Abstract: A method and apparatus for monitoring and controlling exposure to noise related to a headset are described. The method includes sampling an input sound signal to produce samples of the input sound signal, calculating from these samples a headset sound level corresponding to the input sound signal, calculating cumulative exposure of a headset user to the headset sound level at a specific point in time, and calculating a gain adjustment for the input sound signal to ensure that the total sound to which the headset user will be exposed during a selected time period is within the regulatory maximum level. Advantageously, the method and apparatus of the present invention allow accurate real-time monitoring of cumulative exposure to headset noise and real-time adjustment of headset gain to ensure compliance with regulatory maximum sound exposure levels.

Abstract: 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.

Abstract: A telephone includes a transmit channel and a receive channel, each including a bank of sub-band filters having a VAD coupled one to each sub-band filter. Each VAD measures the spectral energy in a sub-band, compares the spectral energy to a first threshold, and produces an output signal representative of whether or not the first threshold is exceeded. The voice activity detector also includes a threshold circuit for calculating a dynamically adjustable noise threshold based upon averaged measured spectral energy. A wide band or system VAD monitors echo canceling circuitry to detect voice activity and double talk.

Abstract: A CMOS implementation for a DC holding circuit in direct access arrangement (DAA) circuitry is disclosed that provides desirable inductive behavior while minimizing power dissipation required by the CMOS integrated circuit, particularly at high loop currents. The DC holding circuitry disclosed may include MOS transistors located on a CMOS integrated circuit and an off-chip power dissipating resistor that acts to dissipate power external to the CMOS integrated circuit. The CMOS implementation disclosed also allows a path for drawing DC current to power other CMOS circuits (e.g., ADCs and DACs) in the CMOS integrated circuit.

Abstract: A method and apparatus for controlling the transmit level of transmitted signals from a telephone terminal device. A gain stage applies a gain or loss to the transmit signal to adjust its signal level. The gain or loss is determined by a transmit level control module. The transmit level control module measures the transmit signal during the course of a call to determine an average signal level during active speech and the average signal level during the call is used to build a historical estimate of average signal level for the device. Following each call, a gain factor is determined based upon the historical estimate and the gain factor is used by the gain stage in setting the gain or loss applied to the transmit signal of a subsequent call. The transmit signal control module provides for an adjustment to the signal level of the transmit signal that is customized to the historical speech characteristics of the user of the device.

Abstract: An apparatus and method for interfacing a communication device, such as a Customer Premise Equipment (CPE) to different telephone networks. The telephone networks typically provide a voltage of 48 volts to the CPE. However, this DC voltage tends to fluctuate. Furthermore,the impedances of the telephone network varies. The apparatus provides a constant current to the communication device while coupled to different telephone networks. Since most communication devices use amplitude modulations for transmitting data, a constant DC biasing current is desired. The apparatus can sense load impedances of the telephone networks, and dynamically adjust the current source so that DC biasing currents remain relatively constant. The apparatus is coupled to the telephone network so that communication between the communication device and the telephone network is optimized.

Abstract: A conference speakerphone comprises a conference telephone host and a plurality of separate microphones. A DSP, a control unit, a telephone interface and a microphone interface are disposed in the conference telephone host. The telephone interface is used to achieve signal connection with a telecommunications network. The control unit is responsible for control of interface and logic action. The DSP is used to cancel echo signals of communication and detect the loss of echo signals. The DSP will send an indication signal to the control unit once detecting abnormal echoes. The control unit will then send out a control command to the microphone via the microphone interface for adjusting the microphone according to the control command. Thereby, automatic detection of abnormal echoes and maintenance of communication quality can be accomplished, and the cost can also be lowered.

Abstract: A method and apparatus for selectively filtering signals on a digital subscriber line (DSL) so as to prevent interference resulting from a telephone instrument switching between its on-hook and off-hook states. One embodiment of the invention utilizes an off-hook detector controlling a variable attenuator element. Another embodiment of the invention uses a switch in parallel with a resistive element to implement the variable attenuator element. Yet another embodiment has an inductive element with a saturable core for providing attenuation to compensate for inconsistencies that result from the changing hookswitch status of a telephone instrument.

Abstract: A switch based feature that allows subscribers to adjust their incoming or outgoing audio signal strength. The value of the transmit or receive pad values on the subscriber line card are adjusted to control the strength of the audio signal transmitted to, or received from, the network. The subscriber controls the feature by sending a hook flash to the switch, entering the DTMF keypad feature code and transmit or receive volume parameters, and then returning to the call.

Abstract: A method and apparatus are provided for establishing a conference call connection among a plurality of conference call participants. The method includes the steps of providing a call pod for interconnecting a plurality of headsets of the plurality of participants, operably connecting a headset interface of a wireless telephone with a wireless telephone audio interface of the call pod and forming a two-way voice path among the plurality of headsets and the wireless telephone interface within the call pod.

Abstract: A telephone annunciator is disclosed which includes a voice ROM with a prerecorded message which is played back in response to a call received from an unwanted caller. A line current modulator is coupled with the voice ROM and the telephone line. A DTMF tone decoder circuit is coupled with the telephone line for decoding at least one DTMF code signal for producing a trigger signal. An on/off control circuit is responsive to the trigger signal for turning on the voice ROM whereby the telephone line current is modulated by the modulator in accordance with the audio signal from the voice ROM. A start-up power supply includes a storage capacitor and stores a charge in response to a ring signal on the telephone line. A main power supply is connected with the telephone line to receive power therefrom when an off-hook signal is detected.

Abstract: A speech communication apparatus comprises voice speed conversion means for changing the time scale of a voice signal of a called party which arrives through a telephone line, and sidetone erasure means for erasing a sidetone signal.

Abstract: This invention provides an attenuation arrangement for ADSL signals fed from a remote point wherein an attenuator is inserted between a remotely located ADSL LT unit and the line, the attenuation arrangement being for the purpose of reducing the mismatch of downstream power level of the ADSL LT unit and downstream power level of other ADSL signals sharing the same cable bundle but fed from a more distant point.

Abstract: A method and apparatus is provided for implementing an unbalanced subscriber line interface circuit with built-in ring circuit. A signal to be conditioned is received. An unbalanced output buffering function is performed upon the signal to be conditioned using an unbalanced buffering circuit. Performing the unbalanced output buffering function includes switching between a plurality of power supplies to maintain a predetermined maximum voltage across a plurality of devices relating to the unbalanced buffering circuit.

Abstract: A hook switch circuit is shown wherein two high-voltage bipolar transistors, a PNP transistor Q1 and a NPN transistor Q2. that are connected in a regenerative feedback manner to form a bi-stable latch. The regenerative structure permits the use of low beta transistors that may be turned on with a low control current, but still conduct a sufficient off-hook current. Also shown is a polarity steering regenerative switch (MP1, MP2) that provides a power supply voltage from a telephone line pair and may be adapted for a polarity signal and can be combined with a current mirror (MP7) to produce a current signal proportional to the line voltage (LV1).

Abstract: The amplitudes of a signal on the microphone input of a telephone and a signal on the line input of the telephone are compared with each other and with two thresholds. The comparisons are sampled and the samples control an accumulator including an up-down counter and logic to provide adjustable thresholds. The count in the counter is compared with two other thresholds and the results of the comparisons are used to apply either variable data or fixed data to the counter.

Abstract: A key signal scanning apparatus of a complex telephone comprises: a keypad having plural row ports, plural column ports, and plural keys for generating a key signal in accordance with pressing of a key by a user; a main microprocessor which operates by externally supplied power for supplying a timing signal to the row ports of the keypad by using row output ports, for receiving the key signal from the column ports of the keypad by using column input ports, for detecting a key pressed by the user by scanning the received key signal, and for outputting a dialing signal corresponding to the scanned key; a sub microprocessor which operates when power is not supplied from an external source for outputting a dialing signal generated according to the key signal inputted from the row ports and the column ports of the keypad; a first separator circuit for cutting off current flow to the row output ports of the main microprocessor from the row ports of the sub microprocessor; and a second separator circuit for cutting

Abstract: A PC (10) connected to a low-voltage electricity supply system (9) via a mains plug (11) and a mains socket outlet (12), into which the said plug is plugged, exchanges messages with other apparatuses via the said electricity supply system by means of signals whose frequency is between 1 MHz and 40 MHz. In order to suppress high-frequency interference signals which are generated by further apparatuses which are connected to the low-voltage electricity supply system (9) via mains plugs (11′) and further mains socket outlets (12′), arranged in local proximity to the said mains socket outlet (12), or which are produced by reflections of signals at open line ends, an adapter (1) is in each case interposed there, which adapter is plugged into the mains socket outlet (12′) and into which adapter the mains plug (11′) of the respective apparatus is plugged.

Abstract: A telephone handset dynamically buffers a real-time audio signal. The handset includes a microphone and a speaker connected to a telephone network interface. A proximity sensor is located near the speaker of the handset. The proximity sensor is connected to a circuit for measuring a coupling between the handset and an ear of a user. A buffer continuously records the real-time audio signal. The recorded signal can than be played back after the handset is first removed from the ear of the user, and second re-applied with the ear of the user using a time-compressed audio signal, until the playback signal is resynchronized with the real-time audio signal.

Abstract: A key arrangement for a telephone including a common plane in which all of the keys are arranged, the plane having a radial focal point and a peripheral area about the focal point. A set of twelve independently manually actuable keys are arranged in the plane with each key having an upper contact surface. Ten of the keys are arranged radially on the peripheral area of the plane about the focal point of the plane along a path defining a closed curve. Two keys are located at opposite sides of the radial focal point. Each key also has means for tactily indicating its position with respect to the other keys including the cross sectional shape of the upper contact surface of each key having a slope indicating the radial location from the central axis of the key arrangement.

Abstract: A communication apparatus including a network control unit for interfacing with a telephone line. The network control unit comprises a direct current circuit in which a loop state direct current can flow, and a direct current limiting device for limiting the loop state direct current to a prescribed value when communication with a foreign country that has adopted a different communication standard is performed.

Abstract: A call recording system includes a processing module operable in a call recording mode for storing compressed call data in a data storage device. The processing module is further operable in a selected one of a near data access mode, where call data retrieval is conducted under the control of a telephone handset connected to the system, a remote data access mode, where call data retrieval is conducted under the control of a remote terminal connected to the system via a telephone network, and a computer network access mode, where call data retrieval is conducted through a computer network connection with the system.

Abstract: In accordance with a first aspect of the present invention there is provided a telephone apparatus including a transmitter portion and a receiver portion, an input transducer for converting input audio signals into electrical signals, a connectable input link between the input transducer and the transmitter portion to deliver when connected an input electrical signal to the transmitter portion to be transmitted by the transmitter portion, an output transducer for converting an output electrical signal into an audio signal and a connectable output link between the receiver portion and the output transducer for delivering when connected an output signal to the output transducer, optionally an echo cancellation circuitry portion adapted to sample the output signal and produce an echo replica signal, optionally a mixer included in the input link for mixing an echo replica signal produced by the echo cancellation circuit with an input signal produced by the input transducer, and an echo suppression circuitry porti

Abstract: Embodiments of the present invention relate to systems and methods for an electronic hook switch for customer premises equipment. In an embodiment, a system includes a first lead configured to be coupled to a tip wire and a second lead configured to be coupled to a ring wire. A diode bridge is coupled to the first lead and the second lead and has a positive output. A low side switch is coupled to the positive output of the diode bridge without a high side switch between the low side switch and the positive output of the diode bridge.

Abstract: An apparatus for attaching a personal computer (40) comprising an audio system to a telephone network. The apparatus comprises first connector (12, 16) for the connection to the base (20) of a telephone set of a telephone system, second connector (14, 22) for the attachment of a handset (30). When the apparatus and the personal computer are powered-off, the connection between the first connector (12, 16) and the second connector means (14, 22) is maintained so that the handset (30) can be directly used in association with its base. In power-on condition of the personal computer, the voice signal generated by the microphone of the handset (30) or an analog signal of the audio system of the PC (40) is being diverted and transmitted to the base (20) of said telephone system.

Abstract: Techniques are described for providing telephony devices with a ring signal that has a voltage offset. For example, a ring signal shifter may receive a ring signal and a tip signal from a source. The ring signal shifter may, for example, receive a ring signal and a tip signal that are identical except for a 180-degree phase difference during the ringing state, i.e., the ring and tip signals are balanced signals. The ring signal shifter may include circuitry that rectifies the tip signal and superimposes the tip signal onto the ring signal in order to obtain a ring signal shifted by an offset voltage. The shifted ring signal may be output to a telephony device that requires an offset voltage in order to operate properly. For example, the shifted ring signal may be output to an answering machine that require a ring signal with an offset in order to respond to calls.

Abstract: A telephone is provided which includes a capacitive sensor via which the environment of the telephone's loudspeaker is monitored continuously to determine whether the operator of the telephone is located close to the loudspeaker.

Abstract: The mobile telephone is provided with the capability for automatically adjusting the gain of a microphone of the telephone based upon the detected noise level in which the cellular telephone is operated. As the noise level increases, the gain of the microphone is automatically decreased, thereby compensating for the natural tendency of telephone users to speak more loudly in noisy environments. Also, by decreasing the microphone gain, any clipping that might otherwise occur as a result of the user speaking more loudly is avoided and the signal-to-noise ratio is not thereby decreased. Furthermore, because the microphone gain decreases, the volume level of the voice of the user as it is output from the other party's telephone is not unduly loud. Hence, the other party need not manually decrease the speaker gain of his or her telephone.

Abstract: A DC/DC converter capable of preventing abnormal temperature increase in a power transistor. The DC/DC converter comprises a loop circuit, a power transistor, an abnormal high temperature detection circuit, and an abnormality processing circuit. The power transistor supplies an electric current to the loop circuit according to a control pulse signal. The loop circuit accumulates electromagnetic energy in an inductor when the electric current is supplied and generates a negative DC voltage by causing a loop electric current to flow by using the electromagnetic energy accumulated in the inductor when no electric current is supplied. The abnormal high temperature detection circuit detects a normal/abnormal state of temperature of the power transistor. The abnormality processing circuit switches the power transistor off when the abnormal high temperature detection circuit has detected that the temperature of the power transistor is abnormal.

Abstract: A subscriber-line interface circuit (SLIC) has tip and ring amplifiers connected to the tip and ring lines, respectively, of customer premises equipment (CPE). The SLIC returns the ringing signal (provided to the CPE from a power supply connected to the CPE's ring line), to ground or to battery, through the SLIC's tip amplifier. In one embodiment, the SLIC has three switches: S1 connecting the power supply to the ring line, S2 connecting the ring amp to the ring line, and S3 connecting the tip amp to the tip line. During ringing, S1 and S3 are closed to return the ringing signal to ground through the tip amp, which is preferably driven to saturation during ringing to reduce power consumption. By eliminating the fourth switch that appears in prior-art SLICs (e.g., connecting the tip line to ground), SLICs of the present invention can be smaller and therefore less expensive to implement.

Abstract: The size and power consumption of a ring trip monitor circuit, which performs one of the BORSHT functions of a telephone line card, is reduced by utilizing an operational amplifier with feedback resistors, a resistor network, and a ring signal generator that is only connected to the line when a ring condition is present.

Abstract: The invention creates a method for adjusting a ringing signal current in a subscriber line (106), a ringing signal generator (114) which generates the ringing signal being connected with one end of the subscriber line (106) and at least one subscriber (102) being connected to another end of the subscriber line (106), comprising the steps of detecting a ringing signal current of the ringing signal; of comparing the detected ringing signal current with a predetermined current value; and when the detected ringing signal current is greater than the predetermined current value, reducing a ringing signal voltage of the ringing signal in such a manner that the ringing signal current is equal to the predetermined current value, the ringing signal voltage being dropped across the subscriber line (106) and a load of at least one subscriber (102). The invention also creates a circuit arrangement for carrying out the method.

Abstract: Systems and methods for remotely diagnosing, trouble shooting, and/or programming an end user telephone by a customer service representative using a modem in communication with the user's telephone during a live telephone call between the customer service representative and the user are disclosed. The user telephone and modem system generally comprises a telephone having a remotely controllable feature and a user modem that alternates between voice and data signal transmissions and communicates with a remote customer service modem. The user modem receives control signals from the remote customer service modem for controlling the controllable feature of the user telephone. The user telephone may be a DSP-enabled telephone with the user modem being embodied in the DSP. Examples of remotely controllable features include volume, frequency response, compression ratio, knee point, programmable memory, an LED light, self-diagnostic test, and/or user hearing test administration.

Abstract: In a microphone signal, the signal component corresponding to, e.g., echo is suppressed using an echo control scheme that estimates the spectral envelope of the echo signal, without having to estimate the waveform for the echo signal. In one embodiment, the input signal (to be applied to a loudspeaker) and the microphone signal are spectrally decomposed into multiple subbands, where echo suppression processing is independently performed on each subband. The echo control of the present invention can be implemented with substantially reduced (1) computational complexity and (2) phase sensitivity, as compared to traditional acoustic echo cancellation, in which the waveform for the echo signal is estimated.

Abstract: A telephone indicator system includes a telephone having a base and a handset. The telephone includes a cradle disposed on the base configured to receive the handset. The system also includes an indicator disposed on an least two elevated surfaces of the telephone to notify a user of a telephone message. The indicator may be disposed on at least two elevated surfaces of the handset. The system may also include another indicator disposed in the cradle of the telephone to notify the user of another telephone message while the handset is in use.

Abstract: A full duplex telephone set for hearing impaired users includes a digital signal processor incorporating a pair of adaptive transversal filters to cancel line and acoustic echo feedback from the tip and ring signals of the set, and to condition and control the amount of a replacement side tone fed back to the receiver. This enables at least 50 dB of gain to be applied to the modified received signal without initiating unstable operation, or howl, in the set, and ensures that the received and side tone signals are heard by the user with equal comfort and clarity. The digital signal processor also enables additional enhancements to be made to the modified received signal that are beneficial to hearing impaired users, such as dynamic range compression, “soft” limiting, and low level emphasis within selectable frequency bands.

Abstract: It is an object of the present invention to provide a communication system, which can manage the contents of control transfer properly while adopting a control transfer method capable of making effective use of a telephone line. When use of a telephone line for a portable telephone 1 is transferred to slave terminals such as a portable telephone 10, a vending machine 11 with communication capability, a personal computer 12 with communication capability, and a car 13 with communication capability, the contents of transfer are stored in a predetermined memory of the portable telephone 1, while the contents of transfer to be transferred to each slave terminal are stored in a built-in memory of the slave terminal. On the other hand, a host computer 2 at an exchange is provided with a predetermined memory for cumulatively storing used transfer contents each time the slave terminal is connected using the transfer. The three memories are checked as appropriate to keep proper use of control transfer.

Abstract: A robust symbol timing recovery circuit for a telephone line modem is provided. The symbol timing recovery circuit comprises a timing estimator and an interpolator. The timing estimator, which performs an operation on input samples and estimates a timing offset of a received symbol, outputs a timing offset estimated for each symbol for a first window interval, and thereafter outputs a timing offset estimated in an immediately previous window interval for the current window interval. The interpolator, which performs interpolation using the input samples, comprises a plurality of shift registers which are serially connected and output the input samples in units of a predetermined plural number of input samples, by sequentially delaying for an input sample 15 period and outputting the input samples. Since the symbol timing recovery circuit is not sensitive to clock instability and employs a stable timing offset estimating method, symbol timing can be recovered stably and reliably.

Abstract: The present invention is directed to the provision of a personalized speaker phone and hands-free telephony. In particular, the present invention allows communications to be output along a narrowly defined path, rather than being broadcast. In this way, a private voice communication signal can be provided to a user, even though the user is not holding the output device to the user's ear. Furthermore, by providing audible signals along narrowly defined paths, different audible signals may be provided to users at the same location, without interfering with one another.

Abstract: An audio conferencing platform includes data bus (e.g., a time division multiplex (TDM) bus), a controller, and an interface circuit that receives audio signals from a plurality of conference participants and provides digitized audio signals in assigned time slots over the TDM bus. The audio conferencing platform also includes a plurality of digital signal processors (DSPs) adapted to communicate on the TDM bus with the interface circuit. At least one of the DSPs sums a plurality of the digitized audio signals associated with conference participants who are speaking, to provide a summed conference signal. This DSP provides the summed conference signal to at least one of the other plurality of DSPs, which removes the digitized audio signal associated with a speaker whose voice is included in the summed conference signal, to provide a customized conference audio signal to each of the speakers.

Abstract: A communication apparatus having a one-way speakerphone function including a handset connected to the communication apparatus by a transmit-receive line, wherein the transmit-receive line is enabled when the handset of the communication apparatus is off-hook; a speaker outputting a sound of the handset communication; an input key part including a selection key for the one-way speakerphone function and a plurality of dial keys; and a central control device controlling the one-way speakerphone function; wherein a conversation signal is transmitted through the speaker when the handset is off-hook, the one-way speakerphone function selection key signal is input, and it is determined that a dialing is completed.

Abstract: A line powered codec which adaptively allows operation with power supplied from a telephone line in many countries as conditions warrant. A startup procedure uses country-specific register settings, which are powered and maintained from a low voltage side other than the telephone line. Thus, during low line power conditions a programmed state of the line powered codec can be maintained even after a power loss in the telephone line. In another aspect, a current and voltage detection module in the line powered codec is always powered from the telephone line. If sufficient power is not present, the line powered codec does not power up. In yet another aspect, a plurality of power rails may be provided.

Abstract: A dual phone, and method of telecommunicating by using the same, have an ISDN phone and IP phone. The dual phone recognizes one of ISDN mode, IP mode, and external connection mode from a user input, and connects or releases a voice path between an ISDN phone and the IP phone based on the recognized mode, thereby enabling calling between an external ISDN phone and an IP phone.

Abstract: A handset port interface including DC measurement and transmit path calibration. In an interface device for interfacing a telephone instrument, such as a headset, a handset, a modem, or a teleconferencing device, to the handset microphone input port of a telephone set base unit, the transmit signal level applied to the microphone input of the base unit must be set to an appropriate level. The appropriate level is determined according to the type of microphone the telephone set base unit is configured to interface with. The microphone can be carbon, electret or dynamic. The interface device detects the type of microphone the base unit is configured to interface with by detecting the DC characteristics of the microphone input port. Then, the interface device determines the appropriate transmit level by correlating the DC characteristics to one of a plurality of predetermined transmit levels. These levels are stored in a table.

Abstract: Systems and methods are provided for switching between power supply rail voltages for a differential driver device of a class G amplifier device. The amplifier device employs power MOSFETs to switch between supplying high supply voltages and low supply voltages to the power rails of the differential driver. The class G amplifier can be employed in driving an ADSL signal over a telephone line. A control device ramps the power supply rail voltage between low power supply states and high power supply states to mitigate noise and spikes that can be coupled to the output signal.

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: A cost-effective technique for inserting a switching module into a line pair of a local telecommunications network is disclosed. In particular, the illustrative embodiment does not replace a punch-down block at a cross-connect, but rather inserts the switching module between the modular connectors that are usually co-located with the punch-down block and that connect the cable pairs to the punch-down block. In other words, the illustrative embodiment provides for a technician to disconnect a pair of modular connectors and to insert a switching module between them, wherein the switching modules inputs and outputs are provided via modular connectors.

Abstract: An adaptive transmit amplifier for automatically adjusting the transmit output characteristics of a headset adapter output stage includes a detector adapted to detect a value of a bias current in a host microphone transmit circuit. The adaptive transmit amplifier further includes a switching stage coupled to the detector and adapted to select a gain level and impedance level of the headset adapter output stage based upon the bias current value. The adaptive transmit amplifier may further include a logic/timing block coupled to the detector and to the switching stage. The logic/timing block is adapted to control a sequence of detection of the bias current and selection of the gain level and impedance level of the headset adapter output stage.

Abstract: The present invention provides a DTMF decoder that combines software and hardware and the method of operating the same. The DTMF decoder that combines software and hardware comprises an amplifier, an analog to digital convert, and a CPU or a digital logic circuit. The amplified DTMF signal is converted from analog to digital via the analog to digital converter according to the present invention. Since the digital DTMF signal converted from analog to digital integrally preserves the spectrum message of the DTMF signal, the digital DTMF signal can be further decoded by the CPU or the digital logic circuit. Therefore, the decoding error problem due to the software decoding method can be solved. In addition, when compared with the DTMF decoder with the hardware decoding method, the DTMF decoder that combines software with hardware of the present invention significantly reduces the cost, and even provides better performance and more flexibility in application when compared with the hardware decoding method.

Abstract: A method and apparatus in a DC-feed controller for controlling a subscriber line interface circuit controlling voltage (alternately, current) on a telephone line comprising a pair of wires. A digital feedback signal is subtracted from a predetermined voltage (alternately, current) limit digital value to provide a digital error signal that represents the difference between the voltage (alternately, current) limit digital value and the digital feedback signal. The digital error signal is multiplied by a predetermined digital gain value to provide a scaled digital error value. The scaled digital error value is integrated over time to generate an integrated digital error signal having a first predetermined number n of significant bits.