Wireless Systems Design

RF Power Analyzer Boosts Yield

When It Comes To Production Testing For Handsets, Traditional Equipment May Be Overkill.

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The production of RF devices is littered with time-consuming tests, especially in the calibration stage. Generally, board-level test takes up more than 50% of the testing process. Aside from being time consuming, this step is very expensive. The Model 2800 RF Power Analyzer from Keithley Instruments, Inc. promises to put an end to these problems. It claims to provide RF power measurements at the speed needed in production and with superior measurement quality. As a result, it reduces test time, cuts costs, and gives manufacturers more confidence in measurement results. At the same time, it reduces false failures.

The compact, production-oriented Model 2800 is designed to only make RF measurements that are vital to the manufacturing of mobile phones (see figure). Typically, this late-stage testing is done on general-purpose, display-based spectrum analyzers and communication test sets. Yet those devices are sometimes best suited to research and development. In production testing, they can be too slow, large, and expensive. Because it's designed specifically for this process, the Model 2800 claims to be faster, easier to use, and lower in cost.

The Model 2800 RF Power Analyzer was specifically engineered for the production testing of wireless phones, RFIC power amplifiers, and related RF devices. It is currently prepared to test devices designed to the following standards: AMPS, cdmaOne, TDMA, GSM, GPRS, EDGE, PDC, cdma2000 1X, cdma2000 3X, and W-CDMA.

The industry standards for wireless-phone transmission mandate the measurement of power in certain specified bandwidths. For example, a cellular-phone power-calibration test routine could require many power measurements per frequency band. This test would have to be performed on every phone leaving the production line. Multi-mode and multi-frequency-band phones have specific needs as well. They demand power measurements for each operating mode and frequency band.

Aside from measuring power in the defined primary transmission channels, the Model 2800 can measure spurious or interfering power at specific frequency offsets. These offsets may include the upper and lower alternate channels, as well as the upper and lower channels that are adjacent to the primary channel.

With these adjacent-channel power measurements, test engineers can determine adjacent-channel power ratios (ACPRs). These ratios are needed to make sure that wireless devices and components don't exceed the limits for spurious emissions/interference as defined by industry standards. For manufacturers, the Model 2800 also measures carrier frequency. Manufacturers can therefore verify that the device-under-test (DUT) is transmitting at the right frequency.

Though these varied measurement capabilities are impressive, the power analyzer may stand out most for its speed. It claims to have the fastest measurement speed available for any product that can make programmable bandwidth measurements. The Model 2800 can, for instance, make a 1.23-MHz-bandwidth cdmaOne primary power measurement and transfer that measurement to a computer in 6 ms. For another example, consider that it takes only 14 ms to make a GSM primary power measurement and two spurious power measurements. In general, the Model 2800 promises measurement times that are four to 10 times faster than competing methods.

To further enhance speed, the power analyzer includes setups for each of the cellular-phone standards. It only takes one command to program the Model 2800 to make power measurements based on a specific standard. Overall, five commands are needed to set up the instrument and make one primary power measurement and four alternate-/adjacent-channel measurements.

The power analyzer also provides a dynamic range that is more than sufficient. In applications involving cdmaOne, for example, the Model 2800 has a dynamic range greater than 90 dB. The basic accuracy is ±0.3 dB. Repeatability is 0.05 dB for CW signals and 0.1 dB for complex modulated signals. The VSWR is under 1.3:1.

To simplify usage, the Model 2800 does not require an external power sensor. It also digitizes all of the circuitry for the intermediate-frequency (IF) stage to the IEEE-488 bus. As a result, it promises very high stability while demanding calibration only once a year.

The Keithley Model 2800 RF Power Analyzer is priced at $15,995. Delivery is six to eight weeks ARO.

Keithley Instruments, Inc.
28775 Aurora Rd., Cleveland, OH 44139-1891; (440) 248-0400, FAX: (440) 248-6168, www.keithley.com.

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