Showing papers on "Amplifier published in 1994"

Design of analog integrated circuits and systems

Abstract: MOS transistor models bipolar transistor models feedback and sensitivity in analogue integrated circuits elementary transistor stages behavioural modelling of operational and transconductance amplifiers operational amplifier design fundamentals of continuous-time and sampled-data active filters design and implementation of integrated active filters.

Ultrasonic surgical handpiece and an energy initiator

Abstract: An ultrasonic oscillator drives a tool at a set frequency. An amplitude control runs the oscillator to set the vibration level. A frequency regulator joins the amplitude and the oscillator. A control feedback loop, in the frequency regulator, keeps handpiece linear dynamics. An operational transconductance amplifier, in the oscillator, governs gain of the loop. A circuit connects to the control to retard the rate of current application over time to the amplifier. The circuit has switching to either retard the rate or reset for start up. The amplifier is a current output device with current directly proportional to the bias current and input voltage with bias as gain change for the loop. The circuit limits the bias to the amplifier to modify frequency response and output current. A capacitor delays application of the bias to the amplifier. Replaceable tools of various lengths or shapes positioned along an axis vibrate for surgery at the frequency and a wave length. Tools longer than one wavelength and of configurations tuned to oscillate around the frequency resonate as a function of their material, length and configuration. A flue surrounds the tool and has a hollow elongate semi rigid central body about an axis with a funnel, at one end thereof and a nozzle, at the other to direct annular irrigant/coolant flow therethrough. The funnel and nozzle are resilient. Reinforcing ridges, inside the nozzle, act to maintain concentricity between the flue and nozzle tip and channel irrigant thereabout.

Low-power digital systems based on adiabatic-switching principles

Abstract: Adiabatic switching is an approach to low-power digital circuits that differs fundamentally from other practical low-power techniques. When adiabatic switching is used, the signal energies stored on circuit capacitances may be recycled instead of dissipated as heat. We describe the fundamental adiabatic amplifier circuit and analyze its performance. The dissipation of the adiabatic amplifier is compared to that of conventional switching circuits, both for the case of a fixed voltage swing and the case when the voltage swing can be scaled to reduce power dissipation. We show how combinational and sequential adiabatic-switching logic circuits may be constructed and describe the timing restrictions required for adiabatic operation. Small chip-building experiments have been performed to validate the techniques and to analyse the associated circuit overhead. >

Cellular communications system with centralized base stations and distributed antenna units

Abstract: A microcellular communications network includes a plurality of base station units and corresponding antenna units. The base station units are housed in a common location. Each includes either conventional transmitters and receivers or all digital transmitter and receiver equipment, and interface circuitry to a mobile telecommunications switching office. The microcell traffic output is applied to a frame generator/multiplexer. The output of the frame generator/multiplexer is applied to a digitally modulated laser. The laser output is conveyed by fiber to a remote antenna unit, which demultiplexes the microcell traffic signal and applies it to a digital-to-analog converter. The output of the digital-to-analog converter is applied to a power amplifier, which in turn is connected to a main antenna. RF signals from the mobile units are received at both a main and a diversity antenna. The received signals are filtered, digitized, multiplexed together and transmitted over the optical fiber back to the base station. The strongest signal is selected for use.

Ultra-wideband receiver

Abstract: An ultrawide (UWB) receiver utilizes a strobed input line (14) with a sampler (10) connected to an amplifier (18). In a differential configuration (18), +UWB inputs (14a) are connected to separate antennas or to two halves of a dipole antenna. The two input lines (14) include samplers (10) which are commonly strobed (12) by a gating pulse with a very low duty cycle. In a single ended configuration, only a single strobe input line and sampler is utilized. The samples integrate, or average, up to 10,000 pulses to achieve high sensitivity and good rejection of uncorrelated signals.

Frequency‐domain description of a lock‐in amplifier

Abstract: The basic principles behind the operation of a lock‐in amplifier are described. Particular emphasis is placed on looking at the frequency components of the signal present at the various stages of the lock‐in during a typical measurement. The description presented here has been used successfully to explain lock‐in operation to upper‐level laboratory students at Oberlin College.

Design of high-efficiency RF Class-D power amplifier

Abstract: In this paper, the losses in a Class-D RF switching power amplifier and their frequency dependence are described. The losses analyzed are the switching, conduction, and gate drive losses. A 300 W, 13.56 MHz, Class-D circuit is designed in the traditional manner to illustrate the magnitude of the different types of loss. A circuit using the ZVS equations developed in this paper is designed. An experimental circuit is built using standard IRF540 devices in TO220 packages. That circuit does not meet its performance goals because of the package inductance. A new low inductance half-bridge package is introduced to solve this problem. Techniques for circuit layout and power measurements for RF applications are also presented in the experimental section. A low loss gate drive circuit is also presented using a Class-E circuit to provide the drive power. The experimental results confirm the accuracy of the design equations derived in this paper. >

All optical wavelength conversion by SOA's in a Mach-Zehnder configuration

Abstract: Penalty free wavelength conversion is demonstrated at 2.5 Gbit/s over a wavelength span of 12 nm by the use of semiconductor optical amplifier (SOA)'s in a Mach-Zehnder configuration. An increase in the extinction ratio is measured for the converted signal compared to the input signal implying signal regeneration as well as wavelength conversion. >

Linearized power amplifier

Abstract: A linearized power amplifier is provided which comprises a non-linear radio frequency (RF) power amplifier, a linearization circuit such as a Cartesian Feedback circuit, an RF feedback circuit; an IF feedback circuit; or a feedforward circuit, and a dynamic bias modulation circuit for modulating an operating voltage of the amplifier. The dynamic bias modulation means includes an envelope determining circuit, signal processing circuits in which predetermined data or a simplified transfer function determined from measured characteristics of the amplifier is stored and used to produce power bias and/or base or gate bias signals, and driver circuits for modulating the power supply voltage and/or base or gate bias voltage of the RF amplifier in response to the bias signals. The dynamic bias modulation may be used with a BJT-based, and FET-based or any other type of RF power amplifier. With the right combination of power supply and base or gate bias modulation the efficiency of the RF amplifier can be maximised for a given output power, and the combination of linearization means and high level power supply and/or base or gate bias modulation gives the benefits of improved spectral control and intermodulation distortion reduction coupled with high efficiency.

Adaptive linearization using predistortion-experimental results

Abstract: This paper describes an adaptive predistortion system to linearize class B and class C radio frequency high power amplifiers. The system, which can handle a 30 dB power control range, uses a digital signal processing microprocessor and memory look-up tables to predistort the baseband drive signals. Low data rate services such as are found in mobile satellite applications ( >

Power amplifier having nested amplitude modulation controller and phase modulation controller

Abstract: Transmitting signals containing amplitude modulated (AM) and phase modulation (PM) components requires a transmitter having AM and PM control loops (515, 517). The PM control loop provides phase modulation, frequency translation and phase predistortion for a transmitter. The phase predistortion/correction is accomplished by using an oscillator (505), thus, the amount of PA phase correction is essentially unlimited. Additionally, the PM control loop (517) is nested about a power amplifier (507) (PA), allowing the PM control loop (517) to correct for any distortion introduced by the PA (507).

A 1-GHz BiCMOS RF front-end IC

Abstract: An RF front-end IC containing a low-noise amplifier and mixer is described. On-chip temperature and supply-voltage compensation is used to stabilize circuit performance. Realized in a BiCMOS process, the circuit consumes 13.0-mA total current from a 5-V supply. The amplifier gain at 900 MHz is 16 dB, the noise figure is 2.2 dB, and the input third-order intermodulation intercept is /spl minus/10 dBm. The mixer input third-order intermodulation intercept is +6 dBm with 15.8 dB noise figure. >

Nonvolatile semiconductor memory

Abstract: A nonvolatile semiconductor memory employs sense amplifiers, circuits for providing stabilized source voltages, and circuits for realizing high-speed and reliable read and write operations. The semiconductor memory has a matrix of nonvolatile erasable memory cell transistors. The semiconductor memory employs an arrangement for effectively using a plurality of source voltages and applying a verify voltage to sense amplifiers and word lines, a write verify arrangement for detecting an output of the sense amplifiers, an arrangement for comparing an output of the sense amplifiers with a reference value to determine whether or not a written state of the memory cell transistors is acceptable, an arrangement for adjusting an output of the sense amplifiers with use of inverters and transistors in response to a current flowing to the memory cell transistors, to improve a drive speed of the sense amplifiers, an internal source voltage generating arrangement using an n-channel depletion transistor connected to an external source voltage (Vcc), the gate of the transistor being connected to a low source voltage (Vss) to provide an internal source voltage (Vci), a combination of an arrangement for dropping the external source voltage (Vcc) for read to a predetermined value to drive a read circuit in the memory and an arrangement for dropping an external voltage (Vpp) for write, to generate a word line potential for a verify-after-write operation, an arrangement for setting a reference voltage (Vref) as a lower threshold (Vth) allowed for cell transistors (11 00 to 11 22 ), and comparing the voltage of a data bus (13) with the reference voltage (Vref), to simultaneously carry out an erase-verify operation on all memory cell transistors, and a pre-read arrangement for accessing the next address during a read time of the sense amplifiers, to improve a read speed.

Low line harmonic ac to dc power supply

Abstract: The PWM control scheme is illustrated in conjunction with a power distribution control circuit (30), wherein the duty cycle of convverter (32) is suitably controlled by a number of feedback loops embodying various parameters, for example a voltage error signal, an average (eg. RMS) value of the input voltage (Vin). Circuit (30) comprises a rectifying circuit (42), a converter circuit (32), for example an AC-DC converter, a capacitor (C), an oscillator and PWM circuit (44), an error signal (46), a multiplier circuit (48), a differencing amplifier (50), and a synthesizing circuit (52). Circuit (30) appears as a resistive load to the line for feed PWM, a fixed load, and a fixed RMS input voltage. To stabilize the output voltage (Vout), the pulse width signal (44a) applied to converter suitably varies in proportion to both changes in the RMS value of the input voltage and the output voltage. The output voltage error signal applied to multiplier circuit by error circuit provides the correction value for Vout variations. The line RMS signal applied to multiplier by the line RMS filter circuit (52) compensates the PWM signal for variations in the RMS value of Vin. In this regard, the RMS loop modulator control signal may be advantageously normalized by Vrms (square) since Pin varies as Vin (square). Decreases in either the output error signal or the RMS signal increase the PWM value.

Cross-talk free, low-noise optical amplifier

Abstract: A low-noise optical amplifier solves crosstalk problems in optical amplifiers by using an optical cavity oriented off-axis (e.g. perpendicular) to the direction of a signal amplified by the gain medium of the optical amplifier. Several devices are used to suppress parasitic lasing of these types of structures. The parasitic lasing causes the gain of these structures to be practically unusable. The lasing cavity is operated above threshold and the gain of the laser is clamped to overcome the losses of the cavity. Any increase in pumping causes the lasing power to increase. The clamping action of the gain greatly reduces crosstalk due to gain saturation for the amplified signal beam. It also reduces other nonlinearities associated with the gain medium such as four-wave mixing induced crosstalk. This clamping action can occur for a bandwidth defined by the speed of the laser cavity. The lasing field also reduces the response time of the gain medium. By having the lasing field off-axis, no special coatings are needed. Other advantages are that the lasing field is easily separated from the amplified signal and the carrier grating fluctuations induced by four-wave mixing are decreased. Two related methods reduce the amplified spontaneous emission power without sacrificing the gain of the optical amplifier.

Efficiency of broadband four-wave mixing wavelength conversion using semiconductor traveling-wave amplifiers

Abstract: We present a theoretical analysis and experimental measurements of broadband optical wavelength conversion by four-wave mixing in semiconductor traveling-wave amplifiers. In the theoretical analysis, we obtain an analytical expression for the conversion efficiency. In the experiments, both up and down-conversion efficiencies are measured as a function of wavelength shift for shifts up to 27 nm. The experimental data are well explained by the theoretical calculation. The observed higher conversion efficiency for wavelength down-conversion is believed to be caused by phase interferences that exist between various mechanisms contributing to the four-wave mixing process. >

The use of parasitic nonlinear capacitors in class E amplifiers

Abstract: The most common class E amplifier configuration uses a single transistor with a shunt capacitor and a series resonant output filter. Until now a linear shunt capacitance has been assumed. However, to achieve operation at 900 MHz and above, it is of interest to rely solely upon the nonlinear parasitic collector-substrate capacitance of the transistor. An analytical theory for operation at 50% duty cycle and nonlinear capacitance is presented in this correspondence, and the effects on the power capability of the amplifier are discussed. >

Evading amplifier noise in nonlinear oscillators.

Abstract: Resonators driven to self-oscillation via active feedback play an important role in technology. Among the stochastic processes driving phase diffusion in such oscillators is noise from the feedback amplifier. Here a technique is described by which phase diffusion due to this noise can be suppressed. We have achieved a 10 dB reduction in phase diffusion by using the technique on an oscillator whose frequency-controlling element is a nonlinear mechanical resonator. The technique, in principle, provides a quantum nondemolition method of tracking a resonator's phase.

Homodyne impulse radar hidden object locator

Abstract: An electromagnetic detector is designed to locate an object hidden behind a separator or a cavity within a solid object. The detector includes a PRF generator for generating 2 MHz pulses, a homodyne oscillator for generating a 2 kHz square wave, and for modulating the pulses from the PRF generator. A transmit antenna transmits the modulated pulses through the separator, and a receive antenna receives the signals reflected off the object. The receiver path of the detector includes a sample and hold circuit, an AC coupled amplifier which filters out DC bias level shifts in the sample and hold circuit, and a rectifier circuit connected to the homodyne oscillator and to the AC coupled amplifier, for synchronously rectifying the modulated pulses transmitted over the transmit antenna. The homodyne oscillator modulates the signal from the PRF generator with a continuous wave (CW) signal, and the AC coupled amplifier operates with a passband centered on that CW signal. The present detector can be used in several applications, including the detection of metallic and non-metallic objects, such as pipes, studs, joists, nails, rebars, conduits and electrical wiring, behind wood wall, ceiling, plywood, particle board, dense hardwood, masonry and cement structure. The detector is portable, light weight, simple to use, inexpensive, and has a low power emission which facilitates the compliance with Part 15 of the FCC rules.

1.55 /spl mu/m polarisation independent semiconductor optical amplifier with 25 dB fiber to fiber gain

Abstract: Using a tapered in width square active waveguide and bulk InGaAsP/InP material we demonstrate a polarisation independent amplifier structure operating at 1550 nm with a reduced far-field divergence. Improvement of coupling efficiency enables us to achieve a 25 dB fiber to fiber gain together with 9 dBm fiber saturation output power for 150 mA bias current. A 200 ps gain recovery time allows fast gating or wavelength conversion. >

Zero intermediate frequency receiver having an automatic gain control circuit

Abstract: A receiver automatic gain control (AGC) circuit includes a first adjustable gain control amplifier (158) which is responsive to a gain control signal (156). The AGC circuit further includes a second adjustable gain control amplifier (114) and a control circuit (116) which receives the gain control signal (156) and provides a modified gain control signal or VCNTRL (152) to the second adjustable control amplifier (114). The control circuit (116) also limits the amount of gain control applied to adjustable gain control amplifiers (114 and 118) when the gain control signal (156) reaches a certain predetermined level. This provides for all further gain reduction to occur at the first adjustable gain control amplifier (158) and thereby reduce the chances for distortion under high input signal conditions.

Hierarchical DRAM array with grouped I/O lines and high speed sensing circuit

Abstract: A random access memory array architecture including a plurality of arrays or subarrays arranged into rows and columns, a plurality of sense amplifiers between the arrays (2), and grouped input/output (I/O) lines. The I/O path includes main I/O lines (24) coupled to all of the arrays, with orthogonal local I/O lines (20) for a column of arrays plus sub I/O lines (16) orthogonal to the local I/O lines for each group of sense amplifiers in a row of sense amplifiers. A plurality of pass transistor pairs and interconnect transistors are coupled to the sense amplifiers and the local and sub I/O lines. Latches are provided for storing data output from each of the subarrays, and a match comparator is connected to at least two of the latches for providing a signal on a complementary pair of match leads indicative of a comparison of the data in the latches. A true lead of the complementary pair of match leads is precharged high before the comparison while a complement lead of the complementary pair of match leads is precharged low.

Four-wave mixing wavelength conversion efficiency in semiconductor traveling-wave amplifiers measured to 65 nm of wavelength shift

Abstract: The efficiency of broadband optical wavelength conversion by four-wave mixing in semiconductor traveling-wave amplifiers is measured for wavelength shifts up to 65 nm using a tandem amplifier geometry. A quantity we call the relative conversion efficiency function, which determines the strength of the four-wave mixing nonlinearity, was extracted from the data. Using this quantity, gain requirements for lossless four-wave mixing wavelength conversion are calculated and discussed. Signal to background noise ratio is also measured and discussed in this study. >

Nonlinearity compensation in digital radio systems

Abstract: Digital radio links with bandlimited pulses exhibit a severe performance degradation when the transmitter high power amplifier operates near saturation. To cope with the increase of nonlinear intersymbol interference due to the amplifier nonlinearities, a discrete-time Volterra system can be used to process the transmitted data. We present an efficient technique for implementing adaptive data predistorters with memory based on a discrete-time Volterra system composed of digital linear filters and memoryless nonlinear devices working at the symbol rate. Third- and fifth-order structures are proposed and a system performance evaluation is presented for several realistic situations. >

Regenerative amplifier incorporating a spectral filter within the resonant cavity

Abstract: A regenerative amplifier includes a resonant cavity having a gain medium and a spectral filter located in the cavity A source is provided to pump the gain medium and thereby-raise it to an excited state Elements are also provided for creating laser seed pulses which are then injected into the resonant cavity, these elements preferably include in part a mode-locked oscillator having a wavelength substantially the same as that at which the gain medium can support amplification of the energy of the injected pulse In a preferred embodiment the gain medium is Ti:Sapphire for both the amplifier and oscillator Also, in the preferred embodiment the seed pulse from the oscillator is stretched in time by multiplicative factors sufficient to ensure that upon amplification, the seed pulse power density remains below the self-focusing threshold of the material through which the pulse is passed The seed laser pulses are injected into the resonant cavity of the regenerative amplifier so as to provide multiple traversals of the resonant cavity and the gain medium therein, thereby amplifying the pulses The pulse is recompressed back to some predetermined pulse width of interest to the user; for example, back to the temporal pulse width that is limited by the spectral bandwidth of the output pulse

Switched-capacitor integrator with chopper stabilization performed at the sampling rate

Abstract: A switched-capacitor integrator with chopper stabilization performed at the sampling rate virtually eliminates the flicker noise and any low frequency interference generated by the amplifier. The integrator samples the input and then passes the sampled input to the feedback capacitor during each chopping phase of the amplifier to thereby provide a double-sampled integrator. The output of the integrator is sampled at the end of each cycle of the chopping signal.

Limits to long-haul coherent transmission set by the Kerr nonlinearity and noise of the in-line amplifiers

Abstract: The effect of Kerr nonlinearity and noise of the erbium amplifiers is investigated in a link in which dispersion is zero to all orders. The analytical expressions for the error probability at the receiver are found for a differential phase shift keying modulation format. The role of the total bandwidth of the amplified spontaneous emission noise is discussed. >

Self-regulating multiwavelength optical amplifier module for scalable lightwave communications systems

Abstract: In a multiwavelength lightwave communications system automatic self-power regulation on a channel-by-channel basis is achieved with a cascade of multiwavelength amplifier modules (200), wherein each multiwavelength amplifier module in the cascade includes a plurality of pump-shared parallel fiber amplifiers (208) operated in gain-saturation and connected between an optical demultiplexer (203) and multiplexer (209). An optional first gain stage (202) improves performance with higher optical signal-to-noise ratio. By self-regulating the power in each channel, the communications system is scalable, allowing the system to grow without deleterious effects due to power spread.

Feed-forward power amplifier system with adaptive control and control method

Abstract: An adaptive control system and method for use with a feedforward linear amplifier, and in particular a multi-channel linear amplifier wherein a distortion (error) detection circuit (109) is used for detecting a nonlinear distortion component of a main amplifier (105) output for using in correcting distortion in amplifying an information signal. The distortion correction can be extracted from a pilot signal (J4), an analysis of distortion from a channel-by-channel sweep or from analysis of selected target channels. Analysis can be based on a single signal, an average of many signals, or a selection of maxima of one or many signals. Subharmonic sampling may be used in analog to digital conversion of an IF signal to detect for distortion within a passband.

Adaptive class AB amplifier for TDMA wireless communications systems

Abstract: In a TDM/TDMA portable radio communications system, the modulated RF signal transmitted by a portable handset unit is amplified for uplink transmission to a port by an adaptive class AB power amplifier. A class AB amplifier provides the necessary amplification for the low power levels to be output by the portable units, but must be biased just slightly "on" with no signal input for required maximum efficiency and linearity. In order to maintain the amplifier at a proper bias level over changing temperature conditions and free from the effects of device aging and device-to-device variations, the drain current of the amplifier is monitored each frame outside the burst interval in which the portable is transmitting and thus when no signal is present at its input. The drain current is then controlled by adjusting the gate voltage to compensate for any variations.