SNR Degradation Research Articles

Design and Implementation of Reference-Free Drift-Cancelling CMOS Magnetic Sensors for Biosensing Applications

Magnetic imagers, which utilize magnetic nanoparticles as labels to realize biodetection assays, hold significant promise for deployment at the point-of-use. Resonance-shift-based sensors can be realized in standard CMOS processes without post-process modifications and offer great sensitivity at low price tags. Unfortunately, CMOS resonant-shift magnetic sensors suffer significant degradation in SNR and long-term stability due to low on-chip inductor quality factors and significant noise introduced from active devices and thermal variations. This makes standard resonant-shift-based imagers undesirable for use in low-signal biodetection assays. Furthermore, and most importantly, the significant long-term drift due to slow-varying noise sources and temperature changes makes these sensors inadequate for bioexperiments which may take timescales on the order of hours to reach completion. In this paper, we propose a transformer-based approach which enables sub-parts-per-million (PPM) signal detection without the need for any thermal compensation. The approach is self-referencing, leading to significant savings in chip area by removing the need for replica reference cells. We analyze the performance of the transformer-based circuit compared to the original second-order system and demonstrate its superiority for rejecting system noise. A proof-of-concept design of a fully integrated $2 \times 2$ CMOS transformer-based magnetic sensor array is presented which achieves reference-free, sub-PPM detection of magnetic signals. The system can be powered and operated completely from a laptop USB interface and each sensing cell can consume less than 3 mW of DC power. Finally, we show the results of an initial DNA biodetection experiment which confirms the capability of the sensor to be used for realistic bioassays.

Systematic Evaluation of Microwave-Assisted Magnetic Recording

Microwave Assisted Magnetic Recording (MAMR) is a type of energy assisted recording technology that uses microwaves to assist in the recording process. This allows for the use of high anisotropy media to maintain good thermal stability at high areal densities [1]. In MAMR, a spin torque oscillator (STO) is placed between the main pole and trailing shield to generate a magnetic field at microwave frequencies. The magnetic recording trilemma [2] is overcome by reducing the coercive field of the media via this microwave field, thereby aiding in the switching of media grains. Appropriate media stack configurations for MAMR and STO optimization have been investigated by both analytical theory and micromagnetic simulation [3], [4], [5]. In this paper, MAMR performance is evaluated on a reference design using our MAMR micro-magnetic model and the results are reported using EWSNR metrics [6]. In this study, we compare performance metrics for MAMR with other recording technologies such as Perpendicular Magnetic Recording (PMR) and Heat Assisted Magnetic Recording (HAMR). Recording media dynamics are modeled using the Landau-Lifshitz-Gilbert (LLG) equation for PMR and MAMR, and utilizing the renormalized LLG method for HAMR [7]. The DC magnetic write field is a current generation PMR writer design with 55 nm physical pole width and 1.0 T peak field strength. The STO stack has an optimized geometry that applies a 3D circularly polarized AC field to the media. STO field strength (∼0.1Hk) and oscillating frequency (∼35GHz) are determined by the magnetic properties of the field generation layer (FGL) and the magnitude of the injected spin current. The magnetic head to media spacing (HMS) is fixed at 6.0 nm and head velocity is modeled to be 20 m/s. For MAMR, single layer media with varying anisotropy are considered. The PMR ECC multilayer media model, which is calibrated based on current PMR products, contains multiple magnetic layers and non-magnetic break layers that provide optimal exchange coupling. The HAMR media is a single layer L1 0 FePt media with a Curie temperature distribution of 3% and anisotropy field distribution of 10%. The down track thermal gradient used in the HAMR model is around 8K/nm, which is consistent with common near field transducer designs. The average media grain size is around 8.0 nm with 17% grain size distribution. A magnetoresistive reader with 30 nm width is used for obtaining the play back signal. Magnetic information is encoded using pseudo random bit sequences (PRBS), which mimic real user data. Figure 1 shows a comparison between PMR, HAMR and MAMR with thick free layer designs in terms of common performance metrics. Ensemble waveform analysis is used to calculate the total spatial SNR, the breakdown between transition and remanence SNR contributions, and the channel bit density (CBD) [6]. Bit error rate (BER) is calculated using a pattern dependent Viterbi detector [8]. The use of an NFT in HAMR allows the recording of much narrower tracks than PMR, with similar CBD and reasonable SNR and BER. In general, MAMR exhibits a large CBD, which may be related to intersymbol interference and track edge erasure caused by the demagnetization field. This high CBD results in much worse BER than both HAMR and PMR at all track width and linear density combinations considered. For the same ADC (shown in the last two table items in figure 1), SNR and BER are much better when the linear density is higher and the track width is larger. Since track edge demagnetization effects seem to have such a large effect in MAMR, this data suggests MAMR should aim to increase ADC via higher linear density and lower track density. For thick free layers, multi domains and multi-scattering contributions to electron’s propagation can greatly deteriorate STO performance. Therefore, SNR versus recording media Hk for MAMR with thin free layer designs below 15 nm and STO width of 40 nm is shown in Figure 2. The figure suggests an optimal for MAMR media of around 25 kOe. MAMR SNR degradation at 20 kOe is due to erasure effects for low Hk material [9]. For high anisotropy media ∼30 kOe, the transition SNR is reasonable (around 12 dB), but remanence noise is high, causing a 2 dB loss in total SNR.

Experimental characterization of the radio over fiber aided twin-antenna spatial modulation downlink.

In this paper, we present the design and the experimental demonstration of a radio over fiber (RoF) network relying on state-of-the-art spatial modulation (SM), that activates one out of multiple antennas. We propose a novel RoF-aided SM encoding scheme, where the optical single side-band signal generated by a Mach-Zehnder modulator (MZM) is used for both the antenna selection and for the classic modulated symbol selection. The SM encoding is optically processed in a centralized fashion, aiming for the reduction of power consumption and for enabling cost-effective maintenance and management, which can be employed in the context of a cloud radio access network (C-RAN) and a small-cell front-haul. Furthermore, an experimental demonstration of the proposed system is discussed and analyzed, where a 20 km standard single mode fiber (SSMF) is used for transmission. In this experiment, a 2 Gbps transmission relying on two transmit and two receive antennas is achieved with less than 1 dB SNR degradation compared to those operating without RoF.

A 12-bit 200MS/s pipeline ADC with 91 mW power and 66 dB SNDR

A 12-bit 200MS/s pipeline analog-to-digital converter (ADC) with sample-and-hold amplifier (SHA) is proposed in this paper. An innovative timing control technology is applied to the SHA in order to eliminate its nonlinear kickback, while the SHA eliminates bandwidth and timing mismatches between the input networks of the flash (sub-ADC) and of the multiplying DAC (MDAC) in the first stage, to improve the analog input bandwidth and to meet the requirements of a high-IF sampling ADC. A novel full complementary op-amp is utilized to reduce the overall power consumption of the ADC, which makes the power consumption of the SHA and of the first stage less than 20mW. A new fully differential reference buffer and a clock receiver with duty-cycle stabilizer (DCS) are applied in the prototype ADC. The jitter of the clock receiver is less than 150 fs to avoid the SNR degradation. The ADC is implemented in 0.18µm CMOS process and consumes 91mW from a 1.8V supply. The ADC achieves an SNDR of 66.10dB and an SFDR of 84.45dB with 10MHz input signal, while maintaining an SNDR >65dB and SFDR >80dB up in the entire Nyquist band. Its input signal frequency is up to 500MHz.

A Desired PAR-Achieving Precoder Design for Multiuser MIMO OFDM Based on Concentration of Measure

For multi-user multiple-input and multiple-output (MIMO) wireless communications in orthogonal frequency di- vision multiplexing systems, we propose a MIMO precoding scheme providing a desired peak-to-average power ratio (PAR) at the minimum cost that is defined as received SNR degradation. By taking advantage of the concentration of measure, we formulate a convex problem with constraint on the desired PAR. Consequently, the proposed scheme almost exactly achieves the desired PAR on average, and asymptotically attains the desired PAR at the 0.001 point of its complementary cumulative distribution function, as the number of subcarriers increases.

On the SNR Variability in Noisy Compressed Sensing

Compressed sensing (CS) is a sampling paradigm that allows to simultaneously measure and compress signals that are sparse or compressible in some domain. The choice of a sensing matrix that carries out the measurement has a defining impact on the system performance and it is often advocated to draw its elements randomly. It has been noted that in the presence of input (signal) noise, the application of the sensing matrix causes SNR degradation due to the noise folding effect. In fact, it might also result in the variations of the output SNR in compressive measurements over the support of the input signal, potentially resulting in unexpected non-uniform system performance. In this work, we study the impact of a distribution from which the elements of a sensing matrix are drawn on the spread of the output SNR. We derive analytic expressions for several common types of sensing matrices and show that the SNR spread grows with the decrease of the number of measurements. This makes its negative effect especially pronounced for high compression rates that are often of interest in CS.

High-fidelity angle-modulated analog optical link.

There has long existed a debate over whether analog or digital optical link is more suitable for wireless convergence applications. Digital link achieves the highest fidelity, with the sacrifice of huge bandwidth due to the high resolution of digitization, and large power consumption due to the exhaustive digital data recovery. Analog link avoids these drawbacks, but it inevitably suffers from the SNR degradation. In this paper, we propose the angle modulation for analog optical link, which successfully breaks the SNR ceiling of amplitude modulation, and achieves ultrahigh link fidelity. Using the digital link (CPRI) equivalent bandwidth, angle modulation exhibits around 30-dB SNR advantage over the conventional amplitude modulation. Combined with its high tolerance on link nonlinearity, angle modulation has great potential in the future SNR-hungry analog optical applications.

A new fully integrated multichannel receiver design for magnetic resonance imaging

AbsractIn this contribution, we introduce a new fully integrated receiver architecture for magnetic resonance imaging (MRI), based on CMOS technology. The design is conceived to be an excellent solution to the size, cost, and complexity problems associated with multiple MRI channels, and potentially removes a technical barrier when implementing arrays of massive numbers of coils. In contrast to conventional MRI receivers, the CMOS integrated solution allows to perform all the required signal processing within a single chip. This includes low‐noise pre‐amplification, frequency down‐conversion, filtering, and analog‐to‐digital conversion. The CMOS chip is designed to be mounted in close proximity to the MR receive coils so as to avoid both signal attenuation as well as the use of bulky coaxial cables which are normally employed to transfer the MRI signals to the spectrometer. The output MR signals from the chip are digital and therefore relatively immune to noise. Operation in the digital domain allows to perform time‐domain multiplexing on the data streams, and to replace the electrical coaxial cables with optical fibers. The simulation results of both the system‐level and the circuit‐level realizations of the new receiver showed successful reconstruction of the MR image with very minimal SNR degradation and no remarkable distortion or artifacts.

BER Analysis for Spatial Modulation in Multicast MIMO Systems

In this paper, we investigate the bit error rate (BER) for multicast multiple-input multiple-output (MIMO) systems, employing spatial modulation (SM) and its variants, called multicast SM-type MIMO systems, in Rayleigh fading channels. The system BER, here, is derived by first attaining the BER of the worst receiver of each channel realization set, and then averaging over all possible sets. We first consider the uncorrelated channels. By exploiting the system statistics, a tight BER upper bound is proposed and the diversity is discussed for the systems. We then perform the asymptotic analysis, and show that the BER of the multicast SM-type MIMO system can be alternatively analyzed by analyzing the simple point-to-point SM-type MIMO system with Weibull fading channels. Through this property, a closed-form asymptotic BER upper bound is provided and the impact of the receiver number on BER is analyzed. Subsequently, our investigation is extended to correlated channels where all the receivers share the same correlation statistics. The BER analysis is performed again through the framework similar to the uncorrelated case. In the analysis, the tight upper bound is derived and the effect of correlations is analyzed. Moreover, we provide an explicit expression for the SNR degradation caused by the receive correlation through the analysis. Finally, simulations are exploited to evaluate the BER of the multicast SM-type MIMO systems and validate the analyses.

UFMC 시스템에서 CFO의 영향

The UFMC(Universal Filtered Multi-Carrier) is one of multi-carrier transmission technique as a candidate of transmission method for the recent 5G communication system. The UFMC can be considered as the system which has both the advantages of OFDM(Orthogonal Frequency Division Multiplex) and the simplicity of FBMC(Filter Bank Multi-Carrier). CFO(Carrier Frequency Offset) causes the problem to lower the BER performance due to a mismatch between the sub-carriers in multi-carrier transmission scheme. The effect of CFO on UFMC is not greater than the OFDM. But it still degrades the system performance caused by interference between the sub-band. In this paper, we analyze the SNR degradation due to changes in the value of EsNo and CFO on UFMC system.

A novel partial volume effects correction technique integrating deconvolution associated with denoising within an iterative PET image reconstruction.

Partial volume effect (PVE) plays an important role in both qualitative and quantitative PET image accuracy, especially for small structures. A previously proposed voxelwise PVE correction method applied on PET reconstructed images involves the use of Lucy-Richardson deconvolution incorporating wavelet-based denoising to limit the associated propagation of noise. The aim of this study is to incorporate the deconvolution, coupled with the denoising step, directly inside the iterative reconstruction process to further improve PVE correction. The list-mode ordered subset expectation maximization (OSEM) algorithm has been modified accordingly with the application of the Lucy-Richardson deconvolution algorithm to the current estimation of the image, at each reconstruction iteration. Acquisitions of the NEMA NU2-2001 IQ phantom were performed on a GE DRX PET/CT system to study the impact of incorporating the deconvolution inside the reconstruction [with and without the point spread function (PSF) model] in comparison to its application postreconstruction and to standard iterative reconstruction incorporating the PSF model. The impact of the denoising step was also evaluated. Images were semiquantitatively assessed by studying the trade-off between the intensity recovery and the noise level in the background estimated as relative standard deviation. Qualitative assessments of the developed methods were additionally performed on clinical cases. Incorporating the deconvolution without denoising within the reconstruction achieved superior intensity recovery in comparison to both standard OSEM reconstruction integrating a PSF model and application of the deconvolution algorithm in a postreconstruction process. The addition of the denoising step permitted to limit the SNR degradation while preserving the intensity recovery. This study demonstrates the feasibility of incorporating the Lucy-Richardson deconvolution associated with a wavelet-based denoising in the reconstruction process to better correct for PVE. Future work includes further evaluations of the proposed method on clinical datasets and the use of improved PSF models.

周波数領域における暗号モジュールに対する電磁波解析の効率化

An efficient analysis method in the frequency domain for the extraction of information under the degradation of signal-to-noise ratio SNR is proposed. When the electromagnetic emission from the cryptographic module on the hardware is analyzed, the electromagnetic fields caused by operation on the other modules interfere to the electromagnetic field from the cryptographic module. Therefore, the amount of the measured data required for the extraction of information under the condition of degraded SNR increases and the analysis for this increase in data needs additional computation time. In order to accelerate the analysis under the degradation of SNR, we focus on only the processing of analysis target data. Furthermore, the signal of information and noises is separated with the analysis on the frequency domain. The proposed method is examined through experiments.

Video Streaming in the Multiuser Indoor Visible Light Downlink

Indoor visible light communication (VLC) using a light emitting diode (LED) transmitter provides a high-signal-to-noise (SNR) link, which is ideal for video transmission. The LED lights illuminate their own attocells and convey video streams in the downlink to multiple mobile terminals (MTs). Three different transmission schemes are considered, namely: the unity frequency reuse, the higher frequency reuse factor-based transmission, and the novel vectored transmission. We then formulate the optimization problems aiming at minimizing the video distortion. This paper commences by evaluating the performance of the MT at specific positions and continues by characterizing the peak SNR (PSNR) degradation across the room. Finally, we quantify the average performance of multiple MTs randomly walking in the room. By investigating the PSNR degradation, the video rate achieved, the energy consumed, and the effects of buffering delay on the video distortion, we demonstrate that the proposed VLC system is capable of supporting high-quality multimedia transmissions.

OFDM subcarrier monitoring using high resolution optical spectrum analysis

In this paper, we demonstrate in-band OSNR monitoring of individual subcarriers in optical OFDM using a high-resolution optical spectrum analyzer. The relationships between OSNR, electrical SNR and BER at the receiver are experimentally analyzed and compared to theoretical results. A linear dependency in dB is found between electrical SNR and subcarrier OSNR for total OSNR values below 26dB. Above this limit, the correlation degree decreases due to the electrical SNR degradation at the edge subcarriers. The BER analysis per subcarrier also shows a clear correlation with the proposed in-band optical measurements.

Circuit level simulation of MRI receive chain using excitation derived from images

ABSTRACTWe introduce a novel component‐level simulation method with which to characterize the performance of the electronic interfaces and circuitry of a magnetic resonance imaging (MRI) receiver. The Matlab‐based toolbox first reconstructs idealized coil free induction decay signals from real MR images, then uses these signals to drive a transistor‐level and extracted‐layout simulation of the desired receiver architecture. The simulated receiver's outputs are read back into the toolbox, which then reconstructs the MR images. By comparing the reconstructed images with the original ones, important design characteristics, such as the circuit's noise figure, linearity, phase noise, and inter‐channel coupling, can be investigated in terms of image quality. To validate the method, a new MRI receiver architecture is designed and simulated. The architecture is a 16‐channel multiplexer, designed for a commercially available 0.35 μm CMOS technology, and employs both frequency‐division and time‐division multiplexing to form a combined output signal. The SNR degradation and the circuit's linearity determined from the MR images compare well with the SNR and linearity point predictions from conventional circuit simulations. © 2015 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 44B: 102–113, 2015

A 3.54 nJ/bit-RX, 0.671 nJ/bit-TX Burst Mode Super-Regenerative UWB Transceiver<newline/> in 0.18-<formula formulatype="inline"><tex Notation="TeX">$\mu{\rm m}$</tex></formula> CMOS

Non-coherent ultra-wideband (UWB) transceiver employing energy detector suffers from degradation in output SNR due to the squarer. A burst mode super-regenerative UWB transceiver which can recover the received signal to rail-to-rail with relatively fewer post-amplification stages is proposed. Unlike other super-regenerative receiver architectures that use oscillator, the proposed architecture employs a positive feedback loop to achieve the super-regeneration of received signal and thus eliminates the need for external resonator or quench signal. The transceiver is suitable for low data rate sensor networks application covering spectrum of 3-5 GHz. Manufactured in CMOS 0.18-μm technology, the transceiver occupies an area of 2.2 mm × 2 mm. By exploiting the duty cycle and the transceiver on-time through the burst mode operation for a given data rate of 1 Mbps, it can achieve transmitter energy efficiency of 0.671 nJ/bit and receiver energy efficiency of 3.54 nJ/bit.

Stray Capacitance Between Magnetic Resonance Imaging Coil Elements: Models and Application to Array Decoupling

The role of capacitive coupling between RF coil elements of MRI arrays is studied extensively in this paper and comprehensive models are obtained. At higher MRI frequencies, capacitive coupling greatly impacts coil coupling and therefore cannot be neglected. We compare lumped and distributed capacitance models and show that they correctly predict impedance variations due to stray and intentional mutual capacitance. The distributed model takes into account the dispersed nature of the mutual impedance, and it is more accurate than the lumped model. The value of stray capacitance obtained by fitting simulated results is shown to depend strongly on substrate and phantom permittivity, while being mostly invariant to changes in frequency. A novel result of this investigation is a method of completely eliminating mutual impedance between adjacent coils, including the mutual resistance. Until recently it was believed that only mutual reactance could be eliminated with lossless passive circuits. The SNR performance of two and four coil arrays with varying degrees of coupling is compared, showing that there is no SNR degradation when the mutual resistance is eliminated in addition to mutual reactance. This result has applications in arrays used in transmission, where mutual resistance leads to losses that degrade transmit efficiency.

A Reconfigurable Direct RF Receiver With Jitter Analysis and Applications

In typical direct radio frequency (RF) sampling receivers, the sample clock jitter results in SNR degradation on received signals that increases log linearly with RF signal frequency. De-jittering received signals is computationally expensive, especially for wideband communications signals, because the induced jitter on received signals varies as a function of RF signal frequency. This paper considers a reconfigurable direct RF receiver (RDRFR) that has a stair-step jitter pattern as a function of RF signal frequency. The RDRFR uses a two-stage sampling circuit. In the first stage, the RF input is bandpass filtered and pulse sampled without quantizing the signal. The discrete-time analog signal is then interpolated with a continuous time low-pass filter, then sampled and quantized by a traditional analog-to-digital converter. With this two-stage sampling circuit, the induced signal jitter from the RF sampling is identical for all in-band signals and is the same to within an integer scale factor for all signals, in-band or out-of-band. This key circuit property means that it is possible to remove jitter with very low computational complexity in the RDRFR. Furthermore, this result can be exploited to improve system performance with non-ideal anti-alias filters by identifying non-desired signals caused by out-of-band leakage.

Stackelberg Game Based Cooperative User Relay Assisted Load Balancing in Cellular Networks

We propose a Stackelberg game based cooperative user relay assisted load balancing (LB) scheme to tackle SNR degradation problem of shifted cell-edge users which commonly occurs in a conventional direct handover LB scheme. In the proposed scheme, users from a lightly loaded cell can be selected as cooperative user-relays and will be paid by the shifted cell-edge users. Stackelberg game theory is applied to optimize the strategies of both the user relays and shifted cell-edge users, in order to maximize both of their utilities in terms of SNR and payment. Theoretical analysis and simulation study are undertaken to show the effectiveness of the proposed scheme.

Design Methodology for Voltage-Overscaled Ultra-Low-Power Systems

This paper proposes a design methodology for voltage overscaling (VOS) of ultra-low-power systems. This paper first proposes a probabilistic model of the timing error rate for basic arithmetic units and validates it using both simulations and silicon measurements of multipliers in 65-nm CMOS. The model is then applied to a modified K-best decoder that employs error tolerance to reveal the potential of the framework. With simple modifications and timing error detection-only circuitry, the conventional K-best decoder improves its error tolerance in child node expansion modules by up to 30% with less than 0.4-dB SNR degradation. With this error tolerance, the supply voltage can be overscaled by 12.1%, leading to 22.5% energy savings.