The Right Counter Saves Time

Design and test engineers need all the help they can get to perform accurate measurements on the continuing parade of newer, faster electronic components and products. They need counters that are easy to use, require little setup and, of course, offer the appropriate measurement functions.

The electronic components and products may be new, but the basic issue remains the same: Which counter will provide the right type of measurements? For example, if you need to measure frequency, period, ratio, pulse width, time interval, duty cycle, rise/fall time and phase, you probably want a universal counter. As its name infers, it handles most counting measurements.

Some recently introduced counters, such as the Model 53132A from Hewlett-Packard, offer a special mode to graphically show if a measurement is within limits. This function allows you to see a reading and quickly make adjustments without having to interpret the 12 digits/s resolution.

Another type of unit is the RF counter. Its popularity is a direct result of the explosion of digital cellular technology. The RF counter also performs direct automatic settling-time measurements, which are important for tracking synthesizer performance.

Another consideration for synthesizer performance is frequency pulling caused by amplitude variations. Pulling occurs when a time-division multiple access burst is powered on. The power ramp can cause a temporary shift in the synthesizer’s output frequency.

A counter with a frequency vs time display provides a direct view of the transient pulling action. You can see how far off frequency the synthesizer is pulled and how long it takes to relock.

Counters also are used to compare the RF eye diagram and the baseband eye diagram. They can help isolate problems in the RF chain. This helps eliminate any guessing about RF performance.

The time interval analyzer (TIA) is a counter also gaining prominence because it measures the instantaneous frequency as a function of time. The TIA shows window margin or histograms to help debug subtle timing problems in hard drives.

The window margin display is a fundamental tool for investigating timing in disk drives. It helps you see peak shift, noise problems and the overall timing margin at a selected error rate.

The window-margin plot function is used to extrapolate a drive’s timing margin to an appropriate error rate. You also can estimate selected portions of acquired data to investigate different noise problems.

The histogram gives insight into timing problems that differ from the window-margin function. For example, it is easier to see asymmetry in a disk drive with a histogram than the window-margin method. Asymmetry often is confused with peak shift in a window margin. The histogram also is appropriate to investigate causes of errors, including timing noise, peak shift, media noise and jitter.

The TIA provides sequential displays and clock simulations to help identify sources of jitter and offset of digital channels. It uses arming and triggering capabilities to help acquire data on signals and signal edges.

Perhaps you need a counter for applications such as chirped radar profiling, carrier frequency measurement, pulsed radar analysis, VCO measurements or frequency-agile system analysis. A microwave counter like the Model 595A/598A from EIP Microwave will provide the capabilities. The unit analyzes frequencies to 170 GHz, and has capabilities to automatically correct power readings and perform frequency and power profiling measurements with windows as narrow as 15 ns.

Choosing the counter that performs to your criteria requires investigation of the capabilities and specifications. To find the information quickly and easily, use EE‘s comparison chart which accompanies this article.

Copyright 1995 Nelson Publishing Inc.

June 1995

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