Radio Frequency Receiver Research Articles

Effective noise estimation and filtering from correlated multiple-coil MR data

Modern magnetic resonance (MR) imaging protocols based on multiple-coil acquisitions have carried on a new attention to noise and signal statistical modeling, as long as most of the existing techniques for data processing are model based. In particular, nonaccelerated multiple-coil and GeneRalized Autocalibrated Partially Parallel Acquisitions (GRAPPA) have brought noncentral-χ (nc-χ) statistics into stake as a suitable substitute for traditional Rician distributions. However, this model is only valid when the signals received by each coil are roughly uncorrelated. The recent literature on this topic suggests that this is often not the case, so nc-χ statistics are in principle not adequate. Fortunately, such model can be adapted through the definition of a set of effective parameters, namely, an effective noise power (greater than the actual power of thermal noise in the Radio Frequency receiver) and an effective number of coils (smaller than the actual number of RF receiving coils in the system). The implications of these artifacts in practical algorithms have not been discussed elsewhere. In the present paper, we aim to study their actual impact and suggest practical rules to cope with them. We define the main noise parameters in this context, introducing a new expression for the effective variance of noise which is of capital importance for the two image processing problems studied: first, we propose a new method to estimate the effective variance of noise from the composite magnitude signal of MR data when correlations are assumed. Second, we adapt several model-based image denoising techniques to the correlated case using the noise estimation techniques proposed. We show, through a number of experiments with synthetic, phantom, and in vivo data, that neglecting the correlated nature of noise in multiple-coil systems implies important errors even in the simplest cases. At the same time, the proper statistical characterization of noise through effective parameters drives to improved accuracy (both qualitatively and quantitatively) for both of the problems studied.

A multi-mode multi-band RF receiver front-end for a TD-SCDMA/LTE/LTE-advanced in 0.18-μm CMOS process

A fully integrated multi-mode multi-band directed-conversion radio frequency (RF) receiver front-end for a TD-SCDMA/LTE/LTE-advanced is presented. The front-end employs direct-conversion design, and consists of two differential tunable low noise amplifiers (LNA), a quadrature mixer, and two intermediate frequency (IF) amplifiers. The two independent tunable LNAs are used to cover all the four frequency bands, achieving sufficient low noise and high gain performance with low power consumption. Switched capacitor arrays perform a resonant frequency point calibration for the LNAs. The two LNAs are combined at the driver stage of the mixer, which employs a folded double balanced Gilbert structure, and utilizes PMOS transistors as local oscillator (LO) switches to reduce flicker noise. The front-end has three gain modes to obtain a higher dynamic range. Frequency band selection and mode of configuration is realized by an on-chip serial peripheral interface (SPI) module. The front-end is fabricated in a TSMC 0.18-μm RF CMOS process and occupies an area of 1.3 mm2. The measured double-sideband (DSB) noise figure is below 3.5 dB and the conversion gain is over 43 dB at all of the frequency bands. The total current consumption is 31 mA from a 1.8-V supply.

A single active nanoelectromechanical tuning fork front-end radio-frequency receiver

Nanoelectromechanical systems (NEMS) offer the potential to revolutionize fundamental methods employed for signal processing in today’s telecommunication systems, owing to their spectral purity and the prospect of integration with existing technology. In this work we present a novel, front-end receiver topology based on a single device silicon nanoelectromechanical mixer-filter. The operation is demonstrated by using the signal amplification in a field effect transistor (FET) merged into a tuning fork resonator. The combination of both a transistor and a mechanical element into a hybrid unit enables on-chip functionality and performance previously unachievable in silicon. Signal mixing, filtering and demodulation are experimentally demonstrated at very high frequencies ( > 100 MHz), maintaining a high quality factor of Q = 800 and stable operation at near ambient pressure (0.1 atm) and room temperature (T = 300 K). The results show that, ultimately miniaturized, silicon NEMS can be utilized to realize multi-band, single-chip receiver systems based on NEMS mixer-filter arrays with reduced system complexity and power consumption.

Design and Noise Optimization of RF Low Noise Amplifier for IEEE Standard 802.11A WLAN

Low noise amplifier is the front end block of radio-frequency receiver system. Its design required various characteristics such as power gain, noise figure, insertion losses and power consumption. In this paper we have proposed a single stage low noise amplifier design with high gain and low noise using inductive source degeneration topology for frequency range of 3 GHz to 7 GHz and also use the active biasing devices. A range of devices like inductors and capacitors are used to achieve 50 � input impedance with a low noise factor. The design process is simulated process is using Advance Design System (ADS) and implemented in TSMC 0.18 µm CMOS technology. A single stage low noise amplifier has a measured forward gain 25.4 dB and noise figure 2.2 dB at frequency 5.0 GHz.

ESD Protection Design for 60-GHz LNA With Inductor-Triggered SCR in 65-nm CMOS Process

To effectively protect the radio-frequency (RF) circuits in nanoscale CMOS technology from electrostatic discharge (ESD) damages, the silicon-controlled rectifier (SCR) devices have been used as main on-chip ESD protection devices due to their high ESD robustness and low parasitic capacitance. In this paper, an SCR device assisted with an inductor is proposed to improve the turn-on efficiency for ESD protection. Besides, the inductor can be also designed to resonate with the parasitic capacitance of the SCR device at the selected frequency band for RF performance fine tuning. Experimental results of the ESD protection design with inductor-triggered SCR in a nanoscale CMOS process have been successfully verified at 60-GHz frequency. The ESD protection design with inductor-triggered SCR has been implemented in cell configuration with compact size, which can be directly used in the RF receiver circuits. To verify the RF characteristics and ESD robustness in the RF receiver, the inductor-triggered SCR has been applied to a 60-GHz low-noise amplifier (LNA). Verified in a silicon chip, the 60-GHz LNA with the inductor-triggered SCR can achieve good RF performances and high ESD robustness.

Computer-Aided Optimization of a 5.8 GHz ETC Receiver Front-End Design Using Memetic Algorithm

Systematic level design and optimization of a Radio Frequency (RF) receiver is a multi-dimensional problem and it is usually an arduous and experience-based work because of the trade-off between various system parameters. In the mean while, co-operated with Genetic Algorithm (GA) and local search, Memetic Algorithm (MA) gradually becomes popular to solve multi-dimensional optimization problems, and it can be an efficient method for computer-aided design of RF receivers. In this paper, the MA method was adopted to aid the design of a 5.8 GHz RF receiver front-end. The transfer function for the signal-to-noise ratio at the front-end output (SNRout) was first derived based on the gain, noise figure and inter-modulation product of each individual circuit component, and the transfer function was then used as the required fitness function for the MA method. The efficacy of the proposed method was validated by ADS simulations.

Real‐time magnetic resonance imaging of normal swallowing

To evaluate the use of a novel real-time magnetic resonance imaging (MRI) technique for the assessment of normal swallowing dynamics. In a cohort of 10 healthy subjects, real-time MRI movies at 24.3 frames per second were obtained in sagittal, coronal, and axial orientation during self-controlled swallows of 5 mL pineapple juice as oral contrast bolus. All studies were performed with the use of a commercial MRI system at 3 T combining two sets of radiofrequency receiver coils. Real-time movies relied on a fast low-angle shot (FLASH) MRI sequence with radial undersampling and image reconstruction by nonlinear inversion yielding 41.23 msec acquisition time for an in-plane resolution of 1.5 mm. Evaluations focused on clinical image quality as well as visualization and temporal quantification of distinct swallowing functions. Throughout the entire process, the swallowing dynamics were well depicted and characterized with almost no visible image artifacts in all subjects. The mid-sagittal plane turned out to be most valuable. The movies allowed for a quantitative determination of the temporal pattern of all swallowing events. The proposed real-time MRI technique yields noninvasive, robust, and quantitative access to the physiology of normal swallowing in healthy subjects at high temporal resolution and image quality.

Experimental Demonstration of the Proportionality of the RF Reception Field to a Complex Conjugate of B1^|^minus;

We demonstrated that the radiofrequency (RF) reception field is proportional to B₁⁻* straightforwardly in magnetic resonance (MR) imaging experiments at 4.7 T. We compared maps of the reception field and the B₁⁻ of a saline phantom in magnitude and phase. First, we measured the image using an adiabatic spin echo (ASE) sequence with homogeneous excitation. That image corresponds to a map of the reception field. Next, we rotated the RF coil with the sample 180° around the vertical axis to measure the map of the transmission field that corresponded to B₁⁻ in the original configuration. The magnitude of the distribution fields of the reception field and B₁⁻ maps was almost identical. Examining the phases of the ASE images in the original and inverted configurations, we observed almost the same distribution in both phase maps, which indicated the proportionality of the reception field to B₁⁻*.

A NOVEL ARCHITECTURE FOR PEER-TO-PEER INTERCONNECT IN MILLIMETER-WAVE RADIO-OVER-FIBER ACCESS NETWORKS

A novel peer-to-peer (P2P) interconnection architecture in a 60-GHz millimeter-wave (mm-wave) radio-over-flber (RoF) access network is proposed for the flrst time. In this scheme, the beating of the lightwaves for downlink and P2P transmissions at the photodiode (PD) can provide signal up-conversion for both signals. Phase noise and frequency instability between the two independent lightwaves can be eliminated by a self-heterodyned radio frequency (RF) receiver (envelope detector) located on the user terminal, which can also down- convert simultaneously the two mm-wave signals to their associated intermediate frequencies. No high-frequency clock sources or other high bandwidth devices are required for signal up/down-conversions. A proof-of-concept experimental demonstration has also been carried out. Error-free transmission of the 1-Gb/ signals is achieved over 50- km flber (downlink) or 25-km flber (P2P) plus 4-m air link.

Investigation of the Asymmetric Distributions of RF Transmission and Reception Fields at High Static Field

When radiofrequency (RF) transmission field represents B(1)(+), the reception field represents B(1)(-)*. The distribution of those maps demonstrates asymmetric features at high field magnetic resonance (MR) imaging. Both maps are in mirror symmetry to one another. Almost symmetric distribution of the B(1) field was expected on the laboratory frame in a symmetric sample loaded inside the RF coil designed to achieve a homogeneous B(1) field. Then, a simple change was made in the coordinate transformation equation of RF fields between the rotating and laboratory frames in both linear and quadrature modes to investigate the source of this feature of asymmetry. The magnitude of rotating frame components, B(1)(+) and B(1)(-), consists of the magnitude and the phase difference of the laboratory frame components. The rotating frame components differ in the sign of the sinusoidal phase difference. B(1)(+) is equal to B(1)(-) at lower field because phase changes that depend on position can be ignored. At higher fields, the magnitude component has a symmetric profile, and distribution in the phase component is antisymmetric. Thus, the distributions of B(1)(+) and B(1)(-) maps demonstrate mirror symmetry. Maps of magnitude and phase components were examined in the laboratory frame. Their maps were computed from B(1)(+) and B(1)(-) maps of the human brain and of a spherical saline phantom measured at 4.7T. It was concluded from these analytical and experimental results that the asymmetric and mirror symmetric distributions in B(1)(+) and B(1)(-) are derived from the phase difference in the laboratory frame.

Reducing the Analog and Digital Bandwidth Requirements of RF Receivers for Measuring Periodic Sparse Waveforms

In this paper, a prototype setup for measuring wideband periodic waveforms whose bandwidth surpasses the analog bandwidth of a radio-frequency receiver is presented. Three major challenges arise in the analog-to-digital stage when measuring such wideband waveforms: the availability of a high sampling rate based on a good amplitude resolution; the availability of the required analog bandwidth to capture the full waveform; and achieving the previous requirements in a cheap way. Those challenges are more pronounced when using wideband modulated signals to test nonlinear devices and when measuring/sensing wideband spectra for cognitive radio applications. For periodic signals, undersampling techniques based on the evolved harmonic sampling can be used to reduce the sampling rate requirements while satisfying a good amplitude resolution. For sparse signals, a technique based on channelization and signal separation is proposed. This technique splits the spectrum of the waveform into parallel channels, downconverts them to the analog frequency band of the analog-to-digital converter (ADC), spreads the channel information, sums them, and then digitizes with a single ADC. Using reconstruction algorithms based on l <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> -norm minimization, the information of the parallel channels can be separated. The original wideband spectrum can be then reconstructed after de-embedding of the channelization process.

이동로봇의 위치측정을 위한 개선된 초음파 위성 시스템

The localization of mobile robot in environment is a major concern in mobile robot navigation. So, many kinds of localization techniques have been researched for several years. Among them, the positioning system using ultrasound has received attention. Most of these ultrasonic positioning systems to synchronize the transmitters and receivers are used for RF (Radio Frequencies). However, due to the use of RF, the interference problems can not be avoided and the performance of radio frequencies directly affects the positioning performance. So we proposed the ultrasonic positioning system without synchronizing RF. The proposed system is based on existing USAT (Ultrasonic Satellite System) adopted infrastructure transmitting type, and consists of transmitter and receiver synchronizing modules instead of the radio frequency transmitters and receiver. The ultrasonic transmitters and receivers are synchronized individually by the transmitter and receiver synchronizing modules. In order to calculate the bias between the transmitter and receiver synchronizing modules, new positioning algorithm similar to GPS was proposed. The positioning performance of the improved USAT without synchronizing RF and the validity of the proposed positioning algorithm are verified and evaluated by experiments.

A transformer-loaded receiver front end for 2.4 GHz WLAN in 0.13 μm CMOS technology

A 2.4 GHz radio frequency receiver front end with an on-chip transformer compliant with IEEE 802.11b/g standards is presented. Based on zero-IF receiver architecture, the front end comprises a variable gain common-source low noise amplifier with an on-chip transformer as its load and a high linear quadrature folded Gilbert mixer. As the load of the LNA, the on-chip transformer is optimized for lowest resistive loss and highest power gain. The whole front end draws 21 mA from 1.2 V supply, and the measured results show a double side band noise figure of 3.75 dB, −31 dBm IIP3 with 44 dB conversion gain at maximum gain setting. Implemented in 0.13 μm CMOS technology, it occupies a 0.612 mm2 die size.

A 5 GHz 7.2 dB NF low power direct conversion receiver front-end with balun LNA

A 5GHz low power direct conversion receiver radio frequency front-end with balun LNA is presented. A hybrid common gate and common source structure balun LNA is adopted, and the capacitive cross-coupling technique is used to reduce the noise contribution of the common source transistor. To obtain low 1/f noise and high linearity, a current mode passive mixer is preferred and realized. A current mode switching scheme can switch between high and low gain modes, and meanwhile it can not only perform good linearity but save power consumption at low gain mode. The front-end chip is manufactured on a 0.13-μm CMOS process and occupies an active chip area of 1.2 mm2. It achieves 35 dB conversion gain across 4.9–5.1 GHz, a noise figure of 7.2 dB and an IIP3 of −16.8 dBm, while consuming 28.4 mA from a 1.2 V power supply at high gain mode. Its conversion gain is 13 dB with an IIP3 of 5.2 dBm and consumes 21.5 mA at low gain mode.

Broadband optimal contrast resolution beamforming

This paper proposes a novel receive beamformer architecture for broadband imaging systems that uses unique finite impulse response (FIR) filters on each channel. The conventional delay-and-sum (DAS) beamformer applies receive apodization by weighting the signal on each receive channel prior to beam summation. Our proposed FIR beamformer passes the focused receive radio frequency (RF) signals through multi-tap FIR filters on each receive channel prior to summation. The receive FIR filters are constructed to maximize the contrast resolution of the system’s spatial response. The broadband FIR beamformer produces spatial point spread functions (PSFs) with narrower mainlobe widths and lower sidelobe levels than spatial PSFs produced by the conventional DAS beamformer. We present simulation results showing that FIR filters of modest tap lengths (3–7) can yield marked improvement in image contrast and point resolution. Specifically we show that 7-tap FIR filters can reduce sidelobe and grating lobe energy by 30 dB and improve contrast resolution by as much as 20 dB compared to conventional apodization profiles. This improvement in contrast resolution comes at the expense of a decrease in beamformer sensitivity. We investigate the effects of phase aberration and show in simulation results that the multi-tap FIR beamformer outperforms the unaberrated DAS beamformer by 8–12 dB even in the presence of moderate aberration characterized by a root-mean-square strength of 28 ns and a full-width at half-maximum correlation length of 3.6 mm. We show experimental results wherein multi-tap FIR filters decrease sidelobe energy in the resulting 2D spatial response while achieving a narrow mainlobe. We also show results where the FIR beamformer improves the contrast to noise ratio (CNR) in simulated B-mode cyst images by more than 4 dB. Our algorithm has the potential to significantly improve ultrasound beamforming in any application where the system response is reasonably well characterized. Furthermore, this algorithm can be used to increase contrast and resolution in one-way beamforming systems such as acousto-optic and opto-acoustic imaging.

Mobile satellite reception with a virtual satellite dish based on a reconfigurable multi-processor architecture

Traditionally, mechanically steered dishes or analog phased array beamforming systems have been used for radio frequency receivers, where strong directivity and high performance were much more important than low-cost requirements. Real-time controlled digital phased array beamforming could not be realized due to the high computational requirements and the implementation costs. Today, digital hardware has become powerful enough to perform the massive number of operations required for real-time digital beamforming. With the continuously decreasing price per transistor, high performance signal processing has become available by using multi-processor architectures. More and more applications are using beamforming to improve the spatial utilization of communication channels, resulting in many dedicated digital architectures for specific applications. By using a reconfigurable architecture, a single hardware platform can be used for different applications with different processing needs. In this article, we show how a reconfigurable multi-processor system-on-chip based architecture can be used for phased array processing, including an advanced tracking mechanism to continuously receive signals with a mobile satellite receiver. An adaptive beamformer for DVB-S satellite reception is presented that uses an Extended Constant Modulus Algorithm to track satellites. The receiver consists of 8 antennas and is mapped on three reconfigurable M ontium TP processors. With a scenario based on a phased array antenna mounted on the roof of a car, we show that the adaptive steering algorithm is robust in dynamic scenarios and correctly demodulates the received signal.

Design of RF subsystem for dynamic spectrum sharing system in UHF band

A radio frequency (RF) subsystem used in ultra-high frequency (UHF) band dynamic spectrum sharing wireless communication system is presented.It is composed of three data RF transceivers and one cognitive RF receiver. Every RF transceiver consists of transmitting chain and receiving chain, and the receiving chain is designed the same as cognitive RF receiver. The measured error vector magnitude (EVM) of transmitting chain is less than 1.5%, when the output signal power is 30 dBm. The measured IMD3 of transmitting chain is less than −50 dBc, when the input signal is two tones with 10 kHz space, and the output signal power is 30 dBm. The measured EVM of cognitive RF receiver and receiving chain is less than 1.0% when the input signal power is −50 dBm. The measured lowest noise figure of cognitive RF receiver and receiving chain is 3.41 dB, and it shows agreement with the analysis result. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26181

Intrathoracic phrenic pacing: A 10-year experience in France

Phrenic pacing is an alternative to positive-pressure ventilation in selected patients, mostly in cases of upper spinal cord injury. We evaluated results of phrenic pacing performed by video-assisted thoracic surgery (VATS). Between 1997 and 2007, after complete neuromuscular investigations, 20 patients requiring full-time ventilation were selected for phrenic pacing (19 with posttraumatic tetraplegia and 1 with congenital central hypoventilation syndrome). Quadripolar cuff electrodes were fixed around each intrathoracic phrenic nerve via bilateral VATS. They were connected to a subcutaneous radiofrequency receiver coupled to an external radiofrequency transmitter. All patients participated in a reconditioning program beginning 2 weeks after implantation and continued until ventilatory weaning. Phrenic pacing was successful in all cases. No intraoperative complications or perioperative mortality were observed. Intraoperative testing detected stimulation thresholds in 19 patients (range, 0.05-2.9 mA). Ventilatory weaning was obtained in 18 patients. Median diaphragm reconditioning time was 6 weeks (2 weeks-11 months). Reconditioning was still in process in a young woman and was not achieved in an elderly woman with a 4-year history of tetraplegia. All the patients weaned from mechanical ventilation reported improved quality of life. Failure or delay in recovery of effective diaphragm contraction was due to nonreversible amyotrophy. VATS implantation of 4-pole electrodes around the intrathoracic phrenic nerve is a safe procedure. Ventilatory weaning correlates with the degree of diaphragmatic amyotrophy. Phrenic pacing, performed as soon as neurologic and orthopedic stabilization is achieved, is the most important prognostic factor for successful weaning.

The feasibility of endorectal MR elastography for prostate cancer localization

The objectives of this study were to evaluate the feasibility of using a rigid radio-frequency receiver endorectal coil for intracavitary prostate magnetic resonance elastography (MRE) and to demonstrate the capability of this technique for generating stiffness maps over a typical prostate volume. An endorectal coil is currently used to help improve the signal-to-noise ratio of images acquired with multiparametric magnetic resonance imaging. We propose that this same coil could also serve to generate shear waves in the prostate gland during imaging, opening up the possibility of incorporating prostate stiffness characterization into multiparametric magnetic resonance imaging. Prostate cancer has been shown to change the elasticity of tissue, suggesting that stiffness imaging (elastography) may provide supplementary diagnostic information. A rigid endorectal coil was mechanically coupled to a piezoceramic actuator and used to investigate full volume (27 slices, 2-mm thick) endorectal MRE in a prostate mimicking phantom. The low-amplitude vibrations (± 8-38 μm displacements) necessary to perform endorectal MRE did not affect the signal-to noise ratio of the coil and endorectal MRE was capable of resolving 0.1 cc (0.6 cm diameter) spherical inclusion volumes. Therefore, the results of this study, in combination with current clinical practice, motivate clinical evaluation of endorectal MRE in patients.

Ressonância magnética do tórax: aplicações tradicionais e novas, com ênfase em pneumologia

The objective of the present review study was to present the principal applications of magnetic resonance imaging (MRI) of the chest, including the description of new techniques. Over the past decade, this method has evolved considerably because of the development of new equipment, including the simultaneous interconnection of phased-array multiple radiofrequency receiver coils and remote control of the table movement, in addition to faster techniques of image acquisition, such as parallel imaging and partial Fourier acquisitions, as well as the introduction of new contrast agents. All of these advances have allowed MRI to gain ground in the study of various pathologies of the chest, including lung diseases. Currently, MRI is considered the modality of choice for the evaluation of lesions in the mediastinum and in the chest wall, as well as of superior sulcus tumors. However, it can also facilitate the diagnosis of lung, pleural, and cardiac diseases, as well as of those related to the pulmonary vasculature. Pulmonary MRI angiography can be used in order to evaluate various pulmonary vascular diseases, and it has played an ever greater role in the study of thromboembolism. Because cardiac MRI allows morphological and functional assessment in the same test, it has also become part of the clinical routine in the evaluation of various cardiac diseases. Finally, the role of MRI has been extended to the identification and characterization of pulmonary nodules, the evaluation of airway diseases, and the characterization of pleural effusion.