Abstract: A method for enhancing the stability associated with an individual telecommunications line interface circuit comprises measuring a phase angle between a battery voltage and an output voltage. The phase angle measurement is processed by a digital signal processor for synthesizing a comparator circuit to generate an output voltage if the phase angle is a value other than forty-five degrees (45°). The new output voltage is then applied to the line interface circuit and the phase angle is recalculated to determine if it is a closer approximation of 45°. In an alternative embodiment, a database including a plurality of output voltage and electrical parameter values is stored in the digital signal processor and indexed by measured phase angles between the battery voltage and the output voltage. If a phase angle other than 45° is measured, the measured phase angle is used to obtain a new output voltage and electrical parameters from the database.

Abstract: A monitor access is gradually applied an removed from a communications circuit, including a digital subscriber line (DSL), by a gradual monitor access (GMA) technique, in which a variable impedance element is gradually applied to the communications circuit until the monitor can be introduced to the communications circuit without data disruption.

Abstract: The invention provides an apparatus for use with a subscriber line interface circuit in a telephone system, the subscriber line interface circuit being interposed between a telephone central office and a subscriber line, the subscriber line being coupled with a subscriber telephone device.

Abstract: Corruption of digital data on a telephone line to which a telephone test set is to be coupled is obviated by inserting a low pass filter circuit in the tip-ring connection path to the test set. The low pass filter provides a low impedance path for only voice band signals, while blocking signals that fall within the high frequency range of digital data that may be present on the telephone line. The low pass filter circuit includes inductors coupled with respective tip and ring leads and a controllably switched, shunt-capacitor circuit coupled across the tip and ring leads. Also, resistors that compensate for impedance variations are coupled in series with the leads and are controllably by-passed, when said telephone test set is to go off-hook.

Abstract: A codec which normally provides impedance synthesis, filtering, suppression of receive signal echoes, and gain equalization for a plurality of line circuits under the control of a microprocessor includes an arrangement for ascertaining the actual impedance of each line that it serves and making a corresponding adjustment of the receive and transmit equalizers and other codec parameters. A series of short tones having precisely known amplitude frequencies throughout the voice band are applied to the line when the line is on-hook and during the off-hook interval before tone is returned to the subscriber. Impedance is measured by observing the echo and obtaining an estimate of the phase by performing a least squares fit during a time interval not exceeding the usual interdigital call signaling interval.

Abstract: Subscriber loop systems often contain bridged taps which may interfere with the transmission of DSL signals. The bridged tap creates at least one local minimum at a notch frequency in the frequency response of the subscriber loop within the frequency range of the DSL signals. Effects of the bridged tap on a subscriber loop are reduced by terminating the bridged tap with a bridged tap canceller. The bridged tap canceller has at least one filter element for each local minimum created by the bridged tap. Each filter element provides substantially complete reflection of DSL signals at the corresponding notch frequency.

Abstract: 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.

Abstract: A device comprises a termination impedance circuit, coupled to a communication link. The termination impedance circuit provides a termination impedance of the device, wherein the impedance is selectable. A second device comprises an echo-cancel hybrid circuit, coupled to a communication link, that provides an echo cancel characteristic, wherein the characteristic is selectable.

Abstract: A first device receives and processes signals from a communication link that supports a plurality of signal protocols. The device comprises a converter, coupled to the communication link, that outputs a sampled data stream, and a digital filter that filters the sampled data stream to separate signals associated with different signal protocols. A second device receives a first input sampled data stream representative of a first signal to be transmitted and associated with a first signal protocol and a second input sampled data stream representative of a second signal to be transmitted and associated with a second signal protocol, and combines the data streams into an output data stream which may be coupled to the communication link.

Abstract: The invention relates to a line circuit and a method for matching impedance in order to have a certain impedance to a signal path. According to an embodiment said circuit comprises a first line, a second line and a terminating point in said first line. At least one impedance determining circuit is connected between said lines, said at least one impedance circuit further including at least one operational amplifier, at least one multiplexer controllable by a control unit and at least one impedance net. The connection of said at least one impedance circuit is arranged such that an output of the operational amplifier is connected to an inverting input thereof, said impedance net being connected between the output of said amplifier and said terminating point of the line circuit. The arrangement is such that a non-inverting input of the operational amplifier is connectable by at least one respective multiplexer either to the terminating point or to said second line.

Abstract: The present invention relates to a filter (45) for filtering signals in a telecommunications system, a method of designing said filter, and a corresponding splitter filter. The inventive filter (45) is characterised in that it is passive and has a complex impedance which gives good impedance matching to the complex impedance of a transmission line. Because the filter is passive, it does not need to be powered and can thus be placed in locations that lack a power supply. The filter will also function in the event of a power failure. Because the filter has an impedance which can be well matched to the complex impedance of a transmission line, problems relating to echo and side tones can be minimised.

Abstract: Methods and apparatus for providing temperature compensation for a communications card, such as a modem or network card, to minimize retrain sequences between the communications card and another communications card during periods of temperature build-up within the communications card are disclosed. It is a feature of the invention to provide this temperature compensation regardless of the speed or temperature of arriving at a steady state temperature and regardless of the make of the communications card, host computer or computing temperature environment under examination. In a preferred embodiment, a keyword between the communications card and a host computer is compared to provide unique heat compensation for these two devices that have generally different, but consistent, heating characteristics.

Abstract: A data access arrangement (DAA) having a transhybrid circuit for separating a transmit signal from a received signal by providing a transmit cancellation signal to the inverting input of a servo-feedback differential amplifier on the receive channel of the DAA. The cancellation signal is provided by a photodiode optically coupleable with a light emitting diode within a optical isolator on the transmission channel of the DAA. The gain of the cancellation signal can be independently controlled.

Abstract: A network interface circuit employing differentially driven capacitive couplings across a high voltage isolation boundary and in which a &Sgr;/&Dgr; CODEC is positioned on the line side of the high voltage interface. In this manner, only four wires cross the high voltage boundary, namely differential pairs for transmit data and receive data. The transfer functions for setting AC and DC parameters, such as impedance matching, are provided by digital filters. Further, with the CODEC on the line side of the high voltage isolation interface, the data which crosses the interface is modulated at the &Sgr;/&Dgr; data rate and, thus, capacitive coupling can be used across the high voltage isolation boundary without the loss of DC data.

Abstract: Apparatus for interconnecting the Tip and Ring telephone line interface to subsequent communications equipment or circuits through a differential line bridge circuit that extracts one or more unidirectional paths containing predominantly far-end energy, wherein, near-end speech signals have been canceled. The differential line bridge circuit maintains the longitudinal balance of the telephone line and exhibits improved noise immunity in the recovered far-end signal. It permits all telephone supervisory, alerting and bidirectional communication signals to pass transparently between the telephone line interface and the subsequent communications equipment or circuits. Access to on-hook service signals, such as calling party identification and short text messaging data transmissions, is inherently provided by the line bridge.

Abstract: Subscriber loops often contain bridged taps which may interfere with the transmission of DSL signals. A bridged tap terminator provides high tap impedance for POTS signals, low insertion loss for DSL signals, and impedance matching for DSL signals when connected to the bridged tap.

Abstract: An interface circuit has a circuit input. The circuit has a first controlled amplifier combined with an at least resistive element. The first amplifier provides at a first output a first output current dependent on a voltage of the circuit input. The circuit also has a second controlled current amplifier. The second amplifier provides at a second output a second output current dependent on a current of the circuit input. The second output is coupled to the first output. The circuit further comprises a third controlled current with a third input. The third input is coupled to the first and second outputs.

Abstract: The present invention provides a switched impedance matching network which may be implemented in a hybrid circuit of a digital subscriber line (DSL) system, or in any other wire-bound communications system for which two-wire-to-four-wire conversion, and vice versa, must be accomplished. In accordance with the preferred embodiment of the present invention, the matching network comprises switchable circuit modules of discrete-valued resistor and capacitor components. Preferably, the circuit modules are assembled into an array of buffered first-order RC circuits. The buffers comprise amplifiers that are switched on or off to control the switching of the circuit modules. The buffer amplifiers also isolate the individual circuit modules from each other and eliminate the need to implement transmission switches between the modules. The switching of the buffer amplifiers clears or blocks the transmission paths between the individual modules, thereby providing the optimum path through the module array.

Abstract: A network interface circuit employs an extended feedback circuit topology for impedance matching across a high voltage boundary between a line side portion and low voltage portion of a network. The network interface circuit includes an operational amplifier-based circuit which is responsive to a signal applied from user equipment on the low voltage portion. Specifically, the present invention includes a transmit path having a first, second, and third amplifier circuit and an impedance element, and a receive path that includes a transfer function implemented as a second order low pass filter for correcting amplifier gain and phase effects in the complex feedback loop of the circuit. The output impedance is remotely set by multiplying the impedance element by a scale factor to match the network impedance. The feedback loop is extended across the high voltage boundary using high voltage interfaces such as linear optical coupling devices (LOCs).

Abstract: A communication interface and a design method therefor simultaneously shape a synthesized terminating impedance matching different frequency bands on different connecting communication circuits and a receive path response to prevent frequency roll-off. In some cases, for example based on specified network requirements in a particular country, the terminating impedance presented by the interface must have different frequency characteristics for received signals in different bands of frequencies. A transconductance amplifier and feedback loop provide the terminating impedance for signals received from the communication circuit and serve as a source impedance for signals transmitted by the interface to the telephone line. Signals with different frequencies will generally be received from the telephone line. These different characteristics are realized using different filter networks in the feedback loop.

Abstract: A communication interface and a design method therefor provide a synthesized terminating impedance matching different frequency bands on a communication circuit. In some cases, for example based on specified network requirements in a particular country, the terminating impedance presented by the interface must have different frequency characteristics for received signals in different bands of frequencies. A transconductance amplifier and feedback loop provide the terminating impedance for signals received from the communication circuit and serves as a source impedance for signals transmitted by the interface to the telephone line. Signals with different frequencies will generally be received from the telephone line. These different characteristics are realized using different filter networks in the feedback loop. Each network provides a matching terminating impedance to the communication circuit according to the frequency band applied to the circuit.

Abstract: A transmission system includes a transmission path from a transmitting station to a receiving station for both voice telephone service occupying the frequency spectrum below a predetermined frequency f.sub.1 and for data service occupying the frequency spectrum above another predetermined frequency f.sub.3, where f.sub.3 is substantially higher than f.sub.1, a plurality of telephone sets at said receiving station connected in parallel with one another to the transmission path, and where each of the telephone sets has an on-hook state which presents a substantially infinite resistance to the transmission path and an off-hook state which presents a predetermined resistance R to the transmission path. A plurality of separate and substantially identical multi-pole low-pass filters are provided for connection between the transmission path and respective ones of the telephone sets, where each of the low-pass filters has a -3 dB frequency f.sub.2 which lies between f.sub.1 and f.sub.

Abstract: The present invention customizes a network connection to customer premises equipment using a calibration signal. A network signal processor emits a tag signal indicating that a signal processing platform is in use. Customer premises equipment (CPE) issues a calibration signal to the network signal processor based on detection of the tag signal. The customer premises equipment outputs the calibration signal to the network signal processor which measures the signal loss, adjusts the gain mapping and issues a calibration signal to the customer premises equipment. The customer premises equipment then estimates spectral shaping based on the calibration signal from the network signal processor and equalizes the receive path so that the signal processing platform is detected and implemented. Embodiments of the present invention are illustrative of a more general concept of the use of CPE as an agent in telephone network maintenance.

Abstract: A transmission line impedance matching apparatus is disclosed that limits longitudinal signals and matches the longitudinal characteristic impedance between two conductors and comprises a common mode choke and an impedance matching device. The common mode choke, comprising two windings wound in the same direction, acts as a high impedance to longitudinal high frequency signals. As a result of this, standing waves are caused by the metallic signals reflecting off the choke. The impedance matching device, comprising two windings wound in the same direction, provides a good match to the longitudinal characteristic impedance and thus reduces standing longitudinal waves and reflections. The apparatus may include a terminal corrector or a mid-line corrector, or a combination thereof. This invention may allow greater bandwidth to be dedicated to services and allow transmission over longer subscriber loops before the minimum S/N ratio is achieved.

Abstract: A subscriber circuit has several SLIC circuits (2, 3, 4, 5) combined in one multiple SLIC. The high-energy components of each SLIC circuit (2, 3, 4, 5) are realized as individual components (30, 31, 36, 37) in standard form. In order to remove non-linearities, the individual components (30, 31, 36, 37) are fed back via the respectively allocated SLIC circuit.

Abstract: The invention provides an apparatus for use with a subscriber line interface circuit in a telephone system, the subscriber line interface circuit being interposed between a telephone central office and a subscriber line, the subscriber line being coupled with a subscriber telephone device.

Abstract: A fixed wireless access subscriber unit containing a wireless transceiver and a telephone subscriber line interface circuit which supports privacy and remote release of hold between the subscriber unit and extension telephones are disclosed. The subscriber unit detects when the primary handset, or an extension telephone set goes off-hook. In response the subscriber unit modifies the voltage and/or current characteristics on the telephone subscriber line which connects the extension sets to the subscriber unit in such a manner that extension sets connected to the telephone subscriber line will sense when the primary handset goes off-hook.

Abstract: A method and apparatus for actively simulating an apparent termination input impedance to a current driven data communication equipment (DCE) device is disclosed. The DCE device utilizes several components to implement the apparent termination impedance. A first component is a current driver for providing a source of current within the DCE device. The current source is configured to actively drive an input-output signal line within a communication link. The current driven DCE also includes a mechanism for sensing an input-output signal line voltage, a mechanism for converting the sensed voltage to a feed back current and an active termination for simulating an apparent termination impedance. The converting mechanism is coupled to a summation node which sums current provided from the current driver and current from the converting mechanism to force the desired termination impedance in the DCE device, whilst performing DCE current drive function.

Abstract: Terminal equipment for telecommunications and information processing with improved electromagnetic compatibility (EMC). The equipment has a human-machine interface (HMI), a metallic telecommunications interface (TCI), and optionally a power line interface (PLI). First common-mode rejection filters consisting of common-mode choke coils and shunt capacitors are placed at the HMI interface of the equipment, while second common-mode rejection filters consisting of the same components are placed at the TCI and PLI interfaces. High-frequency junction points of the first and second common-mode rejection filters are interconnected with a bypass circuit. Being isolated from the signal ground and frame ground of the equipment, the bypass circuit is an independent non-grounded circuit. Such internal structure makes it possible to reject noise signals induced by an external noise source and also to suppress spurious radiation from an internal noise source.

Abstract: A technique for powering telephone lines using an unbalance current source and current sink; and a technique for improving attenuation/frequency distribution and return loss (impedance matching) of transformer-coupled wire-line communications circuits by using secondary series capacitance and an AC current pump signal source; and a generation of ringing voltage as positive voltage pulses with respect to a negative power supply voltage; and a technique for removal of AC power ripple by using an active linear floating filter for the purpose of powering telephone line circuits, and a technique for injection of real time tone samples into T1 transmissions circuits by use of a T1 framer idle code register.

Abstract: To determine the deviation of longitudinal signal components from a predetermined value on a balanced two-wire circuit (A,B), a first voltage is measured between one of the wires (A) and a first reference potential by means of a first voltage measuring means (3), a second voltage is measured between the second wire (B) and a second reference potential by means of a second voltage measuring means (4), and the difference between the first and the second voltage is formed by means of a difference forming means (5), said difference being proportional to the deviation of the longitudinal signal components from the mean value of the first and the second reference potential.

Abstract: A telephone series equipment line circuit for connection between a central office (CO) line and a terminal equipment (TE) line comprising a filter connected between the lines for blocking message signals from passing therebetween and for passing direct current (DC), a DC bypass circuit including a first series switch apparatus connected between the lines around the filter, series equipment connected via a DC blocking circuit and second series switching apparatus to the lines, the first switch apparatus being open and closed reciprocally to the second switch apparatus.

Abstract: A bus system providing increased connection flexibility and hot pluggable connections includes an open collector bus, a receiver connected to the open collector bus via a current sensor, a driver connected to the open collector bus, a peripheral card and a flexible cable operatively coupling the peripheral card, the receiver and the driver so as to provide point-to-point connection between the peripheral card and the open collector bus. The current sensor provides a control signal to the driver to increase the impedance of the driver in the event that a current is produced by the peripheral card.

Abstract: A DC termination device particularly adapted for use in a device coupled to a two wire telecommunications system. The termination device controls the tip-to-ring current through the telecommunications device by means of a voltage controlled current source. The control voltage for the voltage controlled current source is provided by digital signal processing of the tip-to-ring voltage such that the tip-to-ring current is linearly proportional to the tip-to-ring voltage when the voltage is below a specified threshold level, but is maintained constant when the tip-to-ring voltage is over the threshold voltage. Preferably, the constant current is the minimum adequate current needed for operation.

Abstract: A two-wire line and a four-wire line telephone system interface with each other through a hybrid (12). After a connection between the two and four-wire line systems is made, an echo canceler (10) provides training signals to the hybrid on the transmit path an generates echo cancellation signals on the receive path. An adaptive filter (16) is employed to provide the proper echo cancellation signals, while a controller (22) provides filter coefficients based on an error signal. The training signals include the convolution of an impulse function with a sin(x)/x function. Once the filter coefficients are determined for the particular call, the transmit path of the four-wire line system is switched in and voice data between the two systems my commence.

Abstract: A technique for powering telephone lines using an unbalanced current source and current sink; and a technique for improving attenuation/frequency distribution and return loss (impedance matching) of transformer-coupled wire-line communications circuits by using secondary series capacitance and an AC current pump signal source; and a generation of ringing voltage as positive voltage pulses with respect to a negative power supply voltage; and a technique for removal of AC power ripple by using an active linear floating filter for the purpose of powering telephone line circuits, and a technique for injection of real time tone samples into T1 transmissions circuits by use of a T1 framer idle code register.

Abstract: A communication system includes a SLIC device and a SLAC device. The SLIC device and the SLAC device cooperate to control the power level provided to a subscriber line. The SLAC device includes a digital control circuit which receives a parameter signal indicative of a first parameter of the electrical power. The digital control circuit provides a digital control signal to the SLIC device in response to a sample digital control signal and the digital parameter signal. Preferably, the digital parameter signal relates to a sensed current signal and the sample digital control signal relates to a desired voltage signal. The digital control circuit can be implemented hardware or software.

Abstract: A communication loop using a subscriber line interface circuit (SLIC) is modified such that it can operate in unbalanced ringing environments as well as balanced ringing environments. This is accomplished by grounding the tip lead of a telephone instrument and creating an open circuit at the tip lead of the SLIC. The ring lead of the telephone instrument and the ring lead of the SLIC are electrically connected, and an AC voltage applied to the ring lead by the SLIC is increased. A power supply is connected to the SLIC and biased to provide the increased AC voltage on the SLIC ring lead while the average voltage on the SLIC tip lead is maintained substantially at ground. The result of this circuitry is a trapezoidal signal meeting the amplitude, loading and crest factor requirements of Bellcore Technical Requirement Publications TA-NWT-000909 and TR-NWT-000057.

Abstract: A method for reducing frequency-related power losses in a telecommunication line interface circuit comprises operating a switching converter circuit at an optimum frequency. Determination of the optimum frequency is based upon a subscriber loop length. Particularly, the subscriber loop voltage is detected at a battery feed circuit of the line interface circuit, and used to access an optimum frequency stored in an initialized database. The optimum frequency information is received in the switching converter circuit, and determines its operating frequency.

Abstract: A termination is provided for a differential transmission line such as unshielded twisted pair (UTP) to isolate a connected device from electromagnetic interference present on the UTP in the form of differential mode and common mode noise. An example of an electromagnetic interference isolator comprises a common mode and a differential mode termination, a common mode choke which exhibits substantially constant impedance over a wide bandwidth and a centre tapped isolation transformer.

Abstract: A telephone interface circuit with impedance termination during call pauses, comprising first and second terminals to connect to a telephone line and a line termination branch connected to the first terminal across a decoupling capacitor, and to the second terminal. The line termination branch includes an intersection node, a first switch and a first impedance resistor between the first terminal and the intersection node, and a second switch and a second impedance resistor between the second terminal and the intersection node. The intersection node is connected to ground across a third switch. The first switch, the second switch, and the third switch are controlled by a control unit by first, second and third control lines, respectively. The telephone interface circuit further comprises a ring signal detector that is connected to a microprocessor unit capable of activating the control unit in an interval in which the circuit must be terminated for CLID (Calling Line IDentification) transmission.

Abstract: A system and method having automatic selection of impedance values for matching against unknown line impedances. The method stores an expected set of desired return loss measurements at given frequencies and matches the calculated set against the actual measured return losses to arrive at a close approximation of the line impedance. The system is then adjusted based upon this determined close approximation. The starting point for the stored set are standard models established for each network. In situations where the actual varies greatly from the predicted, a different model is selected and the expected scores for that model are used.

Abstract: A device for automatically adapting to the impedance of a supply line to optimally supply a load. The device includes a switched mode voltage regulator from which is drawn a signal to be provided to the load, a regulation loop to adjust the amplitude of the signal to be provided to the load as a function of the line voltage, and means for aligning the output voltage of the voltage regulator with the amplitude of the signal provided to the load.

Abstract: A data access arrangement (DAA) having a transhybrid circuit for separating a transmit signal from a received signal by providing a transmit cancellation signal to the inverting input of a servo-feedback differential amplifier on the receive channel of the DAA. The cancellation signal is provided by a photodiode optically coupleable with a light emitting diode within a optical isolator on the transmission channel of the DAA. The gain of the cancellation signal can be independently controlled.

Abstract: A technique for powering telephone lines using an unbalance current source and current sink; and a technique for improving attenuation/frequency distribution and return loss (impedance matching) of transformer-coupled wire-line communications circuits by using secondary series capacitance and an AC current pump signal source; and a generation of ringing voltage as positive voltage pulses with respect to a negative power supply voltage; and a technique for removal of AC power ripple by using an active linear floating filter for the purpose of powering telephone line circuits, and a technique for injection of real time tone samples into T1 transmissions circuits by use of a T1 framer idle code register.

Abstract: A telephone subscriber line interface circuit includes a first circuit portion and a second circuit portion, a first battery voltage and a second battery input for receiving a second battery voltage. The second circuit portion is coupled to the second battery input. The telephone subscriber line interface circuit further includes a switch for coupling the first circuit portion to one of the first battery input and the second battery input.

Abstract: A balanced amplifier delivers a detection voltage in order to carry out power supply control. A level shift circuit shifts the level of the detection voltage to a level shift voltage for a +5 Volts system, namely, a low withstand voltage system. An adder adds a reference voltage V.sub.REF2 to the level shift voltage as a D.C bias voltage and produces an added voltage. A variable attenuator attenuates the added voltage and produces an attenuated voltage. A subtracter subtracts the reference voltage V.sub.REF2 from the attenuated voltage and produces a subtracted voltage. The subtracted voltage is converted into a current by a voltage-current converting circuit and turns back to the balanced amplifier as a signal for a high withstand voltage system. Thus, a signal process can be carried out by a circuit of a low withstand voltage.

Abstract: Methods and apparatus are provided for enabling an operator to provide pre-recorded information to a customer in an interactive manner. The methods and apparatus utilize an audio storage medium which contains one or more audio information segments that can be accessed and played by an audio device without playing any of the other audio information segments. The audio device is coupled directly to the telephone network via interface circuitry which, among other things, matches the impedance of the audio output of the device to the impedance of the telephone network. Once a telephone call has been established between the operator and the customer, if the customer desires more information, the operator utilizes the audio device to select the appropriate audio information segment from the audio storage medium. It is important to note that when the operator plays the selected segment, both the operator and the customer remain listening.

Abstract: A termination synthesis technique that automatically derives an optimum termination scheme for interconnects in electronic circuits. The termination synthesis technique uses an adaptive partitioning approach to divide a large circuit into separate clusters that can be independently terminated. The technique can thus automatically derive the optimum termination type and location for large and complex circuits.

Abstract: An integrated telephone interface circuit for driving a telephone line includes a line current sensor and a phase converter, both associated with an output stage connected to the telephone line. The circuit is equipped with a protection device against the generation of spurious signals including a comparator connected between the converter and the output stage, a control and monitoring circuit linked operatively to an output of the comparator, and a plurality of switches associated with the input side of the converter, as well as with the current sensor and the output stage. The switches are linked operatively to respective outputs of the control and monitoring circuit to reverse polarity of the line supply upon a predetermined threshold value for the comparator being exceeded.