Acoustic device

Abstract

This acoustic device enables a reduction in the power consumption of an amplifier for driving a capacitive load while suppressing restrictions on the frequency characteristics.　The acoustic device comprises a capacitive load and a driver that drives the capacitive load. The driver includes a first amplifier that amplifies a first frequency component included in an input signal, and a second amplifier that amplifies a second frequency component included in the input signal. The first frequency component may be a low-frequency component in an audible range, and the second frequency component may be a high-frequency component in the audible range. A power supply voltage of the first amplifier is variable to a signal level, and a power supply voltage of the second amplifier may be fixed to the signal level.

Description

sound equipment

[0001] The present technology relates to an acoustic device, and more particularly to an acoustic device provided with a capacitive load.

[0002] In audio equipment, amplifiers that drive capacitive loads are sometimes used. For example, in order to reduce current consumption, there is a technology that provides a resistor that constitutes a low-pass filter together with a capacitor that is equivalent to a piezoelectric element that outputs sound from the vibration of a piezoelectric body (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2018-107752

[0004] However, in the above-mentioned conventional technology, the high frequency characteristics are limited by the low-pass filter, which may restrict the frequency characteristics of the amplifier.

[0005] This technology was developed in light of these circumstances, and aims to reduce the power consumption of amplifiers that drive capacitive loads while minimizing restrictions on frequency characteristics.

[0006] The present technology has been made to solve the above-mentioned problems, and a first aspect thereof is an acoustic device including a capacitive load and a driver that drives the capacitive load, the driver including a first amplifier that amplifies a first frequency component included in an input signal and a second amplifier that amplifies a second frequency component included in the input signal, thereby providing an effect that a single vibrator is driven by two amplifiers having different amplification bands.

[0007] In the first aspect, the first frequency component may be a low-frequency component in an audible range, and the second frequency component may be a high-frequency component in the audible range. This brings about an effect that one capacitive load is driven based on the low-frequency amplifier and the high-frequency amplifier.

[0008] In the first aspect, the power supply voltage of the first amplifier may be variable with respect to a signal level, and the power supply voltage of the second amplifier may be fixed with respect to the signal level, thereby achieving the effect of amplifying large-amplitude low-frequency components while suppressing an increase in power consumption due to simultaneous input of high-frequency components.

[0009] In the first aspect, a power supply voltage of the second amplifier may be lower than a power supply voltage of the first amplifier, thereby suppressing an increase in power consumption due to simultaneous input of high-frequency components.

[0010] In a first aspect, the first amplifier may include a first operational amplifier, a first feedback resistor connected between the input and output of the first operational amplifier, a feedback capacitance connected in parallel to the first feedback resistor, and a first input resistor connected to the input of the first operational amplifier, and the second amplifier may include a second operational amplifier, a second feedback resistor connected between the input and output of the second operational amplifier, a series resistor connected in series with the second feedback resistor, and a second input resistor connected to the input of the second operational amplifier and connected to the connection point of the second feedback resistor and the series resistor. This provides the effect that a low-frequency amplifier and a high-frequency amplifier are configured based on the respective values ​​of the first feedback resistor, the first input resistor, the feedback capacitance, the second feedback resistor, the second input resistor, and the series resistor.

[0011] In the first aspect, the amplifier may further include an inverting amplifier that inverts the output of the first amplifier and inputs the inverted output to the series resistor, thereby reducing dips in the frequency response while enabling a reduction in the high-frequency gain of the low-frequency amplifier using a feedback capacitance.

[0012] In the first aspect, the values ​​of the first feedback resistor, the first input resistor, the second feedback resistor, the second input resistor, and the series resistor may be set so that the frequency characteristic of the combined output of the first amplifier output and the second amplifier output is flattened, thereby achieving the effect of flattening the frequency characteristic of the combined output of the first amplifier output and the second amplifier output without changing the circuit format.

[0013] In the first aspect, the first amplifier may include a first operational amplifier, a first feedback resistor connected between the input and output of the first operational amplifier, and a first input resistor connected to the input of the first operational amplifier, and the second amplifier may include a second operational amplifier, a second feedback resistor connected between the input and output of the second operational amplifier, and a second input resistor connected to the input of the second operational amplifier. This brings about an effect that a low-frequency amplifier and a high-frequency amplifier are configured based on the respective values ​​of the first feedback resistor, the first input resistor, the second feedback resistor, and the second input resistor.

[0014] In addition, in the first aspect, the first amplifier may include a first operational amplifier, a first feedback resistor connected between the input and output of the first operational amplifier, a feedback capacitance connected in parallel with the first feedback resistor, and a first input resistor connected to the input of the first operational amplifier, and the second amplifier may include a second operational amplifier, a second feedback resistor connected between the input and output of the second operational amplifier, a second input resistor connected to the input of the second operational amplifier, and an inverting amplifier that inverts the output of the second operational amplifier. This brings about an effect that a low-frequency amplifier and a high-frequency amplifier are configured based on the respective values ​​of the first feedback resistor, the first input resistor, the feedback capacitance, the second feedback resistor, and the second input resistor.

[0015] In the first aspect, the first amplifier and the second amplifier may each be a single-ended amplifier, thereby providing an effect that a capacitive load is driven based on a single-ended output.

[0016] In the first aspect, the first amplifier and the second amplifier may each be a differential amplifier, thereby providing an effect that a capacitive load is driven based on a differential output.

[0017] In the first aspect, the acoustic device may be a piezoelectric speaker, a MEMS (Micro Electro Mechanical Systems) speaker, a piezoelectric earphone, a MEMS earphone, a piezoelectric headphone, or a MEMS headphone. This brings about an effect that an acoustic device is configured using a capacitive load.

[0018] 1 is a block diagram showing an example of the configuration of an audio device according to a first embodiment; FIG. 2 is a diagram showing an example of the circuit configuration of a driver according to the first embodiment; FIG. 3 is a diagram showing an example of the circuit configuration of a driver according to a second embodiment; FIG. 4 is a diagram showing a transfer function of a low-frequency amplifier according to the second embodiment; FIG. 5 is a diagram showing a transfer function in which the output of a low-frequency amplifier and the output of a high-frequency amplifier according to the second embodiment are combined; FIG. 6 is a diagram showing an example of the circuit configuration of a driver according to a third embodiment; FIG. 7 is a diagram showing an example of the circuit configuration of a driver according to a fourth embodiment; FIG. 8 is a diagram showing an example of the circuit configuration of a driver according to a fifth embodiment; and FIG.

[0019] Hereinafter, modes for implementing the present technology (hereinafter referred to as embodiments) will be described. The description will be made in the following order: 1. First embodiment (an example in which a low-frequency amplifier and a high-frequency amplifier are configured differentially, and a feedback resistor and a feedback capacitor are provided in the low-frequency amplifier) ​​2. Second embodiment (an example in which a low-frequency amplifier and a high-frequency amplifier are configured single-ended, and a feedback resistor and a feedback capacitor are provided in the low-frequency amplifier) ​​3. Third embodiment (an example in which a low-frequency amplifier and a high-frequency amplifier are configured differentially, and a feedback resistor is provided in the low-frequency amplifier) ​​4. Fourth embodiment (an example in which a low-frequency amplifier and a high-frequency amplifier are configured single-ended, and a feedback resistor is provided in the low-frequency amplifier) ​​5. Fifth embodiment (an example in which a low-frequency amplifier and a high-frequency amplifier are configured differentially, and a feedback resistor and a feedback capacitor are provided in the low-frequency amplifier, and phase inversion in the high frequency range is permitted) 6. Sixth embodiment (an example in which a low-frequency amplifier and a high-frequency amplifier are configured single-ended, and a feedback resistor and a feedback capacitor are provided in the low-frequency amplifier, and phase inversion in the high frequency range is permitted)

[0020] 1. First Embodiment FIG. 1 is a block diagram showing an example of the configuration of an audio device according to a first embodiment.

[0021] In the figure, the acoustic device includes a capacitive load 133 and a driver 100. The capacitive load 133 is a piezoelectric speaker, a MEMS (Micro Electro Mechanical Systems) speaker, a piezoelectric earphone, a MEMS earphone, a piezoelectric headphone, or a MEMS headphone. In this case, the capacitive load 133 may include a piezoelectric body or a diaphragm driven by the driver 100.

[0022] Driver 100 drives capacitive load 133. Driver 100 includes low-frequency amplifier 111 and high-frequency amplifier 121. Low-frequency amplifier 111 and high-frequency amplifier 121 can drive capacitive load 133 in parallel. In this case, low-frequency amplifier 111 and high-frequency amplifier 121 may be connected in parallel to capacitive load 133. Low-frequency amplifier 111 and high-frequency amplifier 121 can each operate as a differential amplifier.

[0023] The low-frequency amplifier 111 amplifies a first frequency component included in the input signal Vin. The first frequency component may be a low-frequency component in the audible range. The low-frequency amplifier 111 may be configured using an inverting amplifier or a non-inverting amplifier.

[0024] The high-frequency amplifier 121 amplifies a second frequency component included in the input signal Vin. The second frequency component may be a high-frequency component in the audible range. The high-frequency amplifier 121 may be configured using a non-inverting amplifier.

[0025] The low-frequency amplifier 111 is powered by a power supply voltage VDD via a variable boost circuit 112. At this time, the variable boost circuit 112 boosts the power supply voltage VDD in accordance with the level of the input signal Vin and supplies the boosted voltage to the power supply of the low-frequency amplifier 111. For example, when the level of the input signal Vin is low, the variable boost circuit 112 can reduce the power supply voltage supplied to the power supply of the low-frequency amplifier 111. On the other hand, when the level of the input signal Vin is high, the variable boost circuit 112 can increase the power supply voltage supplied to the power supply of the low-frequency amplifier 111. This allows the low-frequency amplifier 111 to operate as a class H amplifier, thereby reducing power consumption while suppressing a decrease in the low-frequency dynamic range.

[0026] The high-frequency amplifier 121 is powered by a power supply voltage VDD via a step-down circuit 122. At this time, the step-down circuit 122 steps down the power supply voltage VDD and supplies the resulting voltage to the power supply of the high-frequency amplifier 121. The power supply voltage of the high-frequency amplifier 121 can be set to a fixed value. The power supply voltage of the high-frequency amplifier 121 can be lower than the power supply voltage of the low-frequency amplifier 111.

[0027] One end of the capacitive load 133 is connected to a power supply potential via a bias resistor 134 , and the other end of the capacitive load 133 is connected to a ground potential via a bias resistor 135 .

[0028] An input signal Vin is input to the differential inputs of low-frequency amplifier 111 via capacitors 113 and 114. An input signal Vin is input to the differential inputs of high-frequency amplifier 121 via capacitors 123 and 124. Note that capacitors 123 and 124 are not necessarily required; the input voltages of low-frequency amplifier 111 and high-frequency amplifier 121 may be set to the same value, and the outputs of capacitors 113 and 114 may be connected to low-frequency amplifier 111 and high-frequency amplifier 121.

[0029] The differential output of low-frequency amplifier 111 is connected to both ends of capacitive load 133 via resistors 115 and 116 and capacitors 131 and 132, respectively. The differential output of high-frequency amplifier 121 is connected to both ends of capacitive load 133 via capacitors 125 and 126 and capacitors 131 and 132, respectively. Capacitors 113, 114, 123, 124, 131, and 132 can be operated as DC-blocking capacitors. In this case, driver 100 can drive capacitive load 133 based on the combined differential output of low-frequency amplifier 111 and high-frequency amplifier 121.

[0030] FIG. 2 is a diagram illustrating an example of a circuit configuration of a driver according to the first embodiment.

[0031] In the figure, the low-frequency amplifier 111 includes an operational amplifier 210. A feedback resistor 214 is connected between the inverting input and inverting output of the operational amplifier 210. A feedback capacitor 213 is connected in parallel to the feedback resistor 214. An input resistor 211 is connected in series to the inverting input of the operational amplifier 210, and a capacitor 113 is connected in series to the input resistor 211. A resistor 115 is connected in series to the inverting output of the operational amplifier 210, and a capacitor 131 is connected in series to the resistor 115.

[0032] A feedback resistor 216 is connected between the non-inverting input and non-inverting output of the operational amplifier 210. A feedback capacitor 215 is connected in parallel to the feedback resistor 216. An input resistor 212 is connected in series to the non-inverting input of the operational amplifier 210, and a capacitor 114 is connected in series to the input resistor 212. A resistor 116 is connected in series to the non-inverting output of the operational amplifier 210, and a capacitor 132 is connected in series to the resistor 116.

[0033] The resistance values ​​of the input resistors 211 and 212 and the feedback resistors 214 and 216 can be set so as to increase the gain of the low-frequency components of the input signal Vin, and the capacitance values ​​of the feedback capacitors 213 and 215 can be set so as to decrease the gain of the high-frequency components of the input signal Vin.

[0034] The high-frequency amplifier 121 includes an operational amplifier 220. A feedback resistor 223 is connected between the inverting input and inverting output of the operational amplifier 220. An input resistor 221 is connected in series to the inverting input of the operational amplifier 220, and a capacitor 123 is connected in series to the input resistor 221. The inverting input of the operational amplifier 220 is connected to the non-inverting output of the operational amplifier 210 via a capacitor 226 and a series resistor 225. In this case, the phase of the inverting input of the operational amplifier 220 can be reversed to the phase of the non-inverting output of the operational amplifier 210, thereby compensating for phase inversion caused by the low-frequency amplifier 111. A capacitor 125 is connected in series to the inverting output of the operational amplifier 220, and a capacitor 131 is connected in series to the capacitor 125.

[0035] A feedback resistor 224 is connected between the non-inverting input and non-inverting output of the operational amplifier 220. An input resistor 222 is connected in series to the non-inverting input of the operational amplifier 220, and a capacitor 124 is connected in series to the input resistor 222. The non-inverting input of the operational amplifier 220 is connected to the non-inverting output of the operational amplifier 210 via a capacitor 228 and a series resistor 227 in this order. In this case, the phase of the non-inverting input of the operational amplifier 220 can be reversed to the phase of the inverting output of the operational amplifier 210, thereby compensating for phase inversion caused by the low-pass amplifier 111. A capacitor 126 is connected in series to the non-inverting output of the operational amplifier 220, and a capacitor 132 is connected in series to the capacitor 126.

[0036] Here, the resistance values ​​of the input resistors 221 and 222 and the resistance values ​​of the feedback resistors 223 and 224 can be set so as to increase the gain of the high-frequency component of the input signal Vin.

[0037] When an input signal Vin is input to low-frequency amplifier 111 and high-frequency amplifier 121, the low-frequency component of the input signal Vin is amplified by low-frequency amplifier 111, and the high-frequency component of the input signal Vin is amplified by high-frequency amplifier 121. The differential output of low-frequency amplifier 111 and the differential output of high-frequency amplifier 121 are then combined, and capacitive load 133 is driven based on the combined differential output.

[0038] As described above, in the first embodiment, one capacitive load 133 is driven based on the combined differential output of the differential output of low-frequency amplifier 111 and the differential output of high-frequency amplifier 121. As a result, even if the power supply voltage of low-frequency amplifier 111 rises when low-frequency amplifier 111 amplifies large-amplitude low-frequency components, the power supply voltage of high-frequency amplifier 121 can be kept constant while maintaining the gain of the high-frequency components in high-frequency amplifier 121. This makes it possible to suppress a decrease in the dynamic range of the low-frequency components and high-frequency components, while suppressing an increase in power consumption due to simultaneous input of high-frequency components.

[0039] 2. Second Embodiment In the first embodiment described above, low-frequency amplifier 111 and high-frequency amplifier 121 each have a differential configuration, and feedback resistors 214 and 216 and feedback capacitors 213 and 215 are provided in low-frequency amplifier 111. In this second embodiment, the low-frequency amplifier and high-frequency amplifier each have a single-ended configuration, and the feedback resistor and feedback capacitor are provided in the low-frequency amplifier.

[0040] FIG. 3 is a diagram illustrating an example of a circuit configuration of a driver according to the second embodiment.

[0041] In the figure, the driver includes a low-frequency amplifier 311 and a high-frequency amplifier 321. The low-frequency amplifier 311 and the high-frequency amplifier 321 can drive a capacitive load 133 in parallel. In this case, the low-frequency amplifier 311 and the high-frequency amplifier 321 may be connected in parallel to the capacitive load 133.

[0042] The low-frequency amplifier 311 includes an operational amplifier 410. A feedback resistor 414 is connected between the input and output of the operational amplifier 410. A feedback capacitor 413 is connected in parallel to the feedback resistor 414. An input resistor 411 is connected in series to the input of the operational amplifier 410. A resistor 416 is connected in series to the output of the operational amplifier 410, and a capacitive load 133 is connected in series to the resistor 416.

[0043] The resistance values ​​of the input resistor 411 and the feedback resistor 414 can be set so as to increase the gain of the low-frequency component of the input signal Vin, and the capacitance value of the feedback capacitor 413 can be set so as to decrease the gain of the high-frequency component of the input signal Vin.

[0044] The high-frequency amplifier 321 includes an operational amplifier 420. A feedback resistor 423 is connected between the input and output of the operational amplifier 420. An input resistor 421 is connected in series to the input of the operational amplifier 420. The input of the operational amplifier 420 is connected to the output of the operational amplifier 410 via an inverting amplifier 324, a capacitor 323, and a series resistor 425 in this order. The gain of the inverting amplifier 324 can be set to −1. In this case, the phase of the input of the operational amplifier 420 can be inverted from the phase of the output of the operational amplifier 410, thereby compensating for the phase inversion caused by the low-frequency amplifier 311. A capacitor 426 is connected in series to the output of the operational amplifier 420, and a capacitive load 133 is connected in series to the capacitor 426.

[0045] Here, the resistance values ​​of the input resistor 421 and the feedback resistor 423 can be set so as to increase the gain of the high-frequency component of the input signal Vin.

[0046] In this case, the relationship between the input signal Vin and the composite output signal Vo can be given by the following equation: −Vo=(R ２ / R １ * 1 / (1+s(C ｘ +C Ｌ ) R ｘ ) *1 / (1+s(C ２ R ２ ))Vin + R ｘ / (C Ｌ / C ｘ (R ｘ +1 / sC Ｌ ) + R ｘ ) *R ５ / R ４ +R ５ / R ６ *R ２ / R １ * 1 / (1 + sC ２ R ２ )) Vin... (1)

[0047] However, R １ is the resistance value of the input resistor 411, R ２ is the resistance value of the feedback resistor 414, R ４ is the resistance value of the input resistor 421, R ５ is the resistance value of the feedback resistor 423, R ６ is the resistance value of the series resistor 425, R ｘ is the resistance value of resistor 131, C ２ is the capacitance value of the feedback capacitor 413, C ｘ is the capacitance value of the capacitor 132, C Ｌ is the capacitance value of the capacitive load 133.

[0048] The following equation (2) is obtained from equation (1): If the gain m of the high-frequency amplifier 321 is made equal to the gain m of the single amplifier configuration, R ４ =R ５ / m, R ６ = nR ５ As a result, the following equation (3) is obtained: Since the power supply voltage of the high-frequency amplifier 321 is lower than the power supply voltage of the low-frequency amplifier 311, n>1 holds.

[0049] -Vo=(C ２ C ｘ R １ R ２ R ５ R ６ R ｘ s ２ + (R １ R ５ R ６ +R ２ R ４ R ５ ) C ｘ R ｘ s+R ２ R ４ R ６ ) / ((C ２ C ｘ +C ２ C Ｌ ) R １ R ２ R ｘ s ２ + (C ｘ +C Ｌ ) R １ R ４ R ６ R ｘ +C ２ R １ R２ R ４ R ６ ) s + R １ +R １ R ４ R ６ ) Vin...(2)

[0050] -Vo = (mC ２ C ｘ R １ R ２ R ｘ s ２ + (mC ｘ R ｘ +C ｘ R ２ / n)R ｘ s / ((C ２ C ｘ +C ２ C Ｌ ) R １ R ２ R ｘ s ２ + (C ｘ +C Ｌ ) R １ R ｘ +C ２ R １ R ２ ) s + R １ ) Vin... (3)

[0051] In formula (3), for example, R １ = 40 kΩ, R ２ = 800 kΩ, C Ｌ = 80nF, to make the performance of the two-amp low-frequency boost configuration equivalent to that of the one-amp low-frequency boost configuration, ｘ = 1000 nF, R ｘ = 6 kΩ.

[0052] At this time, the transfer function of low-frequency amplifier 311 boosts the low frequencies, as shown in Fig. 4. Also, as shown in Fig. 5, the transfer function of high-frequency amplifier 321 can have a lower gain than low-frequency amplifier 311, allowing for a lower power supply voltage. Also, as shown in Fig. 6, the transfer function of the combined output of the low-frequency amplifier output and the high-frequency amplifier output can achieve characteristics equivalent to those of a one-amplifier low-frequency boost configuration.

[0053] As described above, in the second embodiment, low-frequency amplifier 311 and high-frequency amplifier 321 each have a single-ended configuration, and feedback resistor 414 and feedback capacitor 413 are provided in low-frequency amplifier 311. This makes it possible to suppress a decrease in the dynamic range of the low-frequency components and high-frequency components, while suppressing an increase in power consumption due to simultaneous input of high-frequency components, even when capacitive load 133 is driven in a single-ended manner.

[0054] In the second embodiment described above, an example was shown in which the combined output of the low-frequency amplifier 311 and the high-frequency amplifier 321 has characteristics equivalent to those of a one-amplifier low-frequency boost configuration. However, the constants of the low-frequency amplifier 311 and the high-frequency amplifier 321 may be set so that the characteristics of the combined output of the low-frequency amplifier 311 and the high-frequency amplifier 321 are flattened. In this case, the resistance value R of the input resistor 411 １ , the resistance value R of the feedback resistor 414 ２ , the resistance value R of the input resistor 421 ４ , the resistance value R of the feedback resistor 423 ５ and the resistance value R of the series resistor 425 ６ By changing the frequency response of the low-frequency amplifier 311 and the high-frequency amplifier 321, the characteristics of the combined output can be flattened without changing the circuit configuration of the low-frequency amplifier 311 and the high-frequency amplifier 321.

[0055] 3. Third Embodiment In the first embodiment described above, low-frequency amplifier 111 and high-frequency amplifier 121 each have a differential configuration, and feedback resistors 214 and 216 and feedback capacitors 213 and 215 are provided in low-frequency amplifier 111. In this third embodiment, low-frequency amplifier 111 and high-frequency amplifier 121 each have a differential configuration, and feedback resistors 214 and 216 are provided in the low-frequency amplifier.

[0056] FIG. 7 is a diagram illustrating an example of a circuit configuration of a driver according to the third embodiment.

[0057] In the figure, the driver includes a low-frequency amplifier 511 and a high-frequency amplifier 521. The low-frequency amplifier 511 and the high-frequency amplifier 521 can drive a capacitive load 133 in parallel. In this case, the low-frequency amplifier 511 and the high-frequency amplifier 521 may be connected in parallel to the capacitive load 133.

[0058] Low-frequency amplifier 511 is similar to low-frequency amplifier 111 of the first embodiment except that feedback capacitors 213 and 215 are removed. The resistance values ​​of input resistors 211 and 212 and feedback resistors 214 and 216 can be set so as to increase the gain of the low-frequency component of input signal Vin. The remaining configuration of low-frequency amplifier 511 is the same as that of low-frequency amplifier 111 of the first embodiment.

[0059] High-frequency amplifier 521 is similar to high-frequency amplifier 121 of the first embodiment except that series resistors 225 and 227 and capacitors 226 and 228 are removed. The resistance values ​​of input resistors 221 and 222 and feedback resistors 223 and 224 can be set to increase the gain of the high-frequency component of input signal Vin. The remaining configuration of high-frequency amplifier 521 is the same as that of high-frequency amplifier 121 of the first embodiment.

[0060] In this case, low-frequency amplifier 511 and high-frequency amplifier 521 can form a non-inverting amplifier, which allows the phase polarity of the output of low-frequency amplifier 511 and the phase polarity of the output of high-frequency amplifier 521 to be aligned, making it unnecessary to compensate for phase inversion of low-frequency amplifier 511.

[0061] As described above, in the third embodiment, low-frequency amplifier 511 and high-frequency amplifier 521 are each configured differentially, and feedback resistors 214 and 216 are provided in low-frequency amplifier 511. In this case, the low frequencies can be amplified without phase inversion in low-frequency amplifier 511. This makes it possible to suppress a decrease in the dynamic range of the low-frequency and high-frequency components, while suppressing an increase in power consumption due to simultaneous input of high-frequency components, and also makes it unnecessary to compensate for phase inversion in low-frequency amplifier 511.

[0062] 4. Fourth Embodiment In the third embodiment described above, low-frequency amplifier 511 and high-frequency amplifier 521 each have a differential configuration, and feedback resistors 214 and 216 are provided in low-frequency amplifier 511. In this fourth embodiment, the low-frequency amplifier and high-frequency amplifier each have a single-ended configuration, and feedback resistor 414 is provided in the low-frequency amplifier.

[0063] FIG. 8 is a diagram illustrating an example of a circuit configuration of a driver according to the fourth embodiment.

[0064] In the figure, the driver includes a low-frequency amplifier 611 and a high-frequency amplifier 621. The low-frequency amplifier 611 and the high-frequency amplifier 621 can drive a capacitive load 133 in parallel. In this case, the low-frequency amplifier 611 and the high-frequency amplifier 621 may be connected in parallel to the capacitive load 133.

[0065] Low-frequency amplifier 611 is obtained by removing feedback capacitance 413 from low-frequency amplifier 311 of the second embodiment described above. Here, the resistance values ​​of input resistor 411 and feedback resistor 414 can be set so as to increase the gain of the low-frequency component of input signal Vin. Other configurations of low-frequency amplifier 611 are similar to those of low-frequency amplifier 311 of the second embodiment described above.

[0066] High-frequency amplifier 621 is obtained by removing series resistor 425 and capacitor 323 from high-frequency amplifier 321 of the second embodiment described above. Here, the resistance values ​​of input resistor 421 and feedback resistor 423 can be set so as to increase the gain of the high-frequency component of input signal Vin. Other configurations of high-frequency amplifier 621 are the same as those of high-frequency amplifier 321 of the second embodiment described above.

[0067] In this case, low-frequency amplifier 611 and high-frequency amplifier 621 can form a non-inverting amplifier. This allows the phase polarity of the output of low-frequency amplifier 611 and the phase polarity of the output of high-frequency amplifier 621 to be aligned. This eliminates the need for compensation for phase inversion of low-frequency amplifier 611, and allows the inverting amplifier 324 of the second embodiment to be eliminated.

[0068] As described above, in the fourth embodiment, low-frequency amplifier 611 and high-frequency amplifier 621 each have a single-ended configuration, and feedback resistor 414 is provided in low-frequency amplifier 611. This makes it possible to suppress a decrease in the dynamic range of the low-frequency components and high-frequency components, suppress an increase in power consumption due to simultaneous input of high-frequency components, and eliminate the need for compensation for phase inversion in low-frequency amplifier 611, even when capacitive load 133 is driven in a single-ended manner.

[0069] 5. Fifth Embodiment In the first embodiment described above, low-frequency amplifier 111 and high-frequency amplifier 121 are each configured differentially, and feedback resistors 214 and 216 and feedback capacitors 213 and 215 are provided in low-frequency amplifier 111. In this fifth embodiment, low-frequency amplifier 111 and high-frequency amplifier 521, each configured differentially, are provided in a driver, and phase inversion of high-frequency amplifier 521 is permitted.

[0070] FIG. 9 is a diagram illustrating an example of a circuit configuration of a driver according to the fifth embodiment.

[0071] In the figure, the driver includes a low-frequency amplifier 111 and a high-frequency amplifier 521. The low-frequency amplifier 111 and the high-frequency amplifier 521 can drive a capacitive load 133 in parallel. In this case, the low-frequency amplifier 111 and the high-frequency amplifier 521 may be connected in parallel to the capacitive load 133.

[0072] The low-frequency amplifier 111 can be configured as an inverting amplifier, and the high-frequency amplifier 521 can be configured as a non-inverting amplifier. In this case, the phase polarity of the output of the low-frequency amplifier 511 and the phase polarity of the output of the high-frequency amplifier 521 are mutually reversed. Here, to compensate for the phase inversion of the low-frequency amplifier 511, the differential output of the low-frequency amplifier 111 and the differential output of the high-frequency amplifier 521 can be cross-coupled to each other. That is, the inverting output of the low-frequency amplifier 111 and the non-inverting output of the high-frequency amplifier 521 can be connected to each other via resistor 115 and capacitor 125. The non-inverting output of the low-frequency amplifier 111 and the inverting output of the high-frequency amplifier 521 can be connected to each other via resistor 116 and capacitor 126.

[0073] As described above, in the fifth embodiment, the driver is provided with low-frequency amplifier 111 and high-frequency amplifier 521, each configured differentially, and phase inversion of high-frequency amplifier 521 is permitted. In this case, it is possible to reduce dips that occur in the frequency characteristics of the combined output of the output of low-frequency amplifier 111 and the output of high-frequency amplifier 521, and to flatten the frequency characteristics of high-frequency amplifier 521. This makes it possible to further reduce the power supply voltage of high-frequency amplifier 521, suppressing a decrease in the dynamic range of the low-frequency and high-frequency components, while also suppressing an increase in power consumption due to the simultaneous input of high-frequency components.

[0074] 6. Sixth Embodiment In the fifth embodiment described above, the driver is provided with low-frequency amplifier 111 and high-frequency amplifier 521, each of which is configured differentially, and allows phase inversion of high-frequency amplifier 521. In this sixth embodiment, the driver is provided with low-frequency amplifier 311 and high-frequency amplifier 621, each of which is configured single-ended, and allows phase inversion of high-frequency amplifier 621.

[0075] FIG. 10 is a diagram showing an example of a circuit configuration of a driver according to the sixth embodiment.

[0076] In the figure, the driver includes a low-frequency amplifier 311 and a high-frequency amplifier 621. The low-frequency amplifier 311 and the high-frequency amplifier 621 can drive a capacitive load 133 in parallel. In this case, the low-frequency amplifier 311 and the high-frequency amplifier 621 may be connected in parallel to the capacitive load 133.

[0077] The low-frequency amplifier 311 can be configured as an inverting amplifier, and the high-frequency amplifier 621 can be configured as a non-inverting amplifier. In this case, the phase polarity of the output of the low-frequency amplifier 311 and the phase polarity of the output of the high-frequency amplifier 621 are reversed. Therefore, phase inversion can be tolerated in the high-frequency amplifier 621. In this case, compensation for phase inversion of the low-frequency amplifier 311 can be eliminated, and the inverting amplifier 324 of the second embodiment described above can be eliminated.

[0078] As described above, in the sixth embodiment, low-frequency amplifier 311 and high-frequency amplifier 621, each configured as a single end, are provided in the driver, and phase inversion of high-frequency amplifier 621 is permitted. In this case, it is possible to reduce dips that occur in the frequency characteristics of the combined output of low-frequency amplifier 311 and high-frequency amplifier 621, and flatten the frequency characteristics of high-frequency amplifier 621. This makes it possible to further reduce the power supply voltage of high-frequency amplifier 621, suppressing a decrease in the dynamic range of the low-frequency and high-frequency components, while also suppressing an increase in power consumption due to the simultaneous input of high-frequency components.

[0079] In the above-described embodiment, an example has been shown in which a low-frequency amplifier and a high-frequency amplifier are provided to drive the capacitive load 133. The present invention is not necessarily limited to a configuration in which a low-frequency amplifier and a high-frequency amplifier are provided, and for example, in addition to the low-frequency amplifier and the high-frequency amplifier, a mid-frequency amplifier, an ultra-low-frequency amplifier, or an ultra-high-frequency amplifier may be provided.

[0080] Note that the above-described embodiment shows an example for realizing the present technology, and the matters in the embodiment and the matters specifying the invention in the claims correspond to each other. Similarly, the matters specifying the invention in the claims and the matters in the embodiment of the present technology with the same title correspond to each other. However, the present technology is not limited to the embodiment, and can be realized by applying various modifications to the embodiment within the scope of the gist. Furthermore, the effects described in this specification are merely examples and are not limited, and other effects may also be present.

[0081] The present technology may also be configured as follows. (1) An acoustic device including: a capacitive load; and a driver that drives the capacitive load, wherein the driver includes: a first amplifier that amplifies a first frequency component included in an input signal; and a second amplifier that amplifies a second frequency component included in the input signal. (2) The acoustic device according to (1), wherein the first frequency component is a low-frequency component in an audible range, and the second frequency component is a high-frequency component in the audible range. (3) The acoustic device according to (2), wherein a power supply voltage of the first amplifier is variable with respect to a signal level, and wherein a power supply voltage of the second amplifier is fixed with respect to the signal level. (4) The acoustic device according to (2) or (3), wherein the power supply voltage of the second amplifier is lower than the power supply voltage of the first amplifier. (5) The audio device according to any one of (2) to (4), wherein the first amplifier comprises: a first operational amplifier, a first feedback resistor connected between the input and output of the first operational amplifier, a feedback capacitance connected in parallel to the first feedback resistor, and a first input resistor connected to the input of the first operational amplifier, and the second amplifier comprises: a second operational amplifier, a second feedback resistor connected between the input and output of the second operational amplifier, a series resistor connected in series with the second feedback resistor, and a second input resistor connected to the input of the second operational amplifier and connected to the connection point of the second feedback resistor and the series resistor. (6) The audio device according to (5), further comprising: an inverting amplifier that inverts the output of the first amplifier and inputs it to the series resistor. (7) The audio device according to (5) or (6), wherein the values ​​of the first feedback resistor, the first input resistor, the second feedback resistor, the second input resistor, and the series resistor are set so that the frequency characteristics of a combined output of the output of the first amplifier and the output of the second amplifier are flattened.(8) The acoustic device according to any of (2) to (4), wherein the first amplifier comprises: a first operational amplifier, a first feedback resistor connected between the input and output of the first operational amplifier, and a first input resistor connected to the input of the first operational amplifier, and the second amplifier comprises: a second operational amplifier, a second feedback resistor connected between the input and output of the second operational amplifier, and a second input resistor connected to the input of the second operational amplifier. (9) The acoustic device according to any of (2) to (4), wherein the first amplifier comprises: a first operational amplifier, a first feedback resistor connected between the input and output of the first operational amplifier, a feedback capacitance connected in parallel with the first feedback resistor, and a first input resistor connected to the input of the first operational amplifier, and the second amplifier comprises: a second operational amplifier, a second feedback resistor connected between the input and output of the second operational amplifier, a second input resistor connected to the input of the second operational amplifier, and an inverting amplifier that inverts the output of the second operational amplifier. (10) The acoustic device according to any one of (1) to (9), wherein the first amplifier and the second amplifier are each a single-ended amplifier. (11) The acoustic device according to any one of (2) to (9), wherein the first amplifier and the second amplifier are each a differential amplifier. (12) The acoustic device according to any one of (1) to (11), wherein the first amplifier and the second amplifier are a piezo speaker, a MEMS (Micro Electro Mechanical Systems) speaker, a piezo earphone, a MEMS earphone, a piezo headphone, or a MEMS headphone.

[0082] 100 Driver 111 Low-frequency amplifier 121 High-frequency amplifier 112 Variable step-up circuit 122 Step-down circuit 113, 114, 123, 124, 125, 126, 131, 132 Capacitor 133 Capacitive load 115, 116 Resistor 134, 135 Bias resistor

Claims

1. An acoustic device comprising: a capacitive load; and a driver that drives the capacitive load, wherein the driver comprises: a first amplifier that amplifies a first frequency component included in an input signal; and a second amplifier that amplifies a second frequency component included in the input signal.

2. The acoustic device according to claim 1, wherein the first frequency component is a low-frequency component in the audible range, and the second frequency component is a high-frequency component in the audible range.

3. The acoustic device according to claim 2, wherein the power supply voltage of the first amplifier is variable relative to the signal level, and the power supply voltage of the second amplifier is fixed relative to the signal level.

4. The acoustic device according to claim 2, wherein the power supply voltage of the second amplifier is lower than the power supply voltage of the first amplifier.

5. The acoustic device of claim 2, wherein the first amplifier comprises a first operational amplifier, a first feedback resistor connected between the input and output of the first operational amplifier, a feedback capacitance connected in parallel to the first feedback resistor, and a first input resistor connected to the input of the first operational amplifier; and the second amplifier comprises a second operational amplifier, a second feedback resistor connected between the input and output of the second operational amplifier, a series resistor connected in series to the second feedback resistor, and a second input resistor connected to the input of the second operational amplifier and connected to the connection point of the second feedback resistor and the series resistor.

6. The acoustic device according to claim 5, further comprising an inverting amplifier that inverts the output of the first amplifier and inputs the inverted output to the series resistor.

7. The acoustic device according to claim 2, wherein the values ​​of the first feedback resistor, the first input resistor, the second feedback resistor, the second input resistor and the series resistor are set so that the frequency characteristics of the combined output of the first amplifier output and the second amplifier output are flattened.

8. The acoustic device of claim 2, wherein the first amplifier comprises a first operational amplifier, a first feedback resistor connected between the input and output of the first operational amplifier, and a first input resistor connected to the input of the first operational amplifier; and the second amplifier comprises a second operational amplifier, a second feedback resistor connected between the input and output of the second operational amplifier, and a second input resistor connected to the input of the second operational amplifier.

9. The acoustic device of claim 2, wherein the first amplifier comprises a first operational amplifier, a first feedback resistor connected between the input and output of the first operational amplifier, a feedback capacitance connected in parallel to the first feedback resistor, and a first input resistor connected to the input of the first operational amplifier; and the second amplifier comprises a second operational amplifier, a second feedback resistor connected between the input and output of the second operational amplifier, a second input resistor connected to the input of the second operational amplifier, and an inverting amplifier that inverts the output of the second operational amplifier.

10. The acoustic device according to claim 1, wherein the first amplifier and the second amplifier are each a single-ended amplifier.

11. The acoustic device according to claim 1, wherein the first amplifier and the second amplifier are each a differential amplifier.

12. The acoustic device according to claim 1, which is a piezoelectric speaker, a MEMS (Micro Electro Mechanical Systems) speaker, a piezoelectric earphone, a MEMS earphone, a piezoelectric headphone, or a MEMS headphone.

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