We’ve come a long way since Alexander Graham Bell’s famous words, “Mr. Watson, come here” were spoken and the telephone was born. The simplicity of use of today’s smartphones, tablets, and similar smart devices belies the underlying complexity of creating a device that can connect virtually anywhere, at anytime. While there are other consumer electronic devices that have increased in complexity and capability, the majority of the smartphone’s complex structure is completely hidden from the user. At the same time, “when can I upgrade” is a common mantra of users. The fast-paced and high-volume production required in this environment continues to add complexity to mobile device testing, and has necessitated the rethinking of traditional test methods.
As consumer demand for cellphones has grown, the need for increased network capacity has proliferated. In pursuit of gaining market share, mobile devices have also become more than just phones. Today’s cellphone capabilities include the integration of high-quality cameras, music and video playback, touchscreens, and high-resolution displays (see Figure 1). It’s estimated that the average mobile phone user will upgrade his device about every two years and in the process, gain new and improved capabilities often unrelated to making and receiving phone calls. These dynamics have led to increasing pressure to reduce time-to-market, without compromising phone quality.
Unknown to the average consumer is the evolution of RF technology that has occurred to ensure these devices meet the service expectations of today’s smartphone user (see Figure 2). Today, LTE (Long Term Evolution) – Advanced Carrier Aggregation is the latest technology evolution to create a higher bandwidth pipe between the Internet, or “cloud,” and mobile devices (see Figure 3). This technology allows a service provider to take smaller chunks of their available spectrum and aggregate them into a wider bandwidth channel. LTE-Advanced allows up to five 20- MHz chunks to create an effective 100- MHz channel.
New Testing Needs
Among the leading complaints about cellphones, short battery life usually comes up near the top of the list. As the miniaturization of phones has occurred concurrently with squeezing ever more power-hungry features into phones with high-resolution displays, battery life has been significantly strained. During the design phase, battery life testing is no longer just about talk time; what is of greatest importance is knowing how long the battery lasts for various types of users. Whether a teenager, parent, business person, or heavy data user, each will have a different consumption profile for data, voice, texting, and mobility. Each of these profiles needs to be tested in the design phase so that any issues with battery life can be resolved before the phone is put into mass production.
Conformance testing ensures that the phone design conforms to the standards for which it was designed. This testing is performed using specialized conformance and pre-conformance test equipment at various stages throughout the design process to ensure any issues are uncovered and addressed early. When the design is done, the phone will typically be certified by a third party as meeting the required standards.
With conformance testing completed, the testing required in manufacturing is focused on two key areas: 1) final device calibration and 2) device verification. These tests are done over a range of power settings and channel configurations for a limited set of key items:
- Channel power – Confirms that the device under test (DUT) has accurate power control.
- Occupied bandwidth – Ensures that the transmission bandwidth of the DUT is within limits.
- Adjacent channel leakage power ratio (aka ACP, ACLR) – Verifies that the DUT does not cause interference to adjacent channels.
- Modulation analysis – Measures parameters, such as error vector magnitude (EVM), to ensure that the signal quality from the DUT meets the standards required for the format(s) in the DUT.
Each of these tests, while not timeconsuming to perform individually, add up when you multiply them by the number of formats and channels (or bands) that must be tested. Using the latest nonsignaling manufacturing test process (see Figure 4), almost all of the overhead associated with establishing the call and making mode changes based on commands from the base station (BTS) is eliminated. Compared to prior testing techniques, the time savings has enabled more complex devices to be tested with minimal impact to production volume. Another benefit of non-signaling test is that it requires a far less expensive piece of test equipment since there is no need to duplicate the functionality of a BTS.