AN ACCESSORY KEYBOARD FOR A PORTABLE RADIO TELEPHONE AND A METHOD OF INPUTTING TEXT TO A PORTABLE RADIO TELEPHONE

Abstract: An accessory keyboard (2) is provided for a portable radio telephone (1) of the type having a telephone keypad (16-18), an accessory connector (15), and a man-machine interface (13) with an option for allowing a user to enter a textstring through the telephone keypad. The accessory keyboard has a plurality of alphanumeric keys (31-45), a connector (25) adapted to be detachably connected to the accessory connector (15) of the radio telephone (1), and a controller. The controller receives keystrokes, which are entered among the alphanumeric keys by the user, and in response the controller submits signals representing the keystrokes to the radio telephone.

Description: An accessory keyboard for a portable radio telephone and a method of inputting text to a portable radio telephone. Technical Field The present invention relates to portable radiotele ph ones of the type having a telephone keypad, an accessory connector and a man-machine interface with an option for a l lowing a user to enter a textstring through the t ele p hone keypad. More specifically, the invention relates to a novel accessory keyboard and a method for inputting t ex t t o such a portable radio telephone without having to u s e the ordinary telephone keypad of the radio telephone . Prior Art Portable radio telephones of the kind described are of course commonplace. A well-known example is a cellular or mobile telephone, which operates for instance in a GSM system (Global System for Mobile communications in Europe) or D- A MPS (Digital Advanced Mobile Phone System, in the U nited States of America) . In addition to their basic role as a means for per- forming wireless communication of speech between human users, contemporary mobile telephones often provide a plurality of services other than just communication of speech. One very common service is the ability to send short text messages (for instance SMS - Short Messages S ervices in GSM) , where a user of a telephone may generate a text message, containing a predetermined maximum number of alphanumeric characters, and then send it across the mobile telephone network to an intended receiver. In a standard mobile telephone, the ordinary tele- phone keypad thereof will be used for entering the textstring (string of alphanumeric characters) to be incorporated in the message . Since an ordinary telephone keypad typically only contains keys for the digits 0 through 9, and a few other keys such as a * key and a # key, this limited set of different keys will have to represent a larger number of different alphanumeric characters, for instance the 25 different characters of the English alphabet. In reality, each numeric key 0-9 must represent several different alphanumeric characters. For instance, the numeric key 2 may represent the alphanumeric characters A, B, C, as well as country-specific characters, such as A, A, AE, a, ς, I, and also the digit 2. The user will choose between different characters by depressing the numeric key 2 for a different number of times in sequence. The same approach is used for creating and editing entries in an electronic telephone book, which is normally included in the mobile telephone. While many people use their mobile telephones mainly for speech calls, other user categories frequently use the above options for generating text messages and/or creating/editing entries in the electronic telephone book. In particular, people that have a mobile occupation or lifestyle are in many cases frequent users of such text -based services. Well-known examples of such people are young people (teenagers) and business people. For frequent users of the text -based services of a mobile telephone, the ordinary telephone keypad is a far from perfect tool for inputting text into the mobile tele- phone. Having to press different keys repeatedly for different number of times is tedious, time-consuming and inefficient. Therefore, there is a pronounced need for an improved way of inputting text into a mobile telephone. A previously known solution to this problem is to provide a device, which is a combination between a mobile telephone and a portable computer. Such a device (often referred to as a personal digital assistant - PDA) is disclosed in EP-A-0 776 140 and comprises two separate user interfaces and an outer housing, which can be unfolded. When the outer housing is closed, the device has the appearance and size of an ordinary mobile telephone, wherein a first user interface is available, which substantially corresponds to an ordinary telephone user interface (i.e. a display and a numeric telephone keypad) . When, on the other hand, the outer housing is unfolded, a second user interface is exposed, which offers a larger display and an alphanumeric keyboard. The alphanumeric keyboard of the second user interface may be used for inputting alphanumeric messages (textstrings) , for instance for generating an SMS message or for manipulating an entry in an electronic telephone book. While the device of EP-A-0 776 140 offers several useful features, it has a few distinct drawbacks for certain types of users. Firstly, the device is considerably more advanced than an ordinary mobile telephone. Consequently, the price thereof as well as the necessary knowledge level of the user is considerably higher than for an ordinary mobile telephone. Furthermore, the overall apparatus size, weight and power consumption are larger than for an ordinary mobile telephone. Therefore, for users that either do not have enough money to buy an advanced PDA device known from EP-A-0 776 140, or simply do not find the various advanced features thereof to be of any particular usefulness from their personal point of view, the device of EP-A-0 776 140 does not represent an optimal solution to the problem of facilitating the input of text to a mobile telephone. Summary of the Invention In view of the above, it is an object of the present invention to provide an accessory device, which will make it easier for a user of a mobile telephone to input text into the telephone, without having to rely solely on the ordinary numeric telephone keypad thereof. The above object has been achieved by an accessory keyboard having a plurality of alphanumeric keys, a connector adapted to be detachably connected to an accessory connector of a radio telephone, and a controller, which is adapted to receive keystrokes entered among the alphanumeric keys by a user, and in response submit signals representing the keystrokes to the radio telephone . The object is also achieved by the combination of a portable radio telephone and an accessory keyboard, the portable radio telephone having a telephone keypad and a man-machine interface with an option for allowing a user to enter a textstring on the telephone keypad, and the accessory keyboard being detachably coupled to the radio telephone, being adapted to receive text input from the user, and being adapted to supply the text input to said option of the man-machine interface of the radio telephone, thereby forming said textstring. Moreover, the object is also achieved by a method of inputting text to a portable radio telephone, wherein an accessory keyboard is provided, which has a plurality of alphanumeric keys and is adapted to be detachably connected to the radio telephone; it is detected that the accessory keyboard is connected to the radio telephone; a keystroke is detected among the alphanumeric keys; an alphanumeric character is determined, which corresponds to the keystroke; a digital control signal is formed, which represents the alphanumeric character; and the digital control signal is submitted to the radio telephone. Other objects, features and advantages of the present invention will appear from the following detailed disclosure of a preferred embodiment, from the drawings as well as from the attached subclaims . Brief Description of the Drawings The present invention will now be described in more detail, reference being made to the accompanying drawings, in which: FIG 1 is a schematic view of a portable radio telephone and a detachable accessory keyboard according to a preferred embodiment of the present invention, FIG 2 is a schematic front view of the accessory keyboard shown in FIG 1, FIGs 3 and 4 are lateral views of the accessory keyboard shown in FIG 2, FIG 5 is a flowchart diagram of a method according to the preferred embodiment of the invention, FIG 6 is a process diagram of the internal operation of the accessory keyboard, and FIG 7 is a schematic block diagram of a printed circuit board and the fundamental components thereon according to the preferred embodiment of the accessory keyboard . Detailed Disclosure of a Preferred Embodiment FIG 1 illustrates a portable radio telephone 1 together with an accessory keyboard 2 according to a preferred embodiment of the invention. For the rest of this specification, the portable radio telephone 1 will be exemplified by, and referred to as, a mobile GSM telephone. The mobile telephone 1 is per se essentially known from the prior art and comprises an apparatus housing 10, an antenna 11 mounted on top of the housing, a loudspeaker 12 provided in an upper front portion of the housing, a visual display 13 and a microphone 14, which also are provided at the front portion of the apparatus housing 10. Moreover, the mobile telephone 1 comprises an ordinary numeric telephone keypad having a plurality of numeric keys 16, each of which represents a respective digit 0 through 9. A * key and a # key 17a, 17b are also provided and have ordinary functions. The keypad also comprises a YES key 18a, which in a conventional way is used e.g. for answering an incoming call, or for performing an affirmative action in any routine or option provided by the man-machine interface of the mobile telephone 1. A NO key 18b similarly has a function for providing a negative response to any such function within the man-machine interface. It will also be used in an ordinary way for terminating an ongoing call. Moreover, it may be used as a power-on key for turning on the mobile telephone 1. The telephone keypad also comprises a clear key 18c, which for instance may be used for resetting the man- machine interface to an initial state (escaping from any option within a menu system provided by the man-machine interface) , and arrow keys 18d, 18e, which are used for scrolling through different options in the man-machine interface. The mobile telephone 1 also comprises, at a lower end of the apparatus housing 10, an accessory connector 15, which may be used for connecting the mobile telephone 1 to any commercially available accessory device, such as a hands-free set or a battery charger. The lower portion of FIG 1 discloses a novel accessory keyboard 2 having an external connector 25 to be detachably inserted in the accessory connector 15 of the mobile telephone 1. The accessory keyboard 2, which is illustrated in more detail in the remaining figures, com- prises a plurality of alphabetic character keys 31, including the keys A through Z of the normal English alphabet, as well as a dot character. A plurality of numeric keys 32 represent the digits 0 through 9 and are provided above the alphabetic keys 31 " . A YES key 33 and a NO key 34 are provided at the uppermost right corner of the front surface of the keyboard. A backspace/clear key 35 is provided immediately below the NO key 34. Moreover, arrow keys 36 and 37 are provided at the lowermost right corner of the accessory keyboard 2. The YES key 33, NO key 34, backspace/clear key 35 and arrow keys 36-37 will all have the same function, as if the corresponding key would have been pressed on the ordinary telephone keypad 16-18. A shift key 38 is provided next to the plurality of alphabetic keys 31 and is used in a manner known per se for toggling the function of each alphabetic key 31 between the character value printed on the face of the key (for instance K) and another character, such as the Nordic character 0. The shift key 38 may also be used for toggling the function of the numeric keys 32 between for instance 1 and ! . At the lower portion of the accessory keyboard 2 a space key 39 is provided. Finally, a plurality of function keys 41-45 are provided at the uppermost portion of the accessory keyboard 2. More particularly, the function keys comprise a website command key 41, an attachment key 42, an email key 43, an SMS key 44 and a phonebook key 45. In the following, the various different keys 31-45 will be commonly referred to as "alphanumeric keys" . The accessory keyboard 2 according to the preferred embodiment is particularly well suited for use as a tool for accessing a novel website by submitting email messages and certain website control commands embodied in a standard SMS message. Therefore, when the SMS key 44 is pressed, the logic circuitry inside the accessory keyboard 2 (shown in more detail in FIG 7) will form a digital control signal, preferably in the form of an AT command sequence, which contains a sequence of commands that will cause the mobile telephone 1 to enter an option for generating and sending an SMS message in the man-machine interface of the telephone 1. In other words, striking the SMS key 44 will cause the mobile telephone 1 to enter its menu option for sending an SMS message, and the user will be provided with an empty display 13 having a blinking cursor, which indicates that the mobile telephone 1 is ready to receive an entered text message character by character. Similarly the phonebook key 45 will invoke another option in the man-machine interface of the mobile telephone 1, viz. an option for entering the electronic telephone book thereof. The email key 43 will invoke the same option as the SMS key 44, i.e. the menu option for sending an SMS message. In addition, the characters "To:" will be automatically inserted at the beginning of the text message to be entered by the user. Hence, the user is given the opportunity to specify an Internet email address immediately following the header "To:" and then enter the actual text message. Once the message is completed, the user will press the YES key 18a, and the entered email message will be encapsulated in a standard SMS message, which is sent to a predetermined telephone number. This telephone number is assigned to a specific gateway of the aforesaid website, and the gateway will recognize the incoming SMS message as being in fact an email message, since it begins with the characters "To:". Consequently, the gateway will extract the email address, which was entered immediately following the characters "To:", create an empty email message having as its destination the extracted email address, and then generate an email body from the rest of the characters of the received SMS message. The website and the various functions and features thereof are disclosed in a separate patent application, having the title "Website being accessible for users of portable communication devices", which was filed by the same applicant on the same date as the present application, and which is fully incorporated herein by reference . In the email mode described immediately above, the attachment key 42 will generate the characters "#:" in the text message currently being input by the user. The user may enter the file name of any computer file, which has been stored in advance at the website. The website command key 41 will invoke the above mentioned menu option for sending an SMS message and will also generate the characters "WWW:" at the beginning of the message. The user may enter a website control command following these characters. Such website control commands are described in detail in the above-referenced co-pending patent application and include a command for adding a specified user to a mailing list stored at the website, a command for deleting a user from such a mailing list, a command for setting information in a personal information field stored at the website, a command for setting a status field related to the user of the mobile telephone 1 and stored at the website, and a command for setting a location field stored at the website. The accessory keyboard 2 is shown in different views in FIGs 2-4. The plurality of individual keys of different kinds, which were described with reference to FIG 1, are represented in FIGs 2-4 by the common reference numeral 30. The accessory keyboard 2 comprises an apparatus housing 20 made of plastic and having an upper portion 21, which is firmly mounted to a lower portion 22 by means of a set of screws 23a-23d. Between the upper portion 21 and the lower portion 22 an internal cavity is formed, which receives a printed circuit board, that is schematically illustrated in FIG 7 and will be described in more detail later. As shown in FIG 2, the connector 25 comprises a plu- rality of connecting members or pins 25a as well as two engagement members 25b, the purpose of which is to mate with corresponding engagement recesses in the accessory connector 15 of the mobile telephone 1. The individual connecting members 25a have predetermined electrical functions as signal lines or power supply lines. More specifically, two of the connecting members 25a are power supply pins, which are adapted to engage with corresponding contacts of the accessory connector 15, thereby receiving electric power from the power source (battery) of the mobile telephone 1. Consequently, the accessory keyboard 2 of the preferred embodiment has no internal power source but receives all necessary electric power from the mobile telephone 1. Other connecting members 25a have the purpose of acting as serial communication lines, reference voltage lines etc. Referring now to FIG 7, a schematic illustration of a printed circuit board 700 is given. The printed circuit board 700 is mounted within aforesaid cavity between the upper and lower housing portions 21, 22 of the accessory keyboard 2. A central controller 710 has the main responsibility for controlling and performing the functionality of the accessory keyboard 2, as will be described in more detail with reference to FIGs 5 and 6. In the preferred embodiment, the controller 710 is implemented by a programmable microprocessor of any commercial type. The controller 710 is connected to a keystroke detector circuit 720, which has the purpose of detecting when the user strikes an individual key among the plurality of alphanumeric keys 31-35, and forwarding this information to the controller 710. Moreover, the printed circuit board 700 comprises an electronic memory 730 for storing program instructions to be executed by the controller 710, and also reference data to be used for identifying individual keys as well as selecting the correct AT command sequence to be submitted to the mobile telephone 1 in response to the detection of a particular keystroke. The memory 730 may be implemented by any commercially available electronic memory, such as an EEPROM memory and/or a RAM memory. Moreover, it may advantageously be integrated with the controller 710, particularly if the latter is realized as a programmable microprocessor . According to the preferred embodiment, the accessory keyboard 2 communicates with the mobile telephone 1 over a serial communication interface at a rate of 9600 bps . Therefore, the printed circuit board 700 is provided with a transceiver for performing serial communication with the mobile telephone 1. In the preferred embodiment the transceiver 740 is realized as a Universal Asynchronous Receiver Transmitter (UART) . The transceiver 740 is connected to the connector 25 of the accessory keyboard 2. The overall operating principle of the accessory keyboard 2 is illustrated by way of a flowchart diagram in FIG 5. The details about certain steps thereof will be explained further below with reference to FIG 6. Referring back to FIG 5, in a first step 510 it is assumed that the user of the mobile telephone 1 has just connected the accessory keyboard 2 to the telephone 1. As described above, the accessory keyboard 2 will start receiving supply current from the battery of the mobile telephone 1 through the power supply pins 25a of the connector 25. A main control process 670 (FIG 6) will start to run in the microprocessor 710 (FIG 7) , and the control process 670 will immediately invoke an I/O module 660, which will also run m the microprocessor 710. The I/O module 660 will immediately invoke an initialization subroutine, which will reset and initialize the UART 740, various variables in the memory 730, the keystroke detector 720 as well as internal registers of the microprocessor 710. Once the initialization has been completed in step 510, the I/O module 660 will submit, in a subsequent step 520, a request for identification to the mobile telephone 1 in the form of an AT command sequence having a predeter- mined syntax. The mobile telephone 1 will respond by returning information sufficient to identify the type of the telephone, for instance a model identification number. The type of the mobile telephone 1 will be determined in a step 522 by comparing the response received in step 520 with a set of prestored data. The reason why the accessory keyboard 2 has to identify the type of telephone, to which it is attached, is that different telephones may have different man-machine interfaces. In particular, the way to select the menu options for entering the mode for sending an SMS message or the menu option for entering the electronic telephone book may differ between different telephone models. In a subsequent step 524 it is determined whether a positive identification of the mobile telephone has been made in the preceding step 522, and, if so, whether the identified telephone type is a type that is supported by the keyboard accessory 2. If the answer to this is in the negative, execution is ended in a step 526; otherwise, control is transferred to a main loop, which starts with a step 530 for detecting individual keystrokes on the accessory keyboard 2. The keystroke detector 720 of FIG 7 is adapted to detect such individual keystrokes and forward the information to the microprocessor 710, which upon reception of a detected keystroke in step 530 will continue to a subsequent step 540, wherein the character represented by the keystroke in question is identified. If, however, the user has not pressed any key on the accessory keyboard 2 for a predetermined period of time, a timeout condition is established in step 530, the control continues to a subsequent step 532, where the execution is ended. Following the determination of the actual character in step 540, an AT command sequence will be formed in a step 550. In a subsequent step 560, the AT command sequence thus formed will be submitted, as a digital control signal, over the serial interface provided by the UART 740 and connector 25 to the accessory connector 15 of the mobile telephone 1. Then, control is returned to the keystroke detection step 530, wherein a complete loop is formed. Referring now to FIG 6, the different program modules run by the microprocessor 710 will be given a detailed explanation. As previously mentioned, a main control process 670 is responsible for the overall operation of the accessory keyboard 2. The main control process 670 controls a keyboard scanning module 620, a keystroke processing module 640 and the I/O module 660 already mentioned above. The main control process 670 will initialize modules 620, 640 and 660 in step 510 of FIG 5. The main control process 670 will also preserve power by putting the microprocessor 710 into an idle state, when there is no keystroke to process. The main control process 670 is operatively connected to a key buffer 630, in which individual keystrokes are put by the keyboard scanning module 620, once the user has pressed a certain key on the accessory keyboard. Hence, the main control process 670 regularly checks the key buffer 630 for any keys. If there are any keys in the key buffer 630, the main control process 670 will invoke the keystroke processing module 640, which will process the keystroke in question (step 540 of FIG 5) and form an appropriate AT command sequence (step 550) by consulting a set of prestored command directives 650. The main control process 670 will then invoke the I/O module 660, which will submit the AT command sequence thus formed to the mobile telephone 1. The keyboard scanning module 620 regularly scans the accessory keyboard 2 for detecting any keystrokes thereon. Once a keystroke has been detected, it will be placed in the key buffer 630, which as described above will be monitored by the main control process 670. The keyboard scanning module 620 has a debouncing feature for avoiding "key bouncing", i.e. avoiding a key from being placed multiple times in the key buffer 630, if the key was actually only pressed once. Therefore, any given keystroke will not be placed in the key buffer 630, until it has been detected during a predetermined time by the keyboard scanning module 620. The exact implementation of the keyboard scanning module 620 will depend on the actual implementation of the various keys 31-45 and the underlying contact matrix on the printed circuit board 700, as will be readily realized by a man skilled in the art. The keystroke processing module 640 takes care of processing the keystrokes stored in the key buffer 630 and also forms the corresponding AT command sequences to be submitted to the mobile telephone 1 by the I/O module 660. An important task of the keystroke processing module 640 is to properly handle different telephone types. Since the accessory keyboard 2 operates by submitting keystrokes (encapsulated in AT commands) to the mobile telephone 1 for navigating through the menus of its man-machine interface, and since different telephone types may exhibit differences as regards their specific menu structure, it is necessary to know the type of telephone, to which the accessory keyboard 2 is connected. Particularly important are the option for sending an SMS message and the option for creating/editing an entry in the electronic telephone book. As previously mentioned, the identification of the telephone type is handled by the I/O module 660 in steps 520 and 522 of FIG 5. More specifically, in the preferred embodiment the above information is stored within the module 640 as constants or directly in program code sequence. Alternatively, this information may be stored in a database structure in memory 730. The most important task of the keystroke processing module 640 is to compose the proper AT command sequences to be submitted to the mobile telephone 1 by the I/O module 660. To this end, a set of command directives 650 are available to the keystroke processing module 640. For instance, the command directives 650 comprise a reference specifying that following the detection of a keystroke on the A key of the keyboard 2, an AT command shall be composed, which comprises one occurrence of the numeric key 2, the reason being that one stroke on the numeric key 2 of the ordinary telephone keypad 16 is how the character A would normally be entered in the man-machine interface of the mobile telephone 1. Similarily, a keystroke on key B of the accessory keyboard 2 will generate an AT command, which comprises two occurrences of the numeric key 2, while a keystroke on key C will be represented by an AT command having therein three occurrences of the numeric key 2. The I/O module 660 is responsible for the serial communication with the mobile telephone 1 (the submission of AT commands and the reception of responses from the telephone 1) . As already described, the module 660 is also responsible for identifying the type of the mobile tele- phone 1 upon initialization of the accessory keyboard 2. I- 1 H- 0 Pf

Claims: CLAIMS 1. An accessory keyboard (2) for a portable radio telephone (1) of the type having a telephone keypad (16- 18) , an accessory connector (15) , and a man-machine interface (13) with an option for allowing a user to enter a text string through the telephone keypad, the accessory keyboard being characterized by a plurality of alphanumeric keys (31-45) , a connector (25) adapted to be detachably connected to the accessory connector (15) of the radio telephone (1) , and a controller, which is adapted to receive keystrokes entered among the alphanumeric keys by the user, and in response submit signals representing the keystrokes to the radio telephone. 2. A keyboard as in claim 1, wherein an individual signal comprises at least one control character and at least one information character, wherein the latter represents a specific key as entered by the user. 3. A keyboard as in claim 2, wherein the individual signal comprises an AT command sequence. 4. A keyboard as in any preceding claim, further comprising a transceiver device (740) for serial communication with the radio telephone (1) . 5. A keyboard as in claim 4, wherein the transceiver device (740) is a UART. 6. A keyboard as in any preceding claim, wherein the connector (25) comprises at least one member (25a) , which is adapted to connect to a corresponding at least one power supply member in the accessory connector (15) of the radio telephone (1) , so as to receive electric power therefrom. 7. A keyboard as in any preceding claim, further comprising a function key (33-37, 41-45) , wherein the controller (710) is adapted, when the user strikes the function key, to submit to the radio telephone (1) a control signal, which will invoke a predetermined function of the man-machine interface of the radio telephone. 8. A keyboard as in claim 7, wherein said predetermined function (33-37, 41-45) is one of the following functions: answering an incoming call (YES key), terminating an ongoing call (NO key) , resetting the man- machine interface to an initial state (Clear key) , scrolling through a menu structure of the man-machine interface (arrow key) , entering an electronic telephone book provided by the man-machine interface, or invoking an option for generating a digital message, including said text string, to be sent to another user. 9. A keyboard as in claim 7 and 8, wherein several function keys (33-37, 41-45) are provided for invoking a respective one among several predetermined functions of the man-machine interface of the radio telephone (1) . 10. A keyboard as in any preceding claim, wherein the controller (710) is adapted to submit an interrogation signal to the radio telephone (1) , receive a reply signal from the radio telephone, and in response determine a type or model of the radio telephone. 11. A keyboard as in any preceding claim, wherein the controller (710) is a programmable microprocessor. 12. A portable radio telephone (1) having a telephone keypad (16-18) and a man-machine interface (13) with an option for allowing a user to enter a text string on the telephone keypad, characterized by an accessory keyboard (2) , other than the telephone keypad (16-18) , which is detachably coupled to the radio telephone (1) , is adapted to receive text input from the user, and is adapted to supply the text input to said option in the man-machine interface of the radio telephone, thereby forming said text string. 13. A telephone as in claim 12, wherein said option is a service for sending a digital message, including the text string, to another user. 14. A telephone as in claim 12, wherein said option is a service for creating or editing an entry in an electronic telephone book provided by the man-machine interface. 15. A method of inputting text to a portable radio telephone (1) , characterized by the steps of a) providing an accessory keyboard (2) having a plu- rality of alphanumeric keys (31-45) and being detachably connectable to the radio telephone, b) detecting that the accessory keyboard is connected to the radio telephone, c) detecting a keystroke among the alphanumeric keys , d) determining an alphanumeric character, which corresponds to the keystroke, e) forming a digital control signal, which represents said alphanumeric character, and f) submitting the digital control signal to the radio telephone (1) . 16. A method as in claim 15, comprising the further steps of b') following the detection in step b) , submitting a control signal to the radio telephone (1) , said control signal comprising a request for identification of the radio telephone, b") receiving an identifying signal from the radio telephone, and b (3> ) determining a type or model of the radio telephone from said identifying signal, wherein the type or model determined in step b (3) ) will be used for forming the digital control signal in step e) .

Inventors: BARVESTEN MATS, PERSSON STEFAN, BARVESTEN, MATS, PERSSON, STEFAN
Applicants: ERICSSON TELEFON AB L M, TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)
Application year: 2000
Main classification: H04M1
IPC codes: H04M1