Showing papers on "RF power amplifier published in 1987"

Efficiency of Doherty RF Power-Amplifier Systems

Abstract: A Doherty system combines the outputs of two or more linear RF power amplifiers (PAs) through an impedance-inverting coupler such as a quarter-wave transmission line. At low output levels, the first PA operates linearly, reaching saturation (and maximum efficiency) at some transition voltage below the system peak-output voltage. At higher output levels, the first PA remains saturated and the second PA operates linearly. The instantaneous efficiency and power characteristics of a Doherty system are derived using ideal class-B RF PAs so that the results can easily be scaled for use with real-world PAs. The average efficiency and maximum-efficiency transition points are then determined for a variety of amplitude-modulated signals. The Doherty amplifier can be considerably more efficient than a conventional class-B linear PA. For example, the 28-and 8.9-percent average efficiencies of a class-B PA with Rayleigh-distri buted envelopes with 10-and 20-dB peak-to-average ratios are improved to 60 and 48 percent, respectively, by a two-stage Doherty system. The addition of a third stage further improves the efficiencies to 70 and 66 percent, respectively.

Exact analysis of class E tuned power amplifier at any Q and switch duty cycle

Abstract: Previous analytical descriptions of a Class E high-efficiency switching-mode tuned power amplifier have been based on the assumption of an infinite Q or the minimum possible value of Q . This paper presents an exact analysis of the Class E amplifier at any Q and any switch duty cycle D , along with experimental results. The basic equations governing the amplifier operation are derived analytically using Laplace-transform techniques and assuming a constant current through the dc-fed choke. The following performance parameters are determined for optimum operation: the current and voltage waveforms, the peak collector current and collector-emitter voltage, the output power, the power-output capability, the load-network component values, and the spectrum of the output voltage. It is shown that all parameters of the amplifier are functions of Q . Therefore, the high- Q assumption used in previous analyses leads to considerable errors. For example, for Q at D = 0.5 , some errors are up to 60 percent. The results can be used for designing Class E stages at any Q and switch duty cycle D . The measured performance shows excellent agreement with the design calculations. The collector efficiency was over 96 percent at 2 MHz for all tested values of Q from 0.1 to 10.

Class E Power Amplifiers and Frequency Multipliers with finite DC-Feed Inductance

Abstract: Previous descriptions of class E amplifiers and frequency multipliers have required a radio frequency choke between the dc power supply and the active device "switch." In this paper, it is shown that class E operation may be maintained with the RF choke replaced by a smaller reactance. The analysis technique used is similar to that used by Raab in his description of class E amplifiers in that the equations describing circuit operation are obtained from Fourier series methods and the assumption of an infinite output network Q . The equations so obtained are used to determine (1) optimum operation (maximum power output capability at 100-percent efficiency) at any harmonic and (2) design equations that yield the requisite component values for optimum operation. The equations show that class E circuits may be configured to accommodate devices with arbitrary output capacitance and that class E amplifiers may be configured to provide greater power output capability than can be obtained using an RF choke design. Class E circuits with moderate values of output network Q were constructed and tested. The measured performance of these experimental circuits shows excellent agreement with the theoretical performance predicted by the equations.

Large‐signal time‐domain modeling of low‐pressure rf glow discharges

Abstract: Large‐signal time‐domain modeling (simulation) of rf glow discharges is a very useful and potentially accurate tool for the study of low‐pressure (50–500‐mT) gaseous electronics at high frequencies. Unfortunately, the computational limitations imposed for stability, accuracy, and efficiency can often hinder the production of useful, cost‐effective results. This paper describes a self‐consistent argon rf glow‐discharge simulation at 13.56 MHz for equal‐ and unequal‐area parallel‐plate electrode geometries. Some of the numerical problems associated with this type of simulation are identified and the numerical methods used to overcome them are described. To illustrate the usefulness of this modeling scheme, the plasma potential and the cathode dc bias are examined as functions of electrode area ratio and rf power.

Characteristics of a semiconductor laser pumped brillouin amplifier with electronically controlled bandwidth

Abstract: We demonstrate the operation of a semiconductor laser pumped fiber Brillouin amplifier. An optical gain of 5.5 dB/mW of pump power is obtained. The 15-MHz intrinsic bandwidth of the amplifier was extended more than one order of magnitude by adding frequency modulation to the pump laser. Bit-error-rate receiver sensitivity measurements with an in-line Brillouin amplifier demonstrate a 16-dB improvement in the system gain at 10 Mbit/s and a 8.5-dB improvement at 90 Mbit/s. Noise calculations show that the amplifier has an excess noise factor of 50-500 depending on the amplifier length and pump power.

Output power control circuit for a mobile radio apparatus

Abstract: An output power control circuit is provided in a casing of a mobile radio apparatus together with an automatic power control circuit and an RF signal amplifier. The output power control circuit applied level control signals to the automatic power control circuit for maintaining the power level of the output RF signal of the RF amplifier at one of a plurality of output power levels corresponding to the level control signals. The output power control circuit has a receiver, a temperature sensing circuit and a logic circuit. The receiver receives RF signals transmitted by a master station and detects power level setting command signals included in the received RF signal. The temperature sensing circuit detects an internal temperature of the casing and provides a power reduction signal upon detecting that the internal temperature has exceeded a predetermined temperature. The logic circuit receives the power level setting command signal from said receiver, and generates a level control signal for determining an output power level corresponding to the power level setting command signal, and generates a level control signal for determining an output power level which is lower than that specified by the power level setting command signal upon receiving the power reduction signal from the temperature sensing circuit.

Security tag deactivation system.

Abstract: Security tags which bear a resonant circuit made of conductors on opposite sides of a dielectric are deactivated by applying (20, 22, 24, 25, 26, 28) to a tag sufficiently high RF power at the resonance frequency to produce breakthrough between opposed conductors. A tag presence alert signal (41) is intentionally extended (42) beyond the period of active tag presence detection. During high power operation (23), the system inhibits other nearby RF deactivating and electronic article surveillance systems (45). The RF transmission of all these systems may also be slaved (21, 48). The high power RF produced by the deactivating system is principally dissipated where it causes no undesirable heating effects.

Scanning radio receiver

Abstract: A high-speed, multi-band scanning radio receiver. A frequency synthesizer loaded with a digital code read from memory performs band switching and supplies tracking signals and a local oscillator signal to multi-band RF amplifier and mixer circuitry. An output of an FM detector in the receiver is connected to a squelch circuit which includes a high-pass filter network and a diode detector, with the diode detector output being connected to an internal A/D converter of a microprocessor which converts multiple samples of the incoming signal to digital values and generates a mute signal when the average value of the converted samples is below a predetermined squelch level. An output line from the FM detector to audio output circuitry in the receiver is grounded in response to the mute signal. The microprocessor is also programmed to control receiver tuning during SEARCH mode such that searching continues until the demodulator output signal for an active channel is substantially in the center of the demodulator S curve, as detected by a window detector.

Automatic electrical power control circuit

Abstract: A power control circuit comprises a signal input (1), a controllable attenuator (2), an amplifier (3), an output (5), a power detector (4), a reference circuit, a comparator (6), an external control input (7), an error detector (8), and a controller (9). The comparator (6), error detector (8), and controller (9) are digital circuits realized by a microprocessor. The attenuator (2) is between the signal input (1) and the input (3A) to the amplifier (3) to regulate the amplifier's output (3b). The power detector (3) couples to the amplifier output to generate a measurement signal representing the power at the output. The reference circuit generates a reference signal representing a predetermined minimum output when the signal input is nonzero. The comparator (6) compares the measurement and reference signals and generates a decision signal (6b) indicating if the signal input is nonzero. The external control input (7) receives an external control signal. The error detector (8) is coupled to the power detector (4) and the external control input (7) and computes the difference between the external control signal and the measurement signal. When the measurement signal is at or above the minimum power, the controller (9) provides an integral of the computed difference to control the variable attenuator (2). When the measurement signal is below the minimum power, the controller (9) keeps the attenuator at a prior constant value.

Composite power amplifier with redundancy

Abstract: A power combiner includes an input power splitter driving a plurality (N) of amplifiers. The amplifier outputs have Z0 output impedance and are coupled by transmission (TX) lines of Z0 characteristic impedance to the junction point of a lossless power combiner. Short-circuiting switches located λ/4 from the junction power disconnect failed amplifiers from the combiner. According to the invention, a number M

Harmonic Reaction Amplifier - A Novel High-Efficiency and High-Power Microwave Amplifier

Abstract: A newly proposed high efficiency amplifier, the Harmonic Reaction Amplifier (HRA), is presented. Power-added efficiency of 75°A (85% drain efficiency) is achieved with a 3-W HRA using GaAs FETs in the 1.7 GHz band. The operation principle is derived from a novel second-harmonic injection technique enabling purely class-B biased operation. Amplifier circuits for attaining high efficiency operation can easily be constructed with ordinary microstrip circuits. Besides, precise circuit adjustment is available to maximize the efficiency. The HRA makes high power and high efficiency microwave power amplifiers with zero quiescent current possible. Experimental test results show the feasibility of a quasi-microwave transmitting amplifier for the next generation mobile radio system. However, the HRA can be applied to radio equipment of various fields such as terrestrial microwave radio systems and satellite communications systems using microwave frequency bands.

Broadband power efficient class E amplifiers with a non-linear CAD model of the active MOS device

Abstract: This paper describes how broadband power efficient Class E amplifiers can be designed which are capable of efficiencies approaching 100% over 35%fractional bandwidths. The paper contains a brief review of switching ClassE amplifiers, which are normally narrow band, and describes how these can be made broadband. As an example, a broadband 130 to 180 MHz r.f. amplifier has been designed, built and tested and the results are reported here. To enable an accurate computer simulation of the r.f. power amplifier to be made, a non-linear CAD model of the active device (an r.f. power MOSFET) is developed. CAD techniques for matching the non-linear input impedance of the MOSFET are also presented. Experiment and theory are compared and show close correlation.

Very wide bandwidth linear amplitude modulation of RF signal by vector summation

Abstract: A radio frequency (RF) carrier wave is successively divided and the divided parts are non-linearly, phase modulated in response to a modulating signal. The modulating signal is linearized so that the output of the circuit is linear with the modulating signal and then drives differential drivers to control voltage controlled phase shifters in pairs to differentially phase shift the divided RF signals. These phase shifted signals may be efficiently amplified in non-linear, Class C, RF power amplifiers. After amplification the signals are differentially re-combined in an inverse binary tree of hybrid combiners to produce a synthesis output signal. This synthesis output signal is equivalent to the amplitude modulation, and the amplification, of the RF input signal. By operation of the circuit apparatus in accordance with the invention, amplitude modulation at wide bandwidths including hundreds of megahertz may typically be accomplished on microwave RF signals of high power levels including several kilowatts.

Broadband 1.5μm GaInAsP travelling-wave laser amplifier with high-saturation output power

Abstract: A 1.5μm GaInAsP travelling-wave amplifier (TWA), which has a residual facet reflectivity of 0.04% is realised through the application of SiOx antireflection coatings on both facets. The TWA has wide signal gain spectra with undulation of 1.5dB within one free spectral range for a 24.5dB signal gain. The saturation output power of the 24.5dB signal gain. The saturation output power of the TWA fora 20dB signal gain is +7dBm, which is 20dB greater than that provided by the Fabry-Perot amplifier.

Protection circuit for RF power amplifiers

Abstract: An improved power controller and protection circuit to regulate the RF output power of a radio transmitter and to protect its RF amplifier from overload damage. The controller features a floating input, voltage controlled current source with high common-mode rejection to provide feedback of the DC input current drawn by the RF power amplifier. The controller can use an arbitrary reference voltage, which allows its application universally with power amplifiers designed for different rated output powers and frequency ranges.

Linear amplifier combiner

Abstract: Present performance of cellular systems is restricted by the method used to combine signals before they are transmitted from the cell site. This combining is accomplished using resonant filters which are mechanically tuned. Changing frequency assignments is not easily done. A significant improvement in cellular system performance can be achieved by using a linear amplifier in combination with a broad band passive combiner. In the present system, each individual signal has its' own separate power amplifier. The outputs from these are combined at high power by using frequency isolation to reduce losses. With the linear amplifier, the combining is done at low power where the losses can be tolerated. The combined signals are then amplified by a single linear amplifier to bring them to the transmit power level. The linear amplifier combiner arrangement essentially eliminates the rigid frequency restrictions which now exist. Channel assignments can be changed as required without mechanical tuning. The channel spacing limitation required by the existing combiners is also eliminated. The number of signals which can be transmitted from one antenna is now limited only by total power consideration. The linear amplifier also permits modulation schemes which make more efficient use of the available spectrum.

Extended range composite head power sensor with three circuit branches having a common node

Abstract: A probe for sensing radio frequency power, utilizing two independently-driven radio frequency-sensitive diodes. The two diodes are driven through a common RF input, through a branch network which separates and feeds the probe RF power to each diode independently. The diodes are unequally padded from the RF input, to provide an extended sensitivity range for the probe. One diode, therefore, operates in a lower dBm range, while the other diode operates in a higher dBm range. Two separate outputs are provided from the probe to supply a common power meter which monitors the appropriate output for the present power level of the radio frequency input.

RF pulse control system for a magnetic resonance imaging transmitter

Abstract: A pulse control system for a magnetic resonance imaging transmitter has circuitry for detecting the peak value of the RF current in the transmitter coil for a given RF pulse; circuitry for comparing the detected peak value of the RF current with a desired reference peak value for the RF pulse, for determining the difference between the detected and the desired peak values for the RF pulse, and for determining a gain adjustment factor for the transmitter amplifier for the transmitter necessary to produce the desired peak value of the RF current in the transmitter coil; and circuitry for adjusting the gain of the transmitter amplifier in response to the gain adjustment factor to produce the desired peak value of the RF current for the RF pulse.

Automatic control circuitry for a signal power amplifier

Abstract: The present invention is directed to an automatic power control circuit for a signal power amplifier which maintains the output power to one of a plurality of output power levels. The output power level is controlled by an externally-generally level control signal which is used by a square wave signal generating circuitry for controlling the duty cycle of the generated square wave. The square wave is integrated by a filter network to produce a reference voltage level. The output voltage level of the RF amplifier is compared with the reference voltage level, and the difference between the two signals is used to control a drive circuit for generating the proper control voltage for controlling the RF amplifier so that the desired output power level is maintained.

A Producible 2 to 20 GHz Monolithic Power Amplifier

Abstract: The design, fabrication, and performance of a 0.4-W, 2 to 20 GHz distributed amplifier are described in this paper. Small-signal gain is 5 dB and power-added efficiency is 15%. The amplifier is fabricated on ion-implanted GaAs, and achieves excellent performance through use of series gate capacitors and a tapered drain line. Circuit layout and optimization to obtain process insensitivity and first-pass design success are discussed. A comparison is made to a commercially available state-of-the-art 6 to 18 GHz amplifier designed using conventional (lossy-mismatch) topology. The distributed amplifier is shown to have much improved bandwidth, SWR, gain flatness, and insensitivity to process variations, while retaining similar output power and efficiency.

Phase locked magnetrons as accelerator rf sources

Abstract: The problems associated with operating magnetrons into accelerator cavities is well known However, as the magnetron is a simple inexpensive device, compared with most other rf power tubes, it is an attractive candidate for future accelerator rf systems A test stand has been constructed at GA and has operated a Varian VMP 1702 425 MHz magnetron at a peak power level of 2 MW and a nominal pulse length of 100 ps Included in the test stand is a tetrode cavity amplifier, also at 425 MHz, with a maximum peak power capability of 250 kW The amplifier is driven by a solid state oscillator The intent of the program is to use the tetrode amplifier output to phase lock the magnetron to produce an rf pulse having characteristics suitable for accelerator applications Later it is intended to extend the experiment to address the problems of marrying the magnetron directly to an accelerator cavity 0100 KV

Ultra compact, RF excited gaseous lasers

Abstract: A laser comprising an RF matching unit having an RF power input and an RF power output, an optical cavity including electrode apparatus extending along the optical cavity, receiving the RF power output and defining a discharge gap having a gaseous lasing medium disposed therein, the RF power output being operative to produce a population inversion in the gaseous lasing medium, and an arrangement for providing direct fluid cooling contact with the electrode apparatus generally along its entire extent.

Axially coupled gyrotron and gyro TWTA

Abstract: A tilt-angle gun provides a conically-shaped electron beam formed in a magnetically-shielded region which is injected into a coaxial waveguide of the amplifier embodiment of the invention and into a coaxial cavity of the oscillator embodiment immersed in the main magnetic focussing system to form a hollow gyro beam of large radius. RF power input and the amplified rf power output are simply and easily provided through circular input and output waveguides coupled respectively to each end of the coaxial waveguide by slotted sections. The electron beam and the output rf energy are naturally physically separated so that extraction of the rf output is facilitated and occurs with little rf power loss.

Scan Beam Antenna Intermodulation Improvement Due to Spatial Dispersion

Abstract: In the recent development of scan beams for application tomobile satellite or thin route communication systems, theintermodulation (IM) generated by the element amplifiers isspatially dispersed, such that some of the IM radiated energy failsoutside the intended beam area. In addition, some of the IM fallinginside the beam area have frequencies different from the carriersintended for that area.It is shown that for systems with frequency reuse, an average IM noise reduction of several dB can he realized. The improvementin carrier-to-IM noise ratio can be used to increase system capacity,or for given capacity it can be used to reduce RF power amplifierbackoff, which can be translated into a reduction of spacecraftprime power requirement.

Balanced transformer-less amplifier circuit

Abstract: A balanced transformer-less amplifier having a pair of power amplifers connected in parallel for outputting amplified signals of opposite polarity, offset output detection circuit coupled to the amplifiers for detecting the difference in voltage level between the outputs of the two power amplifiers, and a preamplifier responsive to the offset output detection circuit both for operating the pair of power amplifiers on only a single power source voltage and for compensating for the difference in voltage level between the outputs of the two power amplifiers.

RF-AM transmitter with pulse width modulator

Abstract: An RF-AM transmitter includes a pulse amplifier responsive to a pulse width modulated (PWM) signal derived in response to an information signal. A low pass filter converts pulses derived by the power amplifier into a variable amplitude signal that is DC coupled to a power supply for an RF amplifier. An amplifier system including the pulse and RF amplifiers has stray capacitance coupled to a modulator which derives the PWM signal; the stray capacitance lengthens narrow modulator output pulses so they are excessively long. The amplitude of only the narrow pulses is reduced by a resistor-capacitor timing circuit in series with a switch to substantially preserve the narrow pulse area. The switch provides a low impedance path from the timing circuit to a reference potential terminal when current initially flows in the circuit during pulse transitions and throughout the length of each of the short duration pulses. Thereby, the power amplifier is forward biased but not driven into saturation during the short duration pulses. The switch provides a higher impedance path from the timing circuit to the reference potential terminal after the transition has elapsed, enabling the power amplifier to be saturated during pulses longer than the short duration pulses. The RF power amplifier tube has a tendency to load the power amplifier tube out of saturation during wide pulses. The ampitude of the wide pulses is maintained substantially constant by a resistor shunted by an inductor between the modulator and the power amplifier.

An 8-15 GHz GaAs Monolithic Frequency Converter

Abstract: An MMIC frequency converter with an RF bandwidth of 8-15 GHz and an IF bandwidth of 1.5 GHz has been designed and built. The MMIC chip has 15 dB conversion gain and includes a two-stage RF amplifier, a two-stage LO buffer amplifier, a double-balanced mixer, and a three-stage IF amplifier. This high level of integral ion is realized on a small--48 x 96 mil--area, resulting in good RF yields. The circuit employs a push-pull configuration to eliminate the need for via holes (low-inductance grounds) and facilitate a compact layout.