Abstract: In an electronic inductor circuit, an operational amplifier drives the base of the electronic inductor transistor, and receives negative feedback from the emitter of the transistor. The transistor and operational amplifier combine to form a voltage-controlled, current source (VCCS) with respect to the loop current. A voltage divider connected across the rectified Tip and Ring voltage (or another node of the circuit at an equivalent voltage) provides a DC reference to the positive input of the operational amplifier, so that the line current automatically increases with an increase in line voltage. A capacitor couples the transmit signal driver to the positive input of the operational amplifier. This electronic inductor circuit can be driven using a low voltage supply and provides sufficient linearity for high-speed modem applications.

Abstract: A software decoder for converting standard composite video to RGB color components without a phase-locked loop. Subcarrier phase recovery for each video line is accomplished by performing a single DFT computation on the color burst samples for the frequency closest to the subcarrier frequency. The recovered subcarrier phase is added for each line to the orthogonal subcarriers which are mixed with the modulated chrominance for decoding of color difference signals I and Q. Digital composite video capture and store circuitry may be used to buffer the acquisition of real-time video to the speed of a DSP used for software processing. Interpolation can be used in the processing of digital composite video to improve vertical line alignment. Multiple composite video formats, such as NTSC and PAL, can be decoded with minor modifications in the software decoder operation.

Abstract: A data access arrangement (DAA) having improved surge protection. The DAA incorporates a high voltage clamping device functioning to protect line side circuitry from signal paths created by EMI capacitors. In one embodiment of the invention, EMI capacitors are added between the “plus” and “minus” terminals of the diode bridge of the DAA to balance and reduce noise injection onto the TIP and RING lines. These EMI capacitors also reduce EMI interference. However, by adding EMI capacitors on this side (the “rectified side” or “line side”) of the diode bridge, a high voltage signal path to earth ground is created that may have deleterious effects on the line side circuitry. To effectively negate undesirable signal paths through the EMI capacitors, the DAA includes a high voltage clamping device (e.g., a MOV, SIDACTor™, gas discharge tube or similar device) disposed between the plus and minus terminals of the diode bridge for suppressing high voltage spikes.

Abstract: An improved videofax system for displaying a video image from a digital memory, while the digital memory is being updated with data representing a new image and received from a standard telephone line or other communication channel with relatively slow data access time. A video processor circuit uses a first digital counter to increment the address of a digital memory sequentially and load the stored data to a digital-to-analog converter for display of the resulting analog composite signal on a standard monitor. The video processor uses the address provided by a second digital counter to temporarily switch the digital memory address provided by the first counter and sequentially update the digital memory with new data received from a modem, a microcontroller, or any other data storage components with slow access time, enabling a user to view the new image as it overwrites the old image with a sense of continuity between the old image and the new image.

Abstract: An inertial pointing device and method to determine position coordinates from sensing linear acceleration relative to space (inertia). One or more acceleration sensors detect the acceleration of the pointer in the X, Y, and/or Z directions, respectively. The acceleration of the pointer in each direction is then converted into speed and position at an appropriate integration rate, to determine the coordinates of the pointer on an electronic display. The inertial pointer can be used as a computer mouse, a pointing device for presentation displays, or as a remote control for TV sets.

Abstract: An apparatus for carrying electrical data signals and electrical power over a power line is disclosed. The apparatus includes a data processing device, a power supply, and a data signal transceiver. The apparatus also includes an interference filter coupled to the power line and to the power supply and configured to reject electromagnetic interference. A coupling circuit that is electromagnetically coupled to the power line is also disclosed. The coupling circuit is configured to transmit and receive data signals carried through the power line. The coupling circuit is coupled to the data signal transceiver. The data signal transceiver is configured to transmit and receive the data signals to and from the data processing device.

Abstract: A telephone line interface circuit is disclosed having intelligent line current control that can adjust to the various requirements of worldwide telephone systems (DC masks), and/or can reduce the power consumed by the interface circuit. A controller reads a voltage value and based on the theoretical model of a telephone line network, and the expected current/voltage characteristic, as dictated by the appropriate DC mask. The controller sets the line current (via an output voltage) to an optimum value and causes the line voltage to adjust so as to comply with the DC mask and/or minimize power dissipation in the circuit.

Abstract: In an electronic inductor circuit, an operational amplifier drives the base of the electronic inductor transistor, and receives negative feedback from the emitter of the transistor. The transistor and operational amplifier combine to form a voltage-controlled. current source (VCCS) with respect to the loop current. A voltage divider connected across the rectified Tip and Ring voltage (or another node of the circuit at an equivalent voltage) provides a DC reference to the positive input of the operational amplifier, so that the line current automatically increases with an increase in line voltage. A capacitor couples the transmit signal driver to the positive input of the operational amplifier. This electronic inductor circuit can be driven using a low voltage supply and provides sufficient linearity for high-speed modem applications.

Abstract: A telephone line interface circuit which does not require a hookswitch relay is disclosed. An optoisolator is utilized to place a telephone line interface circuit on-hook and off-hook. In one embodiment, the optoisolator is controlled by an optoisolator control signal generated by a communications device such as a modem. An output of the optoisolator is coupled to an input of a DC control circuit. An output of the DC control circuit is coupled to a AC switch. When the optoisolator input control signal is activated, the optoisolator output enables voltage or current bias to the transistor, which places the telephone line interface circuit off-hook. When the optoisolator input control signal is deactivated, the optoisolator output disables voltage or current bias to the transistor, which places the telephone line interface circuit on-hook. In one embodiment, the DC control circuit is an electronic inductor comprising a pair of NPN transistors connected in a Darlington configuration.

Abstract: Using a telephone line interface circuit with negative feedback, it is possible to control the current through the circuit so that the ratio of the voltage applied across the circuit to the current is the desired value of impedance. Voltage feedback from the line controls the current through the circuit, thereby reflecting a “virtual” impedance to the telephone line. By adequately filtering the voltage feedback, the reflected impedance to the line can be adjusted to any desired impedance function, without using the actual values of the impedance. The circuit is thus ideally suited for applications in which the impedance values need to be varied depending upon the characteristics of the telephone system.

Abstract: In an electronic inductor circuit, an operational amplifier drives the base of the electronic inductor transistor, and receives negative feedback from the emitter of the transistor. The transistor and operational amplifier combine to form a voltage-controlled current source (VCCS) with respect to the loop current. A voltage divider connected across the rectified Tip and Ring voltage (or another node of the circuit at an equivalent voltage) provides a DC reference to the positive input of the operational amplifier, so that the line current automatically increases with an increase in line voltage. A capacitor couples the transmit signal driver to the positive input of the operational amplifier. This electronic inductor circuit can be driven using a low voltage supply and provides sufficient linearity for high-speed modem applications.

Abstract: The line interface circuit of a modem to be connected to a standard RJ11 jack of a digital PBX (Private Branch Exchange) is used along with software routines resident in the modem to detect the presence of a PBX connected to the modem. Upon going off-hook, the modem, by the software routines, determines whether the connection will harm the interface by one of several software routines. If it appears that the interface circuit may be damaged because a PBX line is present, the modem is instructed to go on-hook (hang up), or if the connection is not harmful to the interface, alerts the user that the modem is connected to a wrong jack.

Abstract: An efficient method and circuitry for transferring various levels of power across a high voltage isolation barrier. In one embodiment of the invention, a data access arrangement (DAA) is provided with system side circuitry that provides power to line side circuitry via the high voltage isolation barrier. The line side circuitry includes voltage measurement circuitry, such as an analog-to-digital converter, that periodically measures the line side supply voltage. The resultant information is transmitted across the high voltage isolation barrier to the system side circuitry, where control circuitry or a software process compares the digital representation of the measured voltage level to a predetermined value. Based on the results of this comparison, the control circuitry may alter the amount of power transferred across the high voltage isolation barrier to the line side circuitry in order to optimize power transfer efficiency.

Abstract: A stand-alone modem establishes a physical connection with the PSTN and a logical connection with the Internet. The modem supports basic Internet communication protocols such as E-mail, FTP, and HTTP through an extended AT command set without the need for a host processor.

Abstract: A software decoder for converting standard composite video to RGB color components without a phase-locked loop. Subcarrier phase recovery for each video line is accomplished by performing a single DFT computation on the color burst samples for the frequency closest to the subcarrier frequency. The recovered subcarrier phase is added for each line to the orthogonal subcarriers which are mixed with the modulated chrominance for decoding of color difference signals I and Q. Digital composite video capture and store circuitry may be used to buffer the acquisition of real-time video to the speed of a DSP used for software processing. Interpolation can be used in the processing of digital composite video to improve vertical line alignment. Multiple composite video formats, such as NTSC and PAL, can be decoded with minor modifications in the software decoder operation.

Abstract: Computers commonly connect to remote computers and networks using the telephone lines. A telephone line is composed of a positive line (Ring) and a negative line (Tip). Because there is no guarantee, in general, which line on a two-conductor telephone jack will be positive and which will be negative, diode bridges are often used to assure correct polarity of devices coupled to the telephone lines. Commonly computers connect to telephone lines using modems, which plug into the computer. The modems often contain two jacks, one to connect the modem to the telephone line, the other to provide an outlet for a telephone. Commonly both jacks are wired in parallel. Embodiments of the inventions provide for wiring the telephone jacks in opposite polarity, or switching polarity via jumpers. A method is provided to detect a telephone plug in the jack of incorrect polarity. A user may be instructed in advance or prompted to switch jacks or jumpers if necessary and the need for the diode bridge is eliminated.

Abstract: A simple, low-cost videophone system for transmitting and receiving still video images over a standard telephone line in response to a user command. A video processor circuit, comprising an A/D converter, a digital memory, a digital timing circuit, and a D/A converter, can grab a video image from a standard video camera and store one-half the number of lines of a video frame in the digital memory. A still video image can be displayed in a standard TV monitor by repeatedly sending the data stored in the digital memory to the D/A converter. The data stored in the digital memory can be transmitted using a standard modem to the digital memory of an equivalent system at a remote location, and the same still video image can be displayed at the remote location within a short time. Data compression is accomplished during transmission by decreasing the number of significant bits of the data being transmitted and using standard protocols adopted by the modem.

Abstract: A power supply provides digital data coupling for power-line networking. The power supply includes a power supply side digital interface to transmit and receive a digital data passed through a digital coupler to and from a power-line network access circuitry side digital interface of power-line network access circuitry. The power supply further includes a digital-to-analog converter to process digital data into a high-frequency analog data carrier to provide to a power line of a power-line network. An analog-to-digital converter of the power supply converts a high-frequency analog data carrier from the power line into digital data for the power-line network access circuitry. A power-line analog front end of the power supply transmits and receives the high-frequency analog data carrier to and from the power line. Digital data exchanged between the power supply and the network access circuitry may include control signals for a control circuitry of the power supply.

Abstract: A ring detect/Caller I.D. detect circuit employs first and second operational amplifiers supplied with a differential input from the AC side of a diode bridge. The differential input is converted to a single ended input supplied in a first mode to a ring detect comparator supplied with a plurality of selectable reference voltages and in a second mode to a comparator which produces a digital Caller I.D. output signal. An impedance in the feedback loop of the first and second operational amplifiers is switch-selectable to enable the first and second modes of operation, and each of the selectable reference voltages is chosen to permit proper ring signal detection in a particular corresponding geography.

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.