Patent Translate Powered by EPO and Google Notice This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate, complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or financial decisions, should not be based on machine-translation output. DESCRIPTION JPH0686382 [0001] BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speaker driving device for driving a speaker device. [0002] 2. Description of the Related Art In recent years, with the spread of digital sources and AV sources, there has been a demand for broadening the speaker apparatus (in particular, expanding the frequency band in the low frequency direction). At the same time, with the spread of AV devices, the number of channels has been increased, and downsizing of the speaker device has also been required. [0003] Therefore, in order to obtain wider-band reproduced sound from the same speaker device, a speaker drive device has been developed in which various signal processing circuits are added to a power amplifier for driving the speaker device. [0004] By the way, in general, in the closed-type speaker device, the sound pressure in the low range 08-05-2019 1 decreases at the boundary of the lowest resonance frequency of the speaker cabinet. Furthermore, as the cabinet is miniaturized, this minimum resonant frequency is increased. In addition, the bass reflex type speaker device uses the principle of Helmholtz's resonator as the drive source to resonate the port by using the vibration of air in the cabinet, and utilizes the sound pressure radiated from the port to seal the same volume. The low-frequency reproduction limit can be expanded compared to the speaker device. However, since the magnitude of the sound pressure radiated from the port is determined by the volume of the cabinet and the characteristics of the speaker unit, there is a limit to the expansion of the low frequency reproduction band even if the port resonance frequency is set low. [0005] Therefore, MFB (Motional) as conventionally described in the magazine JAS Journal (published by the Japan Audio Society) in September 1999 pp. 14 to 20 and in March 1991 pp. 25 to 33. There has been a speaker driving device using the Feed Back method. [0006] Hereinafter, a speaker driving device using a conventional MFB method will be described. FIG. 6 shows a conventional speaker driving device using the MFB method. 61 is an amplifier for driving a speaker, 62 is a speaker, 63 is a detector for detecting the vibration state of the speaker 62, and 64 is proportional to the vibration acceleration, velocity and amplitude of the diaphragm of the speaker 62 based on the output of the detector 63 65 is an input signal, 66 is an equalizer for manipulating the frequency characteristic of the input signal 65, and 67 is a subtracter for calculating the difference between the output of the equalizer 66 and the output of the characteristic correction circuit 64, The amplifier 61 receives the output of the subtracter 67 as an input. [0007] As the detector 63, a method for mechanically, acoustically, optically or electrically detecting the vibration state of the speaker 62 is known. FIG. 7 shows a bridge method in the case of using an electrical method for the detector. Other current detection methods are also conceivable, but this 08-05-2019 2 will be described in an embodiment to be described later. In FIG. 7, 71 is the electric impedance (Rv + sLv) of the voice coil of the speaker 61, 72 is the back electromotive force generated in the voice coil, 73, 74, 75 and 76 are the resistors R1, R2, Rf and bridge circuits. Capacitors C2 and 77 are subtracters for calculating the difference between the voltages generated at resistors 74 and 75, respectively. Where Bl is the force coefficient of the speaker and vc is the vibration velocity of the voice coil. [0008] The operation of the bridge-type detector will be described. The voltage Ef generated at both ends of Rf is a combined current of the drive current by the amplifier 1 and the current by the back electromotive force (−B1 · vc). In addition, R1, R2 and C2 have constants set so that the voltage E2 generated at Rf when no back electromotive force is generated is generated at both ends of R2, and the conditions are (Equation 1) and (Equation 2) Become. [0009] Therefore, by calculating the difference between E2 and Ef by the subtractor 77, the difference voltage E0 becomes (Equation 3), and a voltage proportional to the vibration velocity vc of the voice coil can be obtained. [0010] Next, the characteristic correction circuit 64 has a transfer function β (s) shown in (Equation 4), and an acceleration signal and a velocity signal for correcting the characteristics of the speaker 62 from the velocity signal output from the detector 63 And output a voltage proportional to the amplitude signal. Here, βa is an acceleration coefficient, βv is a velocity coefficient, βx is an amplitude coefficient, and s = jω. [0011] The input signal 65 is frequency-compensated (low-pass boost) by the equalizer 66. Then, the 08-05-2019 3 subtracter 67 calculates the difference from the signal output from the characteristic correction circuit 64, and inputs the difference to the amplifier 61. The reason why the equalizer 66 is necessary is that the speaker drive device of this conventional example is compared with a band (middle high band) in which feedback is not performed in a band in which feedback is performed for negative feedback operation (low band to improve characteristics). The sound pressure is reduced by the amount returned. Therefore, the equalizer boosts the low range and compensates so that the sound pressure equivalent to the middle high range can be obtained. [0012] Furthermore, as this MFB method using a current detection method, Yamaha Co., Ltd., such as that described in the magazine "Radio and Experiment" (issued by Seibundo Shinkosha) April 1989, pp. 80-86. There has been a speaker drive device using active servo. [0013] Below, the speaker drive device using the conventional active servo is demonstrated. [0014] FIG. 8 shows a conventional speaker drive device using active servo. In FIG. 8, 81 is a speaker (the impedance viewed from the input terminal is RS), 82 is an amplifier for driving the speaker 81 at a constant voltage (amplification factor is A), 83 is a resistor (R0), 84 is a resistor ( RF), 85 is a detection resistor (pure resistor r) for detecting the current flowing through the speaker 81, 86 is an amplifier for amplifying a voltage generated across the detection resistor 85 (amplification factor is β), 87 is a resistor (R1) 88 is a resistor (R2), 89 is an equalizer (EQ) that changes the frequency characteristics of the input signal input to the speaker driver, and 810 is a resistor (R0). [0015] Next, the operation of this conventional example will be described. The amplifier 82 (the amplification factor A is determined by the ratio of the resistors 83 and 84. 08-05-2019 4 When the speaker 81 is driven at a constant voltage, the current I (S) flows to the speaker 81. The detection resistor 85 is connected in series to the speaker 81 in order to detect the current I (S) flowing to the speaker 81. Therefore, if the output voltage of the amplifier 82 is EO and r << R2, then [0016] The following holds. Therefore, assuming that the voltage I generated at both ends of the detection resistor 85 is Er, the current I (S) flowing to the speaker 81 is [0017] It is determined as: The detected voltage Er is determined by the amplifier 86 (the amplification factor β is determined by the ratio of the resistors 87 and 88). Amplified). Here, since the detection resistor 85 is a pure resistor, the waveform of the voltage Er is similar to the waveform of the speaker current I (S). Further, the equalizer 89 changes the frequency characteristic of the input signal input to the speaker driving device for the reason described later. The sum of the output signal Ein of the equalizer 89 and the output of the amplifier 86 is determined by the amplifier 82 and the resistors 83 and 810, and this sum is amplified (the amplification factor is A). Here, assuming that the output voltage of the amplifier 86 is EF and the voltage applied to both ends of the speaker 81 is ES, the equations (7) to (12) are satisfied. [0018] Therefore, according to (Equation 5) to (Equation 12) [0019] 【0032】となる。 From the above, it is assumed that the output impedance RO of this speaker driving device is Ein = 0. 08-05-2019 5 [0020] If A · β> 0, the open stable negative impedance is obtained. If A · β> 1 and both A and β have flat frequency characteristics, negative resistance is obtained, and if A or β has frequency characteristics, the output impedance can have frequency characteristics. [0021] In the conventional example, the speaker 81 is a bass reflex type speaker device having a Helmholtz resonator port. Now, assuming that the resonance frequency of the port is fp, the sound pressure from the port has a single peak characteristic of -6 dB / oct centered on fp, and the phase of the sound pressure from the speaker unit and the port is in phase, In the band in which the sound pressure characteristic of the speaker unit is -6 dB / oct, the sound pressure of the speaker unit and the port is combined to be flat, but in the other bands, the combined sound pressure is not flat. Therefore, by using the equalizer 89 to correct the frequency characteristics of the input signal, flat sound pressure characteristics can be obtained in the whole area. Therefore, by the above method, the impedance of the voice coil of the speaker unit is canceled by the negative impedance of the speaker driving device, so that the driving ability of the speaker in the low range is enhanced and sufficient sound pressure can be reproduced even at a port having a low resonance frequency. Thus, a wide band (especially in the low frequency direction) reproduction sound is obtained. [0022] That is, the current flowing to the voice coil of the speaker is detected by the detection resistor. Since the detected current is proportional to the vibration speed of the voice coil, the speaker bandwidth is expanded by performing so-called speed feedback in which the voltage generated at both ends of the detection resistor is amplified and fed back to the input. [0023] However, in the above-mentioned conventional configuration, it is necessary to insert a resistor in series between the amplifier and the speaker in order to detect the state of vibration of the diaphragm of the speaker. Therefore, it is necessary to reduce the resistance value of the 08-05-2019 6 detection resistor in order to reduce the power loss due to the problem of power loss due to the insertion of the resistor, and by reducing the resistance value, the detection voltage decreases and the external noise In order to compensate for the low frequency range with the equalizer, a large-output amplifier is required to obtain a sound pressure equivalent to the midrange from the speaker, and the amplifier is large. Had the problem of becoming [0024] The present invention solves the above-mentioned conventional problems, and enables downsizing of the amplifier by using a class D amplifier capable of high-efficiency power amplification as the amplifier, and detects the state of vibration of the speaker unit. Since the detector uses a coil of a low pass filter connected to the output of the pulse amplifier in the class D amplifier, no detection resistor is required, and power loss due to the detection resistor can be eliminated, and the detector The detection level can be optimized by increasing or decreasing the number of turns of the detection coil by using a detection coil that detects the current flowing in the coil of the low-pass filter connected to the output of the pulse amplifier. It is an object of the present invention to provide a speaker drive device that enables [0025] SUMMARY OF THE INVENTION In order to achieve the object, a speaker driving apparatus according to the present invention comprises binary state modulation means for converting an analog signal into a binary state modulation signal, and power amplification of the binary state modulation signal. Pulse amplification means, a first low pass filter which receives an output of the pulse amplification means and passes only a necessary frequency band, and a signal between both ends of a coil of the first low pass filter is an input only necessary frequency band A second low pass filter to be passed, an amplification means for amplifying the output of the second low pass filter, a first integrating means for integrating and amplifying an output of the second low pass filter, and an output of the first integrating means A second integrating means for amplifying, and an operating means for adding an input signal, an output of the amplifying means, an output of the first integrating means and an output of the second integrator, and the output of the operating means being binary It is obtained by a structure for inputting the state modulation means. [0026] Further, the speaker driving device according to the present invention has binary state modulation means for converting an analog signal into a binary state modulation signal, pulse amplification means for power amplification of the binary state modulation signal, and an output of the pulse amplification means as input. A first low pass filter for passing only a necessary frequency band, a current detection coil for detecting a current value flowing in a coil of the first 08-05-2019 7 low pass filter, and an output of the current detection coil as an input to pass only a necessary frequency band A second low pass filter, a first integrating means for integrating and amplifying an output of the second low pass filter, a second integrating means for integrating and amplifying an output of the first integrating means, an input signal and a second low pass The arithmetic unit may be configured to add the output of the filter, the output of the first integrator, and the output of the second integrator, and the output of the arithmetic unit may be input to the binary state modulation unit. It is. [0027] The present invention operates as follows by the above-mentioned constitution. That is, the binary state modulation means converts the analog signal into a binary state modulation signal. Pulse amplification means power amplifies this binary state modulated signal. The first low pass filter processes the output of the pulse amplification means, passes signals in the audio band, and drives the speaker. At this time, a current including the current flowing in the speaker flows in the coil constituting the first low pass filter. Then, the second low pass filter receives the voltage generated at both ends of this coil as an input, and passes the audio band signal. The output of the second low pass filter is proportional to the vibration acceleration of the voice coil of the speaker unit. The amplification means amplifies this acceleration signal. The first integration means integrates and amplifies the acceleration signal to generate a velocity signal. Furthermore, the second integration means integrates and amplifies the velocity signal to generate an amplitude signal. The calculating means adds the outputs of the input signal, the amplifying means, the first integrating means and the second integrating means, and inputs the result to the binary state modulating means. [0028] Further, the present invention operates as follows by the above-described configuration. That is, the binary state modulation means converts the analog signal into a binary state modulation signal. Pulse amplification means power amplifies this binary state modulated signal. The first 08-05-2019 8 low pass filter processes the output of the pulse amplification means, passes signals in the audio band, and drives the speaker. At this time, a current including the current flowing in the speaker flows in the coil constituting the first low pass filter. The current is detected by a current detection coil. Then, the second low pass filter receives a voltage generated at both ends of the current detection coil as an input, and passes an audio band signal. The output of the second low pass filter is proportional to the vibration acceleration of the voice coil of the speaker unit. The first integration means integrates and amplifies the acceleration signal to generate a velocity signal. Furthermore, the second integration means integrates and amplifies the velocity signal to generate an amplitude signal. The calculating means adds the outputs of the input signal, the second low pass filter, the first integrating means and the second integrating means, and inputs the result to the binary state modulating means. [0029] An embodiment of the present invention will be described below with reference to the drawings. [0030] FIG. 1 is a block diagram of a speaker driving apparatus according to a first embodiment of the present invention. In FIG. 1, 1 is a binary state modulator that converts an analog signal into a binary state modulation signal, 2 is a pulse amplifier that power-amplifies the output signal of binary state modulator 1, 3 is audio from the output of pulse amplifier 2 A low pass filter for passing a band signal, 4 is a coil constituting the low pass filter 3, 5 is a capacitor constituting the low pass filter 3, 6 is an output terminal of the present speaker driver, 7 is a speaker, 8 is a coil 4 at both ends A low pass filter 9 receives an output of the low pass filter 8. An integrator 10 integrates and amplifies an output of the low pass filter 11. An integrator 11 integrates and amplifies an output of the integrator 10. 12 is an input terminal of the present speaker driver, 13 is an equalizer for operating the frequency characteristic of an input signal inputted from the input terminal 12, and 14 is an An adder for calculating the sum of the outputs of the integrator 11 output and the integrator 10 and the output of the amplifier 9 of riser 13. [0031] FIG. 2 is an explanatory view for explaining the binary state modulator 1 and the pulse amplifier 2 of the speaker driving apparatus in the first embodiment, 21 is an input terminal for inputting an analog signal, 22 is a comparator, 23 is a triangular wave generation The resistors R1, R2 and 08-05-2019 9 26 are drive amplifiers, 27 is a current amplifier, and 28 is an output terminal. [0032] FIG. 3 shows an example of a specific circuit of the first embodiment, wherein 31 is a power amplifier, 32 is a coil, 33 is a capacitor, 34 is an output terminal, 35 is an input terminal, 36 is an equalizer, 310 to 327 are Resistors 330-332 are capacitors, and 341-348 are amplifiers. [0033] The operation of the first speaker driving device of the present invention configured as described above will be described below. The binary state modulator 1 modulates the input analog audio signal to a binary state, and the pulse amplifier 2 power-amplifies this binary state modulation signal. The binary state modulator 1 and the pulse amplifier 2 constitute a class D amplifier which is a high efficiency power amplifier. The operation of this class D amplifier will be described with reference to FIG. FIG. 2 shows a PWM (Pulse Width Modulation) type power amplifier. The analog audio signal input from the input terminal 21 is input to the inverting input of the comparator 22 via the resistor 24. The triangular wave signal generated by the triangular wave generator 23 is input to the non-inverted input of the comparator 23. The comparator 22 compares the amplitudes of the two types of input signals, and converts the analog audio signal input to the inverting input into a 1-bit digital signal. The output Co of the comparator is as follows. When audio signal 三角 波 triangular wave signal Co = 0, when audio signal <triangular wave signal Co = 1, ie, the audio signal is converted into a binary state modulation signal using the frequency of the triangular wave signal as a carrier. The output of the comparator 22 is power amplified by the drive amplifier 26 and the current amplifier 27. The output of the current amplifier 27 is fed back via the resistor 25 to the inverting input of the comparator and the voltage gain is the ratio R2 / R1 of the resistors 24 and 25. [0034] A low-pass filter 3 consisting of a coil 4 and a capacitor 5 removes the unnecessary frequency components from the binary state modulation signal thus power-amplified, thereby extracting an 08-05-2019 10 audio band signal. That is, the audio signal input to the binary state modulator 1 is power amplified and output from the output terminal 6. When the speaker 7 is connected to the output terminal 6 as a load, current flows through the voice coil and the diaphragm vibrates to generate a sound wave. The current flowing through the coil 4 is the sum of the current flowing through the capacitor 5 and the current flowing through the voice coil of the speaker 7. However, since the current having the component of the audio band does not flow in the capacitor 5, the current having the component of the audio band in the current flowing in the coil 4 is equal to the current flowing in the speaker 7. Further, the current flowing through the speaker 7 is proportional to the vibration speed of the voice coil. Therefore, focusing on the current flowing through the coil 4, the vibration state of the speaker 7 can be detected. [0035] As a current flows in the coil 4, a voltage is generated at both ends of the coil 4. When a voltage generated at both ends of the coil 4 is input to the low pass filter 8 which passes the signal of the audio band, a differential of the current flowing through the voice coil of the speaker 7, that is, a voltage proportional to the vibration acceleration of the voice coil Output from 8 The amplifier 9 amplifies this output. This is feedback of the acceleration component, and the feedback coefficient is determined by the inductance of the coil 4 and the voltage gain of the amplifier 9. Also, the integrator 10 integrates and amplifies the output of the low pass filter 8 to generate a signal proportional to the vibration velocity of the voice coil. This is feedback of the velocity component, and the feedback factor is determined by the inductance of the coil 4 and the voltage gain of the integrator 10. Furthermore, the integrator 11 integrates and amplifies the output of the integrator 10 to generate a signal proportional to the vibration amplitude of the voice coil. This is feedback of the amplitude component, and the feedback coefficient is determined by the product of the inductance of the coil 4 and the voltage gain of the integrator 10 and the voltage gain of the integrator 11. [0036] Next, the equalizer 13 performs frequency correction on the audio signal input from the input terminal 12 for the reason described in the prior art. Then, the adder 14 calculates the sum of the output of the equalizer, the output of the amplifier 9 which is a feedback signal, the output of the integrator 10 and the output of the integrator 11, and outputs the sum to the binary state modulator 1. 08-05-2019 11 [0037] A description will now be given of FIG. The resistors 310 to 314, the capacitor 330 and the amplifiers 341 and 342 constitute a low pass filter 8. The transfer function G1 (s) of the low-pass filter 8 is expressed by Formula 15 when the cutoff angular frequency is ω1 (= 1 / C1 · R1). [0038] Further, assuming that the inductance of the coil 32 is L and the flowing current is I, the voltage generated at both ends of the coil 32 is s · L · I, and the current I is differentiated. Then, the output voltage E3 of the amplifier 342 is expressed by Equation 16. [0039] The resistors 315 to 318 and the amplifiers 343 and 344 constitute the amplifier 9, and the voltage gain is R4 / R3. Assuming that the output voltage of the amplifier 344 is E2, the following equation 17 is established. [0040] The coil 32 constitutes a low pass filter which limits the frequency band of the output signal of the amplifier 31 together with the capacitor 33, and its inductance L is fixed. Therefore, the ratio of the resistors 317 and 318 is changed to determine the constant of the acceleration feedback. [0041] The resistors 319 to 321, the capacitor 331, and the amplifiers 345 and 346 constitute the integrator 10. The transfer function G2 (s) is (Expression 18), the output voltage E3 of the amplifier 346 is (Expression 19), and the voice of the speaker 7 is It outputs a voltage proportional to the vibration speed of the coil. The velocity feedback constant is determined by the capacitor 331 and the resistor 319. 08-05-2019 12 [0042] The resistor 322, the capacitor 332 and the amplifier 347 constitute an integrator 11, and the output voltage E4 of the amplifier 347 becomes (Equation 20), and outputs a voltage proportional to the vibration amplitude of the voice coil of the speaker 7. The amplitude feedback constant is determined by the capacitors 331 and 332 and the resistors 319 and 322. [0043] The audio signal input from the input terminal 35 is corrected in frequency characteristic by the equalizer 36. [0044] The resistors 323 to 327 and the amplifier 348 constitute the adder 14 and add the output of the equalizer 36, the acceleration component that is the output of the amplifier 344, the velocity component that is the output of the amplifier 346, and the amplitude component that is the output of the amplifier 347 And the power amplifier 31 drives the speaker 7. [0045] As described above, in the first embodiment of the present invention, a small, high-power amplifier is realized by using a class D amplifier for the power amplifier, and the vibration acceleration of the voice coil of the speaker is connected to the output of the class D amplifier. The voltage is generated from the voltage generated at both ends of the coil constituting the low pass filter. Then, this signal is integrated to generate the vibration velocity and vibration acceleration of the voice coil, and acceleration, velocity, and amplitude combined feedback are performed to improve the low frequency characteristic of the speaker. [0046] FIG. 4 shows a block diagram of a speaker driving apparatus in a second embodiment of the 08-05-2019 13 present invention. In FIG. 4, 41 is a binary state modulator that converts an analog signal to a binary state modulation signal, 42 is a pulse amplifier that power-amplifies the output signal of binary state modulator 41, 43 is an audio from the output of pulse amplifier 42 A low pass filter for passing signals in a band, 44 is a coil constituting the low pass filter 43, 45 is a capacitor constituting the low pass filter 43, 46 is an output terminal of the present speaker driver, 47 is a speaker, 48 is a current flowing in the coil 44 49 is a low pass filter that receives a voltage signal generated at both ends of the coil 48, 410 is an integrator that integrates and amplifies the output of the low pass filter 49, and 411 is an integrator that integrates and amplifies the output of the integrator 410 , 412 is an input terminal of the present speaker driver, and 413 is an input terminal inputted from the input terminal 412. Equalizer to manipulate the frequency characteristic of the signal, 414 is an adder for calculating the sum of the outputs of the low pass filter 49 of the equalizer 413 and the output of the integrator 410 and the output of the integrator 411. [0047] FIG. 5 shows an example of a specific circuit of the second embodiment, 51 is a power amplifier, 52 is a coil, 53 is a capacitor, 54 is an output terminal, 55 is a coil for detecting the current flowing in the coil 52, 56 is An input terminal 57 is an equalizer, 510 to 519 are resistors, 520 to 522 are capacitors, and 530 to 533 are amplifiers. [0048] The operation of the second speaker driving device of the present invention thus configured will be described below. 4, the binary state modulator 41, the pulse amplifier 42, the low pass filter 43, the coil 44 and the capacitor 45 that configure it, the output terminal 46, the speaker 47, the integrator 410, the integrator 411, the input terminal 412, the equalizer 413, The adder 414 includes the binary state modulator 1, the pulse amplifier 2, the low pass filter 3, the coil 4 and the capacitor 5 constituting the same, the output terminal 6, the speaker 7, the integrator 10, the integrator 11, and the input in FIG. The terminal 12 performs exactly the same operation as the equalizer 13 and the adder 14. [0049] 08-05-2019 14 First, the binary state modulator 41 modulates an input analog audio signal into a binary state signal, and the pulse amplifier 42 power-amplifies the binary state modulation signal. Then, a low-pass filter 43 consisting of a coil 44 and a capacitor 45 removes unnecessary frequency components from the power-amplified binary state modulation signal, and a signal in the audio band is extracted. That is, the audio signal input to the binary state modulator 41 is power amplified and output from the output terminal 46. When a speaker 47 is connected to the output terminal 46 as a load, current flows through the voice coil and the diaphragm vibrates to generate a sound wave. The current flowing through the coil 44 is the sum of the current flowing through the capacitor 45 and the current flowing through the voice coil of the speaker 47. However, since a current having a component of the audio band does not flow in the capacitor 45, a current having a component of the audio band in the current flowing in the coil 44 is equal to the current flowing in the speaker 47. Also, the current flowing through the speaker 47 is proportional to the vibration speed of the voice coil. Therefore, paying attention to the current flowing through the coil 44, the vibration state of the speaker can be detected. [0050] On the other hand, the current detection coil 48 wound around the coil 44 detects the current flowing through the coil 44 by mutual induction, and outputs a voltage generated at both ends of the coil proportional to the current as a detection signal. The low pass filter 49 passes a signal in the audio band from this detection signal to generate a signal proportional to the vibration acceleration of the voice coil of the speaker 47. Since the level of the detection signal generated in the current detection coil 48 can be increased or decreased by increasing or decreasing the number of turns of the current detection coil 48, the amplifier 9 is not necessary as in the first embodiment of the present invention. This will be described later with reference to FIG. [0051] The integrator 410 integrates and amplifies the output of the low pass filter 49 to generate a signal proportional to the vibration velocity of the voice coil of the speaker 47. Further, the integrator 411 integrates and amplifies the output of the integrator 410 to generate a signal proportional to the vibration amplitude of the voice coil of the speaker 47. [0052] 08-05-2019 15 Also, the audio signal input from the input terminal 412 has its frequency characteristic controlled by the equalizer 413 for the reason described in the prior art. The adder 414 adds the input signal output from the equalizer 413, the acceleration signal output from the low pass filter 49, the velocity signal output from the integrator 410, and the amplitude signal output from the integrator 411. The output of the adder 414 performs combined acceleration, velocity, and amplitude feedback input to the binary state modulator 41. [0053] A description will be given of FIG. 5 which shows the above configuration as a specific circuit. The resistor 510 and the capacitor 520 constitute a low pass filter 49. The transfer function of the low pass filter 49 is the same as the low pass filter 8. Assuming that the inductance of the coil 52 is L, the number of turns is N, the flowing current is I, and the number of turns of the current detection coil 55 is M, the voltage across the current detection coil is E5 is Becomes (Equation 22). [0054] The output of the low pass filter 49 is a signal proportional to the acceleration signal of the voice coil. Therefore, the detection level can be changed by changing the number of turns M of the current detection coil 55. [0055] The resistors 511 to 513, the capacitor 521, and the amplifiers 530 and 531 constitute an integrator 410. The transfer function is the same as that of the integrator 10, and the output voltage E7 is (Equation 23). A voltage proportional to the vibration speed of the voice coil of the speaker 47 is output. [0056] The resistor 514, the capacitor 522 and the amplifier 532 constitute an integrator 411, and the output voltage E8 of the amplifier 532 becomes (Eq. 24), and outputs a voltage proportional to 08-05-2019 16 the vibration amplitude of the voice coil of the speaker 47. [0057] The equalizer 57 corrects the frequency characteristics of the audio signal input from the input terminal 56. [0058] The resistors 515 to 519 and the amplifier 533 constitute an adder 414, and an output of the equalizer 57, an acceleration component which is a voltage across the capacitor 520, a velocity component which is an output of the amplifier 531, and an amplitude component which is an output of the amplifier 532 The signals are added and input to the power amplifier 51, and the speaker 47 is driven by the power amplifier 51. [0059] As described above, in the second embodiment of the present invention, a compact, high-power amplifier is realized by using a class D amplifier for the power amplifier, and the vibration acceleration of the voice coil of the speaker is connected to the output of the class D amplifier. The current flowing through the coil constituting the low pass filter is detected by the current detection coil and processed and generated by the low pass filter. Then, this signal is integrated to generate the vibration velocity and vibration acceleration of the voice coil, and acceleration, velocity, and amplitude combined feedback are performed to improve the low frequency characteristic of the speaker. [0060] As described above, according to the present invention, the vibration state (acceleration, velocity, amplitude) of the voice coil is detected from the current flowing through the voice coil of the speaker, and the MFB is performed based on this. By driving the speaker with a class D amplifier that can perform power amplification with high efficiency, an effect of enabling downsizing of the amplifier can be obtained. [0061] In addition, a detector that detects the state of vibration of the speaker unit uses a voltage 08-05-2019 17 generated at both ends of a coil that constitutes a low pass filter that passes audio band signals connected to the output of the pulse amplifier in the class D amplifier. This eliminates the need for the use of a resistor, thus providing the effect of eliminating the power loss due to the detection resistor. [0062] Furthermore, using a detection coil that detects the current flowing through the coil of the lowpass filter connected to the output of the pulse amplifier in the detector, the detection level can be optimized by increasing or decreasing the number of turns of the detection coil. The effect of making it possible to omit is obtained. [0063] Brief description of the drawings [0064] 1 is a block diagram showing the configuration of a speaker drive device according to a first embodiment of the present invention. [0065] 2 is a circuit diagram showing the configuration of the binary state modulator and the pulse amplifier of the speaker driving device in the first embodiment. [0066] 3 is a circuit diagram showing a specific configuration of the speaker drive device of the first embodiment. [0067] FIG. 4 is a block diagram showing the configuration of a speaker driving device according to a second embodiment of the present invention. [0068] 5 is a circuit diagram showing a specific configuration of the speaker drive device of the second embodiment. 08-05-2019 18 [0069] Fig. 6 is a block diagram showing the configuration of a speaker driving device using the conventional MFB method. [0070] Fig. 7 A circuit diagram showing the conventional bridge type detector [0071] FIG. 8 is a block diagram showing the configuration of a conventional speaker drive device using active servo. [0072] Explanation of sign [0073] Reference Signs List 1 binary state modulator 2 pulse amplifier 3 8 low pass filter 4 coil 5 capacitor 6 output terminal 7 speaker 9 amplifier 10 11 integrator 12 input terminal 13 equalizer 14 adder 08-05-2019 19
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