Patent Application
20070096951
The present invention relates generally to time domain measurement instruments, such as an oscilloscope, and more particularly to such an instrument that is able to decode and interpret an input waveform to determine a data sequence represented thereby, such as a Non-Return to Zero (NRZ) data sequence.
Oscilloscopes acquire and display a representation of a received analog waveform. These analog waveforms often are representative of a transmitted digital signal. While apparatuses exist for defining a particular protocol, and decoding the digital signal represented by the analog waveform, they rely on various aspects of the digital protocol to define the interpretation.
In accordance with the present invention, a method and apparatus are provided for determining and displaying a digital bit sequence represented by a generic analog waveform. The invention particularly removes the need for a protocol definition, or other external synchronization tools, such as a tracking PLL, for interpretation. Rather, a received analog waveform is analyzed, transitions through a threshold are determined, and a digital bit stream extracted from the analog waveform is provided.
It is therefore an object of the invention to provide a new data decoder that improves over currently available devices.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification and the drawings.
The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, combination(s) of elements and arrangement of parts that are adapted to affect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.
For a more complete understanding of the invention, reference is made to the following description and accompanying drawings, in which:
The invention will now be described, making reference to the accompanying drawings.
Referring first to
Next, at step 120, the processor also computes the number of samples per bit in the data stream. Alternatively, as will be described below, the user is able to manually enter the desired bitrate. Furthermore, the processor also determines the initial polarity of the data stream so that the algorithm can determine when a transition period is reached, in which direction the transition is taking place (i.e. from a logic “0” to a logic “1 ”, or in the other direction).
After these preliminary steps have been performed, the processor reviews or loops through the data stream (data array, as the data stream is now stored in memory in the oscilloscope) to determine the location of transition edges at step 140. These transition edges comprise portions of the data stream where the signal crosses the 50% threshold level determined in the above description. Once these transition edges have been located, it is necessary to further compute the time during which the signal remained either above or below the transition (time between adjacent transition edges). Therefore, at step 150, for each located transition edge, the number of unit intervals (value corresponding to a single data value) before the next transition edges is computed. Thus, if it is determined that the signal has transitioned to a “1” logic level, and five unit intervals pass before transitioning back to a “0” logic level, the processor determines that the data stream at the portion represents 5 consecutive bits of data that are all at a “1” logic level. These values are written into a data array for storage until all of the desired data in the waveform is decoded. It should be noted that this decoding in accordance with the invention does not require the use of a Phase Locked Loop (PLL) because the process is re-synchronized at every waveform transition edge.
After the desired portion of the waveform has been decoded, the stream of binary values is displayed to the user. There is no need to perform a protocol layer comparison or the like. A stream of “1” and “0” logical values is shown to the user without reference to any particular protocol definition. In accordance with an embodiment of the invention, if a user views a particular portion of the input waveform on the display, a corresponding portion of the binary information may be displayed. In an alternative embodiment, if a user selects one or more of these binary values, a corresponding portion of the stored input waveform may be displayed. Alternatively, a cursor or other indicator may be employed to indicate the portion of the analog waveform corresponding to the selected binary values.
Referring next to
A bitrate menu 220 is shown, which allows a user to select between allowing the oscilloscope to determine the bitrate of signal 215 (by enabling checkbox 218, thus selecting the “Find Bit Rate Automatically” mode, and whose instantaneous bitrate can be updated using control 221) and manually setting the bitrate (by enabling checkbox 219, thus selecting the “Manual Bitrate Selected” mode, whose bitrate value is displayed by indicator 222). In
After these settings have been determined, processing takes place as noted above, and the oscilloscope computes and displays the information shown in menu 225. Thus, upon selection of “Decode NRZ” button 226, the algorithm determines the number of bits in the input data stream (227) and displays the decoded binary values (228). As noted above, the binary data may be correlated with the displayed waveform, and thus, scrolling of the waveform will result in a re-calculated set of binary decoded values each time that Decode NRZ (226) is pressed. In a preferred embodiment, if the waveform contains 256 bits or less, then the NRZ decoder output displays the entire decoded waveform on the interface. If the waveform contains greater than 256 bits, then the NRZ decoder displays the first 256 bits on the interface. All of the bits, however, have been decoded, and the resultant saved binary decoded trace saves all of the decoded binary values (e.g. thousands of bits) into the designated output file.
After the binary data has been determined, the user is provided the option to store the data, such as the waveform, binary data and various oscilloscope settings, to a data file. The storage of data to a storage device is well known to one of ordinary skill in the art. By storing the data, the user is able to recall the information, placing the oscilloscope in the same state as if it had just acquired the data stream and determined the binary bit sequence.
Referring next to
As is evident in the figure, and as was noted above, more of the waveform 315 is shown on display 210. Correspondingly, more binary values 328 are shown. These binary values represent data for the portion of the waveform shown in the display.
Referring next to
While the invention has been described as receiving an NRZ signal, in an alternative embodiment of the invention a PRML, partial response, or other multi-level signal may first be acquired, and converted to an NRZ signal. This generated NRZ signal may then be treated in accordance with the invention as if it had been the initially acquired signal.
It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, because certain changes may be made in carrying out the above method and in the construction(s) set forth without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall there between.
