Abstract: An audio preamplifier includes a first stage including a first triode of a first vacuum tube in a common cathode configuration configured to perform a first gain function favoring one of low frequencies and mid-range frequencies in response to user input; a second stage including a second triode of the first vacuum tube in a common cathode configuration configured to perform a second gain function favoring one of low frequencies and mid-range frequencies in response to user input; a third stage including a first triode of a second vacuum tube in a common cathode configuration configured to perform a tone-shaping function favoring one of low frequencies and mid-range frequencies in response to user input; and a fourth stage including a second triode of the second vacuum tube in a follower configuration configured to perform a tone stack function in response to user input.

Abstract: A distortion device includes a transconductance stage, a current amplifier stage electrically coupled to the transconductance stage, and a transformer portion electrically coupled to the current amplifier stage. The transconductance stage includes a first capacitor to provide a ground to a resistor, and voltage across the resistor develops a current through a second capacitor to the current amplifier stage. The current amplifier stage includes a positive half cycle and a negative half cycle. The positive half cycle and the negative half cycle amplify the current from the transconductance stage and supply the amplified current to a primary winding of a transformer in the transformer portion, and the output of the transformer portion includes a low-level signal.

Abstract: A power amplifier device includes a first amplifier, a second amplifier, a capacitor, a node, and an impedance matching circuit. The second amplifier amplifies a radio frequency signal transmitted from the first amplifier. The capacitor is coupled between an output terminal of the first amplifier and an input terminal of the second amplifier. The node is disposed between the input terminal of the second amplifier and the capacitor. The impedance matching circuit is coupled to the node and a common voltage terminal. The impedance matching circuit is substantially an open circuit at a center frequency of the radio frequency signal. The impedance matching circuit provides substantially a short-circuited path from the node to the common voltage terminal at a frequency twice the center frequency.

Abstract: An apparatus includes a preamplifier stage to receive a power supply voltage and generate an output based upon an input. In particular, the preamplifier stage includes a biasing device coupled between the output and a ground node to bias a DC voltage level of the output independently of the power supply voltage. The preamplifier stage also includes a complementary circuit to receive the input and generate the output. The complementary circuit reuses a current through the preamplifier stage to provide an increased transconductance of the preamplifier stage for a given current level.

Abstract: A power harvesting circuit, a rectifier circuit and a capacitor. The rectifier circuit includes a diode circuit and a diode voltage reduction circuit. The diode circuit passes a current when a received RF signal has a first polarity and to substantially blocks the current when the received RF signal has a second polarity. The diode voltage reduction circuit is operably coupled to reduce a voltage drop of the diode circuit. The capacitor is operably coupled to convert the rectified signal into a DC supply voltage.

Abstract: An apparatus includes a preamplifier stage to receive a power supply voltage and generate an output based upon an input. In particular, the preamplifier stage includes a biasing device coupled between the output and a ground node to bias a DC voltage level of the output independently of the power supply voltage. The preamplifier stage also includes a complementary circuit to receive the input and generate the output. The complementary circuit reuses a current through the preamplifier stage to provide an increased transconductance of the preamplifier stage for a given current level.

Abstract: An embodiment of an amplifier system includes a modifiable signal adjustment device with an RF signal adjustment circuit coupled between first and second nodes. The RF signal adjustment circuit includes an adjustable phase shifter and an adjustable attenuator coupled in series with each other. The device also includes a memory and a controller circuit. The controller circuit retrieves a phase shift value and an attenuation value from the memory. The controller circuit then controls the adjustable phase shifter to apply a phase shift corresponding to the phase shift value to an input RF signal received at the first node, and controls the adjustable attenuator to apply an attenuation corresponding to the attenuation value to the input RF signal. Applying the phase shift and the attenuation results in an output RF signal at the second node.

Abstract: An embodiment of an amplifier system includes a modifiable signal adjustment device with an RF signal adjustment circuit coupled between first and second nodes. The RF signal adjustment circuit includes an adjustable phase shifter and an adjustable attenuator coupled in series with each other. The device also includes a memory and a controller circuit. The controller circuit retrieves a phase shift value and an attenuation value from the memory. The controller circuit then controls the adjustable phase shifter to apply a phase shift corresponding to the phase shift value to an input RF signal received at the first node, and controls the adjustable attenuator to apply an attenuation corresponding to the attenuation value to the input RF signal. Applying the phase shift and the attenuation results in an output RF signal at the second node.

Abstract: A high frequency semiconductor amplifier includes an input circuit, a first semiconductor element, first bonding wires, an interstage circuit, second bonding wires, a second semiconductor element, third bonding wires, an output circuit, fourth bonding wires and a package. The input circuit includes a first DC blocking capacitor, an input transmission line, a first input pad part, and a first bias circuit. The interstage circuit includes a second DC blocking capacitor, an interstage transmission line, a first output pad part, and a second bias circuit, a microstrip line divider, and a second input pad part. The output circuit includes a second output pad part, a microstrip line combiner, a third DC blocking capacitor, an output transmission line, and a fourth bias circuit. The first and second semiconductor elements, the input circuit, the interstage circuit, and the output circuit are bonded to the package.

Abstract: The present invention provides hearing systems and methods that provide an improved high frequency response. The high frequency response improves the signal-to-noise ratio of the hearing system and allows for preservation and transmission of high frequency spatial localization cues.

Abstract: To limit motion in an electromechanical system, an input signal is filtered using an adaptive filter, such as an infinite impulse response filter, to yield a predicted motion, and the input signal is attenuated by an amount controlled by the predicted motion. The filtering may further yield a predicted temperature, and the amount of attenuating may be further controlled by that temperature. Components of the input signal at selected frequencies may be removed, and a portion of the input signal from which the components have been removed may be mixed with a portion of the input signal from which components have not been removed. The removing of components at selected frequencies may include applying a notch filter, and the two portions may be equalized. phase-adjusting the unfiltered portion to account for phase delay introduced by the notch filter. The notch filter may operate at a resonant frequency of the system.

Abstract: A circuit for driving a loudspeaker is disclosed. The circuit includes: a signal generator connected to the loudspeaker, generating a first signal comprising a first pulse with positive value and a second pulse with negative value; a detection circuit connected to the loudspeaker, detecting a second signal produced by the loudspeaker in response to the first signal; and a processing circuit connected to the signal generator and the detection circuit, calculating the impedance of the loudspeaker according to the second signal; wherein each pulse width of the first and second pulses is between 100 ns and 900 ns.

Abstract: A loudspeaker drive circuit comprises an input for receiving an audio signal and a signal processor for processing the audio signal before application to the loudspeaker. The signal processor processes the audio signal to derive a loudspeaker drive signal which results in the loudspeaker membrane reaching its maximum displacement in both directions of diaphragm displacement.

Abstract: In an embodiment, a power amplifier (PA) includes a signal processing path including gain stages to receive a radio frequency (RF) signal and to output an amplified RF signal, sensors coupled to the signal processing path each to sense a characteristic of operation of the PA, and a microcontroller configured to execute instructions and to receive the operation characteristic(s) and to control one or more parameters of the signal processing path responsive this operation characteristic.

Abstract: An example transconductance circuit is provided in accordance with one embodiment. The transconductance circuit can comprise: an output node; at least one transistor; a variable resistance; and a differential amplifier; wherein the at least one transistor and the variable resistance are in series connection with the output node, an output of the differential amplifier is connected to a control node of the at least one transistor, a first input of the amplifier is responsive to an input signal, and a second input of the amplifier is responsive to a voltage across the variable resistance. Such a circuit may overcome noise problems in transconductance circuits which operate over a wide range of input signals with a fixed resistor in series with the at least one transistor.

Abstract: A high voltage resonant step-up convertor converts a lower voltage signal to a higher voltage signal. The converter may be used, for example, to supply power via electromagnetic coupling to an implantable medical device. In some embodiments, a power converter comprises a driver circuit and a resonant circuit. The resonant circuit generates a high voltage output signal at a selected frequency. The driver circuit is controlled by a low voltage signal and periodically generates a higher frequency signal (e.g., approximately twice the selected frequency) to drive the resonant circuit. In some embodiments, the driver circuit comprises another resonant circuit and a switching circuit. The switching circuit periodically pumps current to the other resonant circuit and isolates the two resonant circuits. The other resonant circuit periodically pumps current to the output resonant circuit.

Abstract: A loudspeaker drive circuit comprises an input for receiving an audio signal and a signal processor for processing the audio signal before application to the loudspeaker. The signal processor processes the audio signal to derive a loudspeaker drive signal which results in the loudspeaker membrane reaching its maximum displacement in both directions of diaphragm displacement.

Abstract: A power amplification device, includes: an amplifier to amplify an input signal; a switched capacitor, provided at an output stage of the amplifier, to change capacitance based on a first control signal; a matching unit, provided at the output stage of the amplifier and including a varactor pair in which two varactor diodes are coupled in series or a varactor pair in which two varactor diodes are coupled in parallel, to change capacitance based on a second control signal; a detection circuit to detect power of the input signal; a quantization circuit to quantize a detected power value, form a quantized bit string having a high-order bit group and a low-order bit group, and output the high-order bit group as the first control signal to the switched capacitor; and a conversion circuit to convert the low-order bit group into an analog value and form the second control signal.

Abstract: Embodiments of apparatuses, methods, and systems for a radio frequency amplification circuit providing for fast loadline modulation are generally described herein. Other embodiments may be described and claimed.

Abstract: A post phase-inverter master volume regulator for use in combination with a tube-type musical amplifier having a phase-inverter tube. The signals at both sides of the phase-inverter tube's DC voltage plate are extracted from the amplifier for processing by the master volume regulator. In one embodiment, such signals are extracted by inserting a male/female tube base between the amplifier's phase-inverter tube and its socket. The two voltage plate signals are then transmitted through a multiconductor umbilical to an exterior enclosure. Each signal is connected to ground through its respective user adjustable rheostat, permitting the user to simultaneously change the inverter-tube's two voltage signals (and vary the amplifier's volume). The regulator may also include circuitry adapted to provide a bass-boost, and/or a high frequency cutoff. Sometimes, first and second volume controls may be provided to permit a user to quickly change between two volume settings.

Abstract: A millimetric-wave amplifier arrangement comprises a first amplifier whose output is connected to one input of the second amplifier via an adjustable attenuator. Both amplifiers are integrated on a single substrate.

Abstract: A system for controlling gain in a polar loop is disclosed. Embodiments of the invention provide for a substantially constant gain tolerant of changes in supply voltage, ambient temperature, and/or manufacturing process.

Abstract: A vacuum tube circuit is capable of amplifying an input signal with use of a low source voltage. Ordinarily, the amount of electrons released from a cathode which is heated by a heater is small since a voltage supplied to the heater is low. In the vacuum tube circuit disclosed here, a positive voltage is supplied to a grid terminal, which more effectively attracts the emitted electrons, thereby increasing the amount of electrons arriving at the plate terminal passing through the grid. As a result, a grid current and a plate current flow in the vacuum tube circuit, which achieves an operation for amplifying an input signal from a signal source.

Abstract: The antenna amplifier for mobile FM radio reception includes a signal amplifier, a controllable adjusting element having a PIN diode for impedance adaptation, and a control amplifier for regulating the adjusting element. The antenna amplifier has a compensation for the temperature response occurring as a result of very great differences (summer/winter) in ambient temperature, the PIN diode connection point is optimized, and the control range is maximized.

Abstract: A circuit for matching an amplifier to a radio-frequency line is described. In order to minimize the number of components required for matching the amplifier to different frequency bands, the circuit has a first capacitance for outputting the negative half-cycle of the transmission signal, which is rectified by a diode and is stored in a second capacitance. The stored negative voltage is, if required, fed back via two resistors and an inductance to a further diode.

Abstract: In a predistortion type linearizer including a FET, an input matching circuit connected to the drain of the FET for receiving an input signal, an output matching circuit connected to the source of said the FET for outputting an output signal, and a inductor having a first terminal connected to the gate of the FET and a second terminal for receiving a first control voltage, a variable impedance circuit is connected to the second terminal of the inductor, and the impedance of the variable impedance circuit is adjusted by a second control voltage.

Abstract: There is disclosed a variable-gain amplifier circuit comprising an adjustable impedance circuit part including a bipolar transistor having a base connected to a control terminal for receiving a controlled bias voltage, a collector connected to a positive power supply voltage terminal, and an emitter connected to ground through a diode in such a manner that an anode of the diode is connected to the emitter of the transistor and a cathode of the diode is connected to the ground. The variable-gain amplifier circuit further comprises a variable-gain amplifying circuit part having an amplifying circuit having an input coupled through an DC blocking capacitor to an input terminal for receiving an input signal and an output connected to an output terminal. The emitter of the bipolar transistor is connected to a node between the input terminal and the DC blocking capacitor.

Abstract: The antenna amplifier for mobile FM radio reception includes a signal amplifier, a controllable adjusting element having a PIN diode for impedance adaptation, and a control amplifier for regulating the adjusting element. The antenna amplifier has a compensation for the temperature response occurring as a result of very great differences (summer/winter) in ambient temperature, the PIN diode connection point is optimized, and the control range is maximized.

Abstract: A circuit for matching an amplifier to a radio-frequency line is described. In order to minimize the number of components required for matching the amplifier to different frequency bands, the circuit has a first capacitance for outputting the negative half-cycle of the transmission signal, which is rectified by a diode and is stored in a second capacitance. The stored negative voltage is, if required, fed back via two resistors and an inductance to a further diode.

Abstract: A linearizer is provided which is capable of scaling its circuit down and making it lightweight, of lowering power consumption and of facilitating an input-output calibration. The linearizer is so configured that a first resistor is connected in series to a second resistor, a third resistor is connected to a connecting point between the first and second resistors, an FET (Field Effect Transistor) as a variable resistance element is connected to the third resistor, an inductor is connected between the FET and a GND, and the first, second and third resistors and the FET constitute a T-type attenuator.

Abstract: A high efficiency multiple power level power amplifier has a PIN diode network that selectively associates an impedance transformation network with an interstage impedance matching network to maintain desired gain and linearity characteristics for the power amplifier at different output power levels. The PIN diode network in the off mode (high power), has a high breakdown voltage and high series resistance thereby reducing distortion components. The PIN diode network in the on mode (low power), has a low series resistance thereby reducing insertion losses.

Abstract: A linearizer channel amplifier for use in conjunction with a power amplifier comprises an input series circuit formed of a first variable attenuator, an input drive amplifier and a power limiter, and an output series circuit formed of a second variable attenuator and an output drive amplifier. Between the input and output series circuits is interposed a linearizer. In this linearizer, a splitter produces first and second signal portions, a first path comprises serially interconnected predistorter and third variable attenuator for distorting and adjusting the amplitude of the first signal portion, a second path comprises serially interconnected phase shifter and fourth variable attenuator for phase-shifting and adjusting the amplitude of the second signal portion, and a combiner combines the distorted and amplitude-adjusted first signal portion and the phase-shifted and amplitude-adjusted second signal portion to form a predistorted output signal applied to the output series circuit.

Abstract: An exciter matching circuit (125), interstage matching circuit (134), and harmonic filter matching circuit (140) match impedances at the input to a two-stage power amplifier (130), between the first stage (132) and the second stage (136) of the power amplifier (130), and at the output of the power amplifier (130) for more than one frequency band of interest. In a GSM/DCS dual band radiotelephone (101), the matching circuits (124, 134, 140) provide low return loss at 900 MHz when the dual band transmitter (110) is operating in the GSM mode. The harmonic filter matching circuit (140) also filters out signals at 1800 MHz, 2700 MHz, and high order harmonics. When the dual band transmitter (110) is in DCS mode, however, the matching circuits (124, 134, 140) provide a low return loss at 1800 MHz and filter out signals at 2700 MHz and harmonics of 1800 MHz.

Abstract: The invention provides a high frequency amplifier in which a variable attenuator consisting of a bypass FET, which has a drain connected to a first-stage amplifying FET via a resistor, and a source grounded via a capacitor, is located on a main signal line leading to the gate of the amplifying FET, in order to control the gate potential of a bypass FET using a gain control voltage source, thereby varying the gain of the amplifier.

Abstract: A coupling capacitor 21 is connected in parallel to a diode 23 between an output nord N1 of a differential amplifier circuit 10 and an input nord N3 of another differential amplifier circuit 50. In a test mode, when a test signal TC is applied to a test pad 43, a switch circuit 40 is turned on to shortcircuit a bias resistor 35 thus decreasing a bias potential at the input nord N3. This causes the diode 23 to switch on for amplifying a test low-frequency input signal IN with the differential amplifier circuit 10. By the action of the diode 23, an output of the differential amplifier circuit 10 is bypassed to the differential amplifier circuit 50. The two differential amplifier circuits 10 and 50 can thus be inspected substantially by examining an output signal OUT obtained through an output pad 56 of the differential amplifier circuit 50.

Abstract: A unique method and apparatus modifies the load impedance at the output of a power amplifier by varying a voltage variable capacitor (VVC) (310) to maximize the efficiency of the power amplifier (304). A comparator (509) generates amplifier control signal (211) based upon a detected power output signal (216) and a reference signal. In addition to providing power control, the control signal is also coupled to a VVC circuit (506) to control the output impedance of the power amplifier. In an alternate embodiment, a separate VVC control signal (527) based upon a comparison of the power control signal and the battery voltage is coupled to a VVC. In another alternate embodiment, a second VVC can be coupled in parallel to the first VVC. The second VVC is preferably controlled by a signal (805) based upon the current in the power amplifier.

Abstract: A non-linear power amplifier for amplifying a constant envelope phase modulation component of a modulation signal and combining an amplitude envelope component of the modulation signal into the amplified constant envelope phase modulation component and method for performing the same. The power amplifier receives a constant envelope phase modulation signal and transmits the signal through a pair of amplifier stages which are impedance matched together. The first amplifier stage has a fixed gain which drives an impedance load and, in turn, the second amplifier stage. A variable resistance device is connected between a base of an amplifying transistor in the second amplifier stage and electrical ground for variably controlling the gain of the second amplifier stage by variably controlling the base-to-ground resistance of the amplifying transistor in the second amplifier stage.

Abstract: A gain control circuit (200) for controlling gain of a circuit (100) operative on the basis of a positive supply voltage, in accordance with strength of current pulled out by the gain control circuit from a control node (12) of the gain-controlled circuit (100), comprises: a depletion-type transistor (21) having one end (drain) connected to the control node of the gain-controlled circuit, the other end (source) connected to a voltage supply terminal (25) to which an external supply voltage is applied, and a gate terminal connected to a control signal terminal (16) to which an external positive voltage control signal is applied; and a resistance element (22) connected in parallel to both ends of the depletion-type transistor (21), for shifting a threshold voltage of the transistor in a positive direction by applying a shift voltage between both the ends of the transistor so that turn-on resistance of the transistor can be controlled on the basis of the positive voltage control signal.

Abstract: A unique method and apparatus modifies the load impedance at the output of a power amplifier by varying a voltage variable capacitor (VVC) (310) to maximize the efficiency of the power amplifier (304). A comparator (509) generates amplifier control signal (211) based upon a detected power output signal (216) and a reference signal. In addition to providing power control, the control signal is also coupled to a VVC circuit (506) to control the output impedance of the power amplifier. In an alternate embodiment, a separate VVC control signal (527) based upon a comparison of the power control signal and the battery voltage is coupled to a VVC. In another alternate embodiment, a second VVC can be coupled in parallel to the first VVC. The second VVC is preferably controlled by a signal (805) based upon the current in the power amplifier.

Abstract: A power amplifier has a distortion control circuit responsive to a clipping detector for loading said amplifier input with a signal sufficient to reduce the input to the tube grids to a level below clipping.

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 linear interpolation network for a continuously variable amplifier. The interpolation network includes first and second control terminals from which complementary scanning input currents are demanded. The network includes a plurality of circuit legs. Each leg includes a current source and a diode connect in series therewith. Coupled between each pair of adjacent circuit legs are first and second shunting diodes. The first shunting diode is connected between the adjacent legs to conduct current in a first direction. The second shunting diode is connected between the adjacent legs to conduct current is a second, opposite direction. The shunting diodes shunt current from the current sources to the control terminals to meet the current demands of the complementary scanning current input signals. The remaining current is sourced by one or more legs such that substantially triangular, overlapping current pulses are produced in the legs responsive to the scanning current inputs.

Abstract: A high frequency amplifying system includes an input coupling circuit having an input terminal for receiving a high frequency signal, a pair of amplifiers, and an impedance mismatch circuit for coupling each amplifier to a respective output terminal of the coupling circuit. The impedance mismatch circuit is controllable by a control signal supplied thereto to produce a selected degree of mismatch between the coupling circuit and the input impedances of the amplifiers, to thereby provide adjustable gain control of the amplifying system. The coupling circuit introduces phase shifts between the input and output terminals thereof which attenuates reflection therebetween of intermodulation products resulting from the presence of interfering signals at any of such terminals.

Abstract: A power amplifier used in a portable, radio frequency transmitter is switched between different modes of operation when transmitting differently modulated carriers. The first mode of operation corresponds to amplitude modulation (AM), while a second mode corresponds to angle modulation techniques such as frequency modulation (FM). A switching network alters the impedance of the power amplifier to match network for matching the impedance of the transmitter antenna in order to achieve maximum efficiency in each mode of operation. Various switching methods and impedance matching circuits are disclosed.

Abstract: Phase and amplitude modifications in repeatable RF pulses at the output of a high power pulsed microwave amplifier are made utilizing a digital feed-forward correction system. A controlled amount of the output power is coupled to a correction system for processing of phase and amplitude information. The correction system comprises circuitry to compare the detected phase and amplitude with the desired phase and amplitude, respectively, and a digitally programmable phase shifter and attenuator and digital logic circuitry to control the phase shifter and attenuator. The Phase and amplitude of subsequent are modified by output signals from the correction system.

Abstract: A power amplifier used in a portable, radio frequency transmitter is switched between different modes of operation when transmitting differently modulated carriers. The first mode of operation corresponds to amplitude modulation (AM), while a second mode corresponds to angle modulation techniques such as frequency modulation (FM). A switching network alters the impedance of the power amplifier to match network for matching the impedance of the transmitter antenna in order to achieve maximum efficiency in each mode of operation. Various switching methods and impedance matching circuits are disclosed.

Abstract: A distortion limiter for limiting the amount of distortion of an inverting amplifier is disclosed. A comparator produces a pulse when a signal level at an inverting input of the inverting amplifier exceeds a reference voltage level. The pulse charges a capacitor. When the charge on the capacitor is sufficient to raise the gate voltage of a junction field-effect transistor (FET) above cutoff, the FET shunts the input signal to reduce its level. The distortion characteristics can be controlled by using a voltage divider to adjust the voltage across the FET. A bias voltage at the gate of the FET, keeps the FET turned off when the inverting amplifier is not clipping.

Abstract: A circuit amplifies an input RF band of signals and exhibits a signal gain in decibels that is a linear function of the logarithm of a control signal input. The circuit comprises a first amplifier stage having an output node that exhibits a first RF complex admittance within the RF band of signals. A second amplifier stage has an input node coupled to the output node of the first amplifier stage and exhibits a second RF complex admittance within the RF band of signals. A PIN diode, used as a gain control element, is shunt connected between the control signal input and the output node. An RF reactance circuit is also shunt connected between the output node and a common potential. The RF reactance circuit has a third admittance that is chosen to negate the imaginary portions of the first and second complex admittances, whereby the total admittance is substantially real and enables the PIN diode to see a minimal resistive load.

Abstract: A high frequency amplifying apparatus comprises: an amplifier for broadband-amplifying an input signal; a choke coil having one end supplied with a supply voltage and the other end connected to an output of the amplifier; and an automatic gain control circuit for outputting an amplified input signal with a gain controlled in accordance with an automatic gain control voltage, having: a first diode having an anode connected to the output of the amplifier and a cathode; an impedance element, one end of the impedance element being connected to the cathode of the first diode, the other end of the impedance element being connected to the ground; and a second diode having a cathode connected to the cathode of the first diode and an anode supplied with the automatic gain control voltage. The impedance element comprises a resistor and a second choke coil connected in series with the resistor. However, the second choke coil can be omitted.

Abstract: An operational amplifier (1) and resistors (11) and (12) damp an input signal (V.sub.1) by -6dB. Since a positive input terminal of the operational amplifier (1) is fixed at -3V, DC component of the input signal (V.sub.1) is down-shifted to -3V so that a signal (V.sub.2) is obtained. The signal (V.sub.2) is inputted to an electronic volume (100) wherein the signal (V.sub.2) is damped thereby a signal (V.sub.3) is obtained. An operational amplifier (2) and resistors (13) and (14) amplify the signal (V.sub.3) by 6dB. Since a positive input terminal of the operational amplifier (2) is fixed at OV, DC component of the signal (V.sub.3) is up-shifted to OV thereby a signal (V.sub.5) is obtained. The signal which is to be processed in the electronic volume has only a half voltage relative to that of the input signal.