运用于宽带系统中的可重构模拟基带电路的研究和设计

【作者】 樊锦涵；

【导师】 李巍；

【作者基本信息】 复旦大学 ， 微电子学与固体电子学， 2010， 硕士

【摘要】 随着宽带无线通讯系统的发展,射频芯片对模拟基带的设计要求越来越高。一方面,模拟基带的带宽决定了射频芯片能处理信号的速率,所以在设计时希望其满足大带宽的要求；另一方面,在满足大带宽要求的同时,模拟基带电路需在整个工作频段内都满足系统的各项指标,以实现信号的宽带传输。宽带系统内的模拟基带电路的性能(如线性度)如要达到窄带系统的水平,将付出更大的代价,实现起来更加困难,因为随着频率的升高,系统的传输特性将恶化(如反馈系统中的环路参数)；另外随着频率的升高,许多窄带系统内可以使用的结构在宽带内将不再适用。因此相对于窄带系统,宽带系统模拟基带电路的实现面临更大的挑战。模拟基带电路一般由低通滤波器(low pass filter, LPF)和可变增益放大器(variable gain amplifier, VGA)构成。本文首先从单元结构出发,论述了低通滤波器和可变增益放大器的实现方法。本文分析了低通滤波器的各种实现结构,比较了其优势和缺点。结合工艺稳定性和大带宽的要求,确定了适合宽带系统内模拟基带电路中低通滤波器的实现结构。为使电路对工艺和温度更加不敏感,本文还分析了数字和模拟自调谐校准电路的实现方法,并且电路实现了更为实用的数字校准电路。在可变增益放大器的分析中,本文主要分析了增益可变的实现方法。针对连续可变增益放大器,本文还提出了一种在低增益下显著提高电路线性度的方法。随后,本文从系统角度出发,分析了运用于射频发射机和接收机中的模拟基带的实现方法,主要包括系统指标的确定(这里主要以超宽带系统为标准),结构的选取,以及低通滤波器的近似仿真。在射频发射机和接收机中,低通滤波器最终采用5阶切比学夫近似,采用Nauta结构,这主要是考虑线性度,带外衰减,功耗以及高频应用后确定的方案。在射频接收机中,可变增益放大器采用线性度增强的源极负反馈结构以保证整个接收机线性度的性能。为了在宽带中实现WiMedia和中国标准的兼容,本文在模拟基带电路中实现了调谐功能,以实现工作频率的可重构。文章中还论述了一些辅助电路的设计方法,比如在Nauta结构中,如何合理设计共模稳定电路以满足滤波器的频率响应：可变增益放大器中,如何合理确定直流失调环路与共模反馈环路的电路参数,以获得优良的传输特性；对于采用双二次结构滤波器的线性度问题,本文通过参数提取和Matlab的仿真验证,提出了一个线性度优化的设计方案。更多还原

【Abstract】 With the development of wireless communication system, RF integrated circuit put a higher and higher requirement on the analog baseband circuit. On the one hand, since the bandwith of analog baseband partially determines the velocity of signal transmission in a RF system, it should meet the bandwith requirement; on the other hand, the wide band analog baseband circuit should reach the performance in the large range of bandwith which is much tougher than the case of its narrow bandwith counterpart. Compared to narrow ones, the circuit designers have to make more efforts to achieve the same noise or linearity performance simply because of the degradation of circuit transmission characteristic such as loopgain and of different structure that should be used when the circuit is working in a high frequency range. All the above discussion shows a greater challenge in the wide band analog baseband circuit design.Since the analog baseband circuit is generall composed of a low pass filter (LPF) and a variable gain amplifier (VGA), this thesis starts from unit cell circuit. It analyze several LPF architectures which is suitable for wide band application and concludes the advantages and disadvantages among them and finally confirm the optimized realization. In order to make the circuit insensitive to process and temperature parameters, the self adjust calibration circuit is embedded. The two kinds of calibration circuit (analog and digital) are analyzed and a digital calibration circuit is design and simulated for the wide band LPF application. When it comes to VGA, despite the realization, the thesis also puts forward a method to prominently optimize the linearity when the continuous adjusting VGA is in its low gain condition.Whereafter the thesis analyze the realization of analog baseband circuit in RF transmitter and receiver from a systematic perspective which include the confirmation of systematic performance target (taking ultra wide band as an example), choice of architectures, simulating the model of LPF. In the RF transmitter and receiver, the LPF adopts the chebychev approximation and the OTA-C architecture for the consideration of out band attenuation, power consumption and high frequency applications. In the RF receiver, the VGA makes use of linearity boosting source degeration architecture to achieve the performance target of the chain in the RF receiver. The LPF absorbs the frequency tuning fuction to be reconfigurable between Wimedia and Chinese Standards.Moreover, the thesis also discuss the design method of some assistant circuits include the common mode stability circuit in Nauta architecture, the influence the dc offset cancellation and common mode feedback have on the VGA gains, the linearity issues in the biquad architecture. In addition to the design method,optimized realizations are also proposed.更多还原