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The paper describes the practical realization and characteristics of a small, totally autonomous, passive frequency standard based on the coherent population trapping (CPT) phenomenon. A description of the frequency standard, including physical characteristics, block diagrams of the optical control CPT resonance system and of the digital control electronics is given. The characteristics of the frequency standard relative to general functionality and frequency stability are given, as measured on several units.

The paper summarizes the relative advantages and disadvantages of coherent population trapping (CPT) or intensity optical pumping (IOP) for the implementation of a passive atomic frequency standard using the isotope /sup 87/Rb. This paper outlines the basic principles common to both CPT and IOP when using laser optical pumping, and makes explicit their similarities and their differences. This paper describes experimental results obtained in the same cell on the characteristics of the CPT and IOP /sup 87/Rb-hyperfine-resonance line. The measurements showed that the signal contrast is larger in CPT than in IOP for the same resulting line width; the light shift is smaller in CPT than in IOP, and is easier to control; in principle, a passive frequency standard based on CPT has a smaller size than that based on IOP, due to the absence of a microwave cavity. Conclusions on overall expectations for the future of such frequency standards are drawn.

The authors report on the state-of-the-art power performance of InP-based HEMTs (high electron mobility transistors) at 59 GHz. Using a 448- mu m-wide HEMT with a gate length of 0.15 mu m, an output power of 155 mW with a 4.9-dB gain and a power-added efficiency of 30.1% were obtained. By power-combining two of these HEMTs, an output power of 288 mW with 3.6-dB gain and a power-added efficiency of 20.4% were achieved. This is the highest output power reported with such a high efficiency for InP-based HEMTs, and is comparable to the best results reported for AlGaAs/InGaAs on GaAs pseudomorphic HEMTs at this frequency. >

The first demonstration of GaN digital circuits is reported. First‐generation GaN digital technology has already shown high yields for circuits of considerable complexity. Specifically, a 31-stage ring oscillator was implemented using 217 transistors. Properties of the AlGaN/GaN material system that enable outstanding power handling capabilities of GaN heterojunction field effect transistors (HFETs), i.e. large bandgap, high breakdown field and high saturation velocity, also make it attractive for digital applications in harsh environments. Because of these unique material characteristics GaN digital control circuits have the potential to operate in high radiation environments, at elevated temperature, and directly from high voltage rails. Successful operation of GaN 31-stage ring oscillators at the highest base-plate temperature attainable by test setup of 265°C, indicates these circuits can operate at significantly higher temperatures.

The status of lattice-matched high-electron-mobility transistors (HEMTs) and pseudomorphic AlInAs-GaInAs grown on In substrates is reviewed. The best lattice-matched devices with 0.1- mu m gate length had a transconductance g/sub m/=1080 mS/mm and a unity current gain cutoff frequency f/sub T/=178 GHz, whereas similar pseudomorphic HEMTs had g/sub m/=1160 mS/mm and f/sub T/=210 GHz. Single-stage V-band amplifiers demonstrated 1.3- and 1.5-dB noise figures and 9.5- and 8.0-dB associated gains for the lattice-matched and pseudomorphic HEMTs, respectively. The best performance achieved was a minimum noise figure of F/sub min/=0.8 dB with a small-signal gain of G/sub a/=8.7 dB. >

Record DC and RF performance of AlInAs-GaInAs lattice matched to InP HEMTs (high-electron-mobility transistors) with nominally 0.2- and 0.1- mu m gate lengths have been achieved. The devices were fabricated on material grown by MBE (molecular-beam epitaxy) on Fe-doped InP substrates. The epitaxial layers consisted of an undoped AlInAs spacer, a highly doped AlInAs donor layer, an undoped Schottky-enhancing AlInAs layer, and, finally, a highly doped GaInAs layer contact layer. 50- mu m-wide devices with 0.2- and 0.1- mu m-long T-gates were fabricated. The 0.2- mu m gate-length devices were tested at V-band. The single-stage amplifier (waveguide to waveguide with no correction) exhibited a minimum noise figure F/sub min/ of 1.8 dB with an associated gain 7.5 dB at 63.0 GHz. This translates to an amplifier noise measure of 2.10 dB. The corresponding device performance was a minimum noise figure of 1.4 dB with an associated gain of 8.5 dB. This corresponds to a device noise measure of 1.6 dB. >