1. Calculation of storage time of digital oscilloscope
Do you want to know what you observe with an oscilloscope? What is the typical performance of the signal you want to capture and observe? Does your signal have complex characteristics? Is your signal a repetitive signal or a single signal? What is the bandwidth of the signal transition process or the rise time you want to measure? What signal characteristics do you intend to use to trigger short pulses, pulse widths, narrow pulses, etc.? How many signals do you plan to display at the same time? Analog or digital?
See the previous "Scope Development". In short, the traditional view is that analog oscilloscopes have familiar panel controls and are inexpensive, so they always feel that analog oscilloscopes are "easy to use." However, with the speed of A / D converters increasing year by year and decreasing prices, as well as the increasing measurement capabilities and virtually unlimited functions of digital oscilloscopes, digital oscilloscopes have taken the lead. What about bandwidth?
The bandwidth is generally defined as the frequency when the amplitude of the sinusoidal input signal is attenuated to -3dB, which is 70.7%. The bandwidth determines the basic measurement capability of the oscilloscope on the signal. As the frequency of the signal increases, the oscilloscope's ability to accurately display the signal will decrease. If there is not enough bandwidth, the oscilloscope will not be able to distinguish high-frequency changes. The amplitude will appear distorted, the edges will disappear, and detailed data will be lost. If there is not enough bandwidth, all the characteristics about the signal, ringing and ringing are meaningless.
A rule of thumb to determine the effective bandwidth of the oscilloscope you need is the "5 times criterion"; that is, multiply the highest frequency component of the signal you want to measure by 5. This will allow you to achieve an accuracy higher than 2% in the measurement.
In some applications, you do not know the bandwidth of the signal you are interested in, but you know its fastest rise time. The frequency response of most word oscilloscopes uses the following formula to calculate the associated bandwidth and the rise time of the instrument: bandwidth = 0.35 ÷ The fastest rise time of the signal.
There are two types of bandwidth: repetitive (or equivalent time) bandwidth and real-time (or single) bandwidth. The repetitive bandwidth only applies to repetitive signals, showing samples from multiple signal acquisitions. The real-time bandwidth is the highest frequency that can be captured in a single sampling of the oscilloscope, and the requirements are quite demanding when the captured events do not occur frequently. The real-time bandwidth is related to the sampling rate.
Because wider bandwidth often means higher prices, you should evaluate the frequency components of the signal that you usually observe against your budget. What is the sampling rate?
Defined as the number of samples per second (Sa / s), which refers to the frequency at which the digital oscilloscope samples the signal. The faster the oscilloscope's sampling rate, the higher the resolution and clarity of the displayed waveform, and the lower the probability of losing important information and events.
If you need to observe slow-changing signals over a long period of time, the minimum sampling rate becomes more important. In order to maintain a fixed number of waveforms in the displayed waveform record, the horizontal control button needs to be adjusted, and the displayed sampling rate will also change with the adjustment of the horizontal adjustment button.
How to calculate the sampling rate? The calculation method depends on the type of waveform being measured and the signal reconstruction method used by the oscilloscope.
In order to accurately reproduce the signal and avoid confusion, Nyquist's theorem states that the sampling rate of the signal must not be less than twice its highest frequency component. However, the premise of this theorem is based on infinitely long and continuous signals. Since no oscilloscope can provide an infinite length of record length, and, by definition, low-frequency interference is discontinuous, it is usually not sufficient to use a sampling rate that is twice the highest frequency component.
In fact, the accurate reproduction of the signal depends on its sampling rate and the interpolation method adopted by the signal sampling point gap. Some oscilloscopes provide operators with the following options: sinusoidal interpolation for measuring sinusoidal signals, and linear interpolation for measuring rectangular waves, pulses, and other signal types.
There is a rule of thumb that is useful when comparing sampling rate and signal bandwidth: If the oscilloscope you are looking at has interpolation (through filtering to regenerate between sampling points), then the ratio of (sampling rate / signal bandwidth) should be at least 4: 1. When there is no sinusoidal interpolation, a ratio of 10: 1 should be adopted. How fast is the screen refresh rate?
All oscilloscopes will flash. In other words, the oscilloscope captures the signal a certain number of times per second, and no more measurements will be taken between these measurement points. This is the waveform capture rate, also known as the screen refresh rate, expressed as the number of waveforms per second (wfms / s). Sampling rate refers to the frequency that the oscilloscope samples the input signal in a waveform or period; waveform capture rate refers to the speed at which the oscilloscope acquires the waveform. The waveform capture rate depends on the type and performance level of the oscilloscope and has a wide range of changes. Oscilloscopes with a high waveform capture rate will provide more important signal characteristics and greatly increase the probability that the oscilloscope will quickly capture transient anomalies such as jitter, runt pulses, low frequency interference, and instantaneous errors.
A digital storage oscilloscope (DSO) uses a serial processing structure to capture 10 to 5000 waveforms per second. DPO digital fluorescent oscilloscope adopts parallel processing structure, which can provide a higher waveform capture rate, some up to millions of waveforms per second, greatly improving the possibility of capturing intermittent and difficult events, and allowing you to find faster Problems with the signal. What is the storage depth?
Storage depth is a measure of how many sampling points the oscilloscope can store. If you need to continuously capture a burst, you need the oscilloscope to have enough memory to capture the entire event. Dividing the length of time to be captured by the sampling speed required to accurately reproduce the signal can calculate the required storage depth, also known as the record length.
Capturing the effective trigger of the signal at the correct location can usually reduce the amount of storage that the oscilloscope actually needs.
The storage depth is closely related to the sampling speed. The storage depth you need depends on the total time span to be measured and the required time resolution.
Modern oscilloscopes allow users to select the record length in order to optimize details in some operations. Analyzing a very stable sinusoidal signal requires only a record length of 500 points; but if you want to parse a complex digital data stream, you need a record length of one million points or more. What kind of trigger is required?
The trigger of the oscilloscope can make the signal scan horizontally at the correct position and determine whether the signal characteristics are clear. Trigger control buttons can stabilize repeated waveforms and capture single waveforms.
Most general-purpose oscilloscope users only use edge triggering. You may find it useful to have other triggering capabilities in certain applications. Especially for troubleshooting of newly designed products. The advanced triggering method can separate the events of interest, so as to make the most effective use of sampling speed and storage depth.
There are many oscilloscopes today with advanced triggering capabilities: you can define pulses defined by amplitude (such as short pulses), pulses defined by time (pulse width, narrow pulse, slew rate, settling / hold time) and by logic state or Graphically described pulse (logic trigger) triggers. The combination of extended and conventional trigger functions also helps display video and other signals that are difficult to capture. Such advanced triggering capabilities provide a great degree of flexibility when setting up the test process, and can greatly simplify the work. How many channels are there?
The number of channels you need depends on your application. For the usual economical fault finding application, what is needed is a dual-channel oscilloscope. However, if it is required to observe the correlation of several analog signals, a 4-channel oscilloscope will be required. Many engineers working on systems with both analog and digital signals also consider using 4-channel oscilloscopes. There is also a newer option, the so-called mixed-signal oscilloscope, which combines the logic analyzer's channel counting and triggering capabilities with the oscilloscope's higher resolution into a single instrument with a time-dependent display. 3. Slow-scan oscilloscope (also known as long afterglow oscilloscope) Long afterglow screen display and slow-scan function are available for the measurement and observation of the slow change of the general bottom-frequency electrical parameters Use of XY recorder
Take the common oscilloscope TDS220 (memory depth 2.5k) as an example, such as measuring a 300kHz square wave
The time axis is set to 25us / div. At this time, the sampling point interval is 0.1us, the total recording time is 250us, and the waveform of one cycle is composed of about 34 points.
The time axis is set to 50us / div, at this time the sampling point interval is 0.2us, the total recording time is 500us, and the waveform of one cycle is composed of about 17 points
The time axis is set to 100us / div, at this time the sampling point interval is 0.4us, the total recording time is 1ms, and the waveform of one cycle is composed of about 8 points
Do you want to know what you observe with an oscilloscope? What is the typical performance of the signal you want to capture and observe? Does your signal have complex characteristics? Is your signal a repetitive signal or a single signal? What is the bandwidth of the signal transition process or the rise time you want to measure? What signal characteristics do you intend to use to trigger short pulses, pulse widths, narrow pulses, etc.? How many signals do you plan to display at the same time? Analog or digital?
See the previous "Scope Development". In short, the traditional view is that analog oscilloscopes have familiar panel controls and are inexpensive, so they always feel that analog oscilloscopes are "easy to use." However, with the speed of A / D converters increasing year by year and decreasing prices, as well as the increasing measurement capabilities and virtually unlimited functions of digital oscilloscopes, digital oscilloscopes have taken the lead. What about bandwidth?
The bandwidth is generally defined as the frequency when the amplitude of the sinusoidal input signal is attenuated to -3dB, which is 70.7%. The bandwidth determines the basic measurement capability of the oscilloscope on the signal. As the frequency of the signal increases, the oscilloscope's ability to accurately display the signal will decrease. If there is not enough bandwidth, the oscilloscope will not be able to distinguish high-frequency changes. The amplitude will appear distorted, the edges will disappear, and detailed data will be lost. If there is not enough bandwidth, all the characteristics about the signal, ringing and ringing are meaningless.
A rule of thumb to determine the effective bandwidth of the oscilloscope you need is the "5 times criterion"; that is, multiply the highest frequency component of the signal you want to measure by 5. This will allow you to achieve an accuracy higher than 2% in the measurement.
In some applications, you do not know the bandwidth of the signal you are interested in, but you know its fastest rise time. The frequency response of most word oscilloscopes uses the following formula to calculate the associated bandwidth and the rise time of the instrument: bandwidth = 0.35 ÷ The fastest rise time of the signal.
There are two types of bandwidth: repetitive (or equivalent time) bandwidth and real-time (or single) bandwidth. The repetitive bandwidth only applies to repetitive signals, showing samples from multiple signal acquisitions. The real-time bandwidth is the highest frequency that can be captured in a single sampling of the oscilloscope, and the requirements are quite demanding when the captured events do not occur frequently. The real-time bandwidth is related to the sampling rate.
Because wider bandwidth often means higher prices, you should evaluate the frequency components of the signal that you usually observe against your budget. What is the sampling rate?
Defined as the number of samples per second (Sa / s), which refers to the frequency at which the digital oscilloscope samples the signal. The faster the oscilloscope's sampling rate, the higher the resolution and clarity of the displayed waveform, and the lower the probability of losing important information and events.
If you need to observe slow-changing signals over a long period of time, the minimum sampling rate becomes more important. In order to maintain a fixed number of waveforms in the displayed waveform record, the horizontal control button needs to be adjusted, and the displayed sampling rate will also change with the adjustment of the horizontal adjustment button.
How to calculate the sampling rate? The calculation method depends on the type of waveform being measured and the signal reconstruction method used by the oscilloscope.
In order to accurately reproduce the signal and avoid confusion, Nyquist's theorem states that the sampling rate of the signal must not be less than twice its highest frequency component. However, the premise of this theorem is based on infinitely long and continuous signals. Since no oscilloscope can provide an infinite length of record length, and, by definition, low-frequency interference is discontinuous, it is usually not sufficient to use a sampling rate that is twice the highest frequency component.
In fact, the accurate reproduction of the signal depends on its sampling rate and the interpolation method adopted by the signal sampling point gap. Some oscilloscopes provide operators with the following options: sinusoidal interpolation for measuring sinusoidal signals, and linear interpolation for measuring rectangular waves, pulses, and other signal types.
There is a rule of thumb that is useful when comparing sampling rate and signal bandwidth: If the oscilloscope you are looking at has interpolation (through filtering to regenerate between sampling points), then the ratio of (sampling rate / signal bandwidth) should be at least 4: 1. When there is no sinusoidal interpolation, a ratio of 10: 1 should be adopted. How fast is the screen refresh rate?
All oscilloscopes will flash. In other words, the oscilloscope captures the signal a certain number of times per second, and no more measurements will be taken between these measurement points. This is the waveform capture rate, also known as the screen refresh rate, expressed as the number of waveforms per second (wfms / s). Sampling rate refers to the frequency that the oscilloscope samples the input signal in a waveform or period; waveform capture rate refers to the speed at which the oscilloscope acquires the waveform. The waveform capture rate depends on the type and performance level of the oscilloscope and has a wide range of changes. Oscilloscopes with a high waveform capture rate will provide more important signal characteristics and greatly increase the probability that the oscilloscope will quickly capture transient anomalies such as jitter, runt pulses, low frequency interference, and instantaneous errors.
A digital storage oscilloscope (DSO) uses a serial processing structure to capture 10 to 5000 waveforms per second. DPO digital fluorescent oscilloscope adopts parallel processing structure, which can provide a higher waveform capture rate, some up to millions of waveforms per second, greatly improving the possibility of capturing intermittent and difficult events, and allowing you to find faster Problems with the signal. What is the storage depth?
Storage depth is a measure of how many sampling points the oscilloscope can store. If you need to continuously capture a burst, you need the oscilloscope to have enough memory to capture the entire event. Dividing the length of time to be captured by the sampling speed required to accurately reproduce the signal can calculate the required storage depth, also known as the record length.
Capturing the effective trigger of the signal at the correct location can usually reduce the amount of storage that the oscilloscope actually needs.
The storage depth is closely related to the sampling speed. The storage depth you need depends on the total time span to be measured and the required time resolution.
Modern oscilloscopes allow users to select the record length in order to optimize details in some operations. Analyzing a very stable sinusoidal signal requires only a record length of 500 points; but if you want to parse a complex digital data stream, you need a record length of one million points or more. What kind of trigger is required?
The trigger of the oscilloscope can make the signal scan horizontally at the correct position and determine whether the signal characteristics are clear. Trigger control buttons can stabilize repeated waveforms and capture single waveforms.
Most general-purpose oscilloscope users only use edge triggering. You may find it useful to have other triggering capabilities in certain applications. Especially for troubleshooting of newly designed products. The advanced triggering method can separate the events of interest, so as to make the most effective use of sampling speed and storage depth.
There are many oscilloscopes today with advanced triggering capabilities: you can define pulses defined by amplitude (such as short pulses), pulses defined by time (pulse width, narrow pulse, slew rate, settling / hold time) and by logic state or Graphically described pulse (logic trigger) triggers. The combination of extended and conventional trigger functions also helps display video and other signals that are difficult to capture. Such advanced triggering capabilities provide a great degree of flexibility when setting up the test process, and can greatly simplify the work. How many channels are there?
The number of channels you need depends on your application. For the usual economical fault finding application, what is needed is a dual-channel oscilloscope. However, if it is required to observe the correlation of several analog signals, a 4-channel oscilloscope will be required. Many engineers working on systems with both analog and digital signals also consider using 4-channel oscilloscopes. There is also a newer option, the so-called mixed-signal oscilloscope, which combines the logic analyzer's channel counting and triggering capabilities with the oscilloscope's higher resolution into a single instrument with a time-dependent display. 3. Slow-scan oscilloscope (also known as long afterglow oscilloscope) Long afterglow screen display and slow-scan function are available for the measurement and observation of the slow change of the general bottom-frequency electrical parameters Use of XY recorder
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