Wireless/RF test challenges of highly integrated devices

Electronic News, August 12, 1996 by Ken Donovan

Now that wireless/radio frequency (RF) products are a driving technology, high-volume production test solutions are in demand. Production issues are basically the same for any high-volume technology. Docking, probe cards, contactors and calibration have moved from megahertz to gigahertz and with it come new challenges.

Maintaining RF signal quality is a science. Production-worthy test solutions are now available but emanate from good RF layout techniques, proven calibration techniques and lots of trial and error. LTX is a supplier of mixed-signal, linear, digital and discrete semiconductor test systems. For LTX' Mixed Signal Division, the wireless/RF business level is booming. Wireless/RF is a strategic market focus for the company and will continue into the next millennium. LTX offers several compatible Synchro configurations designed to meet specific RF requirements, the Synchro Plus, Synchro II, or the Synchro RFPAC.

Device integration

Just a few short years ago RF front-end devices consisted of 8- to 16-pin packages that may have contained one or two RF building blocks. The RF building blocks include LNAs, mixers, VCOs, synthesizers, modulators, demodulators and more. Today, standard RF building blocks are integrated with intermediate frequency (IF) blocks, converters and digital control logic in the form of single-chip transceivers. Using a BiCMOS process, integrating RF and IF into a single package caused pincounts to jump from 16 to 80 pins over the past four years. Simultaneously, volume-production automatic test equipment (ATE) demand jumped significantly.

Single-chip GSM (Global Systems for Mobile Communications) transceivers integrate most of the RF blocks into one package. For example, the LTX Synchro is in production testing Lucent Technology's W2020, a single-chip GSM transceiver. The W2020 integrates many of the RF building blocks in a 64-pin package including two fixed-frequency synthesizers and a digitally programmable frequency UHF synthesizer.

As digital wireless standards proliferate, dual-mode ICs are being marketed with analog and digital modulation schemes used in cellular phones. For example, the LTX Synchro is testing Qualcomm's Q5312I-2S2, a single-chip transceiver that supports FM and CDMA (Code Division Multiple Access) modes. CDMA is the latest wireless digital technology and required a test system capable of providing a new modulation scheme to qualify devices. The Q5312I-2S2 is an 80-pin package that contains modulation, demodulation, filtering, digital, analog-to-digital and digital-to-analog converters (ADCs/DACs).

Integrated devices such as the Q5312I-2S2 and W2020 drive test systems to be truly mixed-signal; i.e., they require a seamless integration of intelligent digital, digital signal processing (DSP) and RF subsystems. Now in one application package, test techniques and hardware interfacing are combined for production test of single-chip transceivers on the Synchro test platform.

To handle sophisticated high-volume devices with higher levels of integration, ATE vendors are faced with many challenges.

Wireless/RF test system general requirements

Test systems must be flexible. First, an RF subsystem must handle various wireless standards, such as cordless phones, cellular phones and wireless LANs. The high-volume wireless RF standards operate between 800MHz to 2.5GHz.

Additionally, the IFs are typically anything from 455KHz to 150MHz. The RF subsystem must be a broadband source and measure instrument, not just a high-frequency signal generator. Secondly, DSP techniques simplify testing complex analog and mixed-signal devices. DSP improves test time, repeatability and accuracy. Complex waveforms are easily created and analyzed using traditional DSP tools. Therefore, arbitrary waveform generators (AWG) and waveform digitizers of the test system must be DSP-based.

Finally, device integration has risen to the point where they include digital control circuits, ADCs and DACs. Digital control circuits use a I2C bus typically running between 10-20MHz while converter speeds vary from kilohertz to megahertz. In the end, synchronizing RF, DSP pins and digital is key to testing highly integrated devices. The Synchro offers a 4.3GHz source/measure RF subsystem, DSP-based AWG and digitizer and a digital subsystem. They all share a common master clock frequency reference. Coherent DSP measurements are made to achieve optimum test times. For example, while testing an IQ Modulator, uniting all system instruments together allows multiple spectral components to be analyzed in one measurement within milliseconds. This includes upper side band, lower side band, carrier suppression and other spurious components.

Modular upgrades on common system architecture

Test equipment vendors must stay at the forefront of technology by developing new modulation schemes with the existing system infrastructure. The test system should be designed with future considerations in mind. Enhancing the system's performance through modular upgrades and new software solutions preserves the customer's capital investment of test equipment. Handling today's challenges with an eye on the future is what customers demand. Maintaining one tester platform ensures continuous product flow and revenue generation for device manufacturers over the life of many products.