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The mobile phone market, which produces more than 1 billion mobile phones a year, has become the most competitive area in the semiconductor industry. It has been said that special processes such as gallium arsenide (GaAs), laterally diffused MOS (LDMOS) or silicon germanium (SiGe) bipolar CMOS (BiCMOS) provide manufacturers and designs with less precise geometric accuracy. The short-term cost advantage and linear modulation required by the division. However, the inherent economies of scale of CMOS have driven the industry to invest heavily in it, so its scale has been and will continue to lead other process products.For example, transceiver modules manufactured by commercial special BiCMOS processes such as Infineon, NXP and Skyworks have been implemented in CMOS for a long time, and in some cases it has been integrated into system-on-chips. The phone is inside the main processor. Designers have repeatedly found that while using demanding processes can present circuit module challenges, in the long run, implementing analog modules in standard CMOS will pay off. However, the CMOS process has not been able to successfully enter the field of power amplifier (PA) modules, and the power amplifier is a key component in the mobile phone.
Until now, the development of PA has been carried out using a special GaAs or LDMOS process with hybrid module packaging technology. As a whole, it is a costly manufacturing process, making PA occupy a large part of the cost of mobile phones. Power amplifiers require special semiconductor processes to provide high breakdown voltage, high gain, and high frequency transistor components. Hybrid packaging technology provides high Q passive components to generate 50Ω matching circuits. Implementing PA in standard CMOS means that designers must face the situation of no enhanced transistors and high-Q passives, making the development of fully integrated PAs challenging.
A new technology that has the potential to make PAs using CMOS processes has recently emerged so that PAs can be placed in a simple plastic package. Distributed Active Transformer (DAT) technology, as it is called, its geometry supports the use of semiconductor metals with relatively low Q values ​​to provide transformer-based matching circuits, eliminating the need for module packaging. By assigning the PA core to several blocks and then using a transformer structure to integrate the power supply and many other patented technologies, high breakdown voltage transistors can be eliminated.
Figure 1: DAT-based CMOS power amplifier technology is used in stand-alone GPRS handsets.
The invention of DAT technology is based on research results from the California Institute of Technology. Axiom Microdevices has further improved this technology, commercialized the production of DAT PA, and refined the productization of General Packet Radio Service (GPRS) PA devices, addressing such issues as receiving noise and high voltage batteries. Specific application issues such as work under the group.
Unlike products such as GaAs, since the power core is implemented in CMOS, the small signal control circuit required to bias and adjust the GPRS type PA power can be integrated in the same die as the main power stage circuit, thereby further reducing the cost. The integration of the PA core also provides greater flexibility to support linear modulation schemes. Traditionally, designers have been using one of two methods: one is a “mandatory method†using a linear modulator and PA; the other is a more advanced “envelope reconstruction†method, where a nonlinear, efficient PA is used. Become the core of the polar modulator.
For the latter approach, the use of traditional PA construction techniques will present serious challenges. For example, PA cores implemented in a special process respond differently to temperature and process variations than linearization circuits. This situation often leads to an extremely unreasonable requirement that end users or handset manufacturers must increase factory calibration time to compensate, thereby increasing costs. Conversely, if the PA core is integrated with its controller on the same die, it will provide multiple access for monitoring or controlling the stimulus. This way, when designers develop a delivery architecture with the best performance and cost structure, there are more options.
The next development that can be expected is to further integrate the PA with other components in the handset, such as the baseband and transceiver modules already implemented in the CMOS process. It can be seen from the large shipment of Axiom AX502 devices that DAT-based CMOS power amplifier technology is feasible in a separate GPRS product. It also has the potential for further integration to help the industry continue to meet the needs of manufacturers and designers for smaller and more cost-effective chipsets and to provide more features.
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