MXPA97000906A - Microtelphon interface with reality control - Google Patents

Abstract

A handset interface is described to reduce or eliminate the feedback inducing parasitic oscillation in a handset / hybrid cycle. The interface provides user-selectable volume control settings, each setting representing an amount of gain or loss to be applied to the signals transmitted and received within the telephone set. Gain adjustments to limit the total cycle gain so as to reduce or eliminate any tendency of the handset to generate parasitic oscillation at high gain levels received. The loss inserted in the transmission circuit is removed when it detects the user's speech in the transmission circuit.

Description

FIELD OF THE Di? MCl? W The present invention relates to the field of characteristics of a telephone set and to the apparatus itself, and specifically those aimed at reducing or eliminating the feedback of the handset.

It is not uncommon for currently available telephone sets to be equipped with control volumes to increase or decrease the amount of gain applied to the receiver circuit of the handset. Such controls are added to suit people with damaged hearing, to resolve excessive background noise as well as to compensate for variances in transmission quality from one phone call to the next. They generally limit themselves to adding 12 db or less of gain, so that they minimize the opportunity for the signal fed to the handset receiver to enter the handset transmitter, resulting in the creation of a high volume and unpleasant tone which is sent through the REF: 23789 receiver. This tone, caused by a feedback loop that is established between the receiver and the transmitter of the handset, is usually referred to as parasitic oscillation, but it has also been mentioned as a howl, squeal, high frequency vibration or simply as feedback. However, even in the limit of 12 db that is currently carried out in the practice of receiver gain, there is the potential for parasitic oscillation, based on the impedance of the telephone line and the acoustic environment surrounding the handset. As is well known in the art, the feedback loop which causes the parasitic oscillation is generated in part by acoustic coupling between the handset receiver in the handset handset and the handset microphone and the handset mouthpiece. The feedback loop is completed by electrical coupling between the transmission and reception circuits in the hybrid telephone. As is well known in the art, telephone signals to and from a telephone are transported through two wires, known for a long time in the field of telephony as thread A and thread B or tip and nape threads, respectively. Inside the telephone, these two cables connect to the telephone hybrid. The hybrid divides wire A and wire B into a four-wire circuit, two wires from which the far end of the calling party's signal passes from the hybrid to the handset receiver as a received signal. The two remaining cables carry a transmission signal from the handset transmitter to the hybrid for transmission over the wire A and B to the far end of the calling party. A perfect hybrid would result in a system in which there is no leakage of the signal component between the hybrid's transmitter and receiver circuits, that is, a perfect cancellation of the side tones or an infinite trans-hybrid loss. In practice, the transhybrid loss is never infinite and, instead, depends on how closely the hybrid impedance network matches the impedance of the real line of the telephone line to which the telephone set is connected. Since, in general, the impedance of the telephone line is complex and is not known a priori by the telephone apparatus, the trans-hybrid loss is usually only about 6 db to 10 db. This means that a reduced amplitude version of the transmitted signal will always be present in the received signal. If the sum of the acoustic coupling, the electric coupling through the hybrid and the circuit gain exceed the unit, the telephone will be subject to parasitic oscillation or "howl". For example, if the impedance of the telephone line to which The telephone connection represents a significant lack of impedance for the hybrid, and the handset is placed on a hard, acoustically reflective surface such as a smooth desk or back cover., the gain in this circuit can exceed the unit in some frequencies, which causes the parasitic oscillation to occur. Furthermore, this problem can not be solved simply by reducing the gain of the transmitted signal when the received signal gain is increased, which only reduces the volume of the speech that is heard at the far end by the other calling party. The present invention is directed to solving the drawbacks mentioned in the above that are currently in the known telephone sets.

BRBVB 8SQ-JPCL? DB DB INVBHCIQN The invention provides a handset interface or interconnect apparatus for placement in a telephone apparatus between the telephone hybrid and the telephone set.

The handset interface of the invention is preferably constructed as an electronic circuit controlled by a microprocessor. The handset interface contains a volume control circuit which allows the telephone user to vary up or down the amount of gain applied to the received and transmitted signals that pass between the handset and the hybrid, thereby affecting the amplitude of the signals which finally pass through the A and B wires between the user of the telephone and the calling party at the far end of the call. The volume control is, by way of example, adjustable in a selectable way by the user from one to eight fixed volume points. Each fixed point represents a particular amount of gain that is applied to the signals transmitted and received. All gains are gains in relation to the nominal handset level, that is, without gain in the transmission or reception signal. The gain amounts for each fixed volume point are configured so that the total gain introduced at the handset / hybrid site preferably does not exceed 6.6 db. However, the application of negative amounts of transmission gain during the whole conversation was of difficulty the quality of the call in general, since the transmitted signal must be attenuated while the user of the telephone is talking. This can cause the user's voice to sound low in an unnatural way at the end of the calling party. To solve this potential problem, an additional feature is included in the handset interface. Specifically, the handset interface detects the presence of the transmitted signal, and measures its amplitude at a point in the interface circuits before the gain reduction is applied. If the signal amplitude transmitted before the gain exceeds a predetermined threshold value and the user has selected any of the fixed volume points from four to seven, the fixed volume point is changed through the handset interface to the fixed point three, a fixed point which represents 0 db of gain applied to the transmitted signal. Therefore, if the telephone user selects a high volume setting or regulation, the handset interface automatically removes any signal gain reduction transmitted while the user is talking. Then, the fixed point is reset to the fixed point selected by the user when the user stops talking. For improved operation, the transmitted signal can be filtered before comparison with the threshold values to avoid auto-switching of the handset interface, in the absence of user speech, as a result of acoustic coupling of high-frequency components of the arising sound of the handset receiver. Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. However, it should be understood that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims.

BRIEF DBSC-RIPTION DB THE FIGURES OF DIBIHOS In the drawings, which are illustrative and not to scale, and in which similar reference numbers indicate similar elements throughout the various views: Figure 1 is a schematic block diagram of the main components of a preferred embodiment of an apparatus constructed in accordance with the present invention; and Table 1 is a table showing by way of illustration the amounts of transmitted and received gain applied at each fixed point of volume selectable by the user.

DBgraPTION nRTAT.TAT) A DK TAS With initial reference to Figure 1, a schematic block diagram of an illustrative handset interface 10 constructed with the currently preferred component selection is shown. Of course, it will be recognized by a person ordinarily skilled in the art that the drawing or description of any type of circuit component or device is offered only as a non-limiting example of a currently preferred design alternative, with many choices and alternatives available in electrical and electronic techniques to obtain the desired functionality of the handset interface of the invention. As seen in Figure 1, the interface 10 is designed to be incorporated or placed in the housing of a telephone set (not shown) between the telephone hybrid 18 and the handset 12, both of these telephone components are well known in the art. technique and do not form part of the present invention. The hybrid 18 directs a reception signal sent from a remote or remote end of the person making a conversation on the lines A and B or the circuit 30 to the receiver 14 of the handset, in which the signal is received and converted to a sound that is heard by the user of the phone. The receiver 14 is generally constructed as a small speaker in the handset receiver 12. The user of the local telephone usually speaks on the transmitter 16 of the handset, generally constructed in a manner similar to a microphone in the mouthpiece of the handset 12, which generates a transmission signal which is directed by the hybrid 18 on the thread A and B 30 to be heard as a sound by the person performing the conversation at the far end. The potential feedback paths which can contribute to parasitic oscillation are shown in Figure 1 as the acoustic coupling path 60 and the electrical coupling path 70. Interposed between the hybrid 18 and the transmitter 16 is a transmitting differential preamplifier 20, preferably implemented as an op-amp integrated circuit or a recognized equivalent in the art, for amplifying the transmitted signal generated when the telephone user speaks on the transmitter 16 of the handset. The amplified transmission signal from the preamplifier 20 is fed to a digitally controlled transmission gain circuit 26 which, under the control of the microprocessor 44, is operable to selectively apply negative and positive gain amounts to the transmitted signal. The transmitted signal adjusted in gain is then fed to the hybrid 18 for transmission over the wires A and B 30 to the talking party at the far end, as described above. Interposed between the hybrid 18 and the receiver 14 is a digitally controlled receiving gain circuit 24 which, similarly under the control of the microprocessor 44, is operable to selectively apply negative or positive gain amounts to the received signal that passes from the wires A and B 30 through the hybrid 18, as described above. The received signal adjusted in gain is then fed to the receiver 14 for conversion to an acoustic signal that is to be heard as a sound by the user of the local telephony. Referring now to FIGS. 1 and 2, the amount of gain applied to the transmitted and received signals is selectably controllable by the local telephone user by means of the volume control 42. The volume control 42 is connected to the microprocessor 40 which, in response to the adjustment thereof selected by the user, causes one of the eight combinations of the three volume control bits to be sent to the received gain circuit 24 and to the circuit 26 of transmitted gain. Both circuits 24 and 26 of gain received and transmitted preferably are digitally controlled integrated circuits which, in response to the particular sequence of three bit output controls by the microprocessor 40 vary the gain applied to the reception and transmission circuits respectively. For example, reception and transmission gain circuits 24 and 26 can be implemented as digitally controlled switches that send the respective transmission and reception signals to alternate branches of a resistor network, as a function of the sequence of control bits of the resistor. volume. One of skill in the art will of course recognize many other suitable arrangement methods in a similar manner to vary the gain in response to a volume control signal. As seen in Table 1, each of the eight fixed volume control points, numbered from zero to seven, represents a particular predetermined amount of gain to be applied to the respective reception and transmission signals. For example, a fixed point of one in the volume selected by the user causes, by way of illustration, the output microprocessor 40 to a three-bit volume control signal in which the volume control of bit 2 is equal to zero, the volume control of bit 1 is equal to zero and the volume control of bit 0 is equal to one; this results in 0 db of gain that is applied to the received signal and 0 db of gain that are applied to the transmitted signal. Preferably this is the default adjusted system in which both signals are maintained at their nominal values, i.e., the standard or standard handset volume designed for the particular telephone apparatus. As will be recognized by one of ordinary skill in the art, the nominal design values for the transmission and reception signals will vary, and are generally simple design material of choice. With continuous reference to the table l, as the fixed point of volume selectable by the user is varied, the volume control bits change the values as shown herein. The fixed points of volume numbered zero to three produce the first four currently preferred receive gain values, which range from about -3.3 db to about 6.5 db, staggered in approximately 3.3 db increments. The transmission gain values for all fixed points from zero to three are 0 db. The fixed points numbered to seven provide the four currently preferred receive gain values, which range from about 9.9 db to about 19.8 db, staggered in increments of about 3.3 db, and the remaining currently preferred transmission gain values, the which range from about -3.3 db to about -13.3 db, staggered in increments of about -3.3 db. As will now be apparent, with high fixed volume points, the transmission gain decreases as the received gain increases. The gain amounts for each of the eight fixed volume points are preferably set so that the total gain introduced in the handset / hybrid cycle never exceeds about 6.6 db. In this way, even at significantly increased gain levels received, such as those resulting from the selection of fixed points of volume from four to seven, the parasitic oscillation margin is only 6.6 db less than a nominal telephone without the received gain additional. Therefore, the selective application of negative gain quantities to the transmitted signal path maintains system stability even in gain settings received as high as 19 db, that is, when the fixed volume point is set to seven. The gain values described in the foregoing, of course, are set forth by way of non-limiting example. These values, for example, may vary or be varied as a function of the nominal signal values present in a particular telephone set and in the environment in which the telephone set is to be used. It will be recognized by those ordinarily skilled in the art of telephone apparatus design that the particular gain values described in the table of table 1 are generally the usual design choice material which may be varied to suit a particular application or utility without depart from the spirit of invention. Additionally, the number of fixed volume points may be increased or decreased from eight described herein to suit a particular desire design or requirements, insofar as the value of the gain increase applied from one adjustment to another adjustment, which can be uniform or vary upwards or downwards from +/- 3.3 dB between adjustments. In reality, fixed points and gain values do not need to be provided as a discrete number of fixed points but can vary continuously within a range. Although the addition of negative amounts of gain to the transmitted signal keeps the system stable at high received signal levels, it will be recognized that in some circumstances the arrangement may have a negative impact on the quality of the transmitted signal resulting when the user speaks. You will be introduced to the person who converges on the far end a transmitted signal greatly attenuated, which causes you to listen to the local user at very low volumes, or that you almost do not hear it. To solve this potential drawback, and in accordance with the invention, the microprocessor 40 detects the presence of a transmitted signal and switches the volume adjustment while the transmitted signal is present from the value selected by the user to a preselected fixed point representing the optimal transmission and reception signal levels, preferably a fixed point at which 0 db of transmission gain is applied.

Therefore, even if the local telephone user is speaking, any attenuation applied to the transmitted signal is removed in a manner that maximizes the sound quality at the far end. When the user stops talking, the microprocessor 40 returns to the volume setting for the selected user at the fixed volume point. As currently contemplated, the predetermined optimal transmission and reception levels are presented in, and therefore the preselected fixed point is set to, the fixed point number three of the described mode. This volume switching feature is described further in the following. Therefore, and with reference once again to Figure 1, the speech detection of the user is carried out by a detection circuit which includes a low pass filter 22 and a half wave rectifier, and a filter 28. , connected in series between the output of the transmitting differential preamplifier 20 and the microprocessor 40. The signal transmitted from the filter 22 and the rectifier 28 is fed to the microprocessor 40 in which it is applied to a comparator 44 inside or implemented by the microprocessor 40, or it may be external to the microprocessor 40. The comparator 44 compares the amplitude of the transmitted signal to a predetermined threshold amplitude. If the amplitude of the transmitted signal is equal to or greater than the predetermined threshold amplitude, then the comparator 44 signals the microprocessor 40 to switch the volume settings of the point selected by the user to a predetermined set point, as described. before. When the amplitude of the transmitted signal is below that threshold, the volume adjustment is maintained or returned to the fixed point of volume selected by the user. The selection of the threshold amplitude level for the comparator 44 is a matter of choice of design by those usually experts in telephony, and will depend on factors such as the nominal signal levels present in the telephone set and the environment of expected use, among others. With additional reference to table 1, it will be recognized that the transmitted gain adjustment function described above needs only to be carried out when the volume adjustment is selected by the user is a fixed point of volume of four to seven of the illustrative embodiment described herein, since these are the only adjustments in which negative amounts of gain are applied to the transmitted signal. As mentioned previously, at high reception volume levels, there is the acoustic coupling potential, between the path 60, which may be between the receiver 14 and the transmitter 16. Such coupling may cause the generation of a transmitted signal. which exceeds the threshold level of the comparator even in the absence of user speech, which causes the microprocessor 40 to undesirably switch or change the volume levels when the user is not speaking. This auto-switching condition is more likely to occur at high received signal frequencies, due to the poor remote field coupling characteristics of the handset at low frequencies; in fact, in practice, the acoustic coupling of the handset decreases significantly below 1,000 Hz. It is for this reason that a low pass filter 22 is inserted between the transmitting differential preamplifier 20 and the microprocessor 40 to filter the high frequencies above 1,000 Hz before the transmitted signal reaches the comparator 44 and thus limit the possibility of unwanted auto-switching Additionally, since only the amplitude of the filtered transmission signal is of interest to the comparator 44, the accuracy of the half-wave rectifier and the filter 28 are used to extract the amplitude envelope of the transmitted signal filtered from the filter. low pass, and it is the filtered and rectified signal which then passes to the comparator 44 for comparison with the predetermined threshold amplitude level. Of course, the particular low pass frequency of the filter 22 can be varied to that described so as to suit the frequency characteristics of the particular telephone apparatus into which the interface circuit of the invention or of some other device is to be applied. way as a general matter of design choice. As an additional refinement, hysteresis can be designed in comparator 44 to eliminate rapid unwanted switching between fixed volume points or gain levels, known in the art as jitter or tremolo, at signal levels close to the predetermined threshold level. . It will also be recognized that although the currently preferred embodiment contemplates digital control of the transmitted and received analog signals, the same functionality can alternatively be implemented using fully or partially analog circuits. Likewise, the transmitted and received signals can be digitized, and each of the functions described in the above can be carried out by using digital signal processing techniques. Each of these alternatives, and similar alternatives are considered completely within the scope of the invention and are within the ability of persons usually skilled in the art to carry out telephony. Therefore, although it has been demonstrated and described and indicated, fundamental novel features of the invention applied to the preferred embodiments thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, they can be performed by those skilled in the art without departing from the spirit of the invention. For example, it is expressly considered that all combinations of these elements and / or method steps which perform substantially the same function in substantially the same manner and obtain the same results that are within the scope of the invention. Therefore, it is intended that the invention be limited only as indicated by the scope of the appended claims. It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates. Having described the invention as above, property is claimed as contained in the following:

Claims (12)

1. A telephone interface or interconnection for connecting, in a telephone controlled by the user, a telephone hybrid and a handset which includes a transmitter to produce a transmitted signal and a receiver to receive signals received from the hybrid, the interface is characterized in that comprises: elements, connected between the receiver and the hybrid, to apply a predetermined variable amount of gain to the signal received from the hybrid; elements connected between the transmitter and the hybrid to apply a predetermined amount of gain to the signal transmitted from the transmitter; elements for simultaneously controlling the elements for applying the received signal gain and the elements for applying the transmitted signal gain to vary the amount of gain applied to the received and transmitted signals, and simultaneous control elements that are selectively adjustable by the selection of the user through a plurality of fixed volume points, each representing a received gain value that defines a first amount of gain for application to the received signal and a transmitted gain value that defines a second predetermined amount of gain for application to the transmitted signal, the first and second predetermined gain quantities for each fixed point are selected to minimize the feedback between the transmitter and the receiver and thus prevent parasitic oscillation in the handset; elements, connected to a transmitter, to detect the amplitude of the transmitted signal; and elements, connected to the sensing elements and the simultaneous control elements, for comparing the amplitude of the detected transmitted signal with a predetermined reference amplitude and for operating the simultaneous control elements in response to the comparison when the amplitude. the transmitted signal is greater than the reference amplitude to cause the simultaneous control element to select one of the plurality of preselected fixed points.

2. The interface according to claim 1, characterized in that the detection element additionally comprises elements, connected between the transmission and comparison elements, for generating a filtered transmission signal by filtering high frequency components from the transmission signal. are produced by acoustic coupling of transmission and reception signals and which may affect the comparison.

3. The interface according to claim 2, characterized in that the detection element additionally comprises elements connected between the filtering element and the. Comparison element for deriving an envelope or amplitude protection of the filtered transmitted signal, the amplitude envelope defines the amplitude of the transmitted signal.

4. The interface according to claim 3, characterized in that the plurality of fixed points comprise eight fixed numbered points, the fixed points are numbered zero through three representative reception gain values ranging from about -3.3 db to about 6.5 db in increments of approximately 3.3 db and transmission gain values of 0 db, fixed points numbered from 4 to 7 which represent gain values ranging from approximately 9.9 db to approximately 19.8 db in increments of approximately 3.3 db and gain values transmission rates ranging from about -3.3 db to about -13.3 db in increments of about -3.3 db.

5. The interface according to claim 4, characterized in that a preselected fixed point is the fixed point number three.

6. The interface according to claim 5, characterized in that the simultaneous control element operates in response to the comparison element only if the fixed point selected by the user is one of the points numbered four to seven.

7. The interface according to claim 6, characterized in that the simultaneous control element adjusts the preselected fixed point back to the fixed point selected by the user if the amplitude of the transmission signal is less than the predetermined reference amplitude.

8. The interface according to claim 3, characterized in that the simultaneous control element operates in response to the comparison element only if the fixed point selected by the user receives a gain value greater than the gain value received from the preselected fixed point.

9. The interface according to claim 8, characterized in that the simultaneous control element adjusts the preselected fixed point back to the fixed point selected by the user if the signal amplitude of. transmission is less than the default reference amplitude.

10. A handset interface for connecting, in a telephone controlled by the user, a telephone hybrid and a handset which includes a transmitter for producing a transmitted signal and a receiver for receiving signals received from the hybrid, the interface is characterized in that it comprises: elements connected between the receiver and the hybrid to apply a variable gain amount in a predetermined manner to receive the signal from the hybrid; elements connected between the transmitter and the hybrid to apply a predetermined amount of gain to the signal transmitted from the transmitter; elements for simultaneously controlling the received signal gain application elements and the transmitted signal gain application elements to vary the amount of gain applied to the received and transmitted signals so that the total amount of gain applied to the transmitted and received signals is kept below a predetermined cycle gain value.

11. The interface according to claim 10, characterized in that the predetermined cycle gain value is less than about 12 db.

12. The interface according to claim 11, characterized in that the predetermined cycle gain value is less than about 6.6 db. A handset interface is described to reduce or eliminate the feedback inducing parasitic oscillation in a handset / hybrid cycle. The interface provides user selectable volume control settings, each setting representing an amount of gain or loss to be applied to the signals transmitted and received within the telephone set. The gain settings are selected to limit the total cycle gain so as to reduce or eliminate any tendency of the handset to generate parasitic oscillation at high gain levels received. The loss inserted into the transmission circuit is removed when the user's speech is detected in the transmission circuit.