In today’s mobile phone market, battery life remains one of the top priorities for consumers. Even as users desire advanced multimedia capabilities, they often compromise on these features in favor of longer talk and standby times. Phone designers face a constant challenge: adding new power-hungry functions while trying to maintain or improve battery performance. Although battery technology has made progress over the years, there hasn’t been a major breakthrough. As a result, the responsibility of improving energy efficiency falls on IC manufacturers, who focus on reducing power consumption to enable better battery management.
One of the biggest power drains in a mobile device is the power amplifier (PA), which drives the antenna. Enhancing the efficiency of the PA across all output levels can significantly reduce power usage and extend battery life. This article explores ANADIGICS’ HELPTM technology, used in their CDMA and WCDMA power amplifiers, which helps meet the growing demand for low-power, high-efficiency mobile devices.
To understand how to optimize PA efficiency, it's important to look at real-world usage scenarios. According to data from the CDMA Development Group (CDG), most mobile calls occur at power levels much lower than the maximum transmit power. For example, even though some standards require up to +28 dBm, more than 80% of calls operate below +10 dBm. However, traditional PAs are inefficient at these lower power levels, leading to higher current draw. Improving efficiency at low power can greatly enhance battery life.
Standard WCDMA PAs, for instance, are only 42% efficient at +28 dBm but drop to just 8% at +16 dBm, with a quiescent current of around 50 mA. Traditional RF PAs use bipolar GaAs technology and switch between high and low power modes at +16 dBm, often requiring an external DC-DC converter. This approach increases cost, complexity, and board space usage.
ANADIGICS’ HELPTM PAs, based on InGaP-Plus™ technology, offer a more efficient and cost-effective solution. This technology allows for the integration of high-performance HBTs and pHEMTs on the same chip, enabling BiFET-based designs that boost efficiency without needing external components. The pHEMT switch in the PA allows for dynamic selection of amplifier paths depending on output power needs, resulting in improved efficiency—over 2x at medium power levels and up to 21% at +16 dBm.
The latest generation, HELP3, further reduces power consumption by up to 75% and cuts quiescent current from 50 mA to just 7 mA. These improvements make a significant difference in both active and standby modes.
In practical applications, consider a typical urban mobile phone. The baseband and receiving circuits consume about 125 mA. When evaluating different PA options:
1. A phone using a traditional two-state PA consumes 70 mA in the PA, leading to a total of 241 mA during calls.
2. With a HELP PA, the PA uses 34 mA, bringing total consumption down to 206 mA.
3. Using HELP3, the PA draws only 18 mA, resulting in a total of 193 mA.
These reductions in current consumption also translate into lower power use in standby mode, thanks to the reduced quiescent current.
Of course, power efficiency isn't the only factor when choosing a PA. Linearity, noise performance, and support for advanced services like HSDPA are also critical. However, once the basic performance requirements are met, power management becomes a key differentiator.
Higher integration and added features not only save space but also reduce the bill of materials. For example, HELP3 includes an integrated voltage converter, making it even more attractive for modern mobile designs. Overall, innovations like HELPTM and HELP3 are helping shape the future of energy-efficient mobile devices.
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