Gsm Mobile Phone Front-end Design In The Next Generation Of Cmos Switches (photos) - Front-end

Early mobile phone design with circulator between the transmitter and receiver duplex Communicate

. However, If you want to use the design to support multiple frequency bands, we need more circulator. Such ferrite-based design enables mobile phone is big and expensive volume. And in some situations, the bandwidth is too narrow because circulator simply does not work. Other options are high-frequency switch and filter. They also found the cost or size issue.

GSM mobile phone Duplex at the time based on the work, of course, the best front-end switch with only the implementation of the program. This is because the duplex filter insertion loss is much higher than the switch, but at present, it can not afford the power level GSM. GSM mobile phone share sale 60% share, this article focus on the GSM switching system requirements, and discuss a variety of solid state switch. Meanwhile, the integration of other standards is also worth mentioning, mainly GSM phone UMTS (Universal Mobile Telecommunications System "next generation" global universal cell phone) application, they need to use additional switch path.

GSM front-end problems GSM phone functionality has been greatly expanded, in order to cover the whole planet can support up to four different working frequency bands (see Table 1), the formation of four transmit path and four receive paths. Taking into account the adjacent frequency band is very close to TX, with a power amplifier covering GSM850 and GSM; another amplifier covering DCS and PCS. Each RX path all with a filter, usually SAW filter, so take a total of 6 paths. Such structures are often used SP6T (single-pole 6 throw) switch. In contrast, the most simple GSM mobile phones work only in a single band, just SP2T switch.

Switching function in the cell phone because the front end, its insertion loss performance of power amplifier directly affects the effective PAE (power amplification efficiency) and the system NF (noise value). NF is equal to an increase in direct Antenna And LNA (low noise Amplifiers ) Between the insertion loss, and is given by PAE reduction:

PAE = PAE 10-IL/10 GSM power amplifier working in saturation mode, the output power up to 2W, PAE is also high, about 60%, as mobile phone, half the total current consumption from the power amplifier, high efficiency, therefore it Battery Life is essential. However, the high PAE was vulnerable to the high insertion loss of the adverse impact of front-end architecture. For example, a PAE of 60% of the amplifier, power amplifier and antenna base insertion loss is 1.5dB, then it is only 42.5% effective APE. Switch circuit any additional current consumption will further reduce the effective PAE.

We all know, GSM mobile phone output power requirement is high, up to +33 dBm 2dB, and thus the linearity of the front end also made an extremely demanding. Linearity is the use of harmonic suppression, regulations, requirements provided in the 12.75GHz frequency range, fundamental of all the harmonics should be suppressed below-30dBm.

Order to maintain low insertion loss, the designer at design time, the path is usually not used with high isolation. But 3 or 4 bands mobile phone frequency band, as GSMTX band and GSM850 RX band overlap, PCS TX band and the DCS RX frequency bands overlap, so there will a special problem. During the launch, RX band pass filter and can not leak through the switch into the transmit signal to provide any attenuation. To protect the RX filter in after following the LNA, switching itself must provide at least 35dB of isolation.

GSM standard are expressly provided for switching time requirements. Between transmit and receive retention time of 28ms. When switching from RX to TX time, 10mS period can not send signals to complete the switch action. Despite the 10mS time, designers prefer to set the switching time between the 1-5mS ensure the switch in the TX pre-launch to reach steady state. At the same time, once the amplifier work, the switch should also meet the harmonic suppression requirements. From TX to RX switching time requirements are the same.

As directly connected to the antenna front-end switch, the switch has a difficult task is to have strong ESD tolerance. According to IEC1000-4-2 specification, the phone should be designed to withstand 16KV air discharge. Such ESD model is equivalent to 330W resistor and 150pF capacitor in series, more damage than the human model. Switch itself to have the strength, or to protect the components plus.

Once the technical requirements have been satisfactorily resolved, additional front-end switching solution also has the size and height constraints. Both have strict size and height restrictions, its height must not exceed 1.5mm. As the front-end switch by integrating the multi-layer substrate (such as LTCC LTCC), has established the industry standard factor to reduce the volume provides a road map can be based. Taking into account the ASM (antenna switch module) is the highest part of the package of radio, thereby reducing the size of the various technology ASM highly popular mobile phone manufacturers. LTCC substrate with high quality factor in integrated wireless capability, but the increase in LTCC passive components need additional layers, thereby increasing the thickness of the module. Harmonic filters can be integrated amplifier in the substrate, while the frequency of blocking capacitors and ESD protection has to be placed outside the module. Some of the ASM in the LTCC at the top of CMOS decoder and integrated SAW filter.

Meet the technical requirements for a variety of GSM cell phone switching technology, and each have their own advantages and disadvantages of these technologies in detail in the following discussion.

Switch solutions Seventies of last century, PIN diode switch appears Solid marks the birth of the industry. PIN diode with low device insertion loss and harmonic distortion, is still the dominant technology ASM. However, PIN diode there own shortcomings, not a complete ASM. In order to bias diodes, modules need to set the blocking capacitors and power inductors. In order to produce multiple knife switch, then Xu Yong quarter wavelength of the diode series and parallel combinations (see Figure 1a). LTCC in, 900MHz equivalent of a quarter wavelength of a few centimeters, the transmission line to increase the size of the diode-based ASM.

GaAspHEMT (quasi-crystal high electron mobility transistor) switch (see Figure 1b) can reduce the volume of ASM and reduce its complexity, has become the outside except PIN diode as a viable alternative. With GaAs switches, each path Xuyong multiple FET, a control line needed. In addition, different PIN, pHEMTFET nature can not afford 17.8VpkGSM signal. Only series with more than one FET, the voltage distributed to each device in order to meet the power capacity requirements. Shunt FET can improve isolation and enhance immunity, of course, the number of control signals also doubled from 6 to 12. To meet the demands GSM, 35dB isolation, must use the parallel FET

by: gaga

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