Frequency response

About: Frequency response is a research topic. Over the lifetime, 25705 publications have been published within this topic receiving 332249 citations.

Receiver employing digital filtering for use with an implantable medical device

Abstract: A receiving and filtering circuit includes an antenna, a demodulator circuit coupled to the antenna, and a digital median filter that removes high frequency content of a demodulated digital information signal to produce a filtered digital information signal corresponding to an analog data signal transmitted by a body implantable medical apparatus. The digital filter may include a multiple stage delay line coupled to a multiple tap selection device, a plurality of delay blocks coupled to a register, or a multiple stage delay line coupled to a voting unit. The voting unit produces a first binary output in response to a majority of delay line stages storing a first value, and produces a second binary output in response to a majority of delay line stages storing a second value. The digital filter may also comprise a digital signal processor. The digital filter may include a first filter block and a second filter block. The second filter block may be selectively activated or bypassed. The first filter block removes high frequency content of the digital information signal and the second filter block reduces high frequency noise at an edge of a data bit transition. A control circuit, coupled to the digital filter, provides for respective selection of data rate and frequency response characteristics of the digital filter. The digital filter may be implemented in a Field-Programmable Gate Array (FPGA) or an Application Specific Integrated Circuit (ASIC).

A fast and accurate Rayleigh fading simulator

Abstract: This paper presents a simulator that efficiently generates correlated complex Gaussian variates with a power spectral density as described by Jakes (Jakes, Jr., 1974). The simulator consists of a fixed IIR filter followed by a variable polyphase interpolator, to accommodate different Doppler rates. The IIR filter was designed using an iterative optimization technique known as the ellipsoid algorithm, following an optimization technique that is more generally applicable and can be used to approximate any given magnitude frequency response. Software to implement both the IIR filter design technique and the complex Rayleigh fading simulator itself are available at the author's Website or by email.

Discrete Blockage Detection in Pipelines Using the Frequency Response Diagram: Numerical Study

Abstract: This paper proposes the use of fluid transients as a noninvasive technique for locating blockages in transmission pipelines. By extracting the behavior of the system in the form of a frequency response diagram, discrete blockages within the pipeline were shown to induce an oscillatory pattern on the peaks of this response diagram. This pattern can be related to the location and size of the blockage. A simple analytical expression that can be used to detect, locate, and size discrete blockages is presented, and is shown able to cater for multiple blockages existing simultaneously within the system. The structure of the expression suggests that the proposed technique can be extended to situations where system parameters may not be known to a high accuracy and also to more complex network scenarios, although future studies may be required to verify these possibilities.

Adaptive Blind Background Calibration of Polynomial-Represented Frequency Response Mismatches in a Two-Channel Time-Interleaved ADC

Abstract: This paper introduces an adaptive calibration structure for the blind calibration of frequency response mismatches in a two-channel time-interleaved analog-to-digital converter (TI-ADC). By representing frequency response mismatches as polynomials, we can exploit slight oversampling to estimate the coefficients of the polynomials by using the filtered-X least-mean square (FxLMS) algorithm. Utilizing the coefficients in an adaptive structure, we can compensate frequency response mismatches including time offset and bandwidth mismatches. We develop an analytical framework for the calibration structure and analyze its performance. We show the efficiency of the calibration structure by simulations, where we include examples from the literature.