M228 1MSPS Aperture A/D (Part 2)
It has been three long months since posting the first in this three part series on the new M228 Aperture A/D M-Module. Those three months have been filled with a lot of hard work on, among other things, improving and finalizing the EM405-8 Scripting Utilities. All the while, I haven't forgot about the M228 and would like to continue the discussion with a description of the unique aperture features of this module.
As I touched upon in the first post of this series, the aperture feature controls the M228's decisions on whether or not to store an A/D sample. The M228 performs an A/D conversion at every tick of the sample clock (up to 1 Mega Samples per Second) but it does not necessarily store every A/D conversion into the 32 Meg Sample FIFO. Of course, using the force store feature, the module can be configured to store every conversion, but if that was the only mode of operation, this article would be over when in fact, we are just getting started. The decision by the hardware of whether or not to store a particular sample is based on the current A/D value (the one which the decision is to be made on), the last stored A/D value, the settings of the aperture window(s) and the aperture mode. As shown in the figure below, using the aperture feature can greatly reduce the amount of data required to be stored, parsed, and transferred across the system bus (note: the image uses aperture mode 0 discussed below).
As I touched upon in the first post of this series, the aperture feature controls the M228's decisions on whether or not to store an A/D sample. The M228 performs an A/D conversion at every tick of the sample clock (up to 1 Mega Samples per Second) but it does not necessarily store every A/D conversion into the 32 Meg Sample FIFO. Of course, using the force store feature, the module can be configured to store every conversion, but if that was the only mode of operation, this article would be over when in fact, we are just getting started. The decision by the hardware of whether or not to store a particular sample is based on the current A/D value (the one which the decision is to be made on), the last stored A/D value, the settings of the aperture window(s) and the aperture mode. As shown in the figure below, using the aperture feature can greatly reduce the amount of data required to be stored, parsed, and transferred across the system bus (note: the image uses aperture mode 0 discussed below).
(click image to zoom in)The M228 has two aperture windows. Each aperture window has a high and a low value. The meaning of each value and how the values are used in the decision making process depends on the aperture mode. They will be discussed for each mode below. In some aperture modes only one aperture window is used, in other modes both aperture windows are used. I can't describe much else without getting into the various modes...so lets get to them. In order to keep this article a reasonable length, I will refrain from using examples for each mode and let your imagination do the job.
Aperture Mode 0 - “Store if outside selected aperture window”
Aperture Mode 0 allows the user to store data only if it changes more than a specified amount from the last stored value. For instance, if only signal changes greater than 200mV in the positive direction and 100mV in the negative direction are important, the user can specify Aperture Mode 0 and set Aperture High to 200mV and Aperture Low to 100mV. The A/D reading will be stored if the value is greater than the last stored value plus the Aperture High value or it is less than the last stored value minus the Aperture Low value. In this mode, only positive aperture values can be specified. Since the A/D value is always compared against the last stored value, this mode can be visualized as a window that floats with the signal. Each time a value is stored, the window is repositioned to this level. In this mode, aperture high and low setting of zero causes the M228 to store all.
Aperture Mode 1 - “Store once outside selected absolute window A and outside of aperture window B”
Aperture Mode 1 allows the user to start storing data once the signal level is outside of a specified absolute window, in effect setting a trigger level. For example, if the user would like to start storing data if the signal rises above 1V, Aperture High A would be set to 1V and Aperture Low A would be set to a large negative value. Operation begins with Aperture Set A. If the signal level is outside the specified absolute aperture window the logic stores the value and switches to Aperture Set B. Operation continues with Aperture Set B acting exactly like aperture mode 0 until the FIFO is reset.
Aperture Mode 2 - “Store if outside absolute window A and outside of aperture window B”
Aperture Mode 2 allows the user to only store data if the signal level is outside of a specified absolute window and the delta from the last value stored is greater than some amount. The mode is similar to Aperture Mode 1, except data is only stored if it is outside of the absolute window specified by Aperture Set A. In other words, in contrast to Aperture Mode 1, if the signal returns inside the absolute window, storage will cease until it leaves the absolute window again. Outside of the absolute window, Aperture set B is used exactly as in Aperture Mode 0 and 1.
Aperture Mode 3 - “Store once inside selected absolute window A and outside of aperture window B”
Aperture Mode 3 allows the user to start storing data once the signal level falls inside of a specified window. This mode is very similar to Aperture Mode 1, except data storage will begin if the signal falls or rises to be within a specified window.
Aperture Mode 4 - “Store if inside absolute window A and outside of aperture window B”
Aperture Mode 4 allows the user to only store data if the signal level is inside of a specified window level. This mode is very similar to Aperture Mode 2, except data storage is stored only if the signal is inside a specified window.
Aperture Mode 5 - “Store if outside both absolute window A and B”
Aperture Mode 5 allows the user to store all data that is outside of two absolute windows. For example, if data storage is not important when the signal is between -2V and -3V or between +4V and +8V, aperture set A would be set to -2V and -3V and aperture set B would be set to +8V and +4V. Data will be stored on every sample clock that the data level is not within one of the specified windows.
Aperture Mode 6 - “Store if inside either absolute window A and B”
Aperture Mode 6 allows the user to store all data that is inside of either absolute window. This mode is very similar to Aperture Mode 5, except data is stored only if it is inside either window.
Hopefully, from the above aperture mode descriptions, one can draw enough information to realize the advantages of the data extraction techniques of the M228 and imagine their use in a real world application. The M228 is the most powerful instrument in our transient data acquisition offering. You can download a brochure of our transient data acquisition solutions here.
The final part of the M228 series of articles will discuss the analog front end of the module. With a selection of programmable filters and a set of programmable attenuators and amplifiers, the types of signals that can be acquired by the M228 are numerous.
Aperture Mode 0 - “Store if outside selected aperture window”
Aperture Mode 0 allows the user to store data only if it changes more than a specified amount from the last stored value. For instance, if only signal changes greater than 200mV in the positive direction and 100mV in the negative direction are important, the user can specify Aperture Mode 0 and set Aperture High to 200mV and Aperture Low to 100mV. The A/D reading will be stored if the value is greater than the last stored value plus the Aperture High value or it is less than the last stored value minus the Aperture Low value. In this mode, only positive aperture values can be specified. Since the A/D value is always compared against the last stored value, this mode can be visualized as a window that floats with the signal. Each time a value is stored, the window is repositioned to this level. In this mode, aperture high and low setting of zero causes the M228 to store all.
Aperture Mode 1 - “Store once outside selected absolute window A and outside of aperture window B”
Aperture Mode 1 allows the user to start storing data once the signal level is outside of a specified absolute window, in effect setting a trigger level. For example, if the user would like to start storing data if the signal rises above 1V, Aperture High A would be set to 1V and Aperture Low A would be set to a large negative value. Operation begins with Aperture Set A. If the signal level is outside the specified absolute aperture window the logic stores the value and switches to Aperture Set B. Operation continues with Aperture Set B acting exactly like aperture mode 0 until the FIFO is reset.
Aperture Mode 2 - “Store if outside absolute window A and outside of aperture window B”
Aperture Mode 2 allows the user to only store data if the signal level is outside of a specified absolute window and the delta from the last value stored is greater than some amount. The mode is similar to Aperture Mode 1, except data is only stored if it is outside of the absolute window specified by Aperture Set A. In other words, in contrast to Aperture Mode 1, if the signal returns inside the absolute window, storage will cease until it leaves the absolute window again. Outside of the absolute window, Aperture set B is used exactly as in Aperture Mode 0 and 1.
Aperture Mode 3 - “Store once inside selected absolute window A and outside of aperture window B”
Aperture Mode 3 allows the user to start storing data once the signal level falls inside of a specified window. This mode is very similar to Aperture Mode 1, except data storage will begin if the signal falls or rises to be within a specified window.
Aperture Mode 4 - “Store if inside absolute window A and outside of aperture window B”
Aperture Mode 4 allows the user to only store data if the signal level is inside of a specified window level. This mode is very similar to Aperture Mode 2, except data storage is stored only if the signal is inside a specified window.
Aperture Mode 5 - “Store if outside both absolute window A and B”
Aperture Mode 5 allows the user to store all data that is outside of two absolute windows. For example, if data storage is not important when the signal is between -2V and -3V or between +4V and +8V, aperture set A would be set to -2V and -3V and aperture set B would be set to +8V and +4V. Data will be stored on every sample clock that the data level is not within one of the specified windows.
Aperture Mode 6 - “Store if inside either absolute window A and B”
Aperture Mode 6 allows the user to store all data that is inside of either absolute window. This mode is very similar to Aperture Mode 5, except data is stored only if it is inside either window.
Hopefully, from the above aperture mode descriptions, one can draw enough information to realize the advantages of the data extraction techniques of the M228 and imagine their use in a real world application. The M228 is the most powerful instrument in our transient data acquisition offering. You can download a brochure of our transient data acquisition solutions here.
The final part of the M228 series of articles will discuss the analog front end of the module. With a selection of programmable filters and a set of programmable attenuators and amplifiers, the types of signals that can be acquired by the M228 are numerous.
posted by David Clark at
2:14 PM
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