Showing papers on "RF power amplifier published in 2001"

7T vs. 4T: RF power, homogeneity, and signal-to-noise comparison in head images.

Abstract: Signal-to-noise ratio (SNR), RF field (B1), and RF power requirement for human head imaging were examined at 7T and 4T magnetic field strengths. The variation in B1 magnitude was nearly twofold higher at 7T than at 4T (;42% compared to ;23%). The power required for a 90° pulse in the center of the head at 7T was approximately twice that at 4T. The SNR averaged over the brain was at least 1.6 times higher at 7T compared to 4T. These experimental results were consistent with calculations performed using a human head model and Maxwell’s equations. Magn Reson Med 46:24 ‐30, 2001.

Measurement technique for characterizing memory effects in RF power amplifiers

Abstract: Memory effects are defined as changes in the amplitude and phase of distortion components caused by changes in modulation frequency. These are particularly important in cancelling linearizer systems, e.g., when distortion is reduced by similar distortion in the opposite phase. This paper begins by describing electrical and electrothermal causes for memory effects. A three-tone test setup is then constructed to measure the phase of third-order intermodulation distortion products. This paper also presents the measured results for a bipolar junction transistor and a MESFET amplifier.

An extended Doherty amplifier with high efficiency over a wide power range

Abstract: An extension of the Doherty amplifier, which maintains high efficiency over a wide range of output power (>6 dB), is presented in this paper. This extended Doherty amplifier is demonstrated experimentally with InGaP/GaAs heterojunction bipolar transistors at 950 MHz. Power-added efficiency (PAE) of 46% is measured at P/sub 1dB/ of 27.5 dBm and 45% is measured at 9 dB backed off from P/sub 1dB/. Additionally, PAE of at least 39% is maintained for over an output power range of 12 dB backed off from P/sub 1dB/. This is an improvement over the classical Doherty amplifier, where high efficiency is typically obtained up to 5-6 dB backed off from P/sub 1dB/. Compared to a single transistor class-B amplifier with similar gain and P/sub 1dB/, the extended Doherty amplifier has PAE 2.6 /spl times/ higher at 10 dB back off and 3 /spl times/ higher at 20 dB back off from P/sub 1dB/. Under different bias and output matching conditions, the amplifier was also evaluated with CDMA signals. At the highest measured power of 25 dBm, the extended Doherty amplifier achieves a PAE of 45% with an adjacent channel power ratio of -42 dBc. Generalized design equations are also derived and the consequences of finite device output impedance on amplifier gain and linearity are explored.

Maximum efficiency and output of class-F power amplifiers

Abstract: A class-F power amplifier (PA) improves efficiency and power-output capability (over that of class A) by using selected harmonics to shape its drain-voltage and drain-current waveforms. Typically, one waveform (e.g., voltage) approximates a square wave, while the other (e.g., current) approximates a half sine wave. The output power and efficiency of an ideal class-F PA can be related to the Fourier coefficients of the waveforms, and Fourier coefficients for maximally flat waveforms have been determined. This paper extends that theory by determining the coefficients for the maximum power and efficiency possible in a class-F PA with a given set of controlled harmonics.

Optimum design for linearity and efficiency of a microwave doherty amplifier using a new load matching technique

Abstract: A Doherty amplifier with full load matching circuits of the carrier and peaking amplifiers at both low and high power levels is demonstrated for the first time. In the circuit design, sections of transmission lines are inserted in the load matching network for power-level-dependent load impedances. The circuit elements and bias points are designed and optimized using a large-signal harmonic balance simulation to offer simultaneous improvements in linearity and efficiency. Two 1.4 GHz Doherty amplifiers have been implemented using silicon LDMOS FETs. The RF performances of the Doherty amplifier-I (a combination of a class B carrier amplifier and a bias-tuned class C peaking amplifier) have been compared with those of a class B amplifier alone. The Doherty amplifier-II (a combination of a class AB carrier amplifier and a bias-tuned class C peaking amplifier) has been compared with a class AB amplifier alone. The new Doherty amplifiers show an improved linearity as well as higher efficiency.

Apparatus and method for efficiently amplifying wideband envelope signals

Abstract: Systems and methods for amplifying an RF input signal include employing a moderately power efficient wide bandwidth device, such as an AB-type amplifier, to amplify the power residing in the high frequency components of the input signal, and a highly power efficient narrow bandwidth device, such as a synchronous buck DC/DC converter, to amplify the power residing in the low frequency components of the input signal. The amplified low frequency components and high frequency components are then combined to produce an amplified replica of the RF input signal. A positive feedback loop is provided between the output of the AB-type amplifier and the input of the DC/DC converter to provide stability to the amplified RF signal. A negative feedback loop is provided between the output of the DC/DC converter and the input of the AB-type amplifier to minimize interference introduced by the DC/DC converter.

RF power amplifiers

Abstract: In this thorough overview, Mihai Albulet presents a full account of RF amplifiers and shows that understanding large-signal RF signals is simply a matter of understanding basic principles and their applications. In addition to discussing the basic concepts used in the analysis and design of RF power amplifiers, detailed mathematical derivations indicate the assumptions and limitations of the presented results, allowing the reader to calculate their usefulness in practical designs. Covered are amplification classes, circuit topologies, bias circuits, and matching networks.

A CMOS RF power amplifier with parallel amplification for efficient power control

Abstract: This paper introduces a CMOS radio-frequency (RF) power amplifier that uses parallel amplification to provide high efficiency over a broad range of output power. Three binary-weighted class-F unit amplifiers act in conjunction with an efficient power-combination network to provide a digital-to-analog conversion between a 3-b control signal and the amplitude of the output RF signal. The power-combination network is based on quarter-wavelength transmission lines that also serve as class-F harmonic terminations. A pMOS switch to the positive supply rail is used to avoid power dissipation when a unit amplifier is shut down. The parallel-amplifier architecture, integrated in a 0.25-/spl mu/m CMOS technology, occupies an active die area of 0.43 mm/sup 2/, operates at 1.4 GHz from a 1.5-V supply, and provides an output power adjustment range of 7-304 mW. The amplifier achieves a maximum power-added efficiency (PAE) of 49% and maintains a PAE of greater than 43% over the range of 100-300 mW.

Improvement of third-order intermodulation product of RF and microwave amplifiers by injection

Abstract: This paper discusses the improvement in the third-order intermodulation product (IM3) performance obtainable from RF and microwave amplifiers by two alternative injection techniques. The first is the addition to the amplifier input of the second harmonics of the input spectrum and the second is the addition to the amplifier input of the difference frequencies between the spectral components of the input signal. Both techniques are considered in theory, by simulation and in practice. Both techniques give useful improvements in two-tone IM3 performance. The second harmonic technique reduced the IM3 level by 43 dB in an amplifier at 835 MHz. The difference-frequency technique gave a reduction of 48 dB in an amplifier at 880 MHz. The difference-frequency technique also gives a greater improvement for complex spectra signals.

Bias network for high efficiency RF linear power amplifier

Abstract: A bias network uses resistive biasing, active biasing and current mirror biasing in combination to enhance RF power amplifier linearity and efficiency by forming a bias network that provides temperature compensation, minimizes current drain requirements for the Vbias source and reduces the level of RF linear amplifier quiescent current.

Pulsed RF power delivery for plasma processing

Abstract: A system and method for overcoming the above-described problems relating to the delivery of pulsed RF power to a plasma processing chamber The power reflected from the chamber is reduced using one or more of the following techniques: (1) varying the RF frequency within a pulse period; (2) ramping up the pulse heights at the leading edge of the pulse train; (3) simultaneously transmitting a relatively low CW signal along with the pulsed signal; and (4) rapidly switching the shunt capacitance within a local matching network within a pulse period The amount of power delivered to the plasma by the pulses is measured by way of a time-averaging mechanism coupled to a directional coupler connected to the transmission line The time-averaging mechanism may comprise circuitry to measure temperatures of loads attached to the directional coupler, or analog integrating circuitry attached to the directional coupler, or digital integrating circuitry attached to the directional coupler

Power amplifier with multiple power supplies

Abstract: A power amplifier for receiving an input signal and providing a corresponding amplified output signal. One embodiment of the power amplifier includes a positive half circuit for supplying power to an amplifier during positive half waves of the output signal and a negative half circuit for supplying power to the amplifier during negative half waves of the output signal. Each half circuit has a main power supply, which is typically a switching regulator, and which supplies a first power signal to the amplifier. The slew rate of this first power signal is intentionally limited to control EMI emissions. Each half circuit also has a transient power supply which may be selectively engaged to provide a second power signal to the amplifier when the first power signal is insufficient to power the amplifier. Each half circuit may also include a low voltage power supply which provides a third power signal to the amplifier, allowing the main power supply to be disabled when a low power level is required, further reducing EMI emissions. Each half circuit has a control circuit which regulates the power output from the main and transient power supplies. The control circuit may provide a pulse width modulated control signal or a pulse density modulated control signal to control the switching regulator. If a pulse density control signal is provided, the switching regulator may be a resonant switching regulator. The power amplifier may be modified for use with a bridge amplifier, with multiple channels and may incorporate an overload detection circuit. In another embodiment of power amplifier the transient power supply is replaced with a transient control circuit that, when the first power supply is insufficient to power the amplifier, temporarily forces the first power supply to a 100% duty cycle, and then for a longer period, increases the duty cycle from its normal level to allow the first power supply to adequately power the amplifier more quickly.

Method and apparatus for improving the efficiency of power amplifiers, operating under a large peak-to-average ratio

Abstract: Method and apparatus for improving the efficiency and the dynamic range of a power amplifier operated with signals having a large peak-to-average ratio. A reference level is determined, above which at least a portion of the magnitude of an input signal being a modulated signal that is input to the power amplifier, or a baseband waveform that is used to generate the modulated signal, is defined as an excess input signal. The magnitude of the input signal is continuously sampled, for detecting an excess input signal. A lower level of operating voltage is supplied to the power amplifier, if no excess input signal is detected. The lower level of operating voltage is sufficient to effectively amplify input signals having a magnitude below the reference level. A higher level of operating voltage is supplied to the power amplifier, whenever an excess input signal is detected. The higher level of operating voltage is sufficient to effectively amplify input signals having a magnitude above the reference level.

Design and optimization of CMOS RF power amplifiers

Abstract: A CMOS radio-frequency power amplifier including on-chip matching networks has been designed in a 0.6-/spl mu/m n-well triple-metal digital CMOS process, and optimized using a simulated-annealing-based custom computer-aided design tool. A compact inductor model enables the incorporation of parasitics as an integral part of the parasitic-aware design and CAD optimization; low-Q metal3 spiral inductors are used in the input and output matching networks. A 3-V 85-mW balanced fully integrated Class-C power amplifier with a measured drain efficiency of 55% at 900 MHz has been designed, optimized, integrated, and tested.

System for closed loop power control using a linear or a non-linear power amplifier

Abstract: A system for a closed power control feedback loop (200) allows for the use of a non-linear amplifier for amplifying a phase modulated (PM) signal while introducing an inverse version of the desired amplitude modulation (AM) signal into the feedback loop using a variable gain element (Fig. 2, block 212). By introducing an inverse version of the desired (AM) portion of the signal into the power control feedback loop, the non-linear, and highly efficient, power amplifier may be used to amplify only the (PM) portion of the signal, while the (AM) portion is introduced by the power control feedback loop (200). In another aspect of the invention, an inverse version of the (AM) portion of the desired transmit signal is introduced into the power control feedback loop of an amplifier that is amplifying both a phase modulated signal and an amplitude modulated signal. By introducing an inverse version of the desired (AM) signal into the power control feedback loop, the power control feedback loop may not cancel the (AM) component present at the output of the power amplifier. In yet another aspect of the invention, the desired (AM) signal is injected into the feedback loop with the power control reference signal.

Single output stage power amplification for multimode applications

Abstract: The present invention eliminates the need for complex impedance networks or parallel amplification stages for multi-mode mobile terminals. A wideband power amplifier is configured to amplify signals in different frequency bands corresponding to different operating modes. The supply voltage of the wideband power amplifier is adjusted in light of the load impedance of radiating circuitry to achieve a desired output power for the respective operating modes.

High-efficiency audio power amplifier

Abstract: A high-efficiency audio power amplifier featuring a tracking power-supply and an active noise shaping unit for reducing non-linearity and audible noise. Several variations of a non-inductive switched-capacitor tracking power-supply are presented, which are well-suited to integrated-circuit implementation and battery operation, and which provide an efficient power supply for the output stage over a wide range of voltages that can exceed the voltage limits of the main power source. The output of the tracking power-supply can be fed into an analog power stage, or can be used as a Multi-Level Quantizer for generating the output directly. A feedback and noise shaping allows the use of low-cost components while relaxing design constraints. Some simple switching strategies are disclosed which offer power efficiencies in excess of 80 %.

Swept performance monitor for measuring and correcting RF power amplifier distortion

Abstract: RF power amplifier distortion is measured in the presence of multi-frequency input signals, by sweeping a local oscillator to tune RF input and output receivers. When the power detected by the input receiver exceeds a carrier energy threshold, the operation of a predistortion processor is blanked. This creates an adaptive notch filter, which allows for the direct measurement of low level distortion power in the presence of high power carriers. The unnecessary complexity of using controllably interrupted high isolation switches in the signal flow path of the output receiver in certain applications may be effectively obviated by buffer amplifier—passband filter stages. These buffer-filter stages provide additional gain to offset the fact that the signal level extracted from the output amplifier is very low, and prevent producing IMDs in the swept receiver's mixer. They are preferably implemented of the same bandpass filter in the swept input receiver.

RF power supply with integrated matching network

Abstract: The invention features an RF plasma generator. The RF plasma generator includes a variable frequency RF generator, comprising an H-bridge and an RF output. The RF generator generates electromagnetic radiation having a power. The RF plasma generator further includes a matching network that includes at least one variable impedance component. The matching network also includes a first port that is electromagnetically coupled to the output of the RF generator and a second port. The RF plasma generator also includes a load that is electromagnetically coupled to the second port of the matching network, and a plasma chamber for containing a plasma having a power. The plasma chamber is electromagnetically coupled to the load and receives electromagnetic radiation having a power from the load. Adjusting at least one of the frequency of the RF generator and the variable impedance component in the matching network changes the power in the plasma.

Circuit Design for RF Transceivers

Abstract: 1. RF Design: Concepts and Technology 1.1 RF Specifications 1.1.1 Gain 1.1.2 Noise 1.1.3 Non-Linearity 1.1.4 Sensitivity 1.2 RF Device technology 1.2.1 Characterization and Modeling, Modeling, Cut-off Frequency, Maximum Oscillation Frequency, Input Limited Frequency, Output Limited Frequency, Maximum Available Bandwidth 1.2.2 Technology Choice, Double Poly Devices, Silicon-on-Anything, Comparison, SiGe Bipolar Technology, RF CMOS (updated for newer processes) 1.3 Passives 1.3.1 Resistors 1.3.2 Capacitors (updated for different layouts) 1.3.3 Planar Monolithic Inductors (updated as relation to newer processes) References (updated) 2. Antennas, Interface and substrate 2.1 Antennas 2.2 Bond wires 2.3 Transmission Lines 2.3.1 General Theory 2.3.2 Impedance Matching using Transmission Lines 2.3.3 Microstrip Lines and coplanar Lines 2.4 Bond Pads and ESD Devices 2.4.1 Bond Pads 2.4.2 ESD Devices, ggNMOST ESD Device, pn and np-diode ESD Device (updated for newer processes and detailed scaling effects) 2.5 Substrate 2.5.1 Substrate bounces 2.5.2 Design Techniques to Reduce the substrate bounce References (updated) 3. Low Noise Amplifiers 3.1 Specifications 3.2 Bipolar LNA designs 3.2.1 DCS applications in SOA, Design of the LNA, Measurements 3.2.2 Broadband LNA (new) 3.3 CMOS LNA Design 3.3.1 Single Transistor LNA, Design Steps, Simulation and Measurements 3.3.2 Classical LNA Design, The Design, Measurement Results 3.3.3 Broadband LNA (new) 3.4 Evaluation References (updated) 4. Mixers 4.1 Specification 4.2 Bipolar Mixer Design 4.3 CMOS mixers 4.3.1 Active CMOS mixer 4.3.2 Passive CMOS mixer, 1/f-Noise in mixer transistors, 1/f-Noise due to IF amplifier, 1/f-noise due to Switched-Capacitor Behavior 4.3.3 Concluding remarks References (Updated) 5. Case study Receiver front-ends (new) 5.1 Bluetooth (new) 5.2 IEEE 802.11a Standard (new) 6. RF Power Amplifier 6.1 Specification 6.1.1 Efficiency 6.1.2 Generic Amplifier Classes 6.1.3 Heating 6.1.4 Linearity 6.1.5 Ruggedness 6.2 Bipolar PA design 6.3 CMOS PA Design 6.4 Linearization Principles 6.4.1 Predistortion Technique 6.4.2 Phase-Correcting feedback 6.4.3 Envelope Elimination and Restoration (EER) 6.4.4 Cartesian Feedback 6.5 Case study: Bluetooth PA (new) References (updated) Note: Oscillator chapter: errors removed and updated throughout, sub-section headings probably quite similar but to be defined 7. Oscillators 7.1 Introduction 7.2 Specifications 7.3 LC oscillator 7.4 Ring oscillators 7.5 Phase noise modelling and simulation (new) 7.6 Typical oscillator performance (new) 7.7 Oscillator case studies (new), Wide range oscillators for mobile applications, Oscillators for ultra low-power wireless links, 10GHz CMOS VCO for WLAN, 10GHz QuBIC VCO for Satellite References (updated) 8. Frequency Synthesizers 8.1 Introduction 8.2 Integer-N PLL Architecture 8.3 Tuning System Specifications 8.3.1 Tuning Range 8.3.2

RF power amplifier and methods for improving the efficiency thereof

Abstract: A radio frequency power amplifier characterized by an efficiency and operative to produce an output signal at a desired output power includes an outphasing system (128) with shunt reactance (142 and 144) and a controller (130). The outphasing system with shunt reactance (142 and 144) has a variable phase and is operative to produce the output signal from an input signal. The controller (130) is operative to control the variable phase and the amplitude of the input signal in order to achieve high efficiency at low desired output powers. A method for controlling the output power of a radio frequency power amplifier includes reducing the power of an input signal to the power amplifier when a desired output power is below a threshold and performing outphasing when the desired output power is not below the threshold.

Impedance matching low noise amplifier having a bypass switch

Abstract: An impedance matching low noise amplifier (“LNA”) having a bypass switch includes an amplification circuit, a bypass switching network and a match adjustment circuit. The amplification circuit has an amplifier input and an amplifier output, and is configured to receive a radio frequency (RF) input signal at the amplifier input and apply a gain to generate an amplified RF output signal at the amplifier output. The bypass switching network is coupled to a low-gain control signal and is also coupled between the amplifier input and the amplifier output. The bypass switching network is configured to couple the amplifier input to the amplifier output when the low-gain control signal is enabled in order to feed the RF input signal through to the RF output signal. The match adjustment circuit is coupled to the low-gain control signal and the RF input signal, and is configured to couple the RF input signal to an impedance when the low-gain control signal is enabled.

Wide bandgap semiconductor devices and MMICs for RF power applications

Abstract: High power densities of 5.2 W/mm and 63% power added efficiency (PAE) have been demonstrated for SiC MESFETs at 3.5 GHz. Wide bandwidth MMICs have also been demonstrated with SiC MESFETs, yielding 37 W at 3.5 GHz. Even higher power densities have been obtained with GaN HEMTs, showing up to 12 W/mm under pulsed conditions. Hybrid amplifiers using GaN HEMTs on SiC substrates have demonstrated a pulsed output power level of 50.1 W, with 8 dB gain and PAE of 28% at 10 GHz, and CW power levels of 36 W have also been obtained. A wide bandwidth GaN MMIC amplifier had a peak pulsed power level of 24.2 watts, with a gain of 12.8 dB and PAE of 22% at 16 GHz.

Distributed circular geometry power amplifier architecture

Abstract: The present invention discloses a distributed power amplifier topology and device that efficiently and economically enhances the power output of an RF signal to be amplified. The power amplifier comprises a plurality of push-pull amplifiers interconnected in a novel circular geometry that preferably function as a first winding of an active transformer having signal inputs of adjacent amplification devices driven with an input signal of equal magnitude and opposite phase. The topology also discloses the use of a secondary winding that matches the geometry of primary winding and variations thereof that serve to efficiently combine the power of the individual power amplifiers. The novel architecture enables the design of low-cost, fully-integrated, high-power amplifiers in the RF, microwave, and millimeter-wave frequencies.

Integrated power detector with temperature compensation

Abstract: A power detector (50) detects a power level of an amplified signal (S20) produced by a power amplifier (16) on the same integrated circuit (100). The power detector compensates for an effect of temperature variations on the magnitude of the detected power level.

Distributed inductively-coupled plasma source and circuit for coupling induction coils to RF power supply

Abstract: Apparatus and method for inductively coupling electrical power to a plasma in a semiconductor process chamber. In a first aspect, an array of wedge-shaped induction coils are distributed around a circle. The sides of adjacent coils are parallel, thereby enhancing the radial uniformity of the magnetic field produced by the array. In a second aspect, electrostatic coupling between the induction coils and the plasma is minimized by connecting each induction coil to the power supply so that the turn of wire of the coil which is nearest to the plasma is near electrical ground potential. In one embodiment, the hot end of one coil is connected to the unbalanced output of an RF power supply, and the hot end of the other coil is connected to electrical ground through a capacitor which resonates with the latter coil at the frequency of the RF power supply.

Digitally implemented predistorter control mechanism for linearizing high efficiency rf power amplifiers

Abstract: A digitally-based high distortion rejection scheme for linearizing an RF power amplifier employs a digital signal processor(200.SNL), which executes a first signal processing operator in terms of a digital polynomial-based predistortion function that approximates an inverse of the dynamic memory effects in the nonlinear tr ansfer characteristic of the amplifier, and a second signal processing operator(200-DME) that represents an inverse of static non-linearities in the transfer characteristic of the amplifier. The output of this cascaded filter operation is used to control parameters of a vector modulator(18) in the signal input path to the RF power amplifier(20). The vector modulator thus predistorts the input signal, so as to compensate for dynamic memory effects and static non-linearities in the power amplifier.

Radio Frequency Circuit Design

Abstract: Preface. Communication Channel. Resistors, Capacitors, and Inductors. Impedance Matching. Multiport Circuit Parameters and Transmission Lines. Filter Design and Approximation. Transmission Line Transformers. Class A Amplifiers. Noise. RF Power Amplifiers. Oscillators and Harmonic Generators. RF Mixers. Phase Lock Loops. Emerging Technology. Appendix A: Example of a Solenoid Design. Appendix B: Analytical Spiral Inductor Model. Appendix C: Double--Tuned Matching Circuit Example. Appendix D: Two--Port Parameter Conversion. Appendix E: Termination of a Transistor Port with a Load. Appendix F: Transistor and Amplifier Formulas. Appendix G: Transformed Frequency Domain Measurements Using Spice. Appendix H: Single--Tone Intermodulation Distortion Suppression for Double--Balanced Mixers. Index.

Multiharmonic manipulation for highly efficient microwave power amplifiers

Abstract: Multiharmonic manipulation is presented as the most effective solution to improve power amplifier (PA) efficiency performances. Remarkable improvements in output power, power gain and power-added efficiency (PAE) are demonstrated, properly manipulating the input and output second and third harmonics, as compared to more classical design approaches. Experimental results at 5GHz confirm the feasibility, the validity and effectiveness of the proposed approach, increasing the maximum measured power-added efficiency from 39% to 61% © 2001 John Wiley & Sons, Inc. Int J RF and Microwave CAE 11: 366–384, 2001

High linearity multicarrier RF amplifier

Abstract: A hybrid multicarrier RF power amplifier linearization architecture combines ACT and feed-forward amplifier stages to achieve high output distortion rejection and enhanced amplifier linearity. A carrier cancellation loop (loop 1) is coupled with a main RF power amplifier stage (20) having parallel RF power amplifiers coupled via intermod-complementing predistortion paths. The carrier cancellation loop (loop 1) is coupled to a feed-forward loop (loop 2) containing a feed-forward RF power amplifier, to produce a composite amplified output signal having very reduced intermodulation products. Vector modulators (16) in the main amplifier (20) and feed-forward amplifier stages are controlled by a digital signal processor (50), using outputs from various monitoring subsystems, including pilot tone detection (26), correlator (40), distortion and power detector circuits (80).