Acoustic Technologies, Inc.

Motorola Corporation

Kendall G Moore

Samuel L Thomasson

Richard W Ulmer

Frederic B Shapiro

Michael W Hodel

Donald Allan Lowmiller

Raymond Rubacha

Deborah J Beckwith

Amplitude is corrected by subtracting a component signal from a composite signal to produce a remainder signal, correlating the remainder signal with the component signal to produce a product signal, averaging the product signal, and adjusting the magnitude of the component signal in accordance with the averaged product signal to minimize the product signal. The amplitude of the component signal is adjusted in a programmable gain amplifier controlled by an up-down counter. The up-down counter is part of a digital control loop including a pseudo-multiplier for multiplying the remainder signal with the component signal. The output of the multiplier controls the direction of the count, which is generally continuous except that it cannot roll over or roll under. The remainder signal is the received signal with the echo removed.

Precise amplitude correction circuit

A complementary comb filter includes a plurality of band pass filters and a plurality of notch filters, wherein the notch filters have the same center frequencies as the band pass filters or the same center frequencies as the dead bands defined by the band pass filters. Phase distortion by the notch filters occurs primarily in the notch, thereby eliminating distortion of the signal.

Band pass and notch filters for echo reduction with less phase distortion

A transmitted signal is coupled through a coarse delay and a fine delay to one input of a correlator. Another input of the correlator is coupled to a received signal. The delays are adjusted for maximum correlation and the output of the fine delay is subtracted from the received signal to reduce or eliminate an echo. The delays operate by sampling the signal and storing the samples at successive storage sites. The storage sites are read a predetermined time later, producing the delay. The read operation for the coarse echo includes three readings from separate sites and using the correlation products to indicate the magnitude and direction for changing the delay.

Acoustic and electronic echo cancellation

A low pass limited, low frequency pseudo-random noise signal is added to the input signal for tagging the input signal in order to facilitate correlation with an echo.

Tagging echoes with low frequency noise

Sound is converted into an electrical signal by a microphone and is converted into an inaudible, digitally modulated signal that is combined with the electrical signal from the microphone, amplified, and converted into sound waves by a speaker. Any sound traveling from the speaker back to the microphone includes the inaudible component representing the original sound. The inaudible component is separated from the audible components, and the original sound is reconstructed in a digital demodulator. The reconstructed original sound is subtracted from the signal from the microphone, thereby reducing any echo and canceling feedback. Digital modulation includes any form of shift keying, including coherent and noncoherent techniques for modulating frequency, phase, or amplitude.

Reducing acoustic feedback with digital modulation

A high resolution delay line includes a coarse delay having a minimum period of delay and a fine delay having a total delay, wherein the total delay is equal to or greater than half the minimum period. Each delay can be implemented in analog or digital form and the delay line can be implemented with one portion in analog form and the remainder in digital form. The digital delay can provide a delay upward of 1,500 milliseconds. The fine delay provides a resolution of ten microseconds or less. An unknown delay is measured by coupling a signal into two channels, wherein the first channel includes the unknown delay and the second channel includes the coarse delay and the fine delay. The output signals from the channels are correlated while adjusting the coarse delay for maximum correlation and then adjusting the fine delay for maximum correlation.

High resolution delay line

A sensing circuit (202) uses correlated double sampling to sample a first pixel signal of a pixel stream (V.sub.PIXEL) at two different times to produce a dark signal and a light signal on two capacitors (310, 314). The dark and light signals are amplified in an amplifier (302) to produce a differential output signal (V.sub.PP -V.sub.PN) proportional to their difference. While the samples of the first pixel signal are being amplified, a second pixel signal is double-sampled to produce dark and light signals on two other capacitors (312, 316) for amplifying in the same amplifier. The period of the pixel signal is divided into time slots (T.sub.1 -T.sub.16) by a clocked oscillator (52). Programming signals (PROG1, PROG2) control the time slots in which sampling control pulses (V.sub.S1, V.sub.S2) are generated.

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Tempe, AZ, United States of America

Kendall G Moore