Rohde & Schwarz has developed what is says is the industry's only digital oscilloscope that employs a real-time digital trigger. Designated the R&S RTO Series, the advanced scope significantly enhances productivity and product performance when debugging embedded systems.
The real-time digital trigger in the R&S RTO Scope Series uses a common signal path for both the trigger and acquired data. This eliminates time and amplitude offset between the trigger and signal, enabling signals to be displayed with the least possible trigger jitter and allowing precise results to be achieved when measuring complex waveforms.
Analog triggers typically have a long re-arm cycle, and while re-arming, the instrument cannot react to trigger events, which means signal properties that should act as triggers are masked. Because the R&S RTO Scope Series' digital trigger does not need to re-arm, every sample can trigger data acquisition to avoid missing events.
In addition, errors in serial interfaces are often caused by sporadic signal faults at the physical layer, so high acquisition rates are essential in order to detect them. Since R&S RTO Scope Series acquires and displays signals using hardware, blind time is minimized and errors are located quickly. Also, many embedded systems employ serial data interfaces to control external devices and simply viewing the waveform is not sufficient to fully debug the operation of these systems. The R&S RTO features an integrated trigger and decode feature that allows users to trigger on protocol-specific features and to display the captured waveform in binary, ASCII or HEX formats. The trigger and decode feature supports SPI, I2C, CAN, LIN and RS232.
DrDSP asked for more detail. I assume you mean how does a digital trigger differ from a conventional analog trigger?
Most scopes split the input signal into two paths. One goes to the ADC and the other to a trigger circuit which contains one or more analogue comparators. Calibration techniques are then used to remove amplitude and time delay differences between the two paths.
Calibration at low input frequencies is fairly easy so the trigger point marker on the screen is exactly in the right place, but it gets difficult at high frequencies. Unless the bandwidth responses of the two circuits are identical you can end up with the scope triggering on glitches that the ADC can not capture or alternatively see glitches on screen that can not be triggered on.
Digital triggering avoids all these problems as the triggering is done on the actual digital data after the ADC, this avoids any mismatches.
Digital trigger circuits are fairly simple to implement when ADC sampling rates are low (less than 500MSPS) as the comparators and other circuits can be implemented in gate arrays.
As sampling rates increase however it becomes more difficult. Toggle rates of digital components in FPGAs and custom ASICs are too slow for ADC data rates of say 5GSPS. This requires the data to be demuxed into multiple data paths (eg 16 x 8 bit paths). This then requires 16 parallel digital trigger circuits - you now have 128 digital comparators and registers (and significant timing issues) rather than a single analog comparator.
It seem that DSOs are still being compared with Analog Scopes, it is time that it really needs the technology come out not the comparison with the old one. With Digital Timescale and Quantization techniques it might be possible to capture and display more realistic picture of the waveforms.
Rohde & Schwarz are not correct in saying that they have developed the industry's only digital trigger.
Pico Technology have been using this technique on their oscilloscopes for the last 20 years. I suspect other companies have as well.
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