Abstract: A gain stage with DC offset compensation includes a gain amplifier and a compensation device. The gain amplifier is arranged to amplify an input signal according to a gain control signal. The compensation device is arranged to perform a DC offset compensation applied to the gain amplifier with an operating configuration based on the gain control signal.

Abstract: The present invention quickly detects an offset and prevents cutoff of low frequency signals. Offset detection circuits smooth an output of a variable gain amplifier at a predetermined time constant and detects the offset, which is a DC component. The detected offset is added to the input of the variable gain amplifier by an adder and the offset in the output of the variable gain amplifier is corrected. The time constant in the offset detection circuit is changed by the resistance values of the variable resistors. Then, the time constant is changed to a small time constant when the gain of the variable gain amplifier is changed and thereafter to a large time constant.

Abstract: A displaced electrode amplifier (“DEA”) for measuring signals from high impedance sources. The amplifier may include an operational amplifier (“op-amp”) configured as a unity gain buffer, with a feedback path to the non-inverting input to at least partly compensate for a parasitic input shunt impedance. In cases where the device is to measure AC signals in high ambient temperatures, the non-inverting input may be coupled via a large resistance to a ground reference that is driven with a second feedback signal to magnify the effective value of the large resistance. Where a differential configuration is desired, one or more tuning resistors may be provided to match responses of different input buffer stages, thereby maximizing the common mode rejection. The disclosed amplifier is suitable for use in oil-based mud resistivity imaging tools but is also suitable for other applications.

Abstract: An apparatus comprising an amplifier comprising at least one amplifier transistor, a threshold detection network and a bypass capacitor. The amplifier may be configured to generate an output signal at a collector in response to an input signal received at a base. The threshold detection network may be coupled between the collector and the base of the amplifier transistor. The threshold detection network may include a bias transistor having a collector coupled to the collector of the amplifier transistor and an emitter coupled to the base of the amplifier transistor. The threshold detection circuit may be configured to (i) sense a feedback current and (ii) provide a DC signal to the base of the amplifier transistor for dynamically sourcing bias current to the amplifier. The bypass capacitor may be coupled to the base of the bias transistor.

Abstract: Described are a circuit and system to provide an output signal in response to composite input signal comprising an AC signal component and a DC signal component. An amplifier provides an amplified voltage signal in response to a voltage representative of the composite signal. A filter may provide a filtered voltage signal having a magnitude that is representative of a magnitude of the DC signal component in response to the amplified voltage signal. A DC signal removal circuit may substantially remove at least a portion of the DC signal component from an input terminal in response filtered voltage signal.

Abstract: The present invention relates to an active analog filter including a differential amplifier, an output of which provides a filtered signal and a non-inverting input of which is connected to a median potential between supply potentials of the amplifier, a first series association of a first fixed resistor and a first variable resistor between an input terminal of a signal to be filtered and an inverting input terminal of the amplifier, a second series association of a second fixed resistor and a second variable resistor between the output of the amplifier and its inverting input terminal, and a third variable resistor in series with a filtering capacitor, between a midpoint of one of the series associations and the median potential.

Abstract: An amplifier circuit (14') for canceling variations in an amplifier feedback signal includes compensation circuitry (50) defining a replica of the feedback current therethrough. The replicated feedback current is drawn from a circuit node (N1) which directs the feedback signal to a differential pair (Q1, Q2) of the amplifier circuit 14', whereby any biasing effects on the differential pair (Q1, Q2) due to changes in the feedback signal resulting from changes in a gate drive output voltage (V.sub.GD) of the amplifier circuit (14') are eliminated. Accordingly, the gate drive output voltage (V.sub.GD) may be used to control an ignition coil (L1) drive transistor (16) whereby any changes in gate drive voltage (V.sub.GD) will not cause the coil current (I.sub.L) to deviate from its target coil current limit value.

Abstract: A DC bias controller for an optical modulator includes an optical modulator, a demultiplexer, and a controller. The optical modulator intensity-modulates input DC light by a digital main signal superposed with a DC voltage to convert the DC light to an optical signal. The demultiplexer demultiplexes the optical signal from the optical modulator into output signal light and monitor signal light. The controller detects a change in modulation characteristics of the optical modulator on the basis of the monitor signal light from the demultiplexer to control a value of the DC voltage superposed on the digital main signal.

Abstract: A sensor detection signal extracting circuit comprises a sensor, a control voltage generator, an adder, an amplifier, and a low-pass filter. The control voltage generator comprises two input terminals to one of which a voltage is applied based on the voltage source of the sensor. The output of the control voltage generator is added to the output of the sensor by the adder. The output of the adder is amplified by the amplifier, and its output is outputted to the output terminal and applied to the other input terminal of the control voltage generator through the low-pass filter. As a result, two loop systems are formed, that is, one loop for offsetting the change in the voltage of a voltage source applied to the sensor, and the other loop for offsetting a low frequency change such as that due to change in the environmental temperature. Therefore, the true output of the sensor can be obtained at the output terminal with little effect by the voltage change of the voltage source or by change in temperature.

Abstract: A wideband amplifier circuit having automatic offset voltage and gain control, the circuit comprising a main amplifier chain, a negative feedback loop for controlling gain, and a negative feedback loop for controlling and cancelling any possible offset voltage at its output, said main amplifier chain including a gain control amplifier block having a gain control input connected to the gain control negative feedback loop; wherein the gain control amplifier block is preceded in the main chain by a symmetrizer-adder block of fixed gain having a first input constituting the input of the amplifier circuit and a second input connected to the negative feedback loop for controlling and cancelling any possible offset voltage at the output.

Abstract: The present invention is an audio frequency power amplifier input circuit having improved vacuum tube circuit topology. The improved circuit includes a direct current feedback circuit within the input circuitry which stabilizes the operating point of a phase inverter. The feedback circuit maintains optimum operation of the circuit despite variations in tube characteristics or supply voltages. Another aspect of the improved circuit comprises a low impedance phase inverter which improves the drive capability of the phase inverter to push-pull power output vacuum-tube grids.

Abstract: An NF (Negative Feedback) tone control circuit in which a circuit gain of unity is maintained for a flat frequency response without the addition of active components. A voltage divider circuit which divides only an a.c. component of the output of an operational circuit is connected between the output of the operational amplifier circuit and a variable impedance circuit, the latter including the variable resistors of the tone control circuit.

Abstract: A transformer coupled amplifier circuit that eliminates transformer induced non-linearities by way of a dual feedback path without sacrificing any of the inherent attributes of general transformer coupled amplifiers.

Abstract: A precision gain AC coupled operational amplifier circuit utilizing an integrated resistor voltage divider network and switched capacitors is provided. Precise gain is obtained by the use of integrated capacitors, and a low frequency stabilizing pole in the order of 10 Hertz is created by proper selection of the ratio of the resistors in the divider network.

Abstract: A DC amplifier circuit with transformer coupled isolation comprises a DC amplifier, an electronic switching element connected to the output terminal of the DC amplifier, a pulse generator for driving the electronic switching element, a small pulse transformer having a primary winding and secondary winding. To the primary winding of the small transformer pulsating signals from the electronic switching element are applied, and two substantially identical circuits each having a diode and a condenser in series are connected respectively across the primary winding and the secondary winding of the small pulse transformer. Means for feeding back the smoothed signals from the circuit across the primary winding of the small pulse transformer is connected to a negative input terminal of the DC amplifier.