Abstract: In a method and a circuit for automatic speech direction reversal a reception signal with variable damping is furnished to a loudspeaker and a signal with a variable damping from a microphone is provided as the transmission signal. The reception signal and microphone signal are continuously classified as speech signal or noise. The one signal which is classified as a speech signal, is damped at a first damping value and the other signal is damped at a second damping value, which is greater than the first. These settings are maintained until a signal is classified as noise. When both signals are classified as speech signals, the preceding damping values are retained. When both signals are classified as noise, both attenuations are set at a third damping value located between the first and second damping values.

Abstract: An amplifier circuit for an electret condenser microphone includes an operational amplifier, an operational amplifier, a bias circuit, and a power supply circuit. The operational amplifier has an inverting input terminal for receiving an output of a two-wire lead electret condenser microphone and a noninverting input terminal for receiving a bias voltage. The bias circuit divides a power supply voltage to generate the bias voltage. The power supply circuit applies the power supply voltage to the electret condenser microphone through the bias circuit and a first resistor.

Abstract: A system for automatically adjusting the level of a telephone instrument microphone input signal in response to the level of the telephone instrument sidetone signal. The system may provide a test signal to the handset microphone input and receive the sidetone signal that corresponds to the test signal from the handset speaker output. A signal processor may then measure the amount of distortion present in the sidetone. If the amount of distortion is below a predetermined threshold, the level of the test signal is increased by a predetermined increment by adjusting an attenuation or amplification factor, and the amount of distortion in the sidetone is again measured. These steps are repeated until the measured distortion exceeds the threshold. The level of the test signal is then decreased by a predetermined amount. The final test signal thus has a level that maximizes the microphone input signal level with an acceptable minimum of distortion.

Abstract: An automated method for modifying a speech signal communicated over a telephone network by applying a gain factor in a telephone set before any side tone is added thereto. The gain factor is a function of a received signal indicative of the background noise at the location of the telephone set. The gain applied may be a function of both the background noise level and the original speech signal. Either a linear or a non-linear (e.g., compressed) amplification of the original speech signal may be performed, where a compressed amplification results in the higher level portions of the speech signal being amplified by a smaller gain factor than lower level portions. The speech signal may be separated into a plurality of subbands, each resultant subband signal being individually modified in accordance with the present invention.

Abstract: A handsfree communication apparatus utilizing a plurality of microphones to allow simultaneous communication by a plurality of persons. The plurality of microphones are separately provided apart from one another. An amplifier section (or a noise canceller) includes a plurality of operational amplifiers for signal amplification individually corresponding to the plurality of microphones, and differential amplifier circuit for executing a differential amplification. Through the differential amplification, simultaneously input noise components are canceled out and reduced, and at the same time speech components are extracted.

Abstract: A telephone headset interface circuit is coupled to a telephone line to extract power for use by a headset amplifier and is particularly adapted for use with telephone handsets having dynamic or electret microphones. The telephone line connects a telephone to a service system, such as a Central Office, a PBX system, or a Key system. The interface circuit includes a power extraction circuit having a plurality of circuit portions, each one coupled to a corresponding one of the telephone line wires for providing a predetermined output voltage, so that substantially identical electrical impedance characteristics are introduced to each such wire.

Abstract: A method and apparatus for recording and playing back a sales presentation is disclosed. A telephone interface device is connected to a telephone base, handset and recorder to permit recordation of a sales message using the telephone mouth piece as the recorder microphone. The recorded message has the same sound quality when transmitted over the phone lines as does a normal, live transmission. Transit to and from live and recorded voice is undetected by the party hearing the sales presentation over the phone. Use of the telephone interface device and the recorded sales presentation precludes fatigue and discouragement on the part of the telemarketing sales representative in the face of repeated repetitions of the same sales message and frequent rejections by prospective customers.

Abstract: A reception volume limiting circuit includes a detecting section, an A/D conversion section, a control section, and a speech data calculating section. The detecting section performs detection/rectification and smoothing of a receiver driving AC signal and outputs a DC signal corresponding to the level of the receiver driving AC signal. The A/D conversion section converts the DC signal into a digital signal. The control section calculates a time average value by averaging the digital signal every predetermined time interval, adds the currently stored attenuation amount to the time average value, and compares the time average value with a predetermined threshold value representing a critical sound pressure for protection of listener's hearing.

Abstract: A circuit and method minimizes undesired noise signals associated with the battery utilized in a telephone battery feed circuit. In one embodiment, the noise voltage is amplified and inverted in phase and added back to a location on the ring line in order to provide substantial cancellation of the original noise voltage which would have appeared at the same location. In another embodiment, the noise voltage coupled to the ring line is reproduced as a replica signal. The replica signal is added in series with the tip line so as to provide equal phase and magnitude relationships relative to earth ground, thereby effectively canceling the noise current which would have flowed from the original noise source.

Abstract: An automated method for modifying a speech signal in a telephone network by applying a gain factor which is a function of the level of background noise at a given destination, and transmitting the modified speech signal to the destination. The gain applied may be a function of both the background noise level and the original speech signal. Either a linear or a non-linear (e.g., compressed) amplification of the original speech signal may be performed, where a compressed amplification results in the higher level portions of the speech signal being amplified by a smaller gain factor than lower level portions. The speech signal may be separated into a plurality of subbands, each resultant subband signal being individually modified in accordance with the present invention. In this case, each subband speech signal is amplified by a gain factor based on a corresponding subband noise signal, generated by separating the background noise signal into a corresponding plurality of subbands.

Abstract: A speakerphone for a telephone circuit includes an output stage that comprises a loudspeaker amplifier coupled to a loudspeaker through a coupling capacitor. An auxiliary circuit includes a reference input element that provides first and second reference voltages which are used to charge the coupling capacitor to a given level prior to the input signal being coupled to the loudspeaker through the coupling capacitor to insure a click-free switch-on of the loudspeaker.

Abstract: A digital sound level control apparatus for adjusting the reception sound level from all telephone circuits to a substantially fixed level comprises a region discrimination circuit for discriminating a PCM input data signal from a PCM conversion section, including a segment coder for compressing and decompressing a digital audio signal, among an intrinsic variation signal, a basic normalization level signal and a coding threshold value, a multiplication circuit for outputting an input level signal of 12 bits, an addition circuit, a register for holding a pad multiplication value corresponding to a reception circuit, another multiplication circuit for multiplying the input level value by the pad multiplication value to output a output level signal for outputting sound by a predetermined sound level, and a comparison region discrimination circuit, a subtraction circuit, a division circuit and a register for regenerating an 8-bit digital signal from the output level signal.

Abstract: A telephone privacy device includes first and second connectors that are mateable with a telephone handset and a telephone base, respectively. The handset includes a microphone, and the device includes a variable amplifier that allows the user to amplify the microphone signal to a desired level prior to sending it on to the base. A signal strength display allows the user to monitor the amplitude of the amplified microphone signal. A side tone suppression circuit generates a side tone suppression signal in response to the amplified microphone signal. This side tone suppression signal is used to reduce excessive side tone from the telephone base. An adjustable gain amplifier amplifies the speaker signal supplied by the base for the handset speaker.

Abstract: Existing automatic log on/log off systems in telephone systems determine whether or not a workstation is occupied, and that calls can be directed to that workstation, by determining whether or not the amplifier that provides the interface between the telephone system and the occupant's headset is plugged into the workstation. Recent headsets have a connector in the cord between the headset and the amplifier. This enables the occupant to leave the workstation without unplugging the amplifier, which defeats sensing mechanism of the existing automatic log on/log off system. An amplifier according to the invention replaces the existing amplifier and includes a detector that determines whether the headset is connected to the amplifier, and an activator that activates the existing automatic log on/log off system in the telephone system.

Abstract: A telephone set connected to a telephone line including a supply circuit providing an output current which is an increasing function of the voltage available on the telephone line; a speech amplifier supplied by the output current; and a modulator having a quiescent current and operable to inject into the line a modulation current proportional to a speech signal. The modulator incorporates the supply circuit, the current consumed by the modulator being essentially the current provided to the amplifier by the supply circuit.

Abstract: Disclosed is a network interface device for connecting network wiring to a subscriber's wiring at a subscriber's premises, the network interface device having a door covering a test jack, with means for connecting the network wiring to the subscriber wiring when the door is closed and connecting the network wiring to the test jack when the door is open.

Abstract: An electroacoustic amplifier arrangement comprises a plurality of microphone arrangements each of which includes a microphone coupled to a comparator and coupled via a coupling circuit to a variable gain amplifier. The amplifier arrangement further includes a threshold signal generator. The threshold signal generator has a first and a second input coupled to the input and output, respectively, of the amplifier and is arranged to derive a threshold signal as a function of the signals applied to its two inputs. The output of the threshold signal generator is coupled to a second input of the comparator. The threshold signal generator is arranged to derive a threshold signal as a function of the gain factor adjusted in the amplifier.

Abstract: A headset amplifier, adapted for use with a voltage source such as a battery, includes a time-out-timer circuit for deactivating the headset amplifier after a first predetermined period of time and for reactivating the amplifier in response to a signal fed to an input port of the time-out-timer circuit.

Abstract: A telephone includes an EEPROM memory (26) for storing data, and a microcontroller (14) for controlling operations. The EEPROM (26) contains data for different operating protocols, so that the telephone can be readily adapted for use in different telephone systems. The EEPROM (26) draws a (small) line current when the telephone is in use, but requires no current to maintain its memories, so no standby power is required. Particularly if the telephone is for use in noisy environments, there can a mute/boost feature (30) whereby the receiver gain is boosted and the microphone is simultaneously cut off. This may be effectuated by use of the EEPROM (26).

Abstract: Apparatus for reducing acoustic background noise for use with a telephone handset or a boom microphone device or the like. The apparatus includes first and second microphones which are arranged such that the first microphone receives a desired speech input and the background noise present in the vicinity of the speech, and the second microphone receives substantially only the background noise. The background noise from the second microphone is converted into a corresponding electrical signal and subtracted from a signal corresponding to the speech and background noise obtained from the first microphone so as to produce a signal representing substantially the speech.

Abstract: An amplifier for amplifying a signal received on a telephone line and for providing the amplified signal to a telephone headset. The amplifier draws current from a battery. The current drawn is reduced in the absence of activity on the line. The amplifier includes a timer that generates a first control signal after a time-out time. The timer is reset by a second control signal. A threshold circuit generates the second control signal when the signal on the telephone line is above a threshold level. Finally, a circuit, responsive to the first control signal, reduces the current drawn from the power supply. The amplifier may additionally or alternatively include receive line muting. The amplifier includes an automatic level control circuit that receives the signal received on the telephone line and controls the level of the amplified signal provided to the headset to a set level in response to a second control signal.

Abstract: Telephone headsets used by operators and airline pilot headsets are subject to substantial amounts of interfering ambient noise which detract from the intelligibility of incoming speech. Noise reduction circuitry does not altogether eliminate the interfering sound. A headset speaker and error microphone housing are disclosed which enable a greater amount of unwanted noise elimination. The speaker and microphone are configured closely with respect to each other and also to the user's ear. They are acoustically isolated in their own chamber. The microphone is located approximately on the speaker axis and protrudes substantially into the user's ear; and also is disposed close to the speaker cone surface. Additional acoustical tuning features include venting ports in the housing, and acoustic damping padding at the microphone entrance and on either side of the speaker. These expedients enhance the ability of the noise-cancelling circuitry to effectively reduce the undesired noise heard by the user.

Abstract: Dial tone detection circuitry is employed in a telephone of the type which has its dialing mechanism incorporated into the handset. The dial tone detection circuitry is connected to an annunciating means which indicates to a user that dial tone is present without the need to bring the handset to the user's ear. The dial tone detection circuitry my also be connected to the telephone's automatic redial circuitry to ensure efficient operation of the redial function.

Abstract: The ringer comprises a loudspeaker receiving signals from an amplifier, the amplifier having both a power supply input connected to a ringer line providing a ringer signal via a chopper power supply means, and a melody input which is connected to the ringer line via a regulation unit that provides an image signal representative of the power of the ringer signal, and via a transformation unit that transforms the image signal by means of a melody signal applied to a terminal.

Abstract: The sound volume controlling apparatus comprises UP and DOWN keys (42, 43) depressed manually; a time period detecting circuit (39h, 39d) for detecting time period from when the duration of UP or DOWN key depression reaches a predetermined value (e.g. 0.5 sec) to when the continuous key depression ends; a sound volume value deciding circuit (39e, 39f, 37a) for changing the sound volume value during the time duration detected by the time period detecting circuit; and sound volume changing circuit (37b, 45) for changing the sound volume in accordance with the value decided by the sound volume value deciding circuit.Since the sound volume is changed only after the key is kept depressed for a predetermined time period (e.g. 0.5 sec), it is possible to prevent the sound volume from being changed erroneously due to a short time touch to the keys.

Abstract: An automatic gain controller uses a voltage controlled amplifier coupled to an averaging circuit that feeds back into the amplifier. The averaging circuit supplies a controlling voltage that keeps the amplifier output voltage tending towards a certain reference level. When the amplifier output is generally high, the averaging circuit output is also generally high and the reverse is also true for low signals. For low averaging circuit output voltages corresponding to low intensity signals, amplification of the signal by the amplifier is enhanced or augmented. The result is to boost the signal of low intensity signals significantly, compressing the dynamic range of an incoming signal received from a phone. This reduces the variance of an incoming phone line signal for an analog to digital converter (ADC) in a digital telephone answering device, and the effective dynamic range of the ADC is closer to optimum. A scaling circuit couples the signal from the automatic gain controller to the ADC.

Abstract: An improved transformer-less electronic isolating transformer is obtained with an output subcircuit that outputs a controlled current rather than voltage. Specifically, the improved hybrid comprises an output drive subcircuit that receives an ac signal and creates a corresponding current that is passed to the line that supports two way communication. The subcircuit not only converts the applied voltage to current but includes means for effecting gain. Signals arriving to the hybrid from the line are applied directly to a near-end echo circuit that is also responsive to the signal applied to the output drive subcircuit. Both the input of the output drive subcircuit and the output of the near-end echo subcircuit are isolated with opto-isolators that employ photodiodes in their photo-voltaic mode.

Abstract: A transceiver circuit for use in a high speed data transmission network is disclosed that provides for simultaneous bidirectional transmission of data over coaxial or twisted pair media. A transmitter circuit provides an output data signal to a bridge network. The bridge network develops a cancelling signal and a combined signal. A receiver section includes a high speed subtracting circuit that determines the difference between the cancelling signal and the combined signal to effectively cancel data supplied by the transmitter section.

Abstract: To allow a universal replacement telephone handset, an adaptive amplifier circuit uses DC power available from a host telephone set base to discriminate between low resistance and high resistance base power supplies. It emulates either a carbon microphone or an electret microphone, whichever is appropriate for the set base. The circuit couples a microphone (10) and an output terminal (2a) through a series connection of resistor (R1), input and output leads of an amplifier (12), and a sense circuit (22). The sense circuit controls two current sources (14),(16) in response to the shunt voltage and series current available from the telephone base. Current source (14) connects the amplifier output to an input terminal (1a) and acts either as a bias current source, or as an electronic switch that provides a short circuit from the microphone to the the amplifier output.

Abstract: Existing automatic log on/log off systems in telephone systems determine whether or not a workstation is occupied, and that calls can be directed to that workstation, by determining whether or not the amplifier that provides the interface between the telephone system and the occupant's headset is plugged into the workstation. Recent headsets have a connector in the cord between the headset and the amplifier. This enables the occupant to leave the workstation without unplugging the amplifier, which defeats sensing mechanism of the existing automatic log on/log off system. An amplifier according to the invention replaces the existing amplifier and includes a detector that determines whether the headset is connected to the amplifier, and an activator that activates the existing automatic log on/log off system in the telephone system.

Abstract: A method for automatic speech direction reversal includes supplying a reception signal with variable damping to a loudspeaker, outputting a microphone signal with variable damping from a microphone as a transmission signal; continuously classifying each of the reception signal and the microphone signal as a speech signal or noise; setting the damping of one of the signals classified as the speech signal to a first damping value, setting the damping of the other of the signals to a second damping value being higher than the first damping value, and maintaining the set damping until the one signal is classified as noise. The preceding damping values are maintained if both of the signals are classified as a speech signal. Both damping vlaues are set to a third damping value being located between the first and second damping values if both of the signals are classified as noise.

Abstract: An electrical telephone speech network is disclosed in which the transmitting and the receiving amplifiers are serially connected so as to reduce the minimum working current of the whole speech network. As a result, a telephone set in the network can operate properly with a much lower line current, and more extension telephones can be connected parallelly with the speech network. Further, a bias switching circuit is matched with the speech network. Thus, in pulse dialing mode, the line voltage drop of the network loop during "make" status is automatically decreased so that a pulse dialing signal received by the exchange can be more accurate. At the same time, in DTMF dialing mode, the voltage drop of the telephone set is automatically increased, for the purpose of providing a larger AC signal dynamic range to enable a telephone set to deliver a large DTMF signal and operate with a lower line current.

Abstract: An apparatus 10 is employed for interfacing a telephone handset 18 to a telephone network. Typically, a telephone handset has one of a variety of different microphones disposed therein, such as carbon, electret, etc., where each type of microphone has a different output level and impedance. Conversely, the telephone network with which the microphone is to be interfaced has a preselected input impedance and signal requirement intended to match only one type of microphone. The apparatus 10 includes a plurality of switches 82, 84, 86, 88 and resistors 90, 92, 94 that are manually switchable into the circuit either separately or in combination to match the output impedance and signal level of the microphone with the input impedance and signal level of the telephone network. Alternatively, in a second embodiment of the instant apparatus, a variable resistor is employed to match the output impedance and signal level of the microphone with the input impedance and signal level of the telephone network.

Abstract: A voice-band receive amplifier for telephone handsets that mitigates loud sidetone and acoustic sing. A receive channel (30) with amplification and voice-switched attenuation is disposed between a receive port of a telephone network (80) at terminals (1a), (1b), and an electro-acoustic receiver (20). A transmit channel (70) having voice-switched attenuation that varies inversely with the receive channel attenuation is disposed between a transmit port of the telephone network at terminals (2a), (2b), and an acousto-electrical microphone (10). A controller (60) with an output lead connecting to the transmit and receive channels has an input lead connecting to the microphone, and an input lead connecting to the receiver. The controller provides a varying DC control signal at its output lead in response to varying levels of transmit and receive signals appearing at the input of the controller. Receive signals are attenuated when transmit levels are at or above a predetermined threshold.

Abstract: A volume control for a telephone having a receiver, a manual key for generating a volume increment for each operation of the key; a volume increment counter connected to the manual key for counting volume increments; a controlled gain amplifier connected ahead of the receiver; and a gain control network connected between the controlled gain amplifier and the counter for controlling the gain of the amplifier in response to the number of volume increments counted in the volume increment counter. A unique feature of the volume control is that it maintains the selected gain level when the central office collects or refunds coins or makes an initial rate or coin present test.

Abstract: An identifying telephone controller system using a main computer component with a central processing unit coupled to an in-house AC wiring system and utilizing a plug-in ringer/appliance controller receive and a base-remote telephone system to provide multi-function telephone operations including caller identification and call patching and remote appliance control.

Abstract: In a key telephone system connectable to both ISDN and PSTN, for the purpose of compensation of a difference in speech signal level between ISDN and PSTN, digital pads are incorporated in an ISDN interface unit mounted on a key service unit of this system. In the digital pads, original PCM-code speech signals received/transmitted from/to the ISDN line are converted into PCM-code speech signal with a compensated speech signal level obtained by adding a selected gain to the original speech signal level. Since the difference in the speech signal level between ISDN and PSTN differs according to the conditions, an appropriate gain is selected from a plurality of previously prepared gains. That is, the relationship between telephone numbers and information signals indicative of the selected gain is registered in the key service unit.

Abstract: An audio compression system wherein the compression theshold may be adjusted to a calibrated level. The audio compression system is utilizable in a receiver system whereinan audio input signal received by the receiver system via a communications channel is applied to conditioning circuitry. The conditioning circuitry, in turn, provides a conditioned input signal to an acoustic transducer element for generating a corresponding audio output signal. The audio compression system compares the conditioned input signal and an initial threshold signal to provide a comparator output signal corresponding to the difference between the conditoned input signal and the initial threshold signal. The comparator output signal is provided as a control input to the conditioning circuitry. If the conditioned input signal exceeds the initial threshold signal for a preselected period of time, then the initial threshold signal is switched to a second threshold signal.

Abstract: A multipurpose headset amplifier for the connection of a headset (11) to a telephone instrument comprises a housing (5) having an ascending, thready holder (10) for a headset (11) and connection jacks (21, 22, 23) for the headset (11), the telephone instrument (22) and for the telephone instrument's handset, the housing having at the upper side comprises manuel operating members (6, 7, 8) for the adjustment of the device, and manual controls (15) at the underside for the adaptation of a headset to the impedance and signal level of any telephone instrument. The amplifier comprises an internal power supply (12) and a jack (13) for external power supply. The amplifier is furthermore provided with a microphone switch having a light-emitting diode (9), a volume control (7) and a switch (6).

Abstract: A transistor 12 is provided for interfacing an electret microphone 16 to a carbon compatible telephone network by impedance matching. The transmitter 12 includes a rectifier 14 constructed from a plurality of Schottky diodes 44, 46, 48, 50 to reduce voltage drop therein and to provide a stable DC voltage supply to the transmitter 12. An amplifier 18 receives an audio signal from the electret microphone 16, amplifies it, and delivers this amplified signal onto the carbon compatible network via the rectifier 14. The amplifier 18 accomplishes this impedance matching while minimizing voltage drop therein. The amplifier 18 includes a first bipolar transistor 68 having its base connected to the microphone 16 and its emitter connected to the negative terminal of the rectifier 14. A second bipolar transistor 70 is connected as an emitter follower.

Abstract: In a loudspeaker telephone, improved power transfer is achieved by connecting the drive circuit for the loudspeaker in parallel with the input and output of the usual series regulator, the output of the regulator and one of the power supply connections of the drive circuit being connected, in common, to supply other circuitry in the telephone set. This other circuitry might comprise a microprocessor and other signal processing circuitry. Such a configuration means that the current passing through the speaker drive circuit also passes through the other circuitry. In effect, it is "re-used" instead of being added, as would be the case if the drive circuit were connected in parallel with the other circuitry. In the case of a positive series regulator, the series regulator supplies current when the current requirement of the other circuitry exceeds that received from the drive circuit.

Abstract: A power saving low frequency power amplifier includes a first stage amplifier for receiving and amplifying data signal, a second stage amplifier for amplifying the output of the first stage amplifier, and a power amplifier for amplifying the output of the second amplifier. The first stage amplifier is operated in response to a driving current. The second stage amplifier receives a first idling current for obtaining a predetermined amplification, and the power amplifier receives a second idling current for obtaining a predetermined amplification. A first switching circuit is provided for making and braking paths for the first and second idling currents provided for producing a power save signal to the first switching means for braking the first switching circuit when the power save signal is present.

Abstract: A telephonic therapy training device usable by speech-impaired persons and/or hearing-impaired persons to improve their telephone usage skills. The device is a "learn-by-doing" device wherein the instructor and each student are provided with individual handsets, each of which includes a microphone and a speaker (receiver). Each voice signal is sent through a microphone into an individual amplifier that transmits an amplified signal to an opposite party receiver in the individual handsets. The training device operates on regular household current; the use of commercial telephone lines is avoided in order to escape telephone service fees.

Abstract: A portable device to be carried by a reporter and coupled to a telephone line to a location from which the reporter wishes to transmit a report to a broadcast station to be broadcast live has a casing with a microphone (1) for voice input, a tape input (2) for receiving a tape signal and a monitor (3) for providing acoustic signal to the reporter.The device has signal conditioning circuitry including voice control gain adjustment (20) and amplification (5) for providing a signal to be transmitted by the telephone line in a form suitable for broadcasting. The device is coupled to the telephone line by a hybrid transformer arrangement (7 to 14) which serves to cancel unwanted components of the signal to be sent down a telephone line from that to be received from the telephone line. The device is portable and has its own power supply in the form of batteries or connections for an AC mains auto supply.

Abstract: The disclosure concerns digital telephone sets and, more particularly, those with amplified listening facility and "hands free" telephones. To fulfil the function of the anti-Larsen effect needed in these telephones, there is need for a signal envelope detector which gives a measurement of the mean level of the signal emitted or received on the line. According to the disclosure, the cofidec present in the digital telephones is used to establish an envelope detection system with logarithmic compression. This removes the need to do a logarithmic detection on the analog speech signal. Such a detection would necessitate diodes, upside down with respect to each other, which can be made, particularly, only through bipolar technology. A series/parallel converter, a digital comparator and a counter having a countdown frequency which is far slower than the counting frequency, fulfils the signal envelope detection function.

Abstract: A signal level expansion system for use in a telephone device is described which includes a level expansion circuit and an optional microphone enclosure. The circuit includes a voltage divider circuit which is used as a variable attenuator. The voltage divider has a junction field effect transistor (JFET) in its takeoff leg. The signal provided by the voltage divider is applied to an amplifier and then fed to a switch which detects voice signals. When a voice signal is detected having a level above a predetermined threshold, a timing circuit is energized. The timing circuit is connected to the JFET and, when energized, tends to increase the resistance in the takeoff leg of the voltage divider, increasing the signal level applied to the amplifier. The microphone enclosure surrounds the sides of the microphone with layers of rigid and resilient materials.

Abstract: An electronic telephone set for use with a telephone headset receiver/transmitter apparatus is disclosed. The telephone set is line-powered, and is capable of transmit muting, last number re-dial, and memory dialing. The volume of the received voice signal is controllable by a user, and a visual indication of the volume setting is provided. The receiver and transmitter amplifiers includes circuitry for compensating for the frequency response characteristics of two or more headsets, the compensation circuitry being selectively and automatically engaged by means of a programmable connecting jack. The design of the telephone is such that it consumes very little power, especially during "on-hook" operation. Moreover, an electrical storage device is employed to provide continuous operational power to the dialer circuitry and electronic hook-switch control circuitry, so that the telephone set retains its dialing memory when not in use.

Abstract: An electronic telephone set which includes first and second connection points for a telephone line and a transmission circuit having a send output stage including a first transistor whose first main electrode is coupled to the first connection point by means of a first resistor. The telephone set includes a supply circuit for peripheral circuits. The supply circuit has a first output terminal coupled to the first main electrode of the first transistor and has a second transistor whose first main electrode is coupled to the second connection point and whose second main electrode is coupled to the second output terminal of the supply circuit. This circuit includes an operational amplifier whose output is coupled to the gate electrode of the second transistor. the set also includes a first voltage source connected between the first main electrode of the second transistor and a first input of the operational amplifier.

Abstract: A voice signal compression system wherein the compression threshold may be adjusted to a calibrated level. The system includes a variable gain amplifier for amplifying a voice input signal based on the application of a variable control voltage. A driver increases the power gain of the amplified input signal to provide a power-boosted output signal. In addition to applying the power-boosted output signal to an acoustic output transducer, the power-boosted output is also applied both to a peak detecting comparator and to a threshold reset timer. The comparator produces a digital output that triggers an attack/decay timing generator which produces the control voltage for the variable gain amplifier. The comparator initially is set to a high threshold state by the threshold reset timer. As the levels and peaks of the input signal increase, the comparator begins to trigger digital pulses to the attack/decay timer.

Abstract: A rocker switch is operated by the handset user to vary the impedance of a FET. The FET impedance varies in proportion to the duration of operation of the switch. The handset receiver "volume" increases or decreases in proportion to the FET impedance. An electret condensor microphone stabilizes the receiver supply voltage and provides improved transmitter linearity and low distortion.