As we mentioned some weeks ago, with the U1084A 8-bit digitizer you can switch between 2 different firmware options. One of the firmware available is called “Simultaneous Acquisition and Readout (SAR) and Zero Suppress mode, aka Threshold Gating. Today Jean-Luc Lehmann product manager tells you more about this specific functionnality.Jean-Luc, can you tell us what does the “zero suppress mode” on the U1084A? Which types of applications are targeted by this functionality?
Also known as threshold gating mode, this function allows data below a custom configured threshold to be excluded from the acquisition. Only the relevant portions of the signal is acquired, thus optimizing the use of the data memory. Up to 128 different threshold values can be configured, each with specific window size. The picture below shows a typical signal with decreasing noise floor and pulses which are the relevant part of the signal. Here 3 threshold values have been set to cover the varying noise level, only the pulses above the stair like levels will be acquired.
All applications where part of the signal is irrelevant, and is eventually discarded before processing the data, will benefit from this function. Benefit will increase proportionally with the ratio of irrelevant/relevant signal. In the example above, less than a hundred samples need to be acquired and transferred to have full definition of the 3 relevant pulses, versus more than 100 times more samples (14000) if the whole signal was acquired. More relevant data can then be stored in memory as it is left available by the zero suppress mode, allowing for larger time window to be observed.
So if we understand well, the idea is that with this mode, users can only record the thresholds there are interested in and therefore the data that they have no interest in is left out? What is the advantage of doing that? Is there an influence in the data transfer throughput? What are the advantages of using this functionality?
Using this technique will greatly reduce the amount of data storage, as only the relevant data is acquired. All un-needed data in-between is readily discarded. This will benefit the data throughput, and also later data computing by the host PC as signal does not need to be searched to extract the signal of interest.
All necessary information, such as the exact time at which the acquired segment occurred is saved into memory and read back with the date to allow easy reconstruction of the whole signal in the time domain.
To ensure enough point are available, it is possible to configure a pre-gate as well as a post-gate number of point. This guarantee a given number of samples is acquired before the first point which satisfies the threshold condition and respectively after the last point satisfying the threshold condition. This is show in the graph below:
Note that setting the threshold to the minimum value will cause the digitizer to save all of the acquired data, and conversely setting the value to maximum will cause no data to be saved. In this way a ‘pre-defined time gate’ type acquisition may be achieved. This is another way to ensure only relevant data is acquired and then transferred in a timely fashion to the host PC.
Where would you lead users that would like to know more about this functionality and how to use it?
I recommend reading the manual available here, save the CHM help file on your computer and then launch it, search for “zero suppress” and select the “SFP Control Panel” entry. You will find detailed description on the above as well as on other specific settings available.
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