Abstract:
A digital data processing circuit comprising: a setting unit configured to set setting data on an audio signal processing circuit configured to generate an FM modulated signal based on the setting data, the FM modulated signal being a signal to be transmitted wirelessly to an FM radio receiver; and an output unit configured to output audio data for reproducing a predetermined audio signal while the setting unit sets the setting data on the audio signal processing circuit.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a digital data processing circuit. 
         [0003]    2. Description of the Related Art 
         [0004]    Recently, an FM (Frequency Modulation) transmitting circuit may be used to reproduce music data stored in a portable music reproducing device, etc., on a car stereo, for example (see, e.g., Japanese Patent Application Laid-Open Publication No. 2006-262521 or 2007-88657).  FIG. 6  depicts a common configuration of a transmitting device  200  using an FM transmitting circuit  300  and a microcomputer  310  for transmitting an audio signal. 
         [0005]    A frequency of a carrier in the FM transmitting circuit  300  is determined with consideration given to the frequency of an FM radio, etc., being used in its vicinity. Therefore, firstly, a user needs to set the frequency of the carrier in the FM transmitting circuit  300 . Specifically, the user operates a key (not shown) of a controller  220  so that the frequency of the carrier displayed on a display screen (not shown) of the controller  220  will be a desired frequency. When the frequency of the carrier has been determined, the user then operates a key (not shown) of the controller  220  so that frequency data of the carrier will be output to the microcomputer  310 . The microcomputer  310  transmits the frequency data output from the controller  220  to the FM transmitting circuit  300  as serial data SDA in synchronization with a clock signal SCL. As a result, the frequency of the carrier is set in the FM transmitting circuit  300 , and the FM transmitting circuit  300  becomes capable of transmitting audio signals RIN and LIN to be input thereto to the car stereo by way of an antenna  230 , for example. 
         [0006]    When, in the above transmitting device  200 , environment in the vicinity changes and a reproduced sound of the car stereo is affected by the FM radio, for example, it is necessary to change the frequency of the carrier of the FM transmitting circuit  300 . In changing the frequency of the carrier, the audio signals RIN and LIN, which are outputs of an audio reproducing device  210 , are temporarily stopped and the controller  220  is operated in general. For this reason, the setting of the FM transmitting circuit  300  is changed in a soundless state where no reproduced sound is output from the car stereo. Even in the case where the sound signals RIN and LIN are temporarily stopped while changing the setting, however, as a matter of fact, there is a case where an influence of a harmonic, etc., of the serial data SDA appears in an audible range so that a sound of transmitting the serial data SDA is reproduced as a noise by the car stereo. When the above noise is reproduced, the user may possibly suspect that the transmitting device  200  has a trouble, etc. 
       SUMMARY OF THE INVENTION 
       [0007]    A digital data processing circuit according to an aspect of the present invention, comprises: a setting unit configured to set setting data on an audio signal processing circuit configured to generate an FM modulated signal based on the setting data, the FM modulated signal being a signal to be transmitted wirelessly to an FM radio receiver; and an output unit configured to output audio data for reproducing a predetermined audio signal while the setting unit sets the setting data on the audio signal processing circuit. 
         [0008]    Other features of the present invention will become apparent from descriptions of this specification and of the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    For more thorough understanding of the present invention and advantages thereof, the following description should be read in conjunction with the accompanying drawings, in which: 
           [0010]      FIG. 1  is a diagram illustrating a transmitting device  10  according to a first embodiment of the present invention; 
           [0011]      FIG. 2  is a diagram illustrating a configuration of functional blocks to be realized by execution of a program by a CPU  63 ; 
           [0012]      FIG. 3  is a flowchart for describing an operation of a transmitting device  10 ; 
           [0013]      FIG. 4  is a timing chart for describing an operation of a transmitting device  10 ; 
           [0014]      FIG. 5  is a diagram illustrating a configuration of a transmitting device  11  according to a second embodiment of the present invention; and 
           [0015]      FIG. 6  is a diagram illustrating one example of a common transmitting device. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    At least the following details will become apparent from descriptions of this specification and of the accompanying drawings. 
         [0017]      FIG. 1  depicts a transmitting device  10  according to a first embodiment of the present invention. The transmitting device  10  is a device for transmitting audio signals output from, for example, a music reproducing device  30  as an FM signal from an antenna  31  to be reproduced by a car stereo (not shown). The transmitting device  10  according to a first embodiment is a device that is capable of setting a frequency of the FM signal by an operation of a controller  32  by a user. The transmitting device  10  includes an FM transmitting circuit  20 , a microcomputer  21 , a power amplifier  22 , and a speaker  23 . 
         [0018]    The FM transmitting circuit  20  is a circuit that generates a carrier of a frequency based on serial data SDA from the microcomputer  21  and a stereo composite signal based on audio signals RIN and LIN from the music reproducing device  30 , and modulates the carrier with the stereo composite signal to be output as the FM signal to the antenna  31 . The FM transmitting circuit  20  according to a first embodiment of the present invention includes an audio amplifier circuit  40 , an FM modulating IC (Integrated Circuit)  41 , and a power amplifier  42 . 
         [0019]    The audio amplifier circuit  40  is a circuit that amplifies the audio signals RIN and LIN, and generates the stereo composite signal corresponding to the audio signals RIN and LIN, and outputs the signals to the FM modulating IC  41 . 
         [0020]    The FM modulating IC  41  (audio signal processing circuit) is a circuit that generates the carrier of the frequency based on the serial data SDA from the microcomputer  21  to be modulated with the stereo composite signal. The modulated signal is output as the FM signal to the power amplifier  42  for wireless transmission to an FM radio receiver (not shown) of the car stereo (not shown). The FM modulating IC  41  according to a first embodiment of the present invention includes an IDC (Instantaneous Deviation Control) circuit  50 , a crystal oscillator circuit  51 , a setting register  52 , and a frequency modulating circuit  53 . 
         [0021]    The IDC circuit  50  is a circuit that limits amplitude of the stereo composite signal amplified by the audio amplifier circuit  40  and outputs the signal of limited amplitude to the frequency modulating circuit  53 . 
         [0022]    The crystal oscillating circuit  51  is a circuit that generates a reference frequency, which serves as a reference of the FM modulating IC  51 , together with a quarts crystal (not shown) connected thereto. 
         [0023]    The setting register  52  is a circuit that holds the serial data SDA input from the microcomputer  21  in synchronization with a clock signal SCL, to be output to the frequency modulating circuit  53  as setting data (SET). In the setting register  52  according to an embodiment of the present invention, the setting data is updated after reception of the serial data SDA is completed. 
         [0024]    The frequency modulating circuit  53  is a circuit that generates the carrier of the frequency based on the reference frequency and the setting data, and modulates the carrier with the stereo composite signal from the IDC circuit  50 . The modulated carrier is output as an FM modulated signal to the power amplifier  42 . 
         [0025]    The power amplifier  42  is a circuit that amplifies the FM modulated signal so as to drive the antenna  31 . An output of the power amplifier  42  is the FM signal. 
         [0026]    The microcomputer  21  (digital data processing circuit) is a circuit that controls the FM transmitting circuit  20  and the power amplifier  22  according to an instruction from the controller  32 , which is operated by the user in order to set the frequency of the FM signal. The microcomputer  21  includes an IF (Interface) circuit  60 , a ROM (Read Only Memory)  61 , a DAC (Digital to Analog Converter)  62 , and a CPU (Central Processing Unit)  63 . 
         [0027]    The IF circuit  60  is a circuit for receiving and transmitting various data among the CPU  63 , the FM transmitting circuit  20  and the controller  32 . Specifically, the IF circuit  60  transmits the instruction from the controller  32  to the CPU  63 , and transmits the data from the CPU  63  to the FM transmitting circuit  20 . 
         [0028]    The ROM  61  is a circuit that stores a program to be executed by the CPU  63  and audio data representing a beep sound which is a predetermined stereo audio signal. The ROM  61  according to an embodiment of the present invention outputs the audio data to the DAC  62  when an address in which the audio data is stored is output from the CPU  63 . 
         [0029]    The DAC  62  (converting unit) is a circuit that converts digital audio data output from the ROM  61  into an analog audio signal, to be output to the power amplifier  22 . The DAC  62  according to a first embodiment of the present invention outputs the audio signal when converting the audio data into the audio signal. The converted audio signal has been converted from a stereo signal into a monaural signal. 
         [0030]    The CPU  63  is a circuit that realizes various functions by executing the program stored in the ROM  61  according to the instruction from the controller  32 .  FIG. 2  depicts a configuration of functional blocks to be realized by execution of the program by the CPU  63 . The CPU  63  according to a first embodiment of the present invention realizes a setting unit  70  and an output unit  71  by executing the program. 
         [0031]    The setting unit  70  outputs frequency data for changing the frequency of the carrier of the FM transmitting circuit  20  to the IF circuit  60  in synchronization with a predetermined clock signal according to the instruction from the controller  32 . The IF circuit  60  according to a first embodiment of the present invention outputs the above frequency data and predetermined clock signal as the serial data SDA and clock signal SCL, respectively. 
         [0032]    In accordance with the instruction from the controller  32 , the output unit  71  makes preparations for a storage address of the audio data stored in the ROM  61 , and outputs the storage address to the ROM  61  while the setting unit  70  transmits the frequency data. To be more specific, the output unit  71  outputs the storage address of the audio data to the ROM  61  in such timing that the setting unit  70  starts to transmit the frequency data. The output unit  71  stops outputting the storage address of the audio data to the ROM  61  in such timing that the setting unit  70  completes transmission of the frequency data. 
         [0033]    The power amplifier  22  amplifies the audio signal output from the DAC  62  to drive the speaker  23  so that the audio signal of the DAC  62  is reproduced by the speaker  23  included in the transmitting device  10 . Therefore, in a first embodiment, when the audio signal converted from the audio data is input to the power amplifier  22 , the beep sound is reproduced from the speaker  23 . 
         [0034]    An operation will now be described of the transmitting device  10  with reference to a flowchart shown in  FIG. 3  and a timing chart shown in  FIG. 4 . Here, the frequency of the carrier of the FM transmitting circuit  20  is already set and an operation when changing the frequency will be described. When changing the frequency of the carrier, the audio signals RIN and LIN from the music reproducing device  30  are temporarily stopped and the car stereo (not shown) is in a soundless state. Firstly, the user operates the controller  32  so that the frequency of the carrier of the FM transmitting circuit  20  is changed to a desired frequency (S 100 ). As a result, the instruction corresponding to a result of the operation of the controller  32  is transmitted to the CPU  63  through the IF circuit  60 . Then, the setting unit  70  and the output unit  71  makes preparations for the frequency data and the storage address of the audio data, respectively, according to the instruction from the controller  32  (S 101 ). When the frequency data and the storage address are prepared, the setting unit  70  starts to transmit the frequency data to the IF circuit  60  at time T 1  (S 102 ). As a result, at the time T 1 , the serial data SDA is output from the IF circuit  60  in synchronization with the clock signal SCL. The output unit  71  outputs the storage address of the audio data to the ROM  61  at the time T 1 , in the same timing as that of the start of transmission of the frequency data (S 110 ). When the storage address is specified in the ROM  61 , the audio data is input to the DAC  62 , and as a result, from the time T 1 , the beep sound is reproduced from the speaker  23  (S 111 ). When the setting unit  70  has completed transmission of the frequency data at time T 2  (S 103 ), the output unit  71  stops outputting the storage address. Therefore, in a first embodiment of the present invention, while the IF circuit  60  outputs the serial data for setting the frequency of the carrier of the FM transmitting circuit  20 , the beep sound is reproduced from the speaker  23 . 
         [0035]      FIG. 5  depicts a configuration of a transmitting device  11  according to a second embodiment of the present invention. As is the case with the transmitting device  10  according to a first embodiment of the present invention, the transmitting device  11  is a device for transmitting the audio signal output from, for example, the music reproducing device  30  as the FM signal from the antenna  31  to be reproduced by the car stereo (not shown). The transmitting device  11  is a device that is capable of setting the frequency of the FM signal by the operation of the controller  32  by the user. The transmitting device  11  according to a second embodiment of the present invention includes the FM transmitting circuit  20  and a microcomputer  24 . The FM transmitting circuit  20  in the transmitting device  11  is the same as the FM transmitting circuit  20  of the transmitting device  10 . The music reproducing device  30 , the antenna  31 , and the controller  32  according to a second embodiment are the same as the music reproducing device  30 , the antenna  31 , and the controller  32  according to a first embodiment of the present invention, respectively. 
         [0036]    The microcomputer  24  (digital data processing circuit) is a circuit that controls the FM transmitting circuit  20  according to the instruction from the controller  32 , which is operated by the user in order to set the frequency of the FM signal. The microcomputer  24  includes the IF circuit  60 , the ROM  61 , the CPU  63 , and a DAC  64 . The IF circuit  60 , the ROM  61 , and the CPU  63  are the same as the IF circuit  60 , the ROM  61 , and the CPU  63  in the transmitting device  10 , respectively. 
         [0037]    The DAC  64  (converting unit) is a circuit that converts digital audio data output from the ROM  61  into stereo analog audio signals ROUT and LOUT, and outputs these converted signals to nodes to which the audio signals RIN and LIN in the audio amplifier circuit  40  is input. Therefore, when comparing between the transmitting device  10  of a first embodiment of the present invention and the transmitting device  11  of a second embodiment of the present invention, there is a difference in an output destination of the audio data stored in the ROM  61 . 
         [0038]    An operation of the transmitting device  11  will now be described referring again to the flowchart of  FIG. 3  used when describing the operation of the transmitting device  10 . Here, the frequency of the carrier of the FM transmitting circuit  20  is already set and the operation when changing the frequency will be described. When changing the frequency of the carrier in a second embodiment of the present invention, the audio signals RIN and LIN from the music reproducing device  30  are temporarily stopped and the car stereo (not shown) is in the soundless state. As described above, when comparing between the microcomputer  24  according to a second embodiment of the present invention and the microcomputer  21  according to a first embodiment of the present invention, since the IF circuit  60 , the ROM  61 , and the CPU  63  are common, the microcomputers  24  and  21  differs in only step Sill in a sequence of processing for changing the frequency of the carrier of the FM transmitting circuit  20 . To be more specific, in a second embodiment of the present invention, when the output unit  71  outputs the storage address of the audio data to the ROM  61 , the audio data of the ROM  61  is output to the DAC  64 . The DAC  64  outputs the stereo audio signals ROUT and LOUT based on the audio data. Since the audio signals ROUT and LOUT from the DAC  64  are input to the audio amplifier circuit  40 , an output of the audio amplifier circuit  40  is transmitted from the antenna  31 , through the FM modulating IC  41  and power amplifier  42 , over the carrier of the frequency based on the setting data, which is setting data before being changed, set in the setting register  52 . Therefore, in a second embodiment of the present invention, while the serial data SDA for changing the frequency of the carrier is output from the IF circuit  60 , the beep sound is reproduced from the car stereo (not shown). 
         [0039]    In the transmitting device  10  according to a first embodiment of the present invention and the transmitting device  11  according to a second embodiment of the present invention, each of which has a configuration described above, while the serial data SDA is transmitted to the FM modulating IC  41 , the output unit  71  outputs the storage address of the audio data stored in the ROM  61 . As a result, even in a case where the influence of the harmonic, etc., of the serial data SDA appears in an audible range so that a sound of transmitting the serial data SDA is output from the car stereo, the beep sound, which is a predetermined audio signal, is reproduced, and therefore, it becomes possible to mask the sound of transmitting the serial data SDA. Thus, it is possible to prevent the user from suspecting a trouble of the transmitting device  10  or  11  due to the sound of transmitting the serial data SDA. 
         [0040]    In the transmitting device  10  according to a first embodiment of the present invention, the DAC  62  converts the audio data stored in the ROM  61 , to drive the speaker  23  included in the transmitting device  10  through the power amplifier  22 . Therefore, in the transmitting device  10 , since the beep sound may be reproduced from the speaker  23  included in the transmitting device  10 , the sound of transmitting the serial data SDA may be masked. 
         [0041]    In the transmitting device  11  of a second embodiment of the present invention, the DAC  64  converts the audio data stored in the ROM  61 , to be output to the audio amplifier circuit  40  of the FM transmitting circuit  20 . Therefore, even in a case where the speaker is not provided in the transmitting device itself unlike the transmitting device  10 , since the beep sound may be reproduced in the car stereo (not shown), the sound of transmitting the serial data SDA may be masked. 
         [0042]    The above embodiments of the present invention are simply for facilitating the understanding of the present invention and are not in any way to be construed as limiting the present invention. The present invention may variously be changed or altered without departing from its spirit and encompass equivalents thereof. 
         [0043]    Although, in a first and second embodiments according to the present invention, the frequency of the carrier of the FM transmitting circuit  20  may be set based on the setting data, a power amplifier capable of changing a transmission power may be used, to change the transmission power of the power amplifier based on the setting data, for example. An audio amplifier circuit capable of outputting either the stereo composite signal or the monaural signal may be used in place of the audio amplifier circuit  40 , to output either the stereo composite signal or the monaural signal based on the setting data. In the above cases as well, it is possible to mask the sound of transmitting the serial data SDA by reproducing the beep sound while the serial data SDA is transmitted. 
         [0044]    In a first and second embodiments according to the present invention, there is employed a two-wire system in which the serial data SDA is transmitted in synchronization with the clock signal SCL when changing the setting data of the setting register  52 , however, the same effect may be obtained in the case of one-wire or three-wire data transmission as well.