Digital Oscilloscopes vs Analogue Oscilloscopes
The frequency characteristics of analogue oscilloscopes are determined by vertical amplifiers and cathode oscillators. The introduction of digital processing and microprocessors to oscilloscopes in the 1980s led to the emergence of digital oscilloscopes. Analogue oscilloscopes are now referred to as analogue real-time oscilloscopes (ART) and digital oscilloscopes are referred to as digital storage oscilloscopes (DSO).
ART needs to be compatible with the bandwidth of the amplifier and cathode ray oscilloscope, with the increase in frequency, the cathode ray oscilloscope process requirements are stringent, the cost increases, and the existence of bottlenecks. DSO as long as the bandwidth compatible with the high-speed A/D converter, other modulation, the observation of three-dimensional graphic; waveform memory is not enough to deal with the waveform, and so on.
At present, the shortcomings of the DSO has been basically overcome, but not all the good performance are reflected in the same oscilloscope, that is, each DSO will have certain characteristics, there are certain deficiencies in the choice of model should pay attention to the comparison. Some DSO models have the same waveform update rate as ART, while some DSO models do not, and one DSO has the ability to display three-dimensional graphics on the fluorescent screen of ART, while most DSOs do not have this performance. Most DSOs have the same real-time bandwidth as single time bandwidth, but there are also DSOs that only guarantee real-time bandwidth.
All of the aforementioned DSOs contain A/D converters and microprocessors. In this way, the addition of plug-in cards in the pC machine can also constitute a DSO, but generally lower sampling rate, less functionality, and cheaper. There are also DSO modules using the VXI bus, as well as rack-mounted DSO plug-ins.
DSO memory is second only to the oscilloscope components in the A/D converter components, which saves the measured signal samples for subsequent D / A converter to restore the waveform, and now the storage capacity can reach more than 1M.
Ordinary DSOs have 8-bit vertical resolution, i.e. 256 samples per scan, requiring 256 points of storage, equivalent to 256 bytes. If you improve the resolution, the horizontal axis will be expanded by 10 times, it is equivalent to 20K bytes; the vertical axis is also expanded by 10 times, it is equivalent to 40K bytes. It can be seen that the DSO should be at least 2K bytes, and the medium DSO should be more than 40K bytes. If you want to record 10 times the above waveform, then at least 400K bytes or more. Therefore, the size of the storage capacity is very important.
In turn, the storage capacity also affects the scanning speed, for example, only 50K points of memory per sweep of the trace, record 100μs of data, then the sampling spacing is 2ns, the sampling rate is equivalent to 500MS / s, to the sampling rate is equal to 4 times the bandwidth calculation, real-time bandwidth is equal to 125MHz. obviously, if you need to improve the sampling rate to 1000MS / s, then the recording of 100μs of data, need to be 100K points of memory.
In order to store a complete graph, let the pixel is 1024 × 512 = 0.5M bits, four graphics, to have 2M bits of storage. In the FFT analysis also need additional storage, the new waveform components and the reference waveform or stored waveform for comparison. To facilitate waveform storage, some DSOs provide floppy disks or hard disks for data recording.
