119 results about "Amplitude distortion" patented technology

A method and a system for calibrating the reception and transmission of an antenna array for use in a cellular communication system is disclosed. The calibration of the reception of the antenna array is performed by injecting a single calibration signal into each of a number of receiving antenna sections, in parallel. The signals are collected after having passed receiving components that might have distorted the phase and amplitude. Correction factors are generated and applied to received signals. The calibration of the transmission of the antenna array is performed in a similar way. A single calibration signal is generated and injected into each of a number of transmitting antenna sections, one at a time. The signals are collected, one at a time, after having passed transmitting components that might have distorted the phase and amplitude. Correction factors are generated and applied to signals that are to be transmitted.

A wireless communication apparatus receives an quadrature modulated signal, generate a local signal having a frequency different from a center frequency of the quadrature modulated signal, performs quadrature demodulation on the quadrature modulated signal by using the local signal, to obtain an I channel signal and a Q channel signal, performs Fourier transform on the I channel signal and the Q channel signal, to obtain signals in a frequency domain, and calculates a first correction coefficient for correcting phase distortion and amplitude distortion caused by the quadrature demodulation by using pairs of signals among the signals, each of the pairs are located at symmetrical frequency positions with respect to the frequency of the local signal.

An envelope tracking radio frequency (RF) power amplifier having an adaptive envelope signal processing circuit is disclosed. An RF input voltage is sampled by the adaptive envelope signal processing circuit which provides control signals to the power supply which supplies voltages to RF power devices in order to simultaneously satisfy two operating conditions: a) provide best possible efficiency of the power amplifier stages depending on the input signal characteristics and b) provide compensation for RF transistor AM-AM and AM-PM distortion compensation across the power range. In particular, the voltage control provides for constant power amplifier gain across the input signal dynamic range, thus minimizing power amplifier amplitude distortions and extending the useful power amplifier linear dynamic range up to saturation point. The power amplifier thus exhibits better linearity and efficiency than offered by conventional techniques and topologies.

A transmission signal to be transmitted from a radio transmitter is predistorted in order to compensate for the signal distortion caused by a power amplifier. The transmission signal and a signal modeling a power supply voltage applied to the power amplifier are compared with distortion properties of the power amplifier using these signals. The distortion information is comprised in an amplitude distortion lookup table and a phase distortion lookup table. Transmission signal and power supply signal values are associated with envelope and phase predistortion information comprised in the respective lookup tables and the envelope and the phase of the transmission signal is predistorted accordingly.

According to one embodiment of the invention, an integrated circuit comprises an encoding module, a modulation module and a spectral shaped module. The encoding module includes an interleaver that adapted to operate in a plurality of modes including a first mode and a second mode. The interleaver performs repetitive encoding when placed in the second mode. The modulation module is adapted to compensate for attenuations that are to be realized during propagation of a transmitted signal over the power line. The spectral shaped module is adapted to compensate for amplitude distortion and further compensates for attenuations that will be realized during propagation of the transmitted signal over the power line.

A technique for a combined peak reduction equalizer filter and phase / amplitude pre-distortion is described. The input to a transmitter chain is modified by a combined equalizer filter and pre-distorter, prior to being applied to the transmitter chain. The equalizer filter modifies and smoothen the amplitude of the signal followed by pre-distorter to compensate for phase and amplitude distortion from transmitter chain or power amplifier. The modified and smoothen signal has its peaks reduced before being pre-distorted. The baseband signal pre-distortion results in cancellation of the distortion being introduced by the power amplifier or the transmitter chain. The amplitude pre-distortion is applied to the amplitude of the peak reduced baseband signal using the envelope information from the output of the transmitter chain or power amplifier and the phase pre-distortion is applied to the phase of the peak reduced baseband signal using the differential phase information between input and output of the power amplifier or the transmitter chain.

A variable gain amplifier of low amplitude distortion, and low noise, having a large variable range, is provided. A variable gain differential amplifier that controls a gain by use of bias current is used as each of unit amplifiers (VGAs) making up the variable gain amplifier. A large variable gain range is obtained by series-connecting a plurality of the variable gain differential amplifiers. An attenuator is installed on the input side of the unit amplifier (VGA) at least in the initial stage. By doing so, it becomes possible to prevent amplitude distortion from occurring to the respective VGAs. An attenuator utilizing voltage division by capacitors, generating no noise, is used for lowering noise. Further, the variable gain amplifier is provided with a fixed gain amplifier installed in the final stage as necessary in order to obtain a total gain as desired. With the use of the variable gain amplifier as a variable gain amplifier for output power control of a polar loop transmitter, an excellent function for output power control can be achieved without causing significant deterioration in distortion characteristic and noise characteristic thereof.

The invention provides a stereo matching method based on an improved gradient and an adaptive window, and aims to solve the problem that an existing local stereo matching algorithm is low in precision and is influenced by amplitude distortion easily. Firstly, on the basis that a traditional gradient vector only contains amplitude information, phase information is introduced, conversion is carried out on the original matching cost, and abnormal values are further eliminated. Then, the adaptive window can be built through the criss-cross adaptive window generation method according to the color and spatial position relation between adjacent pixels, wherein a large window is provided for a low-texture area to improve matching precision, a small window is generated in a high-texture area to protect detail information of the edge of an object and the like, and the aggregated cost is selected according to the Winner-Takes-All strategy so that a disparity value corresponding to the minimum value of the total cost can serve as an initial matching result. Finally, a disparity refinement method based on a local disparity histogram is provided, and a high-precision disparity map is obtained. As is shown in experimental results, the stereo matching method is high in machining precision and has high robustness under the condition of amplitude distortion.

The invention discloses a luminosity insensitivity stereo matching method based on self-adapting Census conversion. Firstly, a self-adapting area based on a cross skeleton is determined according to the structure and color information of an image so as to obtain Census conversion windows of any shape and any size; secondarily, the hamming distance after Census conversion is used as a matching cost and a local optimization method is adopted to calculate an initial parallax; finally, a two-step extracting method based on parallax statistics column diagram and left-right consistency verifying is disclosed to organically integrate the self-adapting area of the cross skeleton into the extracting process to obtain a high-precision parallax diagram. The luminosity insensitivity stereo matching method based on self-adapting Census conversion can obtain the high-precision parallax diagram from a stereo image pair with differences in illumination intensity and exposure time, integrate the matching precision and robustness on amplitude distortion, and be better adapted to application context of visual navigation for unmanned planes.

The invention provides a stereo matching method based on the hybrid matching cost and an adaptive window. Firstly, as an improvement on the traditional gradient matching cost, gradient phase information is introduced, wherein to further improve the robustness of the algorithm, the new hybrid matching cost is provided by normalizing the gray level SAD cost through an exponential function. Then, the adaptive window can be built based on the criss-cross adaptive window generation method according to the color and spatial position relation between adjacent pixels, wherein a large window is provided for a low-texture area to improve matching precision, a small window is generated in a high-texture area to protect detail information of the edge of an object and the like, and the aggregated cost is selected according to the Winner-Takes-All strategy so that a disparity value corresponding to the minimum value of the total cost can serve as an initial matching result. Finally, a disparity refinement method based on a local disparity histogram is provided, and a high-precision disparity map is obtained. As is shown in experimental results, the stereo matching method is high in machining precision and has high robustness under the condition of amplitude distortion.

The present invention, generally speaking, provides a method of obtaining very accurate estimates of the phase and amplitude distortions introduced by radio frequency or microwave power amplifiers even where polar modulation is used.

The invention discloses an all-digital logarithm automatic gain control device and a method thereof. A phase shifter extracts an equidirectional branch data I and a quadrature branch data Q of instantaneous outcoming signal, then a power detector obtains the power of outcoming signal, a logarithmic converter performs the linearizing process to the outcoming signal, compares the results with a system preset parameter b to form an error signal, finally an integrator removes the high-frequency component, an index converter performs the reverse-linearizing process to the error signal, a controllable gain amplifier forms a feedback loop. When the outcoming signal power is larger than the preset value,the gain of the controllable gain amplifier is reduced, and when the outcoming signal power is smaller than the preset value,t he gain of the controllable gain amplifier is enhanced, therefore outputting the digit signal with constant power. The invention avoids the limiting amplitude distortion, considerably reduces the complexity of back-end digital signal processing, enhances the anti-interference and stability of the system and effectively reduces the consumption of hardware system resources.

The invention relates to a circuit capable of improving the linearity of a power amplifier. The circuit comprises a power amplifier circuit, wherein a linearity compensating circuit is arranged at the front end of the power amplifier circuit and comprises a current source, a voltage clamp transistor, a state compensating transistor and an isolation resistor, the current source and the voltage clamp transistor are connected to the ground in series and provide bias voltage for the power amplifier circuit, the isolation resistor is connected between the current source and the signal input end of the power amplifier circuit in series, the state compensating transistor is connected between the current source and the signal input end of the power amplifier circuit in series, and the voltage clamp transistor and the state compensating transistor can be diodes, audios, NMOS tubes and the like. The amplitude distortion and phase distortion generated by the power amplifier can be compensated effectively through the simulated predistortion technology. The circuit is simple in structure, convenient to control, and easy to integrate and implement, and the effect of improvement on the linearity of the power amplifier is remarkable.

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.

An evaluation method for linearity evaluations neither performing calculations of error vectors at multiple sampling points nor using a demodulator corresponding to a desired modulation scheme. Measuring devices (164 and 165) measure the input signal and the output signal of an evaluation object (1), to which a predetermined evaluation signal has been inputted. An evaluation unit (166) uses the input signal and the output signal of the evaluation object (1), to determine at least one of an amplitude distortion or a phase distortion of the output signal. An integration unit (169) uses the distortions to perform the integrations weighted by the probability density function of the power-to-average ratio of a predetermined modulated signal. A linearity index calculation unit (170) calculates a linearity index from the results of processing by the integration unit (169).

The invention discloses a predistortion linearization device of a millimeter wave power amplifier and aims at providing the predistortion linearization device which is simple in structure, wide in bandwidth, good in stability and suitable for the millimeter wave high-power amplifier, wherein gain and phase are respectively adjustable. According to the technical scheme, a radio frequency signal is input to the input end of an orthocoupler through a radio frequency input port (1), and two paths of orthogonal signals are produced. The signal of one path enters a path I (6) through the straight end (2) of the orthocoupler, bias voltage is adjusted through a DC feed power supply (12), a component with the phase of non-linear conditions not distorted and amplitude distorted is obtained through a high-resistance wire (17) connected with a diode (16), and a signal with the characteristic of gain expansion is output. The signal of the other path enters a path Q (7) by being connected with the isolation end (4) of the orthocoupler and the coupling end of the orthocoupler of a matched load, and a signal with controllable amplitude is output. The two signals finally pass through a power synthesizer (8), then a signal with amplitude and phase both distorted is output, and the amplitude and the phase are respectively adjustable.

A joint carrier synchronization and channel equalization method for OFDM systems, that is suitable for use in a receiver of said orthogonal frequency division multiplexer (OFDM) systems, comprising the following steps: firstly, receiving a reception signal sample of an OFDM symbol, and obtaining simultaneously a phase error and a gain error on each sub-channel in a frequency domain, through outputting a sub-channel signal on each said sub-channel in said frequency domain; next, obtaining an execution carrier frequency offset factor, an execution phase compensation factor, and an execution gain compensation factor based on said phase error and said gain error; and finally, eliminating a phase offset of said reception signal sample of a next symbol in a time domain based on said factors, and compensating a magnitude distortion and a phase distortion on each said sub-channel in said frequency domain for said reception signal of said next symbol.

Directional hearing is improved given the binaural coverage for a hearing aid user with two hearing aid devices wearable at the ears. The respective signal transit times and / or signal amplitudes and / or amplifications of an electrical signal are respectively measured in a signal path between an input transducer and an output transducer and that data with respect to the measured signal transit times and / or signal amplitudes and / or gains is transmitted onto the respectively other hearing aid device. As a result, the signal transit times and the signal amplitudes of the electrical signals through the two hearing aid devices can be matched to one another. The hearing aid devices thus cause no phase or amplitude distortion, and the natural phase shift as well as the natural amplitude difference of a sound signal incident from a specific direction are thus preserved. The directional information is thus also preserved for the hearing aid user.

The invention discloses an automatic gain control method and device, which are used for resolving the problem that the conventional automatic gain control method may lead to in-band amplitude distortion and greatly reduce the function of a Bluetooth device. The method comprises the steps of measuring the RSSI value of a data frame; determining whether the actual power of the data frame is within alinear zone of curve relationship between the actual power and the measuring power or not based on the RSSI value of the data frame; adjusting the receiving gain of the data frame based on the judging result. The invention is advantageous in that the device can work at the best gain point, and the receiving sensitivity and anti-interference performance can be bettered.

A digital signal receiver and a method for receiving a digital signal. The receiver includes an equalizing unit for compensating for an amplitude distortion of a received signal, an original signal decision unit for deciding an original signal from a signal which is compensated for the amplitude distortion, a carrier recovering and phase lock detecting unit for detecting a phase error between an input of the original signal decision unit and the decided original signal, and outputting a phase lock signal, a re-rotating unit for restoring the signal from the original signal decision unit to its original state and outputting a restored signal to the equalizer, and a coefficients updating unit for receiving the phase lock signal from the carrier recovering and phase lock detecting unit and the restored signal from the re-rotator unit, generating an error for updating the coefficients of the equalizer, and updating the coefficients of the equalizer.

An equalization method suitable for use in a receiver in an orthogonal frequency division multiplexing (OFDM) system utilizing a plurality of sub-carriers. The receiver includes an outer receiver for decoding. The equalization method includes receiving an input signal including at least one preamble symbol containing a training sequence and a plurality of informative OFDM symbols each containing a serial stream of samples, and performing compensations for each of the informative OFDM symbols. Compensation for each of the informative OFDM symbols includes converting the serial stream of samples into parallel samples, performing a fast Fourier transform (FFT) of the parallel samples to obtain a plurality of data symbols, each data symbol corresponding to a sub-carrier, compensating the data symbols for at least one first phase distortion and at least one second phase distortion, and providing at least one amplitude distortion factor to the outer receiver.

A compact fetal sound system delivers high-fidelity sound to a fetus in utero through a miniature, abdominally mounted driver with a convex diaphragm. No gel is necessary at the interface between the diaphragm and the mother's abdomen. Digital signal processing shapes the frequency spectrum of the sound transmitted to the fetus, so that after traveling through the attenuative tissue of the expectant mother the desired volume of sound and frequency content reach the ears of the fetus. As the term of pregnancy progresses, the frequency shaping provided by the digital signal processing automatically varies to compensate for changes in uterine lining thickness and the like. Preferred embodiments also include a microphone attached to the abdomen of the mother and signal processing to correct for frequency and amplitude distortions of sound eminating from the womb. Embodiments also include an elastic belt to maintain the transducer and microphone against the abdomen.

The invention discloses a stereoscopic image objective quality evaluation method on the basis of the structural distortion, which comprises the following steps: firstly, respectively carrying out regional division on left and right viewpoint images of an undistorted stereoscopic image and a distorted stereoscopic image to obtain an eye sensitive region and a corresponding nonsensitive region and then respectively obtaining evaluation indexes of the sensitive region and the nonsensitive region from two aspects of the structural amplitude distortion and the structural direction distortion; secondly, acquiring quality evaluation values of the left and right viewpoint images; thirdly, sampling singular value difference and a mean deviation ratio of residual images of which singular values are deprived to evaluate the distortion condition of the depth perception of a stereoscopic image so as to obtain an evaluation value of stereoscopic perceived quality; and finally, combining the quality of the left and right viewpoint images with the stereoscopic perceived quality to obtain a final quality evaluation result of the stereoscopic image. The method disclosed by the invention avoids simulating each composition part of an eye vision system, but sufficiently utilizes structure information of the stereoscopic image, so the consistency of the objective evaluation result and the subjective perception is effectively improved.