Analysis of main features and working principle of CMMB receiver

China Mobile Multimedia Broadcasting TV (CMMB) standard is a mobile multimedia standard developed and developed by China itself with complete intellectual property rights. Compared with other foreign mobile TV technologies, CMMB's multiple technologies are at the international advanced level. Compared with traditional broadcasting, CMMB's main features are: (1) providing all-digital TV/digital broadcasting programs, integrated information and emergency broadcasting services, and achieving seamless coverage of the integration of satellite transmission and terrestrial network. (2) The slot-based frame structure is adopted, which greatly improves the use time of the receiving terminal. (3) Adopt OFDM modulation technology, LDPC/Reed-Solomon coding and deep interleaving technology, which greatly improves the high-quality mobile reception performance in complex wireless environments. At present, CMMB has reached a stable reception of broadcast television signals at a speed of 250 kilometers per hour. (4) Adopt unified technical standards and unified operations to support users nationwide roaming. CMMB provides some public welfare free radio and television programs, as well as a cryptographic authorization control management system to provide paid services.

Main features of CMMB receiver solution

A basic CMMB receiving terminal consists of four main components: a radio frequency tuner, a baseband demodulator, a multimedia processor, and a display and speaker for the final output signal. The main application areas include: mobile phones, portable TVs, handheld navigation devices, PDAs, MP4s, laptops and other small-screen portable handheld terminals, as well as mobile information terminals on automobiles, trains, ships and airplanes.

In response to market demand, Quantum Microelectronics has introduced a highly integrated CMMB receiver solution that includes a complete CMMB RF tuner and baseband demodulator. The internal functional block diagram is shown in Figure 2. The main features of the program are as follows.

CMMB RF Tuner

Compliant with CMMB GY/T 220 standard; adopts zero-IF tuner architecture, no external SAW filter required; single-chip tuner supports both VHF/UHF bands of terrestrial towers, and live L1, L2 and S bands of satellites; AGC dynamic range :-102dbm ~ -10dbm; built-in fractional PLL frequency synthesizer; built-in low phase noise wideband VCO; built-in bandwidth adjustable image suppression low pass filter; built-in RF and baseband analog adjustable gain amplifier (PGA); integrated low voltage Differential regulator (LDO), which requires only a single 3.3V supply; standard I2C control interface; high component integration, reduced external components; 70mA ultra-low operating power; ultra-small QFN package for portable applications.

CMMB baseband demodulator

Compliant with CMMB GY/T 220 standard; built-in high-speed 10-bit digital-to-analog converter; supports all 8MHz BPSK/ QPSK / 16QAM modulation modes; built-in 4096-point FFT unit, and LDPC/Reed-Solomon Forward Error Correction (FEC) decoder ; Built-in multiplexing function. It can receive one control channel and up to 4 traffic channels at the same time; support flexible and convenient time slot allocation; time slot allocation of traffic channel can be arbitrarily configured; provide common SDIO and SPI interface output received MFS code stream; provide I2C interface and Programmable I/O and interrupts simplify interface to external multimedia processors; embedded high-speed MCUs for device active state initialization, control and scheduling, and signal quality monitoring; available for TV handsets, PMP, and USB TV sticks The application-developed SDK greatly accelerates product development; ultra-low power consumption and standby power consumption. The embedded power management module supports multiple standby modes; it can be used as a single module with the Quantum CMMB tuner in the form of SiP; ultra-small BGA package.

How each module works

RF signal processing: VHF, UHF, and satellite live bands for CMMB, with corresponding low noise amplifier (LNA) and RF adjustable gain amplifier (mixer: mixer with zero IF single-stage conversion architecture, no need External SAW filter.

Baseband signal processing: Includes an image-constrained low-pass filter with adjustable bandwidth, baseband signal PGA.

Single-chip integration: Integrated low-noise VCO and fractional PLL reduce in-band phase noise.

ADC: A high-performance 10-bit ADC is built in to directly sample the input I/Q differential differential baseband analog signals.

AGC control: There are two AGC controls for RF PGA and analog baseband signal PGA. The AGC loop generates the AGC output by the magnitude between the sampled signal and the reference value.

Frequency Tracking/Frequency Correction: This module completes the frequency tracking of the signal, frequency offset correction, and sample rate conversion.

FFT: The FFT module performs a fast Fourier transform to change the OFDM modulated time domain signal to the frequency domain for demodulation.

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