Fathy F. Yassa

A silicon compiler for digital signal processing: Methodology, implementation, and applications

This paper describes a fully integrated silicon compilation tool geared towards digital signal processing applications. The silicon compiler presented here uses a bit-serial architecture with a 1.25- µm CMOS cell library. It accepts as its input a high-level description language tailored for digital signal processing algorithms. The language supports the basic signal processing constructs such as multiplication, addition, subtraction, sample delays, logical operators, relational operators, as well as a conditional assignment. The compiler is equipped with behavioral, logic, and fault simulators, and performs placement and routing. The paper also details the use of the silicon compiler for the implementation of classical DSP algorithms: digital filters, FFT, programmable filters, as well as other more specialized applications such as adaptive algorithms and waveform synthesis. Moreover, some techniques are presented to implement more complex mathematical functions commonly used in DSP. The results of chip designs using the compiler and its impact on future designs are highlighted.

Optimality in the choice of the convergence factor for gradient-based adaptive algorithms

The convergence and the adaptation speed of gradient-based adaptive algorithms are controlled by the chosen value for the convergence factor μ. In this paper, the existence of an optimal value for this convergence factor is investigated for two classes of algorithms. A proof is first presented for the general case of the complex adaptive-linear-combiner (ALC). The results are applied to the complex and real LMS algorithms. This is followed by a second proof for algorithms which are linear only in a subset of their adaptive coefficients. These cases are found in IIR applications such as the hybrid-recursive, lattice-recursive, and recursive algorithms using the direct realization IIR. For each case, the optimal value is shown to be generated using instantaneous signal estimates. The resulting adaptive algorithms become self-optimizing in terms of their convergence factor, and dependence on incoming training signal levels is reduced. Moreover, a correction factor is introduced in each case to regulate the adaptation process and accommodate practical applications where additive signals are present with the desired signal.

An adaptive gating approach for X-ray dose reduction during cardiac interventional procedures

The increasing number of cardiac interventional procedures has resulted in a tremendous increase in the absorbed X-ray dose by radiologists as well as patients. A new method is presented for X-ray dose reduction which utilizes adaptive tube pulse-rate scheduling in pulsed fluoroscopic systems. In current pulsed systems, the X-ray tube is pulsed at a fixed rate of 30 pulses/sec (or higher) and an image is formed at the end of each pulse. In the proposed system, pulse-rate scheduling depends on the heart muscle activity phase determined through continuous guided segmentation of the patients electrocardiogram (ECG). Displaying images generated at the proposed adaptive nonuniform rate is visually unacceptable; therefore, a frame-filling approach is devised to ensure a 30 frame/sec display rate. The authors adopted two approaches for the frame-filling portion of the system depending on the imaging mode used in the procedure. During cine-mode imaging (high X-ray dose), collected image frame-to-frame pixel motion is estimated using a pel-recursive algorithm followed by motion-based pixel interpolation to estimate the frames necessary to increase the rate to 30 frames/sec. The other frame-filling approach is adopted during fluoro-mode imaging (low X-ray dose), characterized by low signal-to-noise ratio images. This approach consists of simply holding the last collected frame for as many frames as necessary to maintain the real-time display rate. Results of simulated system performance on an image sequence from a diagnostic study of left ventricular volume produced an average of approximately 3:1 dose reduction without compromising the diagnostic quality of the generated images. The adaptive pulsed-progressive system concept is viewed as the next evolutionary step in X-ray fluoroscopic systems.

Adaptive pulse rate scheduling for reduced dose X-ray cardiac interventional fluoroscopic procedures

Presents an approach for reducing X-ray absorbed dose during cardiac fluoroscopic interventional procedures. The approach hinges on two main concepts: (1) adapting the X-ray pulse rate to the activity of the organ under investigation (the heart); and (2) maintaining the appearance of a 30-frame/s display rate to the viewer. The first concept was accomplished through the processing of multiple sensor information to determine the onset of the various phases of ventricular motion within the cardiac cycle. For each detected phase of the cardiac cycle, a specific tube pulse rate is assigned or automatically determined (after a learning period) such that high activity phases will have higher tube rate than phases with low activity. In order to maintain a 30-frame/s display rate to the viewer, a last-frame-hold approach was used and the resultant sequence shows minimal jerkiness artifacts as a result of the adaptive-motion-dependent sampling strategy. Preliminary results of the proposed system indicate the possibility of a three-to-one reduction of the tube pulse-rate. This translates to a dose reduction of a similar ratio.<<ETX>>