Abstract: In an integrated circuit audio power amplifier a 6 db per octave frequency-gain roll off is obtained in a conventional manner by converting a high gain inverter to an integrator and driving the integrator from a current source. A second cascaded stage is also provided so that it operates at lower gain and has a matching high frequency roll off. When such characteristics are combined in cascade the result is a 12 db per octave roll off at the higher frequencies. A flat negative feedback loop is employed to maintain a controlled constant low frequency gain. In the response region located between the 12 db per octave slope region and the constant gain region there is a 6 db per octave slope. The configuration is stable without resorting to frequency sensitive feedback.

Abstract: An amplifier including an in phase feedback signal to therefore exhibit negative resistance is receptive of an input alternating signal which includes a frequency F. The output of the amplifier is coupled to a resonator adjusted to a center frequency F and having undesirable resistance which is offset by the negative resistance of the amplifier. The resonator includes an inductor and adjustable capacitor arranged either in series or in parallel with the amplifier to therefore change the value of F.

Abstract: An operational amplifier includes an input stage, an output stage including first, second and third NPN output transistors, and an intermediate stage including first and second emitter follower transistors. The first NPN output transistor sources load current to an output terminal while the second and third NPN output transistors sink load current from the output terminal. A diode is coupled across the collectors of the second and third NPN output transistors to conduct possible short circuit currents. Additionally, a pair of series coupled resistors are coupled across the collectors of the second and third NPN output transistors. A Miller capacitor is coupled between the input of the intermediate stage and the junction of the first and second resistors.

Abstract: The gain and phase characteristics of an operational amplifier are improved by adding a system zero to cancel a pole and thereby broadband the amplifier. This is accomplished by simultaneously driving the base terminals of the second stage gain transistor and preceding follower transistor and biasing the circuit such that the dynamic emitter resistance of the follower transistor is much greater than that of the gain transistor and/or by adding an additional emitter impedance.

Abstract: A negative feedback amplifying circuit comprises an amplifier connected to a load, a voltage negative feedback circuit which negatively feeds back the output voltage of the amplifier to the input side of the amplifier maintaining a frequency selection characteristic, and a current negative feedback circuit which negatively feeds back a current signal obtained by detecting the current flowing through the load to the input side of the amplifier maintaining a frequency selection characteristic. The voltage negative feedback circuit has a frequency selection characteristic comprising a dip at a specific frequency f.sub.0. On the other hand, the current negative feedback circuit has a frequency characteristic comprising a peak at a specific frequency f.sub.0.

Abstract: A low noise amplifier, comprising a grounded emitter transistor amplifier having a parallel impedance element connected between base and collector and a series impedance element connected between emitter and ground. The parallel impedance element is selected to have a pole near a zero of the series impedance element, and the parallel impedance element also has a zero near a pole of the series impedance element. The impedances of the series impedance element and of the parallel impedance element vary oppositely with respect to frequency, so that the input impedance of the amplifier is constant with respect to frequency. However, by selection of two impedances which are thus matched, the gain is increased at high frequencies and slightly reduced at low frequencies. Thus, the total noise figure is improved, due to the higher gain at the higher frequency range.

Abstract: An equalizer amplifier in which non-linear distortion is substantially eliminated. An input signal is applied to the base of a first transistor the output of which is applied to the base of a second transistor of the opposite conductivity type to the first transistor. Currents are supplied to the first and second transistors in a constant ration. The output from the circuit is provided in response to current flowing in one of the first and second transistors. At least one of the amplifier gain determining elements has a reactance component which varies depending on frequency.

Abstract: A split phase delay equalizer is provided which reduces loss without resorting to high values of load impedance. The equalizer has a pair of parallel circuit branches, one of which is through the base and collector of a transistor, and the other through a reactance network connected between the collector and base of the transistor.

Abstract: A unity gain amplifier circuit has a control characteristic which permits a variation of the high frequency roll off as a function of a control voltage. Means are provided to prevent a change of output voltage resulting from the control voltage variation.

Abstract: A constant phase limiter is disclosed utilizing cascaded RC coupled amplifiers with complex feedback. In the illustrative embodiment, five NPN transistors connected in a common emitter configuration are cascaded. The first stage is a signal conditioning amplifier for setting the limiting threshold. By harmoniously selecting the operating conditions for each of the other stages, an overall constant phase/limited output characteristic can be achieved for the desired range of input signal.

Abstract: Stray reactance compensation is provided in a split phase delay equalizer by inserting an auxiliary compensating small reactance in the substantially real arm circuit branch which provides a third order response equal and opposite to the deviation from second to third order in the amplitude response curve caused by stray reactance deviated phase reversal from the ideal.

Abstract: A configuration of two transistors and two capacitors provides a current mode second-order active filter for IC implementation with low-pass, bandpass and high-pass capabilities. The filter frequency is tunable over a wide range, independently of filter Q and gain, by varying a DC bias current. The filter can provide one-port impedance functions, and two-port voltage, current and impedance transfer functions. With the addition of a second biasing current source, the filter Q can be controlled by adjusting the ratio of the two biasing current sources. Enhanced dynamic range and large-signal performance can be achieved by the addition of linear resistors, with trade-offs in tunable frequency range and frequency linearity.

Abstract: An analog integrated filter circuit includes a capacitance multiplier combined with a DC bias controlled current circuit designed to render the filter circuit insensitive to changes in the parameter values of the components caused by process variations or a temperature change therein. The capacitance multiplier circuit includes grounded or ungrounded capacitance multipliers in different combinations operatively coupled to the DC bias controlled current circuit so that the capacitance multiplier circuit can be used to construct a predictable low pass, bandpass or high pass filter circuit with frequency characteristics that do not vary over temperature.

Abstract: In a frequency characteristic adjusting circuit having an arrangement of at least one adder, a filter circuit and feedback and/or feed forward means the transfer factors of which and the peak or dip of the filter circuit are freely selectable. Adjustment of the center frequency and Q are independent.

Abstract: Monolithically integrable lowpass filter circuit having at least one capacitor and one ohmic resistor includes a signal input, a circuit node connected to the signal input, a first series resistor connected between the signal input and circuit node, an operational amplifier, a signal output connected to the output of the operational amplifier and to the circuit node, a second resistor connected between the circuit node and the signal output, a third resistor connected between the circuit node and the non-inverting input of the operational amplifier, and a capacitor connected between the non-inverting input and ground, the signal output being further connected to the inverting input of the operational amplifier.

Abstract: A tunable active high-pass filter particularly for use in hearing aids, which comprises merely a transistor as the active amplifying element. Three series-connected capacitors are connected between the input of the filter and the base of the transistor. A first resistor branches off from the junction between the first and second capacitors, a second resistor branches off from the junction between the second and third capacitors, and both resistors are connected, via a third resistor which is adjustable, to the emitter of the transistor which constitutes the output of the filter. A further resistor extends from the junction between the third capacitor and the transistor base to the source of operating potential which, for example, is positive. Preferably, each of the capacitors forms a high-pass filter with its respectively connected resistor with the first and second resistors, i.e.

Abstract: A throat microphone consists of a dynamic pressure transducer sealed within an airtight tympanic enclosure to be held by an elastic band on the user's throat near the voice box. The electrical signals generated by the transducer are applied as an input signal to an amplifier and speaker unit where the signal is conditioned by a preamplifier stage for further amplification by a second stage that contains a variable reactive negative feedback network that acts as a low pass filter and corrects the phase shift of the different lower frequency audio signal components while emphasizing the higher frequency components so that severe phase distortion of the signal applied to the drive speaker through an output power amplifier stage can be minimized to make the speech sounds reproduced more intelligible.

Abstract: A signal processing circuit for improving the signal-to-noise ratio of input signals, such as audio signals recorded on tape, has a low-pass filter circuit for controllably filtering signals at the lower end of the frequency spectrum, and a high-pass filter circuit for controllably filtering signals at the higher end of the frequency spectrum, with the high-pass filter circuit and the low-pass filter circuit defining the only paths through the signal processing circuit for the input signals. Associated control circuitry provides first and second control signals to control the attenuation of signals at the lower-frequency and higher-frequency parts of the spectrum, respectively, in dependence on the amplitude of the input signals in the respective parts of the spectrum.

Abstract: A filter circuit whose cut-off frequency is easily controlled and which can be manufactured as an integrated circuit. The base electrode of a first transistor is connected to an input terminal by a reactance element, such as a capacitor. Second and third transistors are connected in differential amplifier configuration, and a current source is connected to the common connection of the emitter electrodes thereof. The emitter electrode of the first transistor is connected to the base electrode of the second transistor and the base electrode of the first transistor is connected to the collector electrode of the second transistor. An output terminal is connected to at least one of the collector and emitter electrodes of the first transistor.

Abstract: A sound amplifier is provided in a monolithic integrated circuit form and includes tone compensated volume control achieved by the use of emitter followers and a capacitor connected at one side to ground.

Abstract: A balanced input phonograph preamplifier circuit according to the present invention incorporates a matched differential pair of transistors having a gain control system therefor and having a load matched to standard phonograph cartridge output characteristics by means of a 47,000 ohm resistor and a capacitor that is designed for the particular cartridge involved. A differential voltage amplifier is defined by the matched differential pair of transistors functioning in conjunction with a differential amplifier which is in the form of an operational amplifier functioning in the differential mode. The output signal of the differential voltage amplifier system is processed by a deemphasis network incorporating a voltage amplifier and a current amplifier that are bridged by a feedback loop that is designed specific to the equalization curve of the Record Industry Association of America.

Abstract: A low pass active filter comprises multiple stages including multiple active devices, circuitry including resistance and capacitance AC coupling the stages in series sequence, and high impedance biasing resistance coupled between the first and last stage inputs, whereby the DC operating point is determined by one active device.

Abstract: In an equalizer amplifier of RC attenuation type comprising an RC circuit having RIAA reproduction characteristics, the RC circuit is connected between an input of a first amplifier for amplifying an output signal of the RC circuit and an output of a second amplifier for amplifying an output signal of the first amplifier. One of the amplifiers is a noninverting amplifier, and the other is an inverting amplifier. So constituted, the equalizer amplifier increases apparently impedances of RC elements connected between the input of the first amplifier and the output of the second amplifier and permits the use of a capacitor of a smaller capacitance value which has good electrical characteristics.

Abstract: A filter circuit, preferably a low-pass filter, whose cut-off frequency is easily controlled and which can be manufactured as an integrated circuit. First and second transistors are connected in differential amplifier configuration, and a current source is connected to the common connection of the emitter electrodes thereof. The base electrode of the first transistor is connected to an input terminal. A reactance element is connected between the collector electrode of the second transistor and a source of reference potential, such as ground. A third transistor has its emitter electrode connected to the base electrode of the second transistor and its base electrode connected to the collector electrode of the second transistor. An output terminal is connected to the emitter electrode of the third transistor.

Abstract: An operational amplifier circuit having a first amplification stage that includes a differential pair of matches, low-noise transistors coupled in a common-emitter configuration, with a special reactive network in the emitter circuit of each transistor. Each reactive network comprises an inductor and a resistor, arranged in a shunt configuration, whereby at low frequencies the first stage has a relatively high gain and generates relatively low noise, and whereby at high frequencies the first stage has a relatively low gain and the amplifier circuit has sufficient phase margin to ensure stability.

Abstract: A low distortion phase compensated wideband amplifier system includes a low cost, power efficient Class C amplifier positioned along a primary signal path and a feedback loop coupled to provide negative feedback of distortion signal components in the amplified output signal. The negative feedback significantly reduces noise components including intermodulation noise while variable delay phase compensation permits a greater signal to noise ratio over a broader band of frequencies at the system output.

Abstract: An electronic filter comprised of three active filter sections (A, B, C) is provided to smooth the stepped signal from a digital-to-analog converter. The first section has a noninverting low-pass filter transfer function, and the second has an inverting transfer function designed to pass a narrow frequency band centered at the step frequency of the stepped output signal with sharp cutoff on either side of that narrow band. The third section adds the noninverted output of the first section to the inverted output of the second section. This third section has a lead-lag transfer function designed to reduce the phase angle between the signal at its output terminal and the stepped signal at the input of the first section.

Abstract: The frequency response of the frequency sensitive amplitude equalization circuit disclosed herein can be adjusted by a single potentiometer to be either flat or give a positive or negative gain at a selected frequency.

Abstract: A tone control circuit including an operational amplifier having (a) an input circuit or output circuit and (b) a feedback circuit where circuits (a) and (b) are symmetrically disposed with respect to a reference potential such as ground. Circuitry is also provided to compensate for load and/or feedback impedances. Further, circuitry is provided to reduce the number of switches and capacitors needed to vary the high and low cut-off frequencies of the tone control circuit.

Abstract: Integrable analog active filter suitable for MOS monolithic implementation. The filter utilizes only integrating amplifiers and ratioed capacitors thus being implementable in MOS technology and compatible for use in MOS digital systems. Filters of unlimited complexity and having arbitrary transfer functions can be implemented by the integrable analog active filter.

Abstract: A feedback system for a multi-stage amplifier is disclosed which includes a nest of feedback loops centered on a particular stage, for example, on the output stage. This enables a very large amount of feedback to be applied to that stage, and enables constant return difference to be obtained for that stage over a nominated frequency range. Bode's limits for mid-band loop-gain magnitude and its rate of attenuation with frequency can be exceeded.

Abstract: An amplifier having a high gain in a selected frequency band, e.g. for the preferential amplification of a pilot oscillation, consists of a plurality of cascaded stages each comprising an active component, a coupling network and a negative-feedback network. The coupling and feedback networks are alternately connected in a series circuit between a signal input and a signal output, each of these networks (with the possible exception of those associated with the first stage) comprising a damped parallel-resonant circuit with an inductive branch forming a low-ohmic path for direct current. Each active component has an input electrode connected through a stabilizing resistor to the junction of the associated coupling and feedback networks, its output electrode being tied to the downstream end of the corresponding feedback network.

Abstract: The disclosed amplifier includes first and second gain stages and first and second frequency compensating capacitors. The second gain stage has a first high impedance node coupled to the first gain stage, a second high impedance node, a first circuit coupled between the first and second high impedance nodes, a third high impedance node, and a second circuit coupled between the second and third high impedance nodes. The impedances at the first, second and third high impedance nodes are a function of frequency and the impedance at the second high impedance node is lower at any given frequency than the impedances at the first and third high impedance nodes. The first frequency compensating capacitor is coupled between the first and third nodes and the second frequency compensating capacitor is coupled between the third and second nodes.

Abstract: An amplifier for video signals transmitted by way of coaxial cable includes synchronizing signal separating means for gating synchronizing signals to a level detecting circuit, in order to produce a control voltage. The control voltage controls the gain of an input stage of the amplifier to maintain the level of the synchronizing signals transmitted by the cable, while compensating for different attenuation which may be effected at video frequencies signal frequencies by cables of different length.

Abstract: Improved circuitry for providing bass control in audio playback systems using feedback circuits wherein undesirable deviations in frequency response above the bass region exhibited by previously available Baxandall feedback circuits are substantially eliminated by utilizing, in a preferred embodiment, a voltage follower amplifier, such as an emitter-follower transistor circuit in association with a single capacitance in the bass control circuit, which eliminates the undesirable frequency response deviations at the mid-frequency and higher frequency ranges so that frequency response curves at all settings of the bass control substantially coincide above the bass region.

Abstract: A gain and impedance switching circuit for an amplifier includes an AF amplifier having an input impedance connected between the input terminal thereof and a reference point and a feedback circuit connected between the feedback and output terminals of the amplifier, a first series circuit consisting of a first impedance and a first ON/OFF switch and connected between the input terminal of the AF amplifier and a reference point (such as ground) and a second series circuit consisting of a second impedance and a second ON/OFF switch connected between the feedback terminal of the AF amplifier and the reference point, the first and second ON/OFF switches being ganged with each other so as to change the input impedance and the gain of the AF amplifier simultaneously.

Abstract: An adaptive filter network comprising a controllable filter having an adjustable cut-off frequency and adapted for varying the pass-band of the network. The adaptive filter network further includes a serial arrangement of an algebraic adder for generating control signals, connected to the controllable filter; a weighting filter for converting the control signal spectrum in response to the load sensitivity variation with frequency; a threshold limiter for setting the noise reduction threshold level of the adaptive filter network; a control signal frequency corrector; and an amplitude detector for shaping control signals applied to the control input of the controllable filter. The network analysis of the input audio signal spectrum and the width of its pass-band is varied depending on the present frequency limit of the input audio signal wanted components.

Abstract: An audio power amplifier is designed to have a wide band high fidelity response suitable for FM radio performance. The amplifier rolloff of gain versus frequency is made sufficiently steep to reduce the gain to a negligible level at the standard AM broadcast band. A stabilization network is incorporated into the amplifier to avoid instabilities that might result in oscillation. The amplifier has a very low AM broadcast band radiation so that it is useful in AM-FM radio receivers.

Abstract: A variable equalizer whose frequency characteristic varies in a range of 1-1/Y(f).sup.2when the gain x of a variable amplifier varies from 0 (zero) to .infin. (infinity), and which reduces the number of shaping networks for the variable frequency characteristic.It is constructed of a forward pass circuit which consists of a variable amplifier and a frequency-dependent first circuit connected in the order mentioned between input and output terminals, a feedback pass circuit which is dependent upon the frequency and which feeds-back an output of the variable amplifier to an input thereof, and a feed forward pass circuit which is independent of the frequency and which feeds forward part of the input of the variable amplifier to an output of the first circuit.

Abstract: In a low-level audio preamplifier circuit having complementary connected PNP and NPN bipolar transistors cascode coupled to other complementary PNP and NPN bipolar transistors in receiving the audio input from a low-level transducer in which induced distortion from externally generated radio frequence energy is cancelled.

Abstract: An active filter which can achieve extremely high attenuation of frequencies outside the passband while maintaining a very low phase shift of signals within the passband. A preferred embodiment is described in which two, second-order, multiple-feedback, active filter circuits are cascaded and the output of the second filter is fedback to the input of the first filter to realize a fourth-order filter which has very high attenuation of signals falling outside the passband while providing very low phase shifts of signals within the passband.

Abstract: A feedback amplifier, particularly suitable for use in the video output circuit of a television receiver, has an amplifying circuit, for example, in the form of a differential amplifier, a first feedback circuit for negatively feeding back to the input of the amplifying circuit a low frequency component of the output signal from the amplifying circuit, and a second feedback circuit having substantially the same feedback ratio as the first feedback circuit but being operative to negatively feedback to the input of the amplifying circuit a high frequency component of the output signal.

Abstract: In a low level audio preamplifier circuit having complementary connected PNP and NPN bipolar transistors for receiving the audio input from a low level transducer such as a tape head, in which induced distortion from externally generated radio frequency energy is cancelled with minimal loss of audio fidelity.

Abstract: A tone control circuit for stereophonic amplifiers, guitar amplifiers and the like is disclosed. The tone control circuit includes a bass circuit having a first variable resistor whose movable contact is connected to an output terminal of an amplifier circuit, two resistors equal in resistance connected respectively to two end terminals of the variable resistor, and a capacitor shunting the variable resistor. The tone control circuit also includes a treble circuit having a second variable resistor, a resistor, and a capacitor. The treble circuit is connected in parallel to the bass circuit in such a manner that the gain in a particular frequency range of the amplifier circuit can be changed by varying the resistances of the two variable resistors.

Abstract: An amplifier includes a network which generates additional output current for driving a substantially capacitive load as the frequency of an input signal is increased. The network comprises a plurality of rate discriminators which activate additional current sources at predetermined frequencies.

Abstract: A phase compensator circuit for a multistage amplifier circuit is made up of two capacitors which are connected between input and output terminals of a first amplifier circuit, and a resistor which is connected between a common juncture of the two capacitors and an output terminal of a second amplifier circuit succeeding to the first amplifier circuit. The phase compensation is carried out substantially by the two capacitors in a high frequency region, and by the resistor and the capacitor intervening between the input terminal of the first amplifier circuit and the output terminal of the second amplifier circuit in a low frequency region.

Abstract: An equalizer amplifier of a negative feedback type comprises a common-emitter amplifier, an emitter follower amplifier cascade-connected thereto, and a negative feedback network connected between the output terminal of the emitter follower amplifier and the input terminal of the common-emitter amplifier with its negative feedback level increased as the frequency increases, wherein an inductance element is connected in series with the negative feedback circuit to attenuate harmful signals whose frequencies are higher than those of audio signals, thereby making large the ratio of signal to noise in the equalizer amplifier.

Abstract: A phonograph preamplifier network with infrasonic cutoff response. In one form, the preamplifier network is a single stage active filter configuration with a high gain, high input impedance differential amplifier provided with an RIAA equalization feedback filter network coupled between the amplifier output and inverting input. An RC filter network is coupled between the inverting amplifier input and ground potential to provide a single, low frequency real axis pole. In addition, an input filter feedback network is coupled between the preamplifier input terminal and the non-inverting input of the amplifier, and further boot-strapped to the amplifier inverting input. The network provides a pair of low frequency off-axis complex poles.

Abstract: A feedback resistor is interposed between a reversing input terminal of an audio amplifier and at least one impedance circuit. The impedance circuit is connected to an output terminal of the amplifier to receive an amplified audio signal from the amplifier. The signal controlled in its frequency characteristic in the impedance circuit. A fraction of the signal is negatively fed back to the amplifier through a feedback resistor.

Abstract: An active load circuit is interconnected between a signal source such as a pickup cartridge and an amplifier which acts as an impedance matching resistor. An equivalent resistance provided by the amplifier as viewed from the signal source equals a required resistance for impedance matching, and the noise voltage is considerably reduced as compared with that produced by a conventional matching resistor.