Test Challenges Rising For Mobile Devices

Focus on battery life is pushing companies to a new class of power management integrated circuits, but making sure they work isn’t easy.

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Smartphone and tablets continue to advance at a dizzying pace. On the component side alone, the latest mobile devices are moving towards 64-bit application processors, multi-mode RF front-ends, higher-end cameras and flashy LCD screens. Some systems even boast fingerprint scanners and heart rate sensors.

But an obvious part of the system continues to lag behind the curve—battery life. In response, Apple, Samsung and others have recently rolled out mobile devices that boast new and improved battery life. Still, the insatiable appetite for power-hungry software applications and wireless data is expected to keep battery life a pressing issue for some time.

One way to mitigate the problem is to channel the power more efficiently. To achieve that goal, OEMs are incorporating a new class of power management integrated circuits, or PMICs, into the system. Generally, PMICs are analog/mixed-signal devices, which are designed to regulate and control the power in a system.

In many respects, the power management IC is becoming just as critical, and possibly as complex, as their digital counterparts like the application processor and baseband. “The PMIC is truly an SoC,” said Anthony Lum, business development manager at Advantest, a supplier of automatic test equipment (ATE). “They are getting more and more complex. The integration levels are getting higher. These power management devices, which were under 20 and 25 pins in the past, are now approaching 150 or 200 I/O pins.”

And as smartphone and tablets get more complex, OEMs are adding more power management chips in the same device. “There is a double-whammy here. Before, if you looked at a smartphone or tablet, you would see one power management IC. But now, you get multiple insertions of them, maybe one to three power management devices, in a single system,” Lum said.

The shift toward more complex power management ICs for mobile applications presents some new and major ATE challenges. Like most suppliers of mobile chips, PMIC vendors are under pressure to drive down the cost and hit the market window. This, in turn, requires ATE with more channels, higher levels of parallelism and other features.

Simply put, there is a pressing need for faster test times at lower costs for PMICs. “Cost of test and test times are always a challenge,” said Mark Kahwati, senior product development manager at ATE supplier Teradyne. “They go hand-in-hand. That hasn’t changed and I do not expect that to change.”

PMIC test market heats up
In total, the overall ATE business fell by a whopping 20% to 25% in 2013, due in part to an excess of test capacity in the market, said Risto Puhakka, president of VLSI Research. “The ATE market looks better in 2014, but we’re starting at a low base,” he said.

Advantest, LTX-Credence and Teradyne are the main players in the ATE market. Teradyne has been the dominant player in analog/mixed-signal test, Puhakka said. Advantest also competes in this market, and last year, the company entered the mobile PMIC ATE arena.

PMIC test is a growing part of the overall analog/mixed-signal ATE market. “When you talk about analog, it’s pretty diverse. The challenge is to offer an ATE solution that has flexibility to cover customers’ analog needs, from DC and power to RF. It’s a wide range of testing requirements,” Teradyne’s Kahwati said.

The power management IC market itself is one of the few high-volume segments in the fragmented analog chip business. The total available market for PMICs in smartphones alone is projected to grow from $1.5 billion in 2012 to $2.3 billion in 2015, according to both Gartner and Dialog Semiconductor. The PMIC market for tablets is expected to grow from $400 million in 2012 to $600 million in 2015, according to the firms.

Dialog and Maxim are the two big PMIC players for mobile applications, said Doug Freedman, an analyst with RBC Capital Markets. Dialog dominates the PMIC business at Apple, but the chipmaker is gaining traction at Samsung. Maxim is strong at Samsung and is gaining ground at Apple. In addition, Qualcomm and others also sell PMICs.

Not long ago, PMICs were simple, discrete components. Now, PMICs are integrated, single-chip solutions that help reduce power, save board space and lower the cost in systems, Freedman said. “PMICs are an important part of the solution,” he said. “Dialog’s technology, for example, is playing an important role in enabling longer battery life within secular growth markets, including smartphones, tablets, and ultrabooks.”

In some cases, chipmakers are stacking PMICs with audio codecs in the same device. “Dialog’s solutions can be integrated along with multiple-power management and analog functions on the chip, such as programmable high-performance, low-dropout voltage regulators, intelligent battery charging circuits, USB interfaces, high-efficiency DC/DC voltage converters, sensor analog-to-digital converters and others,” Freedman said.

Basically, the PMIC consists of three main power IC components—boost regulators, buck regulators and low drop-out regulators (LDOs). An LDO regulator is a DC linear voltage regulator. Boost regulators are step-up regulators. Buck regulators, the power delivery workhorse in PMICs, are switched-mode power supply (SMPS) components.

In mobile systems, the PMIC communicates with the baseband. “It regulates all of the power, or all of the voltage rails, in a complex and power-hungry system,” Advantest’s Lum said. “It’s like a bunch of power supplies. Each one has a different voltage and current characteristic. You have many flavors and variations.”

Adding to the complexity is that the number of regulators has increased over time. “Now, it’s not uncommon to find 10 to 15 LDO regulators in a single complex PMIC device. Somewhere between four to six bucks regulators, or switched power supplies, are also in a complex PMIC. You also might see one or two step-up regulators,” Lum said.

PMIC test challenges mount
The ability to test complex PMICs is easier said than done. For these devices, the tester must conduct as many as 2,000 tests for characterization, 500 tests for design verification and another 300 tests during production, according to Advantest.

On the other hand, the test methodology has not dramatically changed for PMICs, or analog/mixed-signal in general, over the years. As before, the tester must make multiple and simultaneous measurements on the various regulators in the chip. “The test techniques have not changed,” Lum said. “You still need to measure a current and a voltage. What has changed is the ability to do parallelism and the speed at which we are acquiring data.”

In other words, testing new and complex PMICs requires a faster tester with more capabilities. “It’s not a simple process,” said Teradyne’s Kahwati. “We are seeing lower core voltages for the application processors. So, there are lower and lower voltages on these PMICs. That requires a tighter accuracy and a dynamic performance from the test equipment.”

Today’s mixed-signal tester for PMICs requires at least three types of pins, Kahwati added. First, the tester requires high-speed digital pins to test the digital interfaces. Second, the tester needs to handle some audio functions. And finally, the tester requires voltage/current (VI) resources, which allows an engineer to precisely measure both current and voltage.

The VI is basically an instrument on an existing tester. The trick is to provide one-to-one matching of VI resources to each regulated supply in the PMIC, according to Advantest. In the past, 16 VI resources per instrument were considered state-of-the-art.

Today’s PMICs require at least 128 VI channels. Last year, Advantest expanded the capabilities of its existing V93000 tester by adding a new high-density device power supply with 128 channels of VI resources per module. Previously, the tester offered 32 channels.

“We think that this is a game changer,” Advantest’s Lum said. “Before, on the tester side, we would have to serialize. We would have to share resources and then multiplex or switch them. Now, we have enough VI resources. Thus, it simplifies the test methodology.”

The next big thing in test for mobile PMICs is parallelism. For years, memory ATE has made use of parallelism to lower the cost of test. This involves the use of separate and high-speed systems called test handlers. With these handlers, the ATE can test multiple devices at the same time.

Now, parallelism is required to lower PMIC test costs. “For memory, you can test up to 256 or even 512 devices in parallel,” Lum said. “We are not there in the analog space yet. But we are following a similar path, where a multi-DUT solution is one of the things to bring your costs down.”

Several years ago, the tester could only test one device at a time. “Now, you are testing two to four devices at the same time. We are pushing 16 to 32 devices at once,” he said. “The limiting factor is the handler.”

What’s next?
Going forward, the PMICs themselves likely will see an increase in digital complexity. For example, the fuel gage and the charger control IC, which have been separate chips, may get integrated into the PMIC. Wireless charging is another possible candidate for integration.

This, in turn, will require vendors to upgrade the analog/mixed-signal tester. “You probably will need more digital functionality and digital pins,” said Teradyne’s Kahwati.

ATE vendors are also waiting for the long-awaited shift towards dynamic voltage scaling (DVS) for PMICs. “This has been talked about for a while,” he said. “This is an interface between the PMIC and the application and baseband processors to be able to dynamically change the voltage levels to optimize the power efficiency. That will require some tight integration within the tester between the digital pins and VI resources. This is so they can dynamically scale the voltage up and down throughout the test.”

Clearly, end-users want more battery life, prompting OEMs to develop new and innovative solutions. PMICs are just one part of the complex solution. All told, ATE vendors must stay ahead of the curve. “The technical challenges are known,” said Advantest’s Lum. “We have to deliver lower cost solutions. Test is a necessary evil and everyone wants to have it at a lower cost.”