Bruce C. Eastmond

Speech detector for automatic level control systems

A speech detection circuit uses a peak detector and a valley detector including offset voltages to reliably detect the absence or presence of speech at audio base band level. This circuit provides a pulse train output when speech is detected which may be used to control an automatic gain control circuit.

Method, apparatus, and communication device for charging a charge storage device which is momentarily connected to a fixed load

The present invention provides a method (100), an apparatus (400), and a communication device (700) for automatically maintaining a state of full charge in a charge storage device, such as a secondary battery (414), to which a fixed load (412) is momentarily connected. Since the load is fixed, a predetermined amount of charge is removed from the charge storage device each time the load is connected. A counter (404) is incremented while the load (412) is connected. From the count, the amount of charge that must be replaced can be determined. As the charge is replaced the count is decremented.

Speech operated noise attenuation device

A speech operated noise attenuation device (SONAD) includes circuitry to measure the noise level in an audio channel. The output of the noise measurement circuitry provides a control signal to an audio attenuator which varies the intersyllable attenuation of the background noise according to the noise level present in the audio.

Audio periodicity squelch system

Squelch circuit responsive to the periodicity of a voice signal for controlling the output of a radio receiver to provide transmission of speech and reject noise. The audio signal from the receiver is amplitude limited and the transitions in the limited wave control a bistable multivibrator having first and second out-of-phase outputs. The outputs are used to activate circuits which produce voltage samples proportional to the time period between zero crossings, with the alternate periods producing voltages across two capacitors. The difference between the successive voltage samples is derived and compared with a reference voltage to provide a control voltage. The control voltage, which is produced as long as the difference between the samples is less than the reference, is applied to a gate circuit which controls the charging of a squelch control capacitor. A control voltage which continues through a plurality of samples causes the voltage across the squelch control capacitor to raise to a level which operates a squelch switch to allow transmission of the audio signal.

Performance of a two-branch radiotelephone selection diversity receiver

This paper describes an 800 MHz two-branch selection diversity receiver designed for use at the base site of a cellular mobile telephone system. Audio S/N and bit error rates measured with a simulated Rayleighfaded carrier signal are compared with computer predicted results generated from audio signal and noise measurements and bit error rate data taken with a nonfaded carrier signal. The receiver audio S/N performance with unequal branch gains is investigated. Results are compared with those obtained for a maximal ratio diversity receiver.