Speakerphone controlled by a comparator with hysteresis
AssigneeCasio PhoneMate, Inc.
InventorFrank Sacca
Life of this patent
Estimating the term…
Abstract
A speakerphone which employs non-linear amplifiers to compress transmit and receive signals, and level detectors to determine levels of the compressed transmit and receive signals. Compressed transmit and receive signal levels are compared against one another by a comparator with hysteresis, to enable one of two speakerphone modes of operation--either a transmit mode or a receive mode. Fixed attenuators are switched into either the receive signal path or into the transmit signal path, depending upon the current speakerphone mode. The speakerphone functions described herein are readily implemented using inexpensive control circuitry and a standard telephone line interface, which can be shared by a telephone handset and other components of an integrated telephone system.
Claims25
A switching type, half duplex, speakerphone, comprising:
- a telephone line interface for receiving a receive signal from a telephone line and transmitting a transmit signal to a telephone line, said telephone line interface including a sidetone cancellation circuit for eliminating a substantial portion of the transmit signal from the receive signal;
- a receive amplifier for amplifying the receive signal;
- a transmit amplifier for amplifying signals from a main microphone to provide the transmit signal;
- a main loudspeaker for converting the receive signal to an audible signal;
- a first non-linear amplifier for compressing the receive signal to provide a compressed receive signal;
- a second non-linear amplifier for compressing the transmit signal to provide a compressed transmit signal;
- a first level detector for detecting a level of the receive signal;
- a second level detector for detecting a level of the transmit signal;
- a comparator with hysteresis for comparing the level of the compressed receive signal with the level of the compressed transmit signal, and providing a comparison output;
- a first signal attenuator responsive to a first state of the comparison output to attenuate the receive signal;
- and
- a second signal attenuator, responsive to a second state of the comparison output to attenuate the transmit signal;
- whereby, when the receive signal is attenuated the transmit signal is unattenuated, and vice-versa.
A switching type, half duplex, speakerphone, comprising:
- a telephone line interface for receiving a receive signal from a telephone line and transmitting a transmit signal to a telephone line, said telephone line interface including a sidetone cancellation circuit for eliminating a substantial portion of the transmit signal from the receive signal;
- a receive amplifier for amplifying the receive signal;
- a transmit amplifier for amplifying signals from a main microphone to provide the transmit signal;
- a main loudspeaker for converting the receive signal to an audible signal;
- a first non-linear amplifier for compressing the receive signal to provide a compressed receive signal;
- a second non-linear amplifier for compressing the transmit signal to provide a compressed transmit signal;
- a first level detector for detecting a level of the receive signal;
- a second level detector for detecting a level of the transmit signal;
- a comparator with hysteresis for comparing the level of the compressed receive signal with the level of the compressed transmit signal, and providing a comparison output;
- a first signal attenuator responsive to a first state of the comparison output to attenuate the receive signal;
- a second signal attenuator, responsive to a second state of the comparison output to attenuate the transmit signal;
- whereby, when the receive signal is attenuated the transmit signal is unattenuated, and vice-versa;
- a telephone handset including a handset loudspeaker and a handset microphone;
- a first switch coupled to the main loudspeaker and disconnecting the main loudspeaker from the receive amplifier;
- a second switch coupled to the main microphone and disconnecting the main microphone from the transmit amplifier;
- a third switch coupled to the handset loudspeaker and connecting the handset loudspeaker to the receive amplifier;
- and
- a fourth switch coupled to the handset microphone and connecting the handset microphone to the transmit amplifier.
A method of operating a switching type, half duplex, speakerphone, comprising:
- interfacing to a telephone line to obtain a receive signal;
- providing a microphone signal for impressing on the telephone line a transmit signal;
- compressing both the microphone signal and the receive signal to provide compressed microphone and receive signals;
- switching from a transmit mode to a receive mode of operation based on a comparison of the compressed microphone and receive signals, wherein the comparison is performed with a comparator having hysteresis;
- causing the speakerphone to remain in a given one of the transmit and receive modes until switching to the other of the transmit and receive modes is instructed based on the comparison of the compressed microphone and receive signals;
- attenuating the receive signal when the speakerphone is in the transmit mode;
- and
- attenuating the microphone signal when the speakerphone is in the receive mode.
Dependencies are inferred from the claim text.