Showing papers on "Amplifier published in 1998"

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, which can result in significant distortion when passed 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 crest factor, and the bit-error rate. Our results show that clipping and filtering is a promising technique for the transmission of OFDM signals using realistic linear amplifiers.

Traveling wave thermoacoustic engine in a looped tube

Abstract: We have built a thermoacoustic engine consisting of a differentially heated stack of plates in a looped tube and observed spontaneous gas oscillations of the traveling wave mode running around the loop. Stability boundary and thermally produced acoustic power are compared with those for the engine tested in a resonator. The engine in a looped tube acts as a traveling wave power amplifier, whose onset temperature ratios are significantly smaller than those for the engine in a resonator.

An MOS transistor model for analog circuit design

Abstract: This paper presents a physically based model for the metal-oxide-semiconductor (MOS) transistor suitable for analysis and design of analog integrated circuits. Static and dynamic characteristics of the MOS field-effect transistor are accurately described by single-piece functions of two saturation currents in all regions of operation. Simple expressions for the transconductance-to-current ratio, the drain-to-source saturation voltage, and the cutoff frequency in terms of the inversion level are given. The design of a common-source amplifier illustrates the application of the proposed model.

RF circuit design aspects of spiral inductors on silicon

Abstract: The design and optimization of spiral inductors on silicon substrates, the related layout issues in integrated circuits, and the effect of the inductor-Q an the performance of radio-frequency (RF) building blocks are discussed. Integrated spiral inductors with inductances of 0.5-100 nH and Q's up to 40 are shown to be feasible in very-large-scale-integration silicon technology. Circuit design aspects, such as a minimum inductor area, the cross talk between inductors, and the effect of a substrate contact on the inductor characteristics are addressed. Important RF building blocks, such as a bandpass filter, low-noise amplifier, and voltage-controlled oscillator are shown to benefit substantially from an improved inductor-Q.

A single-chip 900-MHz spread-spectrum wireless transceiver in 1-/spl mu/m CMOS. I. Architecture and transmitter design

Abstract: A single-chip transceiver for frequency-hopped code division multiple access (CDMA) in the 900 MHz industrial, scientific and medical (ISM) band is implemented in 1-/spl mu/m CMOS. It combines a digital frequency synthesizer, a double quadrature upconverter, an integrated oscillator, and a power amplifier with variable output. Data modulates a carrier hopping at 20 kHz with quaternary frequency-shift keying (4-FSK). At an output power level of +3 dBm, the harmonics and spurious tones lie at -52 dBc or below. When active, the transmitter drains 100 mA from 3 V.

An IC for linearizing RF power amplifiers using envelope elimination and restoration

Abstract: Efficient power amplifiers (PAs) are desirable because power amplifiers typically dominate the power consumed in portable radio devices. Cellular systems such as the advanced mobile phone system (AMPS) employ modulation schemes that generate constant amplitude RF outputs to use efficient but nonlinear PAs. Modern digital communication standards such as the North American dual-mode cellular (NADC) system require nonconstant amplitude RF outputs to maximize frequency spectral usage, and therefore require linear PAs. The traditional approach to linear RF power amplification is to back-off the output power of a PA until its distortion is reduced to an acceptable level. Power back-off can lead to significant reduction in output power and efficiency. The envelope elimination and restoration (EER) system is an alternative to power back-off, to simultaneously achieve efficiency and linearity in RF PAs.

Broad-band power amplifier using dielectric photonic bandgap structure

Abstract: Two class AB GaAs field-effect transistor (FET) power amplifiers have been designed and fabricated in the 4.4-4.8 GHz range. In the first case, a dielectric PBG line was incorporated in the design to tune the second harmonic. In the second case, a 50-/spl Omega/ line is used with no harmonic tuning. The PBG structure allows broad-band harmonic tuning and is inexpensive to fabricate. A 5% improvement in power-added efficiency was achieved at the design frequency of 4.5 GHz, in both simulation and measurement.

Handbook of III-V Heterojunction Bipolar Transistors

Abstract: Basic Properties and Device Physics of III--V Materials. Two--Terminal Heterojunction Devices. D.C. Current Gain. Nonideal D.C. Characteristics. Thermal--Electrical Properties. Collapse of Current Gain. Failure Mechanisms and Reliability Issues. Small--Signal Properties. Epitaxial Layer Design. Geometrical Layout Design. Power Amplifier. Distortion and Noise. Switching Characteristics and Spice Models. Transistor Fabrication. Measured Transistor Performances. Appendices. Glossary of Symbols. Index.

Compact low-voltage power-efficient operational amplifier cells for VLSI

Abstract: Compact low-voltage power-efficient operational amplifiers are described that are very suitable as very-large-scale-integration library cells because of the small die area of 0.08 mm/sup 2/ and the minimum supply voltage of 1.8 V. A key part of the circuit is the rail-to-rail class-AB output stage with folded mesh feedback control that combines power efficiency with operation down to 1.8 V and allows sufficient gain in a compact two-stage topology. A version with rail-to-rail input stage features a rail-to-rail input range for supply voltages down to 2.5 V. The dc gain of the op amps is more than 80 db while driving 10 k/spl Omega/, and the unity-gain frequency is 4 MHz with phase margin of 67/spl deg/ while driving 5 pF. The equivalent input noise voltage is 38 nV//spl radic/(Hz) at a frequency of 100 kHz. The amplifiers have been implemented in a standard digital 1.6-/spl mu/m complementary metal-oxide-semiconductor process.

A wireless implantable multichannel digital neural recording system for a micromachined sieve electrode

Abstract: This paper reports the development of an implantable, fully integrated, multichannel peripheral neural recording system, which is powered and controlled using an RF telemetry link. The system allows recording of /spl plusmn/500 /spl mu/V neural signals from axons regenerated through a micromachined silicon sieve electrode. These signals are amplified using on-chip 100 Hz to 3.1 kHz bandlimited amplifiers, multiplexed, and digitized with a low-power (<2 mW), moderate speed (8 /spl mu/s/b) current-mode 8-b analog-to-digital converter (ADC). The digitized signal is transmitted to the outside world using a passive RF telemetry link. The circuit is implemented using a bipolar CMOS process. The signal processing CMOS circuitry dissipates only 10 mW of power from a 5-V supply while operating at 2 MHz and consumes 4/spl times/4 mm/sup 2/ of area. The overall circuit including the RF interface circuitry contains over 5000 transistors, dissipates 90 mW of power, and consumes 4/spl times/6 mm/sup 2/ of area.

Gyrotron traveling wave amplifier with a helical interaction waveguide

Abstract: A new microwave system in the form of a cylindrical waveguide with a helical corrugation of the inner surface is proposed for a gyrotron traveling wave tube (gyro-TWT). The corrugation radically changes the wave dispersion in the region of small axial wave numbers. This allows significant reduction in the sensitivity of the amplifier to the electron velocity spread and an increase in its frequency bandwidth. An X-band gyro-TWT operating at the second cyclotron harmonic with a 200-keV, 25-A electron beam produced an output power of 1 MW, corresponding to a gain of 23 dB and an efficiency of 20%.

L-band transmitter using Kahn EER technique

Abstract: This paper describes a 20-W peak-envelope power linear L-band transmitter based upon the Kahn envelope-elimination-and-restoration technique. A double envelope-feedback loop assures high linearity. The radio-frequency (RF) power amplifier employs a two-stage monolithic-microwave integrated-circuit driver amplifier and a 20-W power amplifier biased for class-AB operation. The class-S modulator includes a high-speed comparator and 1/2-/spl mu/m heterojunction field-effect transistors in its output stage. A double envelope-feedback loop assures both high linearity and time-delay equalization for RF bandwidths to 150 kHz. With a two-tone signal, the transmitter achieves an efficiency of 56% at full power (41 dBm), and 35% at 18 dB into back-off. The third-order intermodulation distortions for a two-tone signal vary from -30 to -40 dBc over a 20-dB range of back-off. For quaternary phase-shift keying, the first and second adjacent-channel powers are -48 and -57 dBc.

A 0.5-mW passive telemetry IC for biomedical applications

Abstract: A low-power, single-chip, one-channel, fully implantable microtransponder system for low-frequency biomedical sensor applications is described. The circuit is powered by an external RF source at 27/40 MHz. No battery is required. Wireless communication with external monitoring units is realized by absorption modulation. As the radiated power received by a small coil can be as low as a few milliwatts, the data acquisition/transmission system has been optimized for low power consumption. The system has been integrated in a 2-/spl mu/m 40-V BiCMOS technology. It includes a low-offset amplifier, a low-pass notch filter, an A/D converter, a voltage doubler/rectifier, as well as a low-power voltage regulator. The implemented switched-capacitor amplifier features 45-/spl mu/V offset and an integrated noise of 21 /spl mu/V for a bandwidth of 30 Hz while consuming less than 30 /spl mu/W power. The digitized sensor data are transmitted as low duty-cycle PPM-AM signals with a rate of 1 kBd. The entire system, including the 1.6-k/spl Omega/ bridge sensor, consumes only 520 /spl mu/W, which makes it well suited for long-term monitoring of biomedical signals.

Power- conserving drive-modulation method for envelope-elimination-and-restoration (EER) transmitters

Abstract: A method and a circuit for high-efficiency linear RF-power amplification over a wide range of amplitudes from zero to peak output includes a final RF-power amplifier operating at or near saturation, an RF driver amplifier, a high-level amplitude modulator for the final amplifier, preferably a high-level amplitude modulator for the driver amplifier, and a means for determining the supply-voltage input to the final amplifier and for controlling the amplitude of the drive. The means for determining the supply-voltage input and for controlling the amplitude acts so that the final amplifier drive varies from a minimum level to peak as the desired transmitter output varies from zero to peak. The transmitter is preferably of the envelope-elimination-and-restoration type or the envelope-tracking type.

Amplification using amplitude reconstruction of amplitude and/or angle modulated carrier

Abstract: The present invention provides high power linear amplification of an amplitude and/or phase modulated signal using multiple saturated (or if desired, unsaturated) amplifiers (4) driven by an appropriate set of switched (5), and/or phase modulated (6) constant amplitude signals derived from the input signal. The present invention combines three amplitude reconstruction techniques and implements the amplitude reconstruction modulator (11) digitally.

TM surface-wave power combining by a planar active-lens amplifier

Abstract: Power combining of TM surface waves by a planar active-lens amplifier is the subject of this paper. An amplifier gain of 11 dB at 8.25 GHz with a 3-dB bandwidth of 0.65 GHz has been demonstrated. Gain is measured from input to output connector to facilitate comparisons with more conventional amplifiers. Measurements of output power versus input power are also presented. The amplifier behaved in a linear manner and no problems with spurious oscillations were encountered. Construction of the amplifier is compatible with planar fabrication technologies. A key component of the combiner is a microstrip-fed Yagi-Uda slot-array antenna for TM surface-wave excitation of a thick dielectric slab. Design and optimization guidelines for the antenna are presented as well as detailed spectral-domain and finite-difference time-domain (FDTD) analysis results. Measured and simulation results show an input return loss and front-to-back ratio better than 10 dB over a 5% bandwidth. Calculated and measured results for the fields radiated by the antenna confirm forward radiation of the dominant TM mode in the thick dielectric slab. Integration of the computed radiated fields shows the antenna has a surface-wave launching efficiency of 85%.

Optimizing the load transient response of the buck converter

Abstract: The optimized gain of the voltage-error amplifier and current-mode control provide instantaneous transient response and small DC shift of the output voltage for step changes in the load current. This paper analyzes the system, determines the best compensation, provides design guidelines for buck converters powering Pentium(R) II processors and presents results of simulations and experiments.

Gain-flattened tellurite-based EDFA with a flat amplification bandwidth of 76 nm

Abstract: We describe a tellurite-based Er/sup 3+/-doped fiber amplifier (EDFA) with a flat amplification bandwidth of 76 nm and a noise figure of less than 7 dB. Furthermore, a parallel-type amplifier composed of this EDFA and a 1.45-/spl mu/m-band Tm/sup 3+/-doped fluoride fiber amplifier achieved a flat amplification bandwidth of 113 nm.

Time-domain envelope measurement technique with application to wideband power amplifier modeling

Abstract: This paper presents a new time-domain measurement technique for repetitive microwave signals that is applied to modeling wideband power amplifiers. The measurement technique concept consists of recording the microwave signal after conversion to baseband using a calibrated downconverter, which improves measurement accuracy compared to measurements at the carrier frequency. The modeling section describes how such time-domain measurements can be used to model wideband signal effects in nonlinear power amplifiers. The commonly used memory-less envelope model is limited to use on narrowband signals. A new model is developed which includes a filter before the memory-less nonlinearity to capture the memory effects associated with wideband signals. It is demonstrated that the accuracy of wideband signal simulations can be improved by optimizing the model parameters based on time-domain measurements of wideband signals.

Methods and circuitry for correcting temperature-induced errors in microbolometer focal plane array

Abstract: Correction for temperature-induced non-uniformities on the response characteristics of the microbolometers in an infrared focal plane array (FPA) is performed by applying a non-uniform corrective bias to the individual microbolometrs. The corrective bias is applied before or during the bias or integration period during which the detectors are sampled. The bias-correction is applied to two-dimensional detector multiplexers at each column amplifier input, the reference potential for each column amplifier or the voltage supply for each detector element. The magnitude of each corrective bias is determined by calibrating the detectors at different temperatures and different levels of incident infrared radiation. A microbolometer (2) which is thermally-shorted to the substrate on which the read out integrated circuit (ROIC) is formed is used along with the sensing microbolometer (3) to compensate for variations in temperature. Circuitry (31, 32, 36 and 70) for providing on-ROIC substrate temperature control.

Monolithic transformers and their application in a differential CMOS RF low-noise amplifier

Abstract: A 900 MHz low-noise amplifier (LNA) utilizing three monolithic transformers to implement on-chip tuning networks and requiring no external components has been integrated in 2.88 mm/sup 2/ in a standard digital 0.6 /spl mu/m CMOS process. A bias current reuse technique is employed to reduce power dissipation, and process-, voltage-, and temperature-tracking biasing techniques are used. At 900 MHz, the LNA dissipates 18 mW from a single 3 V power supply and provides 4.1 dB noise figure, 12.3 dB power gain, -33.0 dB reverse isolation, and an input 1-db compression level of -16 dBm. Analysis and modeling considerations for silicon-based monolithic transformers are presented, and it is shown that a monolithic transformer occupies less die area and provides a higher quality factor than two independent inductors with the same effective inductance in differential applications.

Peak power and bandwidth efficient linear modulation

Abstract: In portable wireless communication systems, power consumption is of major concern. Traditional modulation and coding schemes have been designed from the standpoint of minimizing average power. However, for linear power amplifiers needed for spectrally efficient modulation formats, amplifier efficiency and hence power consumption are determined by the peak power of the transmitted signal. This paper looks into modulation formats which minimize peak power and retain high spectral efficiency. Peak power is broken into a sum (in terms of decibels) of average power and a peak-to-average power ratio, and a variety of modulation formats are evaluated in terms of peak power efficiency in both a Gaussian noise and Rayleigh fading channel. A generalized phase shift keying (PSK) modulation format is developed and shown to offer superior peak power efficiency relative to that of commonly used linear modulation formats. Two schemes are presented for reducing the peak-to-average power ratio of various modulation formats. First, data translation codes are used to avoid data sequences which cause large peaks in the transmitted signal. This approach was found to be most productive in quadrature amplitude modulation (QAM) formats. Finally, an adaptive peak suppression algorithm is presented which further reduces the peak-to-average power ratios of the PSK and generalized PSK formats. The peak suppression algorithm is also applicable to /spl pi//4-QPSK and was found to improve peak power efficiency of that format by about 1.25 dB over a Rayleigh fading channel.

Erbium-Doped Optical-Waveguide Amplifiers on Silicon

Abstract: Thin-film integrated optics is becoming more and more important in optical-communications technology. The fabrication of passive devices such as planar optical waveguides, splitters, and multiplexers is now quite well-developed. Devices based on this technology are now commercially available. One step to further improve this technology is to develop optical amplifiers that can be integrated with these devices. Such amplifiers can compensate for the losses in splitters or other optical components, and can also serve as pre-amplifiers for active devices such as detectors.In optical-fiber technology, erbium-doped fiber amplifiers, are used in long-distance fiber-communications links. They use an optical transition in Er3+ at a wavelength of 1.54 μm for signal amplification, and their success has set a standard of optical communication at this wavelength. Using the same concept of Er doping, planar-waveguide amplifiers are now being developed. For these devices, silicon is often used as a substrate, so that optoelectronic integration with other devices in or on Si (electrical devices, or Si-based light sources, detectors, and modulators) may become possible. Figure 1 shows an example of a silicon-based optical integrated circuit5 in which a 1 × 4 splitter is combined with an amplifying section.

Switched-mode high-efficiency microwave power amplifiers in a free-space power-combiner array

Abstract: A design-oriented analysis of the microwave transmission-line class-E amplifier is presented. Experiments and harmonic-balance circuit simulations verify the theoretical equations which predict class-E-amplifier output power, maximum frequency of operation, and dc-RF conversion efficiency. Experimental results at 0.5, 1,2, and 5 GHz are presented. At 0.5 GHz, 83% drain efficiency and 80% power-added efficiency (PAE) are measured, with an output power of 0.55 W, using the Siemens CLY5 MESFET. These results are compared to a class-A and class-F power amplifier using the same device. At 5 GHz, 81% drain efficiency and 72% PAE are measured, with an output power of 0.61 W, using the Fujitsu FLK052WG MESFET. Finally, the 5-GHz class-E power amplifier is successfully integrated into an active-antenna array, demonstrating power combining of four elements with an 85% power-combining efficiency. At 5.05 GHz, the class-E power-amplifier antenna array delivers a total of 2.4 W of output power, with a dc-RF conversion efficiency of 74% and a PAE of 64%.

Novel architectures for high-efficiency amplifiers for wireless applications

Abstract: This paper presents three novel architectures for high-efficiency amplifiers relying on new harmonic-tuning techniques. These methods yield high-efficiency power amplifiers and reduce unwanted harmonic radiation from the transmitter front end. The first method uses the active integrated-antenna approach to perform harmonic tuning. The second method uses a nontraditional periodic microstrip filter, which allows broadband harmonic tuning. Finally, the third method combines the previous two approaches. Each technique is illustrated by a design example of a power amplifier integrated with an antenna. Guidelines for choosing the appropriate antenna structure and for designing the periodic structures are also presented. Another design issue is inclusion of the antenna and/or periodic structures into the amplifier simulation. To do this, a hybrid approach combining the finite-difference time-domain (FDTD) analysis and harmonic-balance simulation is employed.

100-TW sub-20-fs Ti:sapphire laser system operating at a 10-Hz repetition rate.

Abstract: We developed a compact three-stage Ti:sapphire amplifier laser system that produced peak power in excess of 100 TW for a pulse duration of less than 19 fs and an average power of 19 W at a 10-Hz repetition rate. A final 40-mm-diameter Ti:sapphire amplifier is pumped by a Nd:YAG master-oscillator–power-amplifier system that produces ?7-J output of 532-nm radiation. The spatial beam quality is approximately 2 times diffraction limited for the full amplified compressed output pulse. With f/3 optics, this system should therefore be capable of producing a focused intensity of ?3×1020 W/cm2.

Design and evaluation of a feedback based phased array system for ultrasound surgery

Abstract: A driving system has been designed for phased array ultrasound applicators. The system is designed to-operate in the bandwidth 1.2 to 1.8 MHz, with independent channel power control up to 60 W (8 bit resolution) for each array element. To reduce power variation between elements, the system utilizes switching regulators in a feedback loop to automatically adjust the DC supply of a class D/E power converter. This feedback reduces the RF electrical power variation from 20% to 1% into a 16 element array. DC-to-RF efficiencies close to 70% for all power levels eliminates the need for large heat sinks. In addition to power control, each channel may be phase shifted 360/spl deg/ with a minimum of 8 bit resolution. To ensure proper operation while driving ultrasound arrays with varying element sizes, each RF driving channel implements phase feedback such that proper phase of the driving signal is produced either at the amplifier output before the matching circuitry or after the matching circuitry at the transducer face. This feedback has been experimentally shown to increase the focal intensities by 20 to 25% of two tested phased arrays without array calibration using a hydrophone.

Sense amplifier circuit

Abstract: This invention provides a sense amplifier circuit capable of determining an output with small power consumption at high speeds and simplifying a control signal. The sources of a pair of driver nMOS transistors in a first amplifier are connected to VSS via an activation nMOS transistor. An output from the first amplifier is directly input to input/output nodes of a second, latch amplifier. The sources of a pair of nMOS transistors in the second amplifier are connected to VSS via an activation nMOS transistor. The input/output nodes are precharged to VCC by a precharge circuit in a standby state. The activation nMOS transistors are simultaneously controlled by a clock signal, and the first and second amplifiers are simultaneously activated to sense, amplify, and latch the potential difference between input/output nodes.

Linear high-efficiency microwave power amplifiers using bandpass delta-sigma modulators

Abstract: A novel amplifier configuration is described, in which a bandpass delta-sigma modulator is used to produce a two-level (digital) signal representing an analog radio frequency (RF) input. Subsequently, a switching-mode amplifier and bandpass filter are used to amplify the signal and remove unwanted spectral components. This configuration has the potential of achieving high efficiency (typical of switching mode amplifiers) together with high linearity. A simulated implementation with GaAs heterojunction bipolar transistors (HBT) is shown.

Methods and devices for controlling the vibration of ultrasonic transmission components

Abstract: A transducer assembly in accordance with the present invention includes at least one transducer element having a first end and a second end. A first electrode is coupled to the first end and a segmented electrode is coupled to the second end. The segmented electrode is adapted to allow the transducer element to be simultaneously driven by a plurality of electric signals. A generator in accordance with the present invention includes a frequency control loop to generate an electrical signal having a desired level of vibration. A first amplifier having a selected gain receives the electrical signal from the frequency control loop. The first amplifier generates a first output signal to drive the transducer element. A second amplifier having a selected gain receives the electrical signal from the frequency control loop. The second amplifier generates a second output signal to drive the transducer element.