In today's mobile phone market, battery life remains one of the top priorities for users. While consumers are excited about advanced multimedia features, many are willing to sacrifice those features in favor of longer talk and standby times. Even as designers work to extend battery life, they face conflicting demands — new features often come with higher power consumption. Although battery technology has seen improvements over the years, there hasn’t been a groundbreaking innovation yet. As a result, the responsibility of improving efficiency falls on IC design manufacturers, who focus on reducing power consumption for better battery performance.
One of the biggest power consumers in a mobile phone is the power amplifier (PA), which drives the antenna. By increasing the efficiency of the PA across all output power levels, it’s possible to significantly reduce power consumption and, in turn, extend battery life. This article explores ANADIGICS’ HELPTM technology used in CDMA and WCDMA power amplifiers, designed to meet modern mobile phone power requirements.
To enhance efficiency, it's important to understand the power levels typically used in real-world scenarios. According to data from the CDMA Development Group (CDG), most mobile phones operate at much lower power than their maximum transmit level. This is because users are usually close to a base station, so the phone doesn't need to use full power. For example, while a standard may require up to +28 dBm, more than 80% of calls only need less than +10 dBm. However, traditional PAs are inefficient at low power levels, leading to higher current draw. Improving efficiency at these levels can significantly extend battery life.
A typical WCDMA power amplifier operates at 42% efficiency at +28 dBm but drops to just 8% at +16 dBm, with a quiescent current of around 50 mA. Traditional RF power amplifiers, made using bipolar GaAs technology, switch between high and low power modes at +16 dBm. One common approach is to use an external DC-DC converter to adjust the voltage for optimal PA efficiency. However, this adds cost, components, and takes up board space.
ANADIGICS’ HELPTM power amplifiers offer a more efficient and cost-effective solution. Based on its patented InGaP-Plus™ technology, these PAs integrate high-performance HBTs and pHEMTs on the same substrate, creating BiFET technology. This allows for high-linearity amplifiers and fast, low-loss switches within the same device. A BiFET-based PA can maximize efficiency without needing an external converter, especially at low output power. The pHEMT switch enables different amplifier paths depending on the power level, resulting in improved efficiency — over 2x at medium power and 21% at +16 dBm. This leads to a 50% reduction in average power consumption.
The third-generation HELP device, called HELP3, further reduces power consumption by up to 75%, with a quiescent current dropping from 50 mA to just 7 mA (Table 1). This makes a significant difference in both active and standby modes.
So how does this translate into real-world applications? Let’s consider a typical urban mobile phone. The receiving circuit and baseband consume 125 mA. The transmitting circuit’s power consumption depends on the PA used. Here are the results:
1. **Phone with traditional PA (two-state PA):**
PA current: 70 mA → Total current: 241 mA (116 mA transmitting + 125 mA baseband/receiving).
2. **Phone with HELP PA (two-level BiFET):**
PA current: 34 mA → Total current: 206 mA (81 mA transmitting + 125 mA baseband/receiving).
3. **Phone with HELP3 PA (three-level BiFET):**
PA current: 18 mA → Total current: 193 mA (68 mA transmitting + 125 mA baseband/receiving).
HELP and HELP3 also reduce quiescent current by 70% and 86%, respectively, helping save power during standby.
Of course, power efficiency isn’t the only factor when choosing a PA. Linearity, noise, and support for advanced services like HSDPA are also important. But once the basic performance meets specifications, power management becomes a key consideration.
Higher integration and added features not only save space but also reduce the bill of materials. For instance, HELP3 includes an integrated voltage converter, making it even more compact and efficient. With such advancements, the future of mobile phone design looks promising, balancing performance with power efficiency.
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