US3691311A - Telephone user set - Google Patents
Telephone user set Download PDFInfo
- Publication number
- US3691311A US3691311A US96685A US3691311DA US3691311A US 3691311 A US3691311 A US 3691311A US 96685 A US96685 A US 96685A US 3691311D A US3691311D A US 3691311DA US 3691311 A US3691311 A US 3691311A
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- United States
- Prior art keywords
- input
- power
- output
- impedance
- signal
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- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M1/00—Substation equipment, e.g. for use by subscribers
- H04M1/60—Substation equipment, e.g. for use by subscribers including speech amplifiers
- H04M1/6008—Substation equipment, e.g. for use by subscribers including speech amplifiers in the transmitter circuit
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M9/00—Arrangements for interconnection not involving centralised switching
- H04M9/08—Two-way loud-speaking telephone systems with means for conditioning the signal, e.g. for suppressing echoes for one or both directions of traffic
- H04M9/10—Two-way loud-speaking telephone systems with means for conditioning the signal, e.g. for suppressing echoes for one or both directions of traffic with switching of direction of transmission by voice frequency
Definitions
- Carbon granule microphones of the type which are widely used in telephone equipment possess a number of disadvantages. They produce harmonic distortion, have a high internal noise level, lose sensitivity with decrease of operating current level, have a tendency to lose sensitivity with packing of the carbon granules, and the basic sensitivity of the device decreases with physical size.
- the carbon granule microphone does possess two desirable featuresthat of low cost and it provides a measure of background noise suppression because of the relative insensitivity of the carbon granules to low level sound.
- disadvantages of the carbon granule microphone research has been conducted to find a replacement.
- Dynamic or magnetic type transducers have found some use in carbon granule replacement apparatus because of the fidelity, low internal noise, and high stability of the sensitivity of these types of transducers.
- microphone apparatus has been fabricated with these types of transducers using relatively simple amplifiers. These prior art apparatus have the disadvantages that they lose sensitivity with decrease in operating current and that the substantially uniform sound sensitivity over a large dynamic range of sound levels enables background noise to produce undesirable levels of output signal compared with the levels of output signal from carbon granule microphones due to background noise.
- the telephone user set and signal conditioner apparatus of the present invention eliminates the problems of the prior art and also maintains field compatibility with like apparatus and with carbon granule microphones when operated in parallel to share current from a single current source in a telecommunications system.
- This field-compatibility is satisfied by the present signal conditioner apparatus which functions with either polarity of terminal voltage bias; operates on as little as five milliamperes of bias current and with no more than about 2.3 volts of terminal voltage at the lower current limit of operation; operate over a thirteen to one change in bias current and a-two to one change in temlinal voltage; while maintaining substantially constant operating characteristics.
- apparatus is capable of miniaturization so that it will not be obtrusive about the person of the user.
- FIG. 4 is a graph showing the output of the apparatus of FIG. 1 compared with the output of a typical carbon granule transducer for a given input sound level as a function of supply current.
- FIG. l there is shown a microphone transducer 11 connected to a preamplifier 12.
- the output of preamplifier 12 is applied through the controllable attenuator 13 to power amplifier 14 and is also applied to the circuitry 16, 17, 18, 20 and 21 which controls the signal transmission characteristics of attenuator l3.
- Signal applied to the input of power amplifier 14 is amplified to a level which is compatible with telephone communications standards (about 1 milliwatt) at a compatible impedance level of about 50 ohms.
- the amplified signal is delivered to the output terminals 81 and 83 through the polarity-steering network 15 which assures that the dc.
- operating bias voltages at terminals A, B and C for the active elements are derived from the voltages appearing on a pair of communication system conductors to which output terminals 81 and 83 may be connected.
- the input impedance of the power amplifier 14 relative to the output impedance of attenuator 13 provides compensation to provide constant amplification of the present invention despite a wide range of supplycurrent values.
- the output impedance of the attenuator 13 is selected to be higher than the normal input impedance of power amplifier 14 operating at midto high-range values of supply current.
- the bias voltage on lines 82 and 84 approaches low range values of about 1.4 volts, the input impedance of attenuator 13, thereby increasing the power conversion or transfer efficiency from attenuator 13 to amplifier 14.
- the controlled attenuator element 18 includes a common-emitter transistor stage 36 which is normally biased to a conducting state through coupling resistor 74 and the collector circuit of the preceding common emitter stage 35.
- any signal produced by the microphone transducer 11 due to background noise in the absence of voice signal is amplified by amplifier 12 but is greatly attenuated by the attenuator 13 which is connected to and controlled by the conductivity of element 18.
- the amplification of these low-level sound signals is substantially linear but at a low gain factor, as shown in FIG. 3.
- voice signals received by the microphone transducer 11 at a level above 80 to 84 db on the sound pressure scale, the associated electrical signals from the microphone transducer 11 are amplified by amplifier l2 and are applied to attenuator l3 and through attenuator 21 to the detector amplifier 16.
- the detector amplifier 16 comprises transistor 34 which is biased to conduction close to collector saturation by resistor 71.
- Detector amplifier 16 also comprises transistor 35 which is direct coupled between transistors 34 and 36 and which is biased substantially to nonconduction for input sound signals at the microphone transducer 11 which are below a threshold value, say 80 to 84 db on the scale previously described. As the signal applied to the detector amplifier 16 increases due to increasing sound level, transistor 34 becomes nonconductive and transistor 35 begins to conduct on half cycles of alternating voice signals. This causes the capacitor 75 in the time-delay network 17 to discharge and removes the forward-biasing signal at the base-emitter junction of silicon transistor 36 after a few milliseconds of delay.
- Transistor 36 is operated with zero d.c. bias on the collector, and capacitor 76, which has relatively small reactance at voice signal frequencies, blocks the dc. return through the circuitry of attenuator 13.
- the present apparatus provides substantially linear signal amplification at a higher gain factor, as shown in FIG. 2.
- a typical difference between the high and low gain factors on highand low-level input signals may be selected at about db for an input sound pressure level of about 80 to 84 db, as shown in FIG. 2, so that the over-all characteristics closely match the change in sensitivity of a carbon-granule microphone to highand low-level sound signals.
- Resistor 77 determines the 10 db value of the amplification change.
- a higher value of amplification change for example 20 db, provides even larger background noise reduction but tends to make the operation of the apparatus more critical with respect to mispositioning of the acoustic transducer near the speakers mouth.
- the signal level at the input of detector amplifier 16 which renders transistor 36 less conductive is determined by the gain of preamplifier 12 and by the bias currents of transistors 34 and 35 and thus this level may be selected by altering the values of resistors 46, 70, 71 and 72.
- the time required for the bias on transistor 36 to change sufficiently to alter the transmission characteristics at attenuator 13 when operating on a highlevel voice signal (attack time) is primarily determined by capacitor 75, resistor 74 and the transistor 35. Voice sounds associated with p and tspeech consonants are essential for proper speech transmission and thus the attack-time delay cannot exceed approximately 10 milliseconds to preclude the altering of these speech sounds.
- Sound pulses of shorter duration than the selected attack time, say 5 milliseconds, determined by delay network 17 are thus attenuated by a value equal to the magnitude of the switched gain.
- the delay network 17 maintains transistor 36 in the nonconductive state during syllable pauses in high-level voice signals so that the transmission characteristics through the attenuator 13 remain substantially unchanged during such pauses.
- This pause-delay time is conveniently longer (typically a few hundred milliseconds) than the attack or build-up time because the charging path for capacitor 75 is through the high resistance 73 whereas the discharge path is through the low resistance 74 and the conducting transistor 35.
- Feedback resistor 57 connected between the emitter of transistor 33 and the base of transistor 32 tends to stabilize the gain of the power amplifier 14 and also adjusts the output impedance level to about 50 ohms for compatible operation with other communications equipment.
- the signal output from the power amplifier l4 appears on lines 82 and 84 which are also the current supply lines for the overall circuit.
- the bridge arrangement 15 of germanium diodes 37-40 couples the signal output on lines 82 and 84 to the output terminals 81 and 83 and also provides unidirectional biasing signal on lines 82 and 84 from signal power normally available on communication conductors to which the output terminals 81, 83 may be connected with random polarity.
- Germanium diodes 37-40 are used in the bridge arrangement because the low forward-conduction voltage drop of about 0.3 volts for germanium assures that adequate biasing voltage for the transistors in the circuit will be available on lines 82 and 84 under conditions where the voltage on the communication lines connected to the output terminals may vary from about 5 volts to as low as about 2.3 volts.
- the series inductor 69 and shunt capacitor 68 comprise a transient-suppressor filter for protecting the components of the circuit from damage due to line transients.
- the unidirectional biasing signals for the active elements of the circuit are derived from the output lines 82 and 84 through the resistors 61, 63, 65 and filter capacitors 62, 64 and from the voltage drop across the forward-biased serially connected diodes 66 and 67.
- a microphone circuit for use in telephone circuits in which power is supplied to said set by the telephone lines to which it is connected power being variable between higher and lower levels, including a microphone having a substantially linear electrical signal output in response to sound vibrations applied thereto, a preamplifier stage having an output and having an input connected to receive an electrical signal from said microphone, a power amplifier stage having an input and an output, a signal attenuator having a step shiftable value and serving to connect the output of said preamplifier to the input of said power amplifier, said attenuator including means responsive to an increase in the signal level from said preamplifier to decrease the amount of attenuation applied to said signal, said power amplifier exhibiting a characteristic input impedance and said preamplifier and attenuator exhibiting a characteristic output impedance, said output impedance being being selected to have a value higher than said input impedance for input power values to said set at the higher level of those supplied on said telephone lines to thereby achieve an impedance mismatch for an applied
- said attenuator includes an electronically controllable circuit branch for step shifting the value of said attenuator from one value to another, a detector circuit for sampling the electrical signal from said preamplifier and for developing a control signal for application to said branch circuit to change the attenuation thereof to a lower value whenever the output of said preamplifier exceeds a predetermined amount so that low level background signals are attenuated and high level speech or intelligence signals are passed with reduced attenuation.
- a telephone user set as in claim 2 in which said branch circuit includes a transistor connected to form a selective conductive path in series in said branch circuit and having a control electrode connected to the output of said detector circuit for operating said transistor.
- said signal attenuator includes a transistor having zero d.c. 6135 on the collector electrode thereof with respect to the emitter electrode thereof; and said detector circuit includes a timing circuit including resistance and reactance connected to apply control signal to the base electrode of said transistor for altering the conductivity thereof after a selected time delay.
- said detector circuit means also includes an amplifier stage which produces an output signal having increasing average dc value for ac signal of increasing amplitude applied to the input thereof.
- said detector circuit includes a transistor at the input thereof, means including said circuit means for biasing said transistor close to collector saturation conduction; and the input impedance of said transistor is lower than the output impedance of an attenuator connected to the input of said transistor, and said input impedance increases to a value approaching said selected attenuator Outfit! imere o pedance with decreasing bias signal applied from said circuit means.
- a microphone circuit for use in telephone circuits in which power is supplied to said set by the telephone lines to which it is connected said power being variable between higher and lower levels, including a microphone having a substantially linear electrical signal output in response to sound vibrations applied thereto, a preamplifier stage having an output and having an input connected to receive an electrical signal from said microphone a power amplifier stage having an input and an output, an attenuator connecting the output of said preamplifier to the input of said power amplifier, said power amplifier exhibiting a characteristic input impedance and said preamplifier and attenuator exhibiting a characteristic output impedance, said output impedance being selected to have a value higher than said input impedance for input power values to said set at the higher levels of those supplied on said telephone lines to thereby achieve an impedance mismatch for an applied power level at said higher range, said power amplifier being of a type in which the input impedance shifts to higher values as the power supplied to said set drops to lower levels so that said impedance mismatch is reduced
Abstract
Description
Claims (8)
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US9668570A | 1970-12-10 | 1970-12-10 |
Publications (1)
Publication Number | Publication Date |
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US3691311A true US3691311A (en) | 1972-09-12 |
Family
ID=22258576
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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US96685A Expired - Lifetime US3691311A (en) | 1970-12-10 | 1970-12-10 | Telephone user set |
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Cited By (11)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3919490A (en) * | 1973-03-30 | 1975-11-11 | Aiphone Co Ltd | Crosstalk prevention in interphone systems and the like |
US4002852A (en) * | 1975-07-08 | 1977-01-11 | International Telephone And Telegraph Corporation | Electronic telephone network |
US4133983A (en) * | 1977-01-10 | 1979-01-09 | Northern Telecom Limited | Electronic network for telephone set |
DE2835845A1 (en) * | 1977-08-18 | 1979-03-01 | Dassault Electronique | METHOD AND DEVICE FOR CIRCULATING A TELEPHONE TRANSMISSION LINE |
US4378467A (en) * | 1980-07-01 | 1983-03-29 | Roanwell Corporation | Audio amplifier |
US4750203A (en) * | 1984-12-27 | 1988-06-07 | Thomson-Csf | Subscriber telephone set with amplified loudspeaker reception with reduction of gain in the case of an insufficient power supply |
USRE35536E (en) * | 1992-02-04 | 1997-06-17 | Acs Wireless, Inc. | Telephone headset amplifier with battery saver, receive line noise reduction, and click-free mute switching |
EP0785659A2 (en) | 1996-01-16 | 1997-07-23 | Lucent Technologies Inc. | Microphone signal expansion for background noise reduction |
US20040196984A1 (en) * | 2002-07-22 | 2004-10-07 | Dame Stephen G. | Dynamic noise suppression voice communication device |
US6807280B1 (en) | 1998-01-26 | 2004-10-19 | Delphi Technologies, Inc. | Audio signal processing circuit for reducing noise in an audio signal |
US20040216415A1 (en) * | 2003-02-04 | 2004-11-04 | Pfeiffer Henry E. | Welded wire reinforcement for modular concrete forms |
-
1970
- 1970-12-10 US US96685A patent/US3691311A/en not_active Expired - Lifetime
Cited By (14)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3919490A (en) * | 1973-03-30 | 1975-11-11 | Aiphone Co Ltd | Crosstalk prevention in interphone systems and the like |
US4002852A (en) * | 1975-07-08 | 1977-01-11 | International Telephone And Telegraph Corporation | Electronic telephone network |
FR2317832A1 (en) * | 1975-07-08 | 1977-02-04 | Int Standard Electric Corp | TELEPHONE STATION CIRCUIT |
US4133983A (en) * | 1977-01-10 | 1979-01-09 | Northern Telecom Limited | Electronic network for telephone set |
DE2835845A1 (en) * | 1977-08-18 | 1979-03-01 | Dassault Electronique | METHOD AND DEVICE FOR CIRCULATING A TELEPHONE TRANSMISSION LINE |
US4378467A (en) * | 1980-07-01 | 1983-03-29 | Roanwell Corporation | Audio amplifier |
US4750203A (en) * | 1984-12-27 | 1988-06-07 | Thomson-Csf | Subscriber telephone set with amplified loudspeaker reception with reduction of gain in the case of an insufficient power supply |
USRE35536E (en) * | 1992-02-04 | 1997-06-17 | Acs Wireless, Inc. | Telephone headset amplifier with battery saver, receive line noise reduction, and click-free mute switching |
EP0785659A2 (en) | 1996-01-16 | 1997-07-23 | Lucent Technologies Inc. | Microphone signal expansion for background noise reduction |
US5708722A (en) * | 1996-01-16 | 1998-01-13 | Lucent Technologies Inc. | Microphone expansion for background noise reduction |
US6807280B1 (en) | 1998-01-26 | 2004-10-19 | Delphi Technologies, Inc. | Audio signal processing circuit for reducing noise in an audio signal |
US20040196984A1 (en) * | 2002-07-22 | 2004-10-07 | Dame Stephen G. | Dynamic noise suppression voice communication device |
US20040216415A1 (en) * | 2003-02-04 | 2004-11-04 | Pfeiffer Henry E. | Welded wire reinforcement for modular concrete forms |
US7437858B2 (en) * | 2003-02-04 | 2008-10-21 | Reward Wall System, Inc. | Welded wire reinforcement for modular concrete forms |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
AS | Assignment |
Owner name: PLANTRONICS, INC., A CORP. OF DE., CALIFORNIA Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:PLANTRONICS, INC., A CA. CORP.;REEL/FRAME:004748/0289 Effective date: 19870610 Owner name: PLANTRONICS, INC., 337 ENCINAL STREET, P.O. BOX 18 Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:PLANTRONICS, INC., A CA. CORP.;REEL/FRAME:004748/0289 Effective date: 19870610 |
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AS | Assignment |
Owner name: CITICORP NORTH AMERICA, INC. AS AGENT Free format text: SECURITY INTEREST;ASSIGNORS:PLANTRONICS, INC., A CORP. OF DE.;PLANTRONICS FUTURECOMMS, INC.;KENTROX INDUSTRIES, INC.;AND OTHERS;REEL/FRAME:005249/0679 Effective date: 19890301 |
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STCF | Information on status: patent grant |
Free format text: PATENTED FILE - (OLD CASE ADDED FOR FILE TRACKING PURPOSES) |