Rigorous Full-Wave Analysis of Rectangular Microstrip Patch Antenna on Suspended and Composite Substrates

In this paper, Galerkin’s method in the Fourier transform domain is applied to the determination of the resonant frequencies and half-power bandwidth of rectangular microstrip patch on composite and suspended substrates. Using Galerkin’s method in solving the integral equation numerically, the complex resonant frequency of the microstrip antenna on suspended and composite substrates is studied with sinusoidal functions as basis functions, which show fast numerical convergence. The validity of the solution is tested by comparison of the computed results with experimental data. Finally, numerical results for the effects of suspended and composite substrates on the resonant frequency and half-power bandwidth are also presented.     

Relationship between measured and intrinsic conductances of MOSFETs

The relationship between measured and intrinsic MOSFET small-signal conductances in the presence of source and drain series resistances given by S.Y. Chou et al. (1987) is modified to include the effect of the source resistance on the substrate bias. The equation relating the measured to the intrinsic conductances of MOSFETs with constant resistances in series with the source and the drain is derived considering the effect of the voltage drops in these resistors on gate-source, drain-source, and substrate-source voltages. The resulting degradation is the same for all small-signal conductances. The general equations make it possible to determine the conditions where the simpler previous equations can be used     

Point-contact diodes in terms of p-n junction theory

A "formed" n-type germanium point-contact diode is qualitatively reminiscent of an idealized model that comprises an abrupt hemispherical p-n junction, both regions of which may have moderate resistivity, terminated on the inner (p) and outer (n) sides by hemispherical ohmic contacts. The extent to which this model can be justified quantitatively is investigated. Low-injection analyses of the static and small-signal, frequency-dependent properties suggest that the model is capable of predicting the corresponding experimentally-observed behavior. Consideration of space-charge-layer widening with reverse bias allows the computation of breakdown and punch-through voltages, which correspond in magnitude range to the observed peak inverse voltages of formed germanium point contacts. A high-injection analysis of the static forward characteristic indicates approximate agreement between theory and experiment, even for the nonlinear spreading resistance.     

Measured Output Voltages of Piezoelectric Devices Depend on the Resistance of Voltmeter

Piezoelectric mechanical energy harvester (MEH) has been developed as an important emerging variant of piezoelectric devices. Experiments in the literature show that the voltage–time curves of piezoelectric devices encompass both positive and negative characteristics even though the strain in the piezoelectric material is always positive during the applied cycling load. This does not agree with the results predicted by the piezoelectric theory of open circuit. Here, both the experiments and theory are performed to understand this important problem. A zirconate titanate (PZT) MEH is fabricated and the output voltages are recorded with three voltmeters. It is found that the measured voltages depend on the resistance of voltmeter. The peak value of voltage increases with the increase of the resistance of voltmeter, which is contrary to the established knowledge that the measurement results are independent of the instruments used. A theoretical model considering the voltmeter with finite resistance is established. The charge is allowed to go through the voltmeter and switch the directions during increasing and releasing of strain. The results by this model agree well with those from the experiments. The findings suggest that the resistance of voltmeter should be reported for voltage measurement of the piezoelectric devices.     

Role of supply voltage and load capacitors in the experimental operation of small-signal MOSFET amplifiers

Experimental investigation has been performed of the role of supply voltage and load capacitors in small-signal MOSFET amplifier circuit. Particular emphasis has been given to addressing basic issues involving MOSFET amplifiers, rather than modifying the design, and hence standard amplifiers have been considered as the topic of study. The study uncovers that while keeping all other circuit parameters constant, the dc bias voltage (V_DD) plays an important role in creating large voltage gain as it sets the condition for the transistor to be in the saturation mode. This is the region of operation of the transistor where linear amplification is achieved.

The influence of load capacitor C_L has been studied by connecting the output of MOS amplifier to a load. The input impedance of the load circuit is the combination of a capacitance in parallel with a resistance. It is found that the load capacitance is important for determining the frequency range for a constant amplifier gain. In general, the lower the load capacitance, the wider is the midband frequency range. At the high frequency end of the spectrum, the gain drops under the influence of C_L, which is consistent with the PSpice simulation results for small-signal amplifiers. At low frequency end of the spectrum, the midband gain decreases because coupling capacitors and bypass capacitors do not act as perfect short circuits.     

Dependency of the highest harmonic oscillation frequency on junction diameter of IMPATT diodes

The effect of series resistance and junction capacitance on the high-frequency limit of IMPATT diode operation is studied with a Read-type small-signal theory, and is confirmed experimentally. Oscillation frequencies from 30 to 400 GHz have been measured with Si p⁺-n-n⁺abrupt junction diodes with a depletion layer width of 0.2 µm. The highest oscillation frequency increases as the junction diameter is decreased, owing to reduced junction capacitance and increased bias-current density. The highest oscillation frequency observed is 423 GHz, which is obtained in the fifth harmonic mode with a diode of 16-µm junction diameter. Fundamental oscillation frequency is found to depend strongly on dc bias-current density, and to be close to the avalanche frequency of the small-signal theory.     

Resonance of a rectangular microstrip patch on a uniaxial substrate

Effects of uniaxial anisotropy in the substrate on the complex resonant frequency of the microstrip patch antenna are investigated in terms of an integral equation formulation. The complex resonant frequency of the microstrip patch antenna is calculated using Galerkin's method to solve the integral equation. The sinusoidal functions that are selected as the basis functions, which show fast numerical convergence. Numerical results indicate that both the resonant frequency and the half-power bandwidth are increased due to positive uniaxial anisotropy and decreased due to negative uniaxial anisotropy     

Linearity and power characteristics of SiGe HBTs at high temperatures for RF applications

In this paper, the power gain, power-added efficiency (PAE) and linearity of power SiGe heterojunction-bipolar transistors at various temperatures have been presented. The power characteristics were measured using a two-tone load-pull system. For transistors biased with fixed base voltage, the small-signal power gain and PAE of the devices increase with increasing temperature at low base voltages, while they decrease at high base voltages. Besides, the linearity is improved at high temperature for all voltage biases. However, for devices with fixed collector current, the small-signal power gain, PAE, and linearity are nearly unchanged with temperature. The temperature dependence of power and linearity characteristics can be understood by analyzing the cutoff frequency, the collector current, Kirk effect and nonlinearities of transconductance at different temperatures.     

Si/Si1-xGex heterojunction bipolartransistors with high breakdown voltage

Heterojunction bipolar transistors are desirable for microwave applications because a low base resistance can be achieved yielding high maximum frequency of oscillation. Here we report Si/Si_1-xGe _x heterojunction bipolar transistors with high breakdown voltages and excellent small-signal microwave characteristics. The transistors structures were grown by molecular beam epitaxy and fabricated by a double-mesa process. Measured f_T and f_max were 10 and 22 GHz, respectively, for transistors with BV_CBO of 40 V     

A nonquasi-static MOSFET model for SPICE-transient analysis

The long-channel MOSFET model is based on an approximate solution to the nonlinear current-continuity equation in the channel. The model includes the large-signal transient and the small-signal AC analyses, although only the transient model is reported here. Comparisons have been made between this model and the 1-D numerical solution to the current-continuity equation, 2-D device simulation (PISCES), and the quasistatic (QS) results. The channel-charge partitioning scheme in the charge-based QS models is shown to be inadequate for the fast transient. This model does not use a charge-partitioning scheme and the currents are dependent on the history of the terminal voltages, not just the instantaneous voltages and their derivatives. For the slow signals (compared to the channel transit time), the nonquasistatic (NQS) model is reduced to the quasistatic 40/60 channel-charge partitioning scheme. The CPU time required for this model is about two to three times longer than that of conventional MOSFET models in SPICE     

A simplified theory of the BARITT silicon microwave diode

A simplified analytical theory is developed for the BARITT microwave diode. This is based on the small-signal concept of effective source conductivity and the large-signal concept of space-charge-limited injection. The impedance parameters of equivalent series resistance and capacitance and the output power and efficiency are evaluated as functions of frequency, r.f. load and biasing conditions. Small-signal negative-resistance Q-factors of about ?20 are obtained at bias current densities in the range from about 50 Amps/cm² to about 200 Amps/cm². Large-signal power generation efficiencies of about 10% can be achieved with Q-factors of about ?100.     

Bridge measurement of tunnel-diode parameters

A specific bridge measurement technique is presented for measuring the important small-signal parameters of the tunnel diode at frequencies up to 100 Mc and at all significant operating levels. Particular attention is paid to the problem of biasing the tunnel diode to eliminate instability in the negative resistance region which would otherwise prevent significant measurements being made in this region. Requirements for stable bias circuits are analyzed in detail and specific criteria for stable operation given. A circle diagram method is presented which allows the significant parameters to be determined from a set of measurements made for a sequence of bias voltages, at a chosen frequency. From the results, curves of shunt capacitance and conductance as a function of bias voltage may be plotted. Measurements made using a Wayne Kerr Type B.801 VHF Admittance Bridge on a particular tunnel diode are presented. The experimentally determined capacitance vs voltage curve is found to agree closely with the theoretical curve of the normal junction diode, with no pecularities through the negative resistance region. Further results show that approximate parameter values may be obtained even when oscillatory or bistable behavior prevents satisfactory measurement in the negative resistance region.     

Metastability of CMOS latch/flip-flop

Optimal device size, aspect ratio, and configurations for the design of the metastable hardened CMOS latch/flip-flops are obtained by using the AC small-signal analysis in the frequency domain instead of the usual time-domain approach. The Miller effect on the metastability is investigated for the configurations which have a better metastable resolving capability. The mean time between failure (MTBF) was measured, and the result verifies this new design approach. The power supply disturbance and temperature variation effects on the metastability were also measured, and the data show that a 0.75-V change of power supply voltage and 75°C change of chip temperature cause a four orders of magnitude difference in the MTBF. The simulation results using the AC small-signal frequency-domain analysis agree well with the measurement data for the different power supply voltages and chip temperatures, confirming that an AC small-signal approach can be used more widely for the design of metastable hardened latch/flip-flops. The other parameters are discussed in terms of their effects on the latch/flip-flop's susceptibility to the metastable state     

Oscillation neuron based on a low-variability threshold switching device for high-performance neuromorphic computing

Low-power and low-variability artificial neuronal devices are highly desired for high-performance neuromorphic com-puting.In this paper,an oscillation neuron based on a low-variability Ag nanodots(NDs)threshold switching(TS)device with low operation voltage,large on/off ratio and high uniformity is presented.Measurement results indicate that this neuron demon-strates self-oscillation behavior under applied voltages as low as 1 V.The oscillation frequency increases with the applied voltage pulse amplitude and decreases with the load resistance.It can then be used to evaluate the resistive random-access memory(RRAM)synaptic weights accurately when the oscillation neuron is connected to the output of the RRAM crossbar ar-ray for neuromorphic computing.Meanwhile,simulation results show that a large RRAM crossbar array(＞128×128)can be sup-ported by our oscillation neuron owing to the high on/off ratio(＞108)of Ag NDs TS device.Moreover,the high uniformity of the Ag NDs TS device helps improve the distribution of the output frequency and suppress the degradation of neural network recognition accuracy(＜1％).Therefore,the developed oscillation neuron based on the Ag NDs TS device shows great poten-tial for future neuromorphic computing applications.     

Modeling the microwave properties of superconductors

In this paper a macroscopic phenomenological model for the microwave properties of superconductors is presented. The model is based on the idea that there are two kinds of current carriers, and instead of the first London's equation a new equation is derived. This model can be applied to both low- and high-temperature superconductors. Using this model, an expression for the microwave surface resistance is derived and the surface resistance versus frequency is calculated. The results show that the relation between resistance and frequency is not R₃~ω² as indicated by both BCS theory and London model, but R_s~ω^a, where a is between 1 and 2 (e.g. a=1.35) for thin film high-T_c superconductors YBa₂Cu₃O_7-δ. The temperature dependence of R_s is simulated using the given model. These relations and the values of the surface resistance agree well with experimental results. A residual resistance may be interpreted from this model     

The noise performance of microwave transistors

Expressions for the noise parameters of microwave transistors are derived. The theory is based on a small-signal common-emitter equivalent circuit which includes a new basic noise equivalent circuit and the dominanting header parasitics. The theory is verified experimentally in the L-band (1 to 2 Gc/s) frequency range using Ge and Si microwave transistors. It is found that the header parasitics have little influence on the minimum noise figure, but do have large effects on the equivalent noise resistance and the optimum source admittance in the frequency region above about one-half of the series-resonant frequency resulting from the parasitics in conjunction with wafer parameters. For a quick evaluation of the noise performance, new approximate expressions are also given for the noise figure and for the optimum current which produces the lowest value.     

Hot small-signal S-parameter measurements of power transistors operating under large-signal conditions in a load-pull environment for the study of nonlinear parametric interactions

This paper presents a setup that enables wide-band (in-band and out-of-band) measurements of hot small-signal S-parameters of nonlinear devices driven by a large-signal single tone (namely, the pump signal). A load-pull characterization is performed at the pump frequency (F/sub 0/), while hot small-signal S-parameters are measured with a perturbating signal at a frequency (f) by the use of a probe tone. Basically, the frequency of the probe tone is swept over a wide bandwidth (at the present time from 300 MHz up to F/sub 0//2). A higher frequency range, from near dc to KF/sub 0/, will be implemented in a similar manner. The measurement setup reported here is applied to on-wafer measurements of S-band HBTs. Hot small-signal S-parameter measurements versus large-signal load impedance and pump level will be shown. An application to the prediction of parametric oscillations will be demonstrated. A parametric oscillation predicted at 373 MHz is confirmed by spectrum measurements.     

The Impact of Gate-Oxide Breakdown on Common-Source Amplifiers With Diode-Connected Active Load in Low-Voltage CMOS Processes

The influence of gate-oxide reliability on common-source amplifiers with diode-connected active load is investigated with the nonstacked and stacked structures under analog application in a 130-nm low-voltage CMOS process. The test conditions of this work include the dc stress, ac stress with dc offset, and large-signal transition stress under different frequencies and signals. After overstresses, the small-signal parameters, such as small-signal gain, unity-gain frequency, phase margin, and output dc voltage levels, are measured to verify the impact of gate-oxide reliability on circuit performances of the common-source amplifiers with diode-connected active load. The small-signal parameters of the common-source amplifier with the nonstacked diode-connected active-load structure are strongly degraded than that with the stacked diode-connected active-load structure due to a gate-oxide breakdown under analog and digital applications. The common-source amplifiers with diode-connected active load are not functionally operational under digital application due to the gate-oxide breakdown. The impact of soft and hard gate-oxide breakdowns on the common-source amplifiers with nonstacked and stacked diode-connected active-load structures has been analyzed and discussed. The hard breakdown has more serious impact on the common-source amplifiers with diode-connected active load.     

Three-step impedance criterion for small-signal stability analysis in two-stage DC distributed power systems

Small-signal stability analysis methods based on an impedance criterion originate from the minor loop gain method and are gradually utilized in two-stage DC distributed power systems. In this paper, we conclude that the impedance criterion directly dependent on output impedance Z/sub o/(s) of the source subsystem and input impedance Z/sub i/(s) of the load subsystem is possible but gives an incorrect stability analysis for systems with a regulated source subsystem. Through introducing a mapped pure impedance of the load subsystems and the preliminary system, we develop a general three-step impedance criterion, with which a correct small-signal stability analysis can be guaranteed, regardless of the type of source subsystem. Furthermore, we introduce the application of the three-step impedance criterion in two small-signal stability analysis cases and utilize it in an example system to predict the stability shift process arising from the variation on the load resistance and input voltage value.