Showing papers on "RF power amplifier published in 1991"

Temperature controlled rf coagulation

Abstract: Radiofrequency medical devices for ohmic heating of tissue of a patient include a temperature sensor (29) carried by and in thermally conductive relationship with a thermally conductive electrode (28). The sensor (29) is connected for feedback to a control circuit (6) that modulates RF power applied to the electrode according to the signal received from the temperature sensor (29). The control circuit (6) and RF power supply alternate between two operating modes. In the first mode the RF power supply applies RF power to the electrode (28). In the second mode the control circuit (6) senses a signal from the temperature sensor (29) in the absence of RF signal. The control circuit (6) compares the signal from the temperature sensor (29) to a set value and modulates the RF power applied to the electrode (28) in accordance with the set value.

The potential of diamond and SiC electronic devices for microwave and millimeter-wave power applications

Abstract: The potential of SiC and diamond for producing microwave and millimeter-wave electronic devices is reviewed. It is shown that both of these materials possess characteristics that may permit RF electronic devices with performance similar to or greater than what is available from devices fabricated from the commonly used semiconductors, Si, GaAs, and InP. Theoretical calculations of the RF performance potential of several candidate high-frequency device structures are presented: the metal semiconductor field-effect transistor (MESFET), the impact avalanche transit-time (IMPATT) diode, and the bipolar junction transistor (BJT). Diamond MESFETs are capable of producing over 200 W of X-band power as compared to about 8 W for GaAs MESFETs. Devices fabricated from SiC should perform between these limits. Diamond and SiC IMPATT diodes also are capable of producing improved RF power compared to Si, GaAs, and InP devices at microwave frequencies. RF performance degrades with frequency and only marginal improvements are indicated at millimeter-wave frequencies. Bipolar transistors fabricated from wide bandgap material probably offer improved RF performance only at UHF and low microwave frequencies. >

Thermal angioplasty system

Abstract: A system for thermal angioplasty provides electrical power to a heating coil located inside a dilatation balloon, receives a signal from a sensor at the coil indicating its temperature and also receives signals from balloon sensors indicating the temperature at their respective positions. An isolation transformer is used to provide RF power and the sensor signals are optically coupled to provide increased electrical isolation for the patient. The heating coil temperature sensor signal is compared to high and low temperature limits and if either is exceeded, a fault signal is generated. The sensor signals from the balloon are compared to predetermined high temperature limits and if exceeded, fault signals are generated. The current drawn from the battery is compared to a predetermined current level and if exceeded, a fault signal is also generated. Upon generation of any of the fault signals, the electrical power to the heating coil is interrupted by fault detection circuitry. An RF ON reset switch is provided to prevent the inadvertent application of RF power to the heating coil. Materials used in the connectors and in the RF generator for connections to the catheter electrical leads are compatible with those leads to avoid a thermocouple effect.

Output level control circuit for use in rf power amplifier

Abstract: An output level control circuit for a high frequency power amplifier for amplifying high frequency signals having the "on" and "off" periods of transmit signals in a fixed recurrent cycle such as in a TDMA radio communication system or a GSM system. The high frequency detecting circuit for the output level control circuit is responsive to part of the output of the high frequency power amplifier and a control signal corresponding to said "on" and "off" periods of transmission power for generating an output level control signal for the high frequency power amplifier. The high frequency detecting circuit has detecting means for detecting the wave height of the high frequency signals and differential voltage generating means for generating, for each of said recurrent cycles, a differential voltage between the detection output during the "on" period and the detection output during the "off" period immediately preceding it. This differential voltage is used as the temperature-compensated output level control signal for the high frequency power amplifier.

A low frequency inductive rf plasma reactor

Abstract: A plasma reactor with rf power inductively coupled into the reactor chamber to produce an rf magnetic field substantially perpendicular to a pedestal on which a wafer is placed for processing. Said pedestal is a powered electrode to which power is coupled to control the sheath voltage of the pedestal. This reactor is particularly suitable for soft etches and processes in which it is advantageous to couple much more power into ion production than into free radical production.

Power amplifying apparatus for wireless transmitter

Abstract: A power amplifying apparatus according to the present invention can provide a stable electric power output with wide range by controlling both of the output amplifier for amplifying the electric power and the pre-amplifier disposed at the front of the output amplifier. Furthermore, in order to avoid the disadvantage that a transmission spectrum is expanded because of no supply of a stable voltage to be supplied to the electric power amplifier, thereby producing a cross-talk, a stabilizing power source circuit is provided to stabilize the voltage between the power amplifier and the power source for supplying the voltage.

Method for controlling the output power of digital cellular telephones

Abstract: A controlled power amplifier system (211) wherein a sample (225) of the output power level of an on/off switched power amplifier (215) is compared with a reference signal (227) to produce a power level control signal (275) that controls the output power level of the power amplifier (215). When the power amplifier (215) is switched off, the control signal (275) is maintained at the level it had just prior to the transition from an on to an off state. The switching is performed offset from the ends of each switched power amplifier pulse envelope to allow the pulse amplitude to be leveled in the center of the pulse and yet allow the pulse rise and fall times of the pulse envelope to follow the power amplifier input.

Power amplifier device having a plurality of power amplifier units connected in parallel

Abstract: A power amplifier device includes m power amplifier units provided in parallel where m is an integer, a distributor for distributing an input signal to the m power amplifier units, and a combining device for combining m amplified input signals output by the m power amplifier to generate an amplified output signal. The power amplifier device includes a group of switches for gradually disconnecting the m power amplifier units from the distributor and the combining device and for gradually connecting the m power amplifier units to the distributor and the combining device.

An experimental TDMA indoor radio communications system using slow frequency hopping and coding

Abstract: The general principles, implementation, and performance of a 1-Mb/s time-division-multiple-access (TDMA), slow frequency hopping and coding, 1.5-GHz radio communications system for a medium-sized office building are discussed. TDMA is provided for service flexibility and slow frequency hopping and coding for immunity against multipath fading and interference. Measurements show that, with a hallway-mounted distributed antenna system installed on one floor of the building and with the mobile unit transmitting only 1 mW of peak RF power from anywhere on that floor, only a single 384-b frame out of a total of 200000 transmitted frames suffered an unrecoverable error. This kind of performance is comparable to that of wired data modems. Similar performance was obtained from a central antenna covering the same floor. However, the required transmitted power in this case was 100 mW. Implementation issues, such as spectrum allocation, cellular subdivisions, and spectrum efficiency, are also discussed. >

Solid state power amplifier with dynamically adjusted operating point

Abstract: RF power is sampled and measured at the input and output of a solid state power amplifier using directional couplers and matched square law detectors. Outputs from the detectors are applied to differential inputs of a DC operational amplifier. Outputs from the detectors are compared and filtered in the operational amplifier and the resulting difference signal is applied to a control input on a switching type power supply. The power supply converts a DC input voltage to the various positive and negative voltages required to operate the RF devices in the solid state power amplifier. When the control loop is closed, the supply voltage varies to maintain a constant operating point resulting in constant gain, efficiency, and linearity for the overall solid state power amplifier despite variations in signal levels and signal composition. In another embodiment, the solid state power amplifier has a series of single-ended low power amplifiers terminating in an output high power module. In the output module, one medium power device acts as a driver stage for four high power devices connected in parallel. The output stages are hybrid coupled, and isolators before and after these hybrid coupled output stages isolate the driver from the final amplifiers and protect the output devices from reflected signals. A dynamically controlled PIN diode variable attenuator at the amplifier input allows the operating point of the amplifier to be selected and adjusted while the closed loop function is in operation. A hybrid matrix power amplifier system is also disclosed.

Power monitor of RF plasma

Abstract: An RF plasma power monitor that monitor voltage, current and DC bias adjacent the plasma load and processes the sensed data in a digital data processor to provide true power at the load. Provision is also made for the control of an RF power source to maintain power at the load at a preset level irrespective on impedance fluctuations and reflections.

Dual mode power amplifier for radiotelephone

Abstract: A dual mode power amplifier operable in etiher the linear mode or the saturation mode. The power amplifier, when comprising a portion of a radio transmitter, permits efficient amplification of either a frequency modulated or a composite modulated signal by operation of the amplifier in the saturation mode or the linear mode, respectively. A processor determines the modulation-type of the signal and generates a signal to cause operation of the amplifier in either the saturation mode or the linear mode.

Model of magnetically enhanced, capacitive RF discharges

Abstract: Magnetically enhanced, capacitive RF discharges (called RF magnetrons or MERIE discharges) are playing an increasing role in thin film etching for integrated circuit processing. In these discharges, a weak DC magnetic field is imposed, lying parallel to the powered electrode surface. The authors determine the RF power transferred to the discharge electrons by the oscillating electron sheath in the presence of the magnetic field. Using this, along with particle and energy conservation, they obtain discharge parameters such as the ion flux and ion bombarding energy at the powered electrode as functions of pressure, RF power, and the magnetic field. Some results of the model show good agreement with experiments done on a commercial MERIE system. >

Power amplifier for broad band operation at frequencies above one ghz and at decade watt power levels

Abstract: An octave band decade watt power amplifier is disclosed using compact and efficient MMIC fabrication techniques. The power amplifier is a two stage amplifier in which the driver transistor has two cells, and the power transistor has four cells, with each power cell double the size of the driver cells. Both transistors are of an optimized topology facilitating efficient broad band operation at matchable impedance levels. They are interconnected by three four section impedance matching networks of which the input network is coupled to a 50 ohm signal input terminal. The input and the interstage network are both formed on the same substrate as the transistors. The output network is formed on a separate substrate having a high dielectric constant (i.e. 37) which facilitates efficient and compact matching of four power transistor cells to a single output terminal for connection to a load at the conventional (50 ohm) impedance.

Transmitter linearization using Cartesian feedback for linear TDMA modulation

Abstract: A linearized power amplifier suitable for low-power portable radio applications is described. One narrow-bandwidth and one wide-bandwidth application are investigated. Up to 40% power-added efficiency can be achieved for a 20-dB reduction of the third-order intermodulation products at 1.5 MHz from the carrier frequency in the wide-bandwidth system. Less than -60 dB out-of-band emission and 38% power-added efficiency can be obtained for a narrow-bandwidth system. >

Variable frequency microwave furnace system

Abstract: A variable frequency microwave furnace system (10) designed to allow modulation of the frequency of the microwaves introduced into a furnace cavity (34) for testing or other selected applications. The variable frequency microwave furnace system (10) includes a microwave signal generator (12) or microwave voltage-controlled oscillator (14) for generating a low-power microwave signal for input to the microwave furnace. A first amplifier (18) may be provided to amplify the magnitude of the signal output from the microwave signal generator (12) or the microwave voltage-controlled oscillator (14). A second amplifier (20) is provided for processing the signal output by the first amplifier (18). The second amplifier (20) outputs the microwave signal input to the furnace cavity (34). In the preferred embodiment, the second amplifier (20) is a traveling-wave tube (TWT). A power supply (22) is provided for operation of the second amplifier (20). A directional coupler (24) is provided for detecting the direction of a signal and further directing the signal depending on the detected direction. A first power meter (30) is provided for measuring the power delivered to the microwave furnace (32). A second power meter (26) detects the magnitude of reflected power. Reflected power is dissipated in the reflected power load (28).

High-power V-band pseudomorphic InGaAs HEMT

Abstract: The author's present the DC and RF power performance of planar-doped channel InGaAs high-electron-mobility transistors (HEMTs). The planar-doped channel (PDC) pseudomorphic GaAs HEMT with 400 mu m of gate width exhibited an output power of 184 mW, corresponding to 460 mW/mm, with 4.6-dB saturation gain and 25% power-added efficiency at 55 GHz. Although higher power density is possible, the authors have designed the device to operate at less than 500 mW/mm for thermal and reliability reasons. Devices with unit gate finger widths ranging from 30 to 50 mu m were fabricated and characterized, with no performance degradation observed from using the longer gate fingers. >

Power control circuit used for both analog/digital dual mode

Abstract: A power control circuit used for both analog/digital dual mode is disclosed which comprises a switching circuit (17) for applying the feedback signal to the gain control terminal (40) of the power amplifier (2) and applying a fixed bias voltage to the attenuation control terminal (30) of the attenuator (10) so that the amplifier operates as a C class amplifier in the case of analog mode, and for applying the feedback signal to the attenuation control terminal (30) of the variable attenuator (10) and applying the predetermined bias voltage to the gain control terminal (40) of the power amplifier (2) so that the amplifier operates as an A class amplifier in the case of digital mode. In the present invention, as a single amplifier operates for both analog mode and digital mode, the configuration is simplified and assembled cheaply.

Transmission output control circuit

Abstract: PROBLEM TO BE SOLVED: To use the title transmission output control circuit for a TDMA system radio transmitter and the like and to stably and highly precisely control a transmission output burst wave for a wide range SOLUTION: Feedback control for controlling the output of a transmission power amplifier 3 with the error voltage (Vcont) of a comparison error amplifier 9 and feed forward control for previously controlling the output level of a variable output drive amplifier 2 so that the input level of the transmission power amplifier 3 is optimized in such a way that the output control characteristic of the transmission power amplifier part 3 always has almost constant control sensitivity are executed. Then, the ramping waveform of the rise and fall of transmission output is controlled and the transmission output level is controlled.

Power control with a constant gain amplifier for portable radio transceivers

Abstract: A system for controlling the power level of RF signals output by a portable radio transmitter having a first voltage supply, a first amplifier stage and a microcomputer coupled to the first amplifier stage for selecting one of a set of power levels. An indicator signals when the radio transmitter is coupled to a vehicular voltage supply and, in response, the microcomputer generates a control signal representative of a desired power level. A second amplifier stage is coupled to the first amplifier stage and receives RF signals at the selected power level. A constant gain control circuit coupled to the second amplifier stage receives the control signal and responds by setting the gain of the second amplifier stage at one of at least two constant gain values so that the output RF signals are provided with the desired power level.

Power amplifier system for radio transmitter and method for using the same

Abstract: A power amplifier system suitable for a mobile radio receiver/transmitter is described. A wave form signal to be transmitted is made smooth during its rise and fall times, thereby making it possible to prevent a transmission spectrum from expanding and interfering with the adjacent channels. The power amplifier system compares an envelope signal of an inputted RF signal and that of an RF signal to be outputted, whereby the power amplifier system as a whole provides linear amplification.

Apparatus and methodology for digital telemetry of biomedical signals

Abstract: Biomedical information is directly digitally telemetered from the patient through a frequency modulated transmitter to a remote receiver and computer station. DC offset on the biopotential leads and signals from the patient is compensated by converting the output of the amplifier, such as an electrocardiographic amplifier, into digital format, determining the average or DC component of the digital signal, and generating a digital correction word which is then converted into analog form and fed back into the input of the electrocardiographic amplifier to cancel out the DC offset. The same circuitry is used to insert a standard test signal instead of a correction signal and the output of the amplifier is then checked not to determine its DC component, but to determine whether or not the gain of the electrocardiographic amplifier is performing at a predetermined calibration point. If not, a digital correction word is generated and provided as a correction signal to the programmable gain amplifier.

Low drive-power integrated acoustooptic filter on X-cut Y-propagating LiNbO/sub 3/

Abstract: The authors fabricated very low power integrated acoustically tunable optical filters using walkoff-compensated miniature interdigital transducers, coupled to narrow-width acoustic waveguides. Nearly 100% transverse electric-transverse magnetic (TE-TM) polarization conversion efficiency was achieved using only 8 mW of applied RF power in a 1550-nm filter of 1.8-nm optical bandwidth. A power handling capacity of almost 100 channels was demonstrated by driving these transducers with 760 mW of RF power. These devices suffer little performance degradation in terms of filter width and sidelobe spectrum. >

Distortion compensation means and method

Abstract: Distortion introduced in phase modulated RF signals by amplifiers and other signal processors is substantially reduced by modifying complex modulating signals I,Q in a way that compensates for the amplifier phase error φ e as a function of amplifier power P. In a preferred embodiment, I, Q are combined to calculate the amplifier power level and scaled by a parameter, e.g., K1=-dφ e /dP, to provide factor B so that compensated signals I"=AQ+BI and Q"=AI-BQ, where A is a constant, can be determined. When an RF carrier modulated by I", Q" is passed through the distorting amplifier the amplifier induced distortion is cancelled. Substantial reduction in bit error probability is obtained. The method can also be used for post-distortion correction.

Telemetry for optical fiber amplifier repeater

Abstract: In this invention telemetry information is transmitted in an optical fiber communication system by providing an amplifier pump (74) with excess power beyond that necessary to pump the amplifier (51). The excess power is not used to pump the amplifier but is rather used to transmit the telemetry information. In a specific embodiment, an optical communication system including a doped optical fiber amplifier such as, for example, an erbium doped amplifier, is provided with an amplifier pump which operates at approximately 1.48µm. The amplifier pump is provided with excess power so as to transmit telemetry information. In a specific embodiment, the telemetry signal can be detected with a low cost photodetector (54) at a subsequent station.

Feed forward amplifier network with frequency swept pilot tone

Abstract: Briefly described the present invention is a feed forward amplifier network employing a frequency swept pilot tone signal in order to reduce the distortion generated by the network's power amplifier. A frequency swept pilot tone, generated for example by a variable frequency oscillator, is injected into the input path of the power amplifier's input signal. Thereafter, distortion cancellation employed to generate an amplified output signal, substantially free of both pilot tone and the distortion signals generated by the power amplifier. The amplified output signal is then detected by a detector, phase locked to the variable frequency oscillator, in order to ascertain the average pilot tone energy remaining within the amplified output signal. In response to a detection, various amplifier network characteristics are adjusted in order to reduce the amount of pilot tone at the amplifier network output.

Power amplifier for a cellular telephone

Abstract: In a cellular telephone of the type capable of operating in both analog and digital modes, a power amplifier is provided which can operate efficiently in both the analog and digital modes of operation. The power amplifier includes a non-linear power amplifier stage and a linear power amplifier stage which are controlled by a switching means. During the analog mode of operation, the switching means causes the non-linear amplifier stage to amplify the RF signals. During the digital mode of operation, the non-linear amplifier amplifies the RF signal when there is a requirement for a relatively low power output. During the digital mode when there is a requirement for a relatively high level output, the switching means causes the non-linear power stage and the linear power stage to amplify the RF signals.

Secrets of RF Circuit Design

Abstract: BUILD THE CIRCUITS THAT MAKE WIRELESS WORK If you like hands-on electronics, you’ll love Secrets of RF Circuit Design, Third Edition, by Popular Electronics writer Joe Carr. This update of the favorite RF circuit guide of thousands of electronics enthusiasts takes you inside wireless technology with step-by-step, illustrated directions for dozens of usable projects. This super guide demonstrates RF theory as it shows you how to overcome the technical and materials challenges facing those who build real-world electronics. You learn how to design and build receiver circuits, RF bridges, amplifiers, receiver preselectors, simple spectrum analyzers, and time domain reflectometers. You get detailed insights into simple RF instruments, as well as UHF and microwave components…complete troubleshooting guidance…and handy parts lists and components sources. This new edition packs the latest information on directional and hybrid couplers, and seven new chapters on demodulators, circuit vectors, measuring L-C circuits, and filtering circuits against EMI. “…a great book on wireless technology for persons starting out in RF electronics, as well as for RF technicians and ham radio operators.” ---Cotter W. Sayre, author of The Complete RF Technician’s Handbook (Amazon.com review) Table of contents Chapter 1: Introduction to RF electronics. Chapter 2: RF components and tuned circuits. Chapter 3: Variable capacitors in RF circuits. Chapter 4: Winding your own coils. Chapter 5: Radio receivers: Theory and projects. Chapter 6: Direct-conversion radio receivers. Chapter 7: RF amplifier and preselector circuits. Chapter 8: Building IF amplifiers. Chapter 9: Interpreting radio receiver specifications. Chapter 10: Building signal-generator and oscillator circuits. Chapter 11: RF directional couplers. Chapter 12: The RF hybrid coupler. Chapter 13: Build simple VLF radio receivers. Chapter 14: What's that mess coming from my receiver? Filtering circuits against EMI. Chapter 15: Measuring inductors and capacitors at RF frequencies. Chapter 16: Building and using the RF noise bridge. Chapter 17: Vectors for RF circuits. Chapter 18: Impedance matching: Methods and circuits. Chapter 19: Using the double-balanced mixer (DBM). Chapter 20: PIN diodes and their uses. Chapter 21: UHF and microwave diodes, transistors, and integrated circuits. Chapter 22: LC RF filter circuits. Chapter 23: Time-domain reflectometry on a budget. Chapter 24: Solving frequency drift problems. Chapter 25: The Smith chart. Chapter 26: Detector and demodulator circuits.

Automatic gain control for RF amplifier

Abstract: A radio receiver simultaneously achieves maximum sensitivity and minimum susceptibility to intermodulation distortion by employing wideband and narrowband automatic gain control which further selects the automatic gain control response in dependence on the detection of intermodulation distortion. An AGC signal is modified to improve sensitivity in the event of a low narrowband signal level except when intermodulation distortion is detected above a predetermined distortion level.