Electronic Design

Instrument Upgrades Any Analog Signal Source To Generate Digital Signals

A vector modulator combines an arbitrary waveform generator, IQ modulator, and RF output and leveling system into one economical test instrument.

Testing, particularly production testing, is one of the biggest costs in IC manufacturing. Therefore, IC designers welcome anything that comes along to simplify testing and reduce its costs. That's precisely the job of an innovative vector modulator from IFR. It lets test engineers extend the life of their analog sources and preserve existing investments. IFR's new 2029 model actually combines a vector modulator with an arbitrary waveform generator (arb) and an RF level control system, which makes it well-suited for manufacturing test. Additionally, the product provides excellent RF accuracy to maximize manufacturing yields.

This product brings an economic advantage: adding the 2029 to an analog source versus replacing an analog source with a digital one saves $6000 to $13,000 per test station. Plus, displacing radio-test-set-based strategies results in even higher savings.

With the 2029 vector modulator, users can turn any analog RF signal generator into a digital signal generator (Fig. 1). They can couple it with any manufacturer's analog RF signal generator for fast conversions of manufacturing lines from testing older wireless formats to quickly testing the latest digital formats. This reduces investment costs for replacement equipment, downtime, and software. The 2029 can test 2G, 2.5G, and 3G formats ranging from 800 MHz to 2.51 GHz. Users can output digital signals in WCDMA, CDMA2000, IS-95, GSM, IS-136, and EDGE formats.

Modularity is a key feature of the instrument, eliminating the need to purchase more-expensive signal generators or air-interface-specific radio testers. This replacement cost can run as much as three times the cost of employing a 2029 with an analog signal generator. In addition, the 2029 is smaller and lighter than radio test sets, ensuring its fit in test stands where space is at a premium.

Although its excellent RF performance makes it an effective solution for testing any digital wireless product, including basestation amplifiers, the 2029 is ideal for handset testing. It was designed specifically to simplify the testing of cellular telephones in manufacturing. A priority of manufacturing test is repeatability. That's why a good solution relies on a signal source built around an arb. Because of its large storage capacity and inherent accuracy, the IFR arb is well suited to provide the precision needed for manufacturing test.

A key advantage of the 2029 is its ability to instantly switch digital formats. This instant format conversion enables testing next-generation wireless formats where wireless devices are designed and upgraded with software, not hardware. Dubbed "software radios," the new modular devices are accommodated by the 2029's flexibility. New wireless formats are simply loaded into memory and are ready to be tested with the same test equipment.

This flexibility provides manufacturers with a path to the future of advanced wireless testing. As manufacturers convert factories from older analog formats to the constantly evolving digital formats, their manufacturing lines can be converted quickly. The 2029 supports multiband, multimode phones that use the same test configuration. This means that the 2029 only requires software upgrades to keep up with the changing wireless standards.

The vector modulator uses an external analog signal generator as a fixed-level unmodulated source to provide its RF input signal. The output from the 2029 is a digitally modulated carrier.

The external generator provides a local oscillator input signal, while the internal arb generates a baseband IQ drive signal. An IQ modulator provides a vector-modulated output signal. The IQ modulator has greater than 15 MHz of analog baseband bandwidth.

The 2029 can provide a variety of modulated carriers, including IS-95, by loading suitable data files into the arb. The arb can be loaded with customer-defined waveforms. The memory can be segmented to define a number of different waveforms, typically equivalent to 15 different IS-95 signals. This allows the selected waveform to be changed without delay.

The RF-level control system allows the output to be varied over a wide range, ensuring its suitability for measuring both receiver sensitivity and overload. Excellent RF-level accuracy in the output control system and attenuator minimizes uncertainty and maximizes repeatability in manufacturing.

An RF combiner is supplied as an option so that other signals can be combined with the 2029 output, or used to connect measuring devices, like power meters and spectrum analyzers. The 2029 has no user interface and is designed for operation via GPIB. An RS-232 port is implemented for firmware and software upgrades.

The arb works with an interpolator (Fig. 2). The interpolation schemes make certain that the size of the source file for the arb is minimized. It preserves the arb output signal quality at the same time. Using the interpolator means that the 2029's arb files need only four-times oversampling.

The vector modulator's internal arbitrary waveform generator stores digital representations of waveforms. It has a large memory for storing waveforms. The arb's memory is segmented into 15 equal blocks, so it can store 15 different waveforms. An example would be 15 IS-95 waveforms that have a duration of 80 ms each. Because waveforms can occupy more than one block, the arb also can store a smaller number of larger waveforms, or even one enormous waveform. Waveforms can be generated once, looped continuously, or run sequentially.

Having a large memory affords much test flexibility. Plus, the waveforms don't have to be for the same transmission standard. The 2029 can be loaded with several waveforms for each of two or more different wireless RF transmission formats. This allows for handsets from two different manufacturing lines, such as one devoted to GSM phones and the other to CDMA phones, to be fed into a single test bay. The 2029 can instantly switch back and forth from testing sets of GSM phones and batches of CDMA handsets without ever having to wait to download the new waveforms.

An arb packager and loader program is part of the soft front panel. The packager configures source files into a format that's readable by the arb, with additional header information attached. The loader transfers the files into the arb over the GPIB. This setup allows flexible file management, maximizes the files that can be stored, and enables fast changeover between files. The 2029's arb decreases testing time because it runs directly from nonvolatile memory, so there's no significant lag time on changing waveform files.

The RF output resolution is 0.01 dB. The RF level accuracy (CW) is ±0.5 dB from 18°C to 28°C for CW signal levels greater than ­110 dBm. Typically, RF level accuracy (modulated) is less than a ±0.15-dB level change from a CW signal level with an IS-95 modulation multichannel signal that's applied from the internal arbitrary waveform generator.

The soft front panel is supplied, but it requires Windows 95/98/NT and a GPIB card. The product is 4.2 in. high, measures 16.5 by 20.5 in., and weighs 22 pounds.

Price & Availability
The 2029 vector modulator costs $15,000. It's available immediately upon receipt of an order. The 2029 Option 1 RF combiner is priced at $800. The 2029 can be used with any commercially available RF signal generator. Recommended IFR signal generators for use with the 2029 include the 2023/35, 2026, 2030, and 2040 series. Prices of these products range from $6442 to $22,465.

IFR, 10200 W. York St., Wichita, KS 67215-8999; (800) 835-2352 or (316) 522-4981; www.ifrsys.com; [email protected]

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