Answering the Call for "Smarter" Smartphones

Aug. 18, 2011
This article gives an overview of smartphone operation with a focus on reducing power consumed by the RF power amplifier and reducing battery charging time.

Fig 1. A smartphone interface, featuring a micro-USB port, creates a smaller-profile “all-in-one” device.

Fig 2. Smartphones perform a range of communication, computing, and entertainment functions.

Fig 3. Worldwide smartphone shipments in the first quarter of 2011 increased 20% year over year. (Source:

Fig 4. Forecasts indicate that the Android will be the top smartphone operating system by 2012. (Source: Gartner)

Fig 5. Average smartphone battery capacity, with typical features as shown, is about 1000 to 1800 mAh.

Fig 6. Fairchild’s FAN5904 buck converter contains a baseband processor, RF transceiver, and 3G Pas, as well as GSM/EDGE PAM.

Fig 7. The chart compares the talk time of a 3G PA with and without the FAN5904 under WCDMA signal modulation and using a 1000-mAh Li-ion battery.

Fig 8. This chart compares the data transmit time of a 3G PA with and without the FAN5904 under WCDMA signal modulation and using a 1000-mAh Li-ion battery

Fig 9. The FAN5904 converter allows for a smaller battery pack without sacrificing talk time.

Fig 10. These thermal images show a 3G PA (POUT = 28 dBm) with the FAN5904 at VPA = 2.97 V (a), the PA only at VBAT = 3.70 V (b), and the PA only during battery charging at VBAT = 4.20 V.

Fig 11. A typical linear charger has an efficiency of about 70%, while a switching charger comes in at approximately 94%.

Fig 12.Utilizing a FAN5400 switching charger can help reduce charging time by 30%.

Fig 13. The FSA1211 single-pole, single-throw, high-speed switch isolates high-speed sources.

Fig 14. With its signal integrity under 48 MHz, the FSA1211 minimizes edge and phase distortion.

Fig 15. Fairchild’s FSA641, a 2:1 MIPI single-pole, double-throw switch, handles two- and one-data-lane modules.

Fig 16. Configured as a triple-pole, double-throw (TPDT) switch, the FSA642 high-speed analog switch offers a pinout that eases differential signal layout.

Fig 17. The single 5-pin micro-USB port manages a host of functions.

Fig 18. The FSA9280A replaces an existing manufacturers’ proprietary connector with a standard mini/micro-USB connector.

Clearly, the smartphone has integrated itself not only into our daily business activities, but our daily life. In the past, smartphones were identified as a cell phone with a dedicated operating system (OS), which meant it was possible to add or install/remove application software. That definition is too simple, though. Today, the smartphone is a small all-in-one device for communication, entertainment, and computing functions (Fig. 1 and Fig. 2)

According to recent reports from analyst firms IDC and Strategy Analytics, global smartphone shipment volume in in the first quarter of 2011 increased by 20% year over year and 17% year over year, respectively (Fig. 3).  Gartner, another analyst firm, forecasts the worldwide smartphone consumption volume will reach 468 million in 2011, a 57% year over year increase.

What Do Customers Want?

Defining customer needs in terms of price and specification/performance can be difficult to pinpoint. Currently, the average price for a low- to mid-range smartphone runs about $150 to $200 with acceptable performance, i.e embedded with ARM11 600-MHz processor, partial touchscreen panel/simple QWERTY keypad, and a basic media player. Forecasts show that the low-range smartphone will drop to $100 or lower this year, and the mid-range smartphone with a Cortex application processor will cost $120 to $150.

High-end smartphones will offer a full-size capacitive touchscreen panel, high-performance media player, high-speed application processor, 8MP ++ camera, GPS/AGPS, and various sensors for motion detection. With their various options, these smartphones will have a much wider cost range than their low- and mid-range counterparts, at about $250 to $350.

Besides hardware considerations, end users look for the corresponding integrated services or value-added services (e.g., video/movie download, on-line digital stores, on-line video games, social networking, and mobile application stores). Though not directly added into the smartphone retail price, these services are important for service providers, since they contribute heavily toward average revenue per user (ARPU).

Due to a high-end smartphone user’s ARPU being 1.5 to 2.0 times that of general 2G/3G phone users, providers typically offer aggressive compensation plans for those who purchase high-end smartphones. At this time, four companies dominate the mobile-application store arena: Apple, Google, Nokia, and RIM. Their market share is more than 65%.

With regard to performance needs, smartphone users continue to show robust, unflagging interest in downloading games and other applications. Nevertheless, not all users can fully experience the fun if using low-end smartphones. Such phones simply don’t offer processor speed and/or hardware configuration to handle a number of the latest games and applications. 

Beyond communication, computing, and entertainment, designers are addressing other applications such as security/monitoring control, mobile payment, and electronic money using near-field communication (NFC) technology. For example, with HSDPA/Wi-Fi and a high-performance computation processor, smartphone users can access in-house Web cameras as a remote security control or baby monitor.

Smartphone OS

By year’s end, Android will likely become the most popular OS—it’s expected to account for 49% of the smartphone market by 2012 (Fig. 4). Apple’s iOS will remain the number two platform worldwide through 2014, despite a slight decrease in share after 2011. However, this pertains only to the Apple iPhone platform, which won’t be released/licensed to other phone makers.

The popularity of Android platform-based smartphones can be traced to several factors:

  • Because it’s free, the OS caught the attention of manufacturers worldwide, and many initially adopted it for low-cost smartphones.
  • Unlike other OSs protected by lots of copyrights, Google chose to keep Android open for everyone. As a result, the company attracted a multitude of programmers to develop applications, while keeping its liabilities to a minimum. With so many people working on the system, newer and better ideas were incorporated into Android.
  • Unlike other mobile OSs, device manufacturers are free to modify Android as per their needs. Users enjoy much needed flexibility and ease of use because manufacturers can now modify anything they need to make the experience a pleasant one.
  • It offers support for Adobe Flash-based Web sites. 
  • Android smartphone users can easily run several different tasks simultaneously. Such multitasking ability will become more critical in the future as smartphones replace the PC and MAC.

Challenging Functionalities

As smartphones continue to improve from a functionality standpoint, the hardware specifications require more power to achieve the performance. Enlarging the battery is the easiest method to meet this requirement, but that will likely mean tradeoffs in increased volume, weight, and materials cost. 

The typical feature phone battery capacity is approximately 600 to 750 mAh, which can support about 350 minutes in talk mode and three days in standby mode (Fig.5). The average smartphone’s battery capacity is in the range, 1000 to 1800 mAh. It’s supposed to have longer talk mode and talk time.  Actually, the standby time equals about one day, with approximately 350 minutes of talk time.

That major difference revolves around the smartphone’s data operation mode. Users can access the mobile Internet and mobile messenger, check/write emails, etc., while the device continues to access the service provider’s network for data exchange. Further increasing the battery capacity thus becomes unrealistic, since it makes the smartphone too bulky and, ironically, not so “smart.”

Subsequently, a crucial factor in hardware design concerns extending a smartphone’s operation time while maintaining smaller battery size. In the smartphone, the RF power amplifier (RFPA), LED backlighting, application processor (AP), and Wi-Fi module now consume more than 75% of battery power. Boosting efficiency in these areas can significantly extend the smartphone operation/standby time.

Solutions for reducing LED backlighting power and improving dc-dc efficiency for the AP or Wi-Fi module can be easily found on the Web. However, the same cannot be said for reducing RFPA power consumption and battery-pack charging time.

Innovative functionalities are the key motivating factors for smartphone makers to launch new models. Those functionalities should satisfy the user’s “smart” desires and ultimately become differentiators from the competition.

Saving RFPA Power

The smartphone market has seen a number of hardware-design advances of late, such as Fairchild Semiconductor’s FAN5904. The 6-W, 3-/6-MHz buck converter, which supports GSM/EDGE PAMs and 3G/3.5G RFPAs, saves space because it doesn’t require two individual buck converters.

The FAN5904 works across globally popular 3G wireless standards ranging from WCDMA to HSUPA+, CDMA200 1x EV-DO. It also supports China’s 3G standard, TD-SCDMA, plus HSUPA under TD-SCDMA signal modulation for higher data rates. The converter will also find homes in the emerging “TEDGE” mobile handsets, which are TD-SCDMA-enabled with backward-compatibility to GSM/EDGE. Figure 6 demonstrates how the FAN5904 interfaces between the baseband chipset, RF transceiver, and PAs.

Examining the output power sweep of a 3G PA with and without the FAN5904 for voice and data transmissions (with RFPA supply voltage set for an ACPR of -39 dBc), the converter can enhance the talk time and data transmit time by 14% and 30% with same battery pack size (Fig. 7 and Fig. 8, respectively).  Thus, smartphones can use smaller Li-ion battery packs without sacrificing the overall talk time and data uploading time (Fig. 9). A smaller battery pack, in turn, significantly reduces the overall phone volume – making it thinner, lighter, and smaller.

Another advantage of implementing a dc-dc solution involves greatly reduced RFPA case temperature. To illustrate, thermal images were taken of a 3G RPFA being powered by FAN5904, connected directly to the battery, and when the battery is being charged at 4.2 V (Fig. 10). With the FAN5904, the temperature of the RFPA barely reaches 50°C while at full output power. However, in the other two scenarios, the temperatures easily reach 50°C and 65°C. As a result, when used over a period of time, the entire handset will heat up rather quickly.

Therefore, a dc-dc solution not only helps lower temperature, but it can simplify the RFPA’s mechanical design for heat dissipation. Components can be placed closer to the RFPA and reduce the PCB size and cost. 

Shorten Li-Ion Charging Time

A cell-phone battery is usually charged with a standard USB port (5 V/500 mA) and external charger adapter. Due to a smartphone’s relatively larger battery pack, charging time takes longer when using a traditional linear charger operation mode. That can improve by increasing the charging current to 1C, but only if it’s connected to an external charger adapter (though not for a standard USB port). Still, a 1C charging mode introduces heat-dissipation issues on the charger IC, too, potentially causing the case to become very hot when the external charger adapter is connected to the phone. Thus, the designer always needs to reserve space on the PCB for heat dissipation.

A traditional linear charger is similar to a low-dropout (LDO) regulator with efficiency up to 70% (Fig. 11).  A switching charger runs like a dc-dc converter with efficiency up to 94%. Even when connecting to a standard 5-V/500-mA USB port, the switching charger can support charging current as high as 650 mA. For example, when using the same configuration with a 900-mAh battery pack, charging time takes 1 hour and 12 minutes. Overall charging time is reduced by 30% and the case temperature drops to less than 40°C (Fig. 12)

The FAN540x switching charger can reduce the charging time and simplify the mechanical design in thermal dissipation. It has high-accuracy input overcurrent protection (OCP) of ±5% and charging overvoltage protection (OVP) accuracy of ±0.5%. The OVP and selectable input OCP can offer extra protection for a charging battery.

Dual-Camera Resolution

Most smartphones feature dual cameras—a high-resolution camera for taking photos and a standard-resolution camera for video calls. Both share the same data bus and an isolation switch, which are required to maintain signal integrity under high-speed resolution mode.

To meet that need, manufacturers have come up with different types of solutions. For instance, Fairchild’s FSA1211 low-power, 12-port, high-speed switch, configured as a single-pole, single-throw (SPST) device, is optimized to isolate a high-speed source (e.g., a cell phone camera interface) (Fig. 13). It features 6-pF on-capacitance (CON), and its wide bandwidth (>720 MHz) is able to pass the third harmonic, resulting in signals with minimum edge and phase distortion (Fig. 14). In addition, channel-to-channel crosstalk minimizes interference.  

Besides using parallel interface, a Mobile Industry Processor Interface (MIPI) is used for high-speed interface for MIPI modules, i.e. cameras or LCD displays.  Along those lines, Fairchild developed the FSA641 and FSA642 switches.

The FSA641 is a 2:1 MIPI switch crafted for two- and one-data-lane modules (Fig. 15). Configured as a single-pole, double-throw (SPDT) switch, it’s optimized for switching between two high-speed or low-power MIPI sources. The device is specially designed for the MIPI specification and allows a connection to either a CSI or DSI module. It features an 8-pF CON, and like the FSA1211, its wide bandwidth (>720 MHz) passes the third harmonic, resulting in signals with minimum edge and phase distortion. Also, channel-to-channel crosstalk minimizes interference.

The FSA642, a bidirectional, low-power, high-speed analog switch, features a pinout that eases differential signal layout (Fig. 16). Configured as a triple-pole, double-throw (TPDT) switch, it’s optimized for switching between two MIPI devices, such as cameras or LCD displays and on-board multimedia application processors (MAPs).

Single Connection Port

The micro-USB has found homes in a wide range of charging and data-transmission applications (Fig. 17). Since the standardized charger interface can reuse the charger adapter, it lowers overall cost and helps from an environmental standpoint. Some phone makers are moving to the micro-USB connector for charging, audio and data transmission, which also helps to further reduce the phone’s profile.

For instance, Fairchild’s FSA9280A is meant to replace an existing manufacturers’ proprietary connector with a standard mini/micro-USB connector. It enables multiple accessories and signals (USB data, stereo and mono audio, UART data and charger detection) to utilize a single USB port, thus saving space and improving standardization.

Edwin Lee, a senior marketing manager at Fairchild Semiconductor, holds an MSc in electronic engineering from the City University of Hong Kong. He can be reached at [email protected].

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