Showing papers on "Amplifier published in 1997"

A 1.5-V, 1.5-GHz CMOS low noise amplifier

Abstract: A 1.5-GHz low noise amplifier (LNA), intended for use in a global positioning system (GPS) receiver, has been implemented in a standard 0.6-/spl mu/m CMOS process. The amplifier provides a forward gain (S21) of 22 dB with a noise figure of only 3.5 dB while drawing 30 mW from a 1.5 V supply. In this paper, we present a detailed analysis of the LNA architecture, including a discussion on the effects of induced gate noise in MOS devices.

Ytterbium-doped fiber amplifiers

Abstract: The ytterbium-doped fiber amplifier offers a number of attractive features, including a broad-gain bandwidth and a high efficiency, due in large part to its freedom from various competing processes seen in other rare-earth dopants. Here we discuss the main features that influence design and possible applications of ytterbium-doped fiber amplifiers.

Sub-20-fs pulses tunable across the visible from a blue-pumped single-pass noncollinear parametric converter.

Abstract: Femtosecond pulses with center wavelengths between 470 and 750 nm are generated in a single-stage type I BBO optical parametric amplifier pumped by a frequency-doubled 1-kHz Ti:sapphire amplifier. A high-quality white-light continuum is used as the seed. Pulse durations as short as 16 fs and pulse energies of as much as 11 microJ are observed. The quantum efficiency is ~25% for both 7- and 40-microJ pump pulses. This unique combination of ultrashort pulse duration and high conversion is made possible by noncollinear phase matching that permits a sufficiently large amplification bandwidth. Simultaneously the group velocities of the signal and the idler are effectively matched. As a result widely tunable sub-20-fs pulses can be generated in a nonlinear crystal as thick as 2 mm.

Class-F power amplifiers with maximally flat waveforms

Abstract: Class-F power amplifiers (PA's) employ harmonic-frequency resonators to shape their drain or collector waveforms to improve efficiency. Generally, the output network must present the drain with either an open or short circuit at the harmonic frequencies. At VHF and higher frequencies, the drain capacitance, lead inductance, lead length, and dispersion make implementation of reasonably ideal tuned circuits difficult. However it is possible to control the impedances at a finite number of harmonics. This note first derives the basic relationships among the Fourier coefficients of the waveforms and the performance of the amplifier. Fourier coefficients for maximally flat waveforms are then derived for inclusion of up to the fifth harmonic. Amplifier performance is then tabulated as a function of which harmonics are included in the voltage and current waveforms. Efficiency increases from 50% of class A toward 100% as harmonics are added. Power-output capability increases by up to 27%.

An active circuit for cancellation of common-mode voltage generated by a PWM inverter

Abstract: This paper proposes an active common-noise canceler (ACC) that is capable of eliminating the common-mode voltage produced by a pulsewidth modulation (PWM) inverter. An emitter follower using complementary transistors and a common-mode transformer are incorporated into the ACC, the design method of which is also presented in detail. Experiments using a prototype ACC, whose design and construction are discussed in this paper, verify its viability and effectiveness in eliminating common-mode voltage in a 3.7 kW induction motor drive using an insulated gate bipolar transistor (IGBT) inverter. Some experimental results show that the ACC makes significant contributions to reducing a ground current and a conducted electromagnetic interference (EMI). In addition, the ACC can prevent an electric shock on a nongrounded motor frame and can suppress motor shaft voltage.

Effects of clipping and filtering on the performance of OFDM

Abstract: Orthogonal frequency division multiplexing (OFDM) is an attractive technique for wireless communication applications. However, an OFDM signal has a large peak-to-mean envelope power ratio (PMEPR), which can result in significant distortion when transmitted through a nonlinear device, such as a transmitter power amplifier. We investigate, through extensive computer simulations, the effects of clipping and filtering on the performance of OFDM, including the power spectral density, the bit error rate, and the PMEPR. Our results show that clipping and filtering is a promising technique for the transmission of OFDM signals using realistic linear amplifiers.

A scalable high-frequency noise model for bipolar transistors with application to optimal transistor sizing for low-noise amplifier design

Abstract: Fully scalable, analytical HF noise parameter equations for bipolar transistors are presented and experimentally tested on high-speed Si and SiGe technologies. A technique for extracting the complete set of transistor noise parameters from Y parameter measurements only is developed and verified. Finally, the noise equations are coupled with scalable variants of the HICUM and SPICE-Gummel-Poon models and are employed in the design of tuned low noise amplifiers (LNA's) in the 1.9-, 2.4-,and 5.8-GHz bands.

Erbium-doped tellurite glass fibre laser and amplifier

Abstract: Er3+-doped tellurite singlemode fibre is fabricated and signal amplification and laser oscillation are demonstrated for the first time. A small-signal gain of 16 dB at 1560 nm is obtained for a pump power of 130 mW at 978 nm. A laser oscillation is observed with a threshold pump power of 120 mW at 978 nm and a slope efficiency of 0.65% using this fibre.

Optical communication systems

Abstract: A return-to-zero pulse optical communication system includes fast saturable absorber means (F1,DSF) to provide substantially zero average dispersion in a single amplifier span (SIF,DSF) to reduce the effect of timing jitter an provide considerably enhanced propagation distances.

Apparatus and method for the generation of high-power femtosecond pulses from a fiber amplifier

Abstract: An apparatus generates femtosecond pulses from laser amplifiers by nonlinear frequency conversion. The implementation of nonlinear frequency-conversion allows the design of highly nonlinear amplifiers at a signal wavelength (SW), while still preserving a high-quality pulse at an approximately frequency-doubled wavelength (FDW). Nonlinear frequency-conversion also allows for limited wavelength tuning of the FDW. As an example, the output from a nonlinear fiber amplifier is frequency-converted. By controlling the polarization state in the nonlinear fiber amplifier and by operating in the soliton-supporting dispersion regime of the host glass, an efficient nonlinear pulse compression for the SW is obtained. The generated pulse width is optimized by utilizing soliton compression in the presence of the Raman-self-frequency shift in the nonlinear fiber amplifier at the SW. High-power pulses are obtained by employing fiber amplifiers with large core-diameters. The efficiency of the nonlinear fiber amplifier is optimized by using a double clad fiber (i.e., a fiber with a double-step refractive index profile) and by pumping light directly into the inner core of this fiber. Periodically poled LiNbO3 (PPLN) is used for efficient conversion of the SW to a FDW. The quality of the pulses at the FDW can further be improved by nonlinear frequency conversion of the compressed and Raman-shifted signal pulses at the SW. The use of Raman-shifting further increases the tuning range at the FDW. For applications in confocal microscopy, a special linear fiber amplifier is used.

Linear transmitter using predistortion

Abstract: A linear transmitter (101) using predistortion includes a modulator (103), a predistorter (107), a digital quadrature modulator (111), an upconverter (113), a power amplifier (115), and an antenna (117). In addition, the transmitter (101) has a feedback loop including a coupler (119), a downconverter (123), a digital quadrature demodulator (125), and a trainer (131). The digital data to be transmitted is provided into the modulator (103), which converts the digital data into in-phase and quadrature component signals. The in-phase and quadrature component signals are then provided to the predistorter (107), which "predistorts" the component signals prior to amplification. The digital quadrature modulator (111) converts the component signals into a single analog signal. The upconverter (113) upconverts this signal from the predistorter (107) into the desired frequency of transmission, which is provided to the power amplifier (115) and the antenna (117) for amplification and broadcast. The coupler (119) provides a portion of the amplified signal to the analog downconverter (123), which lowers the frequency of this signal to a range that is easily processed. The signal is then provided to the digital quadrature demodulator (125), which outputs the in-phase and quadrature component signals of the signal. These in-phase and quadrature component signals are provided to the trainer (131) which analyzes them with the output signals from the modulator. The trainer (131) compares these signals and updates the predistorter (107) so that the digital quadrature demodulator (125) output signals are substantially equivalent to the modulator (103) output signals.

A 12 mW wide dynamic range CMOS front end for a portable GPS receiver

Abstract: This paper describes a CMOS low-noise amplifier (LNA) and mixer intended for use in the front-end of a global positioning system (GPS) receiver. The circuits were implemented in a standard 0.35-/spl mu/m (drawn) CMOS process, with one poly and two metal layers. The LNA has a forward gain (S21) of 17 dB and a noise figure of 3.8 dB. The mixer has a voltage conversion gain of -3.6 dB and a third-order intermodulation intercept point (IP3) of 10 dBm, input referred. The combination draws 12 mW from a 1.5-V supply.

A 250-mW, 8-b, 52-Msamples/s parallel-pipelined A/D converter with reduced number of amplifiers

Abstract: A parallel-pipelined A/D converter with an area and power efficient architecture is described. By sharing amplifiers along the pipeline and also completely eliminating the amplifier from the last stage, an 8-b pipeline is realized using just three amplifiers (instead of seven amplifiers with a conventional pipeline architecture). By using two such pipelines in parallel, a 52 Msamples/s prototype A/D converter that is Intended for a switched digital video application has been implemented in a 0.9-/spl mu/m CMOS technology. The device occupies 15 mm/sup 2/ and dissipates 250 mW from a 5 V supply.

Multistage amplifier topologies with nested G/sub m/-C compensation

Abstract: This paper presents a multistage amplifier for low-voltage applications (<2 V). The amplifier consists of simple (noncascode) low gain stages and is stabilized using a nested transconductance-capacitance compensation (NGCC) scheme. The resulting topology is similar to the well known nested Miller compensation (NMC) multistage amplifier, except that the proposed topology contains extra G/sub m/ feedforward stages which are used to enhance the amplifier performance. The NGCC simplifies the transfer function of the proposed multistage amplifier which, in turn, simplifies its stability conditions. A comparison between the NGCC and NMC shows that the NGCC has wider bandwidth and is easier to stabilize. A four-stage NGCC amplifier has been fabricated using a 2-/spl mu/m CMOS process and is tested using a /spl plusmn/1.0 V power supply. A dc gain of 100 dB has been measured. A gain bandwidth product of 1 MHz with 58/spl deg/ of phase margin and power of 1.4 mW can be achieved. The op amp occupies an active area of 0.22 mm/sup 2/. Step response shows that the op amp is stable.

Effects of concentration on the performance of erbium-doped fiber amplifiers

Abstract: The dependence of erbium-doped fiber amplifier (EDFA) performance on the erbium ion concentration is studied experimentally and theoretically. The quantum efficiency of the amplifier is found to he strongly dependent on the erbium ion concentration, the signal wavelength, and the relative propagation direction of the pump and signal beams. This dependence is fully explained by the presence of an upconversion mechanism between ions residing in pairs or larger clusters and suggests that other sources of amplifier performance degradation (back-ground loss, excited state absorption, homogenous upconversion) are negligible. The experimental data show that in the present EDFA designs with over 80% quantum/conversion efficiency, the aluminum co-doped fibers with erbium ion concentration less than 20/spl times/10/sup 24/ m/sup -3/ (900 molar ppm Er/sup 3+/) are most suitable.

Broadband and gain-flattened amplifier composed of a 1.55 [micro sign]m-band and a 1.58 [micro sign]m-band Er3+-doped fibre amplifier in a parallel configuration

Abstract: The authors construct a broadband and gain-flattened Er/sup 3+/-doped fibre amplifier (EDFA) with a flat amplification bandwidth of 54 nm for wavelength division multiplexed signals This was achieved by employing a 158 /spl mu/m-band EDFA and a 155 /spl mu/m-band EDFA in a parallel configuration Excellent flat amplification characteristics were obtained for 1530-1560 nm and 1576-1600 nm signal wavelength regions, with a gain non-uniformity of <17 dB and a signal gain of 30 dB

Saturation effects in nondegenerate four-wave mixing between short optical pulses in semiconductor laser amplifiers

Abstract: We present a simple, yet powerful method for calculating nonlinear pulse propagation and pulse interaction in active semiconductor waveguides. The model is based on the density matrix equations, which under realistic operation conditions are shown to lead to an accurate description of the material gain, that includes the dynamics of carrier heating and spectral-hole burning (SHB). A very general and compact description of the amplifier dynamics in terms of an integral equation is derived. The model is used to analyze saturation effects in short pulse amplification and nondegenerate four-wave mixing. An analytical expression for the four-wave mixing response is derived, which extends previous results to the case of short and intense pulses. Saturation of the four-wave mixing signal is shown to be strongly pulsewidth dependent due to ultrafast gain dynamics, and self-phase modulation is shown to give excessive broadening of the conjugate pulse. Finally, the impacts on the noise characteristics are calculated and shown to explain recent experimental results.

Low noise amplifier for passive pixel CMOS imager

Abstract: A CMOS imaging system provides low noise read out and amplification for an array of passive pixels, each of which comprises a photodetector, an access MOSFET, and a second MOSFET that functions as a signal overflow shunt and a means for electrically injecting a test signal. The read out circuit for each column of pixels includes a high gain, wide bandwidth, CMOS differential amplifier, a reset switch and selectable feedback capacitors, selectable load capacitors, correlated double sampling and sample-and-hold circuits, an optional pipelining circuit, and an offset cancellation circuit connected to an output bus to suppress the input offset nonuniformity of the amplifier. For full process compatibility with standard silicided submicron CMOS and to maximize yield and minimize die cost, each photodiode may comprise the lightly doped source of its access MOSFET. Circuit complexity is restricted to the column buffers, which exploit signal processing capability inherent in CMOS. Advantages include high fabrication yield, broadband spectral response from near-UV to near-IR, low read noise at HDTV data rates, large charge-handling capacity, variable sensitivity with simple controls, and reduced power consumption.

EDFA transient response to channel loss in WDM transmission system

Abstract: The effects of channel loss on an erbium-doped fiber amplifier (EDFA) in an eight-channel WDM network are investigated. For the loss of 1, 4, or 7 channels, the surviving channels suffer power transients which can be both large and relatively fast. The experiments agree well with a simple analytical model of the amplifier. Pump control, if it is fast enough, is demonstrated to limit the power excursion of the surviving channels.

Wavelength-swept fiber laser with frequency shifted feedback and resonantly swept intra-cavity acoustooptic tunable filter

Abstract: This paper concerns a wavelength-swept fiber laser (WSFL) incorporating frequency shifted feedback and an intracavity passband filter, in which the wavelength of the modeless output is linearly, continuously and repeatedly tuned (in time) over a given range by modulation of the filter peak wavelength and filter strength. We show both numerically and experimentally that amplifier noise plays a key role in determining the operation of frequency-shifted fiber laser systems and that a "noisy" amplifier can be used to suppress the natural tendency of such lasers to pulse, allowing for continuous wave, modeless operation. Furthermore, we show that significant narrowing of a WSFL instantaneous swept linewidth can be obtained if the filter peak transmission wavelength is resonantly swept so as to follow the wavelength shift per pass due to the acoustooptic frequency shift. Using these ideas we go on to demonstrate and characterize a high-power diode-driven Er/sup 3+//Yb/sup 3+/ WSFL incorporating a bulk-optic acoustooptic tunable filter (AOTF). Linewidths as narrow as 9 GHz, sweep ranges up to 38 nm and output powers as high as 100 mW are obtained. Furthermore, we demonstrate the generation of user definable average spectral output by synchronous modulation of the filter strength and multiwavelength pulsed output at higher sweep rates. Excellent agreement between the experimental results and those of the numerical modeling is obtained. Our simulations show that reduced linewidth (<0.02 nm) and improved scan linearity should be readily achievable with realistic system improvements. We believe such sources to be of considerable physical and practical interest, with applications ranging from sensor array monitoring and device characterization through to low-coherence interferometry.

158-microJ pulses from a single-transverse-mode, large-mode-area erbium-doped fiber amplifier.

Abstract: We report the amplification of 10-100-pJ semiconductor diode pulses to an energy of 158 microJ and peak powers >100 kW in a multistage fiber amplifier chain based on a single-mode, large-mode-area erbium-doped amplifier design. To our knowledge these results represent the highest single-mode pulse energy extracted from any doped-fiber system.

Low-heat high-power scaling using InGaAs-diode-pumped Yb:YAG lasers

Abstract: We report to our knowledge the highest to date quasi-CW output power, 600 W and pulse energy, >1 J, for an InGaAs diode-pumped Yb:YAG laser. In separate preliminary results, we have also obtained 225 W of average output power under true CW diode pumping. This performance was obtained using a laser head designed to be part of a master oscillator power amplifier (MOPA) operating at 3 kW. We summarize why the diode-pumped Yb:YAG crystal laser is ideal for scaling to high average powers and the different approaches being pursued. We also report our latest results for side-pumped rod devices.

Ultrabroadband phase-matched optical parametric generation in the ultraviolet by use of guided waves

Abstract: We present what is believed to be the first experimental demonstration of guided-wave phase-matched frequency mixing and harmonic conversion in gases. Broad-bandwidth ultrafast pulses, tunable around 270 nm, were generated from an ultrafast Ti:sapphire amplifier system using 2ω+2ω-ω parametric wave mixing in a capillary waveguide. We achieved nonresonant phase matching by coupling both the fundamental and the second-harmonic light into the lowest-order mode. The output 3ω pulses have an energy of >4 µJ at a 1–kHz repetition rate. Simple extensions of this method can generate higher-energy 10–20-fs pulses tunable throughout the vacuum ultraviolet.

Method and apparatus for amplifying a signal

Abstract: A unique method and apparatus modifies the load impedance at the output of a power amplifier by varying a voltage variable capacitor (VVC) (310) to maximize the efficiency of the power amplifier (304) A comparator (509) generates amplifier control signal (211) based upon a detected power output signal (216) and a reference signal In addition to providing power control, the control signal is also coupled to a VVC circuit (506) to control the output impedance of the power amplifier In an alternate embodiment, a separate VVC control signal (527) based upon a comparison of the power control signal and the battery voltage is coupled to a VVC In another alternate embodiment, a second VVC can be coupled in parallel to the first VVC The second VVC is preferably controlled by a signal (805) based upon the current in the power amplifier Finally, an alternate embodiment incorporates a VVC circuit (506) at the input of the power amplifier to compensate for variations in input impedance to improve other power amplifier parameters such as IM, gain, output power and noise level

The effect of quadrature modulator and demodulator errors on adaptive digital predistorters for amplifier linearization

Abstract: With the increasing importance of spectral efficiency in mobile communications, the power amplifier linearity has become a critical design issue for nonconstant envelope modulation. Imperfections in quadrature modulators and demodulators-gain and phase imbalance and DC offset-have a crippling effect on amplifier linearization circuits, a fact that has previously been noted experimentally. This paper is the first analysis of these effects on an adaptive predistorter. The primary result is an expression that provides an explicit tradeoff among intermodulation power, accuracy of the quadrature modulator and demodulator, and speed of adaptation. Another useful result is a simple and easily measured error figure for quadrature modulators and demodulators.

Exposure control system controlling a solid state image sensing device

Abstract: An exposure adjustment apparatus determines, based on the level of a signal of an object converted by a solid state image sensing device, whether the exposure time or the gain is to be decreased, increased or maintained, and controls the gain of an amplifier and the drive pulse to be generated by a drive pulse generator. Thereby, the output signal level is adjusted by controlling only the exposure time of the solid state image sensing device and the gain of the video signal resulting in a compact and vibration-resistant exposure control system which is inexpensive.

A micro strain gauge with mechanical amplifier

Abstract: A passive micro strain gauge with a mechanical amplifier has been designed, analyzed, and tested. The mechanical amplifier provides a high gain such that residual strain in thin films can be directly measured under an optical microscope. This strain gauge can be in situ fabricated with active micro sensors or actuators for monitoring residual strain effects, and both tensile and compressive residual strains can be measured via the strain gauge. It is shown that a very fine resolution of 0.001% strain readouts can be achieved for a micro strain gauge with a 500 /spl mu/m-long indicator beam. Beam theories have been used to analyze the strain gauge with a mechanical amplifier, and the results were verified by a finite-element analysis. Experimental measurements of both polysilicon and silicon-riched silicon-nitride thin films fabricated by surface micromachining processes are presented.