Showing papers on "RF power amplifier published in 1994"

Automatic control for electrosurgical generator

Abstract: In an ESV a control system responds to impedance and temperature as sensed between and at the electrodes (13) during desiccation each of such electrodes being provided separately and independently through a suitable multiplexer with a specifically controlled RF power. An instantaneous impedance monitor senses impedance variations and controls by means of specific derivative sensitive algorithm part of a feedback loop, the output power delivered through each electrode. A further temperature dependent feedback loop power control system is operative in a multiplexed mode in pair with the above impedance feedback system. Such second system uses an array of temperature sensors placed in the immediate proximity of the each tissue contacting electrode, and an appropriate derivative sensitive algorithm. Both systems are operated in a multiplex mode through a first multiplexer. A second multiplexer shifts the output power to the various electrodes independently and separately.

Dual-channel RF power delivery system

Abstract: A dual-channel RF power delivery system for applying RF energy to dual electrodes of an RF ablation device with independent control of the power level, frequency, phase, and time duration of the RF energy applied to each electrode to more accurately control the ablation of a target tissue. The power delivery system supplies a first controlled RF signal having a first power level, frequency, phase, and time duration to the electrode of a first flexible stylet and a second controlled RF signal having a second power level frequency, phase, and time duration to the electrode of a second flexible stylet. The difference between the first and second power levels and the temperature of the tissue between the first and second stylers are monitored to control the ablation of the target tissue. The supply of the first RF signal is terminated when the monitored temperature of the first stylet exceeds a first predetermined value and the supply of the second RF signal is terminated when the monitored temperature of the second stylet exceeds a second predetermined value. By adjusting the frequency and/or phase of the first and second RF signals, the relative amounts of bipolar and monopolar ablation can be adjusted for accurate control of the lesion volume. The lesion volume can also be controlled by varying the deployment length of the electrodes.

The Gaseous Electronics Conference radio‐frequency reference cell: A defined parallel‐plate radio‐frequency system for experimental and theoretical studies of plasma‐processing discharges

Abstract: A “reference cell” for generating radio-frequency (rf) glow discharges in gases at a frequency of 13.56 MHz is described. The reference cell provides an experimental platform for comparing plasma measurements carried out in a common reactor geometry by different experimental groups, thereby enhancing the transfer of knowledge and insight gained in rf discharge studies. The results of performing ostensibly identical measurements on six of these cells in five different laboratories are analyzed and discussed. Measurements were made of plasma voltage and current characteristics for discharges in pure argon at specified values of applied voltages, gas pressures, and gas flow rates. Data are presented on relevant electrical quantities derived from Fourier analysis of the voltage and current wave forms. Amplitudes, phase shifts, self-bias voltages, and power dissipation were measured. Each of the cells was characterized in terms of its measured internal reactive components. Comparing results from different cells provides an indication of the degree of precision needed to define the electrical configuration and operating parameters in order to achieve identical performance at various laboratories. The results show, for example, that the external circuit, including the reactive components of the rf power source, can significantly influence the discharge. Results obtained in reference cells with identical rf power sources demonstrate that considerable progress has been made in developing a phenomenological understanding of the conditions needed to obtain reproducible discharge conditions in independent reference cells.

Linearized power amplifier

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

Microwave doherty amplifier

Abstract: An improved Doherty amplifier for operation at microwave frequencies using microstrip circuit technology and gallium arsenide devices to achieve greater efficiency and linearity. The circuit divides the input power equally between a carrier amplifier and peak amplifier with a quarter-wave delay at the input to the peak amplifier insuring that the output power of the two amplifiers will be in phase at the load. A three-port network combines the phase-delayed carrier amplifier output with the output of the peak amplifier. The outputs of the two amplifiers are connected together by a quarter wave transmission line of impedance R. A load of one-half the optimum load (R/2) is attached to the output of the peak amplifier. A quarter-wave line section provides the transition from R/2 to the desired impedance, R. When the peak amplifier is off, its output impedance is infinite and the output power of the carrier amplifier is delivered entirely to the load. As the peak amplifier becomes more active, it delivers more of its output power to the load while its output current gradually reduces the effective load impedance seen by the carrier amplifier thus allowing it to deliver more power. In this way the microwave Doherty amplifier allows 6 dB of linear power amplification beyond the point where a normal Class "B" amplifier begins to saturate and the microwave amplifier efficiency remains close to the maximum attainable linear efficiency.

Adaptive class AB amplifier for TDMA wireless communications systems

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

Amplifier and biasing circuit therefor

Abstract: An amplifier contains an RF generated negative supply wherein the RF input of the negative generator is connected to the RF input of a first power amplifier stage. This arrangement allows the power supplies to be turned-on in the correct order, thus, avoiding any damage to the transistors or power supply. After the RF input turns on and the RF generated negative supply turns on, the power amplifier transistors are biased such that no current will flow from the drain to the grounded source. The power amplifier also features the ability to adjust the biasing voltage by increasing Vcontrol so that the bias current from the main supply can be controlled. Since the output power of the amplifier is monotonic with biasing current over the useful range of gate voltages, the output power can thereby be controlled by adjusting the control voltage. Additionally, the negative biasing voltage can be increased to the point where bias current from the main supply is at the correct level to achieve the desired output power. Depending on the required output power control range, it may be necessary to use a voltage controllable attenuator, VCA, to simultaneously adjust the RF level into the amplifier while adjusting the biasing voltage.

Dual mode transmission system with switched linear amplifier

Abstract: A dual mode transmitter circuit is disclosed including a non-linear high-power amplifier having an amplification that can be adjusted and a linear high-power amplifier A first switch and a second switch are connected to the input and output of the linear, high-power amplifier An amplification-adjustable, high-frequency transmitter control amplifier is connected to the input of the non-linear high-power amplifier Apparatus for measuring transmission power such as a directional coupler is connected to the second switch, and a duplex filter is connected to the directional coupler A power level control circuit is responsive to the measured transmission power from the directional coupler and to a power level signal The power level signal is representative of the desired output power of the transmitter The power level control circuit compares the measured power level from the directional coupler with the desired power level and produces a difference signal on its output lead which is connected to both the non-linear high-power amplifier and to the high-frequency transmitter control amplifier A mode selection signal, for designating either an analog or digital type transmission mode is applied to a mode control circuit that is responsive to the mode selection signal and provides switching signals to the first and second switches and a control signal to the linear amplifier The mode selection signal sets the transmitter to function in either the non-linear transmission (analog) mode or the linear transmission (digital) mode

Planar amplifier array with improved bandwidth using folded-slots

Abstract: Active antennas on semiconductor substrates often suffer limited bandwidth. We report on a relatively broadband quasi-optical amplifier cell and 4/spl times/4 array using folded-slot antennas, suitable for monolithic power combining. Two orthogonally polarized CPW-fed folded slots are coupled to the input and output ports of a simple resistive feedback MESFET amplifier. The peak effective isotropic power gain in the transmission mode is 11 dB @ 4.3 GHz with 10% bandwidth for the single cell, a factor-of-ten improvement in bandwidth over a similar amplifier cell using patch antennas, and 32 dB @ 4.24 GHz with 8% bandwidth for the array. >

Communications transceiver using an adaptive directional antenna

Abstract: A directional antenna connected to a portable communications transceiver is adaptively directed towards a remote station in a communication system. The amount of RF power required by the portable device is significantly reduced, relative to a non-directional antenna. The operational period of the transceiver between battery recharges is therefore considerably maximized.

Maximum frequency and optimum performance of class E power amplifiers

Abstract: An analytical method is proposed to discuss class E RF power amplifiers with finite choke inductors. All parameters in these amplifiers can be expressed in terms of circuit-component values and amplifier specifications. The component values of class E amplifiers required to achieve optimum amplification can be directly obtained after the amplifier specifications are fixed. An obvious relationship between the parameters of class E amplifiers with finite choke inductors in optimum performance can be obtained. Hence, the key function of each component in the circuit can be indicated clearly, especially in the case of a finite choke inductor. The finite choke inductor can also be used to compensate for the high intrinsic output capacitance of the active power device to extend operation frequency. To assure optimum performance and safe operation, a criterion is assigned. Based on this criterion and the optimum conditions, a maximum frequency for a transistor safely operating in class E amplifiers can also be obtained.< >

Demonstration of Josephson effect submillimeter wave sources with increased power

Abstract: A submillimeter wave source based on a new design using Josephson junction arrays has been developed and tested. The maximum rf power, delivered to a 68Ω load and detected on chip, was 47 μW at 394 GHz. Significant power was detected at a number of frequencies from 300 to 500 GHz where the power was 10 μW. The observed power at the designed operating frequency near 400 GHz is consistent with all 500 junctions in the series biased array delivering current in phase to the loads. This is in agreement with simulations of smaller arrays of the same design. The linewidth, inferred from the measured resistance at the point of maximum power, with T=4.2 K, is less than 1 MHz. The minimum inferred linewidth near 400 GHz, at somewhat lower power, is about 100 kHz.

High-efficiency single-sideband HF/VHF transmitter based upon envelope elimination and restoration

Abstract: The paper describes a high-efficiency HF/VHF multimode transmitter based upon the Kahn envelope elimination-and-restoration (EER) technique. The major subsystems are a class-D RF power amplifier (PA), a class-S high-level amplitude modulator, a single-sideband (SSB) modulator, a delay-compensation circuit and frequency translators. This experimental transmitter is a prototype for both communication and jamming applications. It can produce a wide variety of signals, including SSB, AM, and FM. Its efficiency is about 60 percent for all signal amplitudes, which makes its average efficiency for voice signals about three times that of a transmitter with a conventional class-B PA, For voice-bandwidth signals, the IMD products are 43 dB or more below the peak carrier output (-43 dBc).< >

Adaptive feedforward linearizer for RF power amplifiers

Abstract: A feed forward amplifier circuit for amplifying an input signal to produce an amplified replica thereof. A first splitter splits the input signal into first and second signal cancellation branches. The first signal cancellation branch contains an amplifier and a first "delay, gain and phase adjuster" (DGPA) connected in series between a-first output of the first splitter and the amplifier; and, a second splitter connected in series with the amplifier's output for splitting the amplified output signal into first and second distortion cancellation branches. The second signal cancellation branch contains a first delay line connected in series between a second output of the first splitter and a first input of a first combiner. The second splitter has a first output coupled to a second input of the first combiner. The first distortion cancellation branch contains a second delay line connected in series between a second output of the second splitter and a first input of a second combiner. The second distortion cancellation branch contains a third splitter connected in series between the first combiner and a second DGPA, and an auxiliary amplifier connected in series between the second DGPA and a second input of the second combiner. A first controller is connected between an output of the third splitter and the first DGPA to adapt the first DGPA to changes in signals at the third splitter's output and to changes in signals output by the first DGPA. A second controller is connected between an output of a fourth splitter and the second DGPA to adapt the second DGPA to changes in signals at, the fourth splitter's output and to changes in signals output by the second DGPA. The fourth splitter is connected to receive the output of the second combiner and provides the amplified replica at its output.

Inductively coupled high density plasma reactor for plasma assisted materials processing

Abstract: The invention is embodied in an inductively coupled plasma reactor including a vacuum chamber for holding a wafer in the interior thereof and capable of containing a plasma gas, and having an RF antenna and an RF power source for supplying RF power to the RF antenna and apparatus for electrically isolating the RF antenna from the RF power source so as to reduce capacitive coupling therebetween. Preferably, the apparatus for isolating the antenna is a transformer having a primary winding connected across the RF power source and a secondary winding connected across the RF antenna. Preferably, the reactor further includes a conductive Faraday shield having plural layers, the Faraday shield being disposed between the RF antenna and the ceiling of the vacuum chamber, the Faraday shield having eddy current-suppressing apertures in each layer thereof facing conductive portions of the shield in an adjacent layer thereof. The ceiling of the vacuum chamber acts as a gas distribution manifold. The inner layer of the ceiling is the shower head of the manifold.

Electrostatic Coupling of Antenna and the Shielding Effect in Inductive RF Plasmas

Abstract: Capacitive coupling from a current-flowing antenna to inductive rf plasma plays an important role not only in the discharge mechanism but also in the impurity release from materials around the antenna. As a result of this coupling, there appears a large negative dc voltage (V DC) on the surface of material which insulates the antenna conductor from the plasma. The magnitude of V DC is directly measured as a function of rf power, thickness of the insulating material, and the position along the antenna. A simple model to describe the electrostatic antenna-plasma coupling is proposed. In addition, the effect of Faraday shields on the inductively coupled rf discharge is presented.

Radio frequency signal power amplifier combining network

Abstract: A dual-mode RF signal power amplifier combining network is comprised of two branches, each having a power amplifier (200 and 201). The first branch contains a non-linear mode power amplifier (200) while the second branch contains a linear mode power amplifier (201). The non-linear mode branch also has an RF switch (210). Both branches are coupled to a common output node (220). The common node (220) is coupled to a filter (107) before going to an antenna (106). The non-linear mode power amplifier (200) operates when an FM signal is to be amplified, while the linear amplifier (201) is biased in an off state. The linear mode power amplifier (201) operates when a digital signal is to be amplified, while the non-linear amplifier (200) is biased in an off state. The RF switch (210) removes the non-linear amplifier (200) from the circuit to prevent loading the on state linear amplifier (201).

Apparatus and method for varying the coupling of a radio frequency signal

Abstract: An apparatus and method for varying coupling of a radio frequency (RF) signal (408). This is advantageously used for increasing the dynamic range of a power detector (406) in an automatic power level control loop (403) of a transmission unit (404), while maintaining transmission unit efficiency at higher power levels. This is accomplished by selecting between a first operating mode of the RF coupler (405) having strong coupling, responsive to a first predetermined power level, such that the RF coupler (405) produces a first coupled RF signal (509) responsive to the RF signal (408) and a second operating mode of the RF coupler (405) having weak coupling, responsive to a second predetermined power level, such that the RF coupler (405) produces a second coupled RF signal (510) responsive to the RF signal (408).

MMIC FET mixer and method

Abstract: A MMIC FET mixer and method includes a RF input port for receiving a RF signal, a feedback control input for receiving a feedback signal, and a LO input port for receiving a LO signal. A feedback controller is coupled to the RF amplifier, the feedback controller for producing a controlled RF signal in response to the feedback signal. A constant current source is coupled to the feedback controller, to the RF amplifier and to the LO input port. The constant current source receives a DC offset voltage, the controlled RF signal, and the LO signal and produces an IF output signal at an IF output port. The IF output signal is proportional to the DC offset voltage, to the RF signal, and to the LO signal.

Linear amplifier control

Abstract: A method and apparatus for controlling a feed-forward compensated power amplifier system is disclosed which uses a spread spectrum technique to cover a control signal or signals and injects a composite signal at a suitable point into the feed-forward amplifier system to reduce distortion. The amount of bandwidth spread is governed by the amount of processing gain needed in the remapping process and the needed time response of the system. Control signals after remapping of the spread spectrum at the output of the system are correlated in a match filter correlator and the result is used to control, in either polar or cartesian coordinates, the injection, in anti-phase, of the extracted distortion into the feed-forward amplifier output.

A 900 MHz CMOS RF Power Amplifier with Programmable

Abstract: The power amplifier module constitutes the largest current drain on a wireless transceiver during transmit mode. In future cellular networks for digital wireless transceivers, the base station will adaptively regulate the transmitted p o i w leeels of each transceiver to enable the largest possible number ofusers to share a wireless channel. This requires a high-efficiency power amplifier with a digitally selectable output level spanning a wide range. The power amplifier reported here is intended for use in an all-CMOS frequency-hopped spreadspectrum transceiver operating in the 902-928 MHz band. It delivers a controllable power between 20-pW and 20. " from a 3-V supply to the antenna.

Impedance plane analysis of class DE amplifier

Abstract: The class DE RF power amplifier is analysed in the normalised effective load impedance plane. The conditions for zero voltage switching (ZVS) and class E switching transitions are obtained. A proposed matching network allows ZVS operation for any resistive load. Class DE transistor utilisation approaches that of class D.

Power Amplifier Bias Control Circuit and Method

Abstract: A control circuit for a multi-stage power amplifier (such as in a portable radio transmitter) compensates for fluctuations in ambient temperature, load, signal level and power supply voltage. The control voltage is set by comparing a biasing level which is related to the amplifier input signal level to a voltage proportional to the power supply current of the last stage of the amplifier. The control voltage resulting from the comparison establishes the operating point of the last stage of the power amplifier.

Transmitter and power amplifier therefor

Abstract: A transmitter comprises a linearised power amplifier circuit (18) consisting of a power amplifier output stage (28) having a feedback loop (34) connected between its output (32) and input (30). The feedback loop (34) includes a coupler (56), a first gain control element (58) and a feedback function stage (64) which collectively determine the loop gain of the amplifier. A second gain control element (54) is provided in the forward gain path of the power amplifier (18). The first and second gain control elements (58,54) are controlled so that the product of their gains is constant. As a result the loop parameters remain substantially constant as the power setting is varied.

Power amplifier circuit for audio signal and audio device using the same

Abstract: A power amplifier circuit for an audio signal is provided with a switching control circuit and a switching circuit between an amplifier and a power source line or ground line and a smoothing circuit which smoothes current from the switching circuit and supplies the current to the amplifier, and the smoothing circuit is provided with a change-over switching circuit which operates to return a commutation current generated during switching OFF time to the smoothing circuit.

Non-uniformly distributed power amplifier

Abstract: An amplifier extracts the maximum power from a plurality of identical three-terminal electronic amplifying devices, herein coined "cells," by additively combining their power contributions. The amplifier, herein coined a "non-uniformly distributed power amplifier," is a distributed amplifying circuit in which the transmission line impedances between adjacent electronic amplifying devices varies throughout the distribution in a prescribed manner so as to optimize the power output and/or amplifying efficiency of the distribution. The distribution may be constructed in one, two, or three dimensions but will always produce an overall mid-band power gain which is equivalent to the sum of the gains of the devices contained in the distribution of an overall power output which is equal to the number of devices times the power contribution of a single contributing device. Regardless of the amplifier's dimensions, microwave input power will be disbursed throughout the amplifier by an array of transmission lines of varying characteristic impedance which interconnects the input terminals of nearest neighbor cells. A similar array of transmission lines having a mirror-image topology interconnect the outputs of nearest neighbor cells to produce an output port. The output end (or outbound edges of a rectangular distribution, or outbound surfaces of a three-dimensional array) of the input array terminated in a resistor to absorb incident signals. However the output transmission line array requires no resistive terminations other than the intended load which will be attached to the output port.

Current sense circuit apparatus for power amplifier control

Abstract: A power control system for controlling the power output of a power amplifier. The power control system draws power from a variable voltage supply, such as a battery, and receives a signal input which indicates the desired power output. The power control system includes a power amplifier for amplifying an electrical signal which draws a current from the variable voltage supply. The power amplifier is of the type wherein the operating current drawn by the power amplifier is indicative of the power output. The power control system additionally includes a current sense circuit, which is operably connected between the variable voltage supply and the power amplifier and which senses the current drawn by the power amplifier and simultaneously produces an output current, which is directly correlated to the sensed current. The output current and the signal input are compared in a controller which produces a control signal for controlling the power output by the power amplifier.

A high-efficiency linear power amplifier using an envelope feedback method

Abstract: This paper describes a high-efficiency linear power amplifier using an envelope feedback method for a digital cellular telephone. Adjacent channel interference due to the amplitude and phase distortions of the amplifier is analyzed for a π/4-shift QPSK modulation scheme. From the analysis amplitude error compensation circuits are proposed and the limit of phase-shift variation caused by AM/PM conversion is discussed. the drain power efficiency of 50 percent at the low operation voltage of 5.8 V is achieved experimentally.