Quality Factor of the Waveguide Re-Entrant Turnstile Junction Circulator

This paper presents a simple idea for improving the linewidth or quality factor (or Q-factor) of an RLC resonant circuit using positive feedback loop. This is achieved by considering a second-order resonant circuit which implements a band-pass filter structure (i.e. having a single zero at the origin). This allowed the loop to be closed without affecting the resonance frequency while at the same time the quality factor is modified. The larger the open-loop gain the more the improvement on the quality factor. It is shown that although in principle this approach has no upper limit to how much improvement can be made on the quality factor, it has the practical limitation which is dictated by the op-amp’s gain-bandwidth product used in the feedback loop.

In this work we define a performance measure for capacitive micromachined ultrasonic transducers (cMUT) in the form of a gain-bandwidth product to investigate the conditions that optimize the gain and bandwidth with respect to device di- mensions, electrode size and electrical termination resistance. For the transmit mode, we define the figure of merit as the pressure- bandwidth product. Fully-metallized membranes achieve a higher pressure-bandwidth product compared to partially metallized ones. It is shown that the bandwidth is not affected by the electrode size in the transmit mode. In the receive mode, we define the figure of merit as the gain-bandwidth product. We show in this case that the figure of merit can be maximized by optimizing the electrode radius. We present normalized charts for designing an optimum cMUT cell at the desired frequency with a given bandwidth for transmit or receive modes. The effect of spurious capacitance and liquid loading effect are considered. Design examples are given to clarify the use of these charts. I. INTRODUCTION It is shown that a large bandwidth is possible with an untuned cMUT immersed in water (1), (2). For such a cMUT, the operation frequency range may extend from very low fre- quencies to the antiresonance of the membrane (3). However, those cMUTs have small conversion efficiencies and are not as sensitive as piezoelectric transducers. In this work, we explore the limits of a cMUT operating in different regimes using the Mason model corrected with finite element method (FEM) simulations. We try to maximize the bandwidth of a cMUT while keeping the output pressure or the conversion efficiency at a reasonable value. For this purpose, we define performance measures in the form of a pressure-bandwidth product or a gain-bandwidth product. We try to maximize this figure of merit by optimizing various geometrical parameters of the cMUT.

A capacitive micromachined ultrasonic transducer (cMUT) is typically fabricated by concatenation of several cMUT cells with identical physical dimensions. If the membrane thick- ness is kept fixed, the radius of the cMUT determines the center frequency of operation. A smaller radius implies a greater center frequency. Therefore, it should be possible to put cMUTs with different sizes in parallel to get a larger bandwidth at the expense of gain. In this study, we investigate the optimization of the bandwidth characteristics of a cMUT by using mixed size cells. We designed two mixed size cMUT arrays with a predicted optimized fractional bandwidth value of about 155% at 5.4 MHz, and 146% at 8.8 MHz. These values are about 55% and 58% better than what can be achieved with a uniform size array at the corresponding center frequencies. There is almost no loss in the gain bandwidth product when two different sized cMUTs are used in parallel. There is about 9% increase in gain bandwidth product when three different sized cMUTs are used in parallel. It is shown, in this study, that gain bandwidth product and bandwidth can be enhanced by use of mixed size cMUT cells.

OP-AMPs finds applications in different domains of electronics engineering including communications. There has been several OP-AMP configurations realized in the last decades for different target applications. But with the evolution of communication standards, to meet the demand for high data rate over the years, requirement for a high frequency and high BW OP-AMP is gaining attention. This makes the design challenge much higher. This paper presents a two-stage CMOS amplifier which uses frequency compensation method to facilitate higher BW. Different parameters like Gain, Gain band width product (GBWP), Phase Margin and Total Power dissipation are considered in this design. A step-by-step procedure for an efficient amplifier design is followed using frequency compensation. We have achieved a gain-bandwidth product (GBWP) of 110 MHz that is capable of driving large capacitive loads. It also achieves 77.7 dB gain with a phase margin of 60o.

In this paper, a resonator based on composite right/left handed transmission line concept is discussed. This resonator excites -1st order resonance mode. We start with half-wave resonators consisting of two unit cells of a composite right/left handed transmission line. From the simulated field distributions, the center of these half-wave resonators can be short-circuited to obtain a quarter-wave resonator in the -1st mode. Susceptance slope parameters are calculated for the resonator. Then this resonator is applied for a 2-pole filter made by LTCC, which can be designed with standard filter design theory owing to the slope parameter. The dimension of the experimental filter implemented by LTCC is 2.5mm by 1.35mm by 0.52mm. The insertion loss is 1.80dB at the 2.4GHz band. Good agreement between measured and computed results is obtained.

Design and performance of miniaturized coplanar waveguide (CPW) bandpass filters (BPFs) using high T/sub c/ superconducting (HTS) films have been studied. In order to realize the miniaturized filters, we coupled highly packed meanderline half-wavelength resonators with interdigital gaps, where admittance inverters (J inverters) were made of interdigital gaps. The exact J values, susceptance slope parameters and the length of the resonators of the meanderline are calculated from the cascade matrix (K-matrix) and scattering matrix (S-matrix) obtained by the 2.5-dimensional electromagnetic field simulator (HP-Momentum). It is shown that the size of the filters can be greatly reduced by introducing CPW with highly packed meanderline geometry (center frequency 2 GHz, fractional band width 15 MHz, ripple 0.1 dB) packed within 10 mm square substrate. Simulated performance was in good agreement with the designed one.

A novel resonator to improve the phase noise of a Voltage-Controlled Oscillator (VCO) utilizing double series resonances or two attenuation zeros to improve the susceptance slope parameter of the resonator circuit is proposed, and its effectiveness is demonstrated by designing a low phase noise K-band VCO. The first series resonance is created by an additional inductor (L) in series to the capacitor (C) in the parallel branch of a conventional LC-tank circuit, and the second one is realized by an additional capacitor in series to the whole resonator circuit. The additional L is realized by defected ground structures (DGS) so that there is no additional burden in the chip size. The proposed resonator is fabricated in 0.18 μm CMOS technology and has active quality factor of 101 and a compact size of 0.009 mm2 (0.00046 λ2). The measured return loss |S11| and insertion loss |S21| of the fabricated prototype resonator are 2.8 and 11 dB, respectively, at a center frequency of 37 GHz with 8 GHz of bandwidth. The resulting active quality (QK-) factor of the proposed resonator is enhanced significantly that, in returns, improves the phase noise. The design is implemented in 0.18 μm CMOS technology, and the post-layout simulation shows that VCO has a tuning range of 3.8% and phase noise of −114.4 dBc/Hz @1 MHz offset at 19.5 GHz oscillation. The VCO consumes 2.96 mW power resulting in a Figure of Merit (FoM) of −195.5 dB. The proposed resonators improve the VCO FoM by more than 5.5 dB compared to conventional LC resonator.

In a silicon hetero-interface photodetector, Si is used as the multiplication material to provide avalanche gain, while InGaAs is used as the absorption material. High quantum efficiency, high gain-bandwidth product, and low noise detection of wavelengths between 1.0 and 1.6 mm can be achieved in this way. We derive expressions for the frequency response for these detectors, present possible design variations, and analyze their performance. The effects of parasitics, transit time, and RC roll-off on frequency response are investigated and the 3-dB bandwidth and gain bandwidth product are calculated. Particular attention is paid to a 10 Gbit/s APD and we show that that a 3-dB bandwidth of 10 GHz and a gain-bandwidth product in excess of 400 GHz should be possible.

Conventional equivalent circuits for the large-signal and small-signal behavior of bipolar transistors are all based on the assumption that carriers flow in the base region by drift and diffusion. For a very narrow base, this assumption becomes questionable, and the equivalent circuits based on it need modification. We find that the interconnections of circuit elements conventionally used still apply, independent of base width; but that the functional dependence of certain parameters of the equivalent circuits change as the base becomes narrower. For the limiting case of very narrow bases, we show that the Early effect vanishes; and we give expressions for the functional dependencies of Beta, saturation current, forward charge-control time constant, transconductance, and gain-bandwidth product. All of these parameters derive less benefit from decreasing base width than conventional theory predicts.

This work discusses the capacitance–voltage (C–V) analysis and frequency dependent capacitance of In2O5Sn (Tin Oxide) gate electrode Recessed Channel (TGRC) MOSFET with an aim to examine the effectiveness of In2O5Sn (Transparent) as a gate material on parasitic capacitance which prominently influences the current driving capability and thus, the switching performance. Moreover, capacitance dependent parameters such as Transconductance Frequency Product (TFP), Energy Delay Product (EDP) and Gain Bandwidth Product (GBP) are also assessed and found that, TFP increases to 6.33 times in comparison to metal gate RC MOSFET owing to a noticeable reduction in parasitic capacitance (Cgg = Cgs + Cgd), due to which EDP and GBP also improve considerably and thus reflects its effectiveness in RF amplifiers and receivers. In addition, the effect of parameter variation such as gate length (Lg) and negative junction depth (NJD) of TGRC is also observed, and results reveal that with Lg = 20 nm and NJD = 5 nm, TGRC unveils outstanding switching performance which is desirable for low power ULSI applications.

This paper presents a voltage-mode biquadratic filter performing completely standard functions: low-pass, high-pass, band-pass, band-reject and all-pass functions, based on single voltage differencing transconductance amplifier (VDTA). The proposed filter has three input voltage and a single output voltage. The features of the circuit are that; the quality factor and natural frequency can be tuned independently; the circuit description is very simple, consisting of merely one VDTA, one resistor and two capacitors; the pole frequency can be electronically adjusted. Additionally, each function response can be selected by suitably selecting input signals with digital method; the double input voltage is not required. Using only single active element, the proposed circuit is very suitable to further develop into an integrated circuit. The PSPICE simulation results are depicted. The given results agree well with the theoretical anticipation.

This paper presents a new approach to symbolic network analysis. The procedure is entirely topology oriented because it operates with a netlist description of the analyzed circuit. The obtained network function has nested form. The method introduces a graph representation of the factorization process, that is constructed directly from a given circuit description. Therefore, it is named Topology Decision Diagram (TDD). This graph serves as a skeleton for network function generation. TDD construction starts from the original circuit and spreads to simplified subcircuits. Every subsequent subcircuit is obtained by replacing a circuit branch with an open or a short. The proposed procedure generates the network function in reverse order. It starts from a single circuit parameter placed as a leaf of TDD. Thereafter, the circuit function grows instantiating the other circuit parameter one by one in a sequential order. The proposed method was developed for analogue CMOS circuits and, consequently, recognizes R, L, C and gm as circuit components.

RF performances at cryogenic temperature of inductors integrated in a FDSOI technology

This article presents a current-mode multifunction filter performing completely standard function: low-pass, highpass, band-pass, band-reject and all-pass functions. The features of the circuit are that: the quality factor and pole frequency can be tuned by DC controlled bias current: the circuit description is very simple, it comprises only active elements, which are 2 current controlled current follower transconductance amplifiers (CCCFTAs) and 2 operational amplifiers (OAs). The proposed circuit is very suitable to further develop into an integrated circuit architecture. The PSpice simulation results are shown. The total power consumption is approximately 23.1mW at ±5V supply voltages. The given results agree well with the theoretical anticipation.

We present an overview on the progress of InP/InGaAs based Hi-Lo APD's, which are important for long-haul optical fiber communications. Much of recent research efforts have been focused on improving the operation reliability, the gain- bandwidth (GB) product, and reducing the excess noise factor. To achieve a high GB product and a reliable operation, the reduction of the thickness of the multiplication layer and an optimum design of the internal electric field distribution are essential. The concept of the planar InP/InGaAs APD is very important from this perspective and the Hi-Lo APD's are expected to play an important role.