Showing papers on "Operational amplifier published in 1972"

Frequency limitations of active filters using operational amplifiers

Abstract: There are many active RC networks that implement the low-pass filter characteristic. It has been the common practice to compare these networks with regard to passive element sensitivities while assuming the amplifier to be ideal. Such an assumption gives results that disagree with experimental observations, particularly when the pole magnitudes are large. This paper characterizes the amplifier by a one-pole rolloff model and discusses the ensuing limitations on four widely used low-pass realizations. The amplifier's open-loop gain-bandwidth product is used as a parameter to generate complex-pole loci that graphically display the effect of the nonideal amplifier. The expression of the slope of these curves at the nominal pole positions is derived and first-order estimates for the resulting changes in the \omega_{0} and Q of the poles are given. These expressions can be used to determine the upper bound on the frequency \omega_{0} that these networks can effectively realize. Experimental results agree with the predicted changes. The methods have also been applied to high-pass, bandpass, band-reject, and other realizations.

Principles of electronic instrumentation

Abstract: Direct Current Circuits. Capacitors and Inductors. Alternating Current Circuits I. Alternating Current Circuits II. Diodes and Some Applications. Test Equipment and Measurement. Transducers. Transistors. Operational Amplifiers. Waveform Generators. Digital Basics. Digital Circuitry. Microprocessor Basics. Digital and Analog I/O. Noise.

High-Q factor insensitive active RC network, similar to the tarmy-ghausi circuit but using single-ended operational amplifiers

Abstract: A high Q, insensitive, active RC network, usable up to several megacycles, is described. It has similar properties to the circuit proposed by Tarmy and Ghausi, but uses operational amplifiers with single-ended output terminals. The circuit can be realised with only two amplifiers; using three, the two capacitors required can be earthed.

Frequency sensitive circuit employing variable transconductance circuit

Abstract: The circuit of the present invention is preferably used in electronic musical instruments such as an electronic organ or music synthesizer, and basically comprises a transconductance means, an integrator, and feedback means intercoupling an output of the integrator and an input of the transconductance means. The transconductance means includes a differential amplifier and current reflector and the integrator comprises an operational amplifier and reactance means. The fundamental circuit is primarily used for voltage controlled filtering and may be easily modified to provide either a high pass filter network, a low pass filter network, or a phase shift network with constant gain.

Insulated electrocardiogram electrodes.

Abstract: An integrated system consisting of an insulated electrode and an impedance transformer has been fabricated, which can be used for the acquisition of electrocardiographic data. The electrode itself consists of a thin layer of dielectric material which has been deposited onto a silicon substrate. The impedance transformer is a Fairchild μA 740 operational amplifier used in the unity-gain configuration. The input impedance of the impedance transformer is at least 100 MΩ and its output impedance is about 5 Ω. Both electrode and impedance transformer are contained in a plastic housing which is identical to that used with the NASA Apollo-type electrode. The lower cutoff frequency of the electrode system is between 0·01 and 1·0 Hz, depending on the dielectric used and its thickness. Clinical-quality electrocardiograms have been obtained with these electrodes.

Electronic watt transducer

Abstract: A potential input circuit and a current input circuit, each having a transformer therein, receives the input information from the power line for which the true electrical power is to be measured. The scaled output from the potential input circuit, and a triangle wave signal from a generator therefor are coupled to a comparator (level crossing detector) employing an open loop operational amplifier (op amp) having an output controlling electronic switches to gate the current transformer secondary current, with a duty ratio proportional to voltage amplitude and polarity. The gated output of the current transformer is filtered and coupled through an amplifier, or directly, to an external load. The filtered output is in the form of a linear direct current analog of true power in the power line.

Low noise detector amplifier

Abstract: An amplifier of electromagnetic wave energy in the visible and infrared range includes a photo sensitive detector coupled to a pair of cascoded field-effect transistors arranged to operate at substantial unity gain. A positive feedback path includes the input capacitances of the amplifier reducing and thereby neutralizing the input capacitances of the amplifier. The bandwidth of the amplifier is extended relative to the neutralization of the input capacitances.

Capacitance multiplier and filter synthesizing network

Abstract: A circuit using a differential amplifier multiplies the capacitance of a discrete integrating capacitor by (R1 + R2)/R2 where R1 and R2 are values of discrete resistor coupling an input signal e1 to the amplifier inputs. The output eo of the amplifier is fed back and added to the signal coupled by the resistor R2 to the amplifier through a resistor of value R1. A discrete resistor Rx may be connected in series for a lag filter and a discrete resistor may be connected in series with the capacitor for a lead-lag filter. Voltage dividing resistors Ra and Rb may be included in the feedback circuit of the amplifier output eo to independently adjust the overall circuit gain ei/eo.

High power bridge audio amplifier

Abstract: A high power audio amplifier includes four power amplifier sections connected in a bridge, with the power supply connected to one opposite pair of nodes and the load terminals connected to a second opposite pair of nodes One of the load terminals may be connected to a ground reference potential and the power supply is floating with reference to ground First and second drive amplifiers are provided, with each of the drive amplifiers being connected to the two power amplifier sections connected to one load terminal The input signal to be amplified is applied to one input of the first drive amplifier and a feedback signal from the load terminal which is not connected to ground is connected to the second input thereof The second drive amplifier receives either the input signal or the signal from the load terminal, and compares the same with the supply potential to balance the bridge To protect the transistors of the power amplifier sections, the currents in the transistors of the amplifier sections driven by the second drive amplifier are sensed and used to control the first drive amplifier, to thereby protect the transistors in all of the power amplifier sections Auxiliary protection circuits are provided for the transistors in the power amplifier sections coupled to each drive amplifier

Participation presenter-audience reaction system

Abstract: A system is described for measuring the response of selected members of an audience, averaging the selected responses and presenting the average to the presenter as the presentation is being made to enable the presenter to adjust his presentation accordingly or respond to the audience response. The system includes a plurality of electrical response circuits having variable resistance manually operable devices individually distributable to the audience. Input resistors are included in each response circuit having resistance values at least 10 times greater than the maximum resistance of its variable resistance devices. The system includes switching means for placing selected response circuits in parallel with each other to a common line in series with an operational amplifier. The system includes a plurality of feedback resistors corresponding to the response circuits with the corresponding feedback resistors being placed in parallel with the amplifier to provide an output signal from the amplifier equal to the average of the selected response signals. It is important that the total feedback resistance placed in parallel with the operational amplifier is substantially equal to the total resistance of the selected response circuits. The output signal is transmitted to a readout device at the presenter's console or lectern to provide the presenter with a continuous reading of the audience's reaction to his presentation.

Method and apparatus for electroanalysis

Abstract: An electrical circuit for providing an output signal having a mathematical operation relationship to an input signal, said operation being either that of semi-integration or semidifferentiation, said circuit including an electrical transmission line. The practical circuit for the transmission line comprises a simulated, lumped-constant line made up of a number of series resistance and shunt capacitance elements or series inductance and shunt resistance units. The preferred circuit for effecting semi-integration or semi-differentiation comprises an operational amplifier having a transmission line either in the feedback or in the input. This feedback or input element may take the form of a long (theoretically infinite) transmission line, e.g. a coaxial cable or a lumped constant network of suitably chosen resistance and reactance elements. For electroanalytical measurements the semi-integrating circuit is connected to electrodes positioned in the solution to be measured. Provision is made for applying two predetermined DC voltage levels to the electrodes with the operational amplifier semi-integrating the current flowing between electrodes.

Some New Configurations for Active Filters

Abstract: Some new active-filter configurations based on the pole-zero cancellation technique are introduced. First, for the range Q \leq 50 a singleamplifier circuit is suggested. For higher selectivity (50 a twoamplifier circuit is proposed. Another easily cascadable two-amplifier circuit with a reduced number of capacitors is discussed. In the latter case the filter function is determined by certain resistive ratios. All the configurations proposed-employ integrated circuit operational amplifiers (OAs). The sensitivity problem is discussed in detail. Effects of the finite OA frequency response are also investigated.

Electronic amplifier with dual automatic slope control

Abstract: An amplifier is characterized by electronically variable slopes (''''tilt'''') at the bounds of its signal amplification gainfrequency passband characteristic. Separate feedback circuitry is responsive to an associated one of two frequency-spaced pilot signals for suitably adjusting the response properties of the amplifier. The pilot signals may be specially generated, or may comprise components of the signal operated upon by the amplifier - such as one high band and one low band video carrier for a CATV television signal distribution application.

Servo control system

Abstract: A digital servo-motor control and drive system is disclosed. A control signal for changing the servo-motor position, and a position signal which is proportional to the servo-motor position are compared with one another by a comparator. A signal proportional to the difference between the control signal and the position signal is delivered to a full-wave rectifier using highgain differential operational amplifiers. The latter circuit produces a signal which is proportional to the absolute magnitude of the error signal. This error signal is delivered to a second comparator which compares the error signal with a reference signal. When the error signal is equal to or greater than the reference signal, The second comparator changes its output condition to indicate the ''''match''''. Logic circuitry is provided for detecting the coincidence between the latter condition of the second comparator and one condition of the first comparator. The detection of such a coincidence produces an output signal over a first lead which drives the servo-motor in one direction. A second drive signal for driving the servo-motor in the opposite direction is produced in response to the detection of coincidence between the match condition of the second comparator and the opposite output condition of the first comparator, thus indicating a reversal of polarity of the difference between the control and position signals. This servo control system has a very precisely controllable ''''deadband'''', and is relatively insensitive to electrical noise.

Practical design considerations for a variable center frequency, constant bandwidth, and constant peak-value active filter

Abstract: Frequency active filters are designed by treating the operational amplifier as ideal. Consequently, the actual circuit's performance may depart considerably from what is expected. This is demonstrated in the design of an active bandpass circuit. However, it is shown that good agreement results between the predicted and actual performance if the operational amplifier's frequency dependence and output resistance are taken into account. Expressions are derived for the pole shift caused by the nonideal amplifier. Subject to given constraints, quantitative results are given that establish an upper bound on the frequency of operation of the bandpass circuit.

Current mirror amplifiers

Abstract: A current mirror amplifier for combining the output currents of an MOS source-coupled differential amplifier comprises first and second bipolar transistors having parallelled base-emitter circuits including emitter degenerative resistors. A similar resistor judicially placed in the collector circuit of one of these bipolar transistors ensures that the differential amplifier will not exhibit an offset potential between its input terminals caused by its component devices being subjected to different conditions of quiescent drain biasing when the differential amplifier supplies its combined output currents by direct coupling to a subsequent grounded-emitter amplifier stage.

A 15-W monolithic power operational amplifier

Abstract: The design of a new general-purpose monolithic power amplifier functional block is described and the flexibility of the block in various applications is discussed. The effects of thermal coupling on the die between components in high-gain dc power amplifiers are examined and a technique is presented for the analytical evaluation of dc circuit performance in the presence of these thermal interactions. Experimental results from the 15-W amplifier are presented. A new integrated power transistor structure is described that includes emitter degeneration resistors as part of the emitter structure. Circuit performance is summarized.

Trigger circuit for recording and transmitting sampled analog waveforms

Abstract: A trigger circuit is provided for generating a digital pulse each time the amplitude of an analog input signal increases by an amount greater than a first voltage increment or decreases by an amount greater than a second voltage increment. The circuit features a sample and hold circuit in combination with a pair of operational amplifiers having current summing points in their input circuitry for comparing the ''''last look'''' value of the input signal, the current value of the input signal, and the first and second voltage increments.

Transducer amplifier with automatic balance

Abstract: An amplifier for strain gages and other transducers in quarter, half or full bridge configurations provides an analog output suited for measurement, control or display purposes. The amplifier includes temperature compensation and automatic zero balance, the former realized from the voltage-temperature characteristic of a silicon PN junction used to affect the offset of an integrated circuit amplifier stage. The signal for zero balance is derived from the amplifier output, sampled and retained in an analog to digital converter and reconverted to analog form for application to a stage of the amplifier in opposition to the measurement signal, resetting for zero balance being under manual control.

Temperature measuring apparatus and method with resistance amplifier

Abstract: Apparatus for operating a bridge network incorporating a resistance temperature detector (RTD) in the null balance configuration. The bridge is balanced by applying a feedback signal from a first operational amplifier connected across the bridge outputs, to a second operational amplifier connected in series with the RTD in one leg of the bridge. The isolation provided by the operational amplifiers permits non-interacting suppression adjustment in the bridge and span adjustments in the output circuit of the first operational amplifier.

Null loop for correcting low frequency error signals in high performance amplifiers

Abstract: A feedback null loop includes a low drift, first loop amplifier connected to the output of a fast settling, large drift amplifier means which is to be corrected for AC and DC errors due to stray signal coupling. A second loop amplifier with high impedance is coupled to the low drift first loop amplifier via electronic switch means. A ground line is provided to the input of the large drift amplifier means; e.g., via the conventional multiplexer apparatus in a multi-channel data acquisition system, whereby the output voltage of the amplifier means is nulled to zero. Prior to opening the switch means in the null loop, a capacitor stores a fixed voltage representing the error signal. Thereafter, as the multiplexer apparatus selects successive channels of the data acquisition system, any DC off-set levels are balanced out via the temporarily stored capacitor voltage.

Trapezoidal waveform generator circuit

Abstract: There is disclosed a ramp generator responsive to a pulse-type signal for providing an output signal which linearly ramps between two voltage values. The ramp generator includes an operational amplifier integrator circuit and a pair of feedback regulating paths around the integrator circuit to regulate the output voltage values.

A high precision monolithic super-beta operational amplifier

Abstract: A single-chip (67/spl times/90 mil) integrated-circuit operational amplifier using thin-film resistors and super-gain transistors has been designed to achieve dc follower accuracies of 0.001 percent with 100-k/spl Omega/ source resistance. The circuit achieves gains of 140 dB using thermally balanced layout designs for both input and output stages, nulled drifts of 0.3 /spl mu/V//spl deg/C, and offset currents well under 1 nA. All other dc specifications including power-supply variation error (PSRR), common-mode gain error (CMRR), etc., are in the 1-10 ppm error range; and a procedure is given by which long-term drifts of less than 10 /spl mu/V/month can be assured. AC performance is comparable to general-purpose integrated-circuit operational amplifiers, i.e., f/SUB t/=300 kHz and slew rate of 1.2 V//spl mu/s at gain of ten. The circuit is externally compensated for unity gain with a single 390-pF capacitor and is fully input and output protected.

Rc active filter circuit

Abstract: The invention comprises an RC active filter circuit, which includes an operational amplifier, and which depending on the circuit topography may function as either a band-pass, or lowpass filter. The circuit has a capacitive network connected between the inverting input of the operational amplifier and earth. This network in conjunction with the feedback network operates to make the feedback, frequency dependent. The frequency dependence of the feedback is adjusted to compensate for variations in the gain of the amplifier with frequency, to give a working range in which the closed loop gain of the amplifier is independent of the frequency.

Proximity probe with output proportional to target distance

Abstract: A proximity probe circuit is disclosed which is responsive to the distance between a proximity probe and a conductive or an inductive target, and has an output directly proportional to the distance between the probe and a conductive target. An amplifier is connected as an oscillator in a bridge circuit with the probe in one arm of the bridge and variations of probe to target distance change the input to the amplifier. An output circuit is connected to the output of the amplifier and has a variable negative feedback to decrease the input to the amplifier as the output of the amplifier increases. This is accomplished by light emitting diodes and light sensitive resistors in one embodiment of the invention and the output circuit provides a means for determining an output voltage proportional to the probe to target distance.

Measurement System for Derivative Studies

Abstract: A system for measuring I‐V, dI/dV, and d2I/dV2 characteristics of two‐terminal devices is described. An operational amplifier integrator is used to produce a sweep voltage. For derivative measurements the dc bias voltage is modulated by a constant ac voltage signal. Current is detected by a near‐zero input impedance circuit with adjustable gain. A simple circuit utilizing an IGFET at zero drain voltage as a voltage controlled resistor compensates for harmonic content in the oscillator signal. It also enhances the detectability of weak harmonic signals in the presence of a strong fundamental signal by rejecting more than 90% of the strong signal. The system has been used to measure devices with impedances from a few ohms to over 105 Ω.

Test arrangement for a two-wire telephone channel

Abstract: There is disclosed an arrangement to test the transmission and signaling function of a two-wire carrier telephone channel. The arrangement includes a central office unit to which a test tone is applied for transmission to a subscriber unit. At the subscriber unit a test tone detector detects the test tone and actuates a switching arrangement to connect the tip conductor and ring conductor of a subscriber set together so as to cause a mistermination of a hybrid circuit in the subscriber unit thereby causing the test tone to be looped back to the central office unit where the magnitude of the test tone is measured. From the measurement of the test tone a faulty operation of the channel can be detected. The test tone detector includes a tuned circuit tuned to the frequency of the test tone, a precision halfwave rectifier circuit including a first solid state operational amplifier coupled to the tuned circuit and an output circuit including a second solid state operational amplifier coupled to the output of the rectifier circuit and to the tuned circuit to produce a full wave rectified output signal with voltage gain upon detection of the test tone to actuate the switching arrangement.

Balanced output operational amplifier

Abstract: An operational amplifier which provides a balanced output signal and whose differential input stage utilizes active loads. A common mode signal is derived from the balanced output signal and used via a comparator and a feedback loop to control the operation of the active loads.

Light amplifier for use in optical communication system

Abstract: A light amplifier comprising a first photo transistor for converting an optical input applied by way of an optical transmission line into an electrical signal, a comparator amplifier connected to the first photo transistor for receiving the output signal of the photo transistor as one of the two inputs thereto, a first and a second light emitting diode emitting light depending on the output current of the comparator amplifier, and a second photo transistor for converting the optical output signal of the first light emitting diode applied through a pair of polarizers into an electrical signal and applying this electrical signal in negative feedback fashion to the comparator amplifier as the other input thereto. The output current of the comparator amplifier is controlled so that coincidence is attained between the output signals of the photo transistors, and the optical output signal of the second light emitting diode is delivered to another optical transmission line as an amplified optical output.