Digital signal

About: Digital signal is a research topic. Over the lifetime, 44213 publications have been published within this topic receiving 345279 citations.

Digital PWM amplifier with simulation-based feedback

Abstract: Systems and methods for performance improvements in digital switching amplifiers using simulation-based feedback. In one embodiment, a digital pulse width modulation (PWM) amplifier includes a signal processing plant configured to receive and process an input audio signal. The amplifier also includes a simulator configured to model processing of audio signals by the plant. The outputs of the plant and the simulator are provided to a subtractor, the output of which is then added to the input audio signal as feedback. The plant may consist of a modulator and power switch, a noise shaper, or any other type of plant. An analog-to-digital converter (AOC) may be provided to convert the output audio signal to a digital signal for input to the subtracter. Filtering may be implemented before or after the ADC, and a decimator may be placed after the ADC if it is an oversampling ADC.

Predictive communication system filtering arrangement

Abstract: A digital communication system includes a predictive decoder (30) that is operative to convert received digital codes into a predictively decoded signal, e.g., speech signal, and to generate a set of predictive parameter signals and a signal representative of the communication system bit rate. A set of filter control signals is generated (325) responsive to the communication bit rate signal. The predictively decoded signal is passed through a filter (335) which modifies the output signal responsive to the filter control signals and the decoder predictive parameter signals to improve the output signal quality. The filter control signals selectively alter the predictive parameter signals to optimize the predictively decoded signal modification for the current transmission bit rate.

Effect of atmospheric turbulence on bit-error rate in an on-off-keyed optical wireless system

Abstract: Atmospheric turbulence produces scintillation at an optical receiver, which leads to fading of the received signal. This fading affects the bit-error-rate (BER) of a digital signal in a way that depends on the depth of the fade, the decision threshold at the receiver, and the average signal-to-noise ratio. The degree of fading can be dramatically reduced by the use of a time-delayed diversity technique, which involves retransmission of the data stream after a short delay, and resynchronization of the received data streams.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Variable sample rate adc

Abstract: A method and apparatus for analog-to-digital conversion using sigma-delta modulation of the temporal spacing between digital samples are provided. The method and apparatus include sigma-delta modulation of the time-base such that errors produced by non-uniform sampling are frequency-shaped to a high frequency region where they are reduced by conventional digital filtering techniques. In one embodiment, a sigma-delta ADC receives an analog input signal and converts the analog input signal to digital samples at an oversampling rate. A decimator, coupled to the sigma-delta ADC, receives the digital samples and decimates the digital samples to produce the digital samples at a preselected output sample rate, less than the oversampling rate. An ADC sample rate control circuit, coupled to the ADC, receives a frequency select signal representing the preselected output sample rate, and produces a noise-shaped clock signal for controlling operation of the ADC at the oversampling rate. The control circuit includes a sigma-delta modulator for sigma-delta modulating the frequency select signal. A randomizer/suppressor circuit, under control of the output of the sigma-delta modulator, receives an input clock signal and adjusts the frequency of the clock signal to produce a noise-shaped clock signal for controlling the oversampling rate of the ADC.

Baseband RF voltage-current probe

Abstract: An RF probe for a plasma chamber picks up current and voltage samples of the RF power applied to an RF plasma chamber, and the RF voltage and current waveforms are supplied to respective mixers. A local oscillator supplies both mixers with a local oscillator signal at the RF frequency plus or minus about 15 KHz, so that the mixers provide respective voltage and current baseband signals that are frequency shifted down to the audio range. The phase relation to the applied current and voltage is preserved in the baseband signals. These baseband signals are then applied to a stereo, two-channel A/D converter, which provides a serial digital signal to a digital signal processor or DSP. A local oscillator interface brings a feedback signal from the DSP to the local oscillator. The DSP can be suitably programmed to obtain complex Fast Fourier Transforms of the voltage and current baseband samples. The frequency-domain spectra are analyzed to obtain, with great accuracy, magnitude of voltage and current and phase angle. Other parameters are derived from these three.