A capacitor-free CMOS low-dropout regulator with damping-factor-control frequency compensation

A 1.5-V 100-mA capacitor-free CMOS low-dropout regulator (LDO) for system-on-chip applications to reduce board space and external pins is presented. By utilizing damping-factor-control frequency compensation on the advanced LDO structure, the proposed LDO provides high stability, as well as fast line and load transient responses, even in capacitor-free operation. The proposed LDO has been implemented in a commercial 0.6-/spl mu/m CMOS technology, and the active chip area is 568 /spl mu/m/spl times/541 /spl mu/m. The total error of the output voltage due to line and load variations is less than /spl plusmn/0.25%, and the temperature coefficient is 38 ppm//spl deg/C. Moreover, the output voltage can recover within 2 /spl mu/s for full load-current changes. The power-supply rejection ratio at 1 MHz is -30 dB, and the output noise spectral densities at 100 Hz and 100 kHz are 1.8 and 0.38 /spl mu/V//spl radic/Hz, respectively.     

A 2-V 2.3/4.6-GHz dual-band frequency synthesizer in 0.35-/spl mu/m digital CMOS process

This brief describes the design of a frequency synthesizer for 2.3/4.6-GHz wireless applications in a 0.35-/spl mu/m digital CMOS process. This synthesizer provides dual-band output signals by means of frequency doubling techniques. Output frequency of the proposed synthesizer ranges from 1.87-2.3 GHz, and 3.74-4.6GHz. This chip consumes a total power of 80 mW from a single 2-V supply, including 45 mW for dual-band output buffers. Core size is 2200 /spl mu/m/spl times/1600 /spl mu/m.     

A 1.7-1.9 THz local oscillator source

We report on the design and performance of a /spl times/2/spl times/3/spl times/3 frequency multiplier chain to the 1.7-1.9 THz band. GaAs-based planar Schottky diodes are utilized in each stage. A W-band power amplifier, driven by a commercially available synthesizer, was used to pump the chain with 100 mW of input power. The peak measured output power at room temperature is 3 /spl mu/W at 1740 GHz. When cooled to 120 K, the chain provides more than 1.5 /spl mu/W from 1730 to 1875 GHz and produced a peak of 15 /spl mu/W at 1746 GHz.     

Self-heating and trapping effects on the RF performance of GaN MESFETs

RF power performances of GaN MESFETs incorporating self-heating and trapping effects are reported. A physics-based large-signal model is used, which includes temperature dependences of transport and trapping parameters. Current collapse and dc-to-RF dispersion of output resistance and transconductance due to traps have been accounted for in the formulation. Calculated dc and pulsed I-V characteristics are in excellent agreement with the measured data. At 2 GHz, calculated maximum output power of a 0.3 /spl mu/m/spl times/100 /spl mu/m GaN MESFET is 22.8 dBm at the power gain of 6.1 dB and power-added efficiency of 28.5% are in excellent agreement with the corresponding measured values of 23 dBm, 5.8 dB, and 27.5%, respectively. Better thermal stability is observed for longer gate-length devices due to lower dissipation power density. At 2 GHz, gain compressions due to self-heating are 2.2, 1.9, and 0.75 dB for 0.30 /spl mu/m/spl times/100 /spl mu/m, 0.50 /spl mu/m/spl times/100 /spl mu/m, and 0.75 /spl mu/m/spl times/100 /spl mu/m GaN MESFETs, respectively. Significant increase in gain compression due to thermal effects is reported at elevated frequencies. At 2-GHz and 10-dBm output power, calculated third-order intermodulations (IM3s) of 0.30 /spl mu/m/spl times/100 /spl mu/m, 0.50 /spl mu/m/spl times/100 /spl mu/m, and 0.75 /spl mu/m/spl times/100 /spl mu/m GaN MESFETs are -61, -54, and - 45 dBc, respectively. For the same devices, the IM3 increases by 9, 6, and 3 dBc due to self-heating effects, respectively. Due to self-heating effects, the output referred third-order intercept point decreases by 4 dBm in a 0.30 /spl mu/m/spl times/100 /spl mu/m device.     

Size-dependent output power saturation of vertical-cavity surface-emitting laser diodes

We demonstrate efficient vertical-cavity surface-emitting laser diodes with high output power levels. Improved output power in these pillar-etched devices is achieved through a 60% lower thermal resistance by using a 15-/spl mu/m-thick Au-plated heat spreading layer on the top surface with a size of 300/spl times/300 /spl mu/m/sup 2/. The maximum continous wave output power increases almost linearly with laser diameter, before it saturates at 42 mW for an unmounted Au-plated device of 64-/spl mu/m diameter. A simple analytical model describes the laser output characteristics and the size-dependent saturation behavior of the maximum output power.     

Room-temperature continuous-wave 1.55 /spl mu/m GaInNAsSb laser on GaAs

The first low-threshold 1.55 /spl mu/m lasers grown on GaAs are reported. Lasing at 1.55 /spl mu/m was observed from a 20/spl times/2400 /spl mu/m as-cleaved device with a room-temperature continuous-wave threshold current density of 579 A/cm/sup 2/, external efficiency of 41%, and 130 mW peak output power. The pulsed threshold current density was 550 A/cm/sup 2/ with >600 mW peak output power.     

Low-threshold high-T/sub 0/ 1.3-/spl mu/m InAs quantum-dot lasers due to p-type modulation doping of the active region

P-type doping is used to demonstrate high-To, low-threshold 1-3 /spl mu/m InAs quantum-dot lasers. A 5-/spl mu/m-wide oxide confined stripe laser with a 700-/spl mu/m-long cavity exhibits a pulsed T/sub 0/ = 213 K (196 K CW) from 0/spl deg/C to 80/spl deg/C. At room temperature, the devices have a CW threshold current of /spl sim/4.4 mA with an output power over 15 mW. The threshold at 100/spl deg/C is 8.4 mA with an output power over 8 mW.     

Low-threshold continuous-wave 1.5-/spl mu/m GaInNAsSb lasers grown on GaAs

We present the first continuous-wave (CW) edge-emitting lasers at 1.5 /spl mu/m grown on GaAs by molecular beam epitaxy (MBE). These single quantum well (QW) devices show dramatic improvement in all areas of device performance as compared to previous reports. CW output powers as high as 140 mW (both facets) were obtained from 20 /spl mu/m /spl times/ 2450 /spl mu/m ridge-waveguide lasers possessing a threshold current density of 1.06 kA/cm/sup 2/, external quantum efficiency of 31%, and characteristic temperature T/sub 0/ of 139 K from 10/spl deg/C-60/spl deg/C. The lasing wavelength shifted 0.58 nm/K, resulting in CW laser action at 1.52 /spl mu/m at 70/spl deg/C. This is the first report of CW GaAs-based laser operation beyond 1.5 /spl mu/m. Evidence of Auger recombination and intervalence band absorption was found over the range of operation and prevented CW operation above 70/spl deg/C. Maximum CW output power was limited by insufficient thermal heatsinking; however, devices with a highly reflective (HR) coating applied to one facet produced 707 mW of pulsed output power limited by the laser driver. Similar CW output powers are expected with more sophisticated packaging and further optimization of the gain region. It is expected that such lasers will find application in next-generation optical networks as pump lasers for Raman amplifiers or doped fiber amplifiers, and could displace InP-based lasers for applications from 1.2 to 1.6 /spl mu/m.     

1.49-/spl mu/m-band gain-shifted thulium-doped fiber amplifier for WDM transmission systems

This paper describes in detail the amplification characteristics of gain-shifted thulium-doped fiber amplifiers (GS-TDFAs) operating in the 1480to 1510-nm wavelength region (1.49-/spl mu/m S-band) for use in wavelength-division-multiplexing (WDM) systems. Gain shifting of a TDFA, which normally has a gain band at 1.47 /spl mu/m (S/sup +/-band), is achieved by two types of dual-wavelength pumping: (1) 1.05 and 1.56 /spl mu/m or (2) 1.4 and 1.56 /spl mu/m. The main pump source at 1.05 or 1.4 /spl mu/m creates population inversion between /sup 3/F/sub 4/ (upper laser level) and /sup 3/H/sub 4/ (lower laser level), while the auxiliary pump source at 1.56 /spl mu/m reduces the average fractional inversion down to approximately 0.4, which is a desired level for gain shifting. We show experimentally that the former provides a low internal noise figure (<4 dB) due to high fractional inversion at the input end of a thulium fiber, while the latter provides a very high optical efficiency but a higher internal noise figure (/spl sim/5 dB) due to the lower fractional inversion at the input end. These characteristics were verified by numerical simulation based on a comprehensive rate equation modeling. We demonstrated a 1.4- and 1.56-/spl mu/m laser-diode-pumped GS-TDFA with an optical efficiency of 29.3% and high output power of +21.5 dBm. Gain flatness and tilt control were also investigated. These results strongly confirm the feasibility of using GS-TDFAs in practical ultralarge-capacity WDM networks.     

192 GHz push-push VCO in 0.13 /spl mu/m CMOS

A 192 GHz cross-coupled push-push voltage controlled oscillator (VCO) is fabricated using the UMC 0.13 /spl mu/m CMOS logic process. The VCO can be tuned from 191.4 to 192.7 GHz. The VCO provides output power of /spl sim/-20 dBm and phase noise of /spl sim/-100 dBc/Hz at 10 MHz offset, while consuming 11 mA from a 1.5 V supply.     

Directional light output from photonic-wire microcavity semiconductor lasers

We have obtained directional light output from a recently realized InGaAsP photonic-wire microcavity ring lasers. The output was achieved by fabricating a 0.45-/spl mu/m-wide U-shape waveguide next to a 10-/spl mu/m diameter microcavity ring laser. The laser has a threshold pump power of around 124 /spl mu/W when optically pumped at 514 nm. It is comparable to the former structure without output coupling. The output coupling efficiency can be controlled carefully by choosing the spacing between the laser cavity and the waveguide.     

High-performance 1.5 /spl mu/m GaInNAsSb lasers grown on GaAs

Substantially reduced threshold current density and improved efficiency in long-wavelength (>1.4 /spl mu/m) GaAs-based lasers are reported. A 20/spl times/1220 /spl mu/m as-cleaved device showed a room temperature continuous-wave threshold current density of 580 A/cm/sup 2/, external efficiency of 53%, and 200 mW peak output power at 1.5 /spl mu/m. The pulsed threshold current density was 450 A/cm/sup 2/ with 1145 mW peak output power.     

A monolithic conditioner for thermocouple signals

The authors discusses a monolithic signal conditioner for direct thermocouple input which provides gain, common-mode signal rejection, and cold-junction compensation. It provides 50 to 1 ambient temperature rejection and a nominal 10 mV//spl deg/C output range. It operates on as little as 800 /spl mu/W, provides a thermocouple fault alarm and has provision for use as a set-point feedback controller as well as for signal measurements. The circuit is fabricated on a standard linear IC process and uses laser-wafer-trimmed thin-film resistors to achieve 1/spl deg/C temperature calibration.     

1.5 V large-driving class-AB buffer amplifier with quiescent current control

A 1.5 V large-driving class-AB buffer amplifier with quiescent current control suitable for output driver application is proposed. An experimental prototype buffer demonstrated that the circuit draws only 80 /spl mu/A static current, and exhibited the rise time of 0.4 /spl mu/s and fall time of 1 /spl mu/s under a 100 /spl Omega///150 pF load.     

Short wavelength (/spl lambda//spl sim/4.3 /spl mu/m) high-performance continuous-wave quantum-cascade lasers

We report continuous-wave (CW) operation of a 4.3-/spl mu/m quantum-cascade laser from 80 K to 313 K. For a high-reflectivity-coated 11-/spl mu/m-wide and 4-mm-long laser, CW output powers of 1.34 W at 80 K and 26 mW at 313 K are achieved. At 298 K, the CW threshold current density of 1.5 kA/cm/sup 2/ is observed with a CW output power of 166 mW and maximum wall-plug efficiency of 1.47%. The CW emission wavelength varies from 4.15 /spl mu/m at 80 K to 4.34 /spl mu/m at 298 K, corresponding to a temperature-tuning rate of 0.87 nm/K. The beam full-width at half-maximum values for the parallel and the perpendicular far-field patterns are 26/spl deg/ and 49/spl deg/ in CW mode, respectively.     

High-power broadly tunable Ho/sup 3+/-doped silica fibre laser

Tuning of the 2.1 /spl mu/m Ho/sup 3+/-doped silica fibre laser is demonstrated for the first time. The /sup 5/I/sub 7//spl rarr//sup 5/I/sub 8/ transition provides tuning over 144 nm, from 2019 to 2163 nm, and a maximum pump-limited output power of 1.58 W at 2100 nm was produced.     

High-power highly reliable 1.02-1.06-/spl mu/m InGaAs strained-quantum-well laser diodes

By growing the InGaAs active layer at temperatures lower than in conventional growth, we extended the lasing wavelength and presented the high reliability in InGaAs strained-quantum-well laser diodes. Equivalent I-L characteristics were obtained for 1.02-, 1.05-, and 1.06-/spl mu/m laser diodes with a cavity length of 1200 /spl mu/m. Maximum output power as high as 800 mW and fundamental transverse mode operation at up to 400 mW were obtained at 1.06 /spl mu/m and an 1800-/spl mu/m cavity. Stable operation was observed for over 14 000 h under auto-power-control of 225 mW at 50/spl deg/C for the 1.02-, 1.05-, and 1.06-/spl mu/m lasers with a 900-/spl mu/m cavity.     

Multi-watt, high efficiency, diffraction-limited Nd:YAG planar waveguide laser

An efficient, longitudinally diode-pumped, diffraction-limited, Nd:YAG double-clad planar waveguide laser was operated on four transitions of the Nd/sup 3+/ ion. Optimized output powers of 4.3, 3.5, and 2.7 W were obtained for absorbed pump powers of /spl sim/7 W, for the transitions at the lasing wavelengths of 1.064 /spl mu/m, 946 nm, and 1.3 /spl mu/m, respectively. Operation of the weak /sup 4/F/sub 3/2//spl rarr//sup 4/I/sub 5/2/ transition, lasing at 1.833 /spl mu/m, was demonstrated at an absorbed pump power threshold of 300 mW and an output power of 400 mW, with a nonoptimized output coupling. Diffraction-limited performance was obtained in both the guided and nonguided axes.     

High-speed driving scheme and compact high-speed low-power rail-to-rail class-B buffer amplifier for LCD applications

A high-speed driving scheme and a compact high-speed low-power rail-to-rail class-B buffer amplifier, which are suitable for small- and large-size liquid crystal display applications, are proposed. The driving scheme incorporates two output driving stages in which the output of the first output driving stage is connected to the inverting input and that of the second driving stage is connected to the capacitive load. A compensation resistor is connected between the two output stages for stability. The second output stage is used to improve the slew rate and the settling time. The buffer draws little current while static but has a large driving capability while transient. The circuit achieves the large driving capability by employing simple comparators to sense the transients of the input to turn on the output stages, which are statically off in the stable state. This increases the speed of the circuit without increasing static power consumption too much. A rail-to-rail folded-cascode differential amplifier is used to amplify the input signal difference and supply the bias voltages for the second stage. An experimental prototype output buffer implemented in a 0.35-/spl mu/m CMOS technology demonstrates that the circuit draws only 7-/spl mu/A static current and exhibits the settling times of 2.7 /spl mu/s for rising and 2.9 /spl mu/s for falling edges for a voltage swing of 3.3 V under a 600-pF capacitance load with a power supply of 3.3 V. The active area of this buffer is only 46.5/spl times/57/spl mu/m/sup 2/.     

High-power nearly diffraction-limited AlGaAs-InGaAs semiconductor slab-coupled optical waveguide laser

Beam-quality measurements on the output of a 915-nm AlGaAs-InGaAs-GaAs slab-coupled optical waveguide laser (SCOWL) are reported. This device had a nearly circular mode (3.8 /spl mu/m by 3.4 /spl mu/m 1/e/sup 2/ widths in the near-field) and was capable of a single-ended continuous-wave output power of greater than 1 W. Measurements of M/sup 2/ indicate that the SCOWL output beam is nearly diffraction-limited in both directions with M/sub x//sup 2/ /spl sim/ M/sub y//sup 2/ /spl sim/ 1.1 over the entire range of output powers measured.