Soft X-ray Absorption and Photoemission Spectroscopy Study of Cobalt-Based Thermoelectric Oxides: \hbox{Ca}_3\hbox{Co}_4\hbox{O}_9, \hbox{Ca}_3\hbox{Co}_2\hbox{O}_6, and \hbox{Bi}_{2}\hbox{Sr}_{2}\hbox{Co}_2\hbox{O}_{y}

The electronic structures of Co-based potential thermoelectric (TE) oxides, including $\hbox{Ca}_3\hbox{Co}_4\hbox{O}_9$ and $\hbox{Bi}_{2}\hbox{Sr}_{2}\hbox{Co}_2\hbox{O}_{y}$ (y = 8 + δ) single crystals and polycrystalline $\hbox{Ca}_3\hbox{Co}_2\hbox{O}_6$ , have been investigated by employing soft x-ray absorption spectroscopy (XAS) and photoemission spectroscopy (PES). Co 2p XAS measurements show that Co ions are nearly trivalent ( $\hbox{Co}^{3+}$ ) in all of these Co-based TE oxides with a small mixture of $\hbox{Co}^{4+}$ ions in $\hbox{Bi}_{2}\hbox{Sr}_{2}\hbox{Co}_2\hbox{O}_{y}$ . Valence-band PES and O 1s XAS measurements show that the occupied Co 3d states are located at the top of the valence bands and that the lowest unoccupied states have the primarily Co 3d character, respectively. These findings suggest the importance of the Co 3d electronic structures in determining TE properties of these Co-based oxides.     

A 97 dB 400 MHz rail to rail fully differential opamp based on split length FGMOS-MOS cell

Recently introduced MOS-FGMOS split length cell has been used to increase the DC gain of a fully differential op amp. Resultant proposed opamp structure exhibits gain of 97 dB and unity gain bandwidth of 400 MHz with power consumption of 1.2 mW. An opamp design has been verified with Cadence Spectre using a 130 nm technology at 1.2 V and has a slew rate of \(53\,\hbox {V}/\mu \hbox {s}\) with a phase margin of \(78^{\circ }\) .     

Cooperative Spectrum Sensing with Adaptive Double-Threshold Based Energy Detector in Cognitive Radio Networks

Spectrum sensing is one of the key functionalities in the implementation of cognitive radio. It is used to sense the unused spectrum in an opportunistic manner. In this paper, we propose an energy detector with adaptive double-threshold for spectrum sensing, to optimize the detection performance at a fixed probability of false alarm $(\text{ P }_\mathrm{f})$ i.e. 0.1, which also overcomes sensing failure problem. In the present work, the detection threshold is made adaptive to the fluctuation of the received signal power in each local detector of cognitive radio (CR) user. Simulation results show that proposed scheme optimizes better detection performance and outperforms both conventional energy detector and cooperative spectrum sensing (CSS) method by 12.8 and 3.3 % at $-$ 8 dB signal to noise ratio (SNR), respectively. While utilizing CSS with proposed adaptive double-threshold scheme, where each CR user use a double threshold detectors for local detection and send detection decisions to fusion center (FC) to give the final decision based on hard decision rule. It is further found that CSS with adaptive double-threshold improves detection performance around 26.8 and 7.6 % as compare to CSS with single threshold and Hierarchical with quantization method at $-$ 10 dB SNR, respectively, under the case when a small number of sensing nodes are used in spectrum sensing.     

Ultra-Low Power Read-Decoupled SRAMs with Ultra-Low Write-Bitline Voltage Swing

We propose an ultra-low power memory design method based on the ultra-low ( \(\sim \) 0.2 V) write-bitline voltage swing to reduce the write power dissipation for read-decoupled SRAM (RD-SRAM) cells. By keeping the write bitlines at ground level (0 V) during standby and charging them to a low voltage \(V_\mathrm{L}\) ( \(\sim \) 0.2 V) during write operations, the power dissipation for the write bitlines is greatly reduced (0.2 V/ \(V_\mathrm{DD})^{ 2 }\,\times \) 100 %) due to reduced voltage swing (from \(V_\mathrm{DD }\)  = 1.2 to 0.2 V) on the write bitlines. The proposed method is applicable to both dual-voltage and single-voltage operations. We analyze the proposed ultra-low write-bitline voltage swing method and investigate its reliability based on 10K Monte-Carlo simulations. We further verify the functionality and performance of our proposed design through measurements on the fabricated prototypes based on the 65 nm CMOS process. By means of a \(256 \times 64\) bit RD-SRAM memory implementation, we show that our proposed method reduces 87 % write power dissipation when compared to a conventional design.     

Anisotropic Thermopower of the Kondo Insulator \hbox {CeRu}_4\hbox {Sn}_6

The intermetallic compound \(\hbox {CeRu}_4\hbox {Sn}_6\) has been tentatively classified as Kondo insulator. This class of material, especially non-cubic representatives, is not yet fully understood. Here we report thermopower measurements on single-crystalline \(\hbox {CeRu}_4\hbox {Sn}_6\) between 2 K and 650 K, along the main crystallographic directions. Large positive thermopower is observed in the directions along which the hybridization is strong and a Kondo insulating gap forms. A negative contribution to the thermopower dominates for the crystallographic \(c\) axis where hybridization is weak and metallicity prevails.     

A Novel 2.5–3.1 GHz Wide-Band Low-Noise Amplifier in 0.18 \upmu \hbox {m} CMOS

Aiming for the simultaneous realization of constant gain, accurate input and output impedance matching and minimum noise figure (NF) over a wide frequency range, the circuit topology and detailed design of wide broadband low noise amplifier (LNA) are presented in this paper. A novel 2.5–3.1 GHz wide-band LNA with unique characteristics has been presented. Its design and layout are done by TSMC 0.18  \(\upmu \hbox {m}\) technology. Common gate stage has been used to improve input matching. In order to enhance output matching and reduce the noise as well, a buffer stage is utilized. Mid-stages which tend to improve the gain and reverse isolation are exploited. The proposed LNA achieves a power gain of 15.9 dB, a NF of 3.5 dB with an input return loss less than \(-\) 11.6, output return loss of \(-\) 19.2 to \(-\) 19 and reverse isolation of \(-\) 38 dB. The LNA consumes 54.6 mW under a supply voltage of 2 V while having some acceptable characteristics.     

A Low-Voltage and Low-Power 3-GHz CMOS LC VCO for S-Band Wireless Applications

A fully integrated 0.18- \(\upmu \hbox {m}\) CMOS LC-tank voltage-controlled oscillator (VCO) suitable for low-voltage and low-power S-band wireless applications is proposed in this paper. In order to meet the requirement of low voltage applications, a differential configuration with two cross-coupled pairs by adopting admittance-transforming technique is employed. By using forward-body-biased metal oxide semiconductor field effect transistors, the proposed VCO can operate at 0.4 V supply voltage. Despite the low power supply near threshold voltage, the VCO achieves wide tuning range by using a voltage-boosting circuit and the standard mode PMOS varactors in the proposed oscillator architecture. The simulation results show that the proposed VCO achieves phase noise of \(-\) 120.1 dBc/Hz at 1 MHz offset and 39.3 % tuning range while consuming only \(594~\upmu \hbox {W}\) in 0.4 V supply. Figure-of-merit with tuning range of the proposed VCO is \(-\) 192.1 dB at 3 GHz.     

A low-power 2nd-order CT delta-sigma modulator with a single operational amplifier

We present a 2nd-order 4-bit continuous-time (CT) delta-sigma modulator (DSM) employing a 2nd-order loop filter with a single operational amplifier. This choice strongly reduces the power consumption, since operational amplifiers are the most power hungry blocks in the DSM. The DSM has been implemented in a 65 nm CMOS process, where it occupies an area of \(0.08\,\hbox {mm}^2\) . It achieves an SNDR of 64 dB over a 500 kHz signal bandwidth with an oversampling ratio of 16. The power consumption is \(76\,\upmu \hbox {W}\) from a 800 mV power supply. The DSM figure-of-merit is 59 fJ/conversion. The CT DSM is well suited for the receiver of an ultra-low-power radio.     

A 5 GHZ CMOS Power VCO with Novel Frequency-Modulation for RF Transmitter

A 5 GHz transformer-feedback power oscillator with novel frequency modulation (FM) up to 10 MHz is presented in this paper. The novel FM is achieved by a CMOS transistor between transformer and ground, which is designed for varying the equivalent inductance and mutual inductance of the transformer and shows no DC connection with the oscillation circuit. The major frequency tuning is realized by the variable capacitor which is controlled by a phase lock loop. The RF VCO with 210 MHz tuning range operates in class-E mode to achieve a cost-effective transmitter, which demonstrates a high DC-to-RF conversion efficiency of 39 %. A RF power of 15.1 dBm and phase noise better than \(-\) 109 dBc/Hz @ 100 kHz from the central frequency of 5.5 GHz is obtained with the biasing conditions V \(_\mathrm{ds}\) = 1.8 V and V \(_\mathrm{gs}\) = 0.65 V. The VCO also demonstrates an ultra-low voltage operation capability: with V \(_\mathrm{ds}\) = V \(_\mathrm{gs}\) = 0.6 V and DC power consumption of 9 mW, the output power is 4.5 dBm and the phase noise better than \(-\) 93 dBc/Hz @ 100 kHz. The die size of the transformer-feedback power oscillator is only \(0.4\times 0.6\) mm \(^{2}\) .     

Electronic Structure and Thermoelectric Properties of Pseudoquaternary \hbox{Mg}_{2}\hbox{Si}_{1-x-y}\hbox{Sn}_{x}\hbox{Ge}_{y}-Based Materials

A theoretical study is presented on complex pseudoternary Bi-doped \(\hbox{Mg}_{2}\hbox{Si}_{1-x-y}\hbox{Sn}_{x}\hbox{Ge}_{y}\) materials, which have recently been revealed to reach high thermoelectric figures of merit (ZT) of ～1.4. Morphological characterization by scanning electron microscopy and energy-dispersive x-ray spectroscopy indicated that the investigated samples were multiphase and that the alloy with nominal composition \(\hbox{Mg}_{2}\hbox{Si}_{0.55}\hbox{Sn}_{0.4}\hbox{Ge}_{0.05}\) contained three phases: \(\hbox{Mg}_{2}\hbox{Si}_{0.35}\hbox{Sn}_{0.6}\hbox{Ge}_{0.05}\) (Sn-rich phase), \(\hbox{Mg}_{2}\hbox{Si}_{0.65}\hbox{Sn}_{0.3}\hbox{Ge}_{0.05}\) (Si-rich phase), and \(\hbox{Mg}_{2}\hbox{Si}_{0.15}\hbox{Sn}_{0.5}\hbox{Ge}_{0.35}\) (Ge-rich phase). The electronic structure of all these phases was calculated in the framework of the fully charge self-consistent Korringa–Kohn–Rostoker method with the coherent potential approximation (KKR-CPA) to treat chemical disorder. Electron transport coefficients such as the electrical conductivity, thermopower, and the electronic part of the thermal conductivity were studied by combining the KKR-CPA technique with Boltzmann transport theory. The two-dimensional (2D) plots (as a function of electron carrier concentration and temperature), computed for the thermopower and power factor, well support the large thermoelectric efficiency detected experimentally. Finally, employing the experimental value of the lattice thermal conductivity as an adjustable parameter, it is shown that ZT ≈ 1.4 can be reached for an optimized Bi content near T ≈ 900 K in case of the nominal composition as well as the Sn-rich phase. The question of the effect of disorder on the convergence of the conduction bands and thus the electron transport properties is addressed through detailed examination of the Fermi surfaces.     

A High Gain and Low Flicker Noise CMOS Mixer with Low Flicker Noise Corner Frequency Using Tunable Differential Active Inductor

This paper presents the design of a high conversion gain and low flicker noise down conversion CMOS double balanced Gilbert cell mixer using \(0.18\,\upmu \hbox {m}\) CMOS technology. The high conversion gain and low flicker noise mixer is implemented by using a differential active inductor (DAI) circuit and cross-coupled current injection technique within the conventional double-balanced Gilbert cell mixer. A cross-coupled current bleeding circuit is used to inject the current to the switching stage to decrease the flicker noise. Instead of spiral inductor, a DAI with high tunability of the inductor and quality factor is used to tune out the parasitic capacitance effect and decrease the leakage current that has a harmonic component and produce the flicker noise. By tuning the DAI, the flicker noise corner frequency is reduced to 150 Hz. The proposed circuit is simulated with Cadence Spectra and the simulation results shows the NF of 11.2 dB, conversion gain of 23.7 dB and IIP3 of \(-6\)  dB for an RF frequency of 2.4 GHz. The excellent LO-RF, LO-IF, RF-LO and RF-IF isolations of \(-60, -110, -52\) and \(-64\)  dB are achieved respectively. The total power consumption is 10.5 mW from a 1.8 V DC power supply.     

Performance of Dualbeam MIMO for Millimeter Wave Indoor Communication Systems

Millimeter wave (MMW) communication provides high data rates for the personal area networks with the availability of 57–64 GHz unlicensed spectrum, in indoor environment. Multipath fading being pre-dominant in indoor, multi input multi output (MIMO) technology is considered to be the ideal choice compared with the existing systems. As spatial diversity in both transmit and receive enhances the diversity gain, the performance of the system is further enhanced by introducing transmit beamforming based antenna beam diversity. In classical \(2\times 2\) MIMO, a diversity gain of 4 is achieved, whereas in this work, space time block code matrix of code rate 1/2 and dualbeam \(2\times 2\) MIMO with diversity gain 8 is considered. Dualbeam is generated by antenna array with four elements per array with out of phase feed configuration. The weight vector of the beamforming network is out of phase as to reduce the interference between the beams. The dualbeam transmitter is designed with unknown channel state information. Training symbols are transmitted to train and track the channel statistics at the receiver. The proposed work is carried out for MMW indoor system. The indoor channel is modeled using Triple Saleh–Valenzuela (TSV) model that takes into account both time of arrival and the angle of arrival information of the rays. Channel estimation is done for classical MIMO and the above proposed model in both Rayleigh and TSV channel. The orthogonal beams facilitate linear processing in the receiver. Hence maximum ratio combiner with maximum likelihood decoder is used in the receiver to decode the transmitted data. Classical MIMO and dualbeam MIMO are evaluated with respect to bit error rate and channel models. An improved diversity order is achieved with dualbeam MIMO compared to classical MIMO, with a power gain of 1.6 dB. The dualbeam MIMO using TSV is found to perform better compared to dualbeam MIMO using Rayleigh in the low Energy per bit to Noise level \((\hbox {E}_{\mathrm{b}}/\hbox {N}_{0})\) with a power gain of 2 dB.     

A Rate \text{ M }_{\mathrm{T}} Full Diversity STF Block Coded 4\times 4 MIMO-OFDM System with Reduced Complexity

Multiple input multiple output (MIMO) communication systems with orthogonal frequency division multiplexing (OFDM) has a great role to play for 4G broadband wireless communications. In this paper, a space time frequency (STF) code is presented with reduced decoder complexity and to achieve code rate $\text{ M }_\mathrm{T}$ with full diversity of $\text{ M }_{\mathrm{T}} \text{ M }_{\mathrm{R}} \text{ N }_{\mathrm{b}}$ L i.e., product of number of transmit antennas ( $\text{ M }_\mathrm{T}$ ), receive antennas $(\text{ M }_{\mathrm{R}})$ , fading blocks $(\text{ N }_{\mathrm{b}})$ and channel taps (L). The maximum achievable diversity with high rate of STF block coded MIMO-OFDM is analyzed and verified by simulation results. The decoder complexity is resolved by employing several approaches like maximum likelihood (ML), sphere decoder (SD) and array processing. The performance of STF code is compared with existing layered algebraic STF code in terms of decoder complexity and bit error rate (BER). Further, the closed form expressions for BER performance of STFBC MIMO-OFDM systems are derived and evaluated for frequency selective block fading channels with MPSK constellations.     

Reductions of peak-to-average power ratio and optical beat interference in cost-effective OFDMA-PONs

The peak-to-average power ratio (PAPR) and optical beat interference (OBI) effects are examined thoroughly in orthogonal frequency-division multiplexing access (OFDMA)-passive optical networks (PONs) at a signal bit rate up to $\sim 20\,\mathrm{{Gb}}/{\hbox {s}}$ per channel using cost-effective intensity-modulation and direct-detection (IM/DD). Single-channel OOFDM and upstream multichannel OFDM-PONs are investigated for up to six users. A number of techniques for mitigating the PAPR and OBI effects are presented and evaluated including adaptive-loading algorithms such as bit/power-loading, clipping for PAPR reduction, and thermal detuning (TD) for the OBI suppression. It is shown that the bit-loading algorithm is a very efficient PAPR reduction technique by reducing it at about 1.2 dB over 100 Km of transmission. It is also revealed that the optimum method for suppressing the OBI is the TD + bit-loading. For a targeted BER of $1 \times 10 ^{-3}$ , the minimum allowed channel spacing is 11 GHz when employing six users.     

Efficient Reverse Converters for 4-Moduli Sets {2^{2n-1}-1, 2^{n}, 2^{n}+1, 2^{n}-1} and {2^{2n-1}, 2^{2n-1}-1, 2^{n}+1, 2^{n}-1} Based on CRTs Algorithm

Speed and complexity of a reverse converter are two important factors that affect the performance of a residue number system. In this paper, two efficient reverse converters are proposed for the 4-moduli sets {2 \(^{2n-1}-1\) , 2 \(^{n}\) , 2 \(^{n}+1\) , 2 \(^{n}-1\) } and {2 \(^{2n-1}\) , 2 \(^{2n-1}-1\) , 2 \(^{n}+1\) , 2 \(^{n}-1\) } with 5 \(n\) -bit and 6 \(n\) -bit dynamic range, respectively. The proposed reverse converter for moduli set {2 \(^{2n-1}-1\) , 2 \(^{n}\) , 2 \(^{n}+1\) , 2 \(^{n}-1\) } has been designed based on CRT and New CRT-I algorithms and in two-level structure. Also, an efficient reverse converter for moduli set {2 \(^{2n-1}\) , 2 \(^{2n-1}-1\) , 2 \(^{n}+1\) , 2 \(^{n}-1\) } has been designed by applying New CRT-I algorithm. The proposed reverse converters are based on adders and hence can be simply implemented by VLSI circuit technology. The proposed reverse converters offer less delay and hardware cost when compared with the recently introduced reverse converters for the moduli sets {2 \(^{n}+1\) , 2 \(^{n}-1\) ,2 \(^{n}\) , 2 \(^{2n+1}-1\) } and {2 \(^{n}+1\) , 2 \(^{n}-1\) , 2 \(^{2n}\) , 2 \(^{2n+1}-1\) }.     

Design and modeling of high-resolution multibit log-domain \Delta \Sigma modulators

Log-domain Delta-Sigma ( $\Delta \Sigma$ ) modulators are attractive for implementing analog-to-digital (A/D) converters (ADCs) targeting low-power low-voltage applications. Previously reported log-domain $\Delta \Sigma$ modulators were limited to 1-bit quantization and, hence, could not benefit from the advantages associated with multibit quantization (namely, reduced in-band quantization noise, and increased modulator stability). Unlike classical $\Delta \Sigma$ modulators, directly extending a log-domain $\Delta \Sigma$ modulator with a 1-bit quantizer to a log-domain $\Delta \Sigma$ modulator with a multibit quantizer is challenging, in terms of CMOS circuit implementation. Additionally, the realization of log-domain $\Delta \Sigma$ modulators targeting high-resolution applications necessitates minimization of distortion and noise in the log-domain loop-filter. This paper discusses the challenges of multibit quantization and digital-to-analog (D/A) conversion in the log-domain, and presents a novel multibit log-domain $\Delta \Sigma$ modulator, practical for CMOS implementation. SIMULINK models of log-domain $\Delta \Sigma$ modulator circuits are proposed, and the effects of various circuit non-idealities are investigated, including the effects of log-domain compression–expansion mismatch. Furthermore, this paper proposes novel low-distortion log-domain analog blocks suitable for high-resolution analog-to-digital (A/D) conversion applications. Circuit simulation results of a proposed third-order 3-bit class AB log-domain $\Delta \Sigma$ loop-filter demonstrate 10.4-bit signal-to-noise-and-distortion-ratio (SNDR) over a 10 kHz bandwidth with a $0.84\,V_{pp}$ differential signal input, while operating from a 0.8 V supply and consuming a total power of $35.5\,\upmu \hbox {W}.$      

A Wide Tuning Range Voltage Controlled Oscillator with a High Tunable Active Inductor

This paper presents a wide tuning range CMOS voltage controlled oscillator (VCO) with a high-tunable active inductor circuit. In this VCO circuit, the coarse frequency is achieved by tuning the integrated active inductor circuit. The VCO circuit is designed in 0.18  \(\upmu \hbox {m}\) CMOS process and simulated with Cadence Spectra. The simulation results show the frequency tuning range from 120 MHz to 2 GHz resulting in a tuning range of 94 %. The phase noise variation is from \(-\) 80 to \(-\) 90 dBc/Hz at a 1 MHz frequency offset, and output power variation is from \(-\) 4.7 to \(+\) 11.5 dBm. The active inductor power consumption is 2.2 mW and the total power dissipation is 7 mW from a 1.8 V DC power supply. By comparing the proposed VCO circuit with the general VCO topology, the results show that this VCO architecture by using the novel, high-tunable and low power active inductor circuit, presents a better performance regarding low chip size, low power consumption, high tuning range and high output power.     

Six Order Cascaded Power Line Notch Filter for ECG Detection Systems with Noise Shaping

This paper presents the design of an operational transconductance amplifier-C (OTA-C) notch filter for a portable Electrocardiogram (ECG) detection system. A six order cascaded filter is utilized to reduce the effect of the power line interference at (50/60 Hz). The proposed filter is based on a programmable balanced OTA circuit. Based on this, PSPICE post layout simulation results for the extracted filter using 0.25  \(\upmu \) m technology and operating under \(\pm \) 0.8 V voltage supply are also given. The six order notch filter provides a notch depth of 65 dB (43 dB for 4th order), input referred noise spectral density with noise shaping of 9  \(\upmu \) Vrms/ \(\surd \) Hz at the pass band frequencies and 9 mVrms/ \(\surd \) Hz at the notch (zero) frequency which provide noise shaping for the ECG signal. These results demonstrate the ability of the filter to be used for ECG signal filtering which is located within 150 Hz.     

Demonstration of using multi-band 16-QAM OFDM modulation with direct-detection in 10 GHz bandwidth for 37.3-Gb/s PON

We propose and experimentally demonstrate a 37.3 Gb/s passive optical network using four-band orthogonal-frequency-division-multiplexing (OFDM) channels within 10 GHz bandwidth. Here, the required sampling rate and resolution of digital-to-analog/analog-to-digital (DA/AD) converter are only 5 GS/s and 8 bits to accomplish the 40 Gb/s OFDM downstream rate. Moreover, to reduce the power fading and fiber chromatic dispersion issues, a $-$ 0.7 chirp parameter Mach-Zehnder modulator is used for the four-band OFDM modulation scheme. Downstream negative power penalty of $-$ 0.37 dB can be obtained at the bit error rate of $3.8\times 10^{-3}$ after 20 km standard single mode fiber transmission without dispersion compensation.     

Analysis of L-probe Proximity Fed Annular Ring Patch Antenna for Wireless Applications

In the present paper, annular ring patch antenna with L-probe feeding has been analyzed using modal expansion cavity model. The proposed antenna shows wide band and ultra wide band operation which depends on the position of L-probe feeding and position of the shorting pin. For the fundamental \(\hbox {TM}_{11}\) mode, the bandwidth and gain is found to be 38.85 % and 7.8 dBi while for higher order \(\hbox {TM}_{12}\) mode bandwidth is obtained 58.71 % with corresponding gain of 6.1 dBi. The effect of shorting pin on the proposed antenna is also studied and it is found that the radiating structure is more compact in nature and improves the bandwidth upto 47.37 % with 8.0 dBi gain. Further, the proposed antenna has broadside radiation pattern over the entire bandwidth. The theoretical results are compared with IE3D simulated results which are in good agreement.