Showing papers on "RF power amplifier published in 1992"

Electrosurgical and ultrasonic surgical system

Abstract: An electrical circuit system (1) which provides electrical energy to a surgical apparatus having ultrasonic fragmentation, aspiration and electrosurgical coagulation capabilities, which system also includes an impedance sensing network (10) and automatic feedback power output control to reduce RF power output as load impedance increases, thereby reducing RF leakage current.

Experimental performance of an adaptive digital linearized power amplifier

Abstract: The authors present experimental results in which an adaptive complex gain predistorter achieved a reduction in out-of-band spectral emissions in excess of 20 dB for a class AB amplifier operating close to saturation. The experimental results demonstrate that a class AB power amplifier may be linearized without sacrificing efficiency. Although significant spectral reduction was achieved in the adjacent channel, the out-of-band spectral floor was flat and approximately -50 dB from the inband spectra. The complex gain predistorter exhibits two distinct advantages: a design engineer is not forced to back off a power amplifier to its linear but highly inefficient operating point; and adaptive correction allows the effects of frequency changes, drift in bias, operating point, aging and thermal stress to be readily compensated. >

Power control circuitry for a tdma radio frequency transmitter

Abstract: A transmitter (604) of a TDMA cellular telephone (600) includes power control circuitry (100) comprised of variable gain stage (104), mixer (106), bandpass filter (109), RF amplifier (110), and directional coupler (112) in a forward path, and two detectors (116 and 117), four A/D converters (118, 119, 121 and 123), digital controller (120), and D/A converter (126) in a feedback path. In operation, the variable gain stage (104) is responsive to a gain control signal AOCCNT (128) for adjusting a modulated IF signal, which is then mixed in mixer (106) with an RF reference signal to produce the transmit RF signal. The temperature and supply voltage are sampled by controller (120) at the beginning of each time slot. Adjustments in the gain control signal (128) dictated by the sampled temperature and supply voltage are made by controller (120) in each time slot prior to keying the RF amplifier (110). The transmit RF signal is amplified by the RF amplifier (110) to produce the transmit output signal which is coupled by the directional coupler (112) and transmit filter (618) to an antenna (620) for transmission The forward power and reverse power of the transmit output signal are sampled by controller (120) at the end of each time slot. The sampled forward power is used by controller (120) in calculating the value of the gain control signal for the next time slot. If the sampled reverse power or supply voltage exceed respective maximum values, the RF amplifier (110) is dekeyed by controller (120).

Low noise high power optical fiber amplifier

Abstract: A rare earth doped optical fiber amplifier is pumped at a first wavelength selected to provide a low noise figure, and at a second wavelength selected to provide a high power efficiency. An erbium-doped fiber amplifier is illustrated, in which the first wavelength is about 980 nm and the second wavelength is about 1480 nm. The amplifier is forward pumped with the 980 nm wavelength adjacent the amplifier input to provide a low noise figure. Backward pumping at the 1480 nm wavelength is provided adjacent the amplifier output to achieve a high power efficiency.

Power amplifier saturation detection and correction method and apparatus

Abstract: A power amplifier controller for detecting saturation of the power amplifier (203) and correcting the automatic output control voltage (231) to avoid any further saturation. The controller detects the power of the RF output signal (211), generates a signal (229) correlated to the detected power, compares changes in that signal (229) to changes in the voltage of the AOC signal (231) in a comparator (217). The comparator (217) generates a signal (233) correlated to saturation of the power amplifier (203) for a DSP (223). The DSP checks the status of this signal (233). Upon detecting saturation, an algorithm contained within the DSP methodically reduces the voltage of the AOC signal (231) until there is a change in the power of the RF output signal (211).

Detection of explosive and narcotics by low power large sample volume nuclear quadrupole resonance (NQR)

Abstract: The sensitive detection of explosives and narcotics by nuclear quadrupole resonance (NQR) is performed at low rf power by assuring that the rf field strength is larger than the local magnetic field. Additionally, it has been recognized that signal-to-noise ratio of a signal induced by a specimen of fixed size decreases by only the square root of the coil size. Thus, rather than scaling power linearly with coil size, as conventionally done to maintain the same rf field intensity, the power needs only be increased by the square root of the increased coil size to assure maintenance of the same signal to noise ratio. This technique permits the use of larger coils than previously used. The invention is useful for both volume coils and surface coils.

Plasma processing apparatus capable of detecting and regulating actual RF power at electrode within chamber

Abstract: A plasma processing apparatus has a process chamber and a pair of electrodes provided in the process chamber to oppose each other. An RF power supply outputs an RF power to be supplied to at least one of the pair of electrodes in the process chamber. A power detector detects an actual RF power to be applied to one of the electrodes in the process chamber. A controller controls the RF power output from the RF power supply to a predetermined value in accordance with the actual RF power detected by the power detector.

Reduction of RF penetration effects in high field imaging.

Abstract: A method of correcting for the RF inhomogeneity in the body by dielectric loading of the coil-to-shield space in an RF resonator (coil and shield assembly) is described. The presence of the RF coil and RF shield have significant effects on RF homogeneity. Based on theoretical calculations, a method for adjusting the RF homogeneity by manipulating the axial propagation constant, kappa z, is proposed. This is accomplished by loading the coil-to-shield space with dielectric material of suitable relative permittivity so as to increase kappa z and decrease the radial propagation constant, kappa rho. In this manner, the radial wavelength (lambda rho = 2 pi/kappa rho) can be increased relative to the body dimensions, and the field amplitude variations in the axial plane minimized. Theoretical calculations indicate that a value of between 30 and 40 for the relative permittivity of the dielectric material in the coil-to-shield space would reduce the RF field inhomogeneity from +/- 15% to about +/- 3% over a central 30-cm-diameter region of a homogeneous 40-cm-diameter body at both 64 and 170 MHz. The theoretical model was verified in laboratory measurements of the [formula; see text] field generated in a test coil at 170 MHz which was scaled to correspond to a body at 64 MHz. However, the improved RF field homogeneity would be accompanied by increased RF power requirements and reduced coil sensitivity.

A new power amplifier topology with series biasing and power combining of transistors

Abstract: A power amplifier topology was demonstrated in a microwave monolithic integrated circuit (MMIC) implementation with GaAs MESFETs. This topology overcomes several limitations of the traditional approach of paralleling of power transistor unit cells. In the new topology, unit cells are both parallel and series combined. The benefits include higher input and output impedances, broadband power matched interstage networks, and high voltage biasing at reduced DC current. Measured results on a MMIC and a hybrid power amplifier implemented with this technique are presented. >

In-phase combiner and RF recovery system

Abstract: A system and method for combining RF signals by a series of in-phase combiners. The system uses a series of switched, high efficiency amplifiers which may be selectively operated to obtain a desired output signal, such as an Amplitude Modulated (AM) signal. The output signals of the amplifiers are combined by a series of in-phase combiners. In a high linearity system a feedback loop is used to correct for combiner losses. The RF power normally lost in the combiners is recovered and available to increase the overall combiner efficiency.

Output level control circuit for use in RF transmitter

Abstract: An output level control circuit for radio-frequency transmitter which intermittently transmits radio-frequency carrier waves such as seen in the TDMA radio communication system and the digital cellular mobile telephone system. The variable gain amplifier unit of this transmitter amplifies the transmitting signal to a predetermined output power level in response to a control signal, the output power level is detected by a detecting diode which receives the application of a temperature-compensated bias voltage, and the sum of the detected output and the bias voltage becomes the detection output to the control loop. The bias voltage of the detecting diode is stored by bias voltage detection circuit during the off-period of the transmitting signal, an input reference voltage that is supplied in synchronism with the turning-on of the transmitting signal and the stored bias voltage are added by reference signal addition circuit, and the added output is served as the reference voltage that corresponds to the predetermined output power level. A power control circuit generates the control signal in response to the added output and the detection output, and the control signal controls the output power level of the variable gain amplifier unit.

Powder Dynamics in Very High-Frequency Silane Plasmas

Abstract: Particulate contamination produced during plasma‐assisted deposition of amorphous silicon devices can be responsible for reduced quality and yield. The threshold for powder formation imposes an upper limit on the radio frequency (rf) power and hence the deposition rate. In this work, the parallel‐plate capacitor discharge volume is illuminated and global, spatio‐temporal powder dynamics are recorded by CCD camera for analysis. The onset of powder production is determined visually and from observed modifications to the discharge electrical properties such as the matching condition, the direct current self‐bias and the rf power transfer efficiency. A systematic study has been made of the powder‐free operational space as a function of rf power, rf frequency (13.56–70 MHz) and substrate temperature.

Power amplifier ramp up method and apparatus

Abstract: The present disclosure includes a discussion of a power amplifier controller which powers up a power amplifier (203) without a substantial burst of frequency noise. The controller has a RF output power detector (211) which generates a signal (229) correllated to the power level of the power amplifier (203). This signal (229) is compared (215) to a reference signal (213) to determine if the power amplifier (203) is active. The signal (227) generated by this comparator (215) is used to determine the voltage level of the Automatic Output Control (AOC) signal (231).

Heterojunction bipolar transistor design for power applications

Abstract: Design rules of AlGaAs-GaAs heterojunction bipolar transistors for power applications are presented and compared to those for Si microwave power transistors. Concepts discussed include the tradeoff between power gain, output power, power-added efficiency in the layout design, layer structure selection, and thermal design. >

Control circuit and method for transmission output

Abstract: A control circuit for a transmission output is used in a TDMA system radio transmitter or the like and can control a transmission output burst wave stably with high accuracy over a wide range. There is provided a closed loop system in which part of the transmission output is taken out and detected to be compared with a reference voltage to control a power amplifier and an open loop system for controlling a drive amplifier connected to an input of the power amplifier, so that a wide range operation of the transmission output and multi-stage control are attained by combining controls of both the loops.

Drive amplifier for power line communications

Abstract: A power line communication amplifier circuit for providing a signal transmission across a power line medium when operating in a transmit mode, and for providing a relatively high input impedance to the power line when in a receive mode includes a unity gain buffer integrally coupled with a filter. The filter operates upon an input signal provided by a digital driver means. A control means is coupled to the digital driver means and to the buffer such that when said amplifier is switched to a receive mode, both the driver means and buffer provide a high input impedance.

Power detector that employs a feedback circuit to enable class B operation of a detector transistor

Abstract: A power detector for detecting the magnitude of a radio frequency (RF) signal comprises a detector transistor (V1) which provides an output signal (DC-OUT) in dependence upon the input RF signal. The detector transistor is biased with a biasing circuit which comprises two transistors (V2,V3) in a feedback loop coupled to the base of the detector transistor (V1). The detector can be used as both current and voltage amplifier. One of the transistors (V3) in the feedback loop provides temperature compensation.

High-speed, 100+W RF switches using GaAs MMICs

Abstract: A low-loss, inductive gate bias network structure which allows a very high stacking level of FET devices for high-power RF switching applications is reported. The design, implementation, and performance of S- and C-band SPDT switches based on this structure are described. Multiple GaAs MMIC chips integrated into a suspended-substrate hybrid circuit are used. At S-band, switch risetimes/falltimes of less than 40 ns and an RF power handling capability of 300 W CW have been demonstrated. This input signal level could be maintained during the switch state transitions (hot-switching), while being switched between the two output ports at rates of up to 500 kHz. >

Pulse width modulation amplifier

Abstract: A pulse-width modulation amplifier includes a triangular signal oscillator (1) for generating a triangular carrier signal. A voltage comparator (2) compares an input analog signal and the triangular carrier signal, and converts the input analog signal into a corresponding pulse-width modulation signal. A power amplifier (3) serves to amplify the pulse-width modulation signal. A low pass filter (4) removes carrier components from an output signal of the power amplifier, and generates a demodulated signal corresponding to the input analog signal. The amplitude of the triangular carrier signal is controlled in response to a power supply voltage fed to the power amplifier so that the amplitude of the triangular carrier signal will be substantially proportional to the power supply voltage.

Method and apparatus for tuning and aligning an FM receiver

Abstract: A method for tuning and aligning an electronically tuned FM broadcast receiver is described. The system described compensates for the mismatch of component values between the antenna and RF amplifier tuned circuits, and the IF offset between the local oscillator frequency and the center frequencies of the antenna and RF resonant circuits by developing independent tuning signals for the circuits. The system also provides temperature compensation, and can be aligned without mechanically adjusting inductors and/or capacitors in the tuned circuits.

Adaptive phase control for a power amplifier predistorter

Abstract: In a QAM microwave radio communications system an IF (intermediate frequency) input signal (10) is amplified (12) and predistorted (14), and the amplified IF signal is mixed (20) with a local oscillator signal (18) to produce an RF (radio frequency) signal which is amplified in a power amplifier (22) for transmission, the predistortion compensating for non-linearity of the power amplifier Adaptive phase control of the predistorter is provided by mixing (30) the local oscillator signal with part of the RF signal (24) to produce an IF output signals (32) representing the output of the power amplifier, detecting (45) phase differences between the IF input and IF output signals to produce a phase difference signal, selectively inverting (56) the phase difference signal in dependence upon whether or not an IF signal amplitude exceeds a comparison level, and integrating (56) the resulting signal to produce a phase control signal for the predistorter

Radio-frequency power amplifier device

Abstract: A radio-frequency power amplifier device, has a radio-frequency power amplifier (2) for an input RF signal. Part of the output signal (4) of the amplifier (2) is extracted, and the extracted voltage is compared with a reference voltage (18a), to apply a negative feedback to the gain control terminal (3) of the power amplifier (2), thereby stabilizing the output power. The output power value is switched in accordance with a power level control signal (10a). A variable attenuator (11) or a variable-coupling-coefficient coupling means provided in front of the detector circuit (6) switches the attenuation or the coupling coefficient depending on the power level, such that the magnitude of the input to the detector circuit (6) is maintained at a constant level. The detector circuit (6) therefore operates at the same operating point regardless of the switching of the power level, and the dynamic range required of the detector circuit (6) may be narrow. The temperature variation of the output power at the time of low power output is small.

Magnetic resonance imaging device

Abstract: PURPOSE:To correct the nonlinearity of an RF amplifier which amplifies the power of RF pulses and feeds RF signals to a transmission coil CONSTITUTION:The input voltage of an RF amplifier 12 is changed by switching switches A16, B17 to a b contact and this output is measured to obtain data about the nonlinearity of an RF amplifier 11 and data about the correction of the nonlinearity is arranged into a table from this nonlinearity data and this correction table is stored in the memory of a computer 5 or the like and RF pulse waveforms(shape, amplitude) fed to the RF amplifier 11 during image pickup are corrected by using the correction table as a reference whereby the linearity of the RF amplifier 11 is maintained

Power detection technique for automatic amplifier power control

Abstract: A controlled-output power amplifier (50) is provided having a wide dynamic range in a plurality of output power levels. The controlled-output amplifier (50) includes an amplifier (12) for receiving an input signal (14) and for providing an output signal (16) therefrom. A power detector (24) is employed for rectifying a sample signal and providing a DC output signal (26) therefrom. An active variable coupling network (52) which preferably includes a varactor (62) is connected between the output of the amplifier (12) and the power detector (24). The variable coupling network (52) receives the amplifier output signal (16) and further receives an isolation voltage (54) and adjusts the amount of isolation between the amplifier (12) and the power detector (24). For high output signals, the isolation voltage (54) causes a high isolation thereby causing less power to be transferred to the power detector (24). The isolation voltage (54), similarly, decreases the isolation for low output signals such that more power is transferred to the power detector (24). The DC output signal (26) is then compared with a fixed voltage reference (30). The voltage comparison provides an error voltage (34) which is used to adjust the gain of amplifier (12) so that the output signal (16) of the amplifier (12) is set to a desired magnitude.

Experimental study of a plasma-filled backward wave oscillator

Abstract: We present experimental studies of a plasma-filled X-band backward wave oscillator (BWO). Depending on the background gas pressure, microwave frequency upshifts of up to 1 GHz appeared along with an enhancement by a factor of 7 in the total microwave power emission. The bandwidth of the microwave emission increased from ≤0.5 GHz to 2 GHz when the BWO was working at the RF power enhancement pressure region. The RF power enhancement appeared over a much wider pressure range in a high beam current case (10–100 mT for 3 kA) as compared to a lower beam case (80–115 mT for 1.6 kA). The plasma-filled BWO has higher power output compared to the vacuum BWO over a broader region of magnetic guide field strength. Trivelpiece-Gould modes (T-G modes) are observed with frequencies up to the background plasma frequency in a plasma-filled BWO. Mode competition between the Trivelpiece-Gould modes and the X-band TM 01 mode prevailed when the background plasma density was below 6×1011 cm−3. At a critical background plasma density of n cr ≅8×1011 cm−3 power enhancement appeared in both X-band and the T-G modes, with mode collaboration. Power enhancement of the S-band in this mode collaboration region reached up to 8 dB. Electric fields measured by Stark-effect method were as high as 34 kV/cm while BWO power level was 80 MW. These electric fields lasted throughout the high power microwave pulse.

Transmitter switch-on in a dual-mode mobile phone

Abstract: A method of providing a positive transmitter power switch-on in a dual-mode mobile phone is disclosed. According to the invention the transmitter is switched on in two or more phases, controlled by the mobile phone microprocessor program. Preferably the power amplifier sections are switched on in sequence, so that the the output power amplifier sections (3 and 4) are first switched on by enabling the transmit enable signal (TXE). Then the input power amplifier sections (1 and 2) are switched on by enabling ramp-up signal (RAMP-UP). Transmission is thereafter enabled by the transmit power control signal (TXC) being switched on, the amplifiers then output the amplified radio frequency input signal (RFIN) to the duplex circuit (10) transmit terminal (TX).

A 0.1-W W-band pseudomorphic HEMT MMIC power amplifier

Abstract: The authors have designed and fabricated monolithic power amplifiers using pseudomorphic InGaAs power HEMTs (high-electron-mobility transistors) with record power and gain performance at W-band frequency The two-stage amplifier has a small-signal gain of 9 dB and can deliver 01-W output power with 59-dB associated gain and 66% power-added efficiency at 935 GHz The successful first pass design of the W-band MMIC (monolithic microwave integrated circuit) power amplifier is due to the superior device performance and the millimeter-wave monolithic power amplifier design techniques >

Circuit containing symmetrically-driven coil for energizing electrodeless lamp

Abstract: An arrangement including an electrodeless discharge lamp having a sealed envelope enclosing an ionizable medium capable of emitting radiant energy when subjected to a radio frequency field and a circuit for operating the lamp. The circuit includes an oscillator for generating an output signal at a given radio frequency, an RF amplifier responsive to the oscillator output signal, and an output tank circuit including an induction coil and a capacitor connected in parallel. The RF amplifier includes a pair of semiconductor switches operating in a Class E mode. The induction coil is positioned in close physical proximity to the medium in the envelope for coupling to the medium an electric field having a magnitude sufficient to initiate ionization of the medium and a magnetic field for maintaining the ionization. In a preferred embodiment, the amount of EMI/RFI noise generated in the circuit is reduced by symmetrically driving the induction coil.

Power amplifier with harmonically trapped heterojunction bipolar transistor

Abstract: Power amplifier operating at a fixed frequency or a narrow bandwidth and based upon a non-linear gain element. The power amplifier includes a resonant circuit operably connected to the non-linear gain element, the circuit being resonant at a harmonic of substantially the band center frequency of the non-linear gain element and being arranged to dissipate energy resulting from harmonic generation by the non-linear gain element during signal amplification. In a particular aspect of the power amplifier, resonant circuits comprising inductor-capacitor harmonic trap circuits tuned to different harmonics are placed at both the input and the output of a gallium arsenide heterojunction bipolar transistor HBT providing the non-linear gain element.

Modular solid state radar transmitter

Abstract: A solid state radar transmitter for use in airborne applications has a modular design which extends into the transmitter. The transmitter is formed of a plurality of power modules the number of which is selected based on the power required for a particular application. For example, two 75 to 100 watt modules may be used for weather radar, while 30 to 60 or more modules may be used for fire control in a military fighter. A radio frequency signal from a stabilized local oscillator is distributed by a splitter to the power modules and a combiner is used to combine the output from the power modules to produce the transmitter output signal. Each power module is formed of parallel connected power amplifiers, preferably formed by GaAs FETs and a power conditioning and control unit. The power conditioning and control unit produces a DC bias across the FETs as desired to produce a particular signal. The transmitter output signals which can be produced in this manner include rectangular, Gaussian on a pedestal and one amplifier at a time for testing purposes.