Radio Frequency Signal Processing Research Articles

Spurious-Free Dynamic Range in Photonic Integrated Circuit Filters With Semiconductor Optical Amplifiers

Among other advantages, radio-frequency (RF) signal processing in the optical domain using photonic integrated circuits (PICs) offers unprecedented bandwidth and tunability. However, modern RF-photonic link applications demand PICs with high spurious-free dynamic range (SFDR). The SFDR of active PICs integrating semiconductor optical amplifiers (SOAs) is limited by amplified spontaneous emission noise and distortion caused by four-wave mixing. Here, we derive an analytical model for the SFDR of SOAs, and extend it to PICs with arbitrary transfer functions integrating many SOAs. The model is general and applicable to any photonic signal-processing circuit operating in the linear amplification regime below saturation. We show analytically the importance of SFDR-driven photonic design over noise-figure-driven design. Using this model, we explore the SFDR of coupled-ring bandpass filters integrated on a high saturation power integration platform and show SFDR as high as 117.0 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm dB}\cdot{\rm Hz}^{2/3}$</tex></formula> for filters with bandwidths in the 1–2 GHz range. We show how the material parameters and PIC design determine the SFDR. Tradeoffs between SFDR and filter bandwidth, extinction, and stopband roll-off are investigated.

An RF Signal Processing Based Diversity Scheme for MIMO-OFDM Systems

This paper proposes a diversity scheme for Multi-Input Multi-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) based on Radio Frequency (RF) signal processing. Although a 2×2 MIMO-OFDM system can double the capacity without expanding the occupied frequency bandwidth, we cannot get additional diversity gain using the linear MIMO decomposition method. The proposed method improves the bit error rate (BER) performance by making efficient use of RF signal processing. Computer simulation results show that the proposed scheme gives additional diversity gain.

Electronically controlled agile lens-based broadband variable photonic delay line for photonic and radio frequency signal processing

To the best of our knowledge, proposed for the first time is the design of an optically broadband variable photonic delay line (VPDL) using an electronically controlled variable focus lens (ECVFL), mirror motion, and beam-conditioned free-space laser beam propagation. This loss-minimized fiber-coupled VPDL design using micro-optic components has the ability to simultaneously provide optical attenuation controls and analog-mode high-resolution (subpicoseconds) continuous delays over a moderate (e.g., <5 ns) range of time delays. An example VPDL design using a liquid-based ECVFL demonstrates up to a 1 ns time-delay range with >10 dB optical attenuation controls. The proposed VPDL is deployed to demonstrate a two-tap RF notch filter with tuned notches at 854.04 and 855.19 MHz with 22.6 dB notch depth control via VPDL attenuation control operations. The proposed VPDL is useful in signal conditioning applications requiring fiber-coupled broadband light time delay and attenuation controls.

CMOS-Integrated RF MEMS Resonators

We present a design approach that enables monolithic integration of high-quality-factor <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(Q)$</tex></formula> radio-frequency (RF) microelectromechanical systems (MEMS) resonators with CMOS electronics. Commercially available CMOS processes that feature two polysilicon layers and field oxide isolation can be used to implement this approach. By using a nonplanar resonator geometry in conjunction with mechanical stress in polycrystalline silicon (poly) gate layers, we create rigid and robust mechanical structures with efficient electromechanical transduction. We demonstrate polysilicon domes with capacitive pickup and arch-bridge resonators with piezoresistive readout. The small footprint of our MEMS structures enables on-chip integration of large arrays of resonators for RF signal processing or sensing applications. Their large surface-to-volume ratio in combination with high rigidity (that alleviates stiction associated with wet chemistry processing) can make these resonators particularly useful for sensors that require surface functionalization. <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hfill$</tex></formula> [2009-0223]

Atherosclerotic plaque components characterization and macrophage infiltration identification by intravascular ultrasound elastography based on b-mode analysis: validation in vivo

Intravascular ultrasound elastography (IVUSE) is a promising imaging technique for early investigation of vulnerable plaques. Compared to radiofrequency signal processing, digital B-mode analysis is simple and of higher portability. However, rare studies have been reported validating the latter technique in vivo. In this study, we developed an IVUSE computer software system involving semi-automatic border delineation and block-matching algorithm and validated the system in vivo. Seven minipigs were fed with atherogenic diet for 40weeks. For each pig, the endothelium of one side of the renal arteries was denuded at the fifth week. With cross-correlation analysis, Lagrangian strain was calculated from two intravascular ultrasound images acquired in situ. Sixty regions of interests were selected from 35 elastograms matched well with the corresponding histological slices. Plaque types within these regions were classified as fibrous, fibro-fatty or fatty on Masson's trichrome and Oil-red O staining. Macrophage infiltration was also evaluated with immunohistology. Comparison between the mean strain value of the region of interest and the histological results revealed significant differences in strain values among different plaque types and non-diseased artery walls. The extent of macrophage infiltration was found to be correlated positively with strain values. For identification of fibro-fatty and fibrous plaques and macrophage infiltration, the system showed high sensitivity (93, 96 and 92%, respectively) and specificity (89, 76 and 66%, respectively), as revealed by receiver operating characteristic analysis. Our IVUSE system based on B-mode analysis is capable of characterizing fibrous and fibro-fatty plaques and macrophage intensity, thus holds potential for identifying vulnerable plaque.

Resonant modelling of two types of tunable carbon nanotube electromechanical oscillators

Nanoelectromechanical system oscillators have been proposed for a variety of applications, such as radio-frequency signal processing and ultrasensitive sensing. Carbon nanotube (CNT) oscillators demonstrated that the resonance frequency can be widely tuned and the motions can be self-detected. The resonant behaviours of two types of CNT oscillators with cantilevered and fixed–fixed CNT resonators are investigated by continuum mechanics-based multiphysics finite-element method simulations using a reduced order model. It is found that these two types of devices have different resonant responses when the DC bias changes: the resonant frequency of fixed–fixed CNTs increases as the DC bias increases, whereas the resonant frequency of cantilevered CNT devices decreases as the DC bias increases. The simulations also show that the fixed–fixed CNT oscillators have better tuning capabilities than the cantilevered CNT devices. Therefore in general fixed–fixed CNTs should be used in the oscillator designs, unless the unique resonant behaviour of the cantilevered devices is desired.

Synthesis of Parametric Map from Raw Ultrasound B-Scan Data

There are presented results of ultrasound radio-frequency signal sampling and processing to synthesize B-scan maps and evaluate two-dimensional visualization of ultrasound signal parameters. Our source of signal was ultrasound echoscope Mentor AdventTM A/B with mechanical scanning transducer of 11 MHz. Radio-frequency signal was digitized with digitizer Picoscope 5203. Amplitude and frequency based parameters were used for mapping B-scan ultrasound images. Standard phantom with axial resolution targets was used for the evaluation of mapping performance. We conclude that the signal processing and image transformation implemented in Matlab programs provide adequate two-dimensional mapping of B-scans. The usage of mean instantaneous bandwidth of radio frequency echoscopic signals enables to improve lateral resolution. Ill. 6, bibl. 11 (in English; summaries in English, Russian and Lithuanian).

Microwave Photonic Signal Processing

This paper reviews the recent advances in the field of radio frequency signal processing using photonic devices and subsystems or microwave photonic (MWP) signal processing. We focus our attention on the results reported during the last six years, as previous work has been adequately addressed in previous review papers. After a brief introduction to the basic concepts involved in MWP signal processing, we focus our attention on the most significant advances reported by different research groups in overcoming their main limitation factors. Recent advances in the emergent topic of integrated MWP signal processors are also covered and the novel approaches toward the evaluation of the main figures of merit are discussed. New proposed applications and future directions of work are also considered.

Switchless hybrid analog-digital variable optical delay line for radio frequency signal processing

The author proposes the design of a novel switchless variable optical delay line (VFODL) for radio frequency (rf) signals that combines an analog mode VFODL with a discrete-state VFODL. This hybrid VFODL proposes the use of a laser with smart, fast (e.g., 1 ns) wavelength tuning in combination with flat-top passband design spatially and temporally dispersive optical elements to simultaneously provide both long and short time delays, thus finely covering a wide nanoseconds delay range. An example design indicates a 9.6-ns time delay range with 6-ps increments, giving 1600 independent delays using a no-moving-parts signal-processing structure. VFODL applications include rf antenna array processing, radar testing, and precision electrical timing systems.

RF Photonics

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In parallel with the development of fiber optics for transmission of digital information, the 1970s and 1980s saw the development of techniques for the transmission of wide-bandwidth analog radio-frequency (RF) signals over optical fibers. The simultaneous need for high linearity and high signal-to-noise in RF photonic links spurred the development of lasers, modulators and detectors matched to the special needs of such links. RF photonics was also explored for the processing of RF signals by means of optically implemented filters and variable-delay lines. Commercial applications of RF photonics included cable television signal distribution and subcarrier-multiplexed digital signals. </para>

Sensitive ultrasonic delineation of steroid treatment in living dystrophic mice with energy-based and entropy-based radio frequency signal processing.

Duchenne muscular dystrophy is a severe wasting disease, involving replacement of necrotic muscle tissue by fibrous material and fatty infiltrates. One primary animal model of this human disease is the X chromosome-linked mdx strain of mice. The goals of the present work were to validate and quantify the capability of both energy and entropy metrics of radio-frequency ultrasonic backscatter to differentiate among normal, dystrophic, and steroid-treated skeletal muscle in the mdx model. Thirteen 12-month-old mice were blocked into three groups: 4 treated mdx-dystrophic that received daily subcutaneous steroid (prednisolone) treatment for 14 days, 4 positive-control mdx-dystrophic that received saline injections for 14 days, and 5 negative-control animals. Biceps muscle of each animal was imaged in vivo using a 40-MHz center frequency transducer in conjunction with a Vevo-660 ultrasound system. Radio-frequency data were acquired (1 GHz, 8 bits) corresponding to a sequence of transverse images, advancing the transducer from "shoulder" to "elbow" in 100-micron steps. Data were processed to generate both "integrated backscatter" (log energy), and "entropy" (information theoretic receiver, H(f)) representations. Analyses of the integrated-backscatter values delineated both treated-and untreated-mdx biceps from normal controls (p < 0.01). Complementary analyses of the entropy images differentiated the steroid-treated and positive-control mdx groups (p < 0.01). To our knowledge, this study represents the first reported use of quantitative ultrasonic characterization of skeletal muscle in mdx mice. Successful differentiation among dystrophic, steroid-treated, and normal tissues suggests the potential for local noninvasive monitoring of disease severity and therapeutic effects.

Analysis of Single Events Effects on Monolithic PLL Frequency Synthesizers

Frequency synthesizers are fundamental building blocks in radio frequency, communications, and analog signal processing for generating high accuracy oscillatory signals. In general, the frequency synthesizer is the most sensitive block in the system since many of the signal processing elements such as clock, filters, and up/down converters depend on the synthesizer generating a clean sinusoidal signal at the given frequency. For radiation environments, the response and the sensitivity of the phase-lock loop (PLL) and the synthesizer block is very critical. This paper examines the effect of single events (SEE) radiation on the PLL locking and steady state response. The PLL circuits operating at 2.4 GHZ were designed and fabricated using a 0.13mum CMOS process This paper presents the experimental and simulations results on the SEE radiation effects on the PLL

Nanocrystalline diamond resonator array for RF signal processing

Two-dimensional arrays of weakly coupled radio frequency (RF) nanomechanical resonators were designed and fabricated in 50–150 nm thick nanocrystalline diamond films using electron beam lithography and dry etch techniques. We present a novel resonator design that allows us to reduce fabrication tolerances and to confine the frequency spread of individual resonators within ∼ 0.6% over the entire modal frequency range up to 100 MHz. Due to an optimized plasma enhanced chemical vapor deposition (PECVD) nanocrystalline diamond deposition process, high quality factors ( Q > 8000) have been demonstrated for particular modes of vibrations in single nanomechanical resonators. 2D arrays of coupled resonators exhibit an acoustic band, formed by the splitting of the individual resonant modes. The propagation of a wide-band signal within the array has been demonstrated using a high magnification optical imaging setup with two independently controlled scanning lasers. In order to alleviate various sources of disorder in resonator arrays and to demonstrate their potential for RF signal processing, nanomechanical resonator fabrication techniques and resonator designs will be detailed and compared in this manuscript.

Two-dimensional array of coupled nanomechanical resonators

Two-dimensional arrays of coupled nanomechanical plate-type resonators were fabricated in single crystal silicon using e-beam lithography. Collective modes were studied using a double laser setup with independent positioning of the point laser drive and interferometric motion detector. The formation of a wide acoustic band has been demonstrated. Localization due to disorder (mistune) was identified as a parameter that limits the propagation of the elastic waves. We show that all 400 resonators in our 20×20 array participate in the extended modes and estimate group velocity and density of states. Applications utilizing the resonator arrays for radio frequency signal processing are discussed.

Multigigahertz range-Doppler correlative signal processing in optical memory crystals

Analog optical signal processing of complex radio-frequency signals for range-Doppler radar information is theoretically described and experimentally demonstrated using crystalline optical memory materials and off-the-shelf photonic components. A model of the range-Doppler processing capability of the memory material for the case of single-target detection is presented. Radarlike signals were emulated and processed by the memory material; they consisted of broadband (> 1 GHz), spread-spectrum, pseudorandom noise sequences of 512 bits in length, which were binary phase-shift keyed on a 1.9 GHz carrier and repeated at 100 kHz over 7.5 ms. Delay (range) resolution of 8 ns and Doppler resolution of 130 Hz over 100 kHz were demonstrated.

Variable-phase-shift-based RF-baseband codesign for MIMO antenna selection

We introduce a novel soft antenna selection approach for multiple antenna systems through a joint design of both RF (radio frequency) and baseband signal processing. When only a limited number of frequency converters are available, conventional antenna selection schemes show severe performance degradation in most fading channels. To alleviate those degradations, we propose to adopt a transformation of the signals in the RF domain that requires only simple, variable phase shifters and combiners to reduce the number of RF chains. The constrained optimum design of these shifters, adapting to the channel state, is given in analytical form, which requires no search or iterations. The resulting system shows a significant performance advantage for both correlated and uncorrelated channels. The technique works for both transmitter and receiver design, which leads to the joint transceiver antenna selection. When only a single information stream is transmitted through the channel, the new design can achieve the same SNR gain as the full-complexity system while requiring, at most, two RF chains. With multiple information streams transmitted, it is demonstrated by computer experiments that the capacity performance is close to optimum.

Signal processing in a Mach-Zehnder intensity modulator for coherent and incoherent light using copropagating and counterpropagating electrical signals

A new application of a Mach-Zehnder intensity modulator is proposed for both radio frequency and baseband signal processing. Accessing both input and output electrical ports, the equivalent of a two-tap transversal filter is easily realized allowing sine- and cosine-shape frequency responses. As only unidirectional optical propagation is utilized, the optical insertion loss can be kept low. Both coherent and incoherent light can be processed.

The Impact of Semiconductor Technology Scaling on CMOS RF and Digital Circuits for Wireless Application

The impact of CMOS technology scaling on the various radio frequency (RF) circuit components such as active, passive and digital circuits is presented. Firstly, the impact of technology scaling on the noise and linearity of the low-noise amplifier (LNA) is thoroughly analyzed. Then two new circuits, i.e., CMOS complementary parallel push-pull (CCPP) circuit and vertical-NPN (V-NPN) circuit for direct-conversion receiver (DCR), are introduced. In CCPP, the high RF performance of pMOS comparable to nMOS provides single ended differential RF signal processing capability without the use of a bulky balun. The use of parasitic V-NPN bipolar transistor, available in triple well CMOS technology, has shown to provide more than an order of magnitude improvement in 1/f noise and dc offset related problems, which have been the bottleneck for CMOS single chip integration. Then CMOS technology scaling for various passive device performances such as the inductor, varactor, MIM capacitor, and switched capacitor, is discussed. Both the forward scaling of the active devices and the inverse scaling of interconnection layer, i.e., more interconnection layers with effectively thicker total dielectric and metal layers, provide very favorable scenario for all passive devices. Finally, the impact of CMOS scaling on the various digital circuits is introduced, taking the digital modem blocks, the various digital calibration circuits, the switching RF power amplifier, and eventually the software defined radio, as examples.

Fiber chromatic dispersion and polarization-mode dispersion monitoring using coherent detection

We propose and experimentally demonstrate a nondestructive method to monitor chromatic dispersion (CD) and polarization-mode dispersion (PMD) in traffic-carrying wavelength-division-multiplexing optical systems. Coherent heterodyne detection is used to down convert the spectrum of digitally modulated signal from optical domain into radio-frequency (RF) domain. By analyzing group delay difference and polarization walkoff between different frequency components through proper RF signal processing, both CD and PMD can be precisely determined. Good agreement between experimental results and theoretical values has been obtained.

Detection performance theory for ultrasound imaging systems

A rigorous statistical theory for characterizing the performance of medical ultrasound systems for lesion detection tasks is developed. A design strategy for optimizing ultrasound systems should be to adjust parameters for maximum information content, which is obtained by maximizing the ideal observer performance. Then, given the radio-frequency data, image and signal processing algorithms are designed to extract as much diagnostically relevant information as possible. In this paper, closed-form and low-contrast approximations of ideal observer performance are derived for signal known statistically detection tasks. The accuracy of the approximations are tested by comparing with Monte Carlo techniques. A metric borrowed and modified from photon imaging, Generalized Noise Equivalent Quanta, is shown to be a useful and measurable target-independent figure of merit when adapted for ultrasound systems. This theory provides the potential to optimize design tradeoffs for detection tasks. For example it may help us understand how to push the limits of specific features, such as spatial resolution, without significantly compromising overall detection performance.