Comparison of digital oscilloscopes and analog oscilloscopes
The frequency characteristics of an analog oscilloscope are determined by the vertical amplifier and cathode oscilloscope tube. In the 1980s, digital processing and microprocessors were introduced into oscilloscopes, and digital oscilloscopes appeared. Nowadays, analog oscilloscopes are called analog real-time oscilloscopes (ART), and digital oscilloscopes are called digital storage oscilloscopes (DSO).
ART requires amplifiers and cathode ray oscilloscope tubes that are compatible with the bandwidth. As the frequency increases, the process requirements for cathode ray oscilloscope tubes are strict, the cost increases, and bottlenecks exist. DSO only needs a high-speed A/D converter that is suitable for the bandwidth. For other modulations, three-dimensional graphics cannot be observed; the waveform storage capacity is not enough, and the waveform cannot be processed, etc.
At present, the shortcomings of DSO have been basically overcome, but not all good performance is reflected in the same oscilloscope. That is, each DSO will have certain characteristics and some shortcomings. You should pay attention to comparison when choosing a model. Some models of DSO have the same waveform update rate as ART, but some models of DSO do not. One type of DSO has the 3D graphics display capability of ART, but most DSOs do not have this capability. The real-time bandwidth of most DSOs is the same as the single-shot bandwidth, but there are also DSOs that only guarantee real-time bandwidth.
The aforementioned DSOs all contain A/D converters and microprocessors. In this way, adding a plug-in card to a PC can also constitute a DSO, but generally the sampling rate is lower, the functions are fewer, and the price is cheap. There are also DSO modules using VXI bus and rack-mounted DSO plug-ins.
The DSO's memory is the second most important component of the oscilloscope after the A/D converter. It stores samples of the measured signal for subsequent D/A converters to restore the waveform. The current storage capacity can reach more than 1M.
Ordinary DSO has 8-bit vertical resolution, that is, there are 256 samples per scan, requiring 256 points of storage, equivalent to 256 bytes. If the resolution is increased and the horizontal axis is expanded 10 times, it is equivalent to 20K bytes; the vertical axis is also expanded 10 times, which is equivalent to 40K bytes. It can be seen that DSO should be at least 2K bytes, and a medium DSO should be more than 40K bytes. If you want to record 10 times the above waveform, it will require at least 400K bytes. Therefore, storage capacity is important.
In turn, the storage capacity also affects the scanning speed. For example, if a memory with only 50K points per scan records 100μs data, the sampling interval is 2ns. At this time, the sampling rate is equivalent to 500MS/s. Calculated based on the sampling rate equal to 4 times the bandwidth, real-time The bandwidth is equal to 125MHz. Obviously, if the sampling rate needs to be increased to 1000MS/s, recording 100μs of data requires 100K points of memory.
In order to store a complete graph, assuming that the pixel size is 1024×512=0.5M bits, four graphs require 2M bits of storage. Additional storage is also required in FFT analysis to compare the components of the new waveform with the reference Waveforms or stored waveforms for comparison. To facilitate waveform storage, some DSOs also provide floppy disks or hard disks for data recording.
