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Future mobile phones will integrate more functions or features that require power consumption, and how to extend battery life has become a major issue. Combining the research and development trend of China's mobile phone products, this article will discuss the challenges of next-generation mobile phone power management and corresponding new technologies and solutions from the aspects of RF, baseband, backlight, audio amplification, charger, etc., and provide some reduction of circuit power consumption. And noise design ideas.
The two major characteristics of China's mobile phone market in the past two years are: As the end-user market still does not see the urgent need for 3G applications, the 3G commercial deployment and operation prospects remain unclear; mobile phone replacement has become the main growth driver of this market for the first time. New user growth has slowed, and telecom service operators need to offer more new services to existing users to increase revenue and expand market share, such as SMS, email, color display, web surfing, multi-chord ringtones, music, Games, videos, news and sports news. Such versatile integration poses a great challenge to the power supply design and management of mobile phones. This is mainly because the high power consumption brought by the versatility greatly reduces the working life of the lithium battery, such as when surfing the Internet using a mobile phone. The phone is out of power for two hours, and battery working time is one of the most important indicators for end users.
In the current situation where new high-energy battery technologies (such as fuel cells) are still immature, the power management of next-generation mobile phones can only start from two aspects: improving power utilization and reducing power consumption. In principle, we can extend the phone as much as possible by using as much as possible of the AC/DC or DC/DC switching power converter with high power conversion efficiency to reduce the power supply voltage and adopt dynamic techniques such as dynamic voltage adjustment. The working life of the battery. Below we will discuss the challenges and design trends of next-generation mobile phone power management from five aspects: RF, baseband, backlight, audio amplification, and charger.
The transmit power amplifier in the RF section is the most power-hungry component in the handset, with a maximum peak current of almost 1A. In a typical application scenario, it consumes almost half of the cell phone's battery power. Therefore, this part of the design engineer should pay special attention to it. At present, the market for mobile power amplifier components still dominates with GaAs HBT, but power amplifiers with enhanced quasi-crystal high electron mobility transistor (E-pHEMT) technology will become a new choice for mobile power amplifiers. The device can operate at voltages as low as 2V, and because it uses an automatic regulation technique to solve the temperature drift problem and avoids the current limiting resistor used in HBT technology, this type of chip can effectively reduce the work of the RF part. Consumption. Typically, amplifiers with E-pHEMT technology can increase battery life by nearly 15%. Such devices are expected to be widely used in CDMA/GSM mobile phones in the future.
The RF transceiver is also a large power component in the RF section, which consumes approximately 50 to 100 mA of current in the transmit or receive state. In addition to power consumption, transceivers present another challenge for design engineers, that is, the noise received from the power supply of other components in the handset can greatly affect the overall performance of the transceiver. Therefore, the design engineer should isolate the transceiver's power supply well to address potential noise issues.
The baseband device of the mobile phone is the place with the largest power consumption except the power amplifier. Usually this part of the power consumption can be further reduced by reducing the operating voltage and operating frequency. For example, the dynamic voltage frequency conversion technology can adjust the operating clock and operating voltage of the processor according to the working state. In addition, the selection of a suitable buck converter is also very helpful to reduce the overall power consumption of the system. Generally speaking, the LDO DC/DC converter has a low quiescent current, which is suitable for applications where the input and output voltages are not much different. The mode DC/DC converter has high power conversion efficiency and is suitable for applications where the input and output voltages differ greatly. As the operating voltages of various functional modules of mobile phones are different in the future, the future power management chips are definitely moving toward multiple output voltages, high output currents and high integration. For example, Anson has recently launched for the mobile phone market. Two highly integrated power management ASICs, the NCP4110, the NCP4110 provides seven LDOs and one synchronous buck converter.
As mobile phones add more audio features, such as MP3 playback, multi-chord ringtones and FM radio, the power consumption of audio circuits increases, and the low-power design of optimized audio circuits is an important aspect of extending battery life. . Mobile applications require audio devices with better noise rejection (PSRR), high efficiency, low operating voltage, and minimal peripheral passive components. LDOs are used in general applications to provide audio amplifier power to achieve the lowest PSRR, which will result in LDOs. Power loss of the channel. According to the analysis of the spectrum generated when the power amplifier device is turned on and off, if the PSRR of the audio amplifier can be increased to more than 60dB, the LDO can be removed, thereby effectively reducing the power consumption of the audio circuit.
Color display is becoming the standard configuration for next-generation mobile phones, while color screens require white LED backlighting. Typically, a uniform backlight of an LCD color screen requires 3 to 4 or more diodes, and a smartphone may require 6 or more. Since gaming functions and wireless access functions require long-term backlighting, backlight power consumption is also an important component of mobile phone power consumption. Technically, achieving a uniform white LED backlight usually presents two major design challenges: one is that the diode forward voltage is 3-4V (same as a lithium battery), so a boost converter is needed; The diode current must be controlled to maintain uniform brightness and color purity. At present, two common boosting schemes are charge pump and inductive boost converter. The former has the advantages of requiring fewer external components and does not need to include a voltage stabilizing circuit. The disadvantage is that the output current is limited, and the latter has the advantage that it can be produced. The high output current and regulated output have the disadvantage of requiring more external parts, requiring a larger PCB area and generating greater EMI. In addition, in order to maintain uniform brightness and color purity, it is necessary to control the diode current difference to be less than 10%. Currently, a current control voltage regulator architecture is mainly used.
In the external mobile phone charger/adapter section, switched-mode transformers are rapidly replacing traditional bulky linear transformers because high-frequency switching transformers are not only very lightweight but also much smaller than linear transformers. Chen Baixun, Analog Devices Semiconductor Analog Devices Product Manager, ON Semiconductor, said: "Any switching power supply developed for charger/adapter applications requires an isolated switching transformer." A key requirement for charger applications is safety, while transformers The high AC voltage can be isolated from the charging voltage of very low portable devices. Its main function is to prevent lightning strikes.
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