基于ADS的微带抽头式发夹型带通滤波器的设计

微带滤波器在通信系统中起着非常重要的作用,其性能的好坏直接影响着整个通信系统的性能。传统的设计滤波器的方法要通过理论进行大量的计算,计算过程繁杂。文章简要介绍了微带抽头式发夹型带通滤波器的设计理论以及如何通过ADS软件进行设计和优化仿真,并结合具体实例验证其可行性。     

Design of minimum sensitivity multiple loop feedback bandpass active filters

A method is described for determining multiple loop feedback topologies which yield minimum sensitivities for symmetrical, all-pole bandpass filters. The procedure begins with a follow-the-leader feedback (FLF) topology and additional feedback loops are constructed until minimum sensitivity is achieved. Filters comprised of identical second-order sections and non-identical sections, respectively, are considered.     

A new type of wave digital filter

This paper proposes a new wave digital filter derived from doubly terminated LC-ladder networks by replacing each series or shunt arm element of the ladder by its equivalent digital two-port. It is shown that such two-ports may be cascaded without the use of adapters defined by Fettweis (1). A number of realizations of the wave digital two-ports, which are canonic with respect to both multipliers and delays, have been obtained. Also a realization which is canonic with respect to multipliers only is given and an example considered using this realization. The sensitivity of this filter with respect to the multiplier coefficient changes due to finite word length is compared with the conventional cascaded digital filter and also the one proposed by Renner and Gupta. It is found that the proposed filter appears to be a more desirable form of implementation than the conventional cascade form and comparable to that of Renner and Gupta (2).     

A new type of transitional filter based on summation of polynomials

A new transitional filter based on the sum of filter polynomials is proposed and discussed. It shall be shown that the approach allows for greater flexibility in adjusting passband and stopband gain shapes. The sensitivity of the filter transfer function is analyzed and related to the approximation problem. Some new modified classical filters are also derived including maximally flat (Butterworth) and equiripple (Chebyshev) types. Several examples of combining Butterworth, Chebyshev and sync-tuned filters are presented and compared to those obtained using the conventional product method. The new transitional filter provides an alternative to other forms and provides a means for isolating the effects of non-uniformly distributed pole angles.     

A family of proportionate normalized subband adaptive filter algorithms

In this paper, the concept of proportionate adaptation is extended to the normalized subband adaptive filter (NSAF), and seven proportionate normalized subband adaptive filter algorithms are established. The proposed algorithms are proportionate normalized subband adaptive filter (PNSAF), μ‐law PNSAF (MPNSAF), improved PNSAF (IPNSAF), the improved IPNSAF (IIPNSAF), the set-membership IPNSAF (SM-IPNSAF), the selective partial update IPNSAF (SPU-IPNSAF), and SM-SPU-IPNSAF which are suitable for sparse system identification in network echo cancellation. When the impulse response of the echo path is sparse, the PNSAF has initial faster convergence than NSAF but slows down dramatically after initial convergence. The MPNSAF algorithm has fast convergence speed during the whole adaptation. The IPNSAF algorithm is suitable for both sparse and dispersive impulse responses. The SM-IPNSAF exhibits good performance with significant reduction in the overall computational complexity compared with the ordinary IPNSAF. In SPU-IPNSAF, the filter coefficients are partially updated rather than the entire filter at every adaptation. In SM-SPU-IPNSAF algorithm, the concepts of SM and SPU are combined which leads to a reduction in computational complexity. The simulation results show good performance of the proposed algorithms.     

华莱士与达尔文的分歧

华莱士与达尔文在性别二态性、杂交与杂种不育及人类的起源问题上存有分歧：达尔文采取多元论,在自然选择学说中引入性选择与相关律的解释,华莱士则坚持适应主义的自然选择一元论,但在人类进化问题上引入了唯灵论的超自然解释。分歧反映出达尔文主义在“非达尔文革命”中的困境：遗传学的不足与进步主义的盛行使神学进化论与科学进化论妥协的可能依然存在。,     

A self-tuning hybrid active noise control system

Active Noise Control (ANC) systems are increasingly used to reduce environmental noises. A hybrid ANC system is a combination of feedforward and feedback structures in which the anti-noise signal is generated using both structures. Employing the advantages of feedforward and feedback structures enables a hybrid structure to have a high performance in controlling unwanted noise. The step size of filters used in ANC systems plays an essential role in its performance. Any variation from the appropriate value leads to divergence or inefficiency of the noise controller system. These parameters are often set experimentally, which is a time-consuming task. In addition, there is no guarantee that the system can adapt itself to situational changes. The objective of this paper is to propose a new self-tuning hybrid ANC method. Using this technique, the system continuously estimates the parameters during its operation. Results of computer simulations demonstrate the robustness of the proposed method.     

Two-dimensional casual filter approximation using a strictly causal filter

A technique is developed for approximating a two-dimensional (2-D) causal recursive digital filter using a strictly casual filter. This is done via singular value decomposition of two finite Hankel matrices and a certain mapping technique. Since the resulting filter is simpler than a causal filter and it is separable in the denominator, the implementation is advantageous and the stability check is very easy. An example is given to illustrate the utility of the proposed technique.