A Josephson adder employing high-gain direct-coupled logic gate

A wide-margin adder with a simple configuration employing high-gain direct-coupled logic gates (HDCL's) was studied. A wide-margin half-adder circuit, consisting of a single junction and three HDCL buffer gates, is proposed. In order to obtain a wide-margin circuit, gates were designed to be protective against a noise signal. The experimental circuit fabricated by a conventional Pb alloy Josephson technology with 5-µm minimum line width has shown wide-margin (more than a ± 30-percent bias signal margin) characteristics, as predicted by a computer simulation. This paper also demonstrates that the adder can be simply modified into a wide-margin full adder with a simple configuration by connecting an additional single junction and a buffer gate for a carry signal.     

Ultra-broad-band GaAs monolithic direct-coupled feedback amplifiers

GaAs monolithic direct-coupled amplifiers with load resistor and feedback resistor have been developed. The fabricated amplifier using the self-aligned implantation for n⁺-layer technology (SAINT) FET's has a 10-dB gain, a 7.2-dB noise figure, and input VSWR less than 2.0 over the frequency range from dc to 4 GHz.     

Nonlinear feedback preamplifier for optical trigger circuits

A nonlinear preamplifier system to improve the performance of a zero-crossover optical trigger circuit is presented. The network is based on a low-noise operational amplifier with a Zener diode feedback. It is proposed to exploit the nonlinear characteristic of this network to reduce timing measurement uncertainty. Accordingly the circuit has been developed and tested in operation.     

Differential log-domain filters with high-gain common-mode feedback

A new class of differential log-domain filters based on common-mode feedback (CMFB) is demonstrated. Conditions for adding CMFB to differential log-domain integrators while preserving external linearity are derived. Because signals within differential log-domain circuits are nonlinear, the definition of "common-mode" in these circuits is not unique. Three possible definitions are explored, and each is illustrated with a simple but practical circuit. The circuits provide large CMFB loop gain, which forces common-mode signals to follow a desired nonlinear function. This allows closed-form expressions for the nonlinear internal signals to be derived, which is highly advantageous for design. Second-order filters using CMFB were compared to filters without CMFB through simulation and through measurements of fabricated filters. Adding CMFB is shown to allow greatly increased undistorted signal swings.     

A 12-dB high-gain monolithic distributed amplifier

By reducing gate and drain line loss associated with the active elements of a distributed amplifier, significant gain improvements are possible. Loss reduction is achieved in a novel monolithic distributed amplifier by replacing the common-source FET's of the conventional design with cascode elements having a gate length of one-quarter micron. A record gain of over 10 dB from 2 to 18 GHz and a noise figure of 4 dB at 7 GHz have been achieved on a working amplifier. Details of the design and fabrication process are described.     

Analysis of distributed feedback lasers using optical low-coherencereflectometry

The analysis of distributed feedback (DFB) lasers by optical low-coherence reflectometry (OLCR) shows the appearance of additional more or less periodic minima in the reflectogram. These do not reflect local minima of the reflectance, but are rather due to multipath interference effects caused by spectral filtering of the white light source by the laser under test. It is shown that the coupling coefficient of the laser can be determined from the period of these minima     

Integration of high-gain and high-saturation-power active regions using quantum-well intermixing and offset-quantum-well regrowth

A novel structure and method for fabricating regions of high and low modal gain on the same chip are reported, which enable diode lasers with maximum efficiency to be monolithically integrated with multiple-section semiconductor optical amplifiers having both high gain and high saturation power. This method uses quantum-well intermixing and an offset-quantum-well regrowth to achieve regions with high and low optical confinement. Fabry-Perot broad-area lasers were used to characterise the material in both regions.     

A high-performance monolithic multiplier using active feedback

Since its conception in 1967, the linearized transconductance multiplier (LTM) has rapidly gained acceptance as the preferred approach to the realization of monolithic analog multipliers, and its simplicity has commended it for use in low-cost modular designs. Accuracies of these units have been limited to about 0.5 to 2 percent, and drift and noise performance have generally been worse than that possible using the dominant alternative technique of pulse-width-height modulation. This paper shows that when careful attention is given to all the sources of error it is possible to attain a five-fold improvement in accuracy and corresponding reductions in the drift and noise levels. Odd-order nonlinearities can be reduced to negligible magnitudes by the use of active feedback, by substituting the usual resistive-bridge feedback path by an amplifier identical to that used as the input stages.     

A broadband PHEMT MMIC distributed doubler using high-pass drain line topology

A broadband frequency doubler, based on distributed amplifier techniques, has been designed to operate from 11 to 21 GHz. In order to reject the fundamental signal over a broadband frequency range, the conventional low-pass drain line structure was replaced with the high-pass structure. This topology can suppress fundamental signals over broadband without any balanced structure so that the chip size can be more compact. Measured conversion losses of better than 10 dB from 11 to 21 GHz input frequencies are achieved with fundamental signal rejection better than 12 dB. To the best of our knowledge, this is the first demonstration of distributed doubler using the high-pass drain line topology.     

Tunable optical-wavelength conversion using anoptically-triggerable multielectrode distributed feedback laser diode

Tunable optical-wavelength conversion with tunability greater than 5 Å using a multielectrode distributed-feedback laser diode (DFB LD) with a saturable absorber is discussed. This device is not dependent on input polarization and can operate at up to 500 MHz. Preliminary results of an optical switching experiment using the tunable wavelength converter and optical narrowband filter with a DFB LD amplifier are also reported     

5-60-GHz high-gain distributed amplifier utilizing InP cascodeHEMTs

A high-gain InP MMIC cascode distributed amplifier was developed which has 12 dB of gain from 5 to 60 GHz with over 20-dB gain control capability and a noise figure of 2.5-4 dB in the Ka band. Lattice-matched InAlAs/InGaAs cascode HEMTs on InP substrate with 0.25-μm gate length were the active devices. Microstrip was the transmission medium for this MMIC with an overall chip dimension of 2.3 mm×0.9 mm. The gain/noise figure advantages of the InP HEMT over the AlGaAs HEMT and the superior gain performance of the cascode HEMT over the common-source HEMT are demonstrated     

Multiple-waveguide distributed feedback lasers

Coupled wave theory is used to examine the performance of lasers formed from an array of coupled stripe waveguides with a grating overlay. It is found that such lasers exhibit inherent longitudinal mode discrimination, and, if the number of coupled guides is small, inherent transverse mode discrimination as well. The conditions for such selectivity are examined in detail, and it is shown that the correct grating distribution to use is one in which the grating fills the overlap region between the coupled guides.     

Low-power-consumption and high-gain CMOS distributed amplifiers using cascade of inductively coupled common-source gain cells for UWB systems

A distributed amplifier with new cascade inductively coupled common-source gain-cell configuration is presented. Compared with other existing gain-cell configurations, the proposed cascade common-source gain cell can provide much higher transconductance and, hence, gain. The new distributed amplifier using the proposed gain-cell configuration, fabricated via a TSMC 0.18-/spl mu/m CMOS process, achieves an average power gain of around 10 dB, input match of less than -20 dB, and noise figure of 3.3-6.1 dB with a power consumption of only 19.6 mW over the entire ultra-wideband (UWB) band of 3.1-10.6 GHz. This is the lowest power consumption ever reported for fabricated CMOS distributed amplifiers operating over the whole UWB band. In the high-gain operating mode that consumes 100 mW, the new CMOS distributed amplifier provides an unprecedented power gain of 16 dB with 3.2-6-dB noise figure over the UWB range.     

Linearisation of microwave power amplifiers using active feedback networks

A new technique for linearising microwave power amplifiers is presented. Analytical and experimental results show that the intermodulation distortion in power amplifiers can be seriously reduced when active feedback networks are employed.     

Principles of distributed feedback and distributed Bragg-reflector lasers

Wave propagation in periodic waveguides is analyzed by decomposing the eigen Bloch waves into traveling-wave components. It is shown that the principal components consist of a primary forward wave, a primary backward wave, and their Bragg-scattered secondary waves. One important parameter is the coupling constantsdue to Bragg scattering, which relates the secondary wave to the respective primary wave. Laser threshold condition is then obtained by applying the continuity of tangentialEandHat the two boundaries. The results thus obtained are general and applicable to thin-film lasers with various waveguide structures. The laser threshold condition of thin-film Bragg lasers is expressed in terms of two effective reflection coefficients for easy comparison with conventional lasers. For appreciable reflection, a significant change either in the propagation constant or in the coupling constant is required. Two basic types of thin-film Bragg lasers are distributed-feedback (DFB) lasers in which Bragg scattering is confined to the active medium and distributed-Bragg-reflector (DBR) lasers in which Bragg scattering is limited to regions beyond the active medium. The threshold gain, frequency control, and mode selectivity for both types are analyzed and the analyses are applied to GaAs and Nd lasers. It is shown that DBR lasers should have a lower threshold gain and a better mode selectivity than DFB lasers. For distributed-feedback effect to play a significant role in thin-film Bragg lasers, the product kLintmust be greater than unity whereKis the distributed-feedback coefficient and Lintis the interaction length. Advantages for having periodic structures outside the active medium so as to relax constraints onkand Lintare also discussed.     

Analysis of optical-injected distributed feedback lasers using complex optical low-coherence reflectometry

A theoretical and experimental investigation of reflectograms obtained for a distributed feedback (DFB) semiconductor laser using a phase-controlled high-resolution optical low-coherence reflectometer was carried out, yielding the effective group refractive index and its variation above threshold, the cavity internal loss, as well as the grating coupling factor of a multiquantum-well DFB laser. In addition, direct measurements of the injection-induced complex-modal index changes are presented for the first time.     

Scanning the laser gain spectrum using distributed feedback and hydrostatic pressure

High-pressure measurements on distributed-feedback GaxIn1-xASyP1-y lasers allow the gain spectrum to be scanned, providing a powerful tool for the study of the intrinsic properties of the laser, including the mechanisms responsible for the high-temperature sensitivity.     

50-GHz-bandwidth baseband amplifiers using GaAs-based HBTs

Baseband amplifiers of 50 GHz, using high-performance AlGaAs/InGaAs HBTs with regrown base contacts, have been demonstrated. The transimpedance amplifier achieved a bandwidth of 50.8 GHz with a gain of 11.6 dB. The transimpedance characteristics were of 49.3-GHz bandwidth with a 43.7-dBΩ transimpedance gain. The resistive and mirror Darlington feedback amplifiers, respectively, achieved a bandwidth of 54.7 GHz with a gain of 8.2 dB and a bandwidth of more than 60.0 GHz with a gain of 6.3 dB. To date, these are the widest bandwidths reported for lumped-circuit-design amplifiers. These results suggest the great potential of these amplifiers for use in future optical communication, microwave and millimeter-wave applications     

Narrow-band distributed feedback reflector design

The theory is developed for a narrowband distributed feedback reflector that reflects at the center of the grating stopband and transmits at frequencies to either side. A perturbational method of analysis is presented which simplifies the algebra and provides helpful insight. The approximate analysis is compared with the exact results. It is shown that the approximate solution is good in the operating region of practical devices. The proposed tunable narrowband reflector can perform well at a reasonable bandwidth of about 40 GHz     

Dry-etched wire distributed feedback laser

We report on the realization and the properties of dry-etched wire and wire-DFB lasers and compare them with two-dimensional (2-D) reference lasers. The starting vertical structure, which was optimized for low threshold, consists of four GaInAs quantum wells embedded in a GaInAsP waveguide. Even for very small longitudinal confinement factors of the order 0.23, the dry-etched wire lasers show laser operation up to 60°C and a threshold current density at room temperature of 5 kA/cm ² for simple oxide stripe lasers. For the wire lasers, an increase of the differential material gain of more than one order of magnitude (about a factor of 20) was measured, compared to conventional 2-D lasers. The wires were also arranged periodically with different grating constants to allow gain-coupled DFB laser operation. Clear single-mode emission has been found, as expected, from the gain-coupling mechanism