CA2085047A1 - Infrared telephone with handset and base unit - Google Patents

Abstract

Abstract An infrared telephone having a first station and a second station is described. The first station is especially a telephone handset, while the second station is especially a fixedly installed remote station, for example table/wall station (base unit). According to one embodiment the first station and the second station have a single frequency oscillator, respectively, the frequency of which modulated by the electrical signals which have to be transmitted controls not only the power of the associated infrared emitter but is also fed to an associated mixing stage. The signal supplied by the associated infrared receiver is mixed with the modulated frequency of the associated frequency oscillator in the mixing stage, and the sum frequency of the received frequency and the modulated oscillator frequency generated by the mixing step is demodulated by means of a frequency demodulator, wherein the function of receipt is obtained from the resulting signal. According to a further embodiment each station works with two frequency oscillators.
Furthermore, the construction of the telephone handset and of the base unit are described.

Description

Infrared telephone with handset and base unit :
' The present invention is directed to an infrared telephone having a first station, especially a telephone handset, with microphone, loudspeaker, an infrared emitter, an infrared receiver, and a second station, especially a fixedly installed remote station, with infrared em;tter, infrared receiver and telephone network connection.

A wireless infrared telephone is known from "telcom report", 3rd year, volume 1, February 1980, pages 24 to 27. According to this infrared telephone the transmission of all signals between a handset and a fixedly installed remote station is realized by infrared light.
Luminescence diodes emit li~ht flashes not perceptible for the human eye which are reflected from the walls, from the ceiling and from the furniture of the room and thus arrive at the photodiodes in the receivers as diffused light. In the receiver the light pulses are reconverted into electrical signals. Accordingly, no visual contact has to exist between the emitter and the receiver. The transmission by means of short and not-visible light flashes results from the used principle of pulsephase modulation. According to this principle the low-frequent speech signal is detected with 9 kHz. The low-frequent information determines the phase location of the detection pulses with respect to .

208~7 one another. The PPM demodulator in the receiver obtains the low-frequent effective signal only from the phase location, i. e. from the timely distance of the pulses from the nominal location. According to the principle of time multiplex transmission the pulses of the opposite direction are introduced between the pulses of one direction of transmission. The transmission is realized according to the same principle as above. In order to avoid feedback, the own receiver is blocked when the emitter works and vice versa.

However, as far as known to the applicant9 the above-de~cribed principle has been never realized in practice.

~he invention is based on the problem to provide an infrared telephone of the indicated kind which is suitable for a multi-channel and duplex transmission and has an especially low susceptibility with respect to failure (external light). Particularly, a good transmission is to be secured with an especially low expense of components.

According to a first solution of the invention this problem is solved by an infrared telephone of the above-cited kind having the following features:
the first station and the second station have a single frequency oscillator, respectively, the frequency of which modulated by the electrical signals which have to be transmitted and which come from the microphone or from the telephone network connection not only controls the power of the associated infrared emitter but is also fed to an associated infrared mixing stage, the frequency oscillators of the first and second station have different mean frequencies, the signal supplied by the associated infrared receiver is mixed with the modulated frequency of the associated frequency oscillator in the mixing stage, and the sum frequency of the received frequency and the modulated oscillator frequency obtained by the mixture is demodulated by a frequency demodulator, and the function of receipt which is to be fed to the loudspeaker or to the telephone network is obtained from the resulting signal.

According to the invention, with the two stations (handset and remote station) communicating with one another the electrical signal supplied by the optical receiver of one station is mixed with the generated oscillation of the frequency oscillator of this ~tation (frequency of the oscillator modulated with the function of emission) in a mixing stage of the same station, respectively. Hereby, among others a sum frequency consisting of the oscillator frequency modulated with the function of emission and of the oscillator frequency modulated with the function of receipt of the other station is developed. This sum frequency is then processed, i. e. demodulated. The function of receipt is ascertained from the demodulated signal since the function of emission of this station is known. Particularly, the function of emission can be removed from the signal of the frequency demodulator in a subtracting stage so that the function of receipt is obtained in an undisturbed manner. The function of receipt is either fed to the loudspeaker or fed to the telephone network.
The frequency oscillators of both stations have different mean frequencies. With only one frequency oscillator per station not only the pulse repetition frequency for the infrared receiver can be generated but also the receiver frequency supplied by the infrared receiver can be transferred to the well-defined and fixed intermediate frequency (sum frequency). The radiation directly transmitted from the infrared emitter to the ~ . ' ' ' ~ ' ' ', ' -2 ~ 7 infrared receiver oF the same station does not result in any deterioration since the (weak) received electrical signal of the opposite station is anyhow mixed with exactly this frequency to the sum frequency. This sum frequency is then subjected to a frequency demodulation whereby a signal is generated which consists of the linear superposition of the information function to be received with the information function to be emitted since the frequency-modulated signal of the frequency oscillator of this station is used for the formation of the intermediate frequency (sum frequency).
According to a special embodiment of the invention the mean frequenciesof the frequency oscillator of both stations are variable, wherein certain well-defined frequencies (channels) are selectable.
Appropriately, the frequency oscillators of both stations have a plurality of mean frequency pairs associated with one another the frequency sum of which has the same constant well-defined value, respectively. In other words, a station of an inventive telephone can only communicate with such another station whose oscillator mean frequency can be added with the oscillator mean frequency of the associated station exactly to this constant well-defined value.
Accordingly, by the selection of the corresponding mean frequencies of the corresponding stations it can be determined which station is to communicate with which other device.

In detail, it is preferable to define two groups of stations. So, the stations of the telephones are to be preferably divided into two groups I and II exactly in such a manner that always a station of group I
communicates with a station of group II. "To communicate" means that electrical signals which represent an information which is to to be transmitted are transmitted between both stations simultaneously in both , 2 0 ~ 7 directions. Then, frequency associations with regard to freely determinable channel designations can be selected exactly in a manner that a station of group I communicates exactly then and only then with a station of group II if the same channel designation is adjusted on both stations. In other words, the same co-ordination between the mean frequency of the frequency oscillator and the channel designation has to be valid for all stations of one group.

However, according to the invention the co-ordination of channels and mean frequencies is not done arbitrarily but rather in such a manner that the arithmetical sum of the frequencies of groups I and II, which each belong to a channel, always results in a constant and channnel-independent sum.

The sum frequency at the mixing stage is then a known and well-defined frequency if the same channel selection is done at the communicating stations.

Accordingly, during the emission each of the stations can simultaneously receive and evaluate the emissions of another similar station. If a plurality of stations is operated side by side in the infrared working range, a defined station of the plurality of stations can be contacted by means of the selection of the mean frequencyg provided that the device which is to be contacted is sensitive with regard to this selected mean frequency with respect to its receiving unit, especially with regard to the electrical filtering.

The mean frequency of the frequency oscillators is preferably stabilized by a phase-locked-loop control circuit. Such a control circuit allows the very precise maintenance of a predetermined mean frequency while 2~$~ 7 modifications of the mean t`requency of short duration, as necessary for the frequency modulation, are possible. Furthermore, the use of a phase-locked-loop control circuit allows the simple adjustment of the mean frequency in a certain frequency pattern (channel selection).
Accordingly, with the above-described inventive solution on the receiver side it is not worked in the base band, but in the intermediate frequency band (also designated sum frequency above). With respect to the base band the advantage of a smaller susceptibility with regard to failure (external light) results. Furthermore, a multi-channel transmission and a complete duplex transmission (simultaneously in both directions) can be achieved in a simple manner, which would be possible only by means of very comprehensive methods (for example time slot methods) if it was worked in the base band.

According to a second solution of the invention the above-cited prob1em is solved with an infrared telephone of the above-described kind by the feature that the first and second station have a first frequency oscillator, respectively, the frequency of which modulated by the electrical signals which are to be transmitted controls the power of the associated infrared emitter, and a second frequency oscillator with mixer for the conversion of the electrical signal receîved by the infrared receiver into the intermediate frequency band.

Accordingly, also with this solution it is worked in the intermediate frequency band on the receiver side, whereby the above-cited advantages are also obtained. According to this solution a second oscillator on the receiver side is necessary for each station, whereby the expense becomes higher than with the above-described first solution. However, an additional loop between the emitter side and the receiver side of the ; ' - .:

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sdme station is no more necessary. The second solution of the invention is especially suited for cases according to which in the telephone connection network only a two-wire line is available, while with four-wire lines both solutions have good results.

According to the second solution of the invention of above an influencing of the receiver side of one station by the own emitter side is preferably avoided by tuning the frequencies of the emitter oscillator and of the receiver oscillator of the same station such that, upon the presence of a function of receipt, the frequency of the emi~ter oscillator is mixed exactly to the intermediate frequency in the mixer of the receiver. If no function of receipt is present, no intermediate frequency is obtained. By this, it is avoided that disturbing combination frequencies are generated by the own emitter oscillator.
As with the above-cited embodiment the carrier frequencies of the frequency oscillators are stabilized by a phase-locked-loop control circuit. By this, the advantages already cited above are obtained.

Preferably, luminescence diodes are used as infrared emitter with a wavelength of 750 nm to 1,000 nm, since these diodes have an especially high efficiency on account of the component's technology and a high flow of radiation is attained accordingly~ A high optical output is favourable with respect to the possible working range of the transmission. The wavelength has no influence on the function;
accordingly, it can be selected in a free manner.

With regard to a large transmission range it is furthermore preferred to control the current flow through the infrared emitter in a sinus-halfwa~e-shaped manner. In other words, the frequency-modulated 8 2~5Q~

and s;nus-shaped oscillation generated by the frequency oscillator controls directly the current flow ~hrough the luminescence diodes in a manner that the current through the diodes is proportional to the momentary value of the positive sinus-halfwave of the frequency oscillator during the positive sinus-halfwave. During the negative sinus-halfwave of the oscillation of the frequency oscillator no current is to flow through the luminescence diodes.

By this kind of diode current control the basic wave portion of the frequency-modulated oscillation in the spectrum of the emitted optical output has a maximum with respect to the signal efficiency of the diodes.

It can be advantageous to use a plurality of infrared receivers in a station since a working range enlargement is obtained hereby.
Photobarrier receivers tphotodiodes) are especially suited as infrared receivers. Of course, the infrared receivers are sensitive ~ith respect to the radiation emitted by the infrared emitters.

Photodiodes with large photosensitive areas are favourable since more optical radiation is received therefrom. An increase of the photosensitive area in the sense of a large transmission range is possible by the use of a plurality of parallel photodiodes.

According to an especially preferred embodiment of the invention the first station is a telephone handset and the second station is a fixedly installed table/wall station. The handset has a microphone, a lou~speaker (receiver shell), a chargeable battery as current source, an infrared emitter and an infrared receiver as well as the corresponding electronics which is described in detail in the following.

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2~5~7 The stationary remote station has also an infrared emitter, an infrared receiver and substantially identical electronics. It is further associated with a battery charging station. Apart from this, the remote station can have a conventional construction according to the known S telephones. It is either always in a switched-on condition oris switched-on ar switched-off by contact with the handset (cradle switch).
If the handset is on the stationary station, the battery of the same is charged. The current can be switched off by means of the corresponding charging current or by means of a separate switch in order to save energy This presupposes that the remote station and a conventional telephone are not separated from one another. If they are separated, the charging stations and the customary telephone means are associated with the conventional apparatus.

Of course, the stations are further provided with structural or circuit components in order to fulfill the customary telephone functions, for example with dial discs, dial keys etc.. Accordingly, in addition to speech signals additional control signals and dial signals have to be transmitted by the infrared telephone. Also such signals can be transmitted in an unrestricted manner as the speech signals.

According to an especially preferred embodiment the inventive infrared telephone has a compander (compressor/expander) for improving the signal-noise distance. Preferably, a microphone amplifier with limiter, a band-pass filter and a compressor are located behind the microphone.
The modulation voltage at the output of the compressor is preferably delayed by 60 ,usec. An expander anda band-pass filter are located behind the frequency demodulator.

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In order to save energy, the inventive infrared telephone preferably includes a rectifier speech control stage which switches off the infrared emitter in the speak pauses. According to a further alternative embodiment the infrared telephone has a pulsewidth control stage for modifying the emitter output. Also by this measure energy can be saved.

As regards the pulsewidth control stage, the invention preferably provides two variants. According to a first variant the pulsewidth control stage compares the signal-noise ratio on the receiver side of the first station with a threshold, supplies an additional signal if the threshold is fallen below or exceeded, transfers the additional signal to the second station by the infrared emitter and the infrared receiver, detectsthe additional signal there and varies the pulse width of the associated emission endstage if the additional signal is present or not present. If the pulsewidth is varied in the direction to narrower pulses, the emission power can be reduced, for example, to a value of 30 %. Accordingly, this variant of the invention enables an emission power regulation in response to the distance.

According to a second inventive variant of the pulsewidth regulation orpulsewidth control the pulsewidth control stage measures the mean value of the diode current, compares this mean value with a preset mean value and, upon deviation, brings the measured value to the preset mean value by variation of the pulse/pause ratio. By this, the current consumption can be reduced and an additional diode protection and endstage protection can be obtained.

Of course, also combinations of both pulsewidth regulation systems are possible.

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It has been pointed out already above that not only sound signals but also control/dial signals, i. e. any special functions, can be transmitted through the infrared distance by means of the inventive infrared telephone. The controltdial signals (special functions)7 for example, can stem from a keyboard andtor a switch of the first or second station. The corresponding signals are processed and fed to the associated emission oscillator for emitting. On the receiver side they are recovered aFter demodulation by corresponding processing.
Preferably, a processor with FSK modem (frequency shift keying modem) as one variant is used for the processing. According to another variant, for example, a special sound combination is generated in response to the row/column of a keyboard matrix by means of a DTMF generator (dual tone multi frequency generator), with which the corresponding emission oscillator is provided. After demodulation the reconversion is carried out by means of a DTMF receiver.

A case of application for the transmission of such special functions is a case according to which alone the telephone handset is provided with a dial keyboard. This dial keyboard can be also associated with further control functions, for example the volume adjustment of the loudspeaker at the handset or the base unit.

Furthermore, the present invention is directed to a handset for a telephone consisting of a base unit and a handset, especially of the above-described kind, said handset comprising an elongated housing with a speaking range at one end portion and a hearing range at the opposite end portion of the lower side of the housing, a microphone associated with the speaking range, a loudspeaker associated with the hearing range, emission means, receiver means and an electronic signal processing unit within the housing as well as optionally a keyboard at an operating surface of the housing.

According to d conventional telephone the handset is connected to the base unit by means of a telephone line. According to a wireless telephone no line connection between the handset and the base unit exists. A telephone handset which is suited herefor has approximately the above-described construction.

It is an object of the invention to provide a handset for a telephone working with infrared transmission between the base unit and the handset which can be operated in an especially comfortable and simple manner and which secures an especially good transmission quality between handset and base unit.

According to the invention this object is achieved with a handset of the above-cited kind which is characterized by the feature that the part of the upper portion of the housing which is associated with the speaking range is made of a transparent or translucent material and Forms an infrared window and includes an infrared emission and receiver unit having a plurality of infrared emission diodes and infrared receiver diodes, wherein the upper side, the front side and the lateral surfaces of the upper portion of the housing provide infrared receiving and/or infrared emitting surfaces~ respectively.

The present invention is based on the idea to accomodate the infrared emission/receiver unit in the lower part of the housing (belonging to the speaking range) and to form this portion of the housing as corresponding infrared window. The speaking range remains on the lower side of the handset, wherein this portion of the housing is made of a customary opaque material in which corresponding microphone openings are , ~D~5~ 7 provided. However, the associated upper portion of the housing, i. e.
the upper side, front side and the two lateral surfaces, consists of a material which is transparent with regard to infrared radiation, i. e.
of a transparent or translucent material. In this portion the infrared emission and receiver unit is disposed. This unit has a plurality of infrared emission and receiver diodes, wherein the diodes are aligned such that preferably each of the four sides of the upper portion of the housing has associated corresponding emission and receiver diodes.
According to a special embodiment only receiver diodes are disposed at the upper side and only emitter diodes are disposed at the front side, while the two lateral surfaces have emitter and receiver diodes, respectively.

Preferably, also the electronic signal processing unit is disposed within the upper portion of the housing which has disposed the emission/receiving means therein. As mentioned above, on the lower side of this portion the microphone of the handset with corresponding speaking range is located. The whole unit can be formed as plug-in module which is connected with the remaining housing of the handset by plugging.

The part of the upper portion of the housing forming the infrared window is preferably shaped approximately rectangularly in a horizontal section. Advantageously, this part merges continuously into the remaining portion of the housing at the two lateral surfaces and at the lower side so that on the whole a compact and flat housing results which ;s approximately rectangular in cross-section. Preferably, a step is provided between the part of the upper portion of the housing forming the infrared window and the remaining part of the upper portion. This step extends upwardly from the infrared window. It is the object of the ~0~5~7 step to put off the infrared window from the remaining portion of the housing and to avoid tha~the user of the handset covers the in~rared w;ndow with his hand during the use of the telephone. Accordingly, this step is to prevent that the user graspsthe hand~ ~ t~ehousing portion forming the infrared window.

By arranging the infrared window at the lower portion of the handset adjacent to the speaking range it is furthermore prevented that the infrared window is covered by the hair of the user, which is of special importance for female users.

Apart from the above-mentioned step the infrared window is completely integrated into the housing, i. e. the lateral surfaces of the infrared window merge continuously into the lateral surfaces of the remaining housing. Accordingly, the infrared window has appropriately the same width as the remaining housing, however, has a smaller height as the same on account of the step.

The keyboard, i. e. the dial keys and the special keys, is disposed on the upper side of the upper portion of the housing. This location has the advantage that one can operate the keyboard from above when the handset has been deposited on a table etc.. In this connection is has to be noted that the hearing range located at the upper end of the lower side is appropriately formed such that the handset can be safely 2S deposited on a plane surface without tilting or sliding. Preferably, this is achieved by forming the hearing range at least partly plane so that a deposition surface results in cooperation with the terminal edge at the speaking range. Since the housing has preferably a convex shape in longitudinal direction, the hearing range forms preferably a portion projecting two-dimensionally from the housing in order to provide thé

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corresponding deposition surface.

The keyboard disposed on the upper side of the upper portion of the housing is preferably located in the central portion of the handset in the longitudinal direction of the same, wherein the keyboard is disposed adjacent to the step if such a step is located besides the infrared window. This location appears to be most favourable for the operation of the keyboard.

According to a special embodiment of the invention the handset has a second microphone which is associated to a second speaking range (free speaking range) on the upper side of the upper portion of the housing adjacent to the infrared window. This second speaking range enables free speaking with deposited handset. For this, the handset has not to be held manually in any manner. The second speaking range can be reached well by the user, especially in a sitting position.

For switching on the free speak;ng means, according to an improvement the handset has a contact switch within the range of the terminal edge adjacent to the first speaking range. If the handset islaid down, the contact switch is actuated and switches on the free speaking means. In other words, according to this embodiment it is always switched over to free speaking when the handset islaid down. Accordingly, upon having laid down the handset, the user can do other works, for example writings, and simultaneously use the telephone without having to hold the handset manually. The operation of the handset is substantially simplified by this.

According to the above-described embodiment the lower side o~ the handset is formed substantially smoothly, apart from the lug of the 2 ~ 7 hearing range. The microphone of the speaking range is disposed within the housing, whPrein the housing preferably includes one or more speaking apertures at this point. According to another embodiment of the invention the microphone accociated with the speaking range is disposed within a nose-like housing portion projecting from the lower side of the housing, wherein this nose-like housing portion is preferably triangularly formed in longitudinal section and wherein a shorter and more inclined side, which has at least one speaking aperture, faces the infrared window. Accordingly, with this embcdiment the at least one speaking aperture is located at a lug which projects relatively steeply from the lower side of the handset so that especially favourable sound reception properties are achieved. The nose-like housing portion is located approximately centrally at the lower side of the handset, seen in transverse direction, and preferably immediately adjacent to the infrared window, seen in longitudinal direction of the handset, wherein the nose-like portion preferably projects onto the infrared window. The at least one speaking aperture is appropriately located within a groove-like depression which extends approximately centrally in the shorter and more inclined side in longitudinal direction of the same. By this feature the sound reception properties are further improved.

An alternative embodiment with regard to the lug of the hearing range proposes that the lug is formed as square receiver cap projecting from the lower side of the handset and having lateral surfaces which extend about vertically with respect to the lower side of the handset.
According to this embodiment the receiver lug does not have a deposition surface inclined with respect to the lower side of the handset.

Dependent on the design of the handset three main embodiments result for the same. According to the first embodiment the handset has not a .
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~ 0 ~ 7 keyboard, i. e. it is only a wireless reoei~er.The keyboard (dial keys and function keys) is provided at the base unit alone. This embodiment can be varied such that the handset has a single key for switching on and switching off and optionally a key for dial repetition.
According to a second more comfortable embodiment not only the handset but also the base unit have an own keyboard, wherein the base unit is optionally provided with a display. Furthermore, the handset is provided with corresponding free speaking means, as mentioned above.
According to a third embodiment the handset is formed as completely mobile apparatus and has a corresponding keyboard. The base unit has only the infrared part, the charging means for the handset and functions as terminal for the telephone network. Optionally, it is provided with a call-signalling.

Furthermore, the present invention is directed to a base unit (remote station) for an infrared telephone, especially of the above-described kind, and fora handset for an infrared telephone, also especially according to the above-described kind. ~ccording to the invention this base unit is characterized in that it comprises an infrared window of transparent or translucent material on the upper side of its housiny in the range of the deposition surface for the handset. This location of the infrared window has the advantage that this position cannot be covered by any items, as paper etc., on account of the deposited handset so that the infrared transmission cannot be deteriorated hereby. A
location of the window in the remaining portion of the housing would have the disadvantage that the danger of covering would be especially great.

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2 ~ 7 Furthermore, the deposition surface of the base unit fnr thP h~ndset has preferably a depression for the lug of the hearing range and for the nose-like housing portion of the handset. By this, a fixed position of the handset on the base unit is secured. Appropriately, the depression for the lug of the hearing range is formed by a holder which projects laterally from the housing and is open in the middle. Accordingly, with this embodiment the handset projects beyond the real housing in its condition deposited on the base unit, wherein the lug of the hearing range is located within the above-mentioned holder which is centrally open.

According to a further embodiment of the invention the deposition surface of the base unit for the handset has three contacts of which two are formed as charge contacts and one is formed as identifying contact for the deposited condition of the handset independent of the charge current. In the deposited condition of the handset the two charge contacts cause a charging of the secondary batteries of the handset. If the handset is removed, the charge process is stopped and the handset is switched on. If the handset is deposited, the same is switched off, and it is started with the charging process. The third contact forms an identifying contact for the deposited condition of the handset. That is, if the handset would be switched off alone by an interruption of the charge current by means of the charge contacts, the case might occur that, upon an interruption of the current supply to the base unit and an ~.
interruption of the charge current resulting herefrom, it is simulated that the handset was removed so that it would be taken in operation hereby. The third contact avoids this andassures that the handset is not taken into operation even upon an interruption of the charge current in the deposited condition.

~, ` ` ' 2 0 ~ 7 Optionally, a mechanical cradle contact can be disposed in the depression for the nose-like housing portion ~microphone) of the handset. Such a contact releases or interrupts the line to the telephone network as a comparable contact of a conventional telephone. If a separate off-key is provided at the handset, a special switch (relay) has to be provided in the base unit in order to interrupt the line to the telephone network when the handset is switched off.

In the following the invention is discussed in detail by means of examples in connection with the drawing. Of the drawing figure 1 shows the schematic construction of an inventive infrared telephone;

15 figure 2 shows a block circuit diagram of the handset of the infrared telephone of figure 1 according to a first variant of the invention;

figure 3 shows a rough circuit diagram of the handset of the infrared telephone of figure 1 according to a second variant of the present invention;

figure 4 shows a rough circuit diagram of the associated base unit according to the second variant of the invention;
figure 5 shows a detailed block circuit diagram of the handset of the infrared telephone according to the second variant of the invention;

30 figure 6 is a block circuit diagram for the illustration of the pulsewidth control in response to the signal-noise rat;o;

figure 7 is a diagram for the illustration of the variation of ~he pulse/pause ratio in response to the mear, value of the diode currenti figure 8 shows a three-dimensional representation of an embodiment of a handset;

0 figure 9 shows the handset of figure 8 with removed cover of the infrared window;

figure 10 shows a side view of a modified embodiment of a handset;
5 figure 11 shows a top view of the handset of figure 10 with removed cover;

figure 12 shows the microphone nose of the embodiment of figures 10 and 11 in a top view and a side view;

figire 13 is a top view of an embodiment of a base unit; and figure 14 is a side view of the base unit according to figure 13.

Figure 1 shows the schematic construction of an infrared telephone.
According to the special embodiment which is shown here the telephone includes a wireless handset 1 which offers a corresponding mobility to the user. The user can freely move with the handset in a room. The corresponding advantages of an infrared transmission in contrast to a telephone working with radio transmission, as for example better security with respect to wire tapping, small mutual influencing, not subject to authorization by the telecommunication administration, are known.

S According to this embodiment the handset 1 is formed as a usual telephone handset and includes a receiver cap with a loudspeaker 4 and a speaking range with a microphone 5. The electronics disposed within the interior of the handset is discussed later in detail. As components of the electronics are only shown a FM receiver 6 with mixing stage and demodulation stage and low frequency amplifier and expander~ which is connected to an infrared receiver 12 in the form of at least one photodiode and to the loudspeaker 4, a modulator (PLL-stabilized oscillator) 7 with compressor and speech control stage which is connected to the microphone 5, and an in~rared emitter 8 having an emitter endstage and at least one luminescence diode 13. Furthermore, the handset 1 includes an off/on-switch 13, a battery 9 and corresponding battery charge contacts 11.

Moreover, the infrared telephone shown in figure 1 includes a fixedly installed remote station 2 designed as table station or wall station.
Apart from the microphone S and the loudspeaker 4 the remote station 2 has a corresponding construction as the handset and includes also three electronical main components, namely a FM receiver 14 with mixing stage, demodulation stage, expander and low frequency amplifier, a modulator (oscillator) 15 with compressor and speech control stage and an infrared emitter 16 with emitter endstage and at least one luminescence diode 18.
The FM receiver is connected to at least one photodiode 17.

Furthermore, the telephone includes a conventional telephone set 3 which is connected to the telephone network. As shown at 19, the output o~ the , , . :

2 ~ 7 component 14 of the remote station is connected -to the microphone of the conventional telephone set, while the output of the component 16 is connected to the receiver of the same, as shown at 20. Moreover, a cradle switch 21 is disposed between the remote staion 2 and the conventional telephone set 3. Finally, battery charge contacts 22 are provided at the telephone set 3.

Accordingly, speech signals introduced into the microphone 5 of the handset 1 are output through the components 7 and 8 and the at least one lQ luminescence diode 13 as infrared radiation and are received by the at least one photodiode 17 of the stationary base station 2. After corresponding processing in stage 14 the signals are supplied as electrical signals to the conventional telephone set. Signals arriving from the same are supplied as infrared signals to the at least one photodiode 12 of the handset 1 through the infrared emitter of the remote station 2 and the associated at least one luminescence diode 18.
After corresponding processing in stage 6 they are supplied as electrical signals to the loudspeaker 4.

The block circuit diagram of figure 1 shows the schematic design of the electronical circuit of the handset 1. Speech signals are converted to electrical signals by the microphone 5 and then ~lied to a microphone amplifier and limiter 44. The microphone amplifier lifts the low microphone signal voltages to a level necessary for further processing.
The limiter prevents over-controlling of the following stages. In a following band-pass filter 43 the frequency range is restricted to a range which is necessary for a speech transmission and in the interest of a minimum band width demand.

Thereafter, the signals are supplied to a compressor 38 of a compander 2 ~

system lcompressor/expander). In the compressor the original dynamic scope is compressed to the half. A frequency oscillator 4 is frequency-modulated by the signal from the compressor 38. This oscillator is stabilized with respect to its mean frequency by a phase-locked-loop control circuit in a known manner. The typical frequency range reaches up to about 20 MHz. A frequency pair (handset/stationary station) is away from one another by the intermediate frequency of 450 k~lz (for example 800 k~z/1255 kHz). The channel distance is 20 - 50 kH~.
The signals supplied from the oscillator 36 are supplied to the infrared emitter 13 consisting of at least one luminescence diode through a pulsewidth control stage 41 and an emitter endstage 42 (amplifier stage with switch-off possiblity).
A rectifier speech control stage 39 is used as measure for the reduction of the current consumption. It is the object of this stage to switch off the emitter in the speak pauses. For this, the modulation signal is rectified and supplied to a decision stage (comparator). If the threshold is exceeded, the emitter is switched on. If the thresho1d is fallen below, the emitter is switched olff again after about 0.5 sec.

The used pulsewidth control stage 41 serves for the modification of the emitter output power. The basic idea consists in reducing the power of emission to a minimum necessary value from the momentary field strength at the handset (field strength output). If, for example, the user is in the vicinity of the stationary station, only a lower power of emission ;s necessary in order to guarantee the transmission. Preferably, a modification of the pulse-pause ratio is carried out for the reduction of the power of emission.

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' ~ ' ' ' ' I ' 2~$~7 The power-modulated radiation impinging on the at least one photodiode of the infrared receiver 17 of the remote station 2 generates there an electrical signal current having the same frequency with which the optical emitter of the handset is pulsed.
.
Now, it is emanated from the fact that a power-modulated infrared radiation from the remote station is transmitted to the handset and is received there by means of the at least one photodiode of the infrared receiver 12. The signal supplied by the infrared receiver 12 is supplied to a FM receiver 30 with mixing stage and demodulator, optionally through a band filter. When doing this the signal is mixed in the mixing stage with the local frequency (with the frequency modulated by the function of emission of the handset) of the associated frequency oscillator 36. For example, the mixing stage can be formed as multiplying member.

The sum frequency in the mixer resulting from the local oscillator frequency (with the function of emission of the handset modulated frequency) and from the received frequency which is supplied by the infrared receiver 12 is supplied to a subtracting stage 31, optionally through a filter and a frequency duplicator 6. The function of receipt is obtained by subtracting the function of emission from the signal of the demodulator 30.

Accordingly, the handset and the stationary station have only one single frequency oscillator. Both devices are distinguished by the frequency of the respective frèquency oscillator. The frequencies are always selected such that the sum of the frequencies is a constant well-defined value.
Frequency pairs of any number can be found which fulfill this , 2~g~7 requirement.

If frequency pairs determined in such a manner are adjusted in the frequency oscillators, it is possible in a simple manner with the signal of the respective frequency oscillator not only to control the corresponding emitter but also to mix the signal of the remote station in the mixer exactly to the sum frequency.

As already mentioned, the modulation voltage at the output of the compressor 38 with which -the PLL oscillator 36 is modulated has to be removed again from the signal demodulated in the FM receiver 30. This is done by a suitable superposition of the demodulated signal of the receiver 30 with the modulation signal in the above-mentioned subtracting stage 31 which is delayed by the running period of the receiver. The modulation voltage at the output of the compressor 36 is delayed by 60 ~sec through a suitable delay section 37.

The function of receipt received in the subtracting stage 31 is supplied to the loudspeaker 4 through an expander 32 and a band-pass filter 33 as well as an amplifier 34. The expander 32 is a reversal of the compressor 38. The compressed dynamic scope is again expanded to the original scope.

Figure 3 shows a rough circuit diagram of the handset 1 of the infrared telephone of fiyure 1 accordiny to a second variant of the present invention. Figure 4 shows a rough circuit diagram of the corresponding base unit 2 according to the second variant of the invention.

In detail! the handset includes a microphone 50 by means of which speech signals are converted into electrical signals. A preamplifier 51 is ~ ' ' ''' ~ '- ~
''; ' '' '~ " ' .

located behind the microphone 50. The amplified el-ectrical signals are supplied to a modulator 52 which serves for the modu1ation of the carrier frequency of a frequency oscillator 53 -the carrier frequency of which being stabilized by means of a PLL control circuit. The carrier frequency of the frequency oscillator 53 which is modulated with the function of emission is supplied to an emitter endstage 54 and fed from the same to an infrared emitter 55 which can consist of at least one luminescence diode as with the first embodiment. The corresponding si~nals are emitted from the infrared emitter 55 as infrared radiation.
The infrared radiation emitted from the remote station ~base unit) shown in figure 4 is received by the infrared receiver 56 and is converted into electrical signals. These signals are supplied to a mixer 58 through a preamplifier 57 and are there mixed with the carrier frequency of a frequency oscillator 59 stabilized by means of a PLL control circuit. The generated combination frequency lying in the intermediate frequency band is then fed to an intermediate frequency amplifier 60 and demodulated by a demodulator 61. The function of receipt resulting herefrom is supplied to a low frequency endstage 62 and from there to a loudspeaker 63.

The carrier frequency of the oscillator 53 on the emitter side is dimensioned such that the own emitter does not disturb the reception. In other words, if a function of receipt is present on the receiver side, this function of receipt is mixed with the carrier frequency of the oscillator 59 on the receiver side or with the frequency of the oscillator 53 on the emitter side always to the intermediate frequency so that no disturbing combination products occur. However, if no function of receipt is present, no corresponding intermediate frequency is obtained. For example, one works with an intermediate frequency of , , ' ' . ~

:, . .

0.455 MHz and with a carrier frequency of the receiver oscillator 59 o~
0.545 MHz. The frequency of the emitter oscillator is 1.~55 MHz. The reception frequency is 1 MHz.

Figure 4 shows the schematic construction of the corresponding base unit. The construction is similar to the handset and comprises an infrared receiver 64 behind which a preamplifier 65 is located. This is a selective preamplifier as with the handset. The signals are brought into the intermediate band by means of a mixer 66 with associated PLL
stabilized oscillator 67 and are supplied to a demodulator 69 through an int~rmediate frequency amplifier 68, where they are demodulated.
Thereafter, the signals are supplied to a usual telephone circuit 70 with connection to the telephone network. Conversely, signals supplied through the telephone network and the telephone circuit 70 are used for the modulation of the carrier fre~uency of a PLL stabilized oscillator 72 (modulator 71). The frequency-modulated signals are then supplied to an emitter endstage 73 and from there to an infrared emitter 74~

According to the shown embodiment not only sound signals but also dial/control signals are transmitted through the infrared line. The handset has a suitable dial keyboard 75 by means of which dial signals, but also control signals, for example high-low-position, can be supplied to the base unit. These dial/control signals are processed either by means of a DTMF generator 76 whichallocates a certain sound combination to each key of the keyboard matrix or by means of a processor 78 and a FSK modem 77 and are supplied additionally as function of emission to the PLL oscillator 53 of the emitter side of the handset. After demodulation in the base unit the corresponding signals are again supplied to the telephone circuit 70 by means of a DTMF receiver 79 or a FS~ modem 80 and a processor 81 or, if the signals are control signals :

2 ~

for the base unit, are fed there to their corresponding use, for example for ~he volume regulation of the loudspeaker of the base unit in the free speaking mode.

Figure 5 shows a detailed block circuit diagram of the handset of figure 3. On the emitter side the signals coming from a microphone 50 are fed to a voltage-controlled oscillator 53 with PLL control circuit 96 through a microphone amplifier 91, a 2:1 compressor 92, a preemphase component 93, a limiter 94 and a deep-pass fil~e~ ofi t~ird order. The frequency-modulated signals are supplied to an infrared emitter 55 consisting of twelve emitter diodes through an emitter endstage 54.

On the receiver side the handset has an infraredreceiver.56 (diodes) which is coupled to a receiver component 82. The receiver component includes a preamplifier, mixer, intermediate amplifier and demodulator.
The mixer is supplied by a voltage-controlled frequency oscillator 5 which is associated with a PLL control circuit 97 which comprises an amplifier (decoupling), divider l/M, phase comparator and deep-pass filter. The PLL control circuit 96 on the emitter side has also a divider l/N, a phase comparator and a deep-pass filter. A pre-divider 99 is associated with both phase comparators as common reference. This pre-divider is connected to an oscillator 98.

All the components of the handset apart from the low frequency endstage (receiver) and the emitter endstage are permanently in operation in order to save transient effects. Both endstages are switched on and switched off by means of condition logics 88 in response to the lift-off and restored condition of the handset. The corresponding supply voltage, for example 4 V, is supplied to the endstages by means of a chargeable battery 86 and corresponding charge contacts 87.

The signals received and demodulated by the receiver component 82 are fed to the loudspeaker 63 within the low frequency band through a deep-pass filter of third order 83, a deemphase component 84, an expander 1/2 85 and the low frequency ends~age 62.

Figure 6 sho~s schematicly a block diagram for carrying out the above-mentioned pulswidth control in response to the signal/noise ratio. As mentioned above, the base unit receives the transmitted signals by means of the infrared receiver 64 and converts the same into electrical signals. The signal/noise ratio is determined by means of a switch threshold detector 110. If the signal/noise ratio is above a threshold, an additional signal having a frequency of 6.5 kHz is introduced by means of a stage 111. This additional signal is also led through the components 72 and 73 and is also e~tt~dthrough the infrared emitter 74 of the base unit. The signals are received by means of the infrared receiver 56 of the handset and the receiver 82. Another switch threshold detector 112 detects the presence of the additional signal (6.5 kHz). If the additional signal is present, a signal smoothing is carried out by means of an integrator 113 and a pulsewidth control of the emitter endstage 54 is carried out by means of the pulsewidth control stage 114, i. e. the pulsewidth is modified in the direction to narrower pulses, so that the power of emission is controlled down, for example to 30 %.
Accordingly, a regulation of the power of emission can be carried out in response to the distance. In figure 5 the above-described pulsewidth reguiation or control is designated with 90 in general.

According to another pulsewidth control, which is generally designated with 89 in figure 5, the mean value of the diode current is measured, compared with a preset mean value and brought to the preset mean value : . .

by variation of the pulse/pause ratio. By this, -the current consumption can be substantially reduced, and a corresponding diode protection and endstage protection is obtained. The scheme of this pulsewidth control is shown in figure 7.

The handset 200 shown in the figures 8 and 9 has an elongated, slightly curved housing 202 which is substantially rectangularly formed in cross-section. The housing 202 has an upper portion 203 and a lower portion 204 which are set one above the other and are connected to one another, for example by means of appropriate screw connections and a surrounding sealing.These screw connections are not shown.

According to the shown embodiment the lower portion 204 of the housing is longer than the upper portion 203. In its part projecting with respect to the upper portion of the housing it has a so-called infrared window 205 which consists of transparent or translucent material. This infrared window 205 comprises the upper side, front side and the two lateral surfaces of the corresponding lower portion of the housing. As the remaining housing the lower side is made of opaque material, for example a suitable plastic material.

A speaking range 207 is located on the lower side 206 of the lower portion 20~ o~ the housing within the end portion adjacent to the infrared window 205. Appropriate speaking apertures (not shown) are located within the corresponding housing wall of the speaking range. A
usual microphone is associated with these speaking apertures. A hearing range 208 is located at the opposite endportion of the lower side 206.
The hearing range is formed as projecting portion with respect to the lower side. Appropriate hearing apertures (not shown) are provided in this hearing range. A corresponding loudspeaker in the interior of the 2 ~ 7 housing is associated with these hearing apertures. the projecting hearing range 208 is formed plane on its lower side so that a deposition surface for the handset is formed which cooperates with the opposite endedge and the infrared window.
s As mentioned above, the upper portion 203 of the housing terminates in front o~ the infrared window 205 and falls off to the same with a step 212. A suitable keyboard 209 having dial keys and special keys is located on the upper side of the upper portion 203 in the vicinity of this step. A free speaking range is provided between the keyboard 209 and the step 212. Here, the free speaking range is shown by a suitable microphone opening 210.

Alternatively, the keyboard can be provided in the lower side of the handset.

Figure 10 shows the exact construction of the housing part forming the infrared window 205. Two printed boards 213, 214 located one above the other are disposed within the infrared window 205 and having located thereon corresponding receiver diodes 216 and emitter diodes 215.
According to this embodiment, on the upper board 214 only receiver diodes 216 are located which are disposed in a balcony-like manner. On the lower board 213 not only receiver diodes 216 but also emitter diodes 215 are located. The arrangement is such that not on1y receiver diodes but also emitter diodes are disposed towards the lateral surfaces, while only em;tter diodes are disposed toward the front side. Accordingly, in this arrangement the upper side of the infrared window 205 forms an infrared receiver surface while the front side is an infrared emitter surface. The two lateral surfaces are not only receiver surfaces but also emitter surfaces.

r `

The necessary electronical unit (not shown) can be disposed either in the housing part forming the infrared window,too~ or in the other housing part. Of course, this unit processes not only the electrical signals supplied by the receiver diodes and supplies the same to the loudspeaker but also processes the electrical signals supplied by both microphones and supplies the same to the emitter diodes. Furthermore, the electronical unit processes the signals input by means of the keyboard and supplies the same to -the emitter/receiver part.

A contact switch 211 is located at the front lower edge of the housing adjacent to the speaking range 207. When restoring the handset on a table etc. this contact switch switches on a free speaking device with the second microphone.

Figures 10 to 12 show another embodiment of a handset which is slightly modified with regard to that of figures i3 and 9. In the following description of this embodiment only features are mentioned which are different from the embodiment of figures 8 and 9.

As shown in figures 10 to 12, the handset has a nose-like housing portion 301 projecting from the lower side of the housing. The microphone 300 associated with the speaking range is disposed within this housing portion 301. The nose-like housing portion 301 is shown in detail in figure 12. It is substantially triangularly formed in longitudinal section and has a side 307 with smaller inclination and a side 303 which is more inclined and faces in the direction to the infrared window 205 of the handset. Speaking apertures 302 for the microphone (schematicly shown at 300 as microphone capsule) accomodated in the nose-like housing portion are provided in this more inclined :` :

side. The three speaking apertures 302 are provided in a depression or groove 306 which is disposed centrally on the side 303~ As shown in figure 11, the nose-like housing portion 301 is located substantially centrally on the lower side of the housing in a range of the lower side 5 adjacent to the infrared window 205.

Furthermore, the embodiment of figures 10 to 12 differs from the same of figures 8 and 9 by the formation of the lug 208 of the hearing range.
According to the present embodiment the lug of the hearing range 10 projects relatively far from the lower side of the housing and has an end surface extending substantially parallel to the lower side. In a top view the lug is substantially squarely formed and suited for the reception of a round receiver capsule.

15 The embodiment of the handset of figures 10 to 12 has a printed board 305 acsomodated in the housing and a printed board 305 disposed within the infrared window and optionally provided with an additional printed board disposed thereabove. Suitable secondary batteries 304 are located within the upper portion of the housing. The housing lid is screwed with 20 the lower side of the housing at three points (schematically shown in figures 10 and 11).

Figures 13 and 14 show an embodiment of a base unit which has a suitable housing with plane bottom surface and plane lateral surfaces as well as 25 a curved upper side. A convenient keyboard 318 and a deposition range or restoring range 311 for the handset are located on the upper side. An infrared window 312, a depression 314 for the accomodation of the nose-like housing portion 301 of the handset and three contacts 316, 317 are located within the deposition range. OF the contacts two are formed as charge contacts 316 and one is formed as identifying contact 317. The 3~

function of these contacts was already discussed above. A holder 315 with open central portion 313 serves for the accomodation of the lug 208 of the hearing range of the handset and extends in prolongation of the deposition range 311 laterally from the housing. Accordingly, in the 5 restored condition the lug 208 of the hearing range is accomodated in the open centre 313 of the holder 315, while the nose-like housing portion 301 of the handset engages into the depression 314. In this manner the handset is fixed on the base unit. In the restored condition of the same the infrared window 312 is covered and released in the lift 10 off condition. With 319 a suitable lower part for the housing 310 is designated.

.

Claims (45)

1. Infrared telephone having a first station, especially a telephone handset, with microphone, loudspeaker, and infrared emitter, an infrared receiver, and a second station, especially a fixedly installed remote station, with infrared emitter, infrared receiver, telephone network connection, characterized in that the first station (1) and the second station (2) have a single frequency oscillator (36), respectively, the frequency of which modulated by the electrical signals which have to be transmitted controls not only the power of the associated infrared emitter (13, 18) but is also fed to an associated infrared mixing stage, the frequency oscillators (36) of the first and second station (1, 2) have different mean frequencies, the signal supplied by the associated infrared receiver (12, 17) is mixed with the modulated frequency of the associated frequency oscillator (36) in a mixing stage, and the sum frequency or difference frequency of the received frequency and the modulated oscillator frequency generated by the mixing are demodulated by means of a frequency demodulator (30), and the function of receipt is obtained from the resulting signal.

2. The infrared telephone according to claim 1, characterized in that the mean frequencies of the frequency oscillators (36) are variable, wherein certain well-defined frequencies (channels) can be selected.

3. The infrared telephone according to claim 2, characterized in that the frequency oscillators (36) of both devices have a plurality of mean frequency pairs associated with one another, the frequency sum thereof having the same constant well-defined value, respectively.

4. The infrared telephone according to claim 3, characterized in that two groups of stations are defined by the association of channel numbers to the adjustable mean frequencies of both frequency oscillators (36) such that a station of the first group communicates with a station of the second group exactly if the same channel number is adjusted at both stations, i. e. a first frequency and a second frequency are associated with each channel.

5. The infrared telephone according to claim 4, characterized in that the association of the mean frequencies to the corresponding channel numbers is selected such that the sum of the frequencies from the first group and the second group, which are associated to any channel, always results in the constant and well-defined sum value.

6. The infrared telephone according to one of the preceding claims, characterized in that the mean frequency of the frequency oscillators (36) is stabilized by a phase-locked-loop control circuit.

7. The infrared telephone according to one of the preceding claims, characterized in that the electrical signals supplied by the infrared receiver (12, 17) are transferred into a frequency range which is favourable with regard to further processing by frequency translation and subsequent frequency multiplication.

8. The infrared telephone according to one of the preceding claims, characterized in that the sum signal resulting from the mixture is limited in its band width by a band filter and is supplied to the frequency demodulator (30), and in that in a subsequent subtraction stage (31) the signal modulating the frequency oscillator (36) of this station is subtracted from the signal of the frequency demodulator (30).

9. An infrared telephone having a first station, especially a telephone handset, with microphone, loudspeaker, an infrared emitter, an infrared receiver, and a second station, especially a fixedly installed remote station, with infrared emitter, infrared receiver, telephone network connection, characterized in that the first and second station have a first frequency oscillator (53, 72), respectively, the frequency of which modulated by the electrical signals which have to be transmitted controls the power of the associated infrared emitter (55, 74), and a second frequency oscillator (59, 67) with mixer (58, 66) for transfering the electrical signals received by the infrared receiver (56, 64) into the intermediate frequency band.

10. The infrared telephone according to claim 9, characterized in that the frequencies of the emitter oscillator (53, 72) and the receiver oscillator (59, 67) of the same station are tuned such that, if a function of receipt is present, the frequency of the emitter oscillator (53, 72) is mixed exactly to the intermediate frequency in the mixer (58, 66) of the receiver.

11. The infrared telephone according to claim 9 or 10, characterized in that the carrier frequencies of the frequency oscillators (53, 72; 59, 67) are stabilized by a phase-locked-loop control circuit.

12. The infrared telephone according to one of the claims 9 to 11, characterized in that the intermediate frequency is 0.455 MHz.

13. The infrared telephone according to one of the claims 9 to 12, characterized in that an intermediate frequency amplifier (60, 68) is located behind the mixer (58, 66).

14. The infrared telephone according to one of the preceding claims, characterized in that luminescence diodes are used as infrared emitter (13, 18; 55, 74), wherein the wavelength of the emitted radiation is in the range of 380 nm to 1,000 nm.

15. The infrared telephone according to claim 9, characterized in that each luminescence diode is controlled by the associated frequency oscillator (36; 53, 72 such that the alternating portion of the infrared intensity radiated by the luminescence diode is sinus-shaped or sinus-halfwave-shaped.

16. The infrared telephone according to one of the preceding claims, characterized in that one or more photobarrier receivers (photodiodes) having a spectral sensitivity in the range of 380 nm to 1,000 nm are used as infrared receiver (12, 17; 56, 64).

17. The infrared telephone according to one of the preceding claims, characterized in that it includes a compander system (compressor/expander) (38, 32) for improving the signal-noise distance.

18. The infrared telephone according to one of the preceding claims, characterized in that a microphone amplifier (44) with limiter, a band-pass filter (43) and a compressor (38) are located behind the microphone (5).

19. The infrared telephone according to one of the preceding claims, characterized in that the modulation voltage at the output of the compressor (38) is delayed by 60 µsec.

20. The infrared telephone according to one of the preceding claims, characterized in that an expander (32) and a band-pass filter (33) are located behind the frequency demodulator (30).

21. The infrared telephone according to one of the preceding claims, characterized in that it includes a rectifier-language control stage (39) switching off the infrared emitter (13, 18) in the non-speech intervals.

22. The infrared telephone according to one of the preceding claims, characterized in that it includes a pulsewidth control stage (41) for changing the emitter output.

23. The infrared telephone according to one of the preceding claims, characterized in that a FM-receiver element (30) with mixing stage and demodulator is used, said FM-receiver element having a field strength output and an incorporated noise cancellation (muting) (35) which switches the sound signal mute if the field strength of the remote station is insufficient.

24. The infrared telephone according to one of the preceding claims, characterized in that the telephone handset (1) is provided with a battery (9, 86), battery charge contacts (11, 87) and an on/off-switch (10, 88).

25. The infrared telephone according to claim 17, characterized in that the pulsewidth control stage compares the signal/noise ratio on the receiver side of the first station with a threshold, supplies an additional signal if the threshold is exceeded or fallen below, transfers the additional signal to the second station by means of the infrared emitter and the infrared receiver, detects the additional signal there, and varies the pulsewidth of the associated emitter endstage if the additional signal is present or is not present.

26. The infrared telephone according to claim 17, characterized in that the pulsewidth control stage measures the mean value of the diode current, compares this mean value with a preset mean value, and, upon deviation, leads the same to the preset mean value by variation of the pulse/pause ratio.

27. The infrared telephone according to one of the preceding claims, characterized in that the electrical signals which have to be transmitted from the first station or from the second station comprise signals of the microphone (50)/of the telephone circuit (70) and control/dial signals corresponding to any special functions.

28. The infrared telephone according to claim 27, characterized in that the control/dial signals stem from a keyboard (75) and/or a switch of the first or second station.

29. The infrared telephone according to claim 27 or 28, characterized in that the control/dial signals on the emission side are processed by means of a processor (78) with FSK modem (77) or by means of a DTMF
generator (76) and are fed to the associated emitter oscillator (53) and, on the receiver side, are recovered after the demodulation stage by means of a processor (81) with FSK modem (80) or a DTMF receiver (79).

30. The infrared telephone according to one of the preceding claims, characterized in that it includes a preemphase and deemphase system for improving the signal-noise distance.

31. A telephone handset for a telephone consisting of a base unit and a handset, especially according to one of the claims 1 to 30, comprising an elongated housing with a speaking range at one end portion and a hearing range at the opposite end portion of the lower side of the housing, a microphone associated with the speaking range, a loudspeaker associated with the hearing range, emission means, receiving means and an electronical signal processing means within the housing and optionally a keyboard on an operation surface of the housing, characterized in that the part of the upper portion of the housing associated with the speaking range (207) is made of transparent or translucent material so that an infrared window (205) is formed, and includes an infrared emission and receiving unit having a plurality of infrared emission diodes and infrared receiving diodes (215, 216), wherein the upper side, front side and lateral surfaces of the upper portion of the housing provide infrared receiving surfaces and/or infrared emission surfaces, respectively.

32. The telephone handset according to claim 31, characterized in that the part of the upper portion of the housing forming the infrared window (205) has a rectangular shape in a horizontal cross-section.

33. The telephone handset according to claim 31 or 32, characterized in that a step (212) is provided between the part of the upper portion of the housing forming the infrared window (205) and the remaining upper portion, said step (212) extending upwardly from the infrared window (205).

34. The telephone handset according to one of the claims 31 to 33, characterized in that the keyboard (209) is located on the upper side of the upper portion of the housing.

35. The telephone handset according to one of the claims 31 to 34, characterized in that it includes a second microphone which is associated with a second speaking range (210) (freespeaking range) on the upper side of the upper portion of the housing adjacent to the infrared window (205).

36. The telephone handset according to one of the claims 31 to 35, characterized in that it includes a contact switch (211) for switching-on a freespeaking means within the range of the terminal edge adjacent to the first speaking range (207).

37. The telephone handset according to one of the claims 31 to 36, characterized in that the housing (202) has a convex shape in longitudinal direction.

38. The telephone handset according to one of the claims 31 to 37, characterized in that the hearing range (208) is formed as lug projecting from the lower side (206) of the housing (202), said lug especially providing a deposition surface.

39. The telephone handset according to one of the claims 31 to 38, characterized in that the microphone (300) associated with the speaking range is disposed within a nose-like housing portion (301) projecting from the lower side of the housing.

40. The telephone handset according to claim 39, characterized in that the nose-like housing portion (301) is approximately triangularly shaped in longitudinal section, wherein a shorter and more inclined side (303), which is provided with at least one speaking opening (302), faces the infrared window (205).

41. A base unit for a telephone consisting of a base unit and a handset, especially according to one of the claims 1 to 30, and for a telephone handset, especially according to one of the claims 31 to 409 characterized in that it has on the upper side of its housing (310) in the range of the deposition surface (311) For the handset an infrared window (312) of transparent or translucent material under which an infrared emission and receiving unit is disposed.

42. The base unit according to claim 41, characterized in that its deposition surface (311) for the telephone handset includes a depression (313, 314) for the lug (208) of the hearing range and the nose-like housing portion (301) of the telephone handset.

43. The base unit according to claim 42, characterized in that the depression (313) for the lug (208) of the hearing range is formed as holder (315) which is open in its centre and projects laterally from the housing.

44. The base unit according to one of the claims 41 to 43, characterized in that its deposition surface (311) for the telephone handset includes three contacts of which two are formed as charge contacts (316) and one is formed as identifying contact (317) for the restored condition of the handset independent of the charge current.

45. The infrared telephone according to one of the claims 1 to 30, characterized in that it includes at least one additional first station, especially handset, only with infrared receiver, loudspeaker and corresponding electronics, which exclusively fulfills functions of receipt.