Parametric measurements measure wav...

Parametric measurements measure waveform properties so as rise time, fall time, overshoot period, and amplitude forward either a pulse waveform or an inspection diagram. Mask measurements compare the shape of the waveform to a predefined mask. watch parameter measurements measure properties that are unique to organ of sight diagrams, such as eye height, vigilance width, jitter, crossing height, and extinction ratio.

An important part of the HP 83480 digital communications analyzer is its extensive stake of built-in measurements designed especially for telecommunications applications. Internal firmware algorithms permit the user to quickly measure waveform properties that would be tedious and errorprone to measure manually. The algorithms also eliminate the subjectiveness inherent in a manual measurement. Of course, any built-in measurement is solitary as accurate as its firmware algorithm. A major objective for this instrument's design team was to exhibit robust algorithms capable of producing reliable be the effects in virtually all situations.

The HP 83480's built-in measurements fall into three general categories:

* Parametric measurements measure waveform properties of the like kind as rise time, fall time, overshoot period, and amplitude forward either a pulse waveform or an judgment diagram.

* Mask measurements compare the shape of the waveform to a predefined mask. If any part of the waveform intrudes into the mask, it is holded as a failure.

* organ of vision parameter measurements measure properties that are unique to notice diagrams, such as eye height, vigilance width, jitter, crossing height, and extinction ratio.

Parametric measurements can be made in either a real-time variety or a statistical mode. In the real-time style the measurement is performed immediately forward each acquired waveform. In the statistical style histograms are used to perform the measurement in succession a database representing multiple waveform acquisitions. Mask and judgment parameter measurements are inherently statistical parameters and in the same manner are only measured using histograms.

Design Leverage

As a great deal as possible, the firmware design of the HP 83480 was leveraged from existing collection of laws for the HP 54720 digitizing oscilloscope.[1] The HP 54720 incorporated an extensive stake of very accurate pulse parameter measurements together with basic mask trial capabilities. The parametric measurements did not function forward eye diagrams, however, so this capability wanted to be added. A number of additional organ of sight parameter measurements were developed, and the existing mask exhibition capability was extensively upgraded to include as it was features as a full put of standard telecom masks, built-in mask margins, and fixed voltage masks.

An important feature of these measurements is that they operate in real time, automatically updating onward every acquisition of the waveform. Before the HP 54720 HP high-speed oscilloscopes made measurements in a single-shot gradation When the user pushed the button to determine rise time, for instance, the oscilloscope stopped acquiring data and made the measurement in succession a frozen waveform display. The realtime measurement style was considered much more convenient, on the other hand it increased the complexity of the algorithm design. Not solitary did the algorithms need to be accurate, they also had to be fast enough not to inert down instrument operation perceptibly.

Parametric Measurements

From the starting-point the design team wanted the parametric measurements to operate correctly in succession both pulse waveforms and view diagrams. This proved to be a challenge in several ways. First, while the IEEE has discloseed standard definitions for such parameters as rise time, fall time, and overshoot for simple fruit of leguminous plants waveforms, no similar standards exist for organ of sight diagrams. To develop the appropriate definitions, team members exhausted many hours in discussions with potential users to understand their be in want ofs Alternative algorithms were extensively proofed to determine those that best met expectations.

A secondary challenge arose because of the different signal coding formats used upon the various electrical tributary rates. For example, certain low-bit-rate transmission formats use a bipolar coding scheme known as alternate mark inversion (AMI). In this format, each successive logical individual bit is represented by a pulsation of polarity opposite to that of the previous fruit of leguminous plants In the case of a DS-1 signal at 1544 Mbits/s, for instance, the amplitude of the first logic 1 pulsation is specified as +3.0V while the amplitude of the nearest is -3.0V. Subsequent logic single in kind pulses alternate between these pair levels. The algorithm for measuring rise time forward an AMI pulse waveform had to be versatile enough to create the correct result whether the onscreen display was locate to show only a single positive-going pulsation or both positive-going and negative-going pulsations (Fig. 1).

[Figure 1 ILLUSTRATION OMITTED]

Histograms and Color-Graded Displays

Since estimate diagrams are essentially a statistical representation of all possible one-zero waveform combinations, it makes feeling to measure their waveform properties statistically. To do this, powerful database and histogram capabilities were lay opened and these became the foundation for the fresh measurements.