Showing papers on "Output impedance published in 1995"

Design of Matching Networks for Low Noise Preamplifiers

Abstract: This paper discusses matching networks that minimize inductive coupling between the antennas within an array while simultaneously insuring minimum noise contributions from preamplifiers. Typical low noise preamplifier designs require a strong mismatch between the source impedance and the amplifier input impedance (reflection coefficient close to one) to achieve optimal noise performance. This is in contrast to the familiar impedance match known from communication theory where input and source impedances have complex conjugate values for maximizing the power transfer from source to amplifier. The high input reflection coefficient of low noise amplifiers can be exploited to reduce antenna currents by using lossless impedance transformations to create a high impedance at the coil terminals while simultaneously maintaining a low noise figure for the amplifier. The networks presented here constitute an improvement over previous work because they give additional freedoms regarding the values of the network components and the amplifier input impedance. The technique has been formalized and coded in MathCad, making the design of realizable networks a simple process.

Automatic antenna tuner for low-cost mobile radio

Abstract: An automatic antenna tuner which conjugately matches the impedance of an electrically small antenna to the impedance of a transmit amplifier output stage by using a pi-type impedance matching network with adjustable capacitive circuit components which are preferably implemented using a low cost escapement mechanism. During an initial set up tuning procedure, a resistive Wheatstone bridge detector is disposed between the output of the power amplifier and the input to the pi network, to feedback a measure a degree of match of the pi network to a controller. The capacitive elements in the legs of the pi network are then electromechanically adjusted under the operator of the controller until an optimum setting is found. These initial impedance values are determined for each frequency in an operating range and then stored in a non-volatile memory. As a second step in the tuning procedure, a fine adjustment is made to the stored optimum impedance values just prior to transmission, to accommodate changing environmental conditions and the like.

Modeling magnetically insulated devices using flow impedance

Abstract: In modern pulsed power systems the electric field stresses at metal surfaces in vacuum transmission lines are so high that negative surfaces are space‐charge‐limited electron emitters. These electrons do not cause unacceptable losses because magnetic fields due to system currents result in net motion parallel to the electrodes. It has been known for several years that a parameter known as flow impedance is useful for describing these flows. Flow impedance is a measure of the separation between the anode and the mean position of the electron cloud, and it will be shown in this paper that in many situations flow impedance depends upon the geometry of the transmission line upstream of the point of interest. It can be remarkably independent of other considerations such as line currents and voltage. For this reason flow impedance is a valuable design parameter. Models of impedance transitions and voltage adders using flow impedance will be developed. Results of these models will be compared to two‐dimensional, time‐dependent, particle‐in‐cell simulations.

Method of programming a desired source resistance for a driver stage

Abstract: The output impedance in a CMOS output driver stage is programmed and compensated by complementary current mirrors that are MOS devices in series with each of the conventional pull-up and pull-down devices. The conduction of these additional complementary devices is controlled according to complementary programming signals that are compensated for variations in manufacturing process parameters as well as for changes in temperature. A P-type programming signal may be referenced to +VDD and be produced from an N-type programming signal referenced to GND by the action of a gate voltage mirror that includes symmetrical N-type and P-type FET's in series. The N-type programming signal may be produced in the first instance from the gate voltage of an N-type FET used in a feedback loop that servos an external programming voltage to track an internally generated reference voltage. That gate voltage exhibits variations that reflect differences attributable to both process variations and to temperature. Those exhibited variations are communicated by a current mirror to a gate voltage mirror that produces the complementary programming signals, and which themselves constitute negative feedback. The complementary current mirrors are of known of gain, which in conjunction with knowing the value of VDD, allows the determination in advance of a definite table of programming resistance values versus output impedances.

High input impedance filters with low component spread using current-feedback amplifiers

Abstract: A new configuration for high input impedance bandpass, lowpass and highpass filters with low component spread using two current-feedback amplifiers is presented. It has the following features: orthogonal control of the natural frequency and quality factor by grounded resistors or capacitors, simple conversion into a voltage-controlled filter, minimum active components, low active and passive sensitivities, low component spread suitable for high-Q applications and low output impedance. Experimental results are given to demonstrate the feasibility of the proposed circuits. >

Apparatus and method for a combination D/A converter and FIR filter employing active current division from a single current source

Abstract: An active current steering semi-digital FIR filter for a digital-to-analog conversion circuit, which includes a shift register having a 1-bit digital input stream and a plurality of output taps, where each output tap provides a 1-bit signal which has a value of a logic 1 or a logic 0, and a plurality of current paths, where each path includes an active element, such as a transistor, having a relatively high output impedance, which is connected to a common current source, and to an op amp for current-to-voltage conversion. The relatively high output impedance of the active current steering element causes any error term resulting from offset at the op amp inputs to be minimized.

A modular, permanent-magnet generator for variable speed wind turbines

Abstract: The variable speed operation of a high pole-number, modular, PM generator is discussed and the benefits of the modular arrangement for variable-speed wind turbine generators are demonstrated. The single phase output of each stator module is rectified and fed to a common DC link. The power delivered by each module is limited by its internal impedance. However, a capacitor connected in parallel with the coil can partly compensate and enhance the output power. The resulting significant improvements are demonstrated by simulation and experiment.

Fast transition RF impedance matching network for plasma reactor ignition

Abstract: An impedance matching network for an RF coupled plasma reactor having RF excitation apparatus receiving RF power through the impedance matching network from an RF generator for producing a plasma in the reactor has at least one capacitor connected to the output of the RF generator and having a capacitance value providing an impedance match to the plasma impedance during a steady state of the plasma, at least a first rapidly tunable capacitor connected in parallel with the one capacitor, the rapidly tunable capacitor being rapidly switchable between a high capacitance value providing a match to the plasma impedance during the onset of plasma ignition and a lesser minimum capacitance value, and a controller for rapidly switching the rapidly tunable capacitor from the high to the lesser capacitance value upon reaching the plasma steady state.

Standby power circuit arrangement

Abstract: A power supply circuit arrangement for electrical equipment, such as a loudspeaker with an integral power amplifier, which can be switched between an operational mode and a standby mode in response to a detected on/off signal, provides a desirable isolation of the main supply voltage from the detector. The arrangement comprises a transformer, having a primary winding and a secondary winding, and a switched impedance device between the transformer and the power supply input. The switched impedance device is switchable between high and low impedance states in response to the detected on/off signal. A control circuit for detecting the on/off signal and switching the variable impedance states is connected in common with a main circuit of the equipment to the secondary winding of the transformer, so that their respective supply voltages are both switched, in common, by switching of the impedance device. The control circuit and variable impedance device isolate the detector from the power supply. In the operational mode, the variable impedance is switched to its low impedance and the common voltage supplied to the main circuit and the control circuit is sufficient to operate both of them. In the standby mode, the variable impedance is high and the common voltage is inadequate for normal operation of the main circuit but adequate for normal operation of the control circuit.

Optoelectronic controlled RF matching circuit

Abstract: A photonic RF impedance matching system that includes an RF photonically controlled impedance matching circuit having adjustable impedance and power transfer characteristics, and feedback control circuitry for optically controlling the impedance matching circuit.

Buffer circuit having variable output impedance

Abstract: An output buffer circuit (20) has an output impedance that is adjustable. An external resistor (32) having a resistance that is a multiple of the desired output impedance is coupled to the output buffer circuit (20). A voltage across the resistor (32) is converted to a digital code using an analog-to-digital (A/D) converter (22). A digital code from the A/D converter (24) is used to adjust a resistance of a binary weighed transistor array (45) to match the resistance of the external resistor (32). A plurality of binary weighted output transistors (153, 154, 155) are selected in response to the digital code to adjust the output impedance to match the characteristic impedance of a load driven by the output buffer circuit (20). The output impedance is easily adjustable by changing the resistance of external resistor (32), allowing the output buffer circuit to drive various load impedances.

Transmitting-receiving circuit for radiocommunication apparatus, semiconductor integrated circuit device including the circuit, and radiocommunication apparatus including the same

Abstract: A changeover switch switches connection between an antenna and a transmitter amplifier and connection between the antenna and a receiver low noise amplifier, from one to the other. A first wire having characteristic impedance of 50 Ω connects the antenna and the changeover switch. A receiver matching circuit matches input impedance of the receiver low noise amplifier with the output impedance of the transmitter amplifier. An antenna side matching circuit matches the input impedance of the receiver low noise amplifier, which is matched with the output impedance of the transmitter amplifier by the receiver matching circuit, and the output impedance of the transmitter amplifier with the characteristic impedance of the first wire. The transmitter amplifier is connected with the changeover switch via a first coupling capacitance, and the receiver matching circuit is connected with the changeover switch via a second coupling capacitance.

High-power high-temperature superconducting microstrip filters for cellular base-station applications

Abstract: We report narrowband microstrip filters with low insertion loss and high power-handling capabilities made from YBa/sub 2/Cu/sub 3/O/sub 7/(-x) high-temperature superconducting films. One 5-pole filter on a LaAlO/sub 3/ substrate, consisting of backward-coupled and forward-coupled resonators, can handle over 27 W input power at 10 K. It has 1% fractional bandwidth and 10-/spl Omega/ internal impedance. The insertion loss increase in passband at 10 K, as the input power changed from a few mW to 27 W, is less than 0.25 dB. We also report a forward-coupled microstrip filter centered at 2 GHz, with a 1.2% fractional bandwidth, 10-/spl Omega/ internal impedance, and parallel-coupled feed lines. We applied over 10 /spl Omega/ to the filter at 45 K without noticeable degradation of the filter performance. The insertion loss at 45 K is less than 0.2 dB. The return loss is better than 12 dB. >

Cascadable current-mode filters using single FTFN

Abstract: A new configuration for realising current-mode filters using a single four-terminal floating nullor (FTFN) is presented. It can realise lowpass, bandpass, highpass, notch and allpass filters from the same configuration. This configuration has a high output impedance, so the synthesised current-mode filters can be cascaded without additional buffers. Moreover, the resultant current-mode filters will be insensitive to the current tracking error of an FTFN. Experimental results that confirm the theoretical analyses are obtained.

New technique for the accurate location of earth faults on transmission systems

Abstract: A new technique for the single-ended location of resistive earth faults on power transmission lines is presented. Unlike previous work, the algorithm developed has inherent insensitivity to setting errors in the remote source impedance value. This is an important feature, since the remote source impedance often varies significantly under operational conditions. The paper shows the theoretical development of the algorithm, together with a detailed consideration of the hardware aspects. Results are presented for a standard 400 kV transmission line application study.

Controlled impedance amplifier

Abstract: An amplifier with controlled output impedance utilizing current and voltage feedback to set gain and output impedance is disclosed. The voltage feedback is provided by feedback resistor connected from the output to the inverting input. The current feedback is provided by feeding a current proportional to the output current directly to the inverting input of the amplifier. An error amplifier is used to maintain the proper ratio of the current feedback to the output current and to cancel the effects of the output device impedance on the overall output impedance. Two such amplifiers driven by complimentary signals form a differential amplifier with controlled output impedance. Because the output impedance is a function of the voltage feedback resistance and the current feedback ratio, it is possible to digitally control the output impedance by changing the feedback resistance and/or the current feedback ratio.

Current mode I/O for digital circuits

Abstract: A digital input/output interface for use with two digital circuits connected by a transmission line having a characteristic impedance Z 0 includes a current driver in one of the digital circuits and a current receiver in the other digital circuit. The current driver is configured to generate a current in the transmission line when a digital signal is applied to the current driver. The current receiver includes a current conversion element connected to the transmission line at an input node through an input impedance Z in and adapted to convert the current in the transmission line into an output voltage, and an active termination element configured to actively adjust the input impedance Z in to match the characteristic impedance Z 0 of the transmission line. An impedance transforming receiver for use with a transmission line having a small characteristic impedance Z 0 and carrying a relatively small current mode signal includes the following: an input element connected to the transmission line and configured to receive the small current mode signal, the input element having a small input impedance Z in that substantially matches the characteristic impedance of the transmission line; and a high impedance output element adapted to convert the small current mode signal into an output binary voltage having a noise margin large enough for digital communication.

Control and implementation of a three-phase voltage-doubler reversible AC to DC converter

Abstract: In this paper, a novel three-phase bidirectional interface is proposed by using only four active switches to simplify the hardware circuit and achieve unity power factor, sinusoidal input current, adjustable output voltage and bidirectional power flow capability. To ensure obtaining clean input current waveform, the current tracking mechanism is analyzed together with graphical aid and some critical design conditions are presented. Finally, a small-signal model is derived and, in addition to the feedback control, an instantaneous voltage detector is proposed for the added feedforward control to achieve almost zero output impedance and zero audio susceptibility. A prototype hardware circuit is constructed and some experimental results are presented for demonstration. >

Small signal analysis of the LCC-type parallel resonant converter using discrete time domain modeling

Abstract: Discrete state-space modeling of the LCC-type parallel resonant power converter is presented. Using these large signal equations, small signal modeling of the power converter is obtained. Multiple loops have been used for the closed loop operation. State variable feedback control has been integrated with the linear small signal state-space model and the associated control aspects are studied. The small signal state-space model has been used to study the small signal behavior of the power converter for open loop and closed loop operation for parameters like control to output transfer function, audio-susceptibility and output impedance. Key theoretical results have been experimentally verified.

System for measuring line to ground impedance

Abstract: A line isolation monitor (LIM) indicates the maximum hazard current of an ungrounded polyphase power distribution system. The LIM is microcontroller based and continuously monitors a fault impedance for the distribution system. The fault impedance is determined by the LIM by injecting a continuous sine wave measurement current into a ground terminal to generate a measurement voltage across the fault impedance. Using the measurement voltage and current, the LIM calculates the fault impedance and, using this impedance, calculates the hazard current based on the maximum line to ground voltage of the ungrounded system. The LIM has means for self-calibration and self-testing while on-line and during a power-up sequence to verify that components in the measurement circuitry are within specified tolerances.

Pulse controlled impedance compensated output buffer

Abstract: An improved buffer circuit, particularly a pulse controlled impedance compensated output buffer. The improvement includes two drivers which are activated during a portion of the switching time of the output. The two drivers are activated for different durations which partially encompass the output transition and may be overlapping. A feedback circuit may also be used, providing further impedance compensation. By the feedback circuit actuating a driver in response to a difference between a reference signal level and an output signal level, the total output drive strength of the buffer is better tailored to the load impedance. The reference signal level may be sampled at a point during the output transition.

Line impedance measurement: a nondisruptive wideband technique

Abstract: Line impedance is the basis for many power system calculations. This paper presents a technique for measuring line impedance as a function of frequency on an energized line in normal operation using commercially available equipment. A small sinusoidal current of predetermined frequency is injected into the line, and a network analyzer calculates line impedance at that frequency from the measured magnitude and phase of the injected current and resulting voltage. The measurement is repeated over a range of frequencies to produce a wideband impedance-versus-frequency characteristic. The element values for lumped equivalent circuit models are extracted from the measurement. These values are shown to be frequency dependent. Inexpensive portable equipment for performing this measurement is also briefly introduced.

Solid state plasma chamber tuner

Abstract: A solid state automatic tuner is used in a plasma processing system for measuring and adjusting a voltage standing wave ratio of the system. The tuner has a switched variable inductor circuit controlled by an automatic control system coupled to an impedance matching circuit. The impedance matching circuit provides an intermediate impedance and matches an output impedance of an RF generator to the varying impedance of a plasma chamber. A variable inductor of the switched variable inductor is constructed as a transformer and allows different values of inductance to be switched in and out of a secondary winding of the transformer. FET switches control pin diodes permitting the different values of inductance to be switched in and out in steps. A VSWR comparator of the control system continuously compares a desired VSWR set point for the system to the current VSWR of the system. A sequence scanner controls the FET switches.

CMOS terminating resistor circuit

Abstract: An improved CMOS termination is disclosed wherein a transmission gate provides the proper impedance for matching a termination with the characteristic impedance of the line.

Signal conditioning apparatus

Abstract: A signal conditioning system that receives inputs from at least one pair of conductors connected to its input. Each such input is processed by an input filter and presented to a buffer amplifier. Each such input filter and buffer amplifier refers to and is powered by independent power sources whose power return reference potentials are independently determined by the potential of the corresponding input signal potential reference conductor for the signal frequencies of interest. The outputs of all such buffer amplifiers, the power return reference potentials, and the power return reference potential of the conditioning circuit output are all appropriately added or subtracted in the next circuit stage. This circuit stage consists of an amplifier buffer having low output impedance which is powered by another independent power source whose power return reference potential is independently determined by the potential of the output signal reference conductor. The output of this circuit stage is connected to an output inductor circuit which in turn drives the output signal conductor. The output includes a filter, and is designed to decouple unstable loading conditions while rejecting external influences on the output signal. The invention also includes means that connect the reference potential of the destination of the output conductors to the system power ground potential. The present invention provides a relatively inexpensive and efficient way of reducing or eliminating interference caused by coax cabling in audio, power and video amplifiers, for example.

Effect of state of charge on impedance spectrum of sealed cells Part I: Ni-Cd cells

Abstract: Alternating current impedance spectroscopy (ACIS) was performed on commercial sealed Ni-Cd cells. A method previously developed in the literature was modified to determine the state of charge of sealed Ni-Cd cells by obtaining the impedance spectrum in a wide frequency range. The impedance parameters were sensitive to state of charge at low frequencies. A modified Randles' circuit was used to fit the impedance data. Appropriate modifications were made to account for an additional high frequency arc or a low frequency finite diffusion element. The effect of the state of charge on the equivalent circuit parameters was determined.

Radio-frequency power amplifier with input impedance matching circuit based on harmonic wave

Abstract: In an RF power amplifier, an input-side RF terminal is connected to a gate of an FET via an input-side matching line. A source of the FET is grounded. A drain of the FET is connected to an output-side RF terminal via an output-side matching line. To a line connected to the drain of the FET, a circuit for controlling an output impedance for the secondary harmonic wave is connected, including a first line and a first capacitor. To a line connected to the gate of the FET, a circuit for controlling an input impedance for the secondary harmonic wave is connected, including a second line and a second capacitor. The length of the second line is set so that an electric length thereof becomes longer than one-fourth of the wavelength for the fundamental wave frequency. Thus, an impedance for the harmonic wave is controlled at the input side of the power transistor.

Transmission line driver with self adjusting output impedance

Abstract: A flexible and efficient integrated circuit chip that includes pad drivers for driving an impedance of a transmission line, wherein the integrated circuit further includes all additional circuitry to automatically adjust a matching impedance of the pad drivers. The integrated circuit chip includes a set of selectively activatable pad drivers and a counter coupled with the drivers for selectively activating an initial number of members of the set of the pad drivers to drive the transmission line with a test pulse. The integrated circuit chip further includes a comparator having a first input for sensing a voltage amplitude of the test pulse and a second input coupled with a voltage reference for comparing the voltage amplitude of the test pulse with the reference voltage. An output of the comparator is coupled with the counter for increasing the counter's initial number of selected members of the set of the pad drivers if the voltage amplitude of the test pulse is less than the reference voltage. Such iterative capabilities of the invention provide an automatic optimal selection of the pad drivers, so that the parallel impedance of the activated drivers provides a good match with the impedance of the transmission line.

An investigation of harmonics attenuation and diversity among distributed single-phase power electronic loads

Abstract: Widely distributed single-phase power electronic loads are an increasingly important source of harmonics in power distribution systems. The objective of this paper is to investigate the cumulative harmonic current characteristics of a large number of such loads. A complete analytical model for the most common load type is derived. This model is then used to investigate the impact of 1) interaction due to a shared source impedance, 2) variation in power level, and 3) variations in circuit parameters, on individual and cumulative current harmonics. The key findings of the paper are that * diversity and attenuation are very important factors in predicting the behavior of distributed single-phase power electronic loads, especially for the higher-order harmonics, and that ** due to these two factors, the commonly-used fixed current injection method, using arithmetic sums of harmonic current magnitudes, can significantly overestimate the cumulative harmonic currents produced by these loads.

Impedance measurement in a high-voltage power system

Abstract: A power monitoring instrument evaluates and displays the source impedance, load impedance, and distribution system impedance of an alternating current power system using voltage and current measurements taken at a source and load of the power system. The power monitoring instrument and associated voltage and current pods for coupling to voltage probes and current clamps incorporate unique safety features to minimize operator exposure to high-voltage. The measurements are performed noninvasively without disconnecting elements of the power system. Evaluation of impedances takes advantage of incidental variations in the load characteristics.