How to choose the right power amplifier to alleviate the power consumption of LTE equipment?

At present, the functions and designs of modern smartphones and high-throughput 4G networks have far exceeded those of several years ago. However, achieving a great mobile broadband experience is not an easy task. Today's smartphones must include a large number of features, including high-definition screens, high-resolution cameras, speakers, various connection options, and fast processors. This has brought severe challenges to mobile phone design, designers must do everything possible to find ways to reduce the three-dimensional size of the mobile phone. Therefore, designers turned to the help of RF component manufacturers in order to obtain a way to achieve higher integration and/or higher efficiency.

Supports multi-mode and multi-frequency requirements to increase the RF front-end space

As the increase of multimedia functions of devices becomes a design trend, the demand for frequency bands and modes in the RF part is also increasing. The worldwide adoption of LTE requires manufacturers to increase the number of frequency bands and related components in the RF part of mobile devices. This has brought great pressure to RF designers, who need to develop new solutions with higher integration to reduce the space requirements of multi-mode and multi-band RF components.

The worldwide deployment of LTE networks is usually to "cover" the existing 3G WCDMA/HSPA networks. Many LTE networks were first used in international metropolitan areas, and WCDMA, HSPA and HSPA+ networks are also included in the coverage area. In order to improve continuous data services for mobile users, LTE mobile phones and other devices must be able to switch to the 3G network when the LTE signal strength decreases, and then reconnect to the LTE network when in another location. Many 4G smart phones now support 2G GSM/EDGE, 3G WCDMA/HSPA+, and two or more LTE frequency bands, which is commonplace.

Current consumption of the power amplifier in 3G and 4G modes

The use of multiple modes and multiple frequency bands not only increases the demand for RF front-end space, but also reduces battery life. The RF power level of a mobile device is determined by the signal-to-noise ratio (SNR) and network requirements in the environment where the device is located. Typical operating power levels range from +23dBm when the mobile phone is searching for the network to -20dBm or lower when the mobile phone is working in an area with excellent SNR.

The distribution of power consumption for measuring battery life promulgated by the GSM Association in its TS09 program is a practical guide for calculating the relative time for 3G devices to transmit at different power levels in a typical WCDMA network (Figure 1). The TS09 distribution shows the typical probability of mobile devices at many different output power levels, with the greatest possibility occurring in the low-power and medium-power regions.

Figure 1: TS09 TX power distribution characteristics.

For this Tx power distribution, optimizing the current consumption of the power amplifier at a low power consumption level is very important to extend the battery life or help reduce the size of the battery. Such optimization was first successfully realized by ANADIGICS using its HELP? (High efficiency at low power) power amplifier. This type of power amplifier uses advanced circuit design techniques and power amplifier gain modes to effectively increase the efficiency in low power and medium power modes (Figure 2).

Figure 2: The relationship between ALT6701 Pout and efficiency.

LTE networks place different requirements on mobile devices. While CDMA and WCDMA networks require phones to be used under power fallback most of the time, LTE networks usually require short bursts of high-power RF transmission during data transmission. Since the power amplifier runs in high power mode for part of the time, the current consumed will be higher than the power consumption shown on TS09 (Figure 3).

Figure 3: LTE TX power distribution characteristics.

Larger battery capacity will allow LTE smart phones to have longer working hours. With more high-end smart phones today, the battery is the single largest component in terms of size and weight. Therefore, many mobile device manufacturers are repeatedly checking the RF front-end, looking for ways to improve efficiency, so that designers can save space and cost by reducing battery size.

Get the high efficiency of 3G and 4G power amplifiers

It is not easy to design a power amplifier with high efficiency and low current consumption in high power mode, because advanced wireless communication has requirements for output power consumption and linear gain. In order to achieve high efficiency, ANADIGICS power amplifier designers use innovative technology to create more efficient amplification links at different power levels. WCDMA and LTE devices require different power amplifier structures (Figure 4). The ANADIGICS HELP4? power amplifier is optimized for low power, medium power and high power modes, providing world-class efficiency for fixed power supplies and a lower average current than TS09 WCDMA power distribution.

Figure 4: ANADIGICS proprietary power amplifier structure.

In order to achieve more excellent space saving, ANADIGICS' new ProEficient? series power amplifiers also adopt a dual-band configuration. Compared with existing single-band solutions, these new devices reduce PCB space by 33% by combining two independent ProEficient power amplifiers in a compact 3 mm × 4 mm package, and they can provide the same as single-band ProEficient power amplifiers. The same efficiency, which again reduces battery consumption.

Figure 5: ProEficient efficiency (in standby).

Similarly, the efficiency in low-power mode has not been ignored, because for most LTE devices, it is very important to be able to work in WCDMA/HSPA mode for a period of time. ANADIGICS' new ProEficient design increases high-power output efficiency by 7%, effectively reducing battery current consumption at high LTE power. ANADIGICS' ProEficient? power amplifiers are optimized to achieve industry-leading efficiency without SMPS at low and medium power. This type of power amplifier can also be used with APT to help provide lower current consumption.

Figure 6: New ProEficient secondary structure.

Average Power Tracking Technology (APT) is a technology used to improve the efficiency of RF front-ends at low and medium output powers. Relying on the precise algorithm of the baseband and the high efficiency of the DC/DC converter, the APT can guarantee the high efficiency operation of the PA under different TX signal amplitudes. The increased efficiency reduces RF current requirements, allowing designers to use smaller batteries.

The HELP4 design can still provide the lowest average power consumption in the 3G TS09 Tx power distribution under the condition of a fixed battery power supply, but the new ProEficient architecture uses the average power tracking technology (APT) of the DC/DC converter for the power amplifier power supply. Even better.

APT increases the complexity of phone design, requires more computing power consumption and additional PMIC functions, so it is not suitable for all design price points. Factory calibration is also more complicated, because voltage must be considered along with frequency, gain, and temperature in the calibration algorithm. In this way, the cost of these additional components used to implement SMPS may increase rapidly. If all the extra components are taken into account, the cost of a complete power amplifier solution is almost twice that of a stand-alone single-band power amplifier when the user implements a DC/DC converter. Therefore, the bill of materials cost of the entire RF part will increase.

Choose your amplifier wisely

Modern LTE smart phones have brought unprecedented challenges to designers. Functional and design goals continue to focus on efficiency and space requirements. And, these requirements are all related to each other through battery capacity. Therefore, it is important to choose a power amplifier that can help reduce the entire battery life. In the past, this was usually achieved by choosing a power amplifier that was more efficient at low and medium power levels. Today, this can be achieved by choosing a power amplifier with excellent efficiency at all power levels.

In order to help designers achieve the goal of a thin and light smartphone with cutting-edge features and long battery life, it is clear that power amplifiers need to provide excellent performance under all working conditions. This includes the ability to achieve high efficiency in high power mode, while providing high efficiency in low and medium power modes without relying on DC/DC converters. This provides designers with the greatest flexibility, who can decide how to use the best RF front-end solution for their equipment.

ANADIGICS provides five ProEficient power amplifiers for the most popular UMTS frequency bands used all over the world. If you need samples and more information about such products, if you want to know how they can help you extend the battery life of high-power LTE devices, please contact us.