1 Introduction
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Generally, the baseband signal can be directly transmitted by the electric signal in close distance, but the baseband signal must be modulated onto the radio frequency signal at a long distance, that is, the low frequency signal spectrum is moved to the high frequency spectrum. The receiving end must demodulate the baseband signal from the modulated signal, that is, move the useful signal from the high frequency signal to the low frequency. At the same time, the receiving end often receives many signals, and we also need to choose the signal we need. The device that requires the desired signal and signal spectrum to move low is the tuner (in the analog TV era, the tuner is usually packaged in a tin box, also known as a tuner).
Tuners are widely used to transmit video, sound, data and more. Among the many tuners of various shapes and shapes, the most common one discussed in this paper is the tuner that transmits video content (the following "tuners" specifically refer to such tuners).
With the Beijing Olympics approaching and the popular broadcasting of terrestrial digital TV programs, USB TV sticks are selling well in China. The reason why a small USB TV stick can receive RF TV signals is due to the maturity of silicon tuner technology. In recent years, semiconductor process technology and IC design technology have developed rapidly, which has led to the continuous upgrading of silicon tuner technology, forming a situation in which multiple technologies of silicon tuner coexist and multiple semiconductor international companies compete. The hot silicon tuner technology is the focus of this article.
2 tuner introduction
2.1 Tuner classification
There are many types of electronic products that receive modulated RF signals, such as satellite set-top boxes, cable set-top boxes, televisions, mobile TVs, computer TV cards, PCMCIA TV cards, USB TV sticks, and the like. These electronic products use a wide variety of tuners depending on their characteristics. These tuners can be categorized from the following perspectives:
From the perspective of the received signal, the tuner is divided into three types: analog, digital, and digital-to-analog. Some of the tuners can also directly output the baseband signal. From the perspective of the receiving signal system, the analog signal can be fully received, and the digital signal receiving is divided into DVB, ATSC, ISDB, DMB, etc. by region.
Different from the network of signal transmission, it can be divided into satellite tuner, cable system tuner, terrestrial broadcast tuner and mobile phone tuner. For example, DVB-C for European cable networks, DVB-T for terrestrial broadcasting, DVB-S for satellite broadcasting, DVB-H for handheld devices, and so on.
The technology for processing signals from the tuner is divided into analog and digital. Traditional iron box tuners use analog technology, while silicon tuners use digital technology.
From the tuner circuit architecture, it can be divided into the following categories: single conversion IF output, single conversion low IF output, single conversion zero IF output, double conversion IF output, double conversion low IF output, and double conversion zero IF output, etc. .
The way to change the tuning frequency from the tuner can be divided into voltage synthesis and frequency synthesis.
2.2 The basic working principle of the tuner
The simplest tuner for a circuit is a single-conversion IF output tuner. The basic components include mixers, oscillators, phase-locked loops (MOPLLs), and high-frequency amplifiers. The high frequency amplifier has an automatic gain control (AGC) function, and the tracking filter is a center frequency adjustable band pass filter. The IF filter is a bandpass filter with special transmission characteristics, typically a surface acoustic wave filter (SAWF). The single-conversion IF output tuner circuit architecture is shown in Figure 1:
The RF TV signal enters the tuner's high-frequency amplifier for amplification, and its gain is automatically controlled by the AGC circuit, and then the image signal is removed by the tracking filter, and the intermediate frequency signal is mixed by the mixer and the local oscillator, and finally the intermediate frequency filter is considered. In addition to clutter, select the desired channel and further adjust the passband characteristics to complete the tuner function.
2.3 status of iron box tuner
At present, the most popular TV sets are analog TVs. These TV sets use iron box tuners. Their basic functions are channel selection and mixing, which are single-conversion IF output architectures.
Iron box tuners are mostly composed of a tuner-specific IC and a number of discrete components. Its main chip uses a Bipolar process, which has the advantage of extremely low cost. Since the tuner processes high frequency signals of several hundred MHz, the iron box tuner uses devices with microstrip and distributed parameters. The induction coil is manually adjusted for its distribution parameters. Early iron box tuners were selected by voltage synthesis. At present, most of them use frequency synthesis. The advantage is that the selection of the platform is simple, the tuning is locked, and it is not easy to run.
After years of technological development, the traditional iron box tuner design and process technology is very mature. Despite its many circuit components and complex structure, production debugging is very difficult. However, at present, the cost is very low, as long as it is less than 10 yuan, which is to make it an absolute advantage in the highly competitive analog TV market, and can not be replaced by silicon tuner. But it will definitely be replaced by analog TVs in countries around the world.
2.4 Several key technical indicators of the tuner
As an electronic product, the tuner has several important electrical performance indicators:
Dynamic Range: Dynamic range is the range of input signal strength that the tuner can receive. Terrestrial television broadcasting has the largest dynamic range requirement, about 60~70dB, and the cable transmission mode is about 30~40dB. The dynamic range of satellite transmission mode is the minimum.
Noise Index: Also called noise figure, it is the ratio of the signal-to-noise ratio before and after the input and output of the system, that is, the signal-to-noise ratio of the output signal is higher than the signal-to-noise ratio of the input signal. It determines the minimum acceptable signal strength of the tuner, or reception sensitivity. At present, the noise floor requirement of digital terrestrial television broadcasting should not be higher than 7dB, and the noise figure of the cable system is less than 10dB.
Image rejection ratio: The ability to filter out the image channel signal. The characteristics of the mixer determine that the channel with a higher or lower intermediate frequency than the desired channel frequency will also be output to the subsequent IF filter, which will interfere with the desired channel. Therefore, a tracking filter (also known as an image rejection filter) must be added in front of the mixer to filter out the image channel. Normal tuner image rejection must be 50~60dB.
Phase noise: Phase noise is defined as the ratio of the signal power to the total power of the signal within a 1 Hz bandwidth at that frequency. The tuner local oscillator signal is susceptible to jitter caused by noise clutter, that is, phase change, which is the phase noise of the tuner. Since digital TV signals mostly use quadrature amplitude modulation (QAM) and four-phase phase shift keying modulation, phase noise directly affects the output signal-to-noise ratio of the digital tuner. Analog TV signals are often less susceptible to phase noise interference by amplitude modulation (AM) or frequency modulation (FM). Usually the tuner phase noise must be above 50dB.
3 Silicon Tuner Technical Analysis
3.1 Silicon Tuner Technology Analysis
Using advanced digital design techniques and silicon semiconductor processes, most of the discrete components in the original tin-box tuner are integrated into a single silicon chip. This is the silicon tuner.
Silicon tuner technology is currently evolving rapidly, and silicon tuners have been used in a variety of electronic products. However, its cost is still high, and the market price is about 3 times that of the iron box tuner, which limits its speed of replacing the iron box tuner. Only in small products such as PCMCIA TV cards and USB TV sticks, silicon tuners are unique in their small size.
As silicon tuner design technology improves, its semiconductor manufacturing process is constantly being updated, with the goal of significantly reducing costs. The first generation of silicon tuners used the SiGe process commonly used in the field of high frequency semiconductors, but it was expensive. Later it went over to the BiCMOS process, but it was still more expensive than the Bipolar process used in the iron box tuners. The latest generation of silicon tuners are available in the popular CMOS process. This allows the silicon tuner to be integrated with a demodulator, decoder, controller, etc. using the same COMS process to form a SoC single chip, which greatly reduces system cost.
Silicon tuners use digital processing techniques to change their characteristics through control port programming. This way, a silicon tuner can easily implement multiple TV reception standards.
The silicon tuner market is currently a situation in which a variety of semiconductor manufacturing processes, multiple technical architectures, and multiple manufacturers and multiple products coexist. Different technical architectures have their own advantages for different applications.
The advantages and disadvantages of various circuit architectures of silicon tuners vary according to the unique technologies of different manufacturers. Therefore, different manufacturers have different preferences for different circuit architectures. At present, the zero-IF and complex-variable mixing architectures are the most promising.
3.2 Common Silicon Tuner
Infineon has introduced silicon tuner chips such as the TUA6041, TUA6045 and TUA6039. The next generation is a silicon tuner product represented by TUA8010 and TUS9090.
Maxim's products include highly integrated single-conversion TV tuners such as the MAX2165, MAX3580, MAX3540, and MAX3541.
Microtune's silicon tuner products include: MT2060 series low power digital tuner and MT2131 and MT2063 multi-standard, multi-mode silicon tuner chips.
Xceive has introduced a new generation of highly integrated silicon tuner XC5000 and tuner chip module SN5000.
NXP's (NXP) silicon tuners include TDA18292HN, TDA18252HN, TDA18271, TDA18251HD, TDA18211HD, etc., covering a variety of applications such as satellite, cable, terrestrial, handheld mobile.
Max-Linear has introduced the world-standard silicon tuner MxL5005S for set-top boxes and mobile reception. The MxL7001 is a silicon tuner chip for mobile TVs that is suitable for the ISDB-T standard.
Freescale Introduces MC44S803 Single-Chip Silicon Tuner
Samsung's silicon tuner S5M8602 can support TV standards in many countries such as DVB-H/T, DAB-IP, ISDB-T and T-DMB.
ST, TI and other companies that have demodulation and decoding chips have integrated silicon tuners with demodulators, decoders, controllers, etc. to form SoC single-chips, such as ST's STB6100 single-chip, TI's " Hollywood" mobile TV chip and so on.
3.3 Silicon Tuner Typical Application
Among the many silicon tuner solutions, this paper selects NXP's new digital-analog integrated silicon tuner TDA18271, which briefly introduces its application examples on computer TV cards. The TDA18271 is compatible with all analog and digital TV standards (PAL, NTSC, SECAM, DVB-T, ISDB-T, ATSC, DVB-C), and the TDA18271 chip itself can send IF signals to the digital IF demodulator TDA8295. Analog TV demodulation, output CVBS analog TV signal, and the intermediate frequency signal is also sent to the channel decoder TDA10048 to solve the digital TV TS stream. The specific application block diagram is shown in Figure 2.
4 Iron box tuner compared to silicon tuner
Although some performance metric silicon tuners are not as good as tin box tuners, silicon tuners also meet the requirements of digital/analog broadcast standards. The high cost at this stage is the main drawback of silicon tuners.
5 Conclusion
The popularity of digital TV broadcasting around the world provides an excellent opportunity for the development of silicon tuners. The small size advantages of silicon tuners also open up new applications for tuners such as USB TV sticks. In the next two years, with the popularity of silicon tuners, the cost will be almost the same as the cost of the iron box tuner, when the silicon tuner will dominate the world. At the same time, with the improvement of the technology level of silicon tuner and the reduction of cost, the competition in the silicon tuner market will become more intense. At present, the "chaos" situation of many varieties of such manufacturers will change. Only a few feature-rich, high-performance, low-cost silicon tuners can meet a variety of needs.
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