatically adjusts the brightness according to different scanning speeds. When the electron beam moves faster, the time it takes for the fluorescent material to be excited becomes shorter, so the brightness must be increased to see the track. Instead, the light spot on the screen becomes bright as the electron beam moves slowly, so it must be dimmed to prevent the fluorescent material from burning out. Thereby extend the lifetime of oscilloscope tube. For the text on the screen, there is a separate brightness control mechanism.
- the focus
The focus control mechanism is used to control the size of the blips on the screen in order to obtain a clear waveform track. For some oscilloscopes, such as the one used as an example in this book, the aggregation is also best controlled by the oscilloscope itself, so that it can maintain a clear waveform trajectory at different intensities and different scans. Manual control of aggregation is also provided.
-- scanning rotation
The control mechanism aligns the X-axis scan line with the horizontal ruler line. Since the earth's magnetic field varies from place to place, this will affect the scan lines shown by the oscilloscope. The sweep rotation function is used to compensate for this. The scanning rotation function is preset and usually only needs to be adjusted after the oscilloscope is moved.
-- rod lighting
The ruler brightness can be controlled separately. This is useful for screen photography or working in low light.
- Z modulation
The brightness of the scan can be changed by an electrical means through an external signal. This is useful in applications where external signals are used to produce horizontal deflection and where the x-y display is used to find frequency relationships. This signal input is usually a BNC socket on the back panel of the oscilloscope.
1. Analog oscilloscope block diagram
CRT is the foundation of all oscilloscopes. Now we know something about it. Now let's look at how the oscilloscope works as the heart of an oscilloscope.
We have seen that the oscilloscope has two vertical deflectors, two horizontal deflectors and an electron gun. The intensity of the electron beam emitted from an electron gun can be controlled electronically.
On the basis of the above technique, a complete oscilloscope can be constructed by adding the circuit described below
Vertical deflection system of oscilloscope tube includes:
- input attenuator (one per channel)
- preamplifier (one per channel)
The electronic switch used to select which input channel to use
-- deflection amplifier
The horizontal deflection system of an oscilloscope consists of a time base, a trigger circuit, and a control circuit of a horizontal deflection amplifier that USES an electronic method to light up and extinguish the trace at the appropriate time.
To make all these circuits work, an oscilloscope needs a power supply. The power source is powered by an alternating current or an internal or external battery to make the oscilloscope work. The basic performance of any oscilloscope is determined by the characteristics of its vertical deflection system, so let's examine this part in detail first.
1. 3 vertical deflection
The sensitivity
The vertical deflection system scales the input signal so that it can be displayed on the screen. An oscilloscope can show a signal whose peak voltage is from a few millivolts to dozens of volts. Therefore, the signal of different amplitude must be transformed to fit the display range of the screen, so that the waveform can be measured according to the scale scale. Therefore, it is necessary to attenuate the large signal and amplify the small signal. The sensitivity or attenuator control of an oscilloscope is set for this purpose.
Sensitivity is measured by the number of volts per cell. If you look at figure 3 below, you know that the sensitivity is set to 1V per cell. Therefore, the signal with a peak value of 6V makes the sweep deflection change within 6 grids in the vertical direction. Knowing the sensitivity Settings of the oscilloscope and the grid number of the electron beam scanning in the vertical direction, we can measure the peak peak voltage of the signal.
On most oscilloscopes, sensitivity control is changed in sequence by 1-2-5. Sensitivity. Set the reverse to 10mV/ grid, 20mV/ grid, 50mV/, 100mV/ grid and so on. Sensitivity is usually controlled by the amplitude up/down knob, while in some oscilloscopes it is done by rotating the vertical sensitivity knob.
If using these sensitivity steps does not adjust the signal so that it can be displayed accurately on the screen as required, then variable (VAR) control can be used. As we will see in chapter 6, measuring the signal rise time using a scale is a good example. The variable control can continuously adjust the sensitivity between the step values of 1-2-5. Often the exact sensitivity value is unknown when variable control is used. We only know that the sensitivity of the oscilloscope is some value between two step values in a 1-2-5 sequence. At this time, we call the Y deflection of the channel uncalibrated or "uncal". This uncalibrated state is usually indicated on the oscilloscope's front panel or screen. In more modern oscilloscopes, such as those we use as examples, color is controlled and calibrated using modern advanced techniques. Therefore, the sensitivity of the oscilloscope can vary continuously between the minimum value and the maximum value, while it is always kept in the calibration state. On an old-fashioned oscilloscope, the channel sensitivity Settings are read from the scale around the sensitivity control knob. On the new oscilloscope, the channel sensitivity Settings are clearly displayed on the screen, as shown in figure 3, or in a separate
CD displays.
In the case of sensitivity of 1v/ lattice, the signal with a peak of 6v deflects the electron beam in the vertical direction by 6 grids
coupling
The coupled control mechanism determines how the input signals pass from the BNC input terminal on the oscilloscope front panel to other parts of the channel vertical deflection system. Coupling controls can be set in two ways: DC coupling and AC coupling. The DC coupling provides a direct connection path to the signal. So the signal provides a direct connection path. Therefore, all components of the signal (AC and: DC) will affect the waveform display of the oscilloscope.
The AC coupling mode is to connect a capacitance between the BDC terminal and the attenuator. In this way, the DC component of the signal is blocked, and the low-frequency AC component of the signal is also blocked or attenuated significantly. The low frequency cutoff frequency of the oscilloscope is the signal frequency when the signal amplitude of the oscilloscope is only 71% of its straight real amplitude. The low frequency cutoff frequency of the oscilloscope depends mainly on the input coupling capacitance. The typical value of the low-frequency cutoff frequency of the oscilloscope is 10Hz, as shown in figure 4.
Figure 4 shows that coupling, input AC and DC grounding and select 50 Ω input impedance function of simplified input circuit and coupling control mechanism about another function is to input grounding function. At this point, the input signal and attenuator disconnect and connect the attenuator input to the ground level of the oscilloscope. When you select ground, you will see a straight line at 0V level on the screen. The position control mechanism can be used to adjust this reference level or scan baseline.
The input impedance
Most of the oscilloscope input impedance is 1 m Ω associated with about 25 pf. This is sufficient for most applications because
Its load effect on most circuits is minimal.
Some signals come from 50 Ω output resistance to the source. In order to measure these signals accurately and avoid distortion, it is necessary to transmit and connect these signals correctly. At this time should be used in 50 Ω characteristic impedance of the cable with load on 50 Ω termination. Some oscilloscope, such as PM3094 and PM3394A, interior is equipped with a 50 Ω load, provide a user can choose the function. To avoid misoperation, the selection of this function needs to be confirmed again. For the same reasons, 50 Ω input impedance function cannot be used and some probe.
location
The vertical position control or POS control mechanism controls the position of the scanning in the Y axis of the screen. Choose ground in the input coupling control and disconnect the input signal so that the location of the ground level can be found. A separate ground level indicator is provided on a more advanced oscilloscope, which allows the user to obtain the reference level of the waveform continuously.
Dynamic range
The dynamic range is the maximum amplitude that the oscilloscope can display the signal without distortion. Under the signal amplitude, the waveform can be observed as long as the vertical position of the oscilloscope is adjusted. For Fluke's oscilloscope, the typical value of the dynamic range is 24 channels (3 screens)
Add and reverse
Simply adding up two signals doesn't seem to make sense. However, by inverting one of the two concerned signals and adding them together, the two signals are actually subtracted. This is useful for eliminating common-mode noise (A.K.A. Alternating) or for making differential measurements.
The distortion caused by the system under test can be measured by subtracting the input signal from the output signal of a system and then scaling it properly.
Since many electronic systems are inherently inverting, adding two input signals from an oscilloscope can achieve the desired reduction.
Alternating and discontinuous
The oscilloscope CRT itself can only show one sweep at a time. However, in many oscilloscope applications, signal comparisons are often made, for example, by studying the relationship between input/output signals, or the delay of a system to a signal. This requires the oscilloscope to actually display more than one signal at the same time.
To achieve this goal, there are two ways to control the electron beam:
1. You can alternate between one sweep and another. This method is called alternate mode, or ALT mode for short.
2. Switch or chopper switch can be performed quickly between two sweeps to draw two sweeps in sections. This is known as the intermittent mode or CHOP mode. The result is two sweeps, one after the other, over the course of a scan. Chopper mode is suitable for displaying low frequency signals at low base rate because the chopper switch can switch quickly. Alternate mode is suitable for displaying high frequency signals that need to be set on a fast basis. The oscilloscopes we use as examples in this book can automatically ALT or CHOP modes at different scanning speeds to give the best display. Users can also manually select the ALT or CHOP mode to suit the specific signal requirements.
bandwidth
The most rooted technical index of oscilloscope is bandwidth. The bandwidth of the oscilloscope indicates the frequency response of the vertical system. The bandwidth of the oscilloscope is defined as the highest frequency that the oscilloscope can display on the screen at an amplitude of not less than 3dB of the real signal. The frequency of the 3dB point is the signal amplitude displayed by the oscilloscope "Vdisp" is the signal frequency of 71% of the true signal value of "Vinput" at the input end of the oscilloscope, as shown in the following formula:
DB (v) = 20log(voltage ratio)
- 3 db = 20 log (Vdisp/Vinput)
- 0.15 = log (Vdisp/Vinput)
10-0.15 = Vdisp/Vinput
Vinput Vdisp = 0.7
Figure 5 shows the typical frequency response curve of a 100MHz oscilloscope.
FIG. 5 a frequency response curve (simplified and actual) typical of a 100MHz oscilloscope for practical reasons, the bandwidth is usually imagined as a tertiary response curve that extends flat to its cut-off frequency, and then descends from that frequency at a slope of -20db /+ octave. Of course, this is a simplified consideration. In fact, the sensitivity of the amplifier begins to decrease from a lower frequency, with the cutoff frequency reaching -3db. In figure 5, both the simplified frequency response curve and the actual frequency response curve are given.
Bandwidth limiter
A bandwidth limiter can be used to reduce the frequency band of a broadband oscilloscope with its usual bandwidth above 100MHz to a typical value of 20MHz. This reduces noise levels and disturbances, which are very useful for highly sensitive measurements.
Rise time
The rise time is directly related to the bandwidth. The rise time is usually defined as the time taken by the signal from 10% to 90% of its steady-state maximum.
Rise time is the fastest transient time that an oscilloscope can theoretically display. The high frequency response curve of the oscilloscope is carefully arranged. This ensures that signals with high harmonic content, such as square waves, can be reproduced precisely on the screen. If the frequency response curve goes down too fast
We can think of an oscilloscope simply as a voltmeter with a graphical display.
A common voltmeter is a pointer or digital display that moves over its dial to give a measurement of the signal voltage. And the oscilloscope is different. An oscilloscope has a screen on which the signal voltage changes over time in a graphical manner, that is, the waveform.
The main differences between an oscilloscope and a voltmeter are:
1. The voltmeter can give the value of the test signal, which is usually the RMS value. But the voltmeter cannot give information about the shape of the signal. Some voltmeters can also measure the peak voltage and frequency of the signal. However, the oscilloscope can display the history of the signal with time by graph.
2. The voltmeter can usually measure only one signal, while the oscilloscope can show two or more signals at the same time.
Display system
The display device of the oscilloscope is the cathode ray tube, abbreviated as CRT, as shown in figure 1. The basis of a cathode ray tube is a system that produces electrons, called an electron gun. The electron gun emits electrons to the screen. The electron emitted by an electron gun is focused to form an electron beam that hits a point in the center of the screen. The inner surface of the screen is coated with fluorescent material so that the dots in the electron beam emit light.
Electrons go through a deflection system on their way from the gun to the screen. Applying a voltage to the deflection system allows the dot to move across the screen. The deflection system consists of a horizontal (X) deflector and a vertical (Y) deflector. This deflection is called electrostatic deflection. A network of horizontal and vertical lines made by etching or etching the inner surface of a screen is called a ruler. The scale is usually 8 in the vertical direction, 10 in the horizontal direction, and each lattice is 1cm. Some lines are further divided into small squares and special lines indicating 0% and 100%. These special lines are used in conjunction with the 10% and 90% rulers to measure the rise time. We'll talk about that later.
As noted above, when bombarded with electrons, the fluorescent material on the CRT glows. When the electron beam is removed, the fluorescent material continues to glow for a short period of time. This time is called afterglow time. The duration of the afterglow varies with the fluorescence substance. The most commonly used fluorescent substance is P31, whose afterglow time is less than one millisecond (ms). However, the afterglow time of fluorescent substance P7 is relatively long, about 300ms, which is very useful for observing slower signals. The P31 material emits green light, while the P7 material glows yellow and green.
The input signal is added to the Y-axis deflector, and the oscilloscope itself makes the electron beam scan along the X-axis. This allows the dot to trace the input signal's waveform on the screen. Such swept signal waveform is called waveform trace.
The control mechanisms affecting the screen include:
- the luminance
The brightness control is used to adjust the brightness of the waveform display. The oscilloscope used as an example in this book USES a circuit that automatically adjusts the brightness according to different scanning speeds. When the electron beam moves faster, the time it takes for the fluorescent material to be excited becomes shorter, so the brightness must be increased to see the track. Instead, the light spot on the screen becomes bright as the electron beam moves slowly, so it must be dimmed to prevent the fluorescent material from burning out. Thereby extend the lifetime of oscilloscope tube. For the text on the screen, there is a separate brightness control mechanism.
- the focus
The focus control mechanism is used to control the size of the blips on the screen in order to obtain a clear waveform track. For some oscilloscopes, such as the one used as an example in this book, the aggregation is also best controlled by the oscilloscope itself, so that it can maintain a clear waveform trajectory at different intensities and different scans. Manual control of aggregation is also provided.
-- scanning rotation
The control mechanism aligns the X-axis scan line with the horizontal ruler line. Since the earth's magnetic field varies from place to place, this will affect the scan lines shown by the oscilloscope. The sweep rotation function is used to compensate for this. The scanning rotation function is preset and usually only needs to be adjusted after the oscilloscope is moved.
-- rod lighting
The ruler brightness can be controlled separately. This is useful for screen photography or working in low light.
- Z modulation
The brightness of the scan can be changed by an electrical means through an external signal. This is useful in applications where external signals are used to produce horizontal deflection and where the x-y display is used to find frequency relationships. This signal input is usually a BNC socket on the back panel of the oscilloscope.
1. Analog oscilloscope block diagram
CRT is the foundation of all oscilloscopes. Now we know something about it. Now let's look at how the oscilloscope works as the heart of an oscilloscope.
We have seen that the oscilloscope has two vertical deflectors, two horizontal deflectors and an electron gun. The intensity of the electron beam emitted from an electron gun can be controlled electronically.
On the basis of the above technique, a complete oscilloscope can be constructed by adding the circuit described below
Vertical deflection system of oscilloscope tube includes:
- input attenuator (one per channel)
- preamplifier (one per channel)
The electronic switch used to select which input channel to use
-- deflection amplifier
The horizontal deflection system of an oscilloscope consists of a time base, a trigger circuit, and a control circuit of a horizontal deflection amplifier that USES an electronic method to light up and extinguish the trace at the appropriate time.
To make all these circuits work, an oscilloscope needs a power supply. The power source is powered by an alternating current or an internal or external battery to make the oscilloscope work. The basic performance of any oscilloscope is determined by the characteristics of its vertical deflection system, so let's examine this part in detail first.
1. 3 vertical deflection
The sensitivity
The vertical deflection system scales the input signal so that it can be displayed on the screen. An oscilloscope can show a signal whose peak voltage is from a few millivolts to dozens of volts. Therefore, the signal of different amplitude must be transformed to fit the display range of the screen, so that the waveform can be measured according to the scale scale. Therefore, it is necessary to attenuate the large signal and amplify the small signal. The sensitivity or attenuator control of an oscilloscope is set for this purpose.
Sensitivity is measured by the number of volts per cell. If you look at figure 3 below, you know that the sensitivity is set to 1V per cell. Therefore, the signal with a peak value of 6V makes the sweep deflection change within 6 grids in the vertical direction. Knowing the sensitivity Settings of the oscilloscope and the grid number of the electron beam scanning in the vertical direction, we can measure the peak peak voltage of the signal.
On most oscilloscopes, sensitivity control is changed in sequence by 1-2-5. Sensitivity. Set the reverse to 10mV/ grid, 20mV/ grid, 50mV/, 100mV/ grid and so on. Sensitivity is usually controlled by the amplitude up/down knob, while in some oscilloscopes it is done by rotating the vertical sensitivity knob.
If using these sensitivity steps does not adjust the signal so that it can be displayed accurately on the screen as required, then variable (VAR) control can be used. As we will see in chapter 6, measuring the signal rise time using a scale is a good example. The variable control can continuously adjust the sensitivity between the step values of 1-2-5. Often the exact sensitivity value is unknown when variable control is used. We only know that the sensitivity of the oscilloscope is some value between two step values in a 1-2-5 sequence. At this time, we call the Y deflection of the channel uncalibrated or "uncal". This uncalibrated state is usually indicated on the oscilloscope's front panel or screen. In more modern oscilloscopes, such as those we use as examples, color is controlled and calibrated using modern advanced techniques. Therefore, the sensitivity of the oscilloscope can vary continuously between the minimum value and the maximum value, while it is always kept in the calibration state. On an old-fashioned oscilloscope, the channel sensitivity Settings are read from the scale around the sensitivity control knob. On the new oscilloscope, the channel sensitivity Settings are clearly displayed on the screen, as shown in figure 3, or in a separate
CD displays.
In the case of sensitivity of 1v/ lattice, the signal with a peak of 6v deflects the electron beam in the vertical direction by 6 grids
coupling
The coupled control mechanism determines how the input signals pass from the BNC input terminal on the oscilloscope front panel to other parts of the channel vertical deflection system. Coupling controls can be set in two ways: DC coupling and AC coupling. The DC coupling provides a direct connection path to the signal. So the signal provides a direct connection path. Therefore, all components of the signal (AC and: DC) will affect the waveform display of the oscilloscope.
The AC coupling mode is to connect a capacitance between the BDC terminal and the attenuator. In this way, the DC component of the signal is blocked, and the low-frequency AC component of the signal is also blocked or attenuated significantly. The low frequency cutoff frequency of the oscilloscope is the signal frequency when the signal amplitude of the oscilloscope is only 71% of its straight real amplitude. The low frequency cutoff frequency of the oscilloscope depends mainly on the input coupling capacitance. The typical value of the low-frequency cutoff frequency of the oscilloscope is 10Hz, as shown in figure 4.
Figure 4 shows that coupling, input AC and DC grounding and select 50 Ω input impedance function of simplified input circuit and coupling control mechanism about another function is to input grounding function. At this point, the input signal and attenuator disconnect and connect the attenuator input to the ground level of the oscilloscope. When you select ground, you will see a straight line at 0V level on the screen. The position control mechanism can be used to adjust this reference level or scan baseline.
The input impedance
Most of the oscilloscope input impedance is 1 m Ω associated with about 25 pf. This is sufficient for most applications because
Its load effect on most circuits is minimal.
Some signals come from 50 Ω output resistance to the source. In order to measure these signals accurately and avoid distortion, it is necessary to transmit and connect these signals correctly. At this time should be used in 50 Ω characteristic impedance of the cable with load on 50 Ω termination. Some oscilloscope, such as PM3094 and PM3394A, interior is equipped with a 50 Ω load, provide a user can choose the function. To avoid misoperation, the selection of this function needs to be confirmed again. For the same reasons, 50 Ω input impedance function cannot be used and some probe.
location
The vertical position control or POS control mechanism controls the position of the scanning in the Y axis of the screen. Choose ground in the input coupling control and disconnect the input signal so that the location of the ground level can be found. A separate ground level indicator is provided on a more advanced oscilloscope, which allows the user to obtain the reference level of the waveform continuously.
Dynamic range
The dynamic range is the maximum amplitude that the oscilloscope can display the signal without distortion. Under the signal amplitude, the waveform can be observed as long as the vertical position of the oscilloscope is adjusted. For Fluke's oscilloscope, the typical value of the dynamic range is 24 channels (3 screens)
Add and reverse
Simply adding up two signals doesn't seem to make sense. However, by inverting one of the two concerned signals and adding them together, the two signals are actually subtracted. This is useful for eliminating common-mode noise (A.K.A. Alternating) or for making differential measurements.
The distortion caused by the system under test can be measured by subtracting the input signal from the output signal of a system and then scaling it properly.
Since many electronic systems are inherently inverting, adding two input signals from an oscilloscope can achieve the desired reduction.
Alternating and discontinuous
The oscilloscope CRT itself can only show one sweep at a time. However, in many oscilloscope applications, signal comparisons are often made, for example, by studying the relationship between input/output signals, or the delay of a system to a signal. This requires the oscilloscope to actually display more than one signal at the same time.
To achieve this goal, there are two ways to control the electron beam:
1. You can alternate between one sweep and another. This method is called alternate mode, or ALT mode for short.
2. Switch or chopper switch can be performed quickly between two sweeps to draw two sweeps in sections. This is known as the intermittent mode or CHOP mode. The result is two sweeps, one after the other, over the course of a scan. Chopper mode is suitable for displaying low frequency signals at low base rate because the chopper switch can switch quickly. Alternate mode is suitable for displaying high frequency signals that need to be set on a fast basis. The oscilloscopes we use as examples in this book can automatically ALT or CHOP modes at different scanning speeds to give the best display. Users can also manually select the ALT or CHOP mode to suit the specific signal requirements.
bandwidth
The most rooted technical index of oscilloscope is bandwidth. The bandwidth of the oscilloscope indicates the frequency response of the vertical system. The bandwidth of the oscilloscope is defined as the highest frequency that the oscilloscope can display on the screen at an amplitude of not less than 3dB of the real signal. The frequency of the 3dB point is the signal amplitude displayed by the oscilloscope "Vdisp" is the signal frequency of 71% of the true signal value of "Vinput" at the input end of the oscilloscope, as shown in the following formula:
DB (v) = 20log(voltage ratio)
- 3 db = 20 log (Vdisp/Vinput)
- 0.15 = log (Vdisp/Vinput)
10-0.15 = Vdisp/Vinput
Vinput Vdisp = 0.7
Figure 5 shows the typical frequency response curve of a 100MHz oscilloscope.
FIG. 5 a frequency response curve (simplified and actual) typical of a 100MHz oscilloscope for practical reasons, the bandwidth is usually imagined as a tertiary response curve that extends flat to its cut-off frequency, and then descends from that frequency at a slope of -20db /+ octave. Of course, this is a simplified consideration. In fact, the sensitivity of the amplifier begins to decrease from a lower frequency, with the cutoff frequency reaching -3db. In figure 5, both the simplified frequency response curve and the actual frequency response curve are given.
Bandwidth limiter
A bandwidth limiter can be used to reduce the frequency band of a broadband oscilloscope with its usual bandwidth above 100MHz to a typical value of 20MHz. This reduces noise levels and disturbances, which are very useful for highly sensitive measurements.
Rise time
The rise time is directly related to the bandwidth. The rise time is usually defined as the time taken by the signal from 10% to 90% of its steady-state maximum.
Rise time is the fastest transient time that an oscilloscope can theoretically display. The high frequency response curve of the oscilloscope is carefully arranged. This ensures that signals with high harmonic content, such as square waves, can be reproduced precisely on the screen. If the frequency response curve goes down too fast