Abstract: The improved full duplex speakerphone system replaces two A/D converters normally required in conventional speakerphone systems with a single A/D converter. This single A/D converter is a higher speed A/D converter which is multiplexed at its input. By alternately connecting the A/D converter between a microphone input circuit and a telephone line input circuit, the single higher speed A/D converter can be used to digitize both input signals. Because the A/D converter samples the data at a much higher rate and uses a digital filter to greatly reduce the impact of aliasing, very simple, low cost external filters may be used.

Abstract: A cordless telephone includes a base unit having a data generator which generates a digital data burst having a transition period, a data encoder which encodes the digital data burst, and a transmitter which transmits the encoded data burst; and a handset having a receiver responsive to and sampling the encoded data burst, and a synchronization device operatively coupled to the receiver for maintaining synchronization between the receiver and the transmitted encoded data burst in accordance with a characteristic of an expected time of transition of an incoming signal of the data encoder by comparing an actual time of transition to the expected time of transition and adjusting a sampling point of the transmitted encoded data burst by a one-sided majority vote of samples around the sampling point.

Abstract: A caller identification device attachable to a telephone line and having a message function includes a line interface coupled to the telephone line, a ring detector for detecting rings of an incoming telephone call, and a line monitor for receiving an incoming telephone call signal from the telephone line in an on-hook state. A caller identification detector is coupled to the line monitor for detecting caller identification information including at least the caller's telephone number when the line monitor receives an incoming telephone call signal. A speech synthesizer generates and transmits speech signals on the telephone line, and a remote detector is coupled to the line monitor for detecting a remote command tone signal. A controller activates the line interface to seize the telephone line when the ring detector detects rings of an incoming telephone call.

Abstract: A backup system for a time of day clock in an electronic device that enables a microprocessor to accurately maintain the time of day clock in the event of a power interruption. The backup system can be used with any AC powered electronic device that maintains a clock. The backup system allows a capacitor to supply backup power to the microprocessor and insures the accuracy of the clock by accounting for component tolerances in the system. The backup system calibrates the time constant of an RC circuit connected to the microprocessor while AC power is still available and stores that value for later use in determining the length of a power interruption. The calibration process allows the system to use lower cost components with higher tolerance values without compromising the accuracy of the time of day clock.

Abstract: An integrated cordless telephone and telephone answering device allows a user to selectively replay messages previously recorded on the telephone answering device either through a loudspeaker or through an earpiece, both of which are provided in the cordless handset, as well as locally at the telephone answering device. The loudspeaker is the same loudspeaker that is used when the cordless handset is in a speakerphone mode. When a user wishes to initiate message retrieval through the cordless handset, a PLAY key is pressed which automatically supplies the audio signal to the loudspeaker. If the user then wishes to listen to messages through the earpiece in the cordless handset, a MODE key is pressed which supplies the audio signal to the earpiece.

Abstract: A telephone answering device includes a line interface for connecting the telephone answering device to a telephone line and a ring detector, coupled to the telephone line, for detecting ringing signals sent from a telephone company central office. A calling party identification (CPID) detector, coupled to the telephone line, is provided for detecting CPID information. A controller controls the line interface to seize the telephone line immediately after the ring detector detects a first ring on the telephone line and the CPID detector detects that the CPID information is blocked. After the line interface seizes the telephone line, the telephone answering device plays an outgoing message to the caller and, thereafter, the caller may record a message for the telephone answering device owner.

Abstract: A digital telephone answering device (DTAD) that allows messages to be forwarded to certain internal mailboxes. Random access memory (RAM) is flexibly and dynamically controlled by a microprocessor or controller. Audio signals in the form of voice messages are digitized and stored in the RAM. Messages can be sorted and allocated to specific mailboxes and made retrievable by pressing a button assigned to that mailbox. Messages can also be moved or re-assigned from a common message area to a certain mailbox or mailboxes. Outgoing messages are also stored in RAM and can be of sufficient number to have an outgoing message correspond to each incoming message storage area. The normal message recording and message playback functions of the DTAD may be activated after the call has been answered on the receiving side. Memos can be appended to messages that have been moved or re-assigned from a common message area to a certain mailbox or mailboxes.

Abstract: In a speakerphone, which operates under software control, transmit and receive signal levels are sampled and compared against one another, with hysteresis, to enable one of two speakerphone modes of operation--either a transmit mode or a receive mode. A single peak detector is multiplexed to sense the transmit and receive signal levels. Fixed attenuators are switched into either the receive signal path or into the transmit signal path, depending upon the current speakerphone operation mode. Signal compression is used to provide for improved mode determination over a wide dynamic range. The level detection and/or attenuation may be performed in software. The speakerphone functions are readily implemented using standard line interfaces and control circuitry. Automatic gain control in the receive mode ensures a constant level of signals at the speakerphone loudspeaker, regardless of telephone line conditions.

Abstract: A telephone answering device, having an automatic page feature for automatically paging a user after a message has been recorded thereon, is programmed to dial the telephone number of a paging service to which the user subscribes each time a message is recorded, and to transmit at least numeric information that will ultimately be displayed on a portable pager. The numeric information can include the number of messages recorded on the telephone answering device, a caller's telephone number or a special predetermined code that lets the user know that the device is paging him. The telephone answering device is designed so as to be compatible with a wide variety of paging services and can be re-programmed if the user changes paging services. The device includes a memory that stores the digits of the paging service telephone number and automatically stores information representing the pauses and audible activity that are present between key presses during the programming process.

Abstract: A telephone answering device (TAD) includes a remote access mode which is operative responsive to dual tone multi-frequency (DTMF) signals. At least three bandpass filters each receive an input signal from a telephone line interface provided in the TAD. A software controlled sampling section receives outputs from all the bandpass filters for sampling outputs from the bandpass filters, the sampling section including a multiplexer which receives the outputs from all of the bandpass filters, and a peak hold circuit coupled to an output of the multiplexer. An analog-to-digital converter receives an output from the peak hold circuit, and a digital controller receives the output of the analog-to-digital converter for controlling operations of the TAD in a remote access mode responsive to the detected DTMF signals. First and second ones of the bandpass filters have respective center frequencies corresponding to frequencies of respective DTMF signals and a third bandpass filter has a different center frequency.

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.

Abstract: A digital automatic gain control system includes an envelope detector coupled to a system input for converting an AC input signal into a DC output signal. An analog-to-digital converter has an input coupled to receive the output signal of the envelope detector and an output coupled to a digital register controlled by a digital control circuit. A programmable gain amplifier has control inputs coupled to receive an output of the digital register for controlling the gain of the programmable gain amplifier such that the signal level at a system output of the programmable gain amplifier remains substantially constant as the signal level at the system input varies within a specified dynamic range.

Abstract: A cordless telephone includes a base unit, a handset, a ring detector in the base unit for detecting ringing signals on a telephone line of an incoming telephone call from a central telephone office, and a line interface in the base unit for detecting the presence of caller information in the incoming telephone call, the caller information including at least a caller's telephone number. A caller identification detector in the base unit, connected to the line interface and to the ring detector, detects the caller information responsive to the ring detector detecting the ringing signals, and converts the caller information in the incoming telephone call to an identification signal. A speaker is provided in the handset. A speech synthesizer in the base unit converts the identification signal to a synthesized speech signal and transmits the synthesized speech signal to the speaker.

Abstract: A telephone answering device with a direct telephone line connection eliminates the need for a transformer, optoisolators and relays that are normally used in telephone answering devices to isolate the telephone answering device system from the central office circuit. Isolation is instead achieved directly at the exposed metal points of the system by physical isolation, switched isolation, resistive isolation and dielectric isolation.

Abstract: A telephone answering device includes a digital recording and playback circuit for digitizing, recording and playing back a message from a telephone line; an audio random access memory for storing messages digitized by the digital recording and playback circuit; and a control unit, coupled to the audio random access memory. The control unit initially performs a test of only part of the memory in an amount sufficient to enable a user to perform predetermined basic functions, immediately after power is supplied to the device, without testing a remainder of the memory. Thereafter, a continuous repetitive series of tests of at least the remainder of the memory is performed while waiting for user input, to determine failed sections of the memory that are to be avoided during recording of a message. The failed sections of the memory, that are to be avoided during recording of a message after the determination, are marked.

Abstract: A telephone answering device (TAD) determines the "distinctiveness" of an incoming ring signal, and responds accordingly. Distinctive ring features of some current telephone utilities have established ring patterns with plural ring signals occurring within a single ring cycle. Normally, one ring signal is present per ring cycle. In the distinctive ring TAD set forth herein, ring cycles with one or more ring signals are discriminated and responded to by playing a different outgoing message corresponding to the distinctiveness of the ring cycle. In a further enhancement, the TAD does not answer the incoming telephone call if the answer ring cycle (upon which the TAD is to answer the call) is cut short, indicating that the telephone call has been answered by a person.

Abstract: An electronic notepad associated with the entry, and storage, dialing of telephone numbers is disclosed. The telephone numbers are entered through a telephone touch pad and is displayed on a liquid crystal display. Attached to a stand alone telephone or a telephone answering device (also know as a TAD), telephone numbers which would otherwise be easily forgotten due to transient presentation are retained by the device for later retrieval or use.