Showing papers on "Output impedance published in 1968"

Frequency selectivity using positive impedance converter-type networks

Abstract: It is shown that positive impedance converter-type networks may be used to realize a driving-point impedance that is ideally a frequency dependent negative resistor. This concept may be used to realize new types of inductorless selective networks. A simple resonant circuit application is discussed.

Linearizing circuit for high output transducers

Abstract: A transducer system which employs in combination an impedance bridge circuit with a differential amplifier and includes a feedback circuit to equalize nonlinearity in the components of the impedance bridge.

Integrated circuit biasing arrangements

Abstract: A low output impedance bias supply for integrated circuit amplifier configurations capable of delivering an output voltage that is a constant fraction of a power supply potential. Two transistors are connected in a degenerative feedback arrangement with a pair of resistors and with a pair of semiconductor diodes, the ratio of the resistors determining the fractional output voltage developed and the diodes serving to provide a low output impedance at high frequencies.

Some electronic problems of myoelectric control of powered orthotic and prosthetic appliances.

Abstract: In this paper the literature on the myoelectric signal is collected and reviewed for purposes of determining the electronic characteristics from which the optimum specifications for an amplifier used in a myoelectric control system are determined. An average figure of 5,000 ohms at 10 cycles per second is given as the output impedance of tissue. Accepting a 1 per cent signal loss, the input impedance of the amplifier should be at least 500,000 ohms. By integrating curves from the literature, it is fourid that the signal energy band is from 25 to 300 cycles per second as determined by the maximum signal/noise ratio in conjuction with a 1 per cent signal loss. The pass band of the amplifier should then be 25 to 300 cycles per second. Various other electronic problems of myoelectric control are discussed such as type of amplifier, electrodes, alternating current noise pickup, signal variation, and tissue noise.

Solid-state high input impedance meter system

Abstract: SYSTEMS OF THIS TYPE BE PREDICTABLY ACCURRATE AND OPERATIVE, THE SYSTEM ALSO INCLUDES A HIGH VOLTAGE PORTABLE TEST UNIT TO TEST THE VOLTMETER AND PROBES. TO INSURE COMPLETE RELIABILITY OF VALUES BEING MEASURED, THE HIGH VOLTAGE PORTABLE TEST SOURCE ITSELF IS SUBJECT TO TEST TO DETERMINE THAT IT IS OPERATING PROPERLY BEFOR IT IS USED TO TEST THE VOLTMETER AND PROBES, AND FOR THIS PURPOSE A HIGH VOLTAGE MEGOHMMETER INSULATION LEAKAGE CURRENT-EMISSION DETECTOR IS PROVIDED TO TEST THE HIGH VOLTAGE PORTABLE TEST VOLTAGE SOURCE, AND TO MEASURE THE HIGH VOLTAGE INSULATION ASSOCIATED WITH THE HIGH VOLTAGE POINT OR TERMINAL BEING MEASURED. INASMUCH AS THE HIGH INPUT IMPEDANCE METERING SYSTEM IS USED IN CONJUNCTION WITH HIGH VOLTAGES, A COLLAPSIBLE AND DETACHABLE INSULATING "HOT STICK" IS PROVIDED TO ISOLATE THE HIGH VOLTAGE COMPONENTS FROM HUMAN CONTACT WHILE IN USE. PRESENTED IS A SYSTEM, INCLUDING APPARATUS AND METHODS OF OPERATION THEREOF, FOR EFFECTING ISOLATED MEASUREMENT AND SENSING OF LINE TO GROUND VOLTAGES, DIFFERENTIAL VOLTAGES, CURRENTS, INSULATION LEAKAGE AND RESISTANCES, CORONA LEVELS, AND OTHER PARAMETERS IN INSULATED CONDUCTORS AND RELATED SYSTEMS ASSOCIATED WITH LOW AND HIGH POWER, LOW AND HIGH VOLTAGE ELECTRICAL AND ELECTRONIC SYSTEMS. THE SYSTEM INCLUDES A HIGH INPUT IMPEDANCE METER UNIT ACTUATED BY A SOLID-STATE AMPLIFIER CIRCUIT INCLUDING A PAIR OF FEEDBACK CIRCUITS THAT COOPERATE WITH TRANSISTOR AMPLIFIERS TO MAINTAIN SUBSTANTIALLY CONSTANT THE RATIO OF INPUT AND OUTPUT FROM THE CIRCUIT OVER A WIDE RANGE OF AC AND DC VOLTAGES AND CURRENTS. IN ITS DIFFERENT APPLICATIONS, THE HIGH INPUT IMPEDANCE METER INCLUDING SOLID-STATE AMPLIFIER CIRCUIT IS USED IN CONJUNCTION WITH A VARIETY OF PROBES, BOTH LOW VOLTAGE AND HIGH VOLTAGE TYPES, FOR MEASUREMENTS OF VARIOUS VOLTAGES, AND MAY BE UTILIZED WITH A PROXIMITY PROBE FOR DIRECT SENSING OF AC FIELDS. THE HIGH INPUT IMPEDANCE OF THE METER MOVEMENT AND SOLID-STATE CIRCUIT ALSO PERMITS THE USE OF CORONA VOLTAGE LEVEL AND DETECTING PROBES FOR BOTH HIGH VOLTAGE DIRECT AND LOW VOLTAGE INDIRECT OR PROXIMITY MEASUREMENT OF VARIOUS LEVELS OF VOLTAGES. INASMUCH AS IT IS IMPORTANT THAT

Temperature-compensated frequency-voltage linearizing circuit

Abstract: A technique is disclosed for providing a desired nonlinear output control voltage which has a continuous first derivative from a linear input command voltage. The output control voltage maintains its curvature and orientation in the presence of ambient temperature variations. This is accomplished by provision of a first circuit impedance which produces the desired nonlinear curvature as a function of a linear input, while a second impedance negates impedance changes in the circuit semiconductor devices due to the temperature changes.

Realization of negative impedance inverter using Kron's mesh primitive-branch approach

Abstract: The effectiveness of Kron's “mesh primitive-branch approach” for the synthesis of complex active networks with uncommon properties, operating under steady state sinusoidal conditions, is demonstrated in a typical simple example, the Negative Impedance Inverter. The tensors C .r r′ and C k .k′ are used for the interconnection of the constituent parts, the forcing function e s (jω), the loading impedance Z L L (jω) and a two-port network, to form a generalized network. Necessary conditions are imposed on this network; these conditions Eqs. 25, 26, 27, and 30 must be satisfied if this network is to perform as a Negative Impedance Inverter. Thus, the NATURES OF and the RELATIONSHIPS among the parameters of this network are established in the frequency domain. Finally, the tensors C v .k″ and C .u r″ are used to interconnect the loading impedance Z L L and the forcing function e. to two fundamental building blocks—each consisting of an operational amplifier and a feedback impedance—and to derive a two current-controlled voltage source equivalent network that satisfies the conditions established; the input impedance (loading impedance negated and inverted) of the established two-port is derived, and verified experimentally, for the case of pure resistive, inductive and capacitive loads. All possible cases are exhibited in Table I. This approach to active network realization can be used as an example illustrating similar establishment of a variety of active network realizations.

A Method for Obtaining Analog Circuits of Impedance Convertors

Abstract: The properties of three terminal positive and negative impedance convertors are defined in terms of the cofactors of the indefinite nodal admittance matrix, the special cases of the ideal transformer, power amplifier, and voltage and current inverting negative impedance convertors being considered in detail. The nodal admittance matrix of a six-node resistive network with two infinite gain amplifiers embedded in it is discussed, and element values are obtained to realize the required analog circuits with a minimum number of components. The analog circuits obtained are simple to set up and are ideal for demonstrating and testing applications of impedance convertors to filter network realizations. Of particular interest is the circuit obtained for the case of a loaded, phase-reversing, positive impedance convertor, which employs only one operational amplifier and four resistors in a bridge circuit, which is thought to be novel, and which can be extended by the introduction of a second amplifier and three resistors to produce a simple realization of a negative impedance invertor (NIV).

A theory of broadband matching of frequency dependent generator and load

Abstract: : The classical theory of matching an arbitrary load to a resistive generator to achieve a desired power gain is extended to matching an arbitrary load to a generator with arbitrary internal impedance. Given the load and generator impedances and the desired power gain, the necessary and sufficient conditions on the power gain has been established such that there exists a lumped lossless 2 port which, when operated between two given impedances, realizes the desired power gain. The constraints on the gain function are formulated in coefficient and integral form. Design procedures are outlined and illustrated by several non-trivial examples. A design chart is prepared to facilitate the engineer to carry out the details involved. (Author)

Twin-t oscillator

Abstract: A twin-T oscillator utilizing positive feedback in which the attenuation through the twin-T feedback network is reduced by unbalancing the components so as to provide a low impedance input side and a high impedance output side, thereby reducing the overgain requirements of the associated amplifier

Small-Signal Characteristics of the Diode-Stabilized Linear Integrated Devices

Abstract: The small-signal characteristics and the frequency response of the diode-stabilized linear integrated devices (circuits) are examined. The built-in feedback property is explained. It is found that the circuit provides low input impedance, high output impedance, and small internal feedback. The frequency response of the circuit with the bias-diode is superior to that without the bias-diode. The current gain of the circuit can be controlled by appropriate design of active or passive elements. The experimental results using discrete components agree with the analysis.

Wide band transistor amplifiers with reduction in number of amplifying stages at higher frequencies

Abstract: A WIDE BAND RELATIVELY HIGH POWER LAW DISTORTION STABLE SIGNAL GENERATOR IS OPERATIVE OVER THE FREQUENCY RANGE 10 HZ. TO 10 MHZ. THE SYSTEM INCLUDES A NUMBER OF AMPLIFLYING STAGES THAT PROVIDE MULITIPLE STAGE AMPLIFICATION AT LOW FREQUENCIES AND SINGLE STAGE AMPLIFICATION EFFECTIVELY AT THE HIGHER FREQUENCIES TO HELP PREVENT UNDESIRED OSCILLATION. NONLINEAR FEEDBACK TECHNIQUES ARE EMPLOYED TO MAINTAIN AVC STABILITY. FEEDBACK FROM THE OUTPUT STAGE IS DERIVED SO THAT THE OUTPUT STAGE EMITTER RESISTORS FORM A PORTION OF THE 50 OHM OUTPUT IMPEDANCE. A NOVEL LADDER ATTENUATING NETWORK PROVIDES PRECISION ATTENUATION WHILE PRESENTING THE SAME 50 OHM IMPEDANCE AT ALL ATTENUATION LEVELS OVER THE FREQUENCY RANGE.

Electrical measuring apparatus for providing an output signal at an output branch characteristic of the relationship of impedances presented at first and second side branches at the frequency of energy applied at an input branch

Abstract: A radio frequency signal source delivers a signal to an input branch through a harmonic filter to provide an output signal on an output branch indicated by indicating means representative of the difference in impedance between a standard impedance connected to one side branch and an unknown impedance connected to the other side branch. A pair of equal resistances connect the high terminal of the input branch to the respective high terminals of the respective side branches. A higher resistor intercouples the high terminals of the side branches so that when the side branches are terminated in their characteristic impedance, typically 50 ohms, the impedance presented at the input branch is substantially equal to the input branch characteristic impedance, typically 50 ohms. Means including isolating resistors and a bridge circuit couples the side branch high terminals to the output branch high terminal, all four branches having low, or grounded terminals, that are interconnected.

Circuit arrangement comprising a high-voltage transistor

Abstract: A circuit for increasing the speed of collector current reduction of a high-voltage transistor, in which an impedance is connected in series with the base to restrict variation in reverse base current. The specification discloses embodiments in which the impedance is a parallel circuit of a resistor and diode connected in the pass direction of base-emitter current, and in which the impedance is a coil.

Unconditionally stable, open loop operational amplifier

Abstract: An open loop semiconductor operational amplifier having a differential amplifying input stage, an output stage having high input and low output impedance, and an intermediate stage interconnecting the input and output stage and having low input impedance and high output impedance. The three stages are collectively responsive to an applied input signal so as to maintain unconditional stability up to unity gain operation without external feedback circuitry.

Impedance bridge transducer circuits

Abstract: A BRIDGE-TYPE TRANSDUCER AND AMPLIFIER CIRCUIT FR PROVIDING A HIGH LEVEL OUTPUT SIGNAL IS ENERGIZED FROM A COMMON SOURCE OF EXCITATION VOLTAGE. A DIFFERENTIAL AMPLIFIER IS CONNECTED TO THE BRIDGE FOR PRODUCING AN OUTPUT SIGNAL BETWEEN AN OUTPUT TERMINAL THEREOF AND A REFERENCE TERMINAL MAINTAINED AT A PREDETERMINED REFERENCE VOLTAGE LEVEL. MEANS CONNECTED ACROSS THE SOURCE OF EXCITATION VOLTAGE AND TO A REFERENCE TERMINALS MAINTAINS THE REFERENCE TERMINAL AT SAID VOLTAGE LEVEL, AND CAN INCLUDE A ZENER DIODE OR AN EMITTER FOLLOWER TO PROVIDE A LOW OUTPUT IMPEDANCE FOR THE REFERENCE TERMINAL.

Improvements in or relating to communication systems

Abstract: 1,136,071. Radio signalling. H. M. POSTMASTER GENERAL. 17 Dec., 1965 [18 Sept., 1964], No. 38219/64. Heading H4L. A communication system includes digital storage apparatus at a ground station providing compensation for variations in the propogation time of a signal, e.g. in communication systems using artificial satellites, comprising a static digital store with means for introducing a variable time delay between the write-in and read-out of digits by varying the rate of readout so that the total of the propogation time of the link and the time delay introduced by the storage apparatus is substantially constant. A store of this type may be incorporated in the receiver of a ground station or in both receiver and transmitter. As shown in Fig. 1, satellite tracking by receiving aerial 1 is controlled by a computer 2 which also provides signals determining the additional delay to be added to the propogation time of the signals. Received signals are fed to a receiver 4 and converted to a baseband signal which is fed to a p.c.m. coder 5 whose output is stored at 6 under the control of "write" pulses from a clock 7. Initially the computer resets a "read" address counter 10 and a write address counter 8 via a reset pulse generator 16 and blocks pulses from "write" clock 7 and "read" clock 9 by means of INHIBIT gates 14, 15 respectively. The computer 2 then sets the "read" counter 10 on the required time delay and restores the outputs of clocks 7 and 9, at the same time controlling the frequency of clock 9 to ensure the required rate of change of the additional time delay. The store 6 may be of the cathode-raytube type, preferably with separate reading and monitoring beams. In a modification, Fig. 2 (not shown), a plurality of separate stores are used, each with its own write and read circuits and address counter and controlled by selectors so that reading and writing does not occur simultaneously in the same store. 1,136,077. Transistor pulse circuits. MARCONI CO. Ltd. 14 Jan., 1966 [9 Feb., 1965], No. 5641/65. Heading H3T. A pulse generator comprises a circuit which includes unilaterally conducting and substantially constant voltage dropping means (diode D1 and Zener diode D2), the circuit being rendered conductive on peaks of alternate half cycles of a high frequency oscillation (applied through transformer P, S), the resulting current through the circuit being employed to produce a voltage (across R1) which is applied to a transistor T to render it conductive, output pulses being taken from an output circuit of the transistor. Resistor R2 limits the base current if the high frequency source impedance is low. Improved rise and fall times are produced by the connection of a capacitor C across R2. The output may be taken from transistor T in emitter follower configuration. The transformer may be replaced by a pushpull transformer, each half of its secondary feeding an arrangement as shown for producing two trains of pulses separated by a half cycle of the input. The output pulse widths may be altered by adjusting the input amplitude or resistor R1.

Video amplifier for driving a delay line between grounded collector and grounded base

Abstract: Transistorized luminance channel of a color television receiver includes emitter follower coupled to input of luminance delay line and common base amplifier coupled to delay line output. Low output impedance of emitter follower and low input impedance of common base amplifier permits reliable termination of both ends of delay line with resistors substantially matching characteristic impedance of delay line. Common emitter amplifier serves to amplify and invert output of common base amplifier, and inverted signal is applied to power output stage via common collector stage providing a low impedance output circuit. Negative feedback established by path between emitters of common collector and common base amplifiers ensures low source impedance required to adequately drive output stage; feedback path provides convenient facility for frequency response control.

Low-pass filters for electromagnetic flowmeters.

Abstract: A simplified method of designing R-C active low-pass filters is presented. The filters employ solid-state differential operational amplifiers, and are designed to present high input impedance and low output impedance. R-C active filters can provide stable and distortion-free operation at low frequencies without the inherent limitations of passive R-C and L-C filters. Two active low-pass filters suitable for use in electromagnetic flowmeter output stages are illustrated; one with a pass-band gain of ×1, uniform frequency response to approximately 20 c/s and linear phase shift of 3°/cycle per second; and a second with a pass-band gain of ×2, uniform frequency response to approximately 30 c/s and linear phase shift of 2·2°/cycle per second. The attenuation rate of these filters is 12 dB/octave. A more versatile R-C active low-pass filter has been developed using two similar stages in cascade. The choice of three cut-off frequencies, 25 c/s, 50 c/s and 100 c/s is provided. Pass-band gain is ×1, while attenuation rates of 12 dB/octave or 24 dB/octave are selected by taking the output from either the first or second stage. Dynamic calibration shows uniform frequency response and linear phase shift in the pass-band, while the response to a step function shows 3 per cent overshoot from the 12 dB/octave channel, and 11 per cent overshoot from the 24 dB/octave channel.

A Current-Mode Trigger Pulse Generator for Fast Coincidence Circuits

Abstract: The design and philosophy of a new current-mode trigger pulse generator are described. The pulse generator uses two transistors in a coupled emitter configuration and only ordinary components. The output impedance at collectors is 93 ohms though this may be reduced where it is desired to match other transmission line impedances. Rise time is less than 3 nanoseconds with jitter in the 10-11 second range. Pulse output is ±2.5 volts and extremely clean and square with little undershoot or overshoot. Pulse length may be chosen, in the normal way, to be from ~10 nsec. up to microseconds. The circuit may be retriggered as soon as the output has recovered to zero. Its layout will be discussed and also its use as a replacement for limiter circuits in fast coincidence measurements.

Lamp arrangement for combined tuning indication and silent tuning in high-frequency receivers

Abstract: Three sets of lamps are used for indicating the tuning conditions by being interconnected at the outputs of two threshold switching circuits. The inputs to the threshold circuits are, in turn, connected to DC voltages of opposite polarity provided by a symmetrical ratio detector or discriminator. Each threshold circuit has a complementary transistor, and the output of the circuit has a pair of lamps connected in parallel, as the output impedance of the circuit. A third single lamp is connected between the two sets of parallelconnected lamps. When the single lamp is turned on the parallelconnected lamps are turned off and vice versa. An indicator board with three viewing areas is associated with the lamps.

Input and output impedances of amplifiers with feedback

Abstract: When the amplification of an amplifier with feedback is given by the well-known formula A = A 0(1 − βA 0)−1, it is shown that the input impedance, changed by the feedback, can be written as: $ Here Z i0 is the input impedance without feedback and Z g is the generator impedance. The output impedance has the same form, but the output impedance without feedback Z u0 has to be substituted for Z i0 and the load impedance Z b, for Z g. This is valid for connection in series, but for connection in parallel the admittances Y have to be substituted for the impedances Z. It is shown that with the given relations for determining the input and output impedances, a minimum effort of calculation is obtained.

Improvements in or relating to voltage stabilising means for dc to dc converters

Abstract: 1,102,494. Converting circuits. E. K. COLE Ltd. 21 March, 1966 [20 March, 1965], No. 11939/65. Heading H2F. [Also in Division H3] A relaxation oscillator used in an A.C. to D.C. converter has its output amplitude stabilized against variations in output impedance by means of a Zener diode 18 connected across the collector-emitter path of the oscillator transistor 4 so as to conduct when the transistor is cut off. The circuit provides an increase in output with a decrease in supply voltage 7 and in order to compensate for this part of the supply voltage may be injected in opposition into the output circuit by replacing link 19 with a potentiometer circuit 20. A plurality of outputs may be provided, each taken from a separate secondary winding 3, and each having its own potentiometer circuit.

Systematic Errors in Ultrasonic Propagation Parameter Measurements. Part 4: Effect of Finite Thickness Elastic Solid Tubes Enclosing the Liquid Cylinder of Interest

Abstract: : The exact formulation of the characteristic or frequency equation for an inviscid liquid cylinder radially enclosed within a finite impedance elastic solid of finite wall thickness is solved for the permissible modes, including degenerations to the surrounding medium being of infinite extent and either an elastic solid or another liquid, as well as to the limiting cases of infinite impedance (rigid boundary) and zero impedance (free boundary). These modes are utilized to expand both the potential within the otherwise unterminated cylinder and the source impedance variation with position of an opposing termination. A piston source of appreciable ka (=100 pi) is found to render further source specification indifferent as to uniform pressure or uniform velocity, and a large radial impedance mismatch (=28) is found to permit a simplifying orthogonality assumption. With the inviscid assumption, the formulation indicates that a judicious selection of experimental configuration can limit diffraction propagation uncertainties to a few parts per million. An incidental result is the demonstration that the zero elastic tube mode exists at all frequencies rather than displaying an upper cutoff frequency as was recently reported. (Author)

Resistive Wall EGD Channel

Abstract: A technique is discussed which eliminates the problem of charge accumulation on dielectric EGD channel walls. A resistive leak path is provided. Use of this technique results in higher voltages, higher short-circuit currents, and a smoother output. Equations are derived which define the system electrically. Experimental data are compared to the theory and found to agree within 10%. Results of the analysis show that the resistive wall channel may be compared to a high internal impedance generator. This is substantiated by the data; peak power occurred when the load resistance and internal resistance were equal, and the current-voltage characteristics were found to be essentially linear.

Improvements in or relating to a circuit arrangement for fault protection in an electronic switch

Abstract: 1,125,302. Transistor switching circuits. M.E.L. EQUIPMENT CO. Ltd. 30 Nov., 1965, No. 50770/65. Heading H3T. A circuit arrangement for fault protection in an electronic switch which supplies current to a load impedance 33 in the event of the load becoming short circuited, includes an amplifier e.g. 34, 36 or 35, 37 having a positive and a negative feedback circuits, the load forming part of the positive feedback circuit, and the arrangement being such that when the load impedance is substantially zero, the voltage across the load is substantially zero, and when the load impedance is above a predetermined value the load is connected to one of two predetermined voltages, + or -16V. Supposing the polarity of the input 12-12 is such that the sine-wave oscillator 4 is operative, oscillator 5 being by-passed by forwardly conducting zener diode 7, then positive pulses rectified at 15 are applied to the bases of transistos 17, 18 switching on transistor 17, and hence transistors 25, 34, 36, and switching off transistors 26, 35 and 37, The + 16V supply is thus connected through transistor 36 and resistor 32 and also through transistor 25 and resistor 30 to the load 33. Should the polarity of the input be reversed, the states of the transistors are reversed and the load is connected to the -16V supply. Should the load become short circuited, the base of transistor 34 is earthed through the load and consequently transistors 34 and 36 are switched off. Transistors 17 and 25 are however not switched off, since the short circuiting of the load does not greatly affect the output impedance of Block 2, resistor 30 being high, of comparable value to that of the load. Block 2 thus acts as a memory to drive Block 3 back into its original state when the short circuit is removed. During short circuit, the load is supplied with current only through transistor 25 and high resistor 30. Each amplifier 34, 36 and 35, 37 is provided with positive feedback from the junction of load 33 and resistor 32 to the bases of transistors 34, 35 and negative feedback from the junction of resistors 42, 43 to the emitters of transistors 34, 35, which feedback paths determine the instability of Block 3 in the active regions.