Calculation of Mutual Coupling between Two RLTs in Millimeter Wave VCO Waveguide Cavities with Mode Matching Methods

In the design of millimeter wave voltage control oscillators (VCOs), mutual coupling effect is of great importance for it influences the tuning and power characteristics of VCOs significantly. In this paper, mutual coupling between two in-line radial line transformers (RLTs) in rectangular waveguide cavities of millimeter wave VCOs has been evaluated with mode matching methods. Mutual coupling characteristics varying with various parameters of resonate cavity such as the distance between two diodes, the position of sliding short, the radii of bias pins, the radii of RLTs, and the height of diodes are presented. Some useful conclusions concerning two RLTs configuration have been derived, which is helpful to design millimeter wave VCO of this structure.     

同轴波导虚阴极振荡器二极管参数优化的研究

采用粒子模拟研究了同轴波导虚阴极振荡器二极管参数对微波效率和频率的影响,得到了由二极管参数改变引起的二极管阻抗变化及其对微波效率的影响规律. 借鉴具有慢波结构的高功率微波器件中微波模式特性阻抗的计算方法,给出同轴波导虚阴极振荡器中微波主模式特性阻抗的理论计算公式. 将理论计算结果与由粒子模拟对器件进行优化后得到的二极管阻抗进行比较,发现当反映电子束特性的二极管阻抗与微波主模式特性阻抗匹配时,虚阴极振荡器具有较高的束波功率转换效率. 进一步用特性阻抗对其他几种典型结构的虚阴极振荡器进行分析,验证了该方法的合理性,为设计高效率虚阴极振荡器提供了理论指导. 关键词： 虚阴极振荡器 同轴波导 二极管参数 特性阻抗     

A dual band CMOS VCO with a balanced duty cycle buffer

This paper proposes a dual band VCO with a standard 0.35 μm CMOS process to generate 1.07 and 2.07 GHz. The proposed VCO architecture with 50% duty cycle circuit and a half adder (HA) is able to produce a frequency two times higher than that of the conventional VCOs. The measurement results demonstrate that the gain of VCO and power dissipation are 561 MHz/V and 14.6 mW, respectively. The phase noises of the dual band VCO are measured to be −102.55 and −95.88 dBc/Hz at 2 MHz offset from 1.07 and 2.07 GHz, respectively.     

The development of nonradiative dielectric waveguide transmitting front-end in Ka-band

The operating theory,design method and experimental results of the nonradiative dielectric waveguide (NRD-guide) transmitting front-end in millimeter wave band are related in details in this paper. As a kind of dielectric waveguide,the NRD-guide possesses fine transmission performances, and it can be used to fabricate the millimeter wave hyterodyne integrated circuits. The two kinds NRD-guide transmitting front-ends substantiated in the paper, the voltage controlling oscillator(VCO) and twin-Gunn-diode power-combiner,have very similar structures to each other and possess compact sizes, fine machinery and electric performances.For the VCO front-end in Ka-band, the frequency modulation band is greater than 150MHz, the output power is larger than 20mW.For the power-combiner, the output power is larger than 40mW,the combination efficiency is better than 90%,the frequency stabilization reaches 1.68×10^–5. Combined with the receiving front-end reported before,the transmitter and receiver can be composed to a dielectric waveguide R/T module to be applied in some millimeter wave sub-systems.     

Nonlinear optical rectification in asymmetric coupled quantum wells

The optical rectification (OR) in the asymmetric coupled quantum wells (ACQWs) is calculated theoretically. The dependence of the OR on the width of the right-well and the barrier is studied. The analytical expression of the optical rectification coefficient is obtained by using the compact density-matrix approach and the iterative method, and the numerical calculations are presented for a typical GaAs/Al_xGa_1 − xAs ACQW. The results obtained show that the OR efficient can reach the magnitude of 10⁻⁴ m/V in this ACQW system, which is 1-2 orders higher than that in single quantum systems. Moreover, the OR coefficient is strongly dependent on the widths of the barrier and the right-well of the ACQWs. An appropriate choice for the width of the barrier and the right-well of the ACQWs can induce a larger OR coefficient.     

Nonlinear Frequency-Modulation Distortion Analysis for VCO Based on Harmonic Balance Method

The analysis methods for the steady-state responses of the voltage tuning negative resistance oscillator (voltage-controlling oscillator, VCO) by the microwave nonlinear autonomous circuit harmonic balance method in millimeter-wave bands are studied in the paper. Firstly, the quasi-periodic characteristic of the steady-state response of the VCO modulated by a periodic signal is proved. Then, on the bases of the harmonic balance analysis and the inter-modulation balance analysis, a novel method for obtaining the steady-state tuning performance and the nonlinear frequency-modulation distortion characteristic of the VCO is presented. The total analysis process is aimed to a kind of NRD-guide Gunn diode VCO. The large-signal lumped equivalent circuit model of the millimeter-wave P⁺N-junction varactor is also given for explaining the algorithm and the principle of the NRD-guide VCO.     

Impedance Characteristics of Two Coplanar RLTs in Millimeter Wave VCO Waveguide Cavities

Impedance characteristics of two coplanar radial line transformers (RLTs) placed in millimeter wave voltage control oscillators (VCOs) waveguide cavities have been studied in this paper. Mode matching methods are employed to calculate self impedance of the RLT mounted on active device and mutual impedance of the two coplanar RLTs. Some general rules concerning impedance characteristics of two coplanar RLTs configuration influenced by the parameters of the structure have been deduced. In addition, an equivalent network is presented based upon the impedance matrix of the coplanar RLTs; the load impedance looking outward from the active device has been derived in virtue of the equivalent network and the impedance of varactor diode. The equivalent network which describes the relationships between the load impedance and the impedance of varactor diode is helpful for developing millimeter wave varactor-tuned VCO of this structure.     

The characteristics of high current amorphous silicon diodes

Amorphous siliconp−n junctions with various doping profiles have been prepared by the glow discharge technique and the effect of the barrier profile on electrical properties investigated. Current densities of up to 40 A cm⁻² with rectification ratios of 10⁴–10⁵ were obtained withn ⁺−ν−p ⁺ structures. The diode quality factor has also been investigated, both in the dark and under illumination.     

The nonlinear optical rectification of a confined exciton in a quantum dot

An exciton in a disc-like quantum dot (QD) with the parabolic confinement, under applied electric field, is studied within the framework of the effective-mass approximation. The nonlinear optical rectification between the ground and the first-excited states has been examined through the computed energies and wave functions in details for the excitons. The results show that the optical rectification susceptibility obtained in a disc-like QD reach the magnitude of 10⁻² m/V, which is 3-4 orders of magnitude higher than in one-dimensional QDs. It is found that the second-order nonlinear optical properties of exciton states in a QD are strongly affected by the confinement strength and the electric field.     

Generation of nanosecond terahertz pulses by the optical rectification method

The possibility of the generation of quasi-cw terahertz radiation by the optical rectification method for broad-band Fourier unlimited nanosecond laser pulses has been experimentally demonstrated. The broadband radiation of a LiF dye-center laser is used as a pump source of a nonlinear optical oscillator. The energy efficiency of terahertz optical frequency conversion in a periodically polarized lithium niobate crystal is 4 × 10⁻⁹ at a pump power density of 7 MW/cm².     

Anomalous polarization dependence of the photon drag and optical rectification fields inn-type gallium phosphide

The photon drag and optical rectification response fromn-type gallium phosphide containing 2.4×10¹⁶ electrons cm^–3 has been studied using laser sources at 10.61 and 2.83m. By using different contact configurations, the existence of an additional electric field term in the propagation direction has been deduced. This field is shown to arise from the spatial derivatives of the photon drag and optical rectification field components caused by absorption of the radiation. The importance of this effect in detector design is considered.     

Predistortion techniques for synthesizing coupled microring filters with loss

A general method based on the predistortion technique is presented for determining the optimum coupling parameters of multiple-coupled microring filters in the presence of known uniform resonator loss. The technique involves predistorting the filter transfer function by shifting its poles and zeros to compensate for loss in the microring resonators due to material absorption, surface roughness scattering, coupling loss and bending loss. It is shown that by sacrificing some in-band insertion loss, both the amplitude and group delay responses of the filter can be recovered when loss is present. Application of the method to synthesizing lossy microring filters in both the digital z-domain and analog s-domain will be presented. The proposed technique is general in that it can be applied to both amplitude and phase filters constructed of coupled microresonators in the most general two-dimensional coupling topology.     

Optical rectification in tellurium from 10.6 μm

Optical rectification in single crystals of tellurium produced by infra-red radiation at 10.6 μm has been observed. The value of |χ⁰ ₁₁₁| is found to be 0.9×10⁻⁶ esu. Preliminary experiments to test the usefulness of the effect to monitor mode-locked infra-red laser pulses have been inconclusive.     

Thermal transport associated with ballistic phonons in asymmetric quantum structures

Using the scattering matrix method, we investigate the thermal conductance associated with ballistic phonons at low temperatures in asymmetric quantum structures. The results show that when the structure is an ideal quantum wire, the universal value π ² κ _B²(3h) can be observed at very low temperatures. However, for asymmetric quantum structure, the thermal conductance is less than the universal value π ² κ _B²(3h), even at T → 0. The results also show that the thermal conductance is strongly dependent on the transport direction. The rectification effect can be observed in the asymmetric structure and can be adjusted by changing the structural parameters. A brief analysis of these results is given.      

Compositionally asymmetrical multiquantum wells: “Pseudo-molecules” for giant optical nonlinearities in the infrared (9–11 μm)

Intersubband transitions in quantum well have extremely large oscillator strengths and induce strong nonlinear effects in structures where inversion symmetry is broken, realized by growing AlGaAs quantum wells with asymmetrical A1 gradients. These compositionally asymmetrical multiquantum wells may thus be viewed as giant “quasimolecules” optimized for optimal nonlinearities in the mid infrared. Optical rectification as well as second harmonic generation have been measured in those structures using a continuous CO₂ laser. At 10.6 μm the nonlinear coefficients are more than 3 orders of magnitude higher in these samples than for bulk GaAs (i.e. χ₀⁽²⁾ = 5.3 × 10⁻⁶m/V, χ_2ω⁽²⁾ = 7.2 × 10⁻⁷ m/V) and are in good agreement with theoretical predictions. We present more complex “pseudo-molecules” involving weakly coupled quantum wells. The optical rectification effects in these devices are so large χ₀⁽²⁾ = 1.6 × 10⁻³ m/V) that application to infrared detection may be envisioned.     

Design of Novel Coplanar Counter Circuit in Quantum Dot Cellular Automata Technology

One of the emerging technology that can be used for replacing CMOS technology is Quantum-dot Cellular Automata (QCA) technology. Counter circuits are widely used circuits in the design of digital circuits. This paper presents and evaluates circuits for 2-, 3-, 4-, and 5-bit coplanar counter in the QCA technology. The designed QCA coplanar counter circuits are based on the modified D-Flip-Flop (D-FF) circuit that is designed in this paper. The designed QCA circuits are implemented and verified by using QCADesigner tool version 2.0.3. The results show that the designed circuits for 2-, 3-, 4-, and 5-bit coplanar counter contain 44 (0.03 μm²), 93 (0.07 μm²), 160 (0.13 μm²), and 245 (0.2 μm²) quantum cells (area). The comparison results indicate that the designed circuits have advantages compared to other QCA circuits in terms of cost, area, and cell count.

     

Digital readout integrated circuit (DROIC) implementing time delay and integration (TDI) for scanning type infrared focal plane arrays (IRFPAs)

This paper presents a digital readout integrated circuit (DROIC) implementing time delay and integration (TDI) for scanning type infrared focal plane arrays (IRFPAs) with a charge handling capacity of 44.8 Me⁻ while achieving quantization noise of 198 e⁻ and power consumption of 14.35 mW. Conventional pulse frequency modulation (PFM) method is supported by a single slope ramp ADC technique to have a very low quantization noise together with a low power consumption. The proposed digital TDI ROIC converts the photocurrent into digital domain in two phases; in the first phase, most significant bits (MSBs) are generated by the conventional PFM technique in the charge domain, while in the second phase least significant bits (LSBs) are generated by a single slope ramp ADC in the time domain. A 90 × 8 prototype has been fabricated and verified, showing a significantly improved signal-to-noise ratio (SNR) of 51 dB for low illumination levels (280,000 collected electrons), which is attributed to the TDI implementation method and very low quantization noise due to the single slope ADC implemented for LSBs. Proposed digital TDI ROIC proves the benefit of digital readouts for scanning arrays enabling smaller pixel pitches, better SNR for the low illumination levels and lower power consumption compared to analog TDI readouts for scanning arrays.     

Fabrication and electrical characterization of Schottky diode based on 2-amino-4, 5-imidazoledicarbonitrile (AIDCN)

The junction characteristics of the organic compound 2-amino-4, 5-imidazoledicarbonitrile (AIDCN) on p-type silicon substrate are studied in detail. AIDCN is deposited on silicon substrate using thermal evaporator. Current–voltage (I–V) characteristic of the device is measured at room temperature. The Au/AIDCN/p-Si device shows non-linear I–V characteristic with rectification ratio of 7.2×10³ at 5 V. The electronic device parameters such as barrier height, ideality factor, and series resistance are calculated using I–V data and observed to be 0.74 eV, 3.00, and 3.73×10⁴ Ω respectively.     

Nonadiabatic corrections to the velocity of a Brownian motor with a complex potential profile

A number of laws have been established that govern the motion of a Brownian particle in a periodic potential profile for the adiabatically fast (with the time τ₀) and adiabatically slow variations in its shape. The average velocity of a particle has been calculated including a nonadiabatic contribution depending on τ₀ and the characteristic times of the system, which are determined by the characteristic features of the potential profile. It has been shown that the nonadiabatic correction to the velocity is proportional to τ₀² for a smooth potential profile and to τ₀ for a hopping movement in a potential containing barriers and wells, and this correction limits the large values of the rectification factor of motion for a high-performance motor operation mode.     

Photoluminescence properties of nitrogen-doped ZnO films deposited on ZnO single crystal substrates by the plasma-assisted reactive evaporation method

Photoluminescence (PL) spectra of nitrogen-doped ZnO films (ZnO:N films) grown epitaxially on n-type ZnO single crystal substrates by using the plasma-assisted reactive evaporation method were measured at 5 K. In PL spectra, free exciton emission at about 3.375 eV was very strong and emissions at 3.334 and 3.31 eV were observed. These two emissions are discussed in this paper. The nitrogen concentration in ZnO:N films measured by secondary ion mass spectroscopy was 10^19-20 cm⁻³. Current-voltage characteristics of the junction consisting of an n-type ZnO single crystal substrate and ZnO:N film showed good rectification. Also, ultraviolet radiation and visible light were emitted from this junction under a forward bias at room temperature. It is therefore thought that ZnO:N films have good crystallinity and that doped nitrogen atoms play a role as acceptors in ZnO:N films to form a good pn junction. From these phenomena and the excitation intensity dependency of PL spectra, emissions at 3.334 and 3.31 eV were assigned to neutral acceptor-bound exciton (A⁰X) emission and a donor-acceptor pair (DAP) emission due to doped nitrogen, respectively.