0 Preface
CMMB (China Mobile MulTImedia BroADCasTIng) is China Mobile Multimedia Broadcasting. It is China's first set of mobile radio and television standards with independent intellectual property rights for mobile terminals. It is also a portable mobile multimedia radio and television product jointly launched by China Mobile Communications Corporation and China Broadcasting Corporation. It mainly provides broadcasting and TV services for small screen portable handheld terminals such as mobile phones and PDAs, as well as terminals such as car TVs. As a basic communication device, mobile phones are required to be able to complete basic communication functions and even multimedia processing functions, so integrating CMMB on mobile phones has become an inevitable trend. The system uses a technology system that combines satellite and terrestrial supplementary forwarding. The broadcast frequency band is U-band (1.55 to 3.4 GHz and S-band (470 to 860 MHz). Because the system uses the broadcast transmission method of the wireless broadcast television network, it is not There will be any traffic fee, which is essentially different from traditional streaming TV, so this mobile TV terminal has a high market demand. This paper proposes a design solution that uses a CMMB dedicated chip IF228 to implement a mobile multimedia broadcast TV receiving terminal .
1 CMMB chip selection
When choosing a CMMB mobile TV chip, we must consider its technology development trend. This technology trend has two aspects. On the one hand, it is the improvement of the chip's own functional indicators, such as anti-interference ability, power consumption, size, and various interfaces provided. On the other hand, it is to reduce the integrated cost and development difficulty of the chip, which facilitates the rapid entry of CMMB terminal solution manufacturers and the mass promotion of products. Considering that the packaged SIP products are the most in line with the standards, the most stable performance, and the most guaranteed supply, in the long run, the all-in-one single chip that integrates functions such as tuner, demodulator, decoding and decryption The solution will be the technical development trend of the CMMB chip. Based on the above factors, the latest IF228 launched by Chuangyi Video is used to design the mobile multimedia broadcast TV receiving terminal. The performance advantages of the IF228 chip are reflected in the following aspects.
The IF228 chip has high integration and small size. The IF228 integrates tuner, demodulator, and UAM conditional reception. It uses a 65 nm process and a TFBGA 5 mm & TImes; 5 mm package. It is the smallest CMMB demodulation chip in the industry, and the solder ball The spacing is still maintained at 0.65mm, which greatly facilitates the customer's PCB design. The CMMB solution based on IF228 can be realized in an area not exceeding 50 mm2. Highly integrated chip design and ultra-small size chip packaging reduce the development difficulty and overall cost of terminal products.
The IF228 chip has superior demodulation performance to support the terminal's maximum moving speed of more than 800 km per hour, easily adapting to high-speed moving vehicles such as EMUs, maglev and even aircraft. At the same time, it also has excellent performance in low-speed mobile urban multi-path environments of tens of kilometers per hour. Under 20 Hz Doppler frequency shift, 6 standard TU6 channels with different strengths and delays, the actual demodulation threshold of QPSK reaches 7.3 dB or less. Another index that fully reflects the performance is the adaptation to the maximum delay of the equal-strength two-path. When the two-path delay reaches 75 μs, the IF228 still has a demodulation carrier-to-noise ratio threshold of 12.5 dB under QAM 16 modulation. Such performance indicators are enough to ensure seamless reception in any situation of single frequency networking.
IF228 chip has a strong ability to resist single frequency interference. Single frequency interference is a key factor affecting the reception performance and user experience of CMMB, a broadband system that uses time-domain synchronization. When the in-band single frequency interference exceeds 15 dB of the received signal, the IF228 can still receive smoothly. It is more important to emphasize that when the interference signal is too strong to be received, the interference signal is gradually weakened, and the IF228 can quickly resume normal reception without the so-called Schmidt reception effect (that is, entering the interference from a weaker interference environment) After a strong environment, it is necessary to weaken the interference signal more to resume normal reception). In today's increasingly crowded electromagnetic environment, this feature can greatly enhance the user's receiving experience. In addition, the additional benefit of this feature is that it greatly reduces the PCB EMI requirements, customers do not have to worry about the possible harmonic interference caused by the application processor and baseband chip, which greatly simplifies the layout of the CMMB part.
IF228 chip has low power consumption. The chip is based on the CMMB time slot receiving technology. Under the working condition of 1/10 of the opening time (4 time slots, normally receiving a set of QPSK modulated programs), the average power consumption is as low as 36 mW, average The power consumption per time slot is less than 10 mW. In addition, the ultra-low current in Power down mode also greatly simplifies the customer's power system design. The customer does not need to configure a separate LDO for the IF228 / IF206 power supply, but only needs to connect the existing I / O and core voltage from the system board. The peak current does not exceed 100 mA, and almost no need to consider the impact on the system power supply. The I / O voltage of IF2 28 directly supports the range of 1.6 to 3.6 V, does not require any adjustment measures, and has PWM output pins, which is convenient for the subsequent application of the built-in antenna.
IF228 chip supports multiple clock frequency inputs. In the design of CMMB terminal solutions, previous demodulators of the same industry generally only support a single clock frequency. If the clock frequency required by AP / BB is inconsistent, it will lead to the need for a terminal design solution. Two crystals support. The newly released IF228 / IF206 can support a variety of mainstream clock frequency inputs, including 10/12/13/18 / 19.2 / 20/24/26/27/30 MHz, etc. Therefore, the CMMB terminal solution using IF228 / IF206 can share a crystal with AP / BB, which can save cost for solution manufacturers and save space for PCB design of terminal solutions.
IF228 chip supports hard descrambling. In terms of MBBMS UAM conditional access, IF228 supports hard descrambling, which can directly realize clear flow output, which greatly reduces the customer's software design workload, reduces the requirements for MIPS, and has higher security.
2 Design scheme of mobile TV terminal using IF228 chip
The design scheme of the mobile communication terminal using the IF228 chip is shown in Figure 1. The mobile phone terminal is mainly composed of two core chips, one is the CMMB single-chip IF228, and the other is the processor chip SH7343 that integrates baseband and AP / CP functions. IF228 is a single chip that integrates tuner, CMMB demodulator and MBBMS UAM into one, and mainly completes the functions of signal reception, channel demodulation and program decryption. The chip SH7343 is a dual-core multimedia baseband processor for mobile communication terminals produced by Renesas. It has a built-in SuperH architecture 32-bit RISC processor and DSP coprocessor. The internal clock frequency of the CPU is 216 MHz and the instruction The processing rate is 478 MIPS, with 16-bit bidirectional data bus and 26-bit address bus, which contains on-chip RAM and Cache units for user operation, 4G address space, 32-bit internal data bus, 8-stage pipeline and on-chip multiplier, chip The required operating voltage is 1.2 V, 1.8 V, 3.3 V, and its functional modules include H.264 / MPEG-4 codec accelerator, RTCMMU (memory management unit), BSC (bus controller), DMAC (direct memory access control Devices), etc., including various functional interfaces, such as FLASH, SDRAM, URAT, I2C, USB, SIU, SPI, LCD, CODEC, MFI, WSIM, WLAN, etc. The processor chip can not only realize the hardware decoding of the TS stream, but also undertake the signal processing and function control of the baseband circuit. At the same time, the SH7343 integrates an efficient power management module, which can optimize the power consumption of the CPU at higher processing rates. Provide a good system solution for the development and perfection of handheld mobile terminals.
It is very convenient to integrate IF228 in mobile communication terminal applications. Due to the ultra-small package and strong anti-interference ability of IF228, as long as the RF signal from CMMB antenna to IF228 has no large insertion loss, it can be placed on any convenient position. The IF228 receives the CMMB signal and outputs the data stream to the multimedia processor SH7343. The multimedia processor only needs to treat the IF228 as a standard SPI / SDIO device, read the received data from it, and process it as streaming media.
Since the IF228 integrates the MBBMS UAM function in the CMMB receiving chip, it is very easy to implement the TD + CMMB terminal solution promoted by China Mobile. It is no longer necessary to separately configure the SD card to complete the UAM decryption function, which reduces costs and saves Resources.
3 Conclusion
CMMB, as a mobile multimedia broadcasting system with independent intellectual property rights in China, uses satellite and terrestrial wireless broadcasting to provide broadcast TV and information services for small screens under 7 inches. It is a new service form of broadcast TV under mobile and portable conditions, and it also fills China's broadcast TV Effective means of service gaps. With the enhancement of IF228's various functional indicators, support for hard descrambling, reduction in size, and reduction in power consumption, it will more rapidly expand its application in the field of mobile communication terminals.
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