Abstract:
An apparatus includes two DC/DC converters including two conversion circuits for converting a power supply voltage to first and second output voltages, respectively, two driving circuits for driving the respective conversion circuit based on first and second pulse wave modulated signals, and two pulse width modulation circuits for performing pulse width modulation on a thinned wave signal formed from a first wave signal and on a second wave signal to generate the pulse wave modulated signals, respectively. One DC/DC converter includes a thinning circuit for removing portions of a first wave signal to form the thinned wave signal. The apparatus includes a speaker for generating sound by inputting a signal based on the voltages.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2006-097251, filed on Mar. 31, 2006, the entire subject matter of which is incorporated herein by reference. 
     FIELD 
     Aspects of the present invention relate to an apparatus with a speaker, particularly, an apparatus with a speaker capable of generating a voltage in a wide range as well as restraining generation of beats. 
     BACKGROUND 
     Up to now, an apparatus with a speaker has been known, the speaker including a generating circuit for generating a sound signal and making a sound by amplifying a sound signal generated in the generating circuit by an amplifier. It has been also known that the apparatus with a speaker is mounted with a DC/DC converter for converting a DC voltage inputted from main power supply into two different kinds of DC voltage to output the two different kinds of converted DC voltage to the generating circuit as a power supply voltage. 
     On the other hand, as for the DC/DC converter, JP-A-2004-503197 discloses a multiple output DC/DC up-converter for independently controlling each output voltage by any of pulse width modulation (PWM) and pulse frequency modulation (PFM) for the purpose of highly efficient operation. 
     In the case of using the output voltage of the above-mentioned multiple output DC/DC up-converter disclosed in JP-A-2004-503197 as a power supply voltage for the above-mentioned generating circuit of the speaker, however, there is a problem as follows. That is to say, a difference in the frequency component between the two different types of output voltage overlaps with a sound signal generated in the generating circuit resulting in beats, which are outputted from the speaker as an unpleasant sound especially when the frequency difference is within an audible range, since each output voltage outputted from the multiple output DC/DC up-converter is independently controlled by any one of pulse width modulation (PWM) and pulse frequency modulation (PFM). 
     SUMMARY 
     Aspects of the invention provide an apparatus with a speaker capable of generating a voltage in a wide range while restraining generation of beats. 
     According to aspects of the invention, an apparatus includes a first DC/DC converter including a first conversion circuit for converting a power supply voltage from a main power supply to a first output voltage, a first driving circuit for driving the conversion circuit based on a first pulse wave modulated signal, a thinning circuit for removing portions of a first wave signal to form a thinned wave signal, and a first pulse width modulation circuit for performing pulse width modulation on the thinned wave signal to generate the first pulse wave modulated signal. Also the apparatus includes a second DC/DC converter including a second conversion circuit for converting a power supply voltage from a main power supply to a second output voltage, a second driving circuit for driving the conversion circuit based on a second pulse wave modulated signal, and a second pulse width modulation circuit for performing pulse width modulation on a second wave signal to generate the second pulse wave modulated signal. In addition, the apparatus can have a speaker driving circuit for generating a speaker driving signal based on the first output voltage and the second output voltage, and a speaker for generating a sound based on the speaker driving signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects of the invention will be described with reference to the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of a multi-function peripheral device in accordance with aspects of the invention; 
         FIG. 2  is a block diagram showing an electrical structure of the multi-function peripheral device; 
         FIG. 3  is a block diagram showing an electric structure of a complex IC in detail; 
         FIG. 4  is a block diagram showing additional illustrative aspects of the invention; and 
         FIG. 5  is a block diagram showing still further additional illustrative aspects of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a front perspective view of a multi-function peripheral device  1  with a speaker according to aspects of the invention. The multi-function peripheral device  1  has a printing function, a copying function, a scanning function and a facsimile function. 
     An opening part  2   a  on a front side of a housing  2  in the multi-function peripheral device  1  is divided inside into upper and lower parts as shown in  FIG. 1 . Provided in the lower part of the opening part  2   a  is a feeding cassette  3  which is configured to be inserted into the opening part  2   a  for feeding a recording medium (recording paper P). Provided in the upper part of the opening part  2   a  is a discharging part (e.g. output tray)  10  from which a recorded sheet of the recording paper P is discharged. The recorded sheet of the recording paper P is discharged in a direction shown by an arrow A. 
     The feeding cassette  3  can hold sheets of the recording paper P in a stack as a recording medium (the recording paper). The recorded paper P may be, for example, A4 size, letter size or card size. A short side of the recording paper is placed in the feeding cassette in a main scanning direction (a Y axis direction, a direction crossing at right angles with an X axis direction (a sheet carrying direction)). 
     An image reader device is provided above the housing  2  for reading an original document when the copying and facsimile functions are invoked. The image reader device includes a cover  13  arranged to pivot with respect to one side end of the housing  2  through a pivot shaft part (not shown) so as to open and close in a vertical direction. In the example of  FIG. 1 , a rear end of the cover  13 , which covers an upper surface of the image reader device, is mounted to the rear end of the image reader device so that the cover  13  can pivot about a pivot shaft in the vertical direction. The cover  13  can be opened upward so that an original can be put on a platen glass and an image on a surface of the original sheet can be read by a scanner for reading an original (a CIS (a contact image sensor), for example). The scanner is provided under the platen glass and configured to move in the main scanning direction (the Y shaft direction). 
     On the upper side of the housing  2  and in a front part of the cover  13 , there is an operation panel  14  including various types of operation buttons, and a liquid crystal display device (referred to as an “LCD”, hereinafter)  15  for displaying an operation command or an operation state. An external memory port  11  for receiving an external memory is provided on the front surface of the housing  2  under the operation panel  14 . The external memory is Compact Flash®, Smart Medium®, Memory Stick®, SD Card® or xD®, for example. 
     A main electrical structure of the multi-function peripheral device  1  will be described with reference to  FIG. 2 .  FIG. 2  is a block diagram showing a main electrical structure of the multi-function peripheral device  1 . The multi-function peripheral device  1  includes an ASIC  20  and a complex IC  21 . 
     Realized on the ASIC  20  is a power supply control circuit  21  for controlling the power supplied to various types of motor and respective circuits, a speaker control circuit  22  and a buffer  23  connected to the speaker control circuit  22 . The buffer  23  is connected to an amplifier  24  and a speaker  25  for outputting sound. 
     The power supply control circuit  21  is connected to a logic control circuit  37  and a reference potential generating circuit  26 . The power supply control circuit  21  sends an I/F signal to the logic control circuit  37  and sends a reference potential generating signal to the reference potential generating circuit  26 . The reference potential generating circuit  26  is connected to a third DC/DC converter  33 , a carriage motor driving circuit  34 , a line field motor driving circuit  35  and a scanner motor driving circuit  36 . The reference potential generating circuit  26  generates potential, which is a standard potential generated in the respective circuits ( 33 - 36 ). 
     The speaker control circuit  22  generates a sound signal. The generated sound signal is outputted to the buffer  23  to be amplified. The sound signal is further amplified in the amp  24  and output from a speaker  25 . In some aspects, an alarm sound due to the occurrence of an error or a line monitor sound may be output. 
     Realized on the complex IC  30  are a main part of a first DC/DC converter  31 , a main part of a second DC/DC converter  32 , a main part of the third DC/DC converter  33 , the carriage motor driving circuit  34  for driving a carriage motor  34   a , the line field motor driving circuit  35  for driving a line field motor  35   a , the scanner motor driving circuit  36  for driving a scanner motor  36   a  and the logic control circuit  37  for controlling the respective circuits realized on the complex IC  20 . 
     The first DC/DC converter  31  carries out pulse width modulation (PWM) and pulse frequency modulation (PFM) to generate a voltage of 1.2 V, which is lower than a power supply voltage VDD of 30 V. The generated voltage of 1.2 V is outputted to the power supply control circuit  21  and the speaker control circuit  22  as a power supply voltage through a wiring  41  and a power supply terminal VCC 1  of the ASIC  20 . 
     The second DC/DC converter  32  performs pulse width modulation (PWM) to generate a voltage of 5.0 V, which is lower than the power supply voltage VDD of 30 V. The generated voltage of 5.0 V is reduced from 5.0 V to 3.3 V by a regulator (Reg)  38 . The reduced voltage of 3.3 V is outputted as a power supply voltage to the buffer  23  through a wiring  42  and a power supply terminal VCC 2  of the ASIC  20 . As such, two different voltages may be needed, 1.2 V for the speaker control circuit  22  and 3.3 V for the buffer  23 , to output a sound signal from the speaker  25 . 
     The third DC/DC converter  33  generates a variable voltage ranging from 15 V to 28V, which is lower than the power supply voltage VDD of 30 V. The generated variable voltage is outputted as a power supply voltage to a print head driving circuit  39  for driving a print head  40 . 
     Now, described in detail will be an electrical structure of the complex IC  30  with respect to  FIG. 3 .  FIG. 3  is a block diagram showing an electrical structure of the complex IC  30  in detail. 
     The logic control circuit  37  outputs an ON/OFF signal of the variable voltage generated in the third DC/DC converter  33  and outputs a signal for setting switching frequencies of the respective DC/DC converters  31  to  33  to a chopping wave generating circuit  80 . 
     The chopping wave generating circuit  80  is connected to each of a PWM circuit  53  via a circuit  52 , a PWM circuit  61  and a PWM circuit  71 . The chopping wave generating circuit  80  outputs a chopping wave for determining the switching frequency for each of the PWM circuit  53  via the thinning circuit  52 , the PWM circuit  61  and the PWM circuit  71 . That is to say, the respective DC/DC converters  31 ,  32  and  33  generate PWM signals as a switching signal with common chopping waves, being used as a reference wave, outputted from the chopping wave generating circuit  80  which may be a common oscillator. Accordingly, all of the respective PWM signals generated by the respective DC/DC converters  31 ,  32  and  33  for the purpose of outputting a voltage of 1.2 V, a voltage of 5.0 V and a variable voltage of 15 to 28 V are generated with the common chopping waves being used as the reference wave so that the respective PWM signals are generated as a signal having a synchronized cycle. Though the chopping wave is used as reference wave in one aspect of the invention, other wave types such as a sawtooth wave may be used instead of the chopping wave. 
     When a cycle of the output voltage of 1.2 V outputted from the first DC/DC converter  31  after pulse width modulation and pulse frequency modulation is not synchronized with a cycle of the output voltage of 3.3 V outputted from the second DC/DC converter  32  and reduced in voltage through the Reg  38  after pulse width modulation, a switching frequency component included in the output voltage of 1.2 V overlaps with a sound signal generated in the speaker control circuit  22  with the output voltage of 1.2 V being used as the power supply. The combination of the sound signal and the output voltage of 3.3 V in the buffer  23  results in overlap of a differential frequency component between the switching frequency component included in the output voltage of 1.2 V and the switching frequency component included in the output voltage of 3.3 V with the PWM signal generated as the sound signal. The differential frequency occurs as beats. When the differential frequency component falls within an audible frequency range, an unpleasant sound may be output from the speaker  25 . 
     On the other hand, when a cycle of the switching frequency component of the output voltage of 1.2 V is synchronized with that of the switching frequency component of the output voltage of 3.3 V, the output of unpleasant sound can be prevented. The synchronizing of these frequency components allows occurrence of beats to be reduced since no differential frequency component exists even when both switching frequency components are combined in the buffer  23 . 
     In the multi-function peripheral device  1  in  FIG. 3 , an inductor  57  is connected to a wiring  41  which is connected to the main power supply VDD, a diode  58  is connected to an input terminal of the inductor  57 , and a capacitor  59  is connected to an output terminal of the inductor  57 . The first DC/DC converter  31  includes an error amplifier circuit  50  and a comparison circuit  51 , which are connected to the output terminal of the inductor  57 , a thinning circuit  52  connected to the comparison circuit  51 , a PWM circuit  53  connected to the thinning circuit  52  and the error amplifier circuit  50 , a driving circuit  54  connected to the PWM circuit  53 , a MOS-FET  56  (referred to as “MOS  56 ”, hereinafter) connected to the driving circuit  54  and a gate, an inductor  57 , a diode  58  and a capacitor  59 . A source of the MOS  56  is connected to the main power supply VDD while a drain of the MOS  56  is connected to the input terminal of the inductor  57 . The MOS  56 , the inductor  57 , the diode  58  and the capacitor  59  convert the power supply voltage to an output voltage of the DC/DC conversion circuit  31 , which is then passed to the wiring  41 . 
     The error amplifier circuit  50  amplifies an error by comparing an output voltage of the output terminal of inductor  57  and the reference potential Vref. The amplified signal is outputted to the PWM circuit  53 . The comparison circuit  51  compares the output voltage of the output terminal of the inductor  57  and the reference potential Vcmp. The output of the comparison circuit  51  causes the thinning circuit  52  to execute a thinning process when the output voltage is greater than the reference potential Vcmp. The thinning circuit  52  thins a part of the reference waveform outputted from the chopping wave generating circuit  80  in accordance with a result of the comparison (the result being a thinning request signal) performed by the comparison circuit  51  and transmits the thinned reference waveform to the PWM circuit  53 . The PWM circuit  53  generates a switching signal as a PWM signal for switching the MOS  56  based on the thinned reference waveform. The driving circuit  54  converts a voltage level of the PWM signal outputted from the PWM circuit  53  to switch the MOS  56 . A switch A is connected between the driving circuit  54  and the gate of the MOS  56  to enable ON/OFF control between the driving circuit  54  and the gate of the MOS  56 . 
     In accordance with the first DC/DC converter  31 , the reference waveform of the chopping waves outputted from the chopping wave generating circuit  80  is thinned by the thinning circuit  52  when the comparison circuit  51  detects that the output voltage is greater than the reference potential Vcmp. The PWM circuit  53  generates the PWM signal as a switching signal based on the thinned chopping waves. This allows a PWM signal having a cycle synchronized with that of the PWM signal generated in the PWM control circuit  61  of the second DC/DC converter  32  to be generated. 
     In the multi-function peripheral device  1 , an inductor  64  is connected to a wiring  42  connected to the main power supply VDD, a diode  65  is connected to an input terminal of the inductor  64 , and a capacitor  66  is connected to an output terminal of the inductor  64 . The second DC/DC converter  32  includes an error amplifier circuit  60  connected to the output terminal of the inductor  64 , a PWM circuit  61  connected to the error amplifier circuit  60 , a driving circuit  62  connected to the PWM circuit  61 , a MOS-FET  63  (referred to as “MOS  63 ”, hereinafter) connected to the driving circuit  62  and a gate, an inductor  64 , a diode  65  and a capacitor  66 . A source of the MOS  63  is connected to the main power supply VDD while a drain of the MOS  63  is connected to the input terminal of the inductor  64 . The MOS  63 , the inductor  64 , the diode  65  and the capacitor  66  convert the power supply voltage to an output voltage of the DC/DC conversion circuit  32 , which is then passed to the wiring  42 . 
     In accordance with the second DC/DC converter  32 , the error amplifier circuit  60  is used for comparing the reference voltage Vref 2  and the output voltage at output terminal of the inductor  64 . The output of the error amplifier circuit  60  is compared with the reference waveform of the chopping waves outputted from the chopping wave generating circuit  80  in the PWM circuit  61 . This allows the PWM signal to be generated. 
     The third DC/DC converter  33  includes a inductor  74  connected to a wiring  43  connected to the main power supply VDD, a diode  75  connected to an input terminal of the inductor  74 , a capacitor  76  connected to an output terminal of the inductor  74 , an error amplifier circuit  70  connected to the output of the inductor  74 , a PWM circuit  71  connected to the error amplifier circuit  70 , a driving circuit  72  connected to the PWM circuit  71  and a MOS-FET  73  (referred to as “MOS  73 ”, hereinafter) connected to the driving circuit  72  and a gate. A source of the MOS  73  is connected to the main power supply VDD while a drain of the MOS  73  is connected to the input terminal of the inductor  74 . The MOS  73 , the inductor  74 , the diode  75  and the capacitor  76  convert the power supply voltage to an output voltage of the DC/DC conversion circuit  33 , which is then passed to the wiring  43 . 
     In accordance with the third DC/DC converter  33 , the error amplifier circuit  70  is used for comparing the reference voltage outputted from the reference potential generating circuit  26  (refer to  FIG. 1 ) and the output voltage at the output terminal of the inductor  74 . The output of the error amplifier circuit  70  is compared with the reference waveform of the chopping waves outputted from the chopping wave generating circuit  80  by the PWM circuit  71 . This allows the PWM signal to be generated. 
     As described above, in accordance with the multi-function peripheral device  1 , the first DC/DC converter  31  and the second DC/DC converter  32  include in common the chopping wave generating circuit  80  for outputting the reference waveform necessary to generate the PWM signal. This allows a cycle of the PWM signal generated in the first DC/DC converter  31  to be synchronized with a cycle of the PWM signal generated in the second DC/DC converter  32  and a differential frequency component between the switching frequency component of the output voltage of the first DC/DC converter  31  and the switching frequency component of the output voltage of the second DC/DC converter  32  to be outside the audible range, so that generation of beats can be reduced. 
     Further, the main part of the first DC/DC converter  31  and the main part of the second DC/DC converter  32  are realized on the complex IC  30 , which is a single integrated circuit chip. This allows influence in variation among components to be reduced, compared with a case that the first DC/DC converter  31  and the second DC/DC converter  32  are separately realized on different integrated circuits, so that a cycle of the PWM signal generated in each DC/DC converter can be easily synchronized. 
     Now, another method of using the first to third DC/DC converters  31  to  33  will be described according to aspects of the invention with reference to  FIG. 4 . The components common to those in the above-described aspects are marked with the same reference numerals and signs and description thereof is omitted. In the a above described aspects is a case that a voltage of 1.2 V is generated from the power supply voltage VDD of 30 V by pulse width modulation and pulse frequency modulation in the first DC/DC converter  31 . 
     In the aspects of  FIG. 4 , connected in parallel are the first DC/DC converter  31  and the second DC/DC converter  32 . The output at the output terminal of the inductor  64  is input to the comparison circuit  60  of the second DC/DC converter  32 . The output at the output terminal of the inductor  64  is connected to the input terminal of the capacitor  66  and the output terminal of the capacitor  66  is connected to an input of the comparison circuits  50  and  51  of the first DC/DC converter  31 . Also, the output at the output terminal of the inductor  74  is connected to the input terminal of the capacitor  76  and the output terminal of the capacitor  76  is connected to an input of the comparison circuits  50  and  51 . 
     A switch A between the driving circuit  54  and the MOS  56  is switched OFF in accordance with an external mode switching signal and an inverter  55  while a switch B between the driving circuit  62  and the MOS  56  is switched ON in accordance with the inverter  55 . A wiring is provided from an output terminal of the inductor  64  of the second DC/DC converter  32  through Reg  81 . After an output voltage of 5.0 V is generated in the second DC/DC converter  32 , the Reg  81  is used for reducing the voltage from 5.0 V to 1.2 V to output a voltage of 1.2 V. In accordance with this method, the first DC/DC converter  31  and the second DC/DC converter  32  are driven in parallel, so that the capacity of the power supply can be increased. 
     Further aspects of using the first to third DC/DC converters  31  to  33  will be described with reference to  FIG. 5 . The components common to those in the above-mentioned aspects are marked with the same reference numerals and signs and description thereof is omitted. The current aspects relate to a method of using the complex IC  30  illustrated in  FIG. 3  and the complex IC  30  illustrated in  FIG. 4  (the Reg  81 , however, is excluded) in a parallel arrangement. In this case, five output voltages in total can be outputted. Also, it is possible to output voltages of an output voltage of 1.2 V, an output voltage of 5.0 V, a variable voltage of 15 to 28 V, an output voltage of 3.3 V and a variable voltage of 15 to 28 V in order from the output voltage in the upper part in  FIG. 5 . This allows the capacity of the power supply to be increased.