Abstract: Apparatus for adaptively reducing dead time in a switching circuit includes overlap detection circuitry for measuring the dead time/overlap of the switches, and control circuitry for setting the dead time to the optimum level (generally the minimum possible dead time without any overlap occurring). The dead time/overlap may be detected by measuring the current through the switches, the current into the power supply, the voltage waveform at the switch point, or the average voltage waveform at the switch point. The dead time may be controlled by utilizing delay elements prior to the drivers, or by utilizing circuitry to control the driver timing.

Abstract: A delta sigma modulator of at least second order includes correction means applied to each feedback loop in the modulator, to account for systemic nonlinear output distortions. Since the output distortion is nonlinear, the correction applied to each feedback loop is nontrivially different. Such a corrected delta sigma modulator may be used in a demodulator including an output digital to analog converter (DAC) to account for systemic imperfections in the pulses formed by the DAC. The corrected delta sigma modulator is also useful in correcting output errors associated with high quality multilevel demodulators and class D power amplifiers. The corrected delta sigma modulator may be one bit or multilevel.

Abstract: An improved multiband audio compressor is well behaved for both wide band and narrow band signals, and shows no undesirable artifacts at filter crossover frequencies. The compressor includes a heavily overlapped filter bank, which is the heart of the present invention. The filter bank filters the input signal into a number of heavily overlapping frequency bands. Sufficient overlapping of the frequency bands reduces the ripple in the frequency response, given a slowly swept sine wave input signal, to below about 2 dB, 1 dB, or even 0.5 dB or less with increasing amount of overlap in the bands. Each band is fed into a power estimator, which integrates the power of the band and generates a power signal. Each power signal is passed to a dynamic range compression gain calculation block, which calculates a gain based upon the power signal. Each band is multiplied by its respective gain in order to generate scaled bands. The scaled bands are then summed to generate an output signal.

Abstract: A digital to analog (D/A) converter for hearing aids and the like includes a delta sigma modulator and a duty cycle demodulator. The delta sigma modulator converts medium rate, high resolution data into medium rate, medium resolution data, and the duty cycle demodulator converts the medium rate, medium resolution data into low resolution, high rate data. The duty cycle demodulator utilizes a lookup function to format the output data in a format having lowered transition rates, resulting in lower power use. The delta sigma converter may include a correction factor in at least one of its feedback loops to compensate for the characteristics of the output data from the duty cycle demodulator.