125 results about "Nonlinear amplifier" patented technology

An apparatus generates femtosecond pulses from laser amplifiers by nonlinear frequency conversion. The implementation of nonlinear frequency-conversion allows the design of highly nonlinear amplifiers at a signal wavelength (SW), while still preserving a high-quality pulse at an approximately frequency-doubled wavelength (FDW). Nonlinear frequency-conversion also allows for limited wavelength tuning of the FDW. As an example, the output from a nonlinear fiber amplifier is frequency-converted. By controlling the polarization state in the nonlinear fiber amplifier and by operating in the soliton-supporting dispersion regime of the host glass, an efficient nonlinear pulse compression for the SW is obtained. The generated pulse width is optimized by utilizing soliton compression in the presence of the Raman-self-frequency shift in the nonlinear fiber amplifier at the SW. High-power pulses are obtained by employing fiber amplifiers with large core-diameters. The efficiency of the nonlinear fiber amplifier is optimized by using a double clad fiber (i.e., a fiber with a double-step refractive index profile) and by pumping light directly into the inner core of this fiber. Periodically poled LiNbO3 (PPLN) is used for efficient conversion of the SW to a FDW. The quality of the pulses at the FDW can further be improved by nonlinear frequency conversion of the compressed and Raman-shifted signal pulses at the SW. The use of Raman-shifting further increases the tuning range at the FDW. For applications in confocal microscopy, a special linear fiber amplifier is used.

A modular ultrafast pulse laser system is constructed of individually pre-tested components manufactured as modules. The individual modules include an oscillator, pre-amplifier and power amplifier stages, a non-linear amplifier, and a stretcher and compressor. The individual modules can typically be connected by means of simple fiber splices.

The present invention relates to a device and a method in a transmitter stage in a radio transmitter for modulating and amplifying an information signal for further transmission through a radio channel. The transmitter stage in the radio transmitter comprises a converting device (5) PCH, an amplifier control device (8) PAC, a power detector (13) and a power amplifier (2). Examples of the problems solved by the present invention are difficulties in reducing the power consumption, non-linearities in the output signal when using non-linear amplifiers in radio transmitters, and achieving a high signal-to-noise ratio in the output signal without connecting filter arrangements after such an amplifier. The solution according to the inventive method and device utilizes an information signal which has in earlier steps been divided in its polar components: a phase reference component signal (Ephr) and an amplitude component signal (Aamp). The phase reference component phase modulates a low noise high power signal source which has a constant amplitude. The amplitude of the obtained signal is then formed in an amplifier, which is controllable with the amplitude component signal (Aamp). Its current consumption is registered and compared to a control value for the current. The amplifier is controlled towards this control value.

An approach is provided estimating non-linear characteristics of an amplifier (such as a Travelling Wave Tube Amplifier) used to amplify a composite signal in a radio communication system. The composite signal, which includes a plurality of inbound signals overlay on an outbound signal, is sampled. The outbound signal is utilized as a training signal. Coarse estimates of the response of the amplifier is generated based on the samples of the composite signal and the training signal. Further, the interference associated with the inbound signals are removed from the estimation of the response of the amplifier by curve-fitting and estimating interference characteristics of the composite signal. An estimated response of the amplifier is thus output, and can be utilized to provide accurate non-linearity compensation and cancellation.

Apparatus and methods configure digital predistortion linearizers for power amplification of bandlimited signals using non-linear amplifiers. The predistorter is configured to achieve both crest factor reduction (CFR) and predistortion for linearization. One embodiment advantageously reduces processing requirements conventionally associated with CFR by considering only the in-band component, that is, the information bearing component, of the desired signal to be reproduced for those cases in which the mitigation of in-band error vector magnitude (EVM) is preferred over the reduction of spurious out-of-band emissions.

A transmitting apparatus 100 operates a high-frequency power amplifier 105 as a nonlinear amplifier in a first mode, and operates high-frequency power amplifier 105 as a linear amplifier in a second mode. When high-frequency power amplifier 105 is operated as a nonlinear amplifier, the input level of high-frequency power amplifier 105 is varied by a variable gain amplifier 107 in accordance with the average output power of a transmit signal. Transmitting apparatus 100 is also provided with a compensation table 121 for reducing error in high-frequency power amplifier 105 mode switching operations.

Apparatus and methods control predistortion of an RF transmitter. A base station or a mobile station can utilize predistortion to improve linearity characteristics of the RF power amplifier. When used effectively, predistortion limits spectral growth such that the amplified signal complies with regulatory requirements. With respect to bursty signals, specific improvement techniques are disclosed. A first technique is related to adaptation using only a smaller subset of samples of a burst. A second technique is related to selective application of digital predistortion, such as, only under high power conditions for a power amplifier. A third technique is directed to adaptation of less than all of the coefficients. These improvements permit the use of a smaller and less expensive amplifier for a given power class and can lengthen battery life for a mobile unit.

An apparatus and method for eliminating the spurious signal of a non-linear amplifier in a base station transmitter of a mobile communication system are provided. A digital predistorter includes first and second predistorters, each having a memoryless non-linearity part using a look-up table and a memory non-linearity part using an finite impulse response (FIR) filter. The first predistorter adaptively updates the look-up tables, while the second predistorter adaptively updates the filtering coefficients of the FIR filters. According to another embodiment of the present invention, a digital predistorter has a memoryless non-linearity part using a look-up table and a memory non-linearity part using an FIR filter, and adaptively updates the look-up table and the filtering coefficients of the FIR filter.

A method for the simulation of responses of a nonlinear amplifier provides for measuring characteristics of nonlinearity of amplitude and of amplitude/phase-shift conversion of the amplifier, each measurement being made at an amplitude that is constant in input. The method further includes measuring the characteristics at different frequencies, developing the characteristics in sequences of direct transfer functions, computing frequency correctors for the direct transfer functions, measuring characteristics of distortion of amplitude modulation, each measurement being performed by modulating the input amplitude, computing modulation transfer functions reproducing the distortion amplitudes at output according to the input modulation amplitudes and correcting the direct transfer functions when the input amplitude is modulated in order to simulate the envelope memory effect. There is a direct application of the invention to the field of the simulation of high efficiency microwave amplification.

A method, apparatus, and computer program for modeling mathematically an effect of a plurality of factors on signal distortion caused by a non-linear amplifier are provided. First, there is computed a global model which incorporates a combined effect of the plurality of factors on signal distortion caused by the non-linear amplifier. Before applying the pre-distorted transmission signal to the non-linear amplifier, a transmission signal is pre-distorted with coefficients derived from the global model thus compensating for the signal distortion caused by the non-linear amplifier.

A switched power amplifier circuit employs non-linear amplifier stages including MOSFET transistors. The transistors each have source, gate, drain and backgate terminals. An input Rf signal is applied to the gate terminals and the source (or drain) terminals are connected to a load. The transistors are operated as switches by selectively applying clock signals to the backgate terminals to activate desired transistors, thus causing the transistors to turn on and allow current to flow through the load to generate power. The power to the load is increased by turning on multiple transistors at any given time.

Provided a pre-chirped management based low-noise fiber femtosecond laser amplifier. The amplifier comprises an ytterbium-doped fiber dispersion management mode-locked laser (1), a spectral interference filter (2), a grating negative dispersive delay line (3), an ytterbium-doped fiber amplifier (4), and a grating pulse compressor (5). The ytterbium-doped fiber dispersion management mode-locked laser (1) generates a breathing soliton pulse sequence; the spectral interference filter (2) adjusts a center wavelength of the breathing soliton pulse sequence and enables it in the gain spectrum center of the ytterbium-doped fiber amplifier (4); the grating negative dispersive delay line (3) introduces a negative chirp into the adjusted breathing soliton pulse sequence, thereby obtaining a seed pulse; the ytterbium-doped fiber amplifier carries out self-similar amplification on the seed pulse, thereby obtaining a parabolic pulse; and the grating pulse compressor (5) compresses the parabolic pulse and generates a femtosecond laser pulse. According to the high-frequency noise of a linear amplifier effectively inhibited by the pre-chirped management based low-noise fiber femtosecond laser amplifier disclosed by the present invention, a Fourier transform-limited femtosecond laser pulse with a narrow pulse width is obtained.

A method of operating a class D amplifier output stage that compensates for nonlinearity introduced by a residual load current during the dead time in the switching of the output stage. The amplifier output stage includes an input, a gate driver circuit, two output transistors, an output, and a current sensing circuit. The transistors are serially connected between the terminals of a power supply. A residual load current flows through the transistors when they are switched off. The gate driver circuit increases or decreases the duty cycles of signals driving the transistors based on the direction of the residual load current flowing through the transistors, thereby causing the duty cycle of the amplifier output to remain substantially constant and equal to the duty cycle of the amplifier input.

Converter system embodiments are formed with signal-processing stages which include successive signal converters and a preceding signal sampler wherein all but a last one of the stages provides an output signal to a succeeding one of the stages and all of said signal converters generate a corresponding digital code. The system embodiments generally address a selected one of the stages and include controllers which are configured to process, at a process rate less than the system's sample rate, a digital error signal and the back-end digital code of back-end ones of signal converters that succeed the selected stage to thereby adjust at least one of the back-end digital code and a control voltage in the selected stage to enhance the accuracy of the system digital code. Once the processes of these embodiments have been applied to the selected stage, they may be successively applied to preceding stages. System embodiments are also directed to nonlinear amplifier gain by including approximations (e.g., piece-wise and polynomial approximations) of amplifier gain so that they are better directed to an amplifier gain that is appropriate for the signal that is being processed through the amplifier.

A distortion compensation circuit compensates for distortion generated by one or more non-linear elements such as a laser device. The distortion compensation circuit may be used in an optical transmitter, such as a laser transmitter used for forward path CATV applications. The distortion compensation circuit may include a primary signal path and a secondary signal path that receive an input signal. The secondary signal path produces distortion of a magnitude corresponding to the magnitude of, but at an opposite phase to, the distortion generated by the non-linear amplifier. The secondary signal path includes a plurality of distortion sub-paths with each of the distortion sub-paths configured to produce intermodulation distortion products of the same distortion order but for different frequency dependent orders in a time dependent series representative of the distortion produced by the non-linear amplifier.

The phase shifted (PS) transmitter provides substantially linear amplification from two non-linear amplifiers by decomposing the original signal into two constant envelope signals with varying phases. The generation of the two constant envelope signals does not require the use of a signal component separator (SCS) or a reference signal generator. The phase shifted transmitter generates directly the required constant envelope, varying phase signals. This eliminates stringent requirements on the circuitry and allows the use of non-linear highly efficient power amplifiers in the transmitter. When the two above mentioned signals are combined, they constructively and destructively interfere to re-form an amplified form of the original signal, which is to be transmitted via an antenna.

An operational amplifier arrangement having a non-linear amplifier and a linear amplifier, both having a pair of input terminals one of which is coupled to an arrangement input terminal, and both having an output terminal that is coupled to an arrangement output terminal. The output terminal of the non-linear amplifier is further coupled to the output terminal of the linear amplifier via a series impedance. The output terminal of the linear amplifier is coupled to the arrangement output terminal via a terminating impedance. The arrangement includes an active back termination arrangement coupled between the arrangement output terminal and either one of the pair of input terminals of the linear amplifier. Preferably, the linear amplifier is receiving a supply voltage that exceeds the supply voltage received by the non-linear amplifier.

A predistortion circuit provides a predistorted input signal that compensates for distortion generated by a non-linear amplifier such as a laser device. The predistortion circuit may be used in an optical transmitter designed for broadband applications, such as a laser transmitter used for forward path CATV applications. The predistortion circuit may include a primary signal path and a secondary signal path that receive an input signal. A second order distortion generator on the secondary signal path generates predistortion of a magnitude corresponding to the magnitude of, but at an opposite phase to, the distortion generated by the non-linear amplifier. The second order distortion generator includes diodes with an adjustable diode bias to control phase, magnitude and/or magnitude/phase versus frequency of the predistortion.

The invention aims to provide a remote underwater sound communication method and belongs to the technical field of underwater sound communication. The method is based on demodulation and decoding combined iterative detection of differential encoding. A transmitter resists multi-path interference by using spread spectrum communication, the problem of phase jump and loop cycle skipping is solved by using differential modulation quadrature differential phase shift keying with high frequency spectrum utilization rate, and the transmitter adopts demodulation and decoding combined iterative technology to eliminate inter-code interference. The method has the beneficial effects that 1) the error bit rate performance of a remote underwater sound communication system is improved by the demodulation and decoding combined iterative technology; 2) the technical requirement on a non-linear amplifier is reduced by differential modulation, and differential modulation has engineering feasibility; and 3) the multi-path interference of a remote underwater sound channel is overcome by spread spectrum communication.

A transmitter includes a dual mode modulator and an amplifier coupled to the dual mode modulator. The dual mode modulator implements a linear modulation scheme during a first mode of the modulator to produce a variable envelope modulated signal. The dual mode modulator implements a non-linear modulation scheme during a second mode of the modulator to produce a constant envelope modulated signal. The amplifier is biased as a linear amplifier during the first mode of the modulator and is biased as a non-linear amplifier during the second mode of the modulator. A feed-forward connection between the dual mode modulator and the amplifier is used to indicate a change in modulation mode and to adjust the bias of the amplifier. A power of the constant envelope modulated signal is increased such that an operating point of the amplifier remains substantially constant during the first and second modes of the modulator.

A circuit for receiving an input signal having a phase component and an amplitude component which carry information, and for producing an output driver signal containing the phase and amplitude component information for driving a non-linear amplifier for generating linear amplification. The circuit includes a voltage controlled oscillator for receiving the phase component and for outputting a phase modulated carrier signal having a duty cycle and a constant amplitude. A driver stage made from a plurality of invertors, each having a pair of MOSFET transistors, receives the carrier signal at the gate terminals of the transistors. The amplitude component is used to drive the invertors by applying the amplitude component to the backgate terminals of at least some of the transistors in the invertors to pulse width modulate the carrier signal. The resulting output signal containing both phase component information and amplitude component information can then be used to drive a non-linear Class S amplifier to generate linear amplification while achieving high efficiency.