Distortion in off-state arsenide MESFET switches

This paper presents the results of an investigation into the origin and level of distortion generated by the off-state gallium arsenide MESFET when used as a microwave semiconductor control element. The results show that the drain-gate and gate-source capacitance nonlinearities generate distortion in the device in its off-state. These nonlinearities, which reflect the capacitance-voltage characteristic of the capacitances, can be reduced in as-fabricated devices by increasing the gate reverse bias voltage. The level of distortion monotonically increases with frequency throughout the usable range of the MESFET when used in a series reflective switch. In an SPDT switch application, where both on and off-state devices are used, the distortion level is relatively constant at frequencies in the vicinity of the gate bias cut-off frequency. The nonlinear off-state model is compared with both a SPICE-based analysis, and with experimental data on a GaAs MESFET SPDT switch. The main conclusions to be drawn from the study are that the dominate distortion generated by a GaAs MESFET used in a switch application occurs in the on-state, and that off-state distortion can be only slightly improved in as-fabricated devices     

RF CMOS Cells for Wireless Applications

There is increasing interest in the use of CMOS circuits for high frequency highly integrated wireless telecommunications systems. This paper presents the results of on-going work into the development of a cell library that includes many of the circuit elements required for the high frequency sub-systems of communications integrated circuits. The cell library studied included an RF control element, single ended Class A amplifier, RF isolator, and Gilbert cell mixer circuit topologies. Circuit design criteria and measurement results are presented. All cells were fabricated using standard 2.0, 1.2, and 0.8 m CMOS integrated circuit fabrication processes with no post-processing performed. The results indicate that 2.0 m CMOS can be used successfully up to approximately 250 MHz with 0.8 m cells useful up to approximately 1000 MHz.     

Linear and nonlinear characteristics of the silicon CMOS monolithic50-Ω microwave and RF control element

Radio-frequency (RF) control elements using silicon CMOS technology are investigated as an alternative to traditional PIN diode and GaAs MESFET control devices. Silicon CMOS RF control elements are attractive because of their potential in all-silicon monolithic CMOS solutions for completely integrated baseband and RF functions in low-cost wireless systems. Results of the study show that silicon CMOS switches can be designed to rival the insertion loss and isolation of gallium arsenide switches at low frequencies. Data are presented that show less than 1 dB insertion loss and isolation of greater than 50 dB at low frequencies for a variety of silicon CMOS fabrication technologies. A model for a distortion intercept point in MOS switches is presented and validated with experimental measurements     

The role of the psychiatric nurse practitioner

Policy, organizational management, and research roles have received little attention in this article because the focus has been on the practice role. It must be noted, however, that psychiatric nurse practitioners often assume these roles. Many psychiatric nurse practitioners have discovered that their expertise in communication and systems assessment prepares them well for policy and management positions. The influence of public and private policy on practice and the lives of mentally ill persons has led psychiatric nurse practitioners to become active in the public policy arena. Similarly, psychiatric nurse practitioners' grounding in practice and training in research allows for participation in planning and conducting studies that will inform policy makers as the mental health reform process continues. The psychiatric nurse practitioner title and role have evolved in response to regulatory desire for consistent titling of advanced practice nurses and community need for practitioners with the skills in assessment, psychotherapy, psychopharmacology, and care management. Nursing academic institutions are working to develop new programs to prepare the psychiatric nurse practitioners of the future in the wide range of skills needed for this role. Practice subspecialties and settings vary, but in all instances the psychiatric nurse practitioner offers a blend of nursing and psychiatric specialty care that, in many cases, is substitutive for that of a psychiatrist. In the current era of health-care reform, fiscal constraint, and burgeoning health-care technology, the practice, research, and policy roles available to and occupied by psychiatric nurse practitioners are many. The primary threat to full actualization of the psychiatric nurse practitioners' potential is that advanced practice nursing will choose to be wedded to anachronistic ideologies regarding nurse practitioners and clinical specialists.     

Optimal linear combination of sensors and actuators to enforce an interior conic open‐loop system

This paper presents techniques to linearly combine the sensor measurements and/or actuator inputs of a linear time‐invariant system to obtain a new system that is interior conic with prescribed bounds. In the optimal sensor combination problem, a desired system output is defined, and in the optimal actuator combination problem, a desired system input is defined, along with a frequency bandwidth in which the desired system input or output should be matched. The simultaneous optimal sensor and actuator combination problem includes desired system outputs and inputs. In all cases, the weighted or norm of the difference between the system with linearly combined sensors or actuators and the desired system is minimized while rendering the new system interior conic with prescribed bounds. The weighting transfer matrix used in the ‐ or ‐optimization problem is determined by the frequency bandwidth of interest. The individual sensor and actuator combination methods involve linear matrix inequality constraints and are posed as convex optimization problems, whereas the combined sensor and actuator method is an iterative procedure composed of convex optimization steps. Numerical examples illustrate superior tracking performance with the proposed sensor and actuator combination techniques over comparable techniques in the literature when implemented with a simple feedback controller. Robust asymptotic stability of the closed‐loop system to plant uncertainty is demonstrated in the numerical examples.     

The frequency-dependent impedance of p-i-n diodes

It is demonstrated that the impedance of a forward-biased p-i-n diode is definable as a function of frequency and depends on the diode's geometry and electronic properties. A procedure for calculating the equivalent series p-i-n diode impedance is presented and compared with experimental resistance versus frequency data for silicon p-i-n diodes. A procedure is also outlined for determining diode parameters for a desired resistance-frequency response     

Properties of Si3N4 Produced by Nitriding Slip-Cast Si Containing Si3N4 Grog Additions

The properties of Si₃N₄ compositions produced by nitriding slip-cast Si bodies containing up to 16% Si₃N₄ grog were determined. The introduction of grog consistently lowered the densities, the room- and high-temperature strengths, and the resistance to oxidation. The open structure of the grog-containing mixes favored low-temperature gas-phase reactions leading to α-Si₃N₄ formation. In higher-density compositions containing predominantly Si, gas-liquid-solid reactions at higher temperatures produced a relatively greater content of the β phase.     

Establishing the minimum reverse bias for a p-i-n diode in ahigh-power switch

An important circuit design parameter in a high-power p-i-n diode application is the selection of an appropriate applied DC reverse bias voltage. Until now, this important circuit parameter has been chosen either conservatively, using the magnitude of the peak RF voltage, or by empirical trials to determine a possible lower value. The reverse bias requirement for a p-i-n diode operating in a high-power RF and microwave environment is explored. It is demonstrated that the minimum reverse bias voltage is equivalent to the p-i-n diode's self-generated DC voltage under similar RF conditions. A concise expression for this self-generated voltage is developed and experimentally verified and should assist the design engineer in more accurately selecting an appropriate minimum value for the applied reverse bias voltage setting     

On-state distortion in high electron mobility transistor microwaveand RF switch control circuits

The origin of the distortion generating mechanism in microwave and RF control circuits using high electron-mobility transistors (HEMTs) is presented in this paper. A model is presented for predicting the distortion in series-connected HEMT switches. The theoretical discussion shows that turn-off voltages in the range of 1.0-1.5 V provide the lowest distortion in series switch configurations. A comparison of the HEMT snitch with MESFET switches shows that the HEMT switch generates more distortion than its MESFET counterpart. In addition, the frequency response of HEMT switches is the opposite of the MESFET switch, with less distortion at low frequencies. The model is validated with experimental data taken on a AlGaAs/GaAs HEMT in the series switch configuration     

Reactance influence on PIN diode attenuators

The reactive component of a PIN diode is known to be a function of current due to conductivity modulation in the I-region. This reactive component can negatively influence predicted attenuation levels in PIN diode attenuators if not properly accounted for. A figure of merit based on the PIN diode parameters, DC forward current, and operation frequency, is proposed that determines the operating conditions where this reactive component can be safely ignored. Simulations and measurement data on PIN diodes of various I-region widths verify the proposed figure of merit.