A low power tunable Gm–C filter based on double CMOS inverters in 0.35?μm

In this article, an inverter based transconductor using double CMOS pair is proposed for implementation of a second order lowpass G_m?CC Filter. The proposed operational transconductance amplifier (OTA) and biquad filter are designed using standard 0.35???m CMOS technology. Simulation results demonstrate the central frequency tunability from 10?kHz to 2.8?MHz which is suitable for the wireless specifications of Bluetooth (650?kHz), CDMA 2000 (700?kHz) and Wideband CDMA (2.2?MHz) applications. The power consumption of the filter is 445?nW and 178???W at 10?kHz and 2.8?MHz from 3.3?V supply voltage, respectively. The active area occupied by the designed filter on the silicon is 215?×?720???m². The proposed approach guarantees the upper bound on THD to be ?40?dB for 300?mVpp signal swing. Employing the double CMOS pair in the inverters causes PSRR to reach 68.6?dB which is higher than similar works.     

Compact SC frequency tuning circuit for continuous-time Gm–C filters

A novel automatic frequency tuning circuit for continuous-time filters is presented. Based on the switched-capacitor technique, the circuit offers an advantage in terms of simplicity resulting from the use of only two matched current sources, an operational amplifier with relaxed specifications and a transconductor that is a replica of the filter transconductors. Despite the simplicity of the scheme, the accuracy of the system is less than 1 % of frequency error. The circuit has been designed in a 0.5 μm CMOS technology with a 3.3 V power supply and simulation results confirm the suitability of the proposed approach.     

Pure-Mode Gm−C Biquad Filters*

A continuous time differential voltage mode G_m–C biquad and its adjoint current-mode version are described, employing FCS (floating current source) circuits as building blocks. The biquad operates in the pure mode, i.e. no resistors are used to convert internally voltage into current or vice versa. Both f_p and Q_p are tunable by current sources applied externally. The current mode version is capable of providing values of Q_p 160. Due to the increasing Loop transmission, THD improves significantly towards low frequencies. The input stage of the voltage mode version employs two OTAs, whose outputs are connected in parallel in order to add their differential inputs. This results in the hitherto unnoticed property of subtracting their common mode input, providing an open loop gain which is high for differential, but low for common mode signals.     

Engineering the current–voltage characteristics of metal–insulator–metal diodes using double-insulator tunnel barriers

The femtosecond-fast transport in metal–insulator–metal (MIM) tunnel diodes makes them attractive for applications such as ultra-high frequency rectenna detectors and solar cells, and mixers. These applications impose severe requirements on the diode current–voltage I(V) characteristics. For example, rectennas operating at terahertz or higher frequencies require diodes to have low resistance and adequate nonlinearity. To analyze and design MIM diodes with the desired characteristics, we developed a simulator based on the transfer-matrix method, and verified its accuracy by comparing simulated I(V) characteristics with those measured in MIM diodes that we fabricated by sputtering, and also with simulations based on the quantum transmitting boundary method. Single-insulator low-resistance diodes are not sufficiently nonlinear for efficient rectennas. Multi-insulator diodes can be engineered to provide both low resistance and substantial nonlinearity. The improved performance of multi-insulator diodes can result from either resonant tunneling or a step change in tunneling distance with voltage, either of which can be made to dominate by the appropriate choice of insulators and barrier thicknesses. The stability of the interfaces in the MIIM diodes is confirmed through a thermodynamic analysis.     

Universal filter using a ‘pseudo’ gyrator

A filter based on a ‘pseudo’ gyrator that simultaneously makes a low-pass, band-pass and notch transfer function is presented. By adding another amplifier, this circuit can also make a high-pass and an all-pass filter. Two prototypes using usual op. amp. or current feed-back operational amplifiers (CFOAs) are proposed. SPICE simulations and measurements on prototypes confirm the validity of the theoretical analysis.     

SIFO–VM/TIM universal biquad filter using single DVCCTA with fully CMOS realization

Analog Integrated Circuits and Signal Processing - In the presented paper, a new biquad topology is reported and described wherein five various types of filtering responses in each voltage mode and...     

An automatic procedure for the synthesis and optimization of very low-frequency Gm–C integrators

Fully integrated low frequency filters are critical cells that should be carefully designed in order to avoid excessive area occupation. In this work we propose an automatic procedure capable of optimizing the design of G_m?CC integrators, which constitute the basis of a wide class of G_m?CC filters. The optimization target is minimizing the cell area with constraints on input range and low frequency noise. Lower and upper bounds can be fixed to most quantities and design parameters in order to avoid solutions that are not compatible with the physical limitations of the process. The program has been developed within the MATLAB^? platform, exploiting the optimization toolbox. The effect of several important design parameters on the optimization of low frequency integrators has been investigated using the proposed routine. The strong interaction between noise and low frequency constraints has been demonstrated, showing the impressive impact of strict noise specifications on the occupied area. The actual effectiveness of parameters such as the current division factor or approaches such as flicker noise rejection by means of chopper modulation has been investigated. Examples of integrator synthesis, performed using the proposed procedure configured with the parameters of a commercial CMOS process, are presented. The consistence between the characteristics of the cells and the initial specifications has been checked using electrical simulations showing a maximum discrepancy with the initial specifications of nearly 80%. A semi-manual method to refine the synthesized cells and improve the accuracy is proposed.     

Excess loop delay cancellation in sigma–delta modulators

Excess loop delay in sigma–delta ( $\Sigma\Delta$ ) modulators, especially by increasing the level of noise in signal bandwidth in continuous kind of them, leads to a dramatic decrease in their efficiency. In this paper, the error originated from the loop delay is calculated analytically and a new structure for sigma–delta modulators is presented based upon this calculation. This new structure can compensate the effect of loop-delay error completely independent of amount of delay. So by changing in loop delay during system working, the proposed structure has ability to consistent itself with new conditions and re-eliminate the error. This ability is independent of being multi-bit and the order of modulator. To evaluate the efficiency of the proposed method and the corresponding structure, first and second order modulators with capability of eliminating the error of loop delay, have been designed and simulated. All of simulations show the correctness of proposed analysis. Comparison of the proposed structures with the previous works shows the effectiveness of our technique.     

Physical parameters extraction from current–voltage characteristic for diodes using multiple nonlinear regression analysis

In this work, the two-step iteration combined with the nonlinear multiple regression technique to extract physical parameters for diodes, using a simple physical-based current–voltage (I–V) model is demonstrated. This statistical method can be applied for sampling for a wide variety of diodes including light-emitting diodes (LEDs) and Schottky diodes. Our results show the technique is an accurate and systematic approach for extracting diode parameters. The calculated recombination currents indicate the recombination efficiency for LEDs and the quality for Schottky diodes.     

An improved method for the design of quadrature mirror filter banks using the Levenberg–Marquardt optimization

This paper presents an improved and efficient method for the design of a two-channel quadrature mirror filter (QMF) bank. In the proposed method, the filter bank design problem is formulated as a low-pass prototype filter design problem, whose responses in the passband and stopband are ideal and their filter coefficients value at quadrature frequency is 0.707. A new method is developed for the design of a low-pass prototype filter which minimizes the objective function by optimizing the filter taps weights using the Levenberg–Marquardt method. When compared with other existing algorithms, it significantly reduces peak reconstruction error (PRE), error in passband, stopband and transition band. Several design examples are included to show the increased efficiency and the flexibility of the proposed method over existing methods. An application of this method is considered in the area of subband coding of the ultrasound images.     

Retrieval of head–neck medical images using Gabor filter based on power-law transformation method and rank BHMT

This research aims to work on the specific medical domain. In this work, retrieval of the head–neck medical images from a database is discussed. Content-based medical image retrieval system (CBMIR) is used for retrieving the head–neck images. CBMIR is automatic and more efficient compared with the text-based approach. Shape and texture features are used for constructing feature vector. Texture feature is extracted using a modified Gabor filter based on power-law transformation method. Shape feature is extracted using rank BHMT (rank-order blur hit or miss transformation) method. Shape and texture features are combined to form a single feature vector. Threshold value very near to zero is used to retrieve images from the database. The proposed method is compared with log-Gabor filters and rank BHMT method. Combinations of modified Gabor filter with rank BHMT gave better performance than other methods.     

Performance of the variable-length stochastic gradient lattice filter in adaptive noise cancellation of nonstationary signals—A simulation case study

The variable-length filter for adaptive noise cancellation of nonstationary signals is introduced. The optimum length of number of filter stages is shown to be chosen in terms of the algorithm noise. It is shown that such an optimal filter can always act positively even when the cross-correlation between the input channels is close to zero. The performance of the variable-length stochastic gradient (SG) lattice filter is theoretically studied for a given nonstationary (time variable) system simulated on a computer. The results of the simulation are then compared with theory. It is shown that, for nonstationary signals, the variable-length filter yields a better noise reduction than the conventional LMS (Widrow et al., 1976) and lattice filters.     

Current‐mode quadrature oscillator using current differencing transconductance amplifiers

This article presents a new electronically tunable single‐element‐controlled current‐mode quadrature sinusoidal oscillator circuit using current differencing transconductance amplifiers (CDTAs). The proposed oscillator is consisted of two CDTAs, two grounded capacitors and one grounded resistor, which is beneficial to monolithic integrated circuit implementation both in CMOS and bipolar technologies. The condition of oscillation and the frequency of oscillation are independently controllable. The frequency of oscillation can also be electronically controlled by adjusting the bias current of CDTA. The circuit provides four quadrature current outputs and two quadrature voltage outputs. The current output terminals possess high impedance level. PSPICE simulation results are used to verify the performance of the proposed circuit implemented at the transistor level. The measurement results support the computer simulations.     

High-accuracy current sensing circuit with current compensation technique for buck–boost converter

A novel on-chip current sensing circuit with current compensation technique suitable for buck–boost converter is presented in this article. The proposed technique can sense the full-range inductor current with high accuracy and high speed. It is mainly based on matched current mirror and does not require a large proportion of aspect ratio between the powerFET and the senseFET, thus it reduces the complexity of circuit design and the layout mismatch issue without decreasing the power efficiency. The circuit is fabricated with TSMC 0.25 µm 2P5M mixed-signal process. Simulation results show that the buck-boost converter can be operated at 200 kHz to 4 MHz switching frequency with an input voltage from 2.8 to 4.7 V. The output voltage is 3.6 V, and the maximum accuracy for both high and low side sensing current reaches 99% within the load current ranging from 200 to 600 mA.     

A 0.5 V tunable complex filter for Bluetooth and Zigbee using OTAs

A 12th-order low voltage tunable differential complex filter for bluetooth and Zigbee applications is proposed in this paper. The filter is based on improved controllable transconductors operating with the ultra-low supply voltage of 0.5 V. Simulation results using a triple-well 0.13 μm CMOS technology verify the filter operation fulfilling all the requirements for the complex filtering stage in bluetooth or Zigbee receivers. The in-band group delay variation is 0.79 μs for bluetooth and 0.46 μs for Zigbee. The image rejection ratio is greater than 71 dB and the achieved in-band spurious free dynamic range is 42 dB.     

A compare of electrical characteristics in Al/p-Si (MS) and Al/C20H12/p-Si (MPS) type diodes using current–voltage (I–V) and capacitance–voltage (C–V) measurements

In this study, both the metal-semiconductor (MS) and metal-polymer-semiconductor (MPS), (Al/C₂₀H₁₂/p-Si), type Schottky barrier diodes (SBDs) were fabricated using spin coating method and they were called as D₁ and D₂ diodes, respectively. Their electrical characterization have been investigated and compared using the forward and reverse bias I–V and C–V measurements at room temperature. The main electrical parameters such as ideality factor (n), reverse saturation current (I_o), zero-bias barrier height (Φ_Bo), series (R_s) and shunt (R_sh) resistances, energy dependent profile of interface states (N_ss), the doping concentration of acceptor atoms (N_A) and depletion layer width (W_D) were determined and compared each other and literature. The rectifying ratio (RR) and leakage current (I_R) at ±3 V were found as 2.06×10³, 1.61×10⁻⁶ A and 15.7×10³, 2.75×10⁻⁷ A for D₁ and D₂, respectively. Similarly, the R_s and R_sh values of these diodes were found as 544 Ω, 10.7 MΩ and 716 Ω and 1.83 MΩ using Ohm’s Law, respectively. In addition, energy and voltage dependent profiles of N_ss were obtained using the forward bias I–V data by taking into account voltage dependent effective barrier height (Φ_e) and n and low-high frequency capacitance (C_LF–C_HF) methods, respectively. The obtained value of N_ss for D₂ (MPS) diode at about the mid-gap of Si is about two times lower than D₁ (MS) type diode. Experimental results confirmed that the performance in MPS type SBD is considerably high according to MS diode in the respect of lower values of N_ss, R_s and I_o and higher values of RR and R_sh.     

New generalized-immittance converter circuits obtained by using the current conveyor†

The realization of special types of the generalized-immittance converters will be given here using the second-generation current conveyor. Of particular interest in this paper is the new realization of the voltage generalized-immittance converter having conversion immittance function proportional to 8² . It will be seen that two realizations exist for each converter.     

Experimental determination of the derivative of the current–voltage characteristic of a nonlinear semiconductor structure using modulation Fourier analysis

The derivative of the nonlinear current–voltage characteristic of two antiparallel p–n junctions is experimentally obtained by the method of modulation Fourier analysis. The derivative of the current–voltage characteristic is reconstructed using the current dependences of the first and higher voltage harmonics. The advantage of modulation Fourier analysis over numerical differentiation is experimentally validated for the first time. The applied technique has no limitations on the current modulation amplitude. Large amplitudes make it possible to identify the nature of the nonlinearity of the dependence under study and to determine the contribution of the nonlinear fraction against the background of significant linearity.     

Optical and mechanical properties of C,Si, Ge,and 3C–SiC determined by first-principles theory using Heyd–Scuseria–Ernzerhof functional

Accurately calculating the band gap and electronic state density distribution of crystals is significant in determining optical properties. First-principles calculations were based on the projector-augmented-wave method with the Perdew–Burke–Ernzerhof generalized gradient approximation functional, pure density functional theory (DFT) and Heyd–Scuseria–Ernzerhof (HSE) hybrid functional. Such calculations account for the lattice parameters, electronic structure, optical properties, and mechanical properties of materials, which include the diamond-C and zinc blende structure of Si, Ge, and 3C–SiC in this study. The results obtained with HSE calculations is more accurate than that of the pure DFT calculations, and consistent with previous experimental values. The band structure and density of states of Si, Ge, and 3C–SiC indicate that these materials are indirect band gap materials. Based on HSE calculation, the band gap of Si and 3C–SiC is in accordance with previous experimental values. The imaginary part of the analytical dielectric function, the refractive index, and the adsorption coefficient also matches previous experimental values. A corresponding relationship exists among the peak of the imaginary part of the analytical dielectric function, the refractive index, and the adsorption coefficient. The optical properties have a direct relationship with the distribution of the crystal band gap and electronic state density. The materials exhibit brittleness. Although 3C–SiC is not as hard and stiff as diamond, it is a better semiconductor than Si and Ge. The mechanical anisotropy of the four materials is inconspicuous. The anisotropy of diamond-C in terms of its Young's modulus is extremely inconspicuous.