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This paper introduces electromechanical delta-sigma modulators which take mechanical forces as inputs and use micromechanical transducers in the loops. A simulator is developed in which various nonidealities could be modeled. A simulation study on the 2nd and the 3rd-order modulators with single and multi-bit quantization is presented. A novel method called complementary pulse density modulation (CPDM) is proposed to realize linear multi-bit feedback using micro actuators.

A new interface combining phased arrays and echo-planar imaging (EPI) technologies was developed for two channel breast MR EPI applications. A detailed design for a dual-channel. EPI-compatible, phased array breast coil is described. EPI digital data multiplexing, signal controlling and sampling schemes are also presented. Results from breast phantoms and patients demonstrate a 55% improvement in signal-to-noise ratio when compared to a conventional two-loop, single channel coil conliguration. This method can be easily expanded to a four or more channel. EPI-compatible, phased array system to improve field-of-view coverage and signal-to-noise ratio.

Wavelet packet division multiplexing (WPDM) is a multiple signal transmission scheme based on wavelet packets. Due to its bandwidth efficiency, channel assignment flexibility, and inherent security features, it has attracted considerable interest. However, before it can be employed as a practical multiplexing technique, the performance of WPDM in various channels has to be fully investigated. In this paper, we explore the system performance when the channel includes impulsive noise as well as Gaussian noise. After briefly reviewing the system model of WPDM, we derive an expression for the probability of error for WPDM in the presence of both impulsive and Gaussian noise. The derivation extends previous work on the performance of digital communication systems when impulsive noise and Gaussian noise are the causes of error to WPDM. For the purpose of comparison, the performance of a TDM system in the same channel environment in also evaluated. The calculations and corresponding simulation results illustrate that WPDM can provide greater immunity to impulsive noise than TDM. This result is intuitively pleasing since one noise burst, which can destroy one bit in TDM, will be spread over all the channels of a WPDM system. In each channel, the spread effects of the impulsive noise may not be strong enough to cause an error.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Publisher Summary Wavelet packet division multiplexing (WPDM) is a multiple signal transmission scheme based on the orthogonality of wavelet packet basis functions. This chapter investigates the performance of WPDM under two types of interference: (1) timing errors between the transmitter and the receiver and (2) the presence of fast flat fading. Pilot symbol assisted modulation (PSAM) is applied to combat the irreducible error because of flat fading. The probability of error of WPDM system with PSAM in flat fading channels is analyzed in the chapter. It also presents a performance comparison between WPDM and FDM. The chapter shows that the pilot spacing for WPDM can be larger than the spacing for FDM. Therefore, WPDM wastes less energy in pilot symbols and gains capacity when compared with FDM scheme.

The existing multiplexing techniques, such as TDM, FDM, and CDM, use different time slots, different frequency bands, and orthogonal codes, respectively, to distinguish each user. In this paper, a multiplexing model based on wavelet packets is presented. This model employs another kind of orthogonality -- the waveform orthogonality. In this approach, the channels are assigned to different users based on the mutual orthogonality of wavelet packets. After a brief review of the properties of wavelet packets, we can see that multiplexing based on the wavelet packets is a generalized form of TDM and FDM and it can be easily realized by the multiresolution algorithm developed for wavelet packets. In the multiplexing techniques, synchronization is an important problem. In this paper, the interference and cross- talk due to non-perfect synchronization between the receiver and transmitter are analyzed. It is demonstrated that with a suitable wavelet function, digital signals can be well recovered under noisy environments even when the synchronization is not accurate. The analysis on the synchronization also leads to the design of optimum wavelets for the application. Simulation results are presented and compared for the use of different wavelets.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A CMOS chopper-stabilized amplifier with both DC and AC offset cancellation, for capacitive readout of motion in MEMS structures, achieves 40 nV//spl radic/HZ noise floor, 10 mV DC offset, and 40 dB sensor offset reduction. The amplifier, integrated into a CMOS-MEMS accelerometer, achieves 50 /spl mu/g//spl radic/Hz noise floor.