With the arrival of the third generation (3G) of mobile communication, phone designers are constantly working on new solutions to tackle the challenges brought by high-speed data transmission. Among these, software performance, screen technology, data processing bandwidth, and battery life stand out as key issues. In second-generation (2G) phones, which only supported voice and low-speed data, these problems weren’t as critical, allowing for simpler and cheaper solutions. For example, in typical 2G handsets, power amplifiers (PAs) were directly powered by the battery—this was straightforward but not very efficient.
In 3G devices, the demand for higher bandwidth and transmission power makes efficiency more crucial. To extend battery life, a more advanced solution is needed. A growing trend among manufacturers is the use of highly specialized step-down DC-DC switching regulators to power the PA. These regulators dynamically adjust the power supply voltage to match the RF signal's amplitude requirements, significantly improving energy efficiency under all conditions except peak transmit power.
Peak power is only necessary when the phone is far from the base station or during high-speed data transmission. As a result, this dynamic adjustment leads to substantial power savings. If the PA’s power supply can be adjusted over a wide range, it may even allow the use of a linear amplifier with fixed gain, eliminating the need for bias control—though many manufacturers still prefer using it for better control. However, some companies focused on W-CDMA technology argue that bias control isn't necessary at all.
Figure 1 shows how a switching regulator like the MAX1820 dynamically adjusts the power supply to the W-CDMA PA, reducing energy consumption and extending battery life. Another important consideration is the specific performance requirements of the switching regulator used in such applications. Understanding the load characteristics of the power amplifier helps tailor the design.
Figure 2 illustrates the varying voltage and current requirements of a fixed-gain W-CDMA PA. At peak power, it needs 3.4V and up to 600mA, while at low power, it only requires 0.4V and 30mA. This wide variation presents a challenge for the switching regulator, which must operate efficiently across a broad range of loads.
The MAX1820 is designed to meet these demands. It offers high efficiency across different load levels, with up to 93% efficiency during data transmission and 85% during voice calls. Its fast output slew rate of 30μs ensures quick adjustments in transmit power, meeting the tight timing requirements of W-CDMA systems. The device also supports stable operation from 9.5% to 100% PWM duty cycle, making it suitable for various battery voltages.
With a 1MHz internal oscillator, the MAX1820 maintains a constant frequency to minimize noise and ripple, while its synchronization feature allows precise alignment with system clocks. This makes it ideal for use in 3G handsets and other wireless devices, helping to achieve smaller, more efficient, and powerful mobile solutions. The MAX1820’s proven efficiency in W-CDMA applications opens the door for broader adoption in other 3G standards and future wireless technologies.
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