Showing papers on "RF power amplifier published in 1989"

Method and apparatus for the calibration of electrosurgical apparatus

Abstract: A method and apparatus for the calibration of electrosurgical apparatus utilizes a non-volatile, read-write storage device (U2) to store calibration parameters. A programmed microprocessor (U3) and an EPROM memory (U1) for the microprocessor (U3) control the flow of data to and from the storage device (U2). For the calibration of the RF power output a test resistor of known value provides a test power reading and the RF power output is adjusted by the adjustment of up/down power select keys until the RF power output substantially equals the test power so that the values stored in the storage device (U2) control subsequent RF power output levels. For the calibration of a return electrode contact monitor (35), a low resistance of known value is input into the storage device (U2) by depressing a key and a high resistance value is input into the storage device (U2) by depressing the same key. These values are stored in the storage device (U2) and provide a transfer function from which a particular output voltage value is generated for each return electrode resistance measurement.

RF amplifier system having multiple selectable power output levels

Abstract: A control circuit for a radio frequency (rf) amplifier having multiple selectable power output levels in response to a plurality of input control signals is presented. The rf amplifier includes a variable gain input which is responsive to the control circuit. The control circuit includes an attenuator coupled to the output of the rf amplifier for providing an attenuated rf signal and an detector coupled to the output of the attenuator for generating a DC output signal which is substantially linearly related to the magnitude of the rf signal output by the rf amplifier. The control circuit also includes a means coupled to the input control signals for selecting one of a plurality of amplification factors. An amplifier is used to amplify the DC output signal generated by the detector using the selected amplification factors. The amplified output is coupled to the variable gain input of the rf amplifier.

Monitoring circuit for an RF surgical apparatus

Abstract: An RF surgical apparatus has an RF power stage, a control circuit for driving the power stage, and an adjustable element for setting a rated value of the output power. To monitor the RF surgical apparatus for the occurrence of an apparatus-caused malfunction, a power measuring unit measures the actual value of the RF power at the output of the RF power stage. Deviations of the actual value from a rated value are monitored. An alarm is generated if the deviation exceeds a selected value. An alarm can be simulated in a test mode by means of an auxiliary circuit.

Analysis and design of a generalized class E tuned power amplifier

Abstract: The authors describe the analysis of a more general class E amplifier configuration that can yield results for most of the other class E amplifier configurations published thus far by simply imposing the proper design conditions. The analysis takes into account most of the important parameters that affect the amplifier performance, such as the DC-feed inductance, the Q/sub L/ factor of the series-tuned circuit and the switching device ON resistance. Design and performance curves are given and discussed for the finite DC-feed inductance, shunt-capacitor, series-tuned configuration. It is seen that the amplifier performance is strongly affected by all of these parameters. Laboratory results show an excellent agreement between experimental values and theoretical predictions. >

Power amplifier for a radio frequency signal

Abstract: A power amplifier is provided for amplifying a radio frequency signal such as in a burst modulation manner for use in GSM cellular radio. The amplifier has means, such as a ROM (16), for producing a predetermined sequence of values in response to a control pulse. Means (21) are provided for converting each value into a power control signal, and control means (9) are provided for controlling the amplifier output power in accordance with said power control signal. In this manner, the power/time characteristic can be made to take the form of a raised cosine. The invention also provides power selection means for selecting a nominal output level from a plurality of discrete levels and for selecting power sub-levels offset from said selected level. An indication is recorded as to which sub-level best represents the nominal power level.

Driver for a high efficiency, high frequency Class-D power amplifier

Abstract: A driver circuit for a voltage-switching, high frequency Class-D power amplifier provides an input sinewave power signal and controls the transition time between switching the two active devices thereof, resulting in substantially lossless switching. The transition time is optimized by controlling the amplitude of the voltage signals at the inputs of the two active devices, depending on the output capacitance of the switching devices, the threshold voltage of the switching devices, the power output requirement, and the impedance of the resonant load network of the Class-D power amplifier.

Hybrid-balun for splitting/combining RF power

Abstract: An in-phase hybrid and a balun in a single stage built with inexpensive coaxial cable which splits or combines RF power and simultaneously performs a balanced-to-unbalanced impedance transformation.

Class E tuned power amplifier with antiparallel diode or series diode at switch, with any loaded Q and switch duty cycle

Abstract: An analysis and experimental results are given for a class E switching-mode tuned power amplifier with an antiparallel diode or a series diode at any loaded Q and any switched duty cycle D. The load resistance and the operating frequency of the amplifier can vary over a wide range while maintaining high efficiency. Using equations derived by the authors in a previous publication (ibid., vol.CAS-34, no.2, p.149-59, 1987), the analysis of the amplifier is performed at any values of the derivative of the switch voltage, load resistance, and operating frequency. The experimental switch current and voltage waveforms were in agreement with theoretical predictions. The measured efficiencies were 91 and 88% at 2 MHz in the amplifier with an antiparallel diode and a series diode, respectively. >

FET monolithic microwave integrated circuit variable attenuator

Abstract: A MMIC variable att4enuator uses depletion mode Schottky gate FETS as variable conductance devices in a "π" configuration to vary attenuation as a function of a DC control voltage. Attenuation is flat within ±1 dB, VSWR is ≦2:1 throughout the operating frequency and control voltage range, and about 12 dB variable attenuation is provided. The "π" is formed by FETs in shunt to ground between attenuator input and output, and by a FET in series between input and output. Resistors and an inductor connected in parallel with the series FET extend attenuator bandwidth to 20 GHZ and improve attenuation linearity versus control voltage. A resistor in series with each shunt FET also improves linearity. The typically 0 to +3 VDC control voltage is applied to the FET gates and drain/source leads permitting attenuation control with a single control voltage. FR power capability is increased without degrading RF performance by using multi-gate FETs wherein the ratio of gate width to number of gates is maintained substantially constant compared to a single-gate FET. Series-connected FETs further increase attenuator RF power capability. Operating from 2-20 GHz, embodiments using a single control voltage handle about 30 mW RF input power and use single-gate and dual-gate FETs, and handle about 250 mW RF input power and use triple-gate FETs. A third embodiment, operating from DC-20 GHz and handling about 500 mW RF input power, employs dual-gate FETs throughout and requires two complementary control voltages.

2-Gbit/s signal amplification at lambda =1.53 mu m in an erbium-doped single-mode fiber amplifier

Abstract: The gain, saturation power, and noise of an erbium-doped single-mode traveling-wave fiber amplifier operating at a wavelength lambda =1.53 mu m are characterized. In continuous-wave (CW) measurements amplification at 2 Gbit/s was demonstrated with up to 17-dB gain for 1*10/sup -9/ bit error rate at 1.531 mu m and a 3-dB full bandwidth of 14 nm. From the determination of the fiber-amplifier's output signal-to-noise ratio versus input signal power during data transmission, it was concluded that, with signal levels used here, signal-spontaneous beat noise limited the receiver sensitivity improvement. With the fiber amplifier acting as an optical preamplifier of the receiver, the best sensitivity was -30 dBm, obtained after installing a polarizer at the fiber amplifier output to reject half of the applied spontaneous emission power. This sensitivity was 6 dB better than without the fiber amplifier, proving that the fiber amplifier can be used as a preamplifier. >

Power transmission and coupling for radiofrequency heating of plasmas

Abstract: RF power is widely used as an auxiliary heating method in fusion devices. This paper reviews the relevant theoretical considerations for the ion cyclotron, lower hybrid and electron cyclotron ranges of frequency, and presents the history, the state of the art, and the plans and prospects for antennas and transmission lines for RF heating. Reactor-relevant concerns are discussed, and the information needed to develop realistic antenna designs for a reactor environment is assessed.

A wide-bandwidth high-gain small-size distributed amplifier with field-emission triodes (FETRODEs) for the 10 to 300 GHz frequency range

Abstract: It is demonstrated that, by a suitable modification of the well-known thin-film field-emission cathode (TFFEC) of C.A. Spindt (1948, 1976) into a FETRODE, a vacuum-type free-electron amplifier with a figure of merit superior to that achieved with triodes and FETs can be established. Analytical evaluation of important parameters of the FETRODE and the distributed amplifier's circuit is carried out. A formula for the RF efficiency of the FETRODE is applied to an approximate relation between the output current and the input RF voltage that gives the dependence of efficiency on the ratio of the RF output impedance and the DC beam impedance. Potential advantages of future FETRODEs over solid-state FETs are discussed, assuming already established DC current emission levels as well as improved levels resulting from low-work-function materials other than Mo cones. >

A method for correctly setting the rf flip angle.

Abstract: Currently the accepted method for setting the correct rf power levels to achieve 90° and 180° rf pulses for MR imaging is to peak the echo amplitude of a rf spin-echo sequence. The echo amplitude of this α-2α pulse sequence is proportional to sin3(α) and has a relatively broad maximum. Recently another method for setting the rf flip angle by maximizing the ratio of the stimulated echo to the primary echo amplitudes (in a 3α sequence) demonstrated accuracy similar to that of the spin-echo method using a shorter repetition time. We present a new, more sensitive, and more accurate method for setting the correct rf power levels for 90° and 180° rf pulses. In this method, based upon the stimulated echo pulse sequence, we are able to accurately set the rf power to within ±0.1 dB by minimizing the signal amplitude of the third spin echo. This null method works for both selective and nonselective rf pulses of flip angle 90° or 180°, allowing the user to accurately adjust the relative amplitudes of the four rf pulse types within a single pulse sequence. © 1989 Academic Press, Inc.

Ultrasound power generating system with sampled-data frequency control

Abstract: A system is provided for applying ultrasound power to treat human tissue comprising a transducer driven by an oscillating signal from a power amplifier. The transducer and power amplifier have a power-conversion-efficiency characteristic which is a function of the frequency of the oscillating signal and the acoustic load on the transducer. Data sampling and frequency adjustment means are provided which continually monitor the current supplied to the crystal and adjust the frequency of the oscillating signal to maximize the power-conversion-efficiency of the transducer and power amplifier.

Class C-E high-efficiency tuned power amplifier

Abstract: A numerical analysis of a Class C-E tuned power amplifier is presented, along with a design procedure and experimental results. The efficiency and the maximum operating frequency of the amplifier are intermediate between those of the Class C and E amplifiers. The collector efficiency of the Class C amplifier is about 70%, whereas that of the Class E amplifier is about 96%. The maximum operating frequency of the optimum-efficiency Class E amplifier is, however, limited by the transistor output capacitance. The operating frequency of the Class C amplifier can be at least 16 times higher than that of the optimum-efficiency Class E amplifier at the same output power, DC supply voltage, and transistor output capacitance. The Class C, E, and C-E amplifiers can be obtained with the same circuit topology. The class of operation depends on the values of the load-network components. The tradeoff between the efficiency and the maximum operating frequency is evaluated for all three classes, using nonlinear time-domain simulation. The experimental and theoretical results are in good agreement. >

A new wide-band Darlington amplifier

Abstract: A wideband Darlington amplifier topology which is well suited for maximum-bandwidth, moderate-gain, matched-impedance applications is described. A test circuit using a silicon bipolar monolithic technology with an f/sub T/ of 9 GHz has been fabricated. Measured results show a 9.3 dB insertion gain and a 3.2 GHz bandwidth for the packaged device. >

S parameter measurements on single superconducting thin-film three-terminal devices made of high-Tc and low-Tc materials

Abstract: We have investigated three‐terminal single‐layer thin‐film superconducting devices made of YBaCuO and Nb. The devices incorporate regions of weak superconductivity in multiple parallel links that are influenced by current in a separate control line. These experiments were designed to study the possible application of this device as an rf amplifier. With the device biased, rf power was applied to the control line and the transmission coefficient, S21, was measured. The reverse transmission coefficient, S12, was also measured for comparison. Upon biasing into a flux flow state, the S21 of the device at rf frequencies was found to increase 10–15 dB over the zero bias value and over the reverse feed (S12 ) value. The device behaved linearly up to power inputs of +5 dBm (1‐dB compression point). The bandwidth was limited only by the impedance transformer.

Highly efficient 978 nm dipole-pumped erbium-doped fibre amplifier with 24 dB gain

Abstract: We report an Er3+-doped fibre amplifier pumped with a strained InGaAs/A lGaAs quantum-well diode laser operating at 978nm. Efficient optical coupling was achieved with a wedge-tipped fibre. An optical gain of 24dB at 1535nm was obtained with only 6.2mW of pump power, corresponding to a gain of 3.9dB/mW of pump power. This is the highest efficiency for a fiber amplifier reported to date.

Plasma etch isotropy control

Abstract: A tapered profile is obtained in oxide etched in a plasma glow discharge by switching the RF power between the side and lower electrodes in a tri-electrode reactor. The etch is isotropic while the RF power is applied to the side electrode and is anisotropic when the RF power is applied to the lower electrode.

Phase modulation compensated amplitude modulator using digitally selected amplifiers

Abstract: An RF amplitude modulated amplifier system is presented incorporating a plurality of RF amplifiers which are compensated for unwanted phase modulation. The system includes a common RF driver for supplying a common RF driver signal. A plurality of actuatable RF amplifiers are provided with each having an input circuit for receiving the common RF drive signal. Each amplifier has a fully on condition for amplifying the common drive signal to provide an amplified RF signal, and a fully off condition. Each of these RF amplifiers exhibits a characteristic in that its input circuit has an input impedance which is greater when fully on than that when fully off, thereby tending to present unwanted phase modulation of the plurality of RF amplifiers. One or more of the RF amplifiers are selectively turned fully on in dependence upon the magnitude of an input signal. The amplified RF signals provided by the RF amplifiers that are turned on are combined so as to provide a combined signal which is amplitude modulated in accordance with the magnitude of the input signal. Circuitry is provided for selectively adding a compensating impedance to the input circuit of each of the RF amplifiers that is not actuated to be fully on. This serves to compensate for any unwanted phase modulation of the plurality of RF amplifiers.

A high efficiency 835 MHz linear power amplifier for digital cellular telephony

Abstract: The authors describe an approach to linear power amplification for digital cellular telephony which exploits the high efficiency of a class-C amplifier. An average efficiency exceeding 50%, with third-order intermodulation products 30 dB down, has been demonstrated. Low cost, moderate complexity, conventional RF technology was used in the amplifier circuitry. A block diagram of the 835 MHz linear power amplifier is presented. >

Efficiency improvement of power amplifiers

Abstract: Circuitry changes the magnitude of power supply voltages to correspond to the desired level of a variable output power. This maximizes the electrical power efficiency of amplifiers. The circuitry also provides for automatic control of the amplitude of the amplifier output signal.

RF power amplifier system having amplifier protection

Abstract: The amplifier includes a bridge circuit having an input circuit adapted for connection across a DC voltage source and an output circuit connected across a load. The bridge circuit includes first and second transistors for, when on, connecting the DC voltage source across the load for DC current flow therethrough in a first direction and third and fourth transistors for, when on, connecting the DC voltage source across the load for DC current flow therethrough in a second direction. The transistors are controlled by an RF signal so that they turn on and off at a frequency dependent upon that of the RF signal such that current flows from the DC source alternately in the first and second directions through the load. An amplifier control serves to apply a reverse bias to the second and fourth transistors to prevent them from conducting current until receipt of a turn on signal, which actuates the controller to remove the reverse bias from the second and fourth transistors such that the reverse bias applied to the fourth transistor is removed during a first half cycle of the RF signal when the fourth transistor is off and that the reverse bias applied to the second transistor is removed during a succeeding half cycle of the RF signal when the second transistor is off. Circuit means are provided that respond to the fourth transistor being turned on subsequent to the removal of the reverse bias applied thereto for removing the reverse bias from the second transistor.

Amplifier linearization using down/up conversion

Abstract: A feedback linearization technique for a power amplifier that does not require the availability of the modulation signals. The RF input signal is down converted to a first IF signal. A portion of the amplifier RF output signal is used to form a feedback signal that is down converted to produce a second IF signal that is subtracted from the first IF signal to produce a different signal. The difference signal is filtered and amplified, and then up converted to RF for input to the power amplifier. Use of feedback at IF avoids stability problems inherent in RF feedback techniques.

Peak level detecting device and method

Abstract: A device and method for detecting a peak level of an input signal. The input signal is amplified by a first amplifier. A switching signal corresponding to an output signal from the first amplifier is generated and a held peak level of the switching signal is fed back to the first amplifier negatively. Also, the switching signal is amplified by a second amplifier. A compensator generates a bias compensating signal for supplying to the first and second amplifiers to offset for the current drain that would otherwise occur.

Transmitter circuit for efficiently transmitting communication traffic via phase modulated carrier signals

Abstract: Transmitter for transmitting communication traffic via phase modulated carrier signals. The device provides for an efficient amplification of a phase modulated carrier signal using Class C amplifier (19) technology. An envelope function is applied to the carrier signal by modulating the Class C amplifier (19) with a related spectrum-suppressing amplitude envelope signal. Phase distortion accompanying the amplitude modulation of the Class C amplifier is compensated by generating a phase offset for the carrier signal. As each envelope function for suppressing the spectrum is generated, a corresponding phase offset may be applied to the carrier signal, avoiding the consequences of phase shift resulting from amplitude modulating the carrier signal in the Class C amplifier (19).

Wrist carried wireless instrument

Abstract: A wrist carried wireless instrument for minimizing the effects of coming in contact with the wrist of the user is provided. A case contains wireless instrument circuitry. A loop antenna extends without the case. An antenna resonance circuit has two capacitors connected in series. The two capacitors are connected to the loop antenna. A connection between two of the capacitors is formed at substantially the half impedance value across the capacitors and is a ground electric potential. An RF amplifier connects the loop antenna to the wireless instrument circuitry.

Rail-to-rail CMOS operational amplifier

Abstract: A CMOS operational amplifier comprises an output gain stage including output transistors coupled between the rails so that for a given amount of current, the output transistors have rail-to-rail gate-to-source voltages. The output transistors can be made smaller in size with the output stage being capable of driving a small resistive load with minimal signal distortion.

Radio transceiver capable of avoiding intermodulation distortion

Abstract: A radio transceiver comprises an RF amplifier 13 and a first frequency mixer 15 which converts and amplified RF signal into a first IF signal and whose output may include intermodulation distortion. A second frequency mixer 19 converts the output of first frequency mixer into a second IF signal. An interference detector 28 detects the intermodulation distortion by seeing if a beat is included in the second IF signal. Upon detection of intermodulation distortion, a controller 29 minimizes the gain of RF amplifier to decrease or eliminate the intermodulation distortion. Responsive to the end of conversation (hook switch 41) the controller maximizes the gain of RF amplifier to increase the reception sensitivity. The controller may periodically maximise the RF amplifier gain after the detection of the intermodulation distortion. If no intermodulation distortion is detected during this gain-maximized period, the controller keeps the gain to be a maximized value. If the intermodulation distortion is not decreased or eliminated even though the RF amplifier gain is minimized, the controller may change frequency used for communication.

Intrinsic GaAs MESFET equivalent circuit models generated from two-dimensional simulations

Abstract: An accurate, physically based two-dimensional GaAs MESFET model is used to generate small-signal and large-signal equivalent circuit models useful for the evaluation of GaAs device structures and GaAs integrated circuits. The models and the simulation techniques described provide a useful means of evaluating RF performance on the basis of the physical properties of the FET. As an example, the small- and large-signal device characteristics are evaluated as a function of drain-source bias voltage and lattice temperature for a 0.8- mu m gate length FET. The small-signal results show severe degradation of frequency response with increase of drain-source bias voltage because of a high electric field in the conduction channel. The large-signal results show that the decrease in RF power capability with temperature increase is primarily due to declining current capability with temperature. >