Abstract: According to a first aspect of the invention, an automatic-gain-control circuit, which generates a control signal that controls the gain of a variable-gain element, modifies the control signal to compensate for changes in the gain control characteristic of the variable-gain element. According to a second aspect of the invention, the automatic-gain-control modifies a fixed value which is added to cancel a direct-current offset, the modification being made in response to changes in the gain control characteristic of the variable-gain element.

Abstract: A rail-to-rail input common mode range differential amplifier operates on rail-to-rail voltages down to approximately one volt by utilizing one p-channel transistor to cover a first portion of the common mode range, and a second p-channel transistor to cover a second portion of the common mode range.

Abstract: Feed forward amplifiers and methods particularly suited for power multichannel microwave amplifiers for cellular phone base stations and the like. The input signal is modulated with a small percentage of modulation at a relatively low frequency before being amplified by the main amplifier. At the same time, the input signal is also coupled to provide inphase and quadrature components thereof to be mixed with the amplifier output and lowpass filtered to extract a component of the low frequency responsive to modulation components in the amplifier output due to the low frequency modulation.

Abstract: A linear power amplifier utilizes active feedback pre-distortion linearization. The power amplifier is a two-stage amplifier which includes a pre-distortion active feedback driver amplifier and a power amplifier. The driver amplifier provides gain expansion and insertion phase decrease as input power is increased, which compensates for the output power amplifier's gain compression and insertion phase increase with input power, resulting in a two-stage amplifier with relatively higher linear power output power capability and associated power-added efficiency. The two-stage linear power amplifier in accordance with the present invention provides improved linear efficiency which can be mass-produced in high volume with excellent repeatability. A voltage bias circuit with an external voltage post enables the two-stage amplifier to be tuned with an external voltage for optimum performance.

Abstract: A circuit having a double half-wave rectifier connected to the outputs of a differential amplifier in order to produce two quantities dependent on the amplitudes of the half-waves of the output signal of the amplifier. Two comparators each having an input are connected to an output of the rectifier and a reference input in order to produce respective output signals when the amplitudes of the respective half-waves are greater than the levels applied to the reference inputs. The circuit also has processing means for generating a signal for regulating the gain of the amplifier in dependence on the durations of the output signals of the two comparators. The circuit may advantageously be used when the signal to be amplified is not symmetrical.

Abstract: The present invention relates to a voltage gain amplifier for converting a single analog input to a differential output and controlling a voltage gain, comprising a single input charging/discharging part, a differential output operational amplifier, a first and second input voltage transferring part, a first and second voltage holding part and a frequency compensating part, and therefore, making it possible to generate a differential input signal, which is used as an input to an ADC(Analog-to-Digital Converter) of an audio CODEC(Coder/Decoder), by using a fully-differential output operational amplifier whose output is transmitted as a differential output. Also, the present invention gives an advantage of making the chip size smaller than the prior art does, resulting from the fact that resistors are replaced by capacitors and switches when integrated into a chip.

Abstract: The photocurrent generated by a photodiode receiving light substantially flows through a feedback resistor when the incident light intensity is low. As the incident light intensity increases, the source and drain of a FET connected in parallel to the feedback resistor establish a conducting state therebetween, whereby the photocurrent is divided into a current flowing through the feedback resistor and a current flowing through the FET connected in parallel to the feedback resistor. Accordingly, transimpedance is equivalently lowered, while the feedback resistor is restrained from lowering the output potential. When the incident light intensity is further increased, a gate bias current flows into the gate of an input-stage FET of an amplifier, whereby the photocurrent is divided into the current flowing through the feedback resistor, the current flowing through the FET connected in parallel to the feedback resistor, and the gate bias current.

Abstract: Low voltage operational amplifier (10) operates in a voltage range of one to eight volts over a temperature range of 0.degree. to 70.degree. centigrade. Op amp input stage (12) uses N-channel depletion-mode MOSFETs to provide amplification of the differential input and maintain constant transconductance. Source follower MOSFET (13) provides unity gain in transferring the AC signal, STAGE-1 OUTPUT, to the base of current sinking transistor (18). Sink control circuit (14) and source control circuit (22) generate the base drive currents for in transistors (18) and (24). The signal at the output of MOSFET (13) either causes the sink transistor (18) to sink current or the signal to be transposed by means of a translinear loop (16) and causes the source transistor (24) to source current.

Abstract: An amplifier is formed by an astable multivibrator having a signal output supplying a two-state output signal to a power stage, that presents an output voltage (V.sub.o) switching between a first and second value. The output voltage presents a duty cycle varying with the input signal (V.sub.in) of the multivibrator. The amplifier, when connected between first and second supply lines that are symmetrical with respect to ground and are subject to supply noise, comprises a current source for generating the bias current of the astable multivibrator and supplying a current (I) that is switchable at each half cycle. The value of the current at each half cycle is proportional to the absolute value of the output voltage (V.sub.o) of the amplifier to vary the duty cycle of the amplifier in a manner correlated the supply noise, so that the average output voltage value is zero.

Abstract: Circuitry for reducing charge injection effects in an offset voltage compensation circuit for a switched-capacitor amplifier is provided. The switched-capacitor amplifier circuitry includes an operational amplifier having inverting and noninverting inputs and an output. An initialization circuit provides the inverting input with a voltage close to the offset voltage of the operational amplifier. A feedback circuit ensures that the voltage at the inverting input attains the offset voltage. In order to attenuate the effects of disengaging the feedback circuit after the input voltage attains the offset voltage, an attenuation circuit is provided. The attenuation circuit prevents the voltage at the inverting input from being affected by charge injection effects that arise when the feedback circuit is disengaged. The offset voltage compensation circuit may be used with switched-capacitor amplifiers configured as comparators, amplifiers, or successive approximation A/D converters.

Abstract: An amplification circuit comprises an operational amplifier, an input resistance unit and a feedback resistance unit. The input resistance unit consists of a plurality of input resistances connected in series, and the feedback resistance unit consists of a plurality of feedback resistances connected in series. A plurality of adjusting pads are provided at respective connecting points of these input and feedback resistances. There is a common pad having an electrical potential fixed at a reference voltage. A first wire selectively bonds one of adjusting pads corresponding to the input resistances with the common pad to set a resistance value of the input resistance unit. And, a second wire selectively bonds one of adjusting pads corresponding to the feedback resistances with the common pad to set a resistance value of the feedback resistance unit.

Abstract: In a variable output amplifier apparatus, an input signal is distributed by a distributing unit as first signals to a plurality of variable gain units having different gains. Second signals generated from the variable gain units are combined by a combining unit to generate an output signal. A plurality of power supply control units apply power supplies to the variable gain units, respectively. The variable gain units and the power supply control units are controlled by a control unit. When one of the variable gain units and one of the power supply control units are activated, the corresponding power supply is turned ON. When they are deactivated, the corresponding power supply is turned OFF.

Abstract: A differential attenuator is described that is capable of automatic calibration using electronically adjustable circuit elements. The differential attenuator has positive and negative inputs and outputs. A resistor and capacitor couple the positive side input and output, while a matching resistor and capacitor couple the negative side input and output. Shunt resistors and shunt capacitors coupled to the positive and negative outputs are augmented and made electronically adjustable by multipliers having their signal inputs coupled to the respective side output nodes. The outputs of one set of multipliers are coupled to the other ends of the shunt resistors, while their multiplication coefficients are controlled by a dc.sub.-- control signal. The outputs of another set of multipliers are capacitively coupled back to their respective side output nodes, while their multiplication coefficients are controlled by an ac.sub.-- control signal.

Abstract: An audio amplifier that does not exhibit a "pop" during a change-of-state such as being turned on. The popless amplifier includes an operational amplifier to power a speaker, a circuit to prevent the application of an output voltage from the operational amplifier to the speaker for a selectable period of time and a circuit to charge the output of the operational amplifier to a selectable mid-rail voltage during the time a voltage from the operational amplifier is prevented from reaching the speaker.

Abstract: In a preamplifier for amplifying an input signal supplied to an input terminal to supply an amplified output signal and a reference output signal to an output terminal and a reference output terminal, respectively, a reference level circuit produces a reference level. An amplifier is connected to the reference level circuit and has a predetermined structure. The amplifier amplifies the input signal into the amplified output signal with reference to the reference level to supply the amplified output signal to the output terminal. A dummy circuit is connected to the reference level circuit and has a structure which is identical with the predetermined structure. The dummy circuit responds to the reference level to produce the reference output signal related to the amplified output signal.

Abstract: A power amplifier includes a plurality of signal amplifying stages. An amplitude compensator positioned prior to the ultimate signal amplifying stage equalizes the signal amplitudes in the frequency band of interest to provide a substantially flat frequency response. Fail-soft operation is established by providing switchably redundant amplifiers. When an operating amplifier is detected as failing, automatic switching is performed to replace the failing unit with an identical unit to maintain amplifier operation. High-power amplification is accomplished by splitting a preamplified signal into a plurality of signals, amplifying the lower level signals so obtained, and then recombining the amplified signals.

Abstract: A tuned radio frequency (RF) amplifier includes serially connected input and output common emitter amplifiers with closed ac and dc loops for maintaining high input impedance and low output impedance. The closed ac loop includes a parallel resonant circuit which is connected to the input and capacitively coupled to the output and across which a small signal appears as the difference between the input and output signals. The collector of the input amplifier transistor is maintained at a constant voltage, thereby minimizing any Miller Effect feedback capacitance, and, therefore, any RF degeneration, at the input.

Abstract: In an amplifier for amplifying a pulsed sinusoidal carrier signal, wherein the amplifier employs an amplifier element operative as Class-C with a saturation operation region which increases the sharpness of leading and trailing edges of a rectangular pulse envelope of the pulsed carrier signal for undesirable spectral spreading of energy of the signal, a method of reducing the spectral spreading of the energy employs a modification of the rectangular envelope of the pulsed carrier signal to a trapezoidal envelope. The leading and the trailing edges of the trapezoidal envelope constitute envelopes of sinusoidal waveforms of increasing and decreasing amplitude, respectively. The peak amplitudes of the largest amplitude sinusoidal of the leading and the trailing edges have powers which exceed a power level inducing the saturated operation of the amplifier element such that there is a decrement in incremental power gain by a factor of approximately 3 dB.

Abstract: A feedforward amplifier system comprises a main amplifier and an auxiliary amplifier. An input signal including one carrier signal used as a first pilot signal, is supplied to a main amplifier to produce an amplified output signal. A second pilot signal is injected into the amplified output signal. The amplified output signal from the main amplifier is supplied to an output of the amplifier system through a delay line. In each of a first loop associated to the main amplifier and a second loop including the auxiliary amplifier, two control signals with pilot signal components arc produced, discrete Fourier transforms of the pilot signal components of the two control signals are calculated, and the amplitude and phase of the input signal of the main or auxiliary amplifiers are adjusted to values making the two Fourier transforms substantially equal to each other. Alternatively, the first pilot signal is produced by a generator and is injected into the input signal.

Abstract: A semiconductor amplifier such as a high-frequency amplifier has a barrier-gate transistor FETQ1 and a circuit connected to the gate of the barrier-gate transistor FETQ1 for controlling an amplification gain of the barrier-gate transistor FETQ1. In one embodiment, the circuit has a resistor RG1 being connected between a GND line and the gate of the barrier-gate transistor FETQ1 and a resistor RG2 being connected between the gate of the barrier-gate transistor FETQ1 and a VGG line for biassing the gate of barrier-gate transistor FETQ1.