Abstract: A method and apparatus is provided reducing false switch hook detection in a line card coupled to a subscriber loop. The method comprises operating in a first state of the line card, receiving a control signal, and disabling switch hook detection in the line card. The method further comprises determining an initial condition of a second state of the line card, operating in the second state of the line card in response to receiving the control signal, wherein the second state begins to operate from the determined initial condition. The switch hook detection in the line card is activated.

Abstract: A method and a system for providing configurable call progress tones in a telephony session by identifying a receiver of the telephony session, selecting a tone in accordance with the preferences of the receiver and providing a configurable call progress tone of the selected tone.

Abstract: A method and apparatus is provided for performing an active impedance differential current feedback. A signal is received. A current feedback of an output signal in an active feedback synthesis mode is performed based upon the signal. The active current feedback includes using an active feedback network for conditioning an output signal, converting the signal into a differential current signal, and summing at least two components of the differential current signal for performing a differential feedback.

Abstract: In a line driver an input current (IINN) feeds a node (K1) which is connected to an input on an amplifier (OTA1). A further input on the amplifier (OTA1) has a reference voltage (VSGND) applied to it. The amplifier (OTA1) controls a current source (MN1) which outputs an output current (IOUTN). A current/voltage converter (R1) is connected between the node (K1) and the current source (MN1). A voltage/current converter (R2) is connected between the current source (MN1) and a ground (VSS).

Abstract: A device and a method for detecting presence of service on a telephone line prior to and during activation of alternative service on the line. The method comprises performing a first voltage detection on a subscriber line (S20), activating a subscriber line interface circuit (SLIC) if no pre-existing service is detected (S30), the SLIC providing an interface between the subscriber line and a service provider, and performing a second voltage detection on the subscriber line after a usage-dependent time has elapsed (S60), the time being determined by heuristics which consider several factors, including usage history of the line and time of day.

Abstract: An adaptive unit that taps into an existing POTS line, DLC POTS line, DLC channel unit designed for sealing current outputs, or AC-DC transformer designed for sealing current output, to provide sealing current to a DSL circuit thereby avoiding having to deploy a separate sealing current unit to supply the desired sealing current to the DSL circuit. The adaptive unit, or sealing current derivation device, is preferably deployed at remote terminals thereby facilitating the offering of new DSL service, but may also be utilized in a central office.

Abstract: A novel line-current protection circuit for detecting excessive line current from a telephone line and protecting line interface circuitry from the excessive line current is presented. The protection circuit is adapted to detect when an excessive current is present on the tip and ring lines indicative of the misconnection of the modem or other line interface device with a telephone network that presents an incompatible interface standard. The preferred embodiment appreciates the multimode hold current specifications throughout the world and evaluates the connection of the line interface circuit with a telephone line to determine the compatibility therewith. When excessive line current is detected, the line-protection circuit switches the vulnerable line interface out of the circuit. When compatible line current levels are detected, the present invention reconfigures the configurable hold circuit into its original operating (e.g., non-testing) state for call processing.

Abstract: A method and apparatus are provided for sensing current in a subscriber line. The method includes receiving a current signal from a driver capable of driving the current signal on the subscriber line, and generating a second signal in response to receiving the current signal, wherein the second signal is proportional to the current signal. The method includes receiving at least a portion of the current signal from a driver capable of sinking the portion of the current signal from the subscriber line, and generating a third signal in response to receiving at least the portion of the current signal, wherein the third signal is proportional to the portion of the current signal. The method further includes adding the second signal and the third signal to generate an output signal.

Abstract: The device for detecting telephone line seizure performs a measurement of voltage (UL) of the telephone line across a first and a second optocoupler (OC1, OC2) connected in series to the telephone line and arranged head-to-tail. The first optocoupler (OC1) makes it possible to discharge a capacitor (C) connected to the telephone line, the second optocoupler (OC2) converts the discharge current (ID) into an image current (ID′) in a measurement circuit (S). This device comprises means ensuring negative feedback of the second optocoupler (OC2) to the first optocoupler (OC1). With this layout, the influence of the transfer coefficients of the optocouplers on the voltage measurement is decreased, so as to increase the accuracy of measurement.

Abstract: In a circuit arrangement for recognizing connection requests at an analog subscriber line in which a number of subscriber terminal devices such as an analog telephone and an MSFM modem, are connected in parallel, set up and clear down connections are enabled independently of one another. For this purpose, a first threshold valve and a second threshold value are defined for the loop current in the subscriber line. A connection request can be respectively initiated by one of the subscriber terminal devices by means of closing its cradle switch. When the cradle switch of this first device is thus closed, the loop current exceeds the first threshold value, and when the cradle switch of a further device for initiating a connection request is also closed, the loop current exceeds the correspondingly defined second (higher) threshold value. As a result of these threshold value transgressions, the connection requests can be recognized and processed independently of one another.

Abstract: A telephone accessory device includes a first circuit that detects an off-hook condition of a telephone and a second circuit responsive to the first circuit wherein the second circuit simulates an on-hook condition when the off-hook condition is detected.

Abstract: A method and apparatus for detecting the presence and the type of network devices connected to a management device via transmission lines. The apparatus may include a pull-up resistor, a pull-down resistor, a filter, and a presence detector, the resistors superimposing a DC or low-frequency voltage on the transmission line. The impact, if any, of the DC voltage one communications equipment and circuitry can be reduced by a coupling that isolates the DC voltage. Similarly, the filter prevents transmitted data signals from interfering with the DC voltage level. The method and apparatus function regardless of whether the network device is functional or powered on, and different values of pull-up or pull-down resistors can be used to indicate the type of device that terminates the transmission line.

Abstract: A current sense circuit for sensing a current in a subscriber loop comprising a transformer having a first and second winding coupled for sensing a differential current in a loop, a sense winding for producing a sense current in response to a magnetic flux induced in the transformer due to the differential current, an amplifier circuit for receiving the sense current and wherein the sense current is indicative of a signal on the loop, and the amplifier being configured such that a transformer introduces a low insertion loss at a frequency of operation of the loop.

Abstract: Multipoint interface devices (MPID) for digital subscriber line environments are provided. In one embodiment an MPID is provided for each item of customer premises equipment that is connected to the telephone line. An MPID may include a signal transform device having a particular signal transform function. For example, a low band MPID individually adapts each voice band device such as a telephone set, facsimile machine, PBX machine, or the like, to a standard telephone line. A high band MPID individually adapts high speed digital modem devices including ADSL, RADSL or HDSL to a customer's telephone line. Thus, each item of equipment is connected in parallel through an appropriate MPID to a common telephone line. In another embodiment an interface device includes selectable low-band and high-band MPIDs. In another embodiment, an MPID includes means for automatically engaging the MPID only when the affected line is in use.

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: An apparatus and method to implement a highly efficient low power line driver. In a first embodiment, the invention provides a method to increase the power efficiency of a line driver. The method includes supplying a digital signal processor output to a first subtractor; supplying the first subtractor output as an input to a modulator of a line driver; subtracting the line driver output from the digital signal processor output at the first subtractor; filtering the line driver output with a low pass filter; routing the line driver output to an impedance match filter; providing a first analog-to-digital converter and a second subtractor to subtract the line impedance match filter output from the low pass filter output; providing a digital filter and a second analog-to-digital converter; and subtracting the digital filter output from the first analog-to-digital converter output at a third subtractor to output a feedback signal to the digital signal processor.

Abstract: A power management circuit for use in a terminal interface device such as a modem which converts available line side power into usable power for use by the terminal interface device to activate a variety of line status indicators. These line status indicators signaling the off-hook status of the terminal interface device, low line side power, or the presence of excessive line current. The line status indicators draw power from the available line side power without placing a burden on the attached digital device or its power source. Certain line status indicators utilize flasher/oscillator circuits to increase the functionality of the line status indicators by providing a frequency based pulse to more accurately describe the operating environment of the circuit.

Abstract: Testing of analog-to-digital and digital-to-analog converters formed in integrated circuits. In one embodiment, a method of testing an analog-to-digital (A/D) converter comprises applying an analog test signal of a first frequency to an input of the A/D converter. Sampling digital byte samples from an output of the A/D converter at a second sampling frequency and comparing select digital byte samples with each other. When the select digital byte samples match, storing a verify bit in a memory to verify the A/D converter is working. In another embodiment, a method of testing a digital-to-analog (D/A) comprises creating repeating digital byte samples with a logic circuit formed in the integrated circuit. Converting the repeating digital byte samples into an analog test signal with the D/A converter. Comparing the frequency of the analog test signal with the frequency of an expected analog signal to determine if the D/A converter is working.

Abstract: In a subscriber line interface circuit, a device applies to a line, associated with the line interface circuit, a substantially constant line current of a first predetermined value for line voltages up to a first voltage having an absolute value which, by a predetermined amount, is lower than the supply voltage of the line interface circuit. For line voltages between the first voltage and a second voltage having an absolute value which, by a predetermined amount, is higher than the first voltage, a line current which is inversely proportional to the line voltage and of a value between said first predetermined value and a second predetermined, lower value is applied to the line. For line voltages between the second voltage and a third voltage having an absolute value which, by a predetermined amount, is higher than the second voltage, a substantially constant line current of the second predetermined value is applied to the line.

Abstract: A computer having a modem is programmed with software (also called a “on-hook/off-hook detector”) that detects a change in status (e.g., on-hook or off-hook) of a device (e.g., a telephone having a handset) by measuring a change in the signal power of a signal flowing through a telephone line connecting the modem and the device. In particular, the computer programmed with the on-hook/off-hook detector detects a status of a telephone handset by measuring power of a reference signal and measuring power of an instantaneous signal on the connection and comparing these two measurements. The reference signal is a constant signal whose power does not change. Then, the computer programmed with the on-hook/off-hook detector is able to detect whether there has been a change in status of the telephone handset by comparing the detected status with a previous status of the telephone handset.

Abstract: A circuit and method for determining connection status of a phone line shared by multiple telecommunications devices, such as modems and phones, are provided. The phone line includes respective tip and ring lines. The circuit comprises a first operational amplifier coupled to receive a signal indicative of a voltage difference between the respective tip and ring lines. The circuit further comprises a lag network coupled to impart a predetermined delay to the output signal from the first operational amplifier. A second operational amplifier is coupled to receive the voltage difference signal. The output signal from the second operational amplifier has a sufficiently fast time response relative to the output signal from the lag network.

Abstract: Activating a switch by a handset where the switch is manually activated when the user wishes to answer an incoming call. While the switch is in the deactivated state, the handset transmits to a sound card within a personal computer a multi-frequency tone which is detectable by the sound card. When the manual switch is activated, the handset ceases to transmit the multi-frequency tone to the sound card. The sound card detects the absence of the multi-frequency tone to determine if the handset is answering a call. In traditional telephony terms, when the manual switch is activated, this is the offhook condition. When the manual switch is deactivated, this is the onhook condition . When the user is done with the call and deactivates the manual switch, the handset again generates the multi-frequency tone that is subsequently detected by the software via the sound card. Then, the software knows to signal the other party on the call that the call has been terminated.

Abstract: A method and apparatus is provided for adjusting DC feed control of a connection. The method includes receiving a signal from the connection and determining if the change in the signal is greater than a first preselected value. The method further includes adjusting the DC feed in response to determining that the change in the signal is greater than the first preselected value.

Abstract: A subscriber loop interface circuit and method for externally programming the on-hook, off-hook, and transition states of the subscriber loop interface circuit. The circuit having an off-hook overhead sufficient for long loop applications and having a continuous loop current to loop voltage relationship. The circuit may have plural means for generating reference currents for comparison with loop currents.

Abstract: Provided is a circuit for terminating a ring signal of a telephone network. A physical impedance is combined with a synthesized impedance to produce an impedance having a magnitude substantially equal to the ring termination impedance of a telephone network. The synthesized impedance is created by generating a current from a voltage controlled current source. By controlling the magnitude of the generated current, the magnitude of the synthesized impedance is also controlled. Because the specified ring termination impedances are known, a satisfactory impedance can be synthesized which results in the ring signal being properly terminated.

Abstract: Deactivating a switch in a handset when a user wishes to answer an incoming call or terminate a call. A sound card within a personal computer transmits a hook tone that is above the human hearing range to a transmitter section of the handset. When the switch is in the activated state, the handset re-transmits the hook tone back to the sound card which converts the hook tone to digital information so that the hook tone can be detected by software running in the personal computer. When the manual switch is deactivated, the handset ceases to re-transmit the hook tone back to the sound card. The software detects the absence of the hook tone to determine if the handset is answering the incoming call. In traditional telephony terms, when the manual switch is deactivated, this is the offhook condition. When the manual switch is activated, this is the onhook condition.

Abstract: A telephone system capable of judging kinds of various signals (line input signals) obtained through a line is disclosed, that enables reduction of the number of parts, detection with high accuracy, reduction of a mounting area, and reduction in costs. The telephone system includes an A/D converter for making A/D conversion of the line input signal such as a CPC signal, a bell signal, and a usage state signal indicating a telephone line usage state to output a digital line input signal, and a frequency analyzing unit for making frequency analysis of the digital signal converted by the A/D converter, and the central processing unit judges the kind of the line input signal based on a result of the frequency analyzing unit.

Abstract: A method and circuit for distinguishing between a first voltage signal having a high amplitude and a second voltage signal having a low amplitude, the first and second voltage signals comprising respective AC components superimposed on a DC level. The DC level of the first and second voltage signals is blocked and the respective AC components of the first and second signals are attenuated by an attenuation factor which is voltage dependent and substantially frequency independent, so that the respective AC components of the first and second voltage signals after attenuation have similar amplitudes. The respective attenuated AC components of the first and second voltage signals are then processed so as to distinguish between the first and second voltage signals according to their respective frequencies.

Abstract: A telephone caller screening device is operable with a pre-existing telephone line with an existing installed telephone device. In one mode, the telephone caller screening device selects and stores caller ID information from incoming telephone calls for later use to compare with caller entered identification data to determine whether the premise telephone user should be alerted to the incoming telephone call. In a second mode the telephone caller screening device controls the telephone system by generating an off-hook condition on the pre-existing telephone line to suppress the ring signal from an incoming telephone call to prevent audible ringing of the telephone device. The telephone caller screening device generates an alerting signal in an alerting device when the caller entered identification data compares with a stored caller identification data.

Abstract: A PNPN structure thyristor and a third P-type impurity region are formed on a semiconductor substrate, and a fixed current circuit using an NPN transistor 20 and a resistor 30 is connected to a cathode terminal K and a gate terminal G of a composite element 10 that has a P-channel MOS transistor Q3 with the third P-type impurity region as a drain connected to a PNP transistor Q1 of the thyristor. If a voltage applied to the anode terminal A of the composite element 10 rises from 0V, initially the thyristor is on and current flows, but once the threshold voltage of transistor Q3 is reached transistor Q3 turns on. A short circuit then exists between the base and emitter of transistor Q3 of the thyristor and current of the composite element 10 itself is cut off. Because of the bipolar structure it is simple to configure a small integrated circuit with a high withstand voltage.

Abstract: An on-hook EOH indicating telephone includes a parallel set detector, an EOH signal detector, and an indication module to activate a configurable audible and/or visual alert indicating that another telephone is off-hook and should be hung up. The audible alert may be a unique ringing of the otherwise conventional ringer (e.g., every 5 minutes, at a unique cadence or frequency, etc.), or may be an audible tone output from the speaker of the on-hook EOH indicating telephone. The visible alert may be, e.g., a text message on a display of the on-hook EOH indicating telephone, a blinking, flashing, etc. of an LED, or other visible attention getting technique. When the central office presents the extended off-hook (EOH) notification signal to the desired telephone line, the invention-equipped telephone detects a parallel set in use, and then listens for the EOH signal.

Abstract: A line card for coupling to customer premises equipment at a termination for detecting hook condition in a telephone system, the line card comprising an interface for transmitting and receiving an analog signal with the telephone line, an AC ring signal generator for generating a ring signal at the customer equipment, a DC signal generator for generating a DC signal when said customer equipment is off hook, and a circuit for determining the duty cycle of a loop current in the customer equipment (telephone) for determining the hook status of the customer equipmen.

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 set, where the state of an own-telephone-set is on-hook, the off-hook state of a parallel-telephone-set is detected by comparing telephone-line voltage value with a first standard voltage value. In the state where the own-telephone-set is off-hook, the off-hook state of the parallel-telephone-set is detected by the following method, i.e., the telephone-line voltage value is measured in detail and a second standard voltage value for judging the off-hook state of the parallel-telephone-set is determined and the voltage value is stored in place of the first standard voltage value while the own-telephone-set is off-hooked, then if the line voltage value exceeds the second standard voltage value, the parallel-telephone-set is regarded as off-hook.

Abstract: The present invention synthesizes a prescribed impedance. The impedance is synthesized by generating a current having a value substantially equal to a voltage divided by a prescribed impedance. Sensing the line voltage and converting that sensed line voltage to its digital equivalent accomplish this first step. The digital line voltage is processed by a factor related to the prescribed impedance to produce an output voltage that has a value substantially equal to the sensed voltage divided by the prescribed impedance. The output voltage controls a voltage to current converter that generates the appropriate current across the points or terminals where the line voltage was measured. Thus, the prescribed impedance is generated across these points or terminals because the line voltage divided by the generated current is substantially equal to the prescribed impedance.

Abstract: A fiber to the curb communication system providing telephone service to subscribers using line cards which are pluggable into a broadband network unit. The line cards provide telephone service to up to six lines per card. The cards are programmable from a central location, and the system includes self-testing of the cards, ring generator testing and provides for testing of the telephone lines from the system to the subscriber's location.

Abstract: A subscriber loop interface circuit having bifurcated common mode control loops includes a DC common mode control for controlling tip and ring DC common mode characteristics, and an AC common mode control for controlling tip and ring AC common mode characteristics, wherein the AC and DC common mode controls are independent. In one embodiment, the DC common mode control includes a tip current source for generating a tip current, idt, and a ring current source for generating a ring current, idr, Each of idt and idr is proportional to a difference between a DC tip voltage (TIPDC) and a control voltage (Vcmcontrol). Thus, in one embodiment, idt=gdt(TIPDC−Vcmcontrol), and idr=gdr(TIPDC−Vcmcontrol). In one embodiment, the AC common mode control includes a tip current source for generating a tip current, iat, and a ring current source for generating a ring current, iar. Each of iat and iar is a function of an AC tip voltage (TIPAC) and an AC ring voltage (RINGAC).

Abstract: A method and apparatus for the detection of one or more telephone off-hook conditions using an analog-to-digital converter to detect voltage changes between tip and ring lines of a telephone network loop. An isolation network provides substantial electrical isolation for a detection device from voltage surges on the tip and ring lines of a “plain old telephone system” (POTS) network. The isolation network also provides a minimal load on the POTS wiring system, so as not to cause a false detection of an off-hook condition by central office equipment. A gain amplifier is used to scale the tip and ring voltage to a suitable range for an analog-to-digital converter (ADC). The ADC outputs a digital voltage value to a decision-making element, such as a microprocessor, a digital signal processor, or a state machine. The decision-making element can detect when multiple POTS devices coupled to the network wiring loop go into an off-hook state.

Abstract: A telephone ring signal detector is coupled to a telecommunication line for detecting a first telephone ring signal, and for discriminating the first telephone ring signal from other line signals on the line. This detector comprises an event generator, coupled to the line, for receiving an incoming signal and for generating an initial event signal and an ending event signal, and a signal characteristic generator, coupled to the line and to the event generator, for generating a signal characteristic of the incoming signal after the initial event signal. This detector further comprises a signal characteristic limit device, for generating a predetermined signal characteristic range limit of the first telephone ring signal, and a signal characteristic comparator coupled to the signal characteristic generator, to the signal characteristic limit device and to the event generator, for comparing the signal characteristic with the predetermined signal characteristic range limit.

Abstract: An apparatus and method for blocking or disrupting data being transmitted over an analog telephone line, the method including detecting single-frequency carrier tones and then opening the line for a predetermined time to disrupt modem synchronization and thereby blocking or disrupting data transmission, and the apparatus including a line-sensing circuit, an operational amplifier acting as input stages to the line sensing circuit, means for detecting a single-frequency carrier tone on the line, a relay for disconnecting the line when a single-frequency tone is detected, and a switch for selecting the disconnect time period.

Abstract: By comparing the measured data of a transmission line to a model of the transmission line comprising models of each individual portion of the line, an estimation of the loop can be determined. Specifically, the transmission line can be modeled by a model of the transmit filter, a model of the receive filter, a model of the analog hybrid circuitry and an ABCD matrix model of the loop.

Abstract: An off-hook management telecommunication system comprising a DTMF detector, an encoder and a microprocessor located within a channel unit. The system allows the user to depress a selected sequence of keys during a line connection which indicate to the microprocessor to hold the line off-hook, via signaling to a central office, despite the fact that the telephone is being returned to an on-hook position. The line is held off-hook for a predetermined amount of time to allow the user to switch telephones.

Abstract: An artificial neural network (ANN) based method and system for automatically optimizing the call progress detection system to a given telephone network environment. The artificial neural network learns or trains using real data to detect and recognize call progress tones or signals. The ANN system generally comprises a training component and a detection component. After the ANN is trained, the training component can be removed and only the detection component is installed on the telephone terminal device.

Abstract: A method and apparatus to detect off-hook and intrusion conditions on a telephone line. A voltage to frequency converter is used to convert the voltage measured between the TIP and RING terminals of a telephone line to a frequency. The voltage is continuously monitored, once during each sample period. The measured frequency is compared to predetermined threshold values to determine the state of the telephone line. The predetermined threshold values are updated in each sample period.

Abstract: A load coil is disposed along a local loop for conditioning POTS signals while permitting passage of higher frequency DSL signals with low attenuation. In one embodiment, the load coil includes a coupled inductor having multiple capacitive elements coupled thereto, the capacitive elements facilitating passage of the DSL signals across the load coil.

Abstract: A communication system of the present invention utilizes ring detection circuitry on both sides of an isolation barrier. More particularly, the ring detection circuitry may include ring burst circuitry on the phone line side of the isolation barrier and ringer timing circuits on the powered side of the isolation barrier. The digital burst peak signal may be transmitted through the isolation barrier to the ringer timing circuits. By splitting the ring detection circuitry so that the ringer timing circuits are placed on the powered side of the isolation barriers, a significant reduction in the power usage on the phone line side of the barrier related to the ring detection function may occur. The outputs of the ringing timing circuits may be provided to circuits on either side of the isolation barrier. Thus, the ring detection function may be accomplished in a system utilizing an efficient bidirectional capacitive barrier while still minimizing power usage on the line side of the barrier.

Abstract: A telephone line connection and disconnection circuit has a diode bridge coupled to the telephone line which converts different voltages of the telephone line into a voltage referenced to ground. A switching circuit is coupled to the diode bridge which opens and closes a conductive pathway for connecting and disconnecting a telephony product from the telephone line. A resistive element is coupled to the diode bridge and the switching circuit which allows for the conductive pathway to be normally closed. An optical isolator is coupled to the switching circuit and the resistive element for sending a control signal to the circuit when required.

Abstract: An apparatus for adding functionality to a private telephone system, comprising: a processing unit monitoring a telephone line and operable to perform said added functionality; a talk battery; and a switch having an input for a telephone, and an output selectable between an input of said private telephone system and said talk battery, said switch being controlled by said processing unit.

Abstract: In a subscriber loop interface circuit, a novel method and apparatus for measuring loop impedance. Measurement of loop impedance including charging and discharging a capacitor using current derived from loop current and loop voltage. The discharge time interval of the capacitor may provide information on loop impedance. A look-up table in a subscriber loop interface circuit may include previously calculated impedance values corresponding to discharge time.

Abstract: An isolation system is provided that is suitable for use in telephony, medical instrumentation, industrial process control and other applications. Preferred embodiments of the invention comprise a capacitive isolation barrier across which a digital signal is communicated. The system provides a means of communication across the isolation barrier that is highly immune to amplitude and phase noise interference. Clock recovery circuitry may be employed on one side of the isolation barrier to extract timing information from the digital signal communicated across the barrier, and to filter the effects of phase noise introduced at the barrier. Delta-sigma converters may be disposed on both sides of the isolation barrier to convert signals between analog and digital domains. An isolated power supply may also be provided on the isolated side of the barrier, whereby direct current is generated in response to the digital data received across the isolation barrier.