Our Engineers' Patent Portfolio - Analog Circuit Design


Line sharing multipoint pots splitter amplifier-based coupler

Patent Number 7,065,205

The eavesdropping prevention system and method of the present invention provides for shunting leakage signals in a communication system. The amplifier-based coupler is constructed with amplifiers configured with a nearly-zero impedance path which effectively prevents the propagation of a leakage signal onto other communication connections which are coupled to the same communication device. Leakage signals are attenuated due to the nearly-zero impedance path, rather than propagating through the higher impedance communication connections.


Local loop interceder

Patent Number 6,408,056

Disclosed is a local loop interceder which interfaces between the local loop and the central office and which provides access to lie public switched telephone network (PSTN). The local loop interceder establishes a first signal pathway from the local loop to the PSTN and a second signal pathway from the local loop to a high speed data modem. The local loop interceder alternates between the first and second pathways depending upon whether the end user desires voice or data communication on the local loop. In a second embodiment, the high speed data modem is a simultaneous voice and data (SVD) modem. In such case, the local loop interceder provides a third signal pathway from the SVD modem to the PSTN for voice communication which is demodulated from a simultaneous voice and data signal received by the SVD modem through the second signal pathway.


Filter system and method to suppress interference imposed upon a frequency-division multiplexed channel

Patent Number 6,744,883

A filter system (and associated filtering method) is disclosed, the filter system being connected between a large-amplitude, high-frequency noise source and a frequency-division multiplexed communications channel. The large-amplitude, high-frequency noise commonly being a POTS (plain old telephone service) ring signal generated by a CO (central office) telephone switch. The frequency-division multiplexed communications channel generally used to carry digital signals at frequencies above the POTS baseband in order to implement a digital subscriber line (DSL). Large-amplitude, high-frequency signal components from the POTS ring signal impair the performance of frequency-division multiplexed channels on a transmission line such as a subscriber loop. The filter system of the present invention utilizes amplitude and also may utilize frequency to selectively suppress the transients and harmonics on the transmission line caused by a telephone ring signal. In addition, the present invention uses bidirectional current limiting filters to implement some of the amplitude-dependent filtering behavior.


Integrated loop current detector apparatus for a PSTN modem

Patent Number 5,600,715

An integrated loop current detector for a public switched telephone network modem. The present invention solves the loop current detect problem in general, and is especially useful in modems employing echo cancellation techniques due the linearity afforded by the invention. In one advantageous embodiment of the present invention, the current detector includes a solid-state loop hold circuit coupled to terminals of the PSTN. A current mirror circuit is coupled in parallel with the loop holding circuit, wherein the current mirror circuit includes a transistor having a control terminal coupled to the DC operating point of the loop holding circuit. The transistor is operable to detect interruptions in loop current. An opto-coupler device having an input coupled to the switching device has an output coupled to a current detect input line of said modem thereby providing an isolated output for quick and reliable indication of current interruptions in said loop hold circuit.


Line-powered modem with capacitive isolation

Patent Number 5,655,010

A modem is disclosed which is separated into two parts, a first modem circuit consisting of digital circuits, and a second modem circuit consisting of a CODEC and analog circuits. The two modem circuits are separately powered by a first and second power source, respectively, and connected by an isolation circuit. The second power source derives all of its power from the telephone line to which the modem is connected. The portions of the isolation circuit which transfer data and control signals between the first and second modem circuits are constructed using coupling capacitors and latch circuits, and a similar capacitor is connected between the reference grounds of the first and second power sources. Each latch circuit uses a nand gate having two inputs, one of which is connected to momentarily receive a potential equivalent to logical zero, thereby providing a reset when the modem is first energized.


Central office filter system and method


Patent Number 6,757,377

A central office (CO) filter system connects between a CO telephone switch and a telephone connection (subscriber loop) that can communicate voice and digital data channels. The CO filter system suppresses transients and harmonics on the connection caused by a telephone ring signal (typically, 90 to 150 Vrms at 15 to 68 Hz) generated by the switch in order to minimize adverse effects on the digital data channel on the connection. Architecturally, the CO filter system includes a first filter designed to implement a first low pass filter function to attenuate frequencies higher than a ring signal so that transients and harmonics produced from the ring signal are suppressed, a second filter designed to implement a second low pass filter function to attenuate frequencies higher than a voice channel, and a current detector designed to detect when a telephone is off-hook. The current detector implements the first filter when the telephone is on-hook, particularly, when the ring signal occurs, and implements the second filter when the telephone is off-hook.


Line sharing multipoint pots splitter controllable line selector

Patent Number 6,771,740

The eavesdropping prevention system and method of the present invention provides a controllable line selection unit which couples a receiver and a transmitter to a selected one of a plurality of subscriber loops according to the current channel of a time-multiplexed communication signal. The controllable line selection unit prevents meaningful detection and amplification of the leakage signal by physically isolating communication connections from each other. In the preferred embodiment, the controllable line selection unit actuates a plurality of switches coupled to a plurality of communication connections. Alternative embodiments of a controllable line selection unit are described.


Line sharing multipoint POTS splitter masking noise

Patent Number 6,775,355

The eavesdropping prevention system and method of the present invention provides a mask signal generator which generates a mask signal superimposed over a leakage signal. The mask signal prevents meaningful detection and amplification of the leakage signal. The amplitude of the mask signal is low enough so as not to interfere with the transmission of analog POTS signals over the communication line on which the mask signal is superimposed. In the preferred embodiment, the amplitude of the mask signal exceeds the amplitude of any anticipated leakage signals which may be manifested on the communication line. Alternative embodiments of a mask signal are described.


DSL-ready pots device and method

Patent Number 6,826,265

A plain old telephone system (POTS) device, for example but not limited to, a telephone, facsimile machine, analog modem, caller identification (ID) system, speaker phone, cordless phone, etc., employs an on-board POTS filter to enable reliable and efficient decoupling of a POTS channel from one or more xDSL channels on a telephone connection, while permitting and not interfering with the xDSL channels. The POTS device, which connects to a subscriber loop associated with the public service telephone system, includes a subscriber loop connection switch (for example, a hook switch), a POTS transmitter, receiver, or transceiver, and a low pass filter interconnecting the subscriber loop connection switch with the transmitter, receiver, or transceiver. The switch effectively isolates the POTS filter from the telephone line when the POTS device is disconnected, or is on hook, and interfaces the telephone line through the POTS filter to the POTS transceiver when the POTS device is connected, or is off hook. The arrangement enhances DSL device performance, network stability, sidetone, ringer load, and termination impedance and allows greater flexibility in the choice of filter elements, in that passive and active elements can be utilized and in that filters of higher order can be employed.


Linear polarity guard and method for DSL-ready pots devices

Patent Number 6,845,157

A plain old telephone system (POTS) device, for example but not limited to, a telephone, facsimile machine, analog modem, caller identification (ID) system, speaker phone, cordless phone, etc., employs an on-board transistor-based linear polarity guard to enable decoupling of a POTS channel from one or more xDSL channels on a telephone connection (subscriber loop associated with a public service telephone network), while reducing undesirable interference, such as intermodulation distortion imposed upon the POTS and xDSL channels. Transistors associated with the polarity guard are operated in the ohmic region, or in a nonsaturated linear mode, to achieve a substantially linear transfer function through the transistors and through the overall linear polarity guard. Current that is input to the polarity guard and the voltage drop across the transistors that conduct the current in the polarity guard exhibit a substantially linear relationship, or linear VI transfer function. Hence, the VI relationship between the overall output voltage and overall input current of the polarity guard is substantially linear in the operating region of the polarity guard.


Local loop interceder

Patent Number 6,658,096

Disclosed is a local loop interceder which interfaces between the local loop and the central office and which provides access to the public switched telephone network (PSTN). The local loop interceder establishes a first signal pathway from the local loop to the PSTN and a second signal pathway from the local loop to a high speed data modem. The local loop interceder alternates between the first and second pathways depending upon whether the end user desires voice or data communication on the local loop. In a second embodiment, the high speed data modem is a simultaneous voice and data (SVD) modem. In such case, the local loop interceder provides a third signal pathway from the SVD modem to the PSTN for voice communication which is demodulated from a simultaneous voice and data signal received by the SVD modem through the second signal pathway.


Method and apparatus for controlling the input impedance of an analog front end circuit of a data communications equipment (DCE) device

Patent Number 6,198,818

The present invention provides a method and apparatus for use with an analog front end circuit of a DCE of a multipoint system for preventing an impedance null from being generated in the frequency bands being used by the DCE. A feedback circuit is employed with the analog front end circuit to force the input current of the analog front end circuit to zero, thus providing the analog front end circuit with a high input impedance, which prevents an impedance null from forming in the frequency bands being used by the DCE. In accordance with the preferred embodiment of the present invention, a sensing resistor is incorporated into the analog front end circuit of the DCE for sensing the input current of the analog front end circuit. A feedback circuit coupled to the sensing resistor detects the input current sensed by the sensing resistor and causes a power driver of the analog front end circuit to force the input current to zero, thus providing the analog front end circuit with a high input impedance that prevents an impedance null from being created in the frequency bands being used by the DCE.


System and method for providing a frequency dependent synthetic termination

Patent Number 6,314,180

A frequency dependent synthetic termination system varies a simulated impedance of a communications device as a function of signals received by the communications device. A feedback mechanism receives signals from a transmission line and attenuates the signals when the signals have a frequency within a predefined frequency range. The feedback mechanism then transmits the signals to a current source which drives the transmission line, thus simulating a termination impedance of the communications device based on the signals transmitted from the feedback mechanism. By varying the impedance of the communications device, the communications device can be designed to support communications of various frequencies over the transmission line.


Passive distributed filter system and method

Patent Number 5,848,150

A plurality of passive distributed POTS filters (DPF) are associated with a respective plurality of POTS communications devices and decouple a POTS channel from a telephone connection, while permitting and not interfering with a second communications channel (e.g., DSL, ADSL, SDSL, RADSL, VADSL, etc.) on the telephone connection that is utilized by a modem. In architecture, the DPF system includes a plurality of POTS communications devices, such as telephones, and a plurality of the DPFs corresponding respectively with and connecting each of the POTS communications devices to the telephone connection. Each of the DPFs comprise an automatic control mechanism and a POTS filter. The automatic control mechanism is configured to isolate the POTS filter when a respective POTS communications device is on-hook. Each DPF is configured to permit POTS communications over a POTS channel on the telephone connection with the respective POTS communications device when the POTS communications device is off-hook. Furthermore, a second communications device, such as a DSL (e.g., ADSL, SDSL, RADSL, VADSL, etc.) communications device, is connected to the telephone connection and communicates signals over a second channel. The POTS and second channel are communicated over the telephone connection concurrently without appreciable interference.


Subscriber line driver and termination

Patent Number 6,782,096

A subscriber line driver (SLD) is provided for the continuous and automatic transformation of the characteristics of a communication system signal so that the signal conforms to a power spectral distribution (PSD) standard. The signal is transformed by the SLD which may increase (amplify) portions of the signal to a predefined specification, decrease (attenuate) portions of the signal to a predefined specification, and/or frequency modulate or filter the transmit signal frequencies to fit within the communication channel frequency bandwidth as defined by a predefined frequency band. After modification by the SLD, the transformed communication signal is injected (transmitted) into a communication transmission line. An SLD device can be employed in a variety of communication systems such as a public telephony system, a private branch exchange (PBX), a coaxial cable system, a fiber optic system, a microwave system, a radio communication system or the like. In the preferred embodiment, the SLD device operates in connection with a telephony system local loop which is operated as a digital subscriber loop (DSL). The SLD has an infinite input impedance at all frequencies. Addition of a parallel resister can enable the design engineer to set the transmission system terminating impedance to any desired value. This SLD can also be implemented in connection with a telephony system central office (CO) or a PBX.