Wireless Systems Design

RFIC Test System Meets Wireless Needs

This Test Software Provides Modulated S-Parameter Measurements For Today's Complex Cellular And WLAN Devices.

For one of the hottest growth areas in the semiconductor market, look to radio-frequency integrated circuits (RFICs). These ICs are an essential part of any wireless device—be it a cell phone, laptop, or multimedia product. To ensure that they work as designed, RFICs require extensive testing. This statement is especially true in the integrated environment of today's mobile devices. For this reason, Credence Systems' ASL 3000RF Test System has garnered a lot of attention. As a mixed-signal RFIC test system for wideband, wireless-communication devices, it includes coverage for IEEE 802.11 WLAN, CDMA, and GSM applications (see figure).

One of the key features of the 3000RF is its modulated-vector-network-analysis (MVNA) technology. This technology allows the measurement of S-parameters on complex, modulated signals. S-parameter measurements are a fundamental way of characterizing high-frequency devices. Traditionally, continuous-wave (CW) signals have been used as inputs to characterize devices. But this method is slow and ineffective when testing today's wireless cellular 3G and WLAN applications.

MVNA technology allows S-parameter measurements to be made with wideband, digitally modulated signals. This approach creates a test scenario that more closely resembles the device's actual operating environment. It also results in more accurate measurements than those that are obtained with traditional CW stimulus.

Utilizing a multi-site test feature, four independent RF measurements can be made in parallel. To achieve modulated S-parameter measurements, the 3000RF MVNA combines traditional network-analysis hardware with high-speed digitization and signal generation. Four 65-MHz digitizers with 14-b resolution simultaneously sample incident, reflected, and transmitted waves. Intermediate-frequency (IF) downconversion is achieved via a superheterodyne architecture. These measurements are used in ratio calculations to determine the S-parameters. An in-phase/quadrature (I/Q) signal generator provides a modulated stimulus signal. Arbitrary modulation schemes can even be generated from a computer file.

Data capture is a vital part of any RFIC test process. It is especially critical for complex wireless systems. For example, Wideband-CDMA and 802.11 utilize bandwidths of 5 and 20 MHz, respectively. The dynamic ranges of modern wireless devices are equally impressive. They reach as much as 80 dB of spurious free dynamic range (SFDR). This parameter relates to the digitizer's in-band harmonics. It indicates the usable dynamic range of an analog-to-digital converter (ADC). Outside of that range, detection problems occur.

The 3000RF receiver-digitizer architecture boasts an IF bandwidth of 20 MHz with attenuation control from 1 to 31 dB. It is therefore well designed to handle these high bandwidths and large dynamic ranges. The IF subsystem has an attenuation resolution of 1 dB.

Behind each digitizer is a 500-MHz DSP PowerPC G4 processor. That processor quickly computes the massive amount of digitized RF data. The parallel-processing architecture greatly enhances processing time over older test systems, which relied on shared buses converging on one processor. In fact, the company claims that the 3000RF has increased throughput by approximately 30% over more expensive, competitive systems.

In addition to its modulated S-parameter measurement capabilities, the 3000RF supports common wireless metrics like adjacent-channel power ratio (ACPR), noise figure, and sinusoidal S-parameters. These RF measurements work with the 3000RF's mixed-signal instrumentation to provide complete device characterization.

Test systems must be flexible enough to meet a wide range of product mix and test needs. The 3000RF vows to achieve this flexibility through a successful instrument-per-pin architecture. Engineers can configure the test system with the optimal mix of power supplies, digital pins, and RF ports that are needed for a particular device under test (DUT). This capability greatly decreases wasted pin measurements, thereby reducing test time and cost.

The 3000RF test system from Credence also supports InTEST's (www.intest.com) ATE test-head interface manipulator. These mechanisms are designed to hold and position test heads for use with any wafer prober and device handler. The ASL 3000RF operates on 50 A at around 208 VAC. It weighs 700 kg. The system's dimensions are 97 × 150 × 193 cm.

The 3000RF is available now. In a typical product configuration, it is priced at $750,000 (U.S.). Please visit the web site for more information.

Credence Systems, Inc.
1421 California Circle, Milpitas, CA 95035; (408) 635-4300, www.credence.com.

TAGS: Mobile
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