Analysis And Design Of Analog Equalizer For Broadband Systems

In the wireless communication system, the signal distortion is caused by the unbalanced transmission parameters of the two port or the multi-port devices and the wireless channel, leading to the ripple of amplitude-frequency characteristics and the fluctuant of group delay characteristics, and this undesirable characteristics result in serious inter-symbol interference(ISI) that will increase the bit error rate significantly. To overcome the signal distortions come from all sorts of unbalanced transmission characteristic of practical devices and wireless channels, we should add some amplitude equalizers or phase equalizers where needed to eliminate or compensation this unbalanced characteristic effect, and by this way can we realize the goal of reducing the signal distortion.In recent years, we have applied the equalizer into the communication system more and more frequently, and the equalizer has become an important part in radio frequency communication systems[1-2]. For the digital equalizer, based on the time variant of the wireless channel, the blind equalizer which can adapt to the change and does not need the training sequence is widely concerned[3]. And for the analog equalizer, based on the area and power consumption, the equalizers which are composed of passive and lumped parameter are often used. The value of equalization has been developed from a few d B to twenty or thirty dB, and its bandwidth is also expanded from low frequency to Ku band. However, an equalizer with excellent performances, simple constructions, easily debugging and low prices is also with great requirements, and it is still need to be researched and developed furtherly.In this paper, based on various equalizers presented at now, the design of broadband analog equalizer has been done, mainly for the analysis and design of amplitude equalizer and phase equalizer. The design requirements of equalizers involves balancing bandwidth, equalization values, group delay characteristics, and so on. However, there are some contradictions exist while doing equalization between amplitude frequency characteristic and phase frequency characteristic. The equalization with not flat group delay often accompanied by deterioration of the amplitude frequency response of the channel, and equalized on the amplitude frequency characteristic may easily cause group delay fluctuations of the system. So how to balance the mutual influences among amplitude frequency characteristic and phase frequency characteristic, and how to realize a breakthrough on the indicators mentioned above in the field of amplitude equalizers and phase equalizers while maintaining its basic characteristics, have become the purposes and meanings of researching this topic. The contents researched are as follows:1) The characteristics, classification and development status of the broadband analog amplitude equalizer and phase equalizer are introduced, and the necessity of designing the equalizer is discussed. In addition, we have introduced the characteristics of the wideband system and discussed the importance of the design of wideband analog equalizer in this paper.2) Design basis of wideband analog equalizer. The basic principle, design specifications and steps of the equalizer are introduced. At the same time, we also have introduced the design considerations of the equalizer, including the solution of transfer function and the design basis of the structure of the micro-strip line.3) The analysis and design of the equalizer. In this article, according to the division of frequency bands and structures diverse, four different types of amplitude equalizer and two types of phase equalizer are designed. In terms of different equalization goals, the design method for lumped parameter and micro-strip parameter are used respectively. Firstly, the construction types of equalizers are presented, and using ABCD network analysis and mathematical analysis methods calculated various transfer functions or the S21 of the equalizers; Secondly, based on this theoretical analysis, using the simulation software of advanced design system(ADS), simulated and debugged various kinds of equalizers; Then, according to the simulation results of ADS, we drew schematic of the equalizer and designed printed circuit board(PCB) with software of Cadence. After manufacturing and processing the PCB board, we carried on welding and debugging for different topology of equalization on real circuits, and analyzed the testing results. Finally, its equalization effect was verified on the EVM systems, and then analyzed its overall performance.4) The analysis and design with improved performance of amplitude equalizer and phase equalizer. We put forward several kinds of structures creatively to furtherly breakthrough its indicators. Using the ADS simulation results, the design content of this article was enriched from the aspect of simulation.I have finished this equalizers as described above, although there are still some deficiencies, but also great improvements are made. Amplitude equalizer have a certain increase in the equilibrium quantity index under the condition of meeting the S11 requirements; Phase equalizer’s progress are made in its group delay equilibrium quantity and its bandwidth in the context of meeting the requirements of S21 and S11.