Showing papers on "Output impedance published in 1996"

Control topology options for single-phase UPS inverters

Abstract: Several control topologies for single-phase UPS inverters are presented and compared, with the common objective of providing a dynamically stiff, low THD, sinusoidal output voltage. Full state feedback, full state command controllers are shown utilizing both filter inductor current and filter capacitor current feedback to augment output voltage control. All controllers presented include output voltage decoupling in a manner analogous to "back-EMF" decoupling in DC motor drives. Disturbance input decoupling of the load current and its derivative is presented. An observer-based controller is additionally considered, and is shown to be a technically viable, economically attractive option. The accuracy transfer function of the observer estimate is used to evaluate its measurement performance. Comparative disturbance rejection is evaluated by overlaying the dynamic stiffness (inverse of output impedance) frequency response of each controller on a single plot. Experimental results for one controller are presented.

Modeling and dynamic analysis of paralleled DC/DC converters with master-slave current sharing control

Abstract: A simple, application-oriented, transfer function model of paralleled converters employing master-slave current-sharing (MSC) control is developed. Dynamically, the master converter retains its original design characteristics; all the slave converters are forced to depart significantly from their original design characteristics into current-controlled current sources. Five distinct loop gains to assess system stability and performance are identified and their physical significance is described. A design methodology for the current share compensator is presented. The effect of this current sharing scheme on "system output impedance" is analyzed.

Method and apparatus for electrode and transthoracic impedance estimation

Abstract: Impedance across a load, such as a pair of face-to-face electrodes, or across electrodes in contact with a patient's chest cavity, respectively, is modeled as a resistor in series with a capacitor, wherein the reactance component of the impedance equals 2π*frequency/capacitance. A reference square wave voltage is applied to the load in series with a selected load resistor, and a response voltage is measured across the load. Both the reference voltage and the response voltage are then used to estimate a transfer function between them. Equating this transfer function to a resistor-capacitor circuit model results in estimation of the actual resistance and capacitance components of the true impedance.

Programmable impedance output driver

Abstract: An output driver circuit is disclosed that generates an accurate and predictable output impedance driver value corresponding to a programmable external impedance. The output driver circuit includes an external resistance device, voltage comparator device, control logic, an evaluate circuit and off-chip driver (OCD) circuit. Voltage from the external resistance device (VZQ) is compared with voltage created from the evaluate circuit (VEVAL) by the voltage comparator device, which indicates to the control logic whether VEVAL is greater than or less than VZQ. The control logic will adjust the evaluate circuit accordingly with a count until the two voltages are basically equal (i.e., the count is alternating between two adjacent binary count values). At which time the control logic operates the OCD with the lower of the two adjacent count values to produce a proper and predictable driving impedance.

Current approaches to analogue instrumentation design in electrical impedance tomography

Abstract: Electrical impedance tomography (EIT) is a novel medical imaging method, which allows reconstructed tomographic images of the internal impedance of a subject to be made with the use of a ring of electrodes. High precision impedance measurements are needed, because the image reconstruction process is ill-conditioned and small errors in measurement can lead to large errors in the final image. In practice, there are formidable instrumentation problems, due to the interaction of finite current drive output impedance, recording amplifier common mode rejection, and unequal skin - electrode impedances. A number of different EIT systems have been constructed or are under development. These employ differing strategies, such as additional electrodes, multiple electrode current injection, or recording at multiple frequencies, to improve image accuracy. This paper reviews the nature of the instrumentation problems and the designs employed by differing groups in attempting to overcome them.

Apparatus for matching a variable load impedance with an RF power generator impedance

Abstract: An apparatus for matching the variable impedance of a load with the fixed impedance of a radio frequency (RF) power generator to provide maximum power transfer. The impedance matching network further allows an RF power generator to vary the frequency of the voltage applied to a load, e.g., a plasma chamber as may be utilized in semiconductor or flat panel plasma display manufacturing processes. The impedance matching network further utilizes fixed solid state components to adjust the impedance of the attached load to provide maximum power transfer between the generator and the load. A parallel switched capacitor network is controlled by an electrical switching means such as PIN diodes to turn fixed capacitors on or off. A means for varying the frequency of the applied voltage is used to match the impedance of the load with the impedance of the RF power generator within milliseconds.

Power dissipation and impedance measurements in radio‐frequency discharges

Abstract: An improved method for the measurement of the power consumed in low pressure, radio frequency discharges is presented. The method involves the measurement of current and voltage waveforms outside the reactor, and the determination of the discharge impedance and the network of parasitics. The measured waveforms are transformed to the equivalent ones at the powered electrode, by using an electrical circuit model of the stray impedance of the cell, with experimentally determined components. A tunable shunt circuit is used for minimizing displacement currents. The equivalent circuit contains elements which account also for resistive power losses in the cell‐shunt circuit. The obtained discharge power is compared with measurements of the total power output of the generator made by a power meter. Results concerning power consumption and impedance in argon and silane discharges are presented as a function of the excitation voltage and the pressure. In both cases there is a discharge impedance drop, for higher voltage or pressure, which leads to higher power consumption in the discharge. The measurements show that only a small, nonconstant part of the power is consumed in the discharge, whereas, the inclusion of resistive loses leads to more accurate results. The mechanisms of the discharge impedance drop are further discussed in terms of their relation to microscopic plasma phenomena and quantities.

Complete characterization of utilization-voltage power system impedance using wideband measurement

Abstract: Inexpensive portable instrumentation is used to measure the impedance of an example utilization-voltage power system. With the power system in normal operation, line-to-neutral, line-to-ground, and neutral-to-ground impedances are measured over a bandwidth of 20 Hz to 24 kHz. The measured impedance is presented as resistance and inductance which vary with frequency. Based on the measurements, additional calculations are performed to find the resistance and inductance of every conductor in the system. This complete wideband characterization of power system impedance provides valuable data for power quality calculations.

Continuous time programmable analog block architecture

Abstract: A programmable analog circuit apparatus receives a differential analog input signal and provides a processed differential analog output signal. The programmable analog circuit apparatus includes a first input transconductor, a differential amplifier, and a feedback transconductor. The first input transconductor has a programmable transconductance and includes an input transconductor positive input terminal and an input transconductor negative input terminal and an input transconductor positive output terminal and an input transconductor negative output terminal. The positive and negative input terminals are coupled to receive the differential analog input signal. The differential amplifier includes first and second amplifier input terminals and first and second amplifier output terminals. The positive and negative input transconductor output terminals are coupled to the first and second differential amplifier input terminals. The amplifier output terminals are coupled to the first and second amplifier input terminals. The amplifier provides the processed differential analog output signal via the amplifier output terminals. The feedback transconductor includes a positive feedback transconductor input terminal and a negative feedback transconductor input terminal and a positive feedback transconductor output terminal and a negative feedback transconductor output terminal. The positive and negative feedback transconductor input terminals are coupled to the first and second amplifier output terminals and the positive and negative feedback transconductor output terminals are coupled to the first and second amplifier input terminals. The feedback transconductor output terminals has a high output impedance.

High-drive CMOS output buffer with noise supression using pulsed drivers and neighbor-sensing

Abstract: A CMOS output buffer has a first stage with smaller driver transistors and a second stage having larger driver transistors. Both stages drive the output in parallel during the first half of a voltage transition, but the larger, second stage is disabled during the second half of the output voltage swing. The output voltage is fed back to an isolation circuit by a pulse generator which is triggered by the output reaching the switching threshold. The pulse generated disables the larger driver for a short period of time but later re-enables the driver. Thus the large driver remains on after the switching is complete, providing large IOH and IOL static currents. The pulse is long enough to keep the large driver disabled while reflections are received and ringing occurs after the voltage transition. Resistors in the smaller first stage absorb these reflections. The output impedance is pulsed to the higher impedance of the first stage when ringing occurs at the end of the voltage transition, but after the pulse ends the lower impedance of the large driver is seen. Pulses are sent to neighboring output buffers and are OR'ed together to disable adjacent output buffer's large drivers when noise in injected into the power or ground supplies.

Thermal impedance extraction for bipolar transistors

Abstract: This paper describes a method for extracting the thermal impedance of bipolar transistors. The measurement is a two-step process: first the fractional temperature coefficients are calibrated at dc and then a transient step response is measured to extract the thermal spreading impedance. Measurement configurations and an example measurement cycle are shown. The measurement results can be fitted to multiple-pole models for use in compact circuit modeling in SPICE.

Low distortion driver employing positive feedback for reducing power loss in output impedance that effectively matches the impedance of driven line

Abstract: A line driver with positive feedback reduces the output signal amplitude excursion required for driving a communication line, and enables the driver's output impedance to be synthesized using a reduced component value, thereby achieving a reduction in power loss through the output resistor, while simultaneously matching the effective electrical value of the driver's output impedance to the line. The line driver includes an operational amplifier having differential polarity inputs and an output. An output resistor, whose value is a fraction of the line impedance, is coupled between the amplifier output and an output node coupled to the line. A negative feedback resistor is coupled between the amplifier output and an inverting input. A further resistor is coupled between the amplifier output and a non-inverting input. The further resistor has a value of k*R, where m=(k+1)/(k-1), R is the value of each of input and negative feedback resistors, and m is the ratio of the desired output resistance Rt to the value Ro of the line driver's output resistor.

Wave shaping transmit circuit

Abstract: An integrated circuit driver for providing data to a communications channel comprises first and second output buffers coupled to first and second output conductors (e.g. bondpads) respectively. Each output buffer comprises a multiplicity of pull-up transistors and a multiplicity of pull-down transistors coupled to the associated output conductor through pull-up resistors and pull-down resistors, respectively. A multiplicity of delay circuits coupled to a data input node supply delayed data signals to the control terminals of the pull-up and pull-down transistors. Control circuitry is included for selectively activating the delay circuits. In a typical case, the control circuitry comprises multiplexers each having an output that is coupled to the input of a corresponding delay circuit. Advantages of the technique include a constant output impedance and waveshaping of the data output for reduction of harmonics. A typical application of the driver is in an Ethernet twisted-pair wire communication system, wherein external components (resistors and center-tapped transformer) may be eliminated.

Small, battery operated RF transmitter for portable audio devices for use with headphones with RF receiver

Abstract: A portable RF transmitter having an audio plug extending therefrom which mates with the earphone or output jack of an audio source such as a portable battery operated CD or tape player and having no external antenna The portable RF transmitter modulates audio signals from the audio source onto an FM carrier and transmits them to an FM receiver mounted on a headset worn by a user The RF transmitter uses its own ground circuit and the ground circuit of the audio source as two elements of a short dipole The two ground circuits are electrically isolated at RF by an RF choke but connected together at audio frequencies by the low impedance of the choke at audio The choke's leakage inductance also reduces the capacitive reactance of the dipole antenna for better power dissipation A transformer coupling the RF output to the dipole transforms the impedance of the dipole to a value closer to the output impedance of the RF transmitter

Universal filter with three inputs using CCII

Abstract: A voltage-mode universal filter with three inputs and one output using only plus-type current conveyors (CCII+) is presented. This circuit uses three CCII+s, three resistors and a minimum number of capacitors. It has low sensitivity, low output impedance and low component spread. The use of only CCII+s simplifies the configuration.

Insensitive current/voltage-mode filters using FTFNs

Abstract: A new configuration for realising insensitive current/voltage-mode filters using two four-terminal floating nullors (FTFNs) is presented. It can provide the curren/voltage-mode filters with reduced sensitivities. Moreover, the current-mode filters can have high output impedance and only grounded capacitors. The proposed universal voltage-mode filter with dual outputs can realise lowpass, bandpass, highpass, notch and allpass filtering functions. Simulation results are given to verify the theoretical analysis.

Stable matching networks for plasma tools

Abstract: Apparatus and method for obtaining stable matching networks for plasma tools for use in the plasma processing industry. In an RF plasma apparatus, running at a matched condition for a transmission line and the plasma tool matching network such that the input impedance at the input to the transmission line is different than that of the output impedance of an RF generator and such that when the plasma density in the plasma tool decreases the input impedance will match the output impedance of the generator.

Method and apparatus for high current electrode, transthoracic and transmyocardial impedance estimation

Abstract: Impedance across a load, such as a pair of face-to-face electrodes and/or a patient's transthoracic and transmyocardial impedance, respectively, is modeled as a resistor in series with a capacitor, wherein the reactance component of the impedance equals 2 π*frequency/capacitance. A reference square wave voltage is applied to the load in series with a selected load resistor, and a response voltage is measured across the load. Both the reference voltage and the response voltage are then used to estimate a transfer function between them. Equating this transfer function to a resistor-capacitor circuit model results in estimation of the actual resistance and capacitance components of the true impedance. Alternately, the impedance may be measured with a high current load, such as during a defibrillator discharge. In this case, the voltage input and outputs are sampled at a much faster rate for the resistance component estimation, with the capacitance initialization adapted for the specific type of defibrillator waveform input.

Regulated supply for voltage controlled oscillator

Abstract: A monolithic CMOS phase-lock loop (PLL) circuit provides a high frequency of operation suitable for RF applications. The PLL produces an output clock with high spectral purity and very low jitter. The output clock has a low static phase error relative to a reference input, making the PLL useful for clock synchronizing applications, such as clock recovery elements in transmission/recording channels. The PLL provides in-phase and quadrature signals from a voltage controlled oscillator (VCO) which has two differential transconductors. The second differential transconductor has a positive input coupled to a positive output of the first differential transconductor, a negative input coupled to a negative output of the first differential transconductor, a positive output coupled to a negative input of the first differential transconductor, and a negative output coupled to a positive input of the first differential transconductor. Each differential transconductor has a negative output impedance. Each differential transconductor includes a current controlled transconductor circuit (CCXG) and a voltage-current converter coupled to a first supply node for providing a current to the CCXG responsive to a voltage applied to a voltage control input of the differential transconductor.

Current-feedback opamp suitable for CMOS VLSI technology

Abstract: A CMOS current feedback opamp, suitable for VLSI technology, is presented. The design is based on a new voltage buffer topology with low output impedance achieved by using local current feedback. Simulation results show low power dissipation, wide bandwidth and very good linearity.

Measurement of Positive Displacement Pump Flow Ripple and Impedance

Abstract: The secondary source method forms the British Standard for pump fluid-borne noise testing. This is a powerful technique but requires care in order to produce accurate results. This paper describes ...

Methods and apparatus for measuring impedance in the body

Abstract: Methods and apparatus are provided for measuring the impedance of a patient's body. Pulse generating circuitry within a rate-responsive pacemaker is used to generate an impedance measurement signal that is applied to the body of the patient with conventional pacemaker leads. The impedance measurement signal contains a series of multiphasic impedance measurement waveforms, which have no net DC value and zero value after second integration. The impedance measurement signal allows the impedance of the body to be measured without interfering with external cardiac monitoring equipment such as electrocardiogram machines.

High speed fully differential operational amplifier with fast settling time for switched capacitor applications

Abstract: A high speed fully differential operational amplifier with fast settling time for switched capacitor applications includes a high gain active cascode applied to the operational amplifier's input stage transistors to improve the gain, provide a higher output impedance, and thus, reduce the Miller feedback gate drain capacitance of the input stage devices. This improves the speed of the amplifier. A biasing technique is used to keep the active cascodes biased during transient overload so that settling will not be adversely affected during the recovery of the cascodes. A pair of transistors are used to feed forward a fraction of the tail current to "keep-alive" the cascode transistors. In other words, the fraction of the tail current that is fed to the source of the cascode transistors via the keep-alive transistors effectively biases the active cascodes sufficiently so that they do not turn off completely during slewing.

High speed, high linearity CMOS buffer amplifier

Abstract: A low-noise class AB buffer amplifier which has a rail-to-rail output swing while driving large resistive and capacitive loads is presented in this paper along with the test results. The amplifier is fabricated in a 3 /spl mu/m double-polysilicon double-metal CMOS technology and has on-chip frequency compensating capacitors. The basic performance factors obtained in this design are: A/sub 0/=70 dB, GBW=5.5 MHz, SR=7 V//spl mu/s, and /spl upsi//sub n/=10nV//spl radic/Hz@100 kHz. With a supply voltage of /spl plusmn/5 V, the amplifier has a /spl plusmn/4.7 V output swing and features a low 30 /spl Omega/ open-loop output impedance. The total harmonic distortion is at a low -77 dB for a 7V/sub out,pp/ output level with the fundamental frequency of 20 kHz. From the test results, it is demonstrated that an overall high performance is achieved with this design.

Transmitter of wireless system and high frequency power amplifier used therein

Abstract: The output of a digital modulator is put into a power amplifying device, is distributed into n pieces in an n-power divider in the power amplifier, passes through n input phase shifters differing individually in the phase change amount, is amplified by n power amplifiers, passes through n output phase shifters to match the phase of n signals, is combined in an n-power combiner, and is issued from an output terminal to a phase shifter, and the output of the phase shifter is issued to a transmission antenna. Herein, the phase value of the phase shifter is determined so as to extend the region of the output load impedance for satisfying the specific value of unwanted radiation, and so that the output load impedance range of the load impedance of the power amplifier may be optimize to the impedance change range of the trans missionantenna, thereby eliminating the isolator and presenting a transmitting device of a portable wireless system realizing smaller size, higher performance, and lower cost of portable wireless system.

Combining multi-layers and composites to increase SNR for medical ultrasound transducers

Abstract: Current 1.5-D and 2-D array elements suffer low capacitance resulting in high electrical impedance. The impedance mismatch between the 50 /spl Omega/ transmitter source impedance and the high impedance array elements decreases efficiency. Multi-layer PZT designs using interlaminar vias have been proposed to solve this problem by lowering the impedance of the array element. Another problem is the poor acoustic match of PZT to tissue, which can be improved with PZT/polymer composite designs. By combining multi-layer PZT and composite designs, new transducers can be developed to further improve SNR. Multi-layer 1-3 composite transducer array elements have been modeled with 3-D FEM simulations and fabricated at 0.9 MHz. Another new design is a 16 PZT layer 2-2 composite with inter-laminar electrodes. According to finite element (PZFlex) simulations, the array element will have a resonant frequency near 4 MHz and an impedance magnitude of 50 /spl Omega/. Unlike conventional transducer arrays, this design operates in the transverse mode. Computer simulations show that despite the loss from operating in the transverse mode, this novel multi-layer 2-2 composite design will yield an overall SNR improvement relative to 2-2 composites and increased bandwidth relative to conventional PZT.

Impedance matching circuit in transmitter circuit and control method thereof

Abstract: In an impedance matching circuit used in a transmitter circuit, an occurrence of a reflection wave in an antenna is suppressed. The impedance matching circuit in a transmitter circuit includes a modulating circuit for modulating an input signal to output a modulation signal, a power amplifying circuit for power-amplifying the modulation signal, an antenna for outputting the signal power-amplified by the power amplifying circuit, a demodulating circuit for demodulating the signal power-amplified by the power amplifying circuit to output a demodulation signal, a band-outside-component detecting circuit for detecting a band-outside-component of the demodulation signal, a control circuit for outputting a control signal based upon the signal derived from the band-outside-component detecting circuit, and an impedance matching circuit for matching an input impedance of the antenna with an impedance of the power amplifying circuit by changing an impedance of the impedance matching circuit based upon the control signal.

High conversion gain CMOS mixer

Abstract: A mixer contains a multiplier circuit that includes MOS transistors configured as a Gilbert multiplier cell without gain resistors such that a first and a second node are directly coupled to a folded cascode output stage. The mixer receives a differential radio frequency (RF) signal and a differential local oscillator (LO) signal, and it generates, at the first and second nodes, a differential intermediate frequency (IF) signal. The mixer further includes output and gain/filter stages coupled to the multiplier circuit. The output stage exhibits a low input impedance and a high output impedance, and it generates an output stage differential current approximately equal to the differential current of the IF differential signal. The gain/filter stage both controls conversion gain of the mixer, and it filters the high frequency components generated by said multiplier circuit. A capacitor, implemented as the gain/filter stage, and a folded-cascode circuit for the output stage are disclosed.