Abstract: A preamplifier for processing an audio signal includes an equalizing and amplifying circuit comprised of parallel operational amplifiers, each with a feedback impedance circuit and an adjustable source impedance circuit. The adjustable source impedance circuit provides the preamplifier with a super-gain region in the high audio and supersonic frequency range. A summer adds the output of the parallel operational amplifiers to produce a single output signal. The parallel operational amplifiers, with the summer, gives the preamplifier unique low noise characteristic with an improved signal to noise ratio over a single operational amplifier with the same gain. The preamplifier may include an optional second stage for further equalizing and amplifying of the output signal.

Abstract: A combiner-amplifier is provided which has first current feedback amplifier which amplifies a first received signal by a predetermined gain value. A second current feedback amplifier amplifies a second received signal by the predetermined gain value. A combiner is operatively coupled to the first and the second current feedback amplifiers to combine the amplified first received signal with the second received signal together to generate a combined signal which is attenuated by the predetermined gain value such that the combined signal has approximately a unity gain over the first and the second received signals within a bandwidth of at least 45 megahertz.

Abstract: An amplifier circuit has a wide frequency range which is broader than the frequency range expected from its circuit parameters. The amplifier circuit comprises a plurality of unit amplifier circuits connected in parallel. Each unit amplifier circuit contains an odd number of inverters serially connected from the first stage to the last stage, an input capacitance connected to the input terminal of the first stage, and a feedback capacitance connecting the output terminal of the inverter of the last stage to the input terminal of the inverter of the first stage. Thus, the amplifier circuit operates in a wide frequency range with little decrease in gain at high frequencies.

Abstract: An amplifying apparatus for linearly amplifying a desired signal using a pair of coupled non-linear amplifiers is disclosed. The amplifying apparatus comprises a limiter for separating amplitude variations from the desired signal and producing a constant amplitude signal bearing the phase of the desired signal and an amplitude related signal. In addition, a drive signal generater produces two drive signals each dependent on the constant amplitude signal and the amplitude related signal such that each drive signal depends on the phase of the desired signal and such that the sum of the squares of the amplitudes of the drive signals is constant. Finally, a coupler couples the two drive signals to produce two constant amplitude signals for driving the pair of non-linear power amplifiers and for coupling the outputs of the power amplifiers to produce two amplified output signals, one of which is the linearly amplified desired signal and the other of which is a waste energy signal.

Abstract: A preamplifier and pre-emphasis network is provided having a differential plifier exhibiting common mode noise rejection. The preamplifier is particularly suited for use with a double-sided sensor element and it includes a double-sided, balanced calibration circuit. First and second variable gain buffers are joined to the differential amplifier for preventing current noise degradation at the differential amplifier inputs. A pre-emphasis network is further provided in conjunction with the variable gain buffers for providing balanced differential gain of the sensor element signal. Further elements of the invention provide for high and low pass filtering, and differential buffering of the output signal.

Abstract: A self-configurable, dual bridge, power amplifier has a window comparator sensing the level of input signals fed to the amplifier which-drives a plurality of configuring switches capable of configuring the amplifier as a single bridge amplifier driving a first and a second loads connected in series or as two distinct bridge amplifiers each driving one of the two loads. As long as the two levels of the input signals remain comprised between a range defined by a negative voltage reference and a positive voltage reference, the amplifier is configured as a single bridge driving the two loads in series, thus reducing sensibly power dissipation. Several embodiments of the configuring means are shown.

Abstract: The apparatus includes output stage amplifiers for receiving the respective outputs of preamplifiers provided in correspondence to the left and right channels in a stereo system. Negative feedback circuits are provided in the respective output stage amplifiers for reducing the amount of low-band negative feedback. Switch circuits are turned on in response to feedback signals from the respective negative feedback circuits for supplying the feedback signals at the input to the output stage amplifiers.

Abstract: An audio amplification circuit includes a ganged pair of logarithmic potentiometers, each potentiometer of the pair having an input terminal, an output terminal, and a wiper terminal. The input terminals of each potentiometer are adapted for connection to an audio input signal from an audio device such as a microphone. A preamplifier stage having an input is connected to the wiper terminals of both logarithmic potentiometers. An amplification stage has a matched pair of operational amplifiers with each operational amplifier having an input connected to the output of the preamplifier stage. Each operational amplifier has a feedback loop which includes the resistance of at least one of the logarithmic potentiometers between the output terminal and the wiper terminal of said logarithmic potentiometer. The outputs of the matched pair of operational amplifiers constitute the outputs of the amplification stage. The outputs may be daisy-chained together, and a floating output stage is also provided.

Abstract: A line driver comprising: an input terminal for receiving an input signal, an output terminal for connecting a load, a first and a second transconductance-controlled transconductor having substantially equal transconductances, each transconductor having a non-inverting input, an inverting input, an output and a common control input for controlling the transconductance, the non-inverting inputs of the first and second transconductors being coupled to the input terminal, the outputs of the first and second transconductors being coupled to the output terminal, the inverting input of the first transconductor being coupled to a point of reference potential, the inverting input of the second transconductor being coupled to the output terminal, and an amplifier having a non-inverting input, an inverting input and an output coupled to, respectively, the input terminal, the output terminal and the common control input of the first and the second transconductors.

Abstract: A programmable gain amplifier including first and second gain elements are connected by an impedance selector which allows programmability of the gain of both gain elements. The impedance selector is connected in series with the output of the first gain element. The impedance selector places an impedance in the feedback path of the first gain element or the input path of the second gain element. Errors introduced in the signal path due to the switches are attenuated by the open loop gain of the first gain element. The gain may be equally divided between both stages of the amplifier to allow for optimum band width. Optimum noise performance may be obtained by placing most of the gain in the first stage. An instrumentation amplifier may also be made which further includes a third gain element connected to the gain element with a second impedance selector in a manner similar to the connection of the first gain element to the second gain element.

Abstract: A main amplifier has an enhanced gain due to current injection from a replica amplifier which has a similar structure and feedback network to that of the main amplifier. The main amplifier has a transconductance stage and an output resistance stage. A coupling transconductance stage receives the same input signal as that received by the main and replica amplifiers and injects a current to the output node of the main amplifier. The injected current is the same as the current to the output node would have been from the main amplifier's transconductance stage, were the replica amplifier not present. The gain can be obtained without a cascode and with short-channel CMOS technology that operates at a low supply voltage. The gain is increased without causing an increase in the output resistance, and without causing a decrease in the common-mode input range or the output swing.

Abstract: A multi-output power amplifier is disclosed. The amplifier is divided into two stages. A single voltage amplifier is used as an input amplifying stage and several current amplifiers are used as a second amplifying stage. The inputs to the current amplifiers share a common connection to the output of the voltage amplifier and feedback is provided from the current amplifier outputs to the voltage amplifier input.

Abstract: A self-configurable, dual bridge, power amplifier has a window comparator sensing the level of input signals fed to the amplifier which drives a plurality of configuring switches capable of configuring the amplifier as a single bridge amplifier driving a first and a second loads connected in series or as two distinct bridge amplifiers each driving one of the two loads. As long as the two levels of the input signals remain comprised between a range defined by a negative voltage reference and a positive voltage reference, the amplifier is configured as a single bridge driving the two loads in series, thus reducing sensibly power dissipation.

Abstract: A method and circuit for increasing the output impedance of an inactive amplifier is provided. The method and circuit allows an increased number of amplifiers to be coupled in parallel to a single transmission line for distributing a plurality of video or other electrical signals to a remote location. The method and circuit increasing the impedance of an amplifier feedback network during inactive operation using a bootstrapping technique (i.e., by driving the feedback network) so as to increase the overall impedance of the amplifier during such operation.

Abstract: A differential amplifier which utilizes a pair of wideband operational amplifiers as output stages for two differential output signals, a pair of high performance DC operational amplifiers to buffer input signals to the pair of wideband operational amplifiers used as output stages and reduce offset voltage error by the amount of the DC gain of the pair of high performance DC operational amplifiers, apparatus for biasing the pair of high performance DC operational amplifiers to provide exceptional DC characteristics and eliminate common mode response from those amplifiers, and apparatus for feeding forward high frequency AC input to the wideband operational amplifiers operating as the output stages without loading the common mode input impedance of the differential amplifier.

Abstract: An amplifier circuit for applying a voltage from a voltage source across a load having a frequency domain transfer function g(s), the circuit being composed of: a coupling member having a frequency domain transfer function f(s); first connecting elements for connecting the coupling member between the source and the load; a compensating member having a frequency domain transfer function r(s); and second connecting elements for connecting the compensating member to both the source and the load.

Abstract: A programmable gain amplifier including first and second gain elements are connected by an impedance selector which allows programmability of the gain of both gain elements. The impedance selector is connected in series with the output of the first gain element. The impedance selector places an impedance in the feedback path of the first gain element or the input path of the second gain element. Errors introduced in the signal path due to the switches are attenuated by the open loop gain of the first gain element. The gain may be equally divided between both stages of the amplifier to allow for optimum band width. Optimum noise performance may be obtained by placing most of the gain in the first stage. An instrumentation amplifier may also be made which further includes a third gain element connected to the gain element with a second impedance selector in a manner similar to the connection of the first gain element to the second gain element.

Abstract: The invention relates to a circuit for driving a transformer coupled line amplifier. The present invention uses a high impedance differential negative feedback from the secondary of the transformer and uses positive feedback from the primary winding of the transformer. This enables the transformer to be smaller in size while still reducing the harmonic distortion, improving the frequency response, eliminating ringing, lowering the output impedance, improving the longitudinal balance, and also improving the overall stability and phase response of the transformer.

Abstract: A Class A high power amplifier having an operating frequency in the range of less than substantially 2 GHz and suitable for aircraft use, is all solid state in that gallium arsenide field effect transistors are utilized. These are mounted in a large copper heat sink which is air cooled to provide for overall cooling by conduction and convection. By the use of microstrip matching circuits, the relatively low impedance of the gallium arsenide FET units is matched to the required higher system impedance. At the same time a 40% band-width is provided due to the superior matching.

Abstract: A voltage-controlled amplifier employs an operational amplifier with negative feedback for setting the gain. A voltage variable resistance such as a junction-field-effect transistor (JFET) is employed as part of a variable voltage divider for controlling the amplifier gain. Resistors in series and in parallel with the JFET determine minimum and maximum resistances corresponding to upper and lower limits for the amplifier gain. Thus, multiple channels of an amplifier can be provided with closely matched characteristics even using separate JFETs in each separate channel which have unmatched characteristics.

Abstract: A cost-effective, low power and low distortion digital data line driver is disclosed with the capability to operate from a limited voltage source while maintaining wide output voltage swings. The line driver has the noise immunity attribute of a fully differential input device without all the usual complex CMFB circuitry normally required. The line driver provides a low distortion output with a low output impedance and maintains its impedance value on the same order of magnitude at frequencies up to four times the Nyquist rate.

Abstract: A differential output stage for electronic equipment, the output stage comprising a two-port network having two paths, each connecting an input terminal to an output terminal, and comprising means for generating a negative feedback voltage from each path for application to the other, and means for providing an output voltage in each path equal to an identical linear combination in each path, of the input voltage to the path and of the negative feedback voltage from the other path.

Abstract: An analogue amplifier circuit has a gain stage comprising two differential operational amplifers (17, 18) and an error correction stage comprising two differential operational amplifiers (20, 21) each connected with its inputs across the inputs of a respective gain stage amplifier and its output connected to the non-inverting input of the other gain stage amplifier. A balanced output from the outputs of the two gain stage amplifiers (17, 18) may be provided or these two outputs may be fed to a final stage amplifier (22) to provide a single output.

Abstract: A multichannel amplifier employs field-effect transistors to vary the gain of operational amplifiers in each respective channel. Gain matching of the respective channels is obtained by providing each channel with a respective DC bias voltage which compensates for differences in pinch-off voltage of the field-effect transistors. The invention permits the use of inexpensive, unmatched JFETs in the amplifier. Close gain tracking achieves very accurate stereo imaging in an audio system.

Abstract: A system for extending the frequency range of an RF amplifier by improving the VSWR, and power handling capability of the amplifier, comprising a broadband reversing transformer, a first and a second amplifier coupled by means of a first and a second through-line quadrature coupler with the first quadrature coupler being connected to the inputs of the two amplifiers and the second quadrature coupler being connected to the outputs of the two amplifiers. The broadband reversing transformer is inserted in series with one of the two amplifiers enabling a signal at frequencies out of the passband of the quadrature couplers to pass through the through-lines port of the quadrature couplers, and thereby greatly extending the frequency range over which quadrature couplers may be used while, at the same time, retaining the usual combining and VSWR advantages of the couplers within their passbands.

Abstract: A new instrumentation amplifier design uses three operational amplifiers (op amps), each of which has a feedback circuit connected from its output to its inverting input. The first op amp has a unity gain feedback, and is connected through a gain setting resistor to the inverting input of the second op amp. The output of the third op amp is connected through a resistor to the inverting input for the second op amp, while the third op amp's non-inverting input is connected to one of the second op amp's inputs. Differential voltage input signals are applied to the non-inverting inputs of the first and second op amps, while a reference voltage is applied to the inverting input of the third op amp. The circuit is capable of operating with a single voltage supply (V+) by setting the negative voltage supply together with the reference voltage at ground potential. It has a simplified gain equation based upon the ratio between the feedback resistor for the second op amp and the gain setting resistor.

Abstract: A pulse amplifier has a driver stage and a following splitter/combiner stage for power division onto two output stages connected in parallel as well as a further splitter/combiner stage that combines the output signals of the output stages. The two splitter/combiner stages each comprise a respective further decoupled port each of which is respectively connected to a switch-over device. The further ports are connected to terminating impedances in a first switch position of the switch-over devices and are connected to one another via an additional signal path in a second switch position and the output stages can be respectively terminated with low impedances at their input sides and output sides via switch elements.

Abstract: A three-terminal operational amplifier includes a current input, in addition to the conventional inverting and non-inverting inputs. The current input is inverted and added to the inverting input current, while its voltage is urged to a level equal to that of the inverting and non-inverting inputs. The new amplifier employs a pair of two-terminal operational amplifiers, the first of which has inverting and non-inverting inputs, and the second of which has the current input and a second input connected in common with an input to the first amplifier. Internal feedback circuits provide the desired current conveyance. The circuit may be implemented either with mutually discrete two-terminal operational amplifiers, or these elements may be merged into a single unified circuit. Applications include a general purpose adder/subtractor circuit, an inverting gain amplifier, an instrumentation amplifier, integrators and differentiators.

Abstract: A dual path amplifier circuit configuration to obtain wideband and precision DC response includes a wideband voltage amplifier, an input termination, a virtual ground feedback amplifier, and a compensated attenuator. The circuit allows precision DC and wideband measurements through a common signal probe while maintaining the input impedance of the measurement instrument. An additional feature of the circuit is to selectively allow DC measurements before or after an attenuator. The circuit can provide combined wideband and DC signal output or separate wideband and DC outputs. Additionally, the circuit can use a DC offset to null the DC level of an input signal.

Abstract: A microwave power amplifier includes first and second circuits each having first, second, third and fourth terminals. Each of the first and second circuits has functions of distributing an input signal to the second and third terminals and generating first and second output signals 180.degree. out of phase with each other through the second and third terminals, respectively, adding a first pair of 180.degree. out-of-phase input signals to the second and third terminals and outputting a first resultant signal through the first terminal, and adding a second pair of in-phase input signals to the second and third terminals and outputting a second resultant signal through the fourth terminal.

Abstract: A differential operational amplifier comprises a differential input circuit that provides a differential output signal to a plurality of independent output circuits. The gains of the differential input circuit and one output circuit are set by a fixed bias source. A variable bias source controlled by an external signal determines the gain of each other output circuit so that various attenuation characteristics are obtained in the other output circuits without affecting the operating conditions of the operational amplifier. A feedback element between the output of the one output circuit and the differential input circuit assures gain stability.

Abstract: An amplifier stage includes an operational amplifier having inverting and non-inverting inputs and an output and a resistive tee network coupled in the feedback loop between the inverting input and output to the non-inverting input which network is reference to the voltage applied at the non-inverting input for setting the gain of the amplifier stage. The amplifier stage may be combined with a differential pressure sensor for providing a single ended output voltage in response to the differential voltage outputs of the pressure sensor being applied to the inverting and non-inverting inputs of the amplifier stage.

Abstract: Method and apparatus for amplification of an electrical signal whose frequency may range from zero to 300 MHz, and whose voltage level may range from 0.5 volt to 0.5 volt, with intermittent resetting of the zero voltage level provided for. One or two incoming signals are divided into low frequency and high frequency components, and amplification of each of these components is optimized by passage of the component through a separate amplification circuit. Input signals to the high and low frequency amplification circuits are intermittently chopped to allow resetting of the zero voltage levels of the amplifier.

Abstract: In an integrated amplifier comprising at least a pair of operational amplifiers which may be connected in a single-ended configuration to form a stereo amplifier or alternatively in a bridge configuration to increase the output dynamics, a single constant current generator for generating a current having a value which is twice the value of the bias current of the input stages of the two operational amplifiers, is connected between an inverting input of one of the two operational amplifiers and ground, and allows for elimination of the offset voltage without contributing to an increase, in any appreciable way, of the noise level at the inputs and without the signal applied to the input terminals of the integrated amplifier causing modulation problems.

Abstract: A serial-type analog-to-digital converter includes a plurality of serially connected folding circuits. Each folding circuit includes a first operational amplifier having an inverting input connected to an input terminal, and a second operational amplifier having a noninverting input connected to the input terminal. The bases of first and second transistors are respectively connected to the outputs of the first and second operational amplifiers. The emitters of the transistors are commonly connected to an output terminal. Feedback connections are provided for coupling the output terminal to the inverting input of each operational amplifier. Furthermore, circuitry is provided for calculating an estimated offset error based on maximum values of a folded analog signal provided at an output terminal of one of the folding circuits.

Abstract: A so-called bridge audio amplifier, particularly for stereophonic car radio sets, comprises a first power amplifier in a non-inverting configuration which is connected to a second amplifier in an inverting configuration. This audio amplifier further comprises a first resistor pair forming a bridge circuit with the resistors of the first power amplifier, as well as a second resistor pair interconnected between a positive supply pole and ground and with the first and second amplifiers having their respective non-inverting inputs connected across the second resistor pair via respective input resistors. The audio amplifier of this invention requires but a very small number of input pins and may be used as a stereophonic amplifier.

Abstract: Negative-feedback amplifier provided with an active amplifier section operating approximately as a nullor and a negative feedback section, the amplifier having a high loop gain. The active amplifier section is constructed in balanced form with two nullors connected in balance, and the negative-feedback section is composed of passive impedances and comprises two negative-feedback loops. In one embodiment each nullor has a series-coupling circuit and a parallel-coupling circuit at the input port. As a result an accurately defined or characteristic input impedance is obtained, and a series- or parallel-coupling circuit is formed in both negative-feedback loops at the output port, so that a high (current output) or low (voltage output) output impedance, respectively is obtained. In another embodiment each nullor has a series-coupling circuit and a parallel-coupling circuit at the output port.

Abstract: A sum/differential signal processing circuit for use in a sound reproduction system, such as a Dolby surround processing system, includes a pair of operational amplifiers, a resistor connected between the inverting input terminals of the operational amplifiers, two resistors connected between the output terminals of the operational amplifiers, a signal output terminal connected to a junction between the two resistors for producing the sum of output signals from the output terminals of the operational amplifiers. A make switch is connected across one of the two resistors, which is selectively rendered ON and OFF. When the make switch is ON, the sum of output signals of the operational amplifiers is derived from the signal output terminal while when the make switch is OFF, the difference between the output signals thereof is derived therefrom. Even when a monaural signal is applied to each of the two signal input terminals, the signal is not cancelled by the circuit thus arranged.

Abstract: An automatic gain control circuit for an amplifier operating over a prescribed frequency range detects the output level of the amplifier; and couples a repeated predetermined waveform occurring at a rate greater than the reciprocal of twice the upper frequency of the prescribed frequency range to the output level signal. The waveform varying level signal is compared to a reference threshold to control the gain of the amplifier through a switched resistive elemement in the amplifier feedback path. The repeated waveform variations about the amplifier output level causes the value of the switched resistance to vary as a function of the output level. A low pass filter connected to the amplifier output removes switching transients resulting from the high frequency changes in the switched resistive element. The gains of a plurality of amplifiers may be determined by a common control for accurate tracking over a wide dynamic range.

Abstract: In an amplifier circuit, there are provided a preamplifier, a first differential-input amplifier and a second differential-input amplifier. An AC negative feedback path is formed between the output terminal of the preamplifier and the inverting input terminal thereof. The inverting input terminal is connected to a ground via a RC series circuit. An input signal containing a DC voltage component is supplied via the junction of the RC series circuit to the inverting input terminal. A voltage appearing at this junction is applied to both the first and second differential-input amplifiers as a reference voltage.

Abstract: An integrated circuit in a seven pin package particularly for audio signal amplification comprises at least two integrated amplifiers selectively commutable in a bridge configuration or in a stereo configuration by means of at least three integrated switches driven by an integrated comparator with threshold set by an internally generated reference voltage and whose input is connected to the SVR pin commonly used to implement the function of common mode signals rejections. The internal commutation between the two selectable configurations is obtained by varying the level of the bias voltage applied to said SVR pin by means of an external voltage divider.

Abstract: An isolator for connection between an informational signal source and a high voltage controlled load may be used with numerous combinations of different input signal type and magnitude and output signal requirements. The compensation for input and output signal variation is accomplished by changing a minimum number of easily accessible plug-in passive circuit components.

Abstract: An amplifier comprises a first amplifier circuit and a second amplifier circuit. An input signal voltage and an input DC bias voltage are applied to the first amplifier circuit, and an input DC bias voltage is applied to the second amplifier circuit. The input DC bias voltages applied to the first amplifier circuit and the second amplifier circuit are common to each other. Output bias voltages of the first amplifier circuit and the second amplifier circuit become equal to each other. The amplified signal voltages are applied to a load connected between outputs of the amplifier circuits.

Abstract: An integrated amplifier circuit includes:first and second operational amplifiers each having a terminal connected to a supply potential node, and a terminal connected to a reference potential node;two ohmic voltage dividers each being formed of two resistors connected between an output of a respective one of the operational amplifiers and a first circuit node, and two further ohmic resistors each being connected between a respective tap of the voltage dividers and a respective inverting input of a respective one of the operational amplifiers, providing real negative feedback of the operational amplifiers;a third ohmic voltage divider formed of two resistors connected between a supply potential node and the first circuit node, an intermediate ohmic resistor connected between a tap of the third voltage divider and a second circuit node, and two ohmic supply resistors each being connected between the second circuit node and a respective non-inverting input of the operational amplifier; an ohmic series resistor c

Abstract: The low-frequency integrated amplifier comprises a voltage amplifier stage and two power amplifier stages including power amplifier means driven by the voltage amplifier stage and fedback by means of a respective feedback network dimensioned so that, at the frequency at which the phase shift of the power stages exceeds 180.degree., the open loop gain thereof is less than 0 dB, so as to prevent, for any kind of load and for every output voltage, any oscillation of said stages, and ensure the absolute stability of the system.

Abstract: An amplifier system having an input active device at its first input and having its second input provided through an inverting means to that first input.

Abstract: A fully integratable bridge amplifier comprises two identical amplifiers (1; 5) each being provided with a first input stage (20; 40) whose inputs constitute the first non-inverting inputs (2; 6) and the first inverting inputs (3; 7) of the amplifier, a second input stage (29; 50) whose inputs constitute the second non-inverting inputs (28; 49) and the second inverting inputs (27; 48) of the amplifier, and an output stage (25; 45). The first inverting input (3; 7) of each amplifier (1; 5) is connected to the output (12) of a buffer amplifier (9) via a first resistor (R.sub.6 ; R.sub.9) which together with a second resistor (R.sub.5 ; R.sub.8) constitutes a negative feedback network between the output (4; 8) of the amplifier (1; 5) and the first inverting input (3; 7). The first non-inverting input (2; 6) is also connected to the output (12) of the buffer amplifier (9). This output (12) and consequently the first inputs (2, 3; 6, 7) of the amplifiers (1; 5) are at half the supply voltage with respect to the d.

Abstract: An amplifier circuit having offset voltage and offset voltage drift corrections which does not require resistive feedback and is suitable for use with unmatched high frequency field effect transistor circuits. The described circuit cancels the offset voltage of a signal amplifier and comprises means for applying differential voltages to an operational amplifier, together with a switchable feedback connecting the output of the amplifier to one of its inputs and a capacitor coupled between the feedback input of the amplifier, and one of the differential voltages. This allows amplifying of low level AC signals while reducing the error introduced by the offset voltage or the offset voltage drift of the amplifier.

Abstract: A bank of differential amplifier circuits includes specialized circuits to provide multi-channel differencing with a minimum number of active devices such that the differences between pairs of analog input signals, such as available from patient monitoring electrodes, are derived with half the number of active devices normally utilized. In one embodiment, two operational amplifier circuits are used in a differencing channel which functions together to provide differencing, a properly delayed input signal for use in another differencing channel, high input impedance buffering, a low impedance output for each differential amplifier channel, time-coincident, matched outputs for each differential amplifier channel, and with an additional operational amplifier, a DC rejection circuit which does not affect the low output impedance or the differencing function, thereby to eliminate the necessity of providing separate buffers and active delay circuits which can result in the use of twice the number of active devices.

Abstract: A second order all pass network for wide-band signals, and comprising second and third voltage-current converting circuits with their respective positive input terminals supplied with input signals from an input terminal of the network and their negative input terminals supplied with output signals from an output terminal of the network. A first voltage-current converting circuit has its positive input terminal supplied with a positive output of the second voltage-current converting circuit and a negative input terminal supplied with the output signals. A first capacitor is connected between the input and output terminals, and a second capacitor is connected between ground and the positive output of the second voltage-current coverting circuit.