Showing papers on "RF power amplifier published in 1990"

Microwave Circuit Design Using Linear and Nonlinear Techniques

Abstract: Foreword by David Leeson. Preface. 1. RF/Microwave Systems. 2. Lumped and Distributed Elements. 3. Active Devices. 4. Two-Port Networks. 5. Impedance Matching. 6. Microwave Filters. 7. Noise in Linear Two-Ports. 8. Small- and Large-Signal Amplifier Design. 9. Power Amplifier Design. 10. Oscillator Design. 11. Microwave Mixer Design. 12. RF Switches and Attenuators. 13. Microwave Computer-Aided Workstations foor MMIC Requirements. Appendix A: BIP: Gummel-Poon Bipolar Transistor Model. Appendix B: Level 3 MOSFET. Appendix C: Noise Parameters of GaAs MESFETs. Appendix D: Derivations for Unilateral Gain Section. Appendix E: Vector Representation of Two-Tone Intermodulation Products. Appendix F: Passive Microwave Elements. Index.

High-efficiency coupling-insensitive transcutaneous power and data transmission via an inductive link

Abstract: A new approach is presented for transmitting RF power and signal via an inductive link. Such an approach optimizes the power efficiency of the overall transmission scheme comprising the power amplifier plus the inductive link. Power amplification is based on the single ended class E concept. The power amplification stage is self-oscillating, and thus the oscillation frequency is influenced by the coupling of the coils. The resulting operating frequency offset yields improved power transmission performance of the circuit, since the oscillation frequency tracks the absolute transmission efficiency maximum. A detailed analysis is given. Realization of the approach requires a minimal number of circuit components. Experimental and theoretical results are in good agreement. >

Characterizing the effects of nonlinear amplifiers on linear modulation for digital portable radio communications

Abstract: The design and performance of linear modulation techniques and RF power amplifiers are discussed Various types of power amplifier are used in the comparison, using simulation, of out-of-band radiation and power efficiency The designs focus on high-frequency silicon bipolar power amplifiers suitable for low-power portable radio applications Two different 4-QAM (4-level quadrature amplitude modulation) schemes are compared Power efficiency as high as 40% can be achieved using a dynamically biased amplifier operating near saturation The effects of nonlinear distortions from power amplifiers on adjacent channel interference as well as bit and block error rate performance are also investigated >

Radio-frequency coagulation device for surgical purposes

Abstract: A radio-frequency coagulation device for surgical purposes has a RF generator (29) and a RF power control circuit (20, 21, 25, 31, 32, 33). Furthermore, provision is made of a coagulation instrument (2) having a coagulation head (7) which has a heating head (11) and a passive region (12). A first temperature sensor (16) is arranged in the heating head (11). A second temperature sensor (17) is arranged in the passive region (12) at a predetermined distance from the first temperature sensor (16). The dissipated RF power of a RF generator (29) is regulated via the temperatures measured in the RF power control circuit (20, 21, 25, 31, 32, 33) by means of the temperature sensors (16, 17) in such a way that the size of the clot (coagulum) formed can be regulated precisely.

A CMOS large-swing low-distortion three-stage class AB power amplifier

Abstract: A CMOS power amplifier with a class AB rail-to-rail output stage is presented. By using a three-stage amplifier with double Miller compensation, the harmonic distortion of the output stage is suppressed by the internal feedback loops. This approach is thoroughly investigated, and it is shown that a three-stage amplifier has apparent advantages for DC gain, harmonic distortion, and power-supply rejection ratio (PSRR). A realized prototype for ISDN applications with a gain bandwidth (GBW) of 5 MHz and with -80-dB THD at 10 kHz for an output current of 20 mA in a load of 81 Omega is presented. >

Telemetry gain adjustment algorithm and signal strength indication in a noisy environment

Abstract: A software-controlled, external programmer for transcutaneously programming and receiving data from an implanted medical device providing a real-time indication of the implanted medical device RF telemetry signal strength to the user of the device programmer while automatically optimizing gain level to minimize interference in the presence of noise. The method and apparatus involves monitoring the validity of received intervals or frames uplinked from the implanted medical device to adjust the gain of the RF amplifier in a pre-determined range. When noise is detected, indicating a relatively small signal-to-noise ratio, the automatic gain control (AGC) level is decreased, effectively tracking this condition. Similarly, lack of any signal or loss of individual RF pulses causes the AGC level to be increased. The signal strength algorithm utilizes this real-time monitoring of signal integrity and signal-to-noise ratio to provide an indication to the user. In addition to the use of current gain level, a secondary factor is included to provide stability of link factor to the signal strength indication to decrease it in the event that a significant quantity of momentary link instabilities are detected. The telemetry gain adjustment algorithm begins operation at minimum signal level, increasing gain value every 45 ms. until a maximum gain level is reached. When at maximum, the gain is reset to minimum, restarting the search. When valid telemetry signals are received, the gain is stabilized for the duration of telemetry transmission.

On the behavior of the LINC transmitter

Abstract: The effects of RF signal processing impairments in a LINC transmitter are analyzed. A theoretical analysis of the effect of three different kinds of imbalances between the parallel signal paths in a real LINC transmitter is presented. These include the power gain and delay (or phase) imbalance between the two RF paths and the different nonlinear characteristics of both RF power amplifiers. In all cases analytical expressions have been obtained in order to evaluate the effect of the imbalances on the performance of the LINC transmitter. The gain and the phase imbalance between both power amplifiers appears as a serious constraint on performance. The system degradations are described in terms of the undesired response rejection at the system output. A classical two tones test has been used. >

Amplifier induced crosstalk in multichannel optical networks

Abstract: The effect of crosstalk introduced due to gain saturation in an optical amplifier when it is used for amplifying multiple channels in a wavelength division multiplexed (WDM) network employing ON-OFF keying with direct detection is studied. The system power penalty is quantified as a function of the amplifier input power, the number of channels, and the extinction ratio. >

Efficient generation of multigigawatt rf power by a klystronlike amplifier

Abstract: This article addresses the new development of high‐power rf klystronlike amplifiers using modulated intense relativistic electron beams. Development of these amplifiers follows earlier research in which the interaction between a high‐impedance (120‐Ω) intense relativistic electron beam and a low‐power rf pulse resulted in the generation of coherent bunches of electrons with excellent amplitude and phase stabilities. In the present experiment a low‐impedance (30‐Ω) large‐diameter (13.2‐cm) annular electron beam of power ∼8 GW was modulated using an external rf source (magnetron at 1.3 GHz) of 0.5 MW power. The interaction of the modulated electron beam with a structure generated a 3‐GW rf pulse that was radiated into the atmosphere. The self‐fields of the intense beam provided significant electrostatic insulation against vacuum breakdown at the modulating gaps and at the rf extraction gap.

Rf phase shifter

Abstract: An electrically controlled RF phase shifter having an active medium formedrom a ceramic material the permittivity of which may be varied by varying the strength of an electric field in which it is immersed. The phase shifter includes the ceramic material having electrodes mounted thereon that are connected to an adjustable d-c voltage source. The phase shifter may be placed in an RF transmission line that includes appropriate input and output impedance matching devices such as quarter-wave transformers. The phase of the RF power exiting the phase shifter will depend on the effective electrical length of the material in the active medium. Because changes in the permittivity of the material will produce corresponding changes in the electrical length of the material, changes in the phase of the RF power transmitted therein will be produced. The quarter-wave transformers may also be made of a similar adjustable permittivity material. Control voltages applied to the transformers are used to adjust the amount of output power. An interdigitated electrode is used to reduce the amount of voltage needed to operate the phase shifter. The phase shifter may be embedded as part of a microwave integrated circuit.

Relativistic klystron amplifiers driven by modulated intense relativistic electron beams

Abstract: An overview is provided for the novel relativistic klystron amplifiers which are under active study at the Naval Research Laboratory. These amplifiers are driven by an annular intense relativistic electron beam (500-kV, 10-kA range), which is modulated by an external RF source (1.3-GHz, 100-kW range). Experiments, theory, simulation, and simple models are presented to illustrate the unusual properties of such devices which result from the intense space charge of the beam. Chief among them are electrostatic insulation against vacuum breakdown at high power levels, efficient current modulation, short bunching length, and amplitude and phase stability of the output signal. Many of these unexpected features were revealed in two separate experiments: one with a lower current beam (5 kA, 2-cm beam radius), and the other one with a higher current beam (16 kA, 6.6-cm beam radius). Three gigawatts of RF power at 1.3 GHz were generated with the large diameter beam at an efficiency of 35% with 37-dB gain. These experiments are reviewed, along with a combination of particle simulation results and analytic models which facilitate the interpretation. Special attention is paid to the unfamiliar features of these amplifiers, and the critical problems which must be solved before such amplifiers can fulfil their potential in a wide range of applications are addressed. >

A high efficiency uhf linear power amplifier

Abstract: An RF amplifier for a phase and envelope varying signal employs a class C operated device (110) for high efficiency. In order to improve the linearity of the class C operated device (110), a signal (s₂(t)) corresponding to the envelope of the amplifier output is formed and a portion thereof is fedback to an envelope modulation element such as a pulse width modulator (140) connected to the class C operated device (110) to reduce distortion at the amplifier output.

Relativistic Klystron amplifiers driven by modulated intense relativistic electron beams

Abstract: An overview is provided for the novel relativistic klystron amplifiers which are under active study at the Naval Research Laboratory. These amplifiers are driven by an annular intense relativistic electron beam (500-kV, 10-kA range), which is modulated by an external RF source (1.3-GHz, 100-kW range). Experiments, theory, simulation, and simple models are presented to illustrate the unusual properties of such devices which result from the intense space charge of the beam. Chief among them are electrostatic insulation against vacuum breakdown at high power levels, efficient current modulation, short bunching length, and amplitude and phase stability of the output signal. Many of these unexpected features were revealed in two separate experiments: one with a lower current beam (5 kA, 2-cm beam radius), and the other one with a higher current beam (16 kA, 6.6-cm beam radius). Three gigawatts of RF power at 1.3 GHz were generated with the large diameter beam at an efficiency of 35% with 37-dB gain. These experiments are reviewed, along with a combination of particle simulation results and analytic models which facilitate the interpretation. Special attention is paid to the unfamiliar features of these amplifiers, and the critical problems which must be solved before such amplifiers can fulfil their potential in a wide range of applications are addressed. >

Automatic gain control apparatus and method

Abstract: An automatic gain control apparatus and method which optimally adjusts the gain of an amplifier to compensate for time-varying energy levels of a received input signal. A control input signal for adjusting the gain of the amplifier is determined by the selective average energy level of a present input signal, the transfer function characteristic of the amplifier and a previous control signal. A fast loop response time maintains the energy level of the amplified output signal at a nominal level.

Linear-modulation type radio transmitter

Abstract: The present invention relates to a radio transmitter which transmits from an antenna a carrier wave linearly modulated based on a signal to be transmitted. Since a monitor wave with the predetermined level applied to a transmission power amplifier is amplified and the level of the amplified monitor wave is thereafter detected, followed by adjustment of the gain of the transmission power amplifier based on its level detected, or since the comparison between the level of an envelope component of a signal prior to modulation and that of an amplified signal is made and the gain of the transmission power amplifier is adjusted based on the result of its comparison, mean transmission power is maintained at a predetermined value.

Adaptive linearisation using pre-distortion

Abstract: One method of linearisation for class C RF power amplifiers is to pre-distort the drive signal. It is necessary to adjust the pre-distort waveform so that it can track changes in amplifier characteristics. An adaptive predistortion technique which uses a digital signal-processing microprocessor and memory look-up tables is described. The method differs from a previously described adaptive predistortion technique by using much smaller table sizes, with the result that conversion speeds are much higher. The disadvantage is that the processing overhead is higher, which puts a limit on the maximum data rate of the system. Low data rate services such as are found in mobile satellite applications ( >

Stored program controlled module amplifier bias and amplitude/phase compensation apparatus

Abstract: A stored program amplifier compensation apparatus utilizing sensing elements to provide the operational states of an RF power amplifier to a controller processor unit which utilizes the operational data to provide a bias control signal to the RF power amplifier. Look-up tables which are stored in the controlled processor unit, contain a bias control signal for all the possible operational combinations.

Amplifying with directly coupled, cascaded amplifiers

Abstract: A signal is amplified with a plurality of amplifiers (12-18), each amplifier having a reference port (22), a reference node (C) coupled to the reference port, and a signal port (22), and each amplifier being supplied by a power source (30-36) with operating potential with respect to the reference node that is coupled to the reference port of that amplifier. The amplifiers (12-18) are cascaded in a manner selected so that the output of a first amplifier (12) (which receives the signal to be amplified at its input port) drives the reference node (22) of a second amplifier (14), and the reference node (22) of the first amplifier (12) provides an input at the signal port (20) of the second amplifier (14), whereby the first and second amplifiers are directly coupled together to amplify the applied signal.

Levelling control circuit

Abstract: A levelling control arrangement for an RF transmitter circuit which additionally compensates for filter ripple, i.e. frequency dependant power variations caused by the filter (7) disposed between a transmitter amplifier (3) and an antenna (8). The forward and reflected power is sampled by a dual directional coupler (5) between the amplifier (3) and the filter (7). Signals V fwd and V rev are thus obtained indicative of the forward and reflected power levels respectively. The reflected signal V rev is subtracted from the forward signal V fwd at comparator (22) and the difference signal V diff is compared with a reference signal Vref at comparator (25) to produce a signal V c which is used to control the gain of the amplifier (3) in such manner that the power developed by the amplifier increases as the signal V rev increases and vice versa. To protect against excessive reflected power levels a limiter (23) may be included which causes the power developed by the amplifier to be reduced only if V rev exceeds a pre-set threshold.

Method and apparatus for reducing the peak envelope voltage of an RF transmitter while maintaining signal average power

Abstract: The average RF power output of an independent sideband diversity radio transmitter, modulated by a multiple tone data signal, is increased while the RF output peak envelope voltage is held constant. For diversity operation the same information, as a combination of the data tones, is applied to both the upper and lower sideband channels of the RF translator. Adding predetermined phase shifts between the upper and lower sideband audio tone pairs results in a reduced peak envelope voltage at the composite RF output. The final RF amplifier gain can then be increased resulting in a higher average RF power output.

Spectral dependence of gain and noise in erbium-doped fiber amplifiers

Abstract: A two-level model of the erbium-doped fiber amplifier is used to analyze the dependence of the amplifier gain saturation, saturated output power, and excess noise factor on pump and signal wavelengths. Measured data are presented confirming that the dependence of the gain, output saturation power, and noise of erbium-doped fiber amplifiers on the signal and pump wavelength can be described by simple equations derived from the model. >

Procedure for forming low power levels in a radio telephone transmitter

Abstract: The present invention concerns a procedure for forming low power levels in a radio telephone transmitter in which high power levels are produced in a controllable amplifier stage (1), for instance in a class-C power amplifier. According to the procedure, a RF signal is before the amplifier stage (1) divided into two branches in a power divider (4), in one of which the Rf signal is conducted to said amplifier stage (1) for forming high power levels, and in the other branch the RF signal is conducted to an element (5) by which low power levels are produced, and said branches are com­bined in the output (RFout) of the transmitter. The element (5) is e.g. a PIN diode attenuator.

A low-power wide-band amplifier using a new parasitic capacitance compensation technique

Abstract: A 3-mW 800-MHz amplifier with a voltage gain of 10 dB is discussed. The parasitic junction capacitance of a transistor is the major factor limiting the bandwidth particularly for low-power amplifiers. In addition to the pole at the input node, the pole at the output node may become dominant in low-power amplifiers, which use high-speed bipolar transistors. A parasitic capacitance compensation technique to expand the bandwidth in this type of amplifier is discussed. This technique compensates for both capacitances at the input and output nodes and enhances the bandwidth and the gain-bandwidth product. The measured data demonstrate that this technique expands the bandwidth to about twice that of a conventional differential amplifier. In addition, circuit simulation predicts that this technique expands the bandwidth by about 40% over a conventional peaking technique. A stable frequency response without any overpeaking or oscillation problem has been achieved by utilizing the parasitic junction capacitances of dummy transistors as the compensation capacitance. >

High gain two-stage amplification with erbium-doped fibre amplifier

Abstract: Unsaturated net gain of 51 dB is obtained for 1.551 mu m signal light by using two-stage erbium-doped fibre amplifiers pumped by 1.48 mu m laser diodes. This is achieved by using both an optical bandpass filter to suppress amplified spontaneous emission from the first stage amplifier and a bidirectional pumping scheme in the second amplifier to increase saturation output power. >

Fully differential CMOS power amplifier

Abstract: Fully differential power amplifier comprising one high gain input stage (A1) and one AB class output stage (A2) realized in CMOS technology. Each of the two stages (A1, A2) is provided with a common mode feedback circuit (CMF1, CMF2) to set the working point thus optimizing the amplifier overall dynamic range. Besides a power dissipation reduction circuit (PWD) is provided to limit the power dissipated during the idle state of the power amplifier. In particular, the topology of the amplifier is fully symmetrical. In this way, a wide range output signal on a low resistive load, a very small harmonic distortion, as well as a low power consumption are achieved.

Wideband class AB (push-pull) current amplifier in CMOS technology

Abstract: A wideband class AB (push-pull) current amplifier realised with only ten MOS devices is described which provides very low input resistance, good large signal behaviour and large bandwidth. Detailed analysis of the proposed circuit is presented. The two amplifier circuits composed of simple and cascode current mirrors are simulated and their performance characteristics compared.

Transmitter arrangement for digitally modulated signals

Abstract: A radio transmitter arrangement for e.g. QAM signals compri­ sing a class C output transistor amplifier (AMP). The control voltage generator (CVG) comprises a memory, whereby the I,Q -signals (I,Q) of the modulating signal (DM) address the control voltage generator (GEN), the information of which is used as a control signal (CS) acting as the collector voltage to control the amplifier output level (RF). The information can be modified to compensate for temperature variations and other non-linearities.

Monitoring and/or control of optical amplifiers

Abstract: Briefly, in this invention, the output optical power of an optical amplifier is determined by detecting and measuring the electrical signal induced on the bias lead of the optical amplifier when an optical data stream with additional amplitude modulation passes through the optical amplifier. This additional amplitude modulation can consist of a base band signal, a pilot tone and/or a sub-carrier which is amplitude modulated, frequency modulated or phase modulated. The modulation depth and bandwidth of the additional amplitude modulation should be kept small enough that the data stream is not excessively affected. The induced electrical signal provides a measurement of the optical power at the output facet of the optical amplifier. Control of the output power of the optical amplifier is effected by controlling the bias current applied to the bias lead of the optical amplifier. Thus, the output power of an optical amplifier can be monitored and telemetry signals can be received without interception of the data stream. The additional amplitude modulation of the data stream can be effected at the transmitter or by modulation of the bias current of an optical amplifier for transmission downstream. With this invention, no optical power is lost when the output power generated by an optical amplifier is monitored and modulation of the data stream can be effected without the use of additional optical components.

Rf wideband high power amplifier

Abstract: A r.f. wideband high power amplifier (1) receives an input signal at its input via a coupler (7) whenever a signal for amplification is applied to an input port (15). The output of the amplifier (1) is tapped by a coupler (8) and fed to an input of a comparator (3). The input signal applied at the input port (15) is fed to a second input of the comparator (3) via a delay line (5), arranged to introduce a delay substantially equal to that of the power amplifier (1). The comparator (3) produces at its output an error signal representative of the difference between the input signal fed via the amplified and the delayed path. A combiner (16) serves to introduce the amplified error signal to the amplifier output signal such that the error signal is in anti-phase therewith. Thus, the resultant signal produced at an output port (4) has had feed forward distortion cancellation. In accordance with the present invention the arrangement further includes an amplitude compensating network (8) in the form of a PIN-diode attenuator, controlled by a signal from a comparator (14). The comparator (14) provides a control signal to the attenuator (8) in accordance with the respective levels of signal from a first detector (17) and a second detector (18). The feedback control loops are arranged to function with a fast response time with respect to the period of the highest frequency of the input signal.

Ultra high speed scan system

Abstract: A high speed scanning radio has conventional RF amplifier, a mixer, a frequency synthesizer for the generation of local oscillator signals, an IF amplifier, a demodulator, and an audio output stage. The receiver includes a memory for storing a plurality of frequency codes corresponding to respective radio channels and a scan control for reading those codes, two for each channel, into the frequency synthesizer. A linear combination of each pair of distinct frequency codes is utilized to generate a local oscillator signal. A squelch circuit including a multi-order analog highpass filter, noise diode detector, a multiplexer, an analog to digital converter, and an arrangement for storage of successive average values of noise, and for comparing those successive noise values with one another to provide a noise difference and for comparing successive noise differences with a predetermined squelch control value, detection of the presence of a signal on a channel being indicated when successive noise differences exceed the predetermined squelch control value. The squelch circuit disables the audio output stage in the absence of a detected signal on any one of the channels corresponding to said sequentially read pair of frequency codes, and the squelch circuit is deactivated and the scan control interrupted upon detection of the presence of a signal on a channel.