Showing papers on "Linear 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.

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.

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%.

Dual-band, dual-mode power amplifier

Abstract: A power amplifier circuit for a radio transceiver has a linear mode amplifier and a saturated (nonlinear) mode amplifier, a diplex matching circuit coupled to the linear mode amplifier for impedance matching and for separating transmitted signals in a plurality of frequency bands, a low pass matching circuit coupled to the output of the saturated mode amplifier and means for selectably placing the power amplifier circuit in a linear mode for or a saturated mode, corresponding to digital and analog modes of operation of the cellular telephone, respectively in linear or digital mode, the linear amplifier is biased in the on state and the saturated mode amplifier may be biased in the off state. Similarly, in the saturated or analog mode of operation, the saturated mode amplifier is biased in the on state and the linear amplifier may be biased in the off state. The amplifier circuit may include a switch or circuit, coupled to an output of the diplex matching circuit and the output of the low pass matching circuit, for selectably coupling the first diplex matching circuit output or the low pass matching circuit output to an output line when the amplifier circuit is selectably placed in linear mode or saturated mode, respectively.

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%.

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.

Power amplifier output module for dual-mode digital systems

Abstract: A power amplifier output module 200 having low insertion loss and self-shielding properties for dual-mode digital systems is provided. Module 200 has a first power amplifier drive circuit comprising a first power amplifier 220 and a first output impedance matching network having integrated suppression of higher order harmonics 222. A second power amplifier drive circuit comprising a second power amplifier 224 and a second output impedance matching network having integrated suppression of higher order harmonics 226 is also provided. Module 200 also comprises a single diplexer 228 coupled to the first impedance matching network and the second impedance matching network. Module 200 also comprises a single broadband directional coupler 230, coupled to the diplexer 228, for coupling both the first power amplifier drive circuit and the second power amplifier drive circuit. Module 200 provides an integrated solution involving greater performance in a smaller package.

Frequency selective predistortion in a linear transmitter

Abstract: A system for linearly transmitting an amplified output signal using predistortion is disclosed. The system uses a straight inverse modeling scheme to more easily and accurately determine the inverse of the distortion caused by a power amplifier (1002) of a RF transmitter. The direct inverse modeling scheme of the present invention indexes the LUT (1020) using the modulated input signals instead of the potentially noisier output signals, which helps to increase the accuracy of the predistortion. The predistorter system (1010) stores complex coefficients in the LUT (1020), which are then used as the tap weights of a digital filter implementing the predistorter (1022). Finally, the trainer (1008) uses a modified version of the power amplifier (1002) output signal. The modified power amplifier (1002) output signal has the in-band distortion removed from the power amplifier (1002) output signal.

Predistortion technique for high power amplifiers

Abstract: A predistortion technique for high power amplifiers includes an adaptive predistortion algorithm that operates independently of data samples to write a set of complex gain values, or predistortion parameters, to a lookup table. The algorithm may be processor-driven. The gain values are taken from the lookup table and multiplied by a complex digital baseband waveform. The gain values may first be subjected to interpolation. The downconverted output of the amplifier is measured to gauge the efficacy of the predistortion. Based on the effect of the predistortion upon the ratio of in-band power to out-of-band power, decisions are made on the set of predistortion parameters for the next iteration of the algorithm. The algorithm runs continuously, perturbing parameters and adapting the predistortion functions accordingly in an effort to continually reflect instantaneous amplitude-modulation and phase-modulation relationships that may change over time with temperature variation or component aging.

A low-voltage low-power wide-range CMOS variable gain amplifier

Abstract: In this paper, a compact low-power (LP) low-voltage (LV) metal-oxide-semiconductor-only (MOS-only) variable gain amplifier (VCA) is introduced. This amplifier based on complementary MOS (CMOS) transistors operating in strong inversion is composed of a pseudo-exponential current-to-voltage converter, analog multiplier, and output stage. The gain of the amplifier is controlled exponentially by a novel wide-range pseudo-exponential current-to-voltage converter implemented with two back-to-back connected current mirrors exhibiting superb exponential characteristic. Also, a new LV/LP composite transistor is introduced to increase the input dynamic range of the multiplier. The amplifier is fabricated using a 2-/spl mu/m MOSIS n-well process, and its simulation and measurement results are shown in detail.

System and methods for stimulating and training a power amplifier during non-transmission events

Abstract: A LINC amplifier of a radio frequency transmitter provides substantially linear amplification from two nonlinear amplifiers by decomposing the original signal into two constant amplitude envelope, phase varying signals, which, when combined, constructively and destructively interfere to re-form the original signal. The output of the LINC amplifier, which is to be transmitted via an antenna, is an amplified form of the original signal. The LINC amplifier uses a digital control mechanism to control and adapt a digital compensation network that directly compensates for the imperfections of the analog RF environment, including the amplifiers. The mechanism monitors the combined amplifier output and adjusts the signal components in order to precisely compensate for any differences in the characteristics of the separate signal paths which would cause the combination not to accurately represent the original signal. The mechanism also corrects the component signals using information which can be applied to the amplifiers independent of the signal to be transmitted.

Compensation system and methods for a linear power amplifier

Abstract: A LINC amplifier of a radio frequency transmitter provides substantially linear amplification from two nonlinear amplifiers by decomposing the original signal into two constant amplitude envelope, phase varying signals, which, when combined, constructively and destructively interfere to re-form the original signal. The output of the LINC amplifier, which is to be transmitted via an antenna, is an amplified form of the original signal. The LINC amplifier uses a digital control mechanism to control and adapt a digital compensation network that directly compensates for the imperfections of the analog RF environment, including the amplifiers. The mechanism monitors the combined amplifier output and adjusts the signal components in order to precisely compensate for any differences in the characteristics of the separate signal paths which would cause the combination not to accurately represent the original signal. The mechanism also corrects the component signals using information which can be applied to the amplifiers independent of the signal to be transmitted.

Digital control of a linc linear power amplifier

Abstract: The inventive LINC amplifier provides substantially linear amplification from two nonlinear amplifiers by decomposing the original signal into two constant amplitude envelope, phase varying signals, which, when combined, constructively and destructively interfere to re-form the original signal. The output of the LINC amplifier, which is to be transmitted via an antenna, is an amplified form of the original signal. The inventive LINC amplifier utilizes a digital control mechanism to control and adapt a digital compensation network that directly compensates for the imperfections of the analog RF environment, including the amplifiers. The mechanism monitors the combined amplifier output and adjusts the signal components in order to precisely compensate for any differences in the characteristics of the separate signal paths which would cause the combination not to accurately represent the original signal. The mechanism also corrects the component signals using information which can be applied to the amplifiers independent of the signal to be transmitted.

Method and apparatus for linear transmission by direct inverse modeling

Abstract: A system for linearly transmitting an amplified output signal using predistortion whereby a straight/direct inverse modeling scheme (503) is used to determined the inverse of the distortion caused by a power amplifier (103). The predistorter system (407) stores complex coefficients in a LUT (603), which are then used as tap weights of a digital filter (601) implementing the predistorter. The predistortion is done by a non-linear filter (601) which incorporates both instantaneous and average envelope power or magnitude effects thereby compensating for modulation envelope memory effects of the power amplifier (103). The LUT (603) is addressed as a function of the instantaneous power or magnitude of the current sample and a profile of the power or magnitude envelope of previous samples. The LUT (603) is updated with values that are indexed as a function of the powers or magnitudes of past samples and the power or magnitude of the current sample.

Method and apparatus for wideband predistortion linearization

Abstract: A predistortion signal is generated which compensates for third order and higher order intermodulation distortion over a wideband. The predistortion signal is applied to an input radio frequency signal, for example a multi-tone radio frequency signal. The predistortion signal is a low order polynomial having adjustable coefficients. The predistortion signal can compensate for intermodulation products produced a nonlinear amplifier, and the polynomial coefficients can be adjusted based on the difference between the amplifier output and the input radio frequency signal.

Dual-band, dual-mode power amplifier with reduced power loss

Abstract: A power amplifier circuit has a driver amplifier stage including a low band driver amplifier and a high band driver amplifier. A final amplifier stage includes a linear mode amplifier for amplifying digitally modulated signals and a saturated (nonlinear) mode amplifier for amplifying frequency modulated (analog) signals. A switching network interconnects the driver amplifier stage and the final amplifier stage. Depending on the desired mode of operation, an appropriate driver amplifier can be coupled to an appropriate final amplifier to most effectively and efficiently amplify analog or digital RF signals in either of a plurality of frequency bands. A matching circuit is coupled to the linear mode final amplifier for impedance matching and for separating D-AMPS (800 MHz band) and PCS (1900 MHz band) digital signals. A power impedance matching circuit is coupled to the output of the saturated mode final amplifier. In one embodiment, an isolator is coupled to the output of one or more of the low band or high band outputs of the duplex matching circuit. In the low band analog path, a duplexer is provided ahead of the coupling means for reducing the RF power requirements on the coupling means. The switching network and input filter stage may precede a driver amplifier stage.

Radio-frequency power amplifier of mobile communication equipment

Abstract: A radio-frequency power amplifier of mobile communication equipment includes a differential amplifier arranged to balanced-input and amplify a radio-frequency signal delivered from a frequency converter of a transmission system of the mobile communication equipment located downstream of a modulator of the transmission system. The radio-frequency signal delivered from the differential amplifier is further amplified and balanced-output by a push-pull circuit. The differential amplifier and the push-pull circuit are respectively supplied with bias currents varying in dependence on a gain control signal, whereby respective amplification gains of the differential amplifier and the push-pull circuit are variably adjusted.

Apparatus and method for amplifying a signal

Abstract: The apparatus includes an amplifier (204) having an input and an output, the amplifier output coupled to an input of a Doherty amplifier (208). The Doherty amplifier (208) includes a control input and a Doherty output. The apparatus further includes a detector (224) having an input coupled to the output of the Doherty amplifier (208). The detector provides a detected signal at its output, to a controller (228), the controller responding to the detected signal by producing a first (230) and second control output (231). The first control output is coupled to a switching regulator (232) input, the switching regulator having an output coupled to the control input of the Doherty amplifier. The second control output is coupled to a control input of a variable attenuator (202), the output of the variable attenuator coupled to the input of the amplifier (204).

Dual band cellular phone with two power amplifiers and a current detector for monitoring the consumed power

Abstract: A transmitter for a cellular phone comprising an antenna and being operable at a first radio frequency band and a second radio frequency band is disclosed. The transmitter comprises a first power amplifier and a second power amplifier. The first power amplifier has a first input for a first signal at the first radio frequency band, a second input for a first control signal and a first output for an amplified first signal. The first output is connectable to the antenna. The second power amplifier has a third input for a second signal at the second radio frequency band, a fourth input for a second control signal and a second output for an amplified second signal. The second output is connectable to the antenna. The transmitter further comprises a single control module which receives a signal indicative of a current an active power amplifier draws. The control module uses this signal indicating the drawn current to generate a control signal to control the active power amplifier.

Wide band optical amplifier

Abstract: A wide band optical amplifier employing a split-band architecture in which an optical signal is split into several independent sub-bands which then pass in parallel through separate branches of the optical amplifier. Each branch may be optimized for the sub-band that traverses it. The independent sub-bands are combined before output, resulting in a broad band, high efficiency amplifier. Alternative, hybrid split-band amplifiers are described. As a result of their desirable characteristics, these wide band optical amplifiers may be used in dense WDM communications systems.

Controller and associated methods for a linc linear power amplifier

Abstract: A LINC amplifier of a radio frequency transmitter provides substantially linear amplification from two nonlinear amplifiers by decomposing the original signal into two constant amplitude envelope, phase varying signals, which, when combined, constructively and destructively interfere to re-form the original signal. The output of the LINC amplifier, which is to be transmitted via an antenna, is an amplified form of the original signal. The LINC amplifier uses a digital control mechanism to control and adapt a digital compensation network that directly compensates for the imperfections of the analog RF environment, including the amplifiers. The mechanism monitors the combined amplifier output and adjusts the signal components in order to precisely compensate for any differences in the characteristics of the separate signal paths which would cause the combination not to accurately represent the original signal. The mechanism also corrects the component signals using information which can be applied to the amplifiers independent of the signal to be transmitted.

Power amplifier saturation prevention method, apparatus, and communication system incorporating the same

Abstract: An apparatus for controlling the power level of an output signal from the output of an electronic amplifier. The electronic amplifier has a control signal input for receiving an amplifier control signal and has a power input for receiving current from a power supply. The apparatus comprises an amplifier output power detector, coupled to the output of the amplifier, used for generating a power measurement signal representing the output power of the amplifier. The apparatus contains a current detector arranged to detect the current received by the amplifier from the power supply and to provide a current measurement signal dependent on the amount of current received from the power supply. The apparatus contains a digital signal processor which receives the current measurement signal and provides a reference signal dependant on the current measurement signal. The apparatus also contains a comparator coupled to receive the reference signal and the power measurement signal which is used for generating the control signal to prevent saturation of the amplifier.

Power saving device for radio communication terminal

Abstract: A power saving device for a radio commmunication terminal reduces current consumption by changing the number of power amplifying stages. A power amplifier in the radio communication terminal includes a first amplifier (300) for high power and a second amplifier (208) for low power. A signal path selector (209) switches an input signal to an input node of the first or second amplifier in response to a switching control signal. An output path selector selects one of output signals from the first and second amplifiers in response to the switching control signal. An RSSI detector (105) detects signal strength of a signal received from a base station. A controller generates the switching control signal of a first state, when the signal strength is low, to enable the signal path selector to switch the input signal to the first amplifier (300) and enable the output path selector to select the output signal of the first amplifier, and generates the switching control signal of a second state, when the signal strength is high, to enable the signal path selector to switch the input signal to the second amplifier (200) and enable the output path selector to select the output signal of the second amplifier. A power supply (107) blocks a first supply voltage to the first amplifier in response to the switching control signal of the second state, and blocks a second supply voltage to the second amplifier in response to the switching control signal of the first state.

Simple model of optical amplifier chains to evaluate penalties in WDM systems

Abstract: A simple model to evaluate the penalty due to amplifier gainshape in a wavelength division multiplexing (WDM) optical system is proposed. The model requires only knowledge of the overall gain of the amplifier chain for all channels and provides signal-to-noise ratio (SNR) penalties for given launched powers. It also provides the input power distribution required for SNR equalization, and the associated SNR penalty, by solving an eigenvalue/eigenvector problem. The penalty predicted by the model agrees well with recent field measurements on a transoceanic cable. The model can also be applied to predict the gainshape of the amplifier chain from a measurement of the output noise spectrum with no input signal. The capacity of a long amplifier chain can thereby be determined from the receiving terminal only.

High-efficiency harmonic-control amplifier

Abstract: A half-sinusoidally driven class-A harmonic-control amplifier (hHCA) combines the advantage of high gain of class A with the advantage of high drain efficiency of class F. Consequently, power-added efficiency is increased as compared with state-of-the-art high-efficiency amplification techniques. As this innovative amplifier concept consists of a pulse-forming class-B amplifier stage followed by a class-A power-amplifier stage, intermodulation distortion is low even in saturation. The realization of such a two-stage hHCA offers 71% overall efficiency, 27.9 dBm output power, and 22.4 dB gain at 1.62 GHz. Two-tone measurements at 1 dB gain compression, where the amplifier's single-carrier (SC) overall efficiency is still 64%, has demonstrated thirdand fifth-order intermodulation distortion of -29 and -21 dBc, respectively.

Mobile station having dual band RF detector and gain control

Abstract: A multi-band mobile station (10) includes a plurality of RF amplifier sections, one for each frequency band of interest; a controller (18) for selectively enabling, when transmitting, only one of the RF amplifier sections; a directional coupler circuit for detecting the power of an amplified RF signal that is output from the enabled one of the RF amplifier sections; and a single error detection circuit, coupled to the detecting circuit, for generating an error signal. The error signal has a magnitude that is indicative of a difference between the detected power and a desired power. The error signal is coupled to the enabled one of the RF amplifier sections so as to minimize the magnitude of the error signal. The controller may place a non-enabled RF amplifier section into a low power consumption mode. The directional coupler circuit includes an RF detector coupled to the directional coupler, and an impedance matching circuit coupled between the directional coupler and the RF detector. The impedance matching circuit operates so as to cause the signal output from the RF detector to have about the same magnitude for a given level of output power from any one of the enabled RF amplifier sections. In an illustrative embodiment of this invention one frequency band of interest includes 836 MHz, and another frequency band of interest includes 1880 MHz.

Optical fiber amplifier having variable gain

Abstract: An optical amplifier device intended for WDM light signals comprises a preamplifier (3) and a power amplifier (11) of the optical fiber amplifier type, which are connected in series and have gain curves dependent on the wavelength. A controllable attenuator (5) is connected between the amplifiers (3 and 11) and is controlled by a control device (7). The signal input to the preamplifier (3) has a low power and is amplified to provide an output signal where the signals of the input channels have been amplified with different gains. The input signal of the power amplifier (11) then has a larger power resulting in a gain characteristic different from that of the preamplifier (3). By adapting the attenuation of the attenuator (5) for variations in the input signal the gain characteristic of the power amplifier (11) can be set so that the signal output from the amplifier device has a spectral dependence that is the same as the original spectral dependence obtained without variations. Also, the same spectral dependence can be maintained when the pump light power of the power amplifier is changedand then the total amplifier gain is changed, by adapting the attenuation of the attenuator (5) so that the gain of the power amplifier is not changed. In the amplifier the lower possible noise from the preamplifier stage is added to the input signal and the full output power is always available from the power amplifier. If the input signal is e.g. increased the SNR of the signals passing through the amplifier is correspondingly improved. This improves the performance of an optical network in which the amplifier is used.

Microwave power amplifier efficiency improvement with a 10 MHz HBT DC-DC converter

Abstract: This paper presents a technique for raising power efficiency in portable wireless transmitters by integrating a variable voltage output DC-DC converter together with a MESFET RF power amplifier. Significant increases in power efficiency are obtainable over a large range of output power levels. The system includes an envelope detector, a closed feedback loop, and a pulse width modulator operating at 10 MHz. A 300 mW transmitter is shown for which battery life can be extended by over 1.4 times.

Method and apparatus for reducing power dissipation in multi-carrier amplifiers

Abstract: A method and apparatus are provided for reducing power dissipated by an amplifier circuit such as a line driver in a Digital Subscriber Line (DSL), a power amplifier in a radio environment, etc. The power supplied to the amplifier circuit changes depending upon the level of input signal to the amplifier circuit. A higher power is supplied to the amplifier circuit when the level of the input signal exceeds a threshold. Otherwise, a lower power is supplied to the amplifier circuit.