Adaptive two-loop Voltage-mode control of DC-DC switching converters

A new two-loop control scheme for voltage-mode control (VMC) of dc-dc switching converters is presented. The proposed method adds a high-gain robust loop with two controllers to the conventional VMC loop, achieving an analog "adaptive" loop in which the "equivalent voltage regulator" varies with the changing power stage parameters given as follows: 1) input voltage; 2) load; and 3) component tolerances. The loop significantly improves the disturbance rejection of the control system, i.e., closed-loop output impedance and audiosusceptibility while preserving the stability and the loop gain crossover frequency to a significant extent. Both the small-signal analysis and the experimental results carried out on a buck converter demonstrate the superiority of the proposed scheme with respect to the conventional single loop.     

Use of sigma-delta modulation to control EMI from switch-mode powersupplies

Conducted electromagnetic interference (EMI) is a major cause of concern in switch-mode power supplies (SMPSs) which commonly use standard pulsewidth modulation (PWM). In this paper, sigma-delta (ΣΔ) modulation is proposed as an alternative switching technique to reduce conducted EMI from an SMPS. The result of using ΣΔ modulation is a spread in the spectrum of the conducted emissions so that large concentrations of power at discrete frequencies are avoided. Experimental time-domain waveforms and spectra of the switching function of first-order and second-order ΣΔ modulators are presented to prove the viability of the scheme for EMI mitigation. These modulators are then applied to a DC-DC converter in an off-the-shelf computer power supply and experimental results show a reduction of roughly 5-10 dB·μV in EMI emissions over standard PWM modulators     

A novel vertical Δκ directional coupler switch usingliquid crystals

To decrease the switching length of the directional coupler switch and to use the advantages of the electro-optic properties of (LC's), we propose a novel vertical Δκ directional coupler switch using LC's and present the calculated results relevant to the design considerations. Because of the large birefringence of LC's, a very short switching length less than 60 μm is possible. Besides, a N×N switch is also proposed for practical applications     

1/f noise in MOS devices, mobility or number fluctuations?

Recent experimental studies on 1/f noise in MOS transistors are reviewed. Arguments are given for the two schools of thought on the origin of 1/f noise. The consequences of models based on carrier-number ΔN or mobility fluctuations Δμ on the device geometry and on the bias dependence of the 1/f noise are discussed. Circuit-simulation-oriented equations for the 1/f noise are discussed. The effects of scaling down on the 1/f noise is studied in the ohmic region as well as in saturation. In the ohmic region the contribution of the series resistance often can be ignored. However, in saturation the noise of the gate-voltage-dependent series resistance on the drain side plays a role in lightly doped drain LDD mini-MOST's. Surface and bulk p-channel devices are compared and the differences between n-and p-MOST's often observed is discussed. The relation between degradation effects by hot carriers or by γ-irradiation on the one hand and the 1/f noise on the other is considered in terms of a ΔN or Δμ. Experimental results suggest that 1/f noise in n-MOST's is dominated by ΔN while in p-MOST's the noise is due to Δμ     

CMOS current steering logic for low-voltage mixed-signal integratedcircuits

A quiet logic family-complementary metal-oxide-semiconductor (CMOS) current steering logic (CSL)-has been developed for use in low-voltage mixed-signal integrated circuits. Compared to a CMOS static logic gate with its output range of ΔV_logic≈V_dd , a CSL gate swings only ΔV_logic≈V_T+0.25 V because the constant current supplied by the PMOS load device is steered to ground through either an NMOS diode-connected device or switching network. Owing to the constant current, digital switching noise is 100× smaller than in static logic. Another useful feature which can be used to calibrate CSL speed against process, temperature, and voltage variations is propagation delay that is approximately constant versus supply voltage and linear with bias current. Several CSL circuits have been fabricated using 0.8 and 1.2 μm high-V_T n-well CMOS processes. Two self-loaded 39-stage ring oscillators fabricated using the 1.2 μm process (1.2 V power supply) exhibited power-delay products of 12 and 70 fJ with average propagation delays of 0.4 and 0.7 ns, respectively. High-V_T and low-V_T CSL ALU's were operational at V _dd≈=0.70 V and V_dd≈0.40 V, respectively     

A 63-μW standby power microcontroller with on-chip hybridregulator scheme

Presents a 32-b RISC microcontroller having an on-chip dc-dc converter. The chip standby power including the dc-dc converter is reduced to 63 μW with a new hybrid regulator scheme in which the microcontroller selects a switching regulator in active mode and a series regulator in standby mode. The achieved standby power corresponds to only about 1% of the standby power with a conventional scheme which always uses a switching regulator. Off-chip power transistor-type configuration suppresses pin-count increase caused by implementing an on-chip switching regulator. A series regulator that could be used instead of the switching regulator in active mode was also implemented on the chip. The series regulator does not impact the chip size because it is divided and inserted into I/O area that was originally left unused     

A 2D CMOS microfluxgate sensor system for digital detection of weakmagnetic fields

This paper presents a CMOS two-dimensional (2-D) vector magnetic sensor system integrating two planar microfluxgate sensors and the complete electronics for sensor excitation and signal readout. The system is based on an industrial 0.8-μm double-poly, double-metal CMOS technology with ferromagnetic NiFeMo cores added in a simple postprocessing sequence. The fluxgate sensors are embedded in a ΣΔ analog-to-digital converter for a stable and precise digital detection of weak magnetic fields. A cascaded ΣΔ modulator topology is utilized to obtain second-order noise shaping and to suppress pattern noise. Within the range of ±50 μT, the system nonlinearity is less than 1.5 μT. The angular resolution as a 2D vector sensor is less than 4° for a measured magnetic induction of 50 μT. This makes the 2-D microfluxgate magnetometer suitable for use as fully integrated electronic compass     

MOCVD InP/AlGaInAs distributed Bragg reflector for 1.55 μmVCSELs

A new MOCVD InP/AlGaInAs distributed Bragg reflector for long-wavelength VCSELs is presented. The InP/AlGaInAs system presents a high potential for 1.55 μm VCSELs owing to the combination of its high refractive index contrast (Δn≃0.34) and its low conduction band discontinuity (ΔEc≃150 meV). InP/AlGaInAs mirrors and one half VCSEL (bottom mirror and λ cavity) have been fabricated for the first time using AlGaInAs transparent to 1.55 μm     

Rejection of an FH signal in a DS spread-spectrum system usingcomplex adaptive filters

The performance of a direct sequence QPSK spread-spectrum receiver using adaptive filters in the presence of frequency hopped interference is analyzed. The analysis includes both the adaptive prediction error filters and the adaptive transversal filters with two-sided taps. If the product of the instantaneous frequency offset Ω_l, between the jamming signal and the carrier of the spread-spectrum signal, and the sampling period Δ is 360° (Ω_l·Δ=360°), the filter gain is reduced to zero. The filter gain G highly depends on the filter adaptation rate μ. Depending on μ, G can vary from zero to more than 20 dB for a jammer/signal power ratio (J/S) of 20 dB. If Ω _l·Δ is small enough (⩽10°), the performance of the transversal filter is better than that of the prediction error filter, in the case when μ is small. For larger values of μ or Ω_l·Δ, these performances are approximately the same. Numerical results for the hopping sequence of the jamming signal are also presented. Besides the filter gain the analysis of the adaptation rate (time constant) filter misadjustment and the system bit error probability is also included     

Adaptive robust fast control for induction motors

A new induction motor position controller that exhibits fast response and robustness is proposed. The control strategy is based on the well-known linear quadratic regulator design principle. By adaptively adjusting a penalty parameter, it is shown that the control strategy enables the induction motor system to exhibit fast convergence. Meanwhile, since the sliding mode will occur in the transient process, the fast control inherits the robustness in matched uncertainties of the sliding-mode control. In addition, to alleviate the chattering effect of the switching control signal, a low-pass filter is used to smooth the control and its design is integrated with the switching control design. The performance of the proposed control strategy is verified by experimental results     

Long-wavelength (λ=10 μm) quadrupolar-shaped GaAs-AlGaAsmicrolasers

In this paper, we present experimental results of our investigations on deformed GaAs-AlGaAs microlasers emitting around λ=10 μm. These quantum cascade lasers exhibit interesting features regarding the threshold current densities, optical output, and far-field pattern. A slight aberration from a circular cross section decreases the threshold current density for microlasers (which have a radius of 50 μm). For larger deformations ϵ, the threshold starts to increase because of the increasing mirror losses. For smaller microlasers (radii between 22 and 34 μm), the threshold current density increases already for slight deformations due to the increase of the mirror losses. The experimental results can be fitted very well with the mirror losses as a fitting parameter using a well-known and simple model. Threshold currents as low as 170 mA are measured for a cylindrical microlaser with a radius of 22 μm. The peak optical output is increasing quasi-exponentially with rising deformation. Lasing emission from slightly concave resonator shapes is detected. The bow-tie mode and other modes-different from Whispering-gallery modes-are responsible for highly directed emission along the diagonal axis and along the short axis, respectively, of the microlasers. Single-mode emission with a side-mode suppression ratio larger than 25 dB is shown over the entire drive current range for a highly deformed microlaser. The laser line can be temperature tuned with Δν/T=-0.027 cm^-1/K. A dual mode switching depending on the drive current with a mode spacing of Δν=8.1 cm^-1 between 999 and 1007.1 cm^-1 is observed for a less deformed microlaser     

Design and realization of an integrated optic switch for crossbarswitching arrays

An electrooptic switch that is insensitive to parameter tolerances is proposed for use in crossbar switching arrays. It makes use of intrinsically mismatched and tapered directional couplers and allows the realization of switching arrays with the same switching voltage for each element. Computations are carried out to verify a realization with Ti:LiNbO₃ waveguides and to compare the latter with conventional directional couplers. Switching elements on Z-cut LiNbO₃ with a crosstalk of -27 dB for zero voltage and a switching voltage of 27.5 V have been realized for use at 1.3 μm     

Polarization-independent strained InGaAs/InGaAlAs quantum-wellphase modulators

Polarization-independent phase modulation in In_1-xGa _xAs/InGaAlAs multiple-quantum-well waveguides is demonstrated for the first time. It is shown that by increasing the Ga fraction and hence the tensile strain in the quantum well the electric-field-induced refractive index change in the TM polarization Δn_TM can be made to approach that in the TE polarization Δn _TE. At 1.523 μm, the ratio Δn_TM /Δn_TE=1 for x=0.7 with a phase shift coefficient of 17.4°/V-mm was achieved. Polarization independence was maintained over the entire range of reverse bias voltage     

Long-wavelength InP-based quantum-dash lasers

Self-assembled InAs quantum-dash (QD) lasers with emission wavelengths between 1.54 and 1.78 μm based on the AlGaInAs-AlInAs-InP material system were grown by gas source molecular beam epitaxy. Threshold current densities below 1 kA/cm² were achieved for 1-mm-long mirror coated broad area lasers with a stack of four QD layers. The devices can be operated up to 80°C in pulsed mode and show a high T₀ value of 84 K up to 35°C. In comparison to quantum-well lasers a much lower temperature sensitivity of the emission wavelength was achieved. The temperature shift of Δλ/ΔT = 0.12 nm/K is as low as that caused by the refractive index change     

Two-dimensional mode size transformation by Δn-controlledpolymer waveguides

We report a new type of polymer waveguide for two-dimensional (2-D) mode size transformation in which Δn (refractive index difference between core and cladding) is properly controlled along the waveguide axis while the core cross section is kept uniform. The beam diameter in the Δn-controlled waveguide where the core diameter is 3.7 μm and Δn changes from 0.0027 to 0.0009 toward one end in the 5 mm-gradient Δn, region, is about twice as large as that in a normal waveguide where Δn is 0.0027. The optical loss accompanied by mode size transformation is calculated to be less than 2.5% based on beam propagation methods (BPM's)     

Electroabsorption properties of InGaAs/InAlAs multiple quantum wellstructures at 1.5 μm

The electroabsorption properties of InGaAs/InAlAs MQW structures are characterised in terms of Δα, Δα/F and Δα/α₀, where Δα is the electroabsorption, α₀ is the residual absorption coefficient under zero bias, and F is the applied electric field. The limitations of these structures for 1.5 μm modulators are primarily due to the relatively small Δα/F values as a result of the small well width. The results are compared with the literature     

Quantized Probability Circuit Design Principles Applied to Linear Circuits

A circuit design method for linear circuits is needed which will adequately predict circuit per formance as a function of component tolerances. This paper describes a method which weights the probable component variation from its nominal value into one of three groups; the group assignment depends on how seriously the component variation affects over-all performance This technique, identified as the quantized probability design (QPD) method, is compared with the absolute worst case (AWC), the Taylor worst case (TWC), and the uniform probability (UP) methods. The QPD procedure is given, based on the circuit performance equation. Two linear circuit applications are presented and analyzed whic show the effect each component will have on circuit performance. A comparison of design methods shows that the quantized probability design predicts less amplifier gain variation. Actual experience has shown that a closer correlation exists with the quantized probability design method, and therefore its use for linear circuits is recommended.     

All-optical switching with low-peak power in microfabricated AlGaAswaveguides

We report all-optical switching with low-peak power in a microfabricated AlGaAs waveguide operating at 1.6 μm. We show that by using a 1-μm long microfabricated strongly-guided waveguide with 0.8 μm by 0.9 μm mode cross-sectional area, switching is achieved with an average power of 1.2 mW for 82-MHz mode-locked 430 fs pulses. The estimated peak pump power and pulse energy inside the microfabricated waveguide were ~30 W and ~14.6 pJ, respectively, which is 5-10 times lower than the values needed with conventional waveguides. In terms of a practicality index defined via switching power times waveguide length, this waveguide has around the best value     

Fabrication of variable bandwidth filters using arrayed-waveguidegratings

Variable bandwidth filters have been fabricated using silica-based N×N arrayed-waveguide gratings. The centre wavelengths are λ₀=1.55 μm for all channels. The 3 dB bandwidths are 40, 78, 116 and 154 GHz, for the filter with a path length difference ΔL=63 μm. In the filter with ΔL=8.6 μm, the 3 dB bandwidths are 414, 769, 1198 and 1608 GHz. The on-chip losses are 2.1-2.9 dB and sidemode suppression ratios are larger than 27 dB     

Efficient coupling between annealed K+-Na+ion-exchanged channel waveguides and 10/125 single-mode fibers atλ=1.321 μm

The process of thermal annealing of K⁺-Na⁺ ion-exchanged channel waveguides has been studied with the aim of optimizing their coupling efficiency with commercial single-mode fibers at λ=1.321 μm. Waveguides obtained in soda-lime glass slides, with mask apertures ranging between 13.4 and 2.6 μm, were characterized before the annealing by combining nearfield measurements and an etching procedure. The experimental results were successfully compared with a theoretical model based on the variational principle. The refractive index distribution of K⁺-Na⁺ ion-exchanged channel waveguides supporting one or a low number of modes was given: compared to the corresponding slab case, the refractive index step Δn_o remained constant, while the waveguide depth was lower. The thermal annealing process of the channels was then performed and modeled by means of the standard diffusion theory. As a result, the channel fabrication parameters for optimum guide-fiber coupling could be predicted: 0.23-dB mode mismatch losses were measured between the optimized channel and a commercial 10/125 single-mode fiber, at λ=1.321 μm