In-vehicle infotainment systems are a hot topic in the automotive world today. At the heart of the complex automotive infotainment platform is the high-performance car radio tuner, a must-have component for advanced broadcast listening experiences for drivers and passengers. The car radio market is quite large and continues to grow as car production increases. In 2012, the global production of cars and commercial vehicles reached 84.1 million units. In the first half of 2013, vehicle production reached 44 million units1. The size of the automotive aftermarket is even larger, with more than one billion vehicles on the road estimated to be on the road2. Assuming that there is at least one radio per vehicle, considering the size of such a large market, why are only a few car radio tuner suppliers able to compete in this huge and growing market?
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Success factors in the car radio tuner market
The field of car radio tuner is a semiconductor market with a high technical threshold. The main reasons are as follows:
Today's complex, ever-changing driving environment requires high-performance radio tuning technology
· The car is usually in a moving state. This constant mobility requires a car radio tuner to receive radio signals under various conditions. The tuner must be able to handle various types of signal attenuation, such as multipath interference due to the reflection of broadcast signals by mountains and buildings. The amplitude phase of the received signal changes at any time, causing the received broadcast signal to be distorted or lost.
· Weak signals in remote areas affect reception quality.
• Power lines and broadcast towers can interfere with broadcast radio signals or further degrade reception performance.
Interference in the car electronics
· Poor motor EMI protection in the car, such as windshield wipers, windows, sunroofs and other body/compartment parts, and even engine and horn can cause interference. Improper antenna configuration can also degrade reception performance. Other disturbances may also come from DC-DC converters, LCD screens, and other high-speed digital circuits placed on the car radio board.
Competitive pressures have prompted tuner IC suppliers to offer highly integrated and uncompromising tuner
· Traditional tuners are manufactured using the previous generation of BiCMOS process technology. With today's rising cost pressures, RF tuner designs have been converted to cost-effective CMOS technology in foundries such as TSMC to achieve lower mixed-signal IC production costs in deep sub-micron node processes. There are only a handful of car radio tuner providers in the world that offer a low-cost RFCMOS car tuner solution based on a digital low-IF architecture.
· In order to meet the automotive OEM front-end customer market, tuner IC suppliers must usually be an ISO/TS16949-certified company that provides AEC-Q100-compliant tuner ICs to the market.
Car radio tuner suppliers must be able to cover the globe and provide on-site support for design and drive testing worldwide. RF PCB layout and automotive drive test require local support to shorten the design cycle and help with proper tuning during the drive test.
These factors have led to high market entry barriers for car radio tuners, so that only a few semiconductor companies can provide high-quality tuners for the global automotive infotainment market.
Car radio tuner requirements
The challenging environment in which car radio tuner operates requires a range of demanding core performance parameters and features. These parameters include:
Excellent sensitivity: help receive weak signals
Sensitivity is the ability of the tuner to receive weak signals from the station. If you live in a rural area away from most radio transmitters, the sensitivity of the tuner is very important. A tuner with -3.5dBuV sensitivity is capable of capturing signals as small as 0.5uV, so that even if the tuner is 100 miles away from the tower it is likely to receive a signal from the tower.
Excellent selectivity and dynamic bandwidth control: good for receiving weak signals between strong stations
Selectivity refers to the ability of the tuner to receive weak signal stations when there is a strong signal station at a small frequency offset and the degree of suppression of left and right neighbors when receiving the current station, as shown in Figure 1. This feature is especially important for receivers in urban environments where the FM spectrum is crowded. Adjacent channel selectivity refers to the ability of the signal to suppress adjacent signals at ±100 kHz of the FM broadcast frequency, which is particularly important in the European market because the adjacent channel interference of FM broadcasts in the border area is close to ±100 kHz. High-performance car radio tuners should have at least 65dB selectivity at ±100kHz interference. Some tuners can achieve this selectivity through powerful advanced radio DSP algorithms that dynamically optimize the expected channel bandwidth by measuring multiple signal parameters, including adjacent and inter-phase channel conditions, to narrow the bandwidth in the presence of strong interference.
Figure 1: Excellent selectivity and dynamic bandwidth control is very important when receiving weak signals between strong stations. Excellent IP3: best protection against intermodulation distortion
IP3 is a measure of the quality of the tuner's linearity. Higher IP3 means better linearity and less distortion. The most severe distortion is third-order intermodulation distortion (IMD3), which is an interfering signal generated by the third harmonic distortion of two short-range interfering signals, entering the useful channel causing crosstalk. (See Figure 2.) The crowded FM spectrum is very common in cities, and interference that is too close to the useful channel is not easily filtered out. In order to reduce the interference result of third-order distortion, IP3 performance must be increased. Tuners with lower IP3 require very expensive high Q tracking filters to avoid IMD3 interference and poor listening experience. An excellent car radio tuner has an IP3 specification of up to 117dBuV and a sensitivity of -3.5dBμV at full RF gain. It should also provide a wide IMD dynamic range and provide IMD3 interference protection when there is no external filtering module.
Figure 2: Good IP3 provides strong intermodulation distortion protection
Fast AF (Alternate Station Frequency) check: Allow fast response time of 6ms or less
In Europe, AF can allow a car radio tuner to tune to a different frequency that provides the same radio content when the signal is too weak or when the radio signal coverage is exceeded. This is common in European car radios, which is initiated by sending an AF list in the RDS data. In high-end cars, two tuners are always in place, one of which is dedicated to the scan AF list, and the AF station parameters are provided to the host to jump to the AF station when the main station signal becomes unacceptable. In a cost-sensitive radio (the previously mentioned dual tuner is too expensive), a single tuner detects the AF station and then retunes to the main station without causing an appreciable audio interruption. The maximum time that can be accepted by the AF check operation is 10ms. Most tuners on the market can only monitor the Received Signal Strength Indication (RSSI) of an AF station. The outstanding car radio tuner performs AF inspections in 6ms and monitors up to four parameters including RSSI, SNR, frequency offset and multipath interference.
FM multipath interference processing: channel equalizer reduces multipath interference
Multipath interference is the primary source of FM broadcast performance degradation in mobile environments, especially at high speeds. Multipath distortion is caused by two or more radio broadcast signals from the same source arriving at the receiver at different times and phases, the level of attenuation being dependent on the signal reflection of different objects. Before the RF signal arrives at the receiver, the amplitude and phase change due to two types of multipath fading: flatness and frequency selectivity. In urban environments, the reflection from close objects (such as buildings) results in short-delay multipath fading, causing broadband deep fading. In this case all spectral component signals suffer from amplitude attenuation (flat fading) at the same time, resulting in harsh audio clicks and breaks. In turn, longer multipath delays (frequency selective fading) come from reflections of objects a few kilometers away (such as hills and tall buildings). In this case, some of the frequency components are attenuated, causing a large distortion of the channel signal, causing audio distortion.
The traditional approach is to use multiple techniques to mitigate the effects of multipath interference, such as backing up from mono audio to mono audio, installing low-pass audio filters (hi-cut and hi-blend), reducing high-frequency components to reduce Extremely harsh audio due to severe multipath interference and soft muting when forced. Car radio tuner should have the above basic mitigation measures, which can automatically run, start and monitor by continuously detecting signal quality parameters.
A good car radio tuner should have an FM channel equalizer in order to eliminate frequency selective multipath fading and produce the least distorted audio. The equalizer's adaptive algorithm continually seeks to recover the frequency components that are affected by frequency selective fading, even if the vehicle is traveling in a multipath interference environment. The result is reduced audio distortion and reduced effects of multipath interference mitigation on audio (eg stereo mono adjustment and hi-cut/hi-blend).
FM dual antenna phase diversity for higher resolution
In recent years, European automotive OEMs such as BMW, Audi, Volkswagen and Daimler have used glass/sMD active antenna systems to abandon passive whip antennas. However, the use of a small glass antenna will result in impaired FM radio performance. In a dual-antenna/phase-diversity tuner system, OEMs circumvent this problem by using dual antennas to provide greater signal strength and significantly improving the effects of multipath fading.
The leading car radio tuner enables a dual tuner phase diversity system with a channel equalizer to overcome flat and frequency selective fading. Dual tuner outputs are combined to mitigate signal fading and improve audio quality. In an antenna phase diversity system, the RF signal is received by two spatially incoherent antennas that have an optimized spacing from each other and are connected to two tuners tuned to the same frequency. The signal fading path may produce deep fading at one antenna location, while another signal fading path may achieve a good listening experience at another antenna location.
The dual tuner antenna phase diversity solution can be combined with multiple antenna outputs to minimize the effects on the received signal due to flat fading. The two receivers use a common reference clock to ensure that they are tuned to the same channel frequency, taking turns to obtain the IF signal and associated signal quality parameters from the secondary receiver and the primary receiver. The two IF signals are phase aligned and combined at the primary receiver using proprietary phase diversity logic. The combined IF signal is then subjected to channel equalization, FM demodulation, MPX decoding, and signal conditioning in the primary receiver. Finally, the output stereo audio is transmitted to the audio signal processing unit in the system.
The rise of AM/FM HD RadioTM
In the United States, HD Radio digital radio broadcasting is leading the development of car radios. In order to meet market demand, HD Radio, which was previously only found in high-end cars, has gradually migrated to mid-level platforms. Automotive OEMs that have adopted HD Radio include Ford, Volvo and BMW (to name a few). More OEMs will join this list in the near future. It is estimated that more than 50% of cars in the United States will be equipped with HD Radio reception by 2015. The HD Radio tuner must be certified by iBiquity (http://), a developer and certification licensor of HD Radio technology that can evaluate AM/FM tuner performance ratings for automotive OEMs. .
Looking to the future
In-vehicle infotainment system developers are being asked to achieve higher car performance quality at lower system cost. Today's consumers also expect a CD-quality listening experience from their car radio. Automotive OEMs and Tier 1 suppliers understand this trend and adapt to consumer demand by designing advanced infotainment systems that include state-of-the-art car radio tuners, excellent sensitivity and selectivity, excellent IP3 performance and FM phase Diversity reception, while supporting digital radio standards such as iBiquity's HD Radio technology. Automotive radio tuners with superior performance and cost advantages, such as Silicon Labs' Si475x and Si476x tuner families, are now being used in large-scale production projects by automotive OEMs and Tier 1 infotainment providers. These advanced car radio tuners have set a new benchmark for automotive customers at a price/performance ratio, while also providing consumers with an excellent in-car audio listening experience. This article is selected from the electronic enthusiast network July "Automotive Electronics Special Issue"
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