Dealing with the mobile TV design challenge - Embedded.com

Dealing with the mobile TV design challenge

This “Product How-To” article focuses how to use a certain product in an embedded system and is written by a company representative.

In reviewing mobile TV technology trends, one needs to differentiatebetween product feature set, packaging, performance, semiconductorprocesses used and, most importantly, the RF receiver performance.

Most single-standard demodulators currently available are thosedeveloped in CMOS processes ranging from 130nm down to 65nm. Thesesolutions come with an RF transceiver in a system-in-package to providethe front-end mobile TV block.

However, while performance varies among the various solutionsavailable, it is just a matter of time before most products meet therequired transmission standards.

The major challenges ahead include achieving system powerrequirements below 50mW in “Time Slicing Mode” (including the RF andmemory for multiservice); small form factors; and overcoming thecomplexity of system integration into consumer platforms. However, itis clear that as this market matures, the greatest challenges aremeeting fast development cycle times and bringing down product cost.

Coming up with a solution Infineon embraced these challenges anddeveloped the OmniVia TUS9090, a monolithic IC designed with anin-house RF CMOS 130nm process (Figure1, below ).

The SoC integrates the multiband RF receiver (VHF, UHF and L-bandsfor Europe and North America), the DVB-T demodulator block, and the PHYfor the DVB-H and corresponding embedded memory required for both thefirmware and multiservice data reception.

Figure1: The block diagram shows the system architecture of the TUS9090 fromthe antenna input to the SDIO interface output leading to a host ormultimedia processor block.

The TUS9090 does not require external components such as filters andmemories; however, one external LNA would be required if the TUS9090 isused for reception of DVB-T in the VHF band. The TUS9090 is capable ofhandling all link-layers and FEC functions using the integrated on-chipmemory and logic.

Table 1 below highlights abrief overview of the DVB-H standard along with other globally emergingstandards. To reach such a monolithic solution, a great deal of designengineering expertise and experience in the development of mixed-signalmonolithic IC is required.

It starts from the system partitioning where performancerequirements are analyzed and mapped toward the optimum mix hardwareand software partitioning.

The design optimization phase that follows implements advancedsignal processing algorithms, but engineers require a very deepunderstanding and knowledge of the noise issues that can propagate fromthe high-speed digital blocks to the more sensitive analog RF functionssuch as the LNA's.

Without such careful design and exhaustive testing, robustnesscannot be achieved, which leads to performance degradation andultimately customer disappointment.

Furthermore, the reception environment for mobile TV can becomequite challenging due to adjacent channels (blockers), deep and fastsignal fading (terminal moving in a car or a train) and poor indoorreception (signal power loss).

The TUS9090 monolith IC is fully compliant with Mobile and PortableDVB-T/H Radio Access Interface (MBRAI) II specifications. The RFsensitivity is better than -98dBm in DVB-H mode and the RF tuner noisefigure is 4dB, excluding the external balun.

Minimum C/N has been measured down to 8.4dB for a QPSK modulation,1/2 code rate, 1/4 guard interval, 3/4 MPE FEC rate, 8KFFT in TU6 channel conditions (with MPE frame-error rate of 5 percent).The respective phase shift Fd3dB@MBRAI is 170Hz for the sameconditions. Similar performances are measured for Single FrequencyNetwork (SFN) situations.

The TUS9090 is available in a 0.8mm-, 8.5mm x 8.5mm SGA package.However, in order to provide the smallest possible form factor theTUS9090 monolithic IC is bumped, and therefore can be provided as baresilicon (<0.4mm-thick bumped bare die) allowing for very low-profilemodules to be developed at lower costs . Removing the packaging processfurther reduces the costs.

System architecture
The block diagram in Figure 1 showsthe system architecture from the antenna inputs to the secure digitalinput/output (SDIO) interface output leading to a host or multimediaprocessor block.The first part of the front-end of the mobile TV is theantenna required for the RF signal reception.

Table1. There are several mobile TV standards emerging globally.

The recovery of the mobile TV signal is subject to variousimpairments that include specific system integration issues.Considering the wide bandwidth of a UHF receiver and the sizelimitation of the antenna for the mobile terminal, the antenna designis quite challenging.

Although low-noise receiver designs can alleviate this problem, theantenna is still the best LNA in the system. Hence, it makes sense tolook for alternative antenna approaches. Tuned or resonant antennas canexhibit significantly better performance.

However, nonlinear tuning elements such as varactor diodes candegrade the wanted signal in the presence of the strong GSM transmittersignal, since the isolation between cellular and DVB-H antennas is onlyabout 10-20dB. The TUS9090 has a balanced configuration in order toobtain the best possible linearity and lowest noise.

The noise figure of the RF tuner is 4dB for the UHF stage,fulfilling the MBRAI II standard. In cases where specific applicationsrequire higher performance, an additional external LNA can be added toachieve a noise figure in the range of 2dB or better.

Following the antenna and input stage, the embedded RF receiverblock is a direct conversion receiver with integrated LNA, mixer,channel filter, crystal oscillator, PLL, on-chip loop filter, voltage-controlled oscillator and IF gain control. The fully differentialsignal path from RF to I/Q signals provides a high degree of noiserejection.

In addition, an integrated wideband RF AGC loop follows theintegrated LNA's. This RF block has the ability to detect the signaldirectly following the LNA, so that it can directly respond to allsignals seen by the mixer, hence avoiding any linearity problems causedby any string adjacent channels.

For the wideband AGC, an analog gain control loop is used and thedigital baseband gain control uses a programmable gain step sizecontrolled via a dedicated digital AGC bus. Furthermore, an integratedhigh-performance crystal oscillator supporting a wide range of standardcrystal frequencies allows the operation of the RF block independentlyof system clock availability.

However, the RF block can also work with a good quality systemclock. Thus, the cost of the crystal can be saved. Note that zero-IFdirect conversion receivers have become the mainstream architecture forDVB-H because they meet specifications for the analog and RF section ofthe receiver while offering the least amount of external components andreducing power consumption.

Low-IF RF architectures are an alternative to the zero-IF but sufferfrom stringent image-rejection requirements caused by the N ± 1blocker. However, the use of advanced CMOS process technologies enablesvarious mixed-signal calibration and circuit techniques to overcome theshortcomings of zero-IF direct conversion architectures, such as theDC-offsets.

The high bandwidth and large number of sub-carriers used for DVB-Tand DVB-H allow for the reduction of several kilohertz of spectrumaround DC without noticeably degrading performance. Furthermore, recentproduct developments have shown it is possible to integrate the LNAinto an RF tuner developed using a pure CMOS process technology despitethe wide input frequency range required for DVB-H.

System noise figures below 3.5-4dB at the RF reference point arefeasible, achieving the required sensitivity. Another hurdleBlocking isanother design challenge on several levels. The wide spectrum that amobile TV receiver needs to cover translates to a potentially highnumber of unwanted signals that need to be addressed by the receiver'sdynamic range.

This requires high linearity in conjunction with a good noisefigure, as well as a wideband RF gain control loop to protect the mixerand succeeding stages from being saturated by the far-off blocker. Thefirst two requirements ultimately set the power consumption of theanalog receiver section.

Hence, single-frequency applications requiring somewhat lesslinearity have the advantage of being further optimized with respect topower consumption and noise figure. The TUS9090 implements the digitaldemodulation of the OFDM signals defined by the ETSI EN 300 744 andETSI EN 302 304.

The PHY module integrates all the OFDM features includingsynchronization, FFT, channel estimation, de-mapper, innerde-interleaver, inner decoder, outer de-interleaver and outer decoder.

A power control block designed to minimize power consumption andoptimize synchronization is also included. Furthermore, an internalhigh performance multilayer bus interconnects the different IP blockssuch as the on-chip processor, allowing for a high level of parallelbus activities that in-turn allows for an increase in system throughputdue to the reduction in the overall system latency.

The host connection is made through a slave SDIO interface that canassure the FW download into the chip during the boot and then transferIP data streams back to the host. It serves also as link to controlsome of the receiver configurations.

Clock rates up to 50MHz can be handled in order to minimize the timethe receiver is ON in DVB-H mode.The mobile nature of the terminals maycause fast time-varying channels and Doppler frequency shifts of thereceived signal and its echoes.

Receiver performance under these conditions is largely determined bythe modulation used, protection offered by the standard, as well as theperformance of the signal processing algorithms. DVB-H addresses theseimpairments and offers a variety of configurations to adjustperformance trade-offs to actual requirements.

The IC also hosts the complete firmware including automatic featuressuch as channel profile detection, frequency scanning, PSI/SI parsing,etc. Infineon also provides the DVB-H host drivers that are compatiblewith major middleware products in the market.

Lionel Federspiel is SeniorManager, TV Receiver Business, Infineon Technologies AG

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