We propose a method to derive the loop gain from the open-loop and closed-loop output impedances in a dc-dc buck converter with voltage mode and current mode controls. This enables the loop gain to be measured without injecting a signal into the feedback loop, i.e. without breaking the feedback loop; hence the proposed method can be applied to the control circuits implemented on an IC. Our simulation and experiment show that the loop gain determined by the proposed method closely matches that yielded by the conventional method, which has to break the feedback loop. These results confirm that the proposed method can accurately estimate the phase margin.

According to a new kind of permanent contactor, this paper analyses the dynamic behavior of the contactor with and without current-feedback system. And it presents a method to obtain the dynamic characteristics of the contactor with current-feedback system. The experiments prove that the method is correct. Then, it compares the contactor without current-feedback system with the one with current-feedback system. The result shows that the contactor with current-feedback system can avoid this flaw of the contactor without current-feedback system.

A new blind identification method of transfer functions between variables in feedback systems is introduced for single sweep type of MEG data. The method is based on the viewpoint of stochastic/statistical inverse problems. The required conditions of the model are stationary and linear Gaussian processes. Raw MEG data of the brain activities are heavily contaminated with several noises and artifacts. The elimination of them is a crucial problem especially for the method. Usually, these noises and artifacts are removed by notch and high-pass filters which are preset automatically. In the present paper, we will try two types of more careful preprocessing procedures for the identification method to obtain impulse functions. One is a careful notch filtering and the other is a blind source separation method based on temporal structure. As results, identifiably of transfer functions and their impulse responses are improved in both cases. Transfer functions and impulse responses identified between MEG sensors are obtained by using the method in Appendix A, when eyes are closed with rest state. Some advantages of the blind source separation method are discussed.

In a typical indoor environment such as in a building, delay spread tends to be small, which causes frequency non-selective fading. Therefore resolvable paths at the RAKE receiver can not be obtained, and effective path diversity can not be achieved. This paper proposes an artificial path diversity system in which one or multiple sectors at the base station are pre-selected according to the channel conditions for transmitting data. Each sector's signal is delayed by several chips to create artificial paths which can then be combined by using a RAKE receiver at the mobile station creating a diversity effect for an indoor environment. Moreover, only pre-selected sector antennas transmit signals to reduce inefficient signal usage in the sectors whose paths are blocked by using all sectors, therefore the transmission power is used efficiently at the base station. As a result of sector selection, the better BER performance and the reduction of interference signals between different channels can be achieved by means of sector selection. The performance of the proposed system is analyzed and demonstrated by computer simulation in a Rayleigh and log-normal fading indoor environment.