Showing papers on "Output impedance published in 1998"

Differential signal transmission circuit

Abstract: Differential signal transmission circuit for transmitting a high speed signal through a differential transmission line with: a CMOS (complementary metal oxide semiconductor) differential driver for receiving a transmitted from an LSI for high speed signal and passing the signal to a differential transmission cable; and an impedance matching circuit provided between an output of the CMOS differential driver and ground to reduce an output impedance of the CMOS differential driver; wherein said impedance matching circuit comprises a series termination circuit which is provided between the output of the CMOS differential driver and the differential transmission cable, and a pair of parallel resistors, which are provided between the output of the CMOS differential driver and mass which, with the sum of the resistance of series termination circuit and an overall impedance is adjusted at the output of the CMOS differential driver to a characteristic impedance of the differential transmission cable, and wherein the total impedance at the output of the CMOS differential driver is set by the parallel resistors.

Impedance matching circuit for power amplifier

Abstract: An impedance matching circuit for a multi-band power amplifier has an input port for receiving RF signals from an amplifier, a first path for communicating RF signals in a first frequency band to a first output port, and at least one second path for communicating RF signals in a second frequency band to a second output port. The first path includes impedance matching circuitry for matching the impedance of the first output port and the input port in the first frequency band, and the second path includes impedance matching circuitry for matching the impedance of the second output port and the input port in the second frequency band. The first path contains circuitry which blocks RF signals in the second frequency band; and the second path contains circuitry which blocks RF signals in the first frequency band. A multiband power amplifier includes a multi-band amplifier coupled with an impedance matching circuit for a multiband power amplifier.

Digitally controlled output driver and method for impedance matching

Abstract: The present invention is generally directed to a PVT compensated variable impedance output driver for driving a signal through a signal pad on a semiconductor device. In accordance with one aspect of the present invention, the output driver includes a plurality of p-channel field effect transistors (PFETs) electrically connected in parallel. A source node of each of the plurality of PFETs are electrically connected together, and a drain node of each of the plurality of PFETs are electrically connected together. The driver further includes a plurality of n-channel field effect transistors (NFETs) electrically connected in parallel. A source node of each of the plurality of NFETs are electrically connected together and a drain node of each of the plurality of NFETs are electrically connected together. Further, the drain nodes of the plurality of PFETs are electrically connected with the source nodes of each of the plurality of NFETs, and are further electrically coupled (preferably through an ESD resistor) to the signal pad. A first PFET of the plurality of PFETs has a gate node that is driven by an output of a pull-up predriver circuit and a first NFET of the plurality of NFETs has a gate node that is driven by an output of a pull-down predriver circuit. The remaining PFETs and NFETs, however, have gate nodes that are driven by signals from the pull-up and pull-down predeiver circuits, as controlled by calibration words generated by a control circuit. In accordance with yet another aspect of the present invention, a method is provided for controllably varying the output impedance of an output driver circuit that is configured to drive a signal through a signal pad on a semiconductor device.

Impedance matching device

Abstract: An impedance matching device includes a variable capacitor constituted by a non-linear dielectric thin film and an upper electrode disposed on a lower electrode formed on a substrate. The non-linear dielectric thin film is formed by a deposition, screen-printing, electroplating, or other technique, and changes its relative dielectric constant according to applied voltage. Therefore, the capacity of the variable capacitor is controlled and the impedance is matched, by simply controlling the applied voltage across the non-linear dielectric thin film. Consequently, the arrangement makes it possible to cut down the impedance matching device in size and cost, compared to an arrangement incorporating a capacitor and a coil for adjustment, effects a much simpler matching operation, and facilitates a manufacturing process.

Impedance control circuit

Abstract: Briefly, in accordance with one embodiment of the invention an integrated circuit includes: a digital feedback control circuit to adjust the impedance of an interface circuit output buffer based, at least in part, on having adjusted the impedance of a non-data signal output buffer coupled to an external impedance. Briefly, in accordance with another embodiment of the invention, a method of digitally adjusting the impedance of an interface circuit output buffer comprises: digitally adjusting the impedance of a non-data signal output buffer coupled to an external impedance, and digitally adjusting the impedance of the interface circuit output buffer based, at least in part, on the digitally adjusted impedance of the non-data signal output buffer.

Distributed impedance matching circuit for high reflection coefficient load

Abstract: An impedance matching circuit in accordance with the principles of the present invention employs series-connected transmission lines to match a high reflection coefficient source impedance with a load impedance. The matching circuit is formed on a dielectric substrate material and accommodates the relatively limited capabilities of photo-lithographic circuit production. The new impedance matching circuit may be constructed of three series-connected transmission line sections. A first section, the section that is to be connected to the source, transforms the high source impedance into a relatively low valued impedance that is substantially resistive. The reflection coefficient of the first section is substantially equal to the reflection coefficient of the source. A second may be implemented as a quarter-wave transformer that transforms the low impedance developed by the first section into an intermediate impedance value. The third section transforms this intermediate value impedance into an impedance that substantially matches that of the load.

Calibration sharing for CMOS output driver

Abstract: A circuit for matching the impedance of a first array of transistors to an external resistor is used to produce a first set of control signals. This first set of control signals is used to control another array of transistors to replicate the impedance of the first array of transistors. This replicated impedance is then used by another circuit for matching impedance to produce a second set of control signals that control an array of transistor of a different type to match the impedance of the first two array. The two sets of control signals may then be used as calibration signals for the pull-up and pull-down transistors of multiple output drivers.

Circuits and methods for dual-gated transistors

Abstract: A circuit and method for an improved inverter is provided. The present invention capitalizes on a switched source impedance to prevent subthreshold leakage current at standby in low voltage CMOS circuits. The switched source impedance is provided by dual-gated transistors. The dual gates of the transistors are biased to modify the threshold voltage of the transistors (Vt). This design provides fast switching capability for low power battery operated CMOS circuits and systems. The devices can be used in a variety of applications, digital and analog, wherever a more compact structure with low power consumption and fast response time is needed.

Vehicle starting battery cold-cranking AMPS meter and method

Abstract: A vehicle starting battery cold-cranking amps meter and associated method includes providing a current source, a voltage meter, a current meter and a control. The current source produces a current pulse during a brief time interval at a known magnitude that is less than rated cold-cranking amps of the vehicle starting battery being tested. The volt meter measures battery terminal voltage of the vehicle storage battery being tested while the current source is sourcing current to or sinking current from the vehicle starting battery being tested. The control determines internal impedance of the vehicle starting battery being tested from the terminal voltage of the vehicle starting battery while the current source is sourcing current to or sinking current from the vehicle starting battery being tested and determines cold-cranking amps from the internal impedance and an output of the temperature meter.

Internal impedance of conductors of rectangular cross section

Abstract: It is shown that the high-frequency (skin effect) internal resistance and internal inductive reactance are not equal for conductors of rectangular cross section as they are for conductors of circular cross section such as wires. A numerical method is used to demonstrate this and to show the errors incurred in using this approach.

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

Abstract: A portable FM stereo RF transmitter having an audio plug extending therefrom directly or via a cable and 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. A phase lock loop controls the carrier frequency to remain in the center of the channel even as the battery voltage drops.

Methods for controlling an RF matching network

Abstract: Disclosed are methods and devices for tuning an impedance matching network to a tune point where power reflection is at a minimum. The impedance matching network is coupled between an rf generator and a load to transmit rf power to the load. The impedance matching network includes a set of variable impedance elements. The method includes measuring a network impedance value of the impedance matching network including the load at current values of the variable impedance elements. The method further includes computing directions (i.e., increasing or decreasing) and relative rates of change for the variable impedance element values in response to the network impedance of the network such that the directions and relative rates of change for the variable impedance elements are adapted to change the reflected power in the direction of the most rapid decrease in reflected power. In addition, the method includes driving the variable impedance elements by adjusting the variable impedance elements in the computed directions by the computed relative rates of change such that the variable impedance elements are driven to new current values in the direction of the most rapid decrease in reflected power. The method also includes repeating operations (a) through (c) until a desired level of tuning precision is obtained at the current values of the variable impedance elements.

Start up circuit for DC powered field instrument

Abstract: A direct current (DC) powered process instrument start up circuit includes an energy storage device, a switching regulator circuit, a variable impedance circuit, and a voltage measurement circuit. The energy storage device is coupled between first and second power supply terminals. The switching regulator circuit is coupled to the energy storage device and has a regulated voltage output. The variable impedance circuit is coupled between the energy storage device and the first power supply terminal and has an impedance control input. The voltage measurement circuit has a measurement input coupled to the energy storage device and a measurement output coupled to the impedance control input.

System for impedance matching and power control for apparatus for high frequency plasma treatment

Abstract: The invention provides an impedance matching and power control system not resorting to mechanical control for a device for high frequency plasma treatment. An impedance matching unit 14 inserted in the terminal end of a power feed line 3 extending from a high frequency power oscillator 1 to a plasma chamber 2 comprises phase detecting means 17, a load-associated detector 19 having the function of detecting voltage, current, and phase angle, and an arithmetic and output section 21, whereby the impedance matching unit delivers a frequency control signal corresponding to the detected phase and a power signal representing the consumed power of the plasma chamber as calculated from the voltage, current and phase angle. The high frequency power oscillator comprises an oscillation control section 24 for controlling the oscillation frequency thereof according to said frequency control signal, and an output control section including a summing amplifier 25 which receives an external set power signal and the detected power signal to find the difference between the two values of power, thus controlling its own output power according to the difference.

Variable gain amplifier using impedance network

Abstract: A circuit includes a transconductance device which converts an input signal voltage to a signal current. An output terminal is coupled to receive signal current from the transconductance device. A gain-control circuit has an impedance network coupled to the output terminal to maintain a constant impedance at the output terminal and selectively steers current from the transconductance device through at least first and second different nodes of the impedance network to vary the current supplied to the output terminal. The circuit has reduced noise figure degradation as compared to known current steering circuits by controlling gain without dumping signal current directly to the supply and without changing the impedance at the output terminal. The circuit is particularly useful in the RF section of radio receivers and transmitters, such as in cellular phones.

Ultra-wideband impedance sensor

Abstract: The ultra-wideband impedance sensor (UWBZ sensor, or Z-sensor) is implemented in differential and single-ended configurations. The differential UWBZ sensor employs a sub-nanosecond impulse to determine the balance of an impedance bridge. The bridge is configured as a differential sample-and-hold circuit that has a reference impedance side and an unknown impedance side. The unknown impedance side includes a short transmission line whose impedance is a function of the near proximity of objects. The single-ended UWBZ sensor eliminates the reference side of the bridge and is formed of a sample and hold circuit having a transmission line whose impedance is a function of the near proximity of objects. The sensing range of the transmission line is bounded by the two-way travel time of the impulse, thereby eliminating spurious Doppler modes from large distant objects that would occur in a microwave CW impedance bridge. Thus, the UWBZ sensor is a range-gated proximity sensor. The Z-sensor senses the near proximity of various materials such as metal, plastic, wood, petroleum products, and living tissue. It is much like a capacitance sensor, yet it is impervious to moisture. One broad application area is the general replacement of magnetic sensors, particularly where nonferrous materials need to be sensed. Another broad application area is sensing full/empty levels in tanks, vats and silos, e.g., a full/empty switch in water or petroleum tanks.

Analog video line driver with adaptive impedance matching

Abstract: A new principle for an adaptive line driver is presented. This type of line driver can adapt its output impedance automatically to the applied load. This results in automatically corrected output impedance for different cables with terminations. Also, the line-driver output impedance becomes insensitive to process variations. As an example, a line driver for analog video signals has been designed. The circuit operates from a 2.4-V supply in a 0.35-/spl mu/m CMOS technology. The realized circuit adapts between 38 and 85 /spl Omega/ loads, has total harmonic distortion of <-50 dB at 1.2 V/sub pp/ for 0-10 MHz, 0.09-mm/sup 2/ area, and 9-mW static power consumption.

Plasma monitoring apparatus

Abstract: A plasma monitoring apparatus for monitoring a condition of plasma of a plasma load to which power is supplied from a high frequency power source through an impedance matcher provides with a first input impedance calculator for calculating an impedance as a first input impedance from a supply-side terminal of the matcher to the plasma load-side based on voltage, current and phase difference detected at the supply-side terminal of the matcher, a second input impedance calculator for calculating an impedance as a second input impedance from a load-side terminal of the matcher to the plasma load based on a impedance of a element of the matcher and the first input impedance and a plasma impedance calculator for calculating an impedance of the plasma load from the second input impedance and an impedance of a supply-side connecting the matcher and the plasma load.

High output impedance current-mode multifunction filter with minimum number of active and reduced number of passive elements

Abstract: A new current-mode multifunction filter with a single input and three outputs employing only three positive type CCIIs and five passive elements is presented. The proposed filter realises three filter functions simultaneously all at high impedance outputs. No component matching is required and all passive sensitivities are low.

Circuit and method for controlling an output of a ring oscillator

Abstract: A circuit and method configured to generate a variable impedance. The circuit may comprise a voltage controlled resistor configured to generate the variable impedance in response to (i) a first transistor configured to receive a first control signal and (ii) a bias transistor configured to receive a bias signal. In one example, the variable impedance may be generated in further response to a clamp transistor.

Automated characterization of HF power transistors by source-pull and multiharmonic load-pull measurements based on six-port techniques

Abstract: An original measurement system for nonlinear microwave power-transistor characterization using six-port reflectometers is presented. It allows independent active tuning of the output impedances at f/sub 0/ and 2f/sub 0/ (multiharmonic load-pull) and variation of the source impedance at the input port at f/sub 0/ (source-pull). An appropriate search algorithm enables automatic optimization of the output impedances and leads to fast user-friendly operation of the system. Experimental results are shown for a commercial GaAs MESFET power transistor at f/sub 0/=2 GHz.

Patient-instrument connection errors in bioelectrical impedance measurement

Abstract: Bioelectrical impedance in vivo measurement errors due to the connection between instrument and patient are analysed theoretically and experimentally. Special attention is paid to the patient cable capacitances and to the reduction of unwanted common-mode signals at the voltage amplifier input. Experiments with single-ended and symmetrical current sources, with different simulated body impedance values, with five types of cable connection and with three types of cable screen driving are carried out. The use of a balanced voltage-to-current transverter with a floating common point is recommended. Four separate patient cables should be used with separately driven screens by high-quality unity-gain buffers. Thus the impedance module measurement error can be reduced to below 1% in the range of 20 to and the phase measurement error to less than , for frequencies from 1 kHz to 300 kHz. Keywords: bioelectrical impedance, impedance spectroscopy, instrumentation, patient-instrument interface, measurement errors

Transmission line impedance matching apparatus

Abstract: A transmission line impedance matching apparatus is disclosed that limits longitudinal signals and matches the longitudinal characteristic impedance between two conductors and comprises a common mode choke and an impedance matching device. The common mode choke, comprising two windings wound in the same direction, acts as a high impedance to longitudinal high frequency signals. As a result of this, standing waves are caused by the metallic signals reflecting off the choke. The impedance matching device, comprising two windings wound in the same direction, provides a good match to the longitudinal characteristic impedance and thus reduces standing longitudinal waves and reflections. The apparatus may include a terminal corrector or a mid-line corrector, or a combination thereof. This invention may allow greater bandwidth to be dedicated to services and allow transmission over longer subscriber loops before the minimum S/N ratio is achieved.

Impedance matched CMOS transimpedance amplifier for high-speed fiber optic communications

Abstract: A transimpedance amplifier according to the present invention is designed for high-speed fiber optic communications. The transimpedance amplifier preferably includes an input stage, a second stage and a bias generator. The input stage is operably coupled to the second stage and has an input impedance. The second stage has an output impedance. The bias generator is operably coupled to the input stage and the second stage, and operates to bias the input stage and second stage such that the input impedance substantially matches the output impedance. In this manner, the input and output impedances of a transimpedance amplifier of a fiber optics communication receiver are controllable to a desired impedance for interfacing with a transmission line.

Controlled output impedance buffer using CMOS technology

Abstract: CMOS technology is used to create a controlled output impedance output buffer circuit. An output buffer driver uses buffer circuits having impedance elements with linear characteristics. A control circuit uses a known impedance load to control the impedance of the buffer circuits. The control circuit monitors a known current flowing through the known impedance load to determine whether the output buffer circuit's output impedance needs to be adjusted to match a transmission line's impedance. Adjustments occur when the control circuit generates control signals to turn on or off various buffer circuits (and their impedance elements) contained within the output driver. In doing so, the output buffer circuit ensures that its output impedance will match the impedance of a transmission line over the entire range of output voltages regardless of the variations caused by the manufacturing process, operation temperature and power supply voltage.

A novel highly linear CMOS buffer

Abstract: A high input impedance, low output impedance, highly linear CMOS buffer is very desirable in many analog CMOS circuits. Conventional buffers employ feedback which severely limits bandwidth and linearity at even medium range frequencies. A recent open loop buffer, although linear, suffers from large power supply voltage requirement. This makes it undesirable for low voltage deep submicron processes. Here going to basics leads us to a very simple and very linear buffer which shows more than 26 dB THD improvement over conventional designs.

Frequency control of MOSFET full bridge power inverter for maximizing output power to megasonic transducer at 3 MHz

Abstract: The frequency of the MOSFET DC-to-RF power inverter is precisely set at the series resonant frequency of a megasonic transducer by controlling the oscillation frequency of the PLL when the MOSFET DC-to-RF power inverter is used to drive the megasonic transducer having an impedance of as low as 5 to 6 ohms or less. The frequency control system features a current sensor having an effective internal impedance of as low as 0.25 ohm which is negligible compared with the impedance of the megasonic transducer at the series resonant frequency. The impedance of the inverter load composed of the output transducer, matching capacitor, coaxial cable, megasonic transducer, and current sensor is calculated to determine the frequency control range of the PLL. In accordance with the result of calculation, the performance of the phase-frequency comparator, low pass filter, and VCO is decided. When the RF output power of the MOSFET power inverter was 60 W with a power conversion efficiency of 95%, the frequency control range was 2.8 MHz to 3.2 MHz. The PLL covers the range of frequency shifts and variations in the megasonic transducer and VCO.

Method and apparatus for reducing input impedance of a preamplifier

Abstract: A feedback circuit is provided for reducing the input impedance of a preamplifier circuit, such as for use with a sensing coil in an imaging system. The feedback circuit permits adjustment of the input impedance by balancing inductive and capacitive components of a feedback control circuit. The imaginary component of the input impedance may be adjusted independently of the real component, to provide a substantially zero input impedance, while allowing adjustment of the stability of the system. The circuitry may function in conjunction with a reactance matching circuit to reduce cross-talk in multiple sensing coil arrangements.