Real-time Analog Signal Processing Research Articles

Spectrum Aggregation Dual-Band Real-Time RF/Microwave Analog Signal Processing From Microstrip Line High-Frequency Hilbert Transformer

A uniplanar microstrip line RF/microwave real-time analog signal processing (RAP) units are proposed in this article to operate concurrently at two frequencies for spectrum aggregation applications. First, a fundamental building block novel microstrip line dual-band Hilbert transformer (DBHT) is developed by integrating a dual-band 180° coupler and a dual-band delay line (DBD). The theoretical analysis is carried out to determine the relation of coupler and delay line forming closed loop resonance in the proposed circuit topology. Then, a dual-band edge detector from DBHT and a dual-band single-sideband (DBSSB) modulator composed of dual-band power divider/combiner (DBPD/DBPC), DBHT, and DBD are developed for dual-band real-time RF/microwave signal processing. To verify the proposed concept, a prototype of microstrip line DBHT working at 0.9 and 1.98 GHz is designed, and the measurement and simulation agree well with theoretical analysis. To demonstrate the real-time RF/microwave analog signal processing, a dual-band edge detector composed of DBHT is verified in the experiment. Furthermore, a prototype of microstrip line DBSSB modulator is fabricated and validated in the experiment to demonstrate the real-time single-sideband modulation at two concurrent RF/microwave frequencies.

Nonlinear Loss Model in Absorptive-Type Ferrite Frequency-Selective Limiters

Absorptive-type ferrite-based frequency-selective limiters (FSLs) utilize nonlinear (NL) phenomena in magnetized ferrites to provide real-time analog signal processing of RF/microwave electromagnetic (EM) signals. There are no commercially available modeling tools that simulate these interactions, and the development and optimization of FSLs are largely done experimentally. FSL modeling and design is complicated by NL, multiscale, and multiphysics nature of operation. In this article, an NL loss model in a ferrite is proposed and implemented in an efficient numerical algorithm. The equivalent linear magnetic loss tangent is represented in a closed form. A full-wave numerical EM model with high-fidelity meshing is set up so that material properties are assigned to each mesh element and are iteratively adjusted depending on the local magnetic field. The numerical model is sliced along the EM wave propagation, and an NL eigenvalue is obtained for each slice as a function of frequency, power, and external magnetic bias field and stored in lookup tables. The slices are cascaded, and power attenuation is calculated with loss changing along the wave path according to the lookup tables. The resulting data are processed to be suitable for equivalent circuit models. Numerical results for coplanar waveguide FSL are validated by measurements. The proposed modeling approach is useful for engineering FSL devices.

Enhanced Bandwidth and Diversity in Real-Time Analog Signal Processing (R-ASP) Using Nonuniform C-Section Phasers

We show that a continuously nonuniform coupled-line C-section phaser, as the limiting case of the step-discontinuous coupled-line multisection commensurate and non-commensurate phasers, provides enhanced bandwidth and diversity in real-time analog signal processing (R-ASP). The phenomenology of the component is explained in comparison with the step-discontinuous using multiple-reflection theory and a simple synthesis procedure is provided. The bandwidth enhancement results from the suppression of spurious group delay harmonics or quasi-harmonics, while the diversity enhancement results from the greater level of freedom provided by the continuous nature of the nonuniform profile of the phaser. These statements are supported by theoretical and experimental results.

Surface Acoustic Wave Functional Devices Coupled with Film-Bonded Semiconductor Active Elements

In this study, we investigate a future high-speed real time analog signal processing circuit by co-integrating a semiconductor active array device with a surface acoustic wave (SAW) device in one chip. We propose a novel semiconductor coupled SAW functional device with a traveling wave amplifier structure and show basic characteristics of the devices using a circuit simulator. Using epitaxial liftoff film bonding technology, we fabricated a basic test device on LiNbO3 substrate and measured the basic characteristics of the functional device.

Microcalorimeter EDS: Benefits and Drawbacks

The commercial introduction of high-count-rate, near-room-temperature silicon drift detectors (presently available) and high-energy-resolution cryogenic microcalorimeters (forthcoming) is an exciting development in x-ray microanalysis, in which detector choices and capabilities have been essentially stable for many years. Both of these new energy-dispersive detectors promise improved capabilities for specific applications, e.g., faster EDS mapping (silicon drift detectors) and nanoscale particle analysis (microcalorimeters). In this paper, we briefly examine some of the important benefits and drawbacks of microcalorimeter EDS (μcal EDS) for x-ray microanalysis.The primary benefit of μcal EDS over conventional semiconductor EDS is the factor of ∼ 20 improvement in energy resolution (∼ 4 eV, real-time analog signal processing), as shown in Figure 1.

A Digital Readout Scheme for Arrays of Microcalorimeter X-Ray Detectors

While the performance of single-pixel microcalorimeter x-ray detectors has been shown to be very useful for microanalysis1, arrays of microcalorimeters will have a further impact on energy dispersive spectroscopy (EDS) by providing higher total count rates and larger effective areas. We are developing a system with a 32x32 pixel array with a total area of 40 mm2 and with a total count rate between 105 and 106 s-1. One of the challenges in constructing an array-based system will be the readout electronics.In a typical microcalorimeter EDS setup, shown in Fig. 1, the microcalorimeter is readout using a cryogenic amplifier (SQUID system) and analog feedback electronics to control the SQUID. The signal from the room-temperature SQUID electronics is either attached to a spectroscopy-grade shaping amplifier and MCA for real-time analog signal processing or attached to a digitizer for optimal pulse processing.

Reading a Neural Code

Traditional approaches to neural coding characterize the encoding of known stimuli in average neural responses. Organisms face nearly the opposite task--extracting information about an unknown time-dependent stimulus from short segments of a spike train. Here the neural code was characterized from the point of view of the organism, culminating in algorithms for real-time stimulus estimation based on a single example of the spike train. These methods were applied to an identified movement-sensitive neuron in the fly visual system. Such decoding experiments determined the effective noise level and fault tolerance of neural computation, and the structure of the decoding algorithms suggested a simple model for real-time analog signal processing with spiking neurons.

A Short History of Microwave Acoustics

Microwave acoustics may be defined as the subject embodying the propagation of acoustic waves in solid-state materials at-micron-order wavelengths where analysis, design, and componentry realizations are similar to those used by the microwave engineer exploiting electromagnetic waves. Microwave acoustics has a short history, being about 25 years old, but is underpinned by the theory of sound propagation due to Lord Rayleigh of 100 years ago. Microwave acoustic components inherently have several distinct physical origins including volume acoustic waves in solids excited by piezoelectric thin-film transducers and magnetic propagating modes in yttrium iron garnet, both at conventional microwave frequencies; the later surface acoustic-wave (SAW) technology for operation at VHF/UHF and the realm of acoustooptics, which can embody any of the earlier three. Over its 25-year history, microwave acoustics has matured to become a necessary building-block in many radar and communication systems for efficiently carrying out real-time analog signal processing. Contributions to microwave acoustics have been truly international and have spanned many diverse disciplines. The growth of this subject has led to the formation of several companies dedicated to its application.