This paper interprets the four basic characteristics of RF circuits from four aspects: RF interface, small expected signal, large interference signal and interference of adjacent channels, and gives important factors that need special attention in PCB design process.
RF interface for RF circuit simulation
Wireless transmitters and receivers are conceptually divided into two parts: the fundamental frequency and the radio frequency. The fundamental frequency contains the frequency range of the transmitter's input signal and also the frequency range of the receiver's output signal. The bandwidth of the fundamental frequency determines the basic rate at which data can flow through the system. The fundamental frequency is used to improve the reliability of the data stream and to reduce the load imposed by the transmitter on the transmission medium below a specific data transmission rate. Therefore, when designing a baseband circuit for a PCB, a large amount of signal processing engineering knowledge is required. The transmitter's RF circuitry converts, upconverts, and upconverts the processed baseband signal into a designated channel and injects this signal into the transmission medium. Conversely, the receiver's RF circuit can take signals from the transmission medium and convert and down-convert them to the fundamental frequency.
The transmitter has two main PCB design goals: the first is that they must emit as much power as possible while consuming the least amount of power. The second is that they cannot interfere with the normal operation of the transceivers in adjacent channels. As far as the receiver is concerned, there are three main PCB design goals: first, they must accurately restore small signals; second, they must be able to remove interfering signals outside the desired channel; the last point, like the transmitter, they must consume the power Very small.
Large interference signal of RF circuit simulation
The receiver must be sensitive to small signals, even when large interfering signals (barriers) are present. This occurs when an attempt is made to receive a weak or long-range transmit signal, with a powerful transmitter nearby broadcasting in an adjacent channel. The interference signal may be 60~70 dB larger than the expected signal, and may block the reception of the normal signal by a large amount of coverage in the input phase of the receiver or by causing the receiver to generate excessive noise during the input phase. If the receiver is in the input phase and the interferer drives the non-linear region, the above two problems will occur. To avoid these problems, the front end of the receiver must be very linear.
Therefore, "linear" is also an important consideration when designing a receiver for a PCB. Since the receiver is a narrowband circuit, the nonlinearity is measured by measuring "intermodula distortion". This involves using two sine or cosine waves of similar frequency and located in the center band to drive the input signal and then measure the product of its intermodulation. In general, SPICE is a time-consuming and costly simulation software because it has to perform many loop operations to get the required frequency resolution to understand the distortion.
Small expected signal for RF circuit simulation
The receiver must be sensitive to detect small input signals. In general, the receiver's input power can be as small as 1 μV. The sensitivity of the receiver is limited by the noise generated by its input circuitry. Therefore, noise is an important consideration when designing a receiver for a PCB. Moreover, the ability to predict noise with simulation tools is indispensable. Figure 1 is a typical superheterodyne receiver. The received signal is filtered first and then amplified by a low noise amplifier (LNA). This signal is then mixed with this signal using the first local oscillator (LO) to convert this signal to an intermediate frequency (IF). The noise performance of the front-end circuitry is primarily dependent on the LNA, mixer, and LO. Although the noise of the LNA can be found using conventional SPICE noise analysis, it is useless for the mixer and LO because the noise in these blocks is severely affected by the large LO signal.
A small input signal requires the receiver to have a very large amplification function, which typically requires a gain of 120 dB. At such high gains, any signal that is coupled back to the input from the output can cause problems. An important reason for using a superheterodyne receiver architecture is that it distributes the gain across several frequencies to reduce the probability of coupling. This also makes the frequency of the first LO different from the frequency of the input signal, preventing large interfering signals from "contaminating" to small input signals.
For some different reasons, in some wireless communication systems, a direct conversion or homodyne architecture can replace the superheterodyne architecture. In this architecture, the RF input signal is directly converted to the fundamental frequency in a single step, so most of the gain is in the fundamental frequency and the LO is the same frequency as the input signal. In this case, the influence of a small amount of coupling must be known, and a detailed model of the "stray signal path" must be established, such as coupling through the substrate, package pins and bond wires. Coupling between (bondwire) and coupling through the power line.
Interference from adjacent channels of RF circuit simulation
Distortion also plays an important role in the transmitter. The non-linearity produced by the transmitter in the output circuit may spread the bandwidth of the transmitted signal in adjacent channels. This phenomenon is called "spectral regrowth." Before the signal reaches the power amplifier (PA) of the transmitter, its bandwidth is limited; however, the "intermodulation distortion" in the PA causes the bandwidth to increase again. If the bandwidth is increased too much, the transmitter will not be able to meet the power requirements of its neighboring channels. When transmitting a digital modulation signal, in fact, SPICE cannot be used to predict the re-growth of the spectrum. Since approximately 1000 digital symbol transfer operations must be simulated to obtain a representative spectrum and also need to be combined with high frequency carriers, these will make SPICE transient analysis impractical.
- The Description of 3G 4G LTE/5G Antenna
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2G base station: GSM: 900/1800MHz; CDMA: 800 MHZ;
3G base station: CDMA2000&WCDMA: 2100MHz; Td-scdma: 1880-1920201 0 0-2025232-2370 MHZ;
4G base station: TDD-LTE: 2320-2370,2570-2620MHz; -
This paper discusses the key technologies in 3G/4G/5G (third generation/fourth generation/fifth generation) communication systems, and then discusses the differences in the antenna technologies adopted by them. After reading and studying a large number of papers on the key technologies of 3G/4G/5G communication system, here I make some analysis and summary of my own. With the rapid development of science and technology, mobile communication technology has undergone profound changes, from 1G to 2G, to 3G, and then to 4G and 5G. On December 4, 2013, the fourth generation of mobile communication 4G technology was officially operated in the Chinese market, which means that China's mobile communication industry has entered the 4G era. At this time, research institutes in various countries and world-renowned enterprises engaged in communication technology research have entered the research and development of the new generation of mobile communications, namely 5G (fifth generation mobile communication system). No matter which generation of communication system, the research technology is to analyze the characteristics of wireless communication channel to overcome the noise interference. A lot of researchers are now looking at Massive MIMO technology. How is it different from the antenna technology used in 3G/4G communication systems? Will it become the core technology of the next generation of wireless communications? 1 Key technologies of 3G/4G/5G Communication System 1.1 Key technologies of 3G Communication System Since the early 1990s, the mobile communication industry began to actively study the standards and technologies of the third generation of mobile communication. In January 2009, China's Ministry of Industry and Information Technology issued 3G licenses to China Mobile, China Telecom and China Unicom, indicating that China entered the ERA of 3G mobile communications. The third generation mobile communication system mainly includes WCDMA, CD-MA2000 and TD-SCDMA. Its key technologies include: A. Rake receiving technology; B. Channel coding and decoding technology; C. Power control technology; D. Multi-user detection technology; E. Smart antenna; F. Software radio. 1.2 Key technologies of 4G Communication System In December 2013, China officially entered the era of 4G (fourth generation mobile communication system) communication network. In 4G mobile communication system, OFDM(Orthogonal frequency Division multiplexing) technology is adopted. OFDM technology is due to its spectrum utilization
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It is widely regarded as high rate of 2 and good anti-multipath fading performance. In the future, RESEARCH related to OFDM technology will also be carried out in 5G communication networks. The main key technologies of 4G communication system include: a. OFDM technology; B. MIMO technology; C. Multi-user detection technology; D. Software radio; E. Smart antenna technology; F. IPv6 technology. China's Ministry of Industry and Information Technology has just issued 4G licenses to the three major operators, and they are still deploying their networks on a large scale with a small number of users. At this time, China Mobile said it will start the RESEARCH and development of 5G communication system. Analysts pointed out that the three major operators are participating in THE RESEARCH and development of 5G, one is to keep up with the changes of The Times, and the other is that the demand is faster than the technology development. Li Zhengmao, vice-president of China Mobile, said at the 2014 MWC in Barcelona: "China Mobile will fully support the development of 5G projects, hoping to lead the industry in THE development of 5G technology and the setting of technical standards." With the deepening of mobile communication technology research, the key support technologies of 5G will be gradually defined and enter the substantive standardization research and formulation stage in the next few years. The jury is still out on what core technologies will be used in the future. However, I have compiled a list of nine key technologies that have been the focus of discussion in various high-end mobile forums. A. Large-scale MIMO technology; B. Filter bank based multi-carrier technology; C. Full duplex technology; D. Ultra-dense heterogeneous network technology; E. Self-organizing network technology; F. Use of high frequency band; G. Software-defined wireless networks; H. Wireless access technology: (1) BDMA (Beam Split multiple Access technology)
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3 (2) NOMA (Non-orthogonal multiple Access technology) i. D2D (device-to-device) communication. Figure 1 is the layout of Massive MIMO antennas in 5G communication networks. I am studying Massive MIMO technology in my lab. Figure 1 shows users communicating with each other centered on a large-scale antenna. The performance of wireless communication systems is mainly restricted by mobile wireless channels. Wireless channel is very complex, and its modeling has always been a difficult point in system design. Generally, statistics are made according to the measured values of communication systems in specific frequency bands. Wireless fading channel is divided into large scale fading channel model and small scale fading channel model. The so-called large-scale fading model describes the field intensity variation over a long distance (hundreds or thousands of meters) between the transmitter and receiver, and reflects the rule that the received signal power changes with the distance caused by path loss and shadow effect. A small scale fading model describes the rapid fluctuations of the received field intensity over a short distance or time. The large scale fading channel model is caused by the influence of the surface contour (such as mountains, forests, buildings, etc.) between the receiver and the source. The small-scale fading channel model is caused by the multipath effect and doppler effect. If there are a large number of reflected paths but no LOS (direct signal) signal component, the small-scale fading is called Rayleigh fading, and the envelope of the received signal is described statistically by the Rayleigh probability density function. If LOS is present, the envelope is subject to Rician distribution. Multipath effect phenomena cause flat fading and frequency selective fading.
The Picture of 3G 4G LTE/5G Antenna
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