Microstrip circuit applications of high-Q open microwaveresonators

An open microwave resonator can be formed above a planar microstrip substrate by suspending a spherical reflector above it. A theory is developed to account for the coupling between such an open resonator mode and a microstrip line. The open resonator is shown to have useful circuit properties similar to a dielectric resonator, but with the potential of efficient operation well into the millimeter-wave range. Experimental confirmation of the theory is demonstrated by a scale model of a microstrip-based single-pole bandpass filter, which shows a loaded Q of 860 and a minimum loss of 0.8 dB±0.4 dB at 10 GHz     

A monolithic Ka-band 0.25 μm GaAs MESFET transmitterfor high volume production

A monolithic Ka-band transmitter consisting of a voltage-controlled oscillator (VCO) and a power amplifier using 0.25 μm MESFET technology has been developed for high volume production. An output power of 21.5 dBm at 35.4 GHz with a tuning range of 600 MHz has been achieved. Hundreds of these monolithic transmitters have been fabricated, and an RF yield of 40% has ben achieved from the GaAs MMIC pilot line based on the total number of wafers started. The high yield obtained from this high level integration of multifunctional MMIC chips indicates the maturity of the design and processing capability of millimeter-wave (MMW) GaAs MESFET technology     

Modulation performance of a semiconductor laser coupled to anexternal high-Q resonator

The dynamic response of a semiconductor laser coupled to an external resonator is studied using the single-mode rate equations modified to account for the dispersive feedback. Both the frequency and the damping rate of relaxation oscillations are affected by the feedback. The frequency chirp that invariably accompanies amplitude modulation is significantly reduced. The feedback also reduces the phase noise and the linewidth. To investigate the usefulness of external-resonator lasers in high-speed optical communication systems, the rate equation have been solved numerically to obtain the emitted chirped pulse; the pulse is propagated through the fiber, detected, and filtered at the receiver. The simulated-eye diagrams show that such lasers can be operated at high bit rates with negligible dispersion penalty owing to their reduced frequency chip     

A monolithic digital chirp synthesizer chip with I andQ channels

A monolithic digital chirp synthesizer (DCS) chip has been developed using GaAs/AlGaAs HI²L technology. The 6500-HBT-gate DCS chip is capable of producing linear frequency-modulated (chirp) waveforms or single-frequency waveforms. The major components of the DCS are two 28-b pipelined accumulators, a 1.8 kb sine ROM, a 1.8 kb cosine ROM, and two 8 b digital-to-analog converters (DACs). The total chip area is 4.877 mm×6.172 mm using a minimum feature size of 1.5 μm. All components of the DCS are fully functional and the device has been clocked to 450 MHz with a power dissipation of 18 W     

A positive-feedback transconductance amplifier with applications tohigh-frequency, high-Q CMOS switched-capacitor filters

The authors describe a high-bandwidth amplifier that simultaneously achieves high gain by using internal positive feedback. The results obtained when the amplifier is used in a general-purpose switched-capacitor biquadratic building block are also presented. This device achieves 150-kHz center-frequency operation with Q accuracy of 15% when clocked at 7.5 MHz with 10-V ±10% supplies from -55°C to +125°C. With a minimum power supply of 4.5 V, this filter operates with center frequencies up to 100 kHz when clocked at 5 MHz, while performing with the same accuracy and across the same temperature range as above     

A low-loss bandpass filter using electrically coupled high-Q TM01δ dielectric rod resonators

For a TM_01δ mode dielectric rod resonator placed coaxially in a TM₀₁ cutoff circular waveguide, characteristics such as the resonant frequency, its temperature coefficient, the unloaded Q, and the other resonances are discussed on the bases of accurate calculations using the mode-matching method. The results show that this resonator compares favorably with a conventional TE_01δ mode dielectric resonator, particularly for realization of a high unloaded Q. Analytical results also verify that interresonator coupling between these two resonators can be expressed equivalently by a capacitively coupled LC resonant circuit. A four-stage Chebyshev filter having a ripple of 0.035 dB and an equiripple bandwidth of 27 MHz at a center frequency of 11.958 GHz was fabricated using these resonators. Its insertion loss is 0.5 dB, which corresponds to an unloaded Q of 17000, and no spurious response appears in the frequency range below 17 GHz     

I and Q decomposition of self-noise in square-lawclock regenerators

A method for obtaining power spectra for the self-noise components in phase and in quadrature to the desired generated clock signal for PAM systems is described. A previously recognized cross spectrum is also discussed. Results can be expressed either in a closed form or as the sum of rapidly convergent series, depending on the signalling waveform used. A computation of the in-phase and quadrature spectra for Nyquist pulses for excess bandwidth factors ranging from 0.1-0.9 is included, along with demonstration showing that for signalling waveforms with even or odd symmetry, cross power spectrum is zero at all frequencies. It is also shown that if the cross power spectrum is not zero due to asymmetry in the signalling waveform, sampling keyed to other than zero-crossing of the timing wave can give a lower timing jitter     

Data reduction method for Q measurements of strip-lineresonators

A technique that enables the attenuation constant α of a microstrip line to be found from the measured return loss curve as a function of frequency for a half-wavelength resonator is described. Data averaging is incorporated and the effects of dispersion are included. This method does not require the use of an equivalent resonator model for the stripline, nor does it rely on graphical techniques     

A new I-V model for short gate-length MESFET's

An I-V model for short gate-length MESFETs operated in the turn-on region is proposed, in which the two-dimensional potential distributions contributed by the depletion-layer charges under the gate and in the ungated region are separately obtained by conventional 1-D approximation and the Green's function solution technique. Moreover, the bias-dependent parasitic resistances due to the modulation of the depletion layer in the ungated region for non-self-alignment MESFETs are also taken into account in the developed I-V model. It is shown that good agreement is obtained between the I-V model and the results of 2-D numerical analysis. Moreover, comparisons between the proposed analytical model and the experimental data are made, and excellent agreement is obtained     

High-efficiency waveguide-coupled λ=1.3 μmInxGa1-xAs/GaAs MSM detector exhibiting largeextinction ratios at L and X band

The design and fabrication of a 1.3-μm waveguide-coupled strained-layer In_xGa_1-xAs/GaAs MSM detector with an optimized active layer thickness is reported. For 100-μm-long devices, a responsivity of 0.58 mA/mW is observed. Using the detector as an optoelectronic switch, on/off ratios better than 40 dB were achieved at L and X band     

Electrooptically Q-switched 2.79 μm YSGG:Cr:Er laserwith an intracavity polarizer

Single Q-switched pulses have been generated in YSGG:Cr:Er with a 360-ns-risetime LiNbO₃ electrooptical modulator. It is shown that birefringence losses can be avoided and spiking emission eliminated by placing an additional polarizing LiNbO ₃ prism inside the laser resonator. Reproducible single Q -switched pulses of 200-ns duration have been generated     

I/Q channel reversal correcting properties of anSQPSK Costas loop with integrated symbol synchronization

An integrated-carrier loop/symbol synchronizer, using a digital Costas loop with matched arm filters to demodulate staggered quaternary phase-shift keyed (QPSK) signals, is analyzed. An expression is derived for the S curve, parameterized by bit synchronization error. This result suggests that the demodulator structure offers an inherent I/Q channel reversal correcting capability. Computer simulation results are presented that support this conclusion, and suggest that ambiguity resolution performance depends on the ratio of carrier and synchronization loop bandwidths     

A simple series for personal computer computation of the errorfunction Q(·)

A simple series for computation of the error function Q(·) is derived. It is well suited for implementation on a personal computer, having six or more significant figure accuracy over a wide range of argument and requiring few lines of code to program. Its advantage over other series is its rapid convergence over a wide range of argument     

Noise characteristics of femtosecond fiber Raman soliton laser withhigh-Q cavity

The amplitude noise characteristics of femtosecond optical pulses generated from a synchronously pumped all-fiber Raman soliton laser with high-Q cavity are investigated under different operation states of the laser. By suppressing the soliton self-frequency shift (SSFS) effect in the high-Q fiber cavity, real femtosecond soliton oscillation can be obtained in the laser. Low-noise 400 fs optical pulses with a white amplitude noise level of -120 dBc/Hz have been generated from the laser operating in such an SSFS-free state     

Analysis of a type II hybrid ARQ scheme with codecombining

An analysis is presented of the selective-repeat type II hybrid AR Q (automatic-repeat-request) scheme, using convolutional coding and exploiting code combining. With code combining, at successive decoding attempts for a data packet, the decoder for error correction operates on a combination of all received sequences for that packet rather than only on the two most recent received ones as in the conventional type II hybrid ARQ scheme. It is shown by means of analysis and computer simulations that with code combining, a significant throughput is achievable, even at very high channel error rates     

Analytical model for I-V characteristics ofion-implanted MESFET's with heavily doped channel

A theoretical model for the I-V characteristics of ion-implanted metal-semiconductor field-effect transistors (MESFETs) has been developed. A formula for effective drift saturation velocity for electrons and a Gaussian approximation for the inverse of reduced distances in the channel have erased the process of formulation. Theoretical formulas for early saturation of drain current and transconductance obtained in the framework of the Lehovec-Zuleeg procedure are quite simple and accurate. When calculated results from the present model are compared with available experimental results, an encouraging correspondence between the two is observed. A study of the appropriateness of the velocity overshoot and the softening of pinch-off voltage indicates that both of these phenomena are real in short-channel MESFETs and need to be carefully accounted for in a realistic model. The model is equally applicable also to ion-implanted JFETs     

Modeling temperature effects in the DC I-Vcharacteristics of GaAs MESFET's

A simple model is presented to account for the main temperature effects influencing the DC performance of GaAs MESFETs. The model is based on a consistent solution of heat flow and current equations that accounts for nonuniform power dissipation within the device. The simulation results are satisfactorily compared with experimental data obtained with pulsed and DC measurements performed on conventional devices as well as on suitable test structures     

7.8 GHz small-signal modulation bandwidth of 1.3 μm DQWGaInAsN/GaAs laser diodes

High frequency characterisation of double quantum well GaInAsN laser diodes emitting at 1.28 μm is reported. The 3 dB bandwidth of ridge waveguide lasers was measured to be 7.8 GHz at 120 mA under CW operation demonstrating the potential for high speed operation of these devices     

Noise spectra and noise correlation functions of the single-modelaser with a low-Q cavity

The noise characteristics of a single-mode laser with a low-Q cavity are investigated theoretically. After the electric field is adiabatically eliminated from the Maxwell-Bloch equations, coupled Langevin equations with both additive and multiplicative white noises are examined. The equations are solved using Rice's method in a framework of quasilinear Fourier analysis. Noise spectral densities are calculated analytically to study the dependence of the relative intensity noise (RIN) on the pumping. Through an investigation of the auto- and cross-correlations of the light intensity and population noises, their variances are obtained in order to compare their properties to the good-cavity case. The stationary intensity cumulants, the photon counting coefficient, and the photon counting probability are explicitly derived and compared with the results of a Fokker-Planck analysis previously carried out for both the good- and bad-cavity cases     

1.3 μm monolithic integrated optoelectronic receiver using anInGaAs MSM photodiode and AlGaAs/GaAs HEMTs grown on GaAs

The first 1.3 μm monolithic integrated optoelectronic receiver using an InGaAs MSM photodiode and AlGaAs/GaAs HEMTs grown on a GaAs substrate has been fabricated. At differential output of the implemented multistage amplifier the transimpedance is 26.8 kΩ (into 50 Ω). The bandwidth of 430 MHz implies suitability for transmission rates up to 622 Mbit/s