Microphone module

Abstract

To provide a microphone module that can reduce power consumption.SOLUTION: A microphone module 100 includes a capacitive microphone 10 and a preamplifier 20 connected to the microphone. The preamplifier includes a power supply terminal 20a that receives a first voltage, a booster circuit 30 that generates a second voltage higher than the first voltage, and a first switch 8 that switches between a first connection state in which the booster circuit and one end of the microphone are connected and a second connection state in which the power supply terminal and one end of the microphone are connected.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of this specification relate to a microphone module.

Background Art

[0002] In a microphone module having a capacitive microphone and a preamplifier, a voltage boosted by the preamplifier is constantly supplied to the microphone, and a signal from the microphone is amplified by the preamplifier and output to the subsequent stage (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a microphone module, as an operation mode of the preamplifier, in addition to the first mode of amplifying a signal from the microphone, there may be a second mode of detecting whether or not a signal from the microphone exceeds a predetermined level.

[0005] However, when a voltage boosted by the preamplifier is constantly supplied to the microphone, a large current continues to flow even when the preamplifier operates in the second mode, and the power consumption may increase wastefully, and it is desired to reduce the power consumption.

[0006] An object of the present invention is to provide a microphone module capable of reducing power consumption in view of the above.

Means for Solving the Problems

[0007] In order to solve the above-described problems and achieve the object, a microphone module according to one aspect of the present invention includes a capacitive microphone and a preamplifier connected to the microphone. The preamplifier includes an external power supply terminal that receives a first voltage from the outside, a booster circuit that boosts the first voltage received at the external power supply terminal to generate a second voltage, and a first switch that switches between a first connection state in which the booster circuit is connected to one end of the microphone and a second connection state in which the external power supply terminal is connected to one end of the microphone. , an output terminal, an amplifier circuit connected to the other end of the microphone, a comparison circuit connectable to the other end of the microphone, and a second switch for switching between a third connection state in which the amplifier circuit and the output terminal are connected and a fourth connection state in which the comparison circuit and the output terminal are connected It has.

Advantages of the Invention

[0008] According to the present invention, power consumption can be reduced.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the microphone module will be described in detail with reference to the drawings. In the following embodiments, parts denoted by the same reference numerals perform the same operations, and overlapping descriptions will be omitted as appropriate.

[0011] (Embodiment) The microphone module according to the embodiment has a microphone and a preamplifier. The microphone in the microphone module is a capacitive microphone, which is a type of condenser microphone and can be configured as a MEMS (Micro Electro Mechanical Systems) chip. Different from an ECM (Electret Condenser Microphone) type microphone or a piezoelectric type microphone, the capacitive microphone is a type of microphone that receives a supply of a bias voltage to operate. The preamplifier boosts the power supply voltage to generate a bias voltage and constantly supplies the bias voltage to the microphone. Thereby, the sensitivity of the microphone can be adjusted to a sensitivity that meets the specifications.

[0012] The signal from the microphone is processed by the preamplifier. As an operation mode, the microphone module may have, in addition to a first mode in which the signal from the microphone is amplified by the preamplifier, a second mode in which the preamplifier detects whether or not the signal from the microphone exceeds a predetermined level. When the bias voltage boosted by the preamplifier is constantly supplied to the microphone, a large current continues to flow through the preamplifier even when operating in the second mode, and the power consumption may increase wastefully.

[0013] Therefore, in the present embodiment, in the preamplifier of the microphone module, the bias voltage to be supplied to the microphone is configured to be switchable between a boosted voltage and the power supply voltage before boosting, thereby enabling reduction of power consumption according to the operation mode.

[0014] Specifically, the microphone module 100 can be configured as shown in FIG. 1. FIG. 1 is a diagram showing the configuration of the microphone module 100. The microphone module 100 has a microphone 10 and a preamplifier 20. The microphone 10 is a type of microphone that receives a supply of a bias voltage to operate, for example, a capacitive microphone. The preamplifier 20 is connected to the microphone 10. The preamplifier 20 can supply a bias voltage to the microphone 10 and can process the signal from the microphone.

[0015] The microphone 10 can be configured as a MEMS chip. In this case, the microphone 10 is also called a MEMS microphone. The preamplifier 20 can be configured as a semiconductor chip. Thereby, miniaturization of the microphone 10 and the preamplifier 20 is possible, and for example, they can be mounted on a common circuit board.

[0016] The microphone 10 has an input terminal 10a, an output terminal 10b, a chip body 11, and a transducer 12. The input terminal 10a is electrically connected to the preamplifier 20 via a line L1. The output terminal 10b is electrically connected to the preamplifier 20 via a line L2. The transducer 12 has a vibrating electrode 12a and a fixed electrode 12b. The vibrating electrode 12a is fixed to the chip body 11. The vibrating electrode 12a is electrically connected to the input terminal 10a via a line L11 arranged on the chip body 11. The fixed electrode 12b is supported by the chip body 11 so as to be vibratable. The fixed electrode 12b is electrically connected to the output terminal 10b via a line L12 arranged on the chip body 11.

[0017] The transducer 12 converts sound into an electrical signal. In the transducer 12, when the fixed electrode 12b receives a sound wave while the vibrating electrode 12a is applied with a bias voltage via the line L1, the input terminal 10a, and the line L11 from the preamplifier 20, the distance between the vibrating electrode 12a and the fixed electrode 12b changes, and a voltage corresponding to the change is generated as a signal at the fixed electrode 12b. At this time, the greater the magnitude of the bias voltage applied to the vibrating electrode 12a in the transducer 12, the greater the intensity of the signal generated at the fixed electrode 12b in response to the change in distance can be. The signal generated at the fixed electrode 12b is output to the preamplifier 20 via the line L12, the output terminal 10b, and the line L2.

[0018] The preamplifier 20 includes an input terminal 20a, an output terminal 20b, an input terminal 20c, an output terminal 20d, an input terminal 20e, a chip body 21, a booster circuit 30, a switch (first switch) 8, an amplifier circuit 5, a comparison circuit 6, a switch (second switch) 7, and a switch 9. The input terminal 20a is a power supply terminal and receives a power supply voltage VDD from the outside (for example, a controller). The output terminal 20b is a connection terminal to the microphone 10 and is connected to the input terminal 10a of the microphone 10 via a line L1. The input terminal 20c is a connection terminal to the microphone 10 and is connected to the output terminal 10b of the microphone 10 via a line L2. The output terminal 20d is a connection terminal to a subsequent-stage circuit and outputs an output signal OUT to the subsequent-stage circuit. The input terminal 20e is a ground terminal and receives a ground voltage GND from the outside (for example, a controller). The power supply voltage VDD and the ground voltage GND can be supplied to each circuit within the preamplifier 20.

[0019] The booster circuit 30 is electrically connected between the switch 9 and the switch 8. When receiving the power supply voltage VDD, the booster circuit 30 boosts the power supply voltage VDD to generate a bias voltage and outputs the bias voltage.

[0020] The boost circuit 30 includes a band gap reference circuit (BGR), an oscillator circuit (OSC) 32, and a charge pump circuit (CP) 33. The band gap reference circuit 31, the oscillator circuit 32, and the charge pump circuit 33 are connected in parallel to the switch 9 and in series to the switch 8. That is, the input nodes 31a, 32a, and 33a of the band gap reference circuit 31, the oscillator circuit 32, and the charge pump circuit 33 are connected to the other end 9b of the switch 9, and one end 9a of the switch 9 is connected to the second end 8b of the switch 8. Also, the third end 8c of the switch 8 is connected to the output node 33c of the boost circuit 30. When the band gap reference circuit 31 receives the power supply voltage VDD via the line L22, the switch 9, and the input node 31a, it generates a reference voltage according to the band gap using the power supply voltage VDD and the ground voltage GND, and supplies the reference voltage from the output node 31b to the oscillator circuit 32. When the oscillator circuit 32 receives the power supply voltage VDD via the line L22, the switch 9, and the input node 32a and receives the reference voltage via the input node 32b, it performs an oscillation operation using the power supply voltage VDD, the reference voltage, and the ground voltage GND, and supplies an oscillation signal having a frequency corresponding to the reference voltage from the output node 32c to the charge pump circuit 33. When the charge pump circuit 33 receives the power supply voltage VDD via the line L22, the switch 9, and the input node 33a and receives the oscillation signal via the input node 33b, it generates a bias voltage obtained by boosting the power supply voltage VDD using the power supply voltage VDD, the oscillation signal, and the ground voltage GND, and outputs the bias voltage from the output node 33c.

[0021] The switch 9 is electrically connected between the input terminal 20a and the boost circuit 30. By turning on the switch 9, the boost circuit 30 is electrically connected to the input terminal 20a. By turning off the switch 9, the boost circuit 30 is electrically disconnected from the input terminal 20a.

[0022] One end 9a of switch 9 is electrically connected to input terminal 20a via line L22 and line L21, and the other end 9b is electrically connected to each of bandgap circuit 31, oscillation circuit 32, and charge pump circuit 33. Line L22 is electrically connected between node N1 and switch 9. Node N1 is the node between input terminal 20a and switch 8 on line L21. When switch 9 is turned on, each of bandgap circuit 31, oscillation circuit 32, and charge pump circuit 33 is electrically connected to input terminal 20a. When switch 9 is turned off, each of bandgap circuit 31, oscillation circuit 32, and charge pump circuit 33 is electrically disconnected from input terminal 20a.

[0023] Switch 8 is electrically connected between input terminal 20a, boost circuit 30, and input terminal 10a of microphone 10. Switch 8 switches between a first connection state and a second connection state. The first connection state is a state in which boost circuit 30 and input terminal 10a of microphone 10 are connected. The second connection state is a state in which input terminal (power supply terminal) 20a and input terminal 10a of microphone 10 are connected.

[0024] A first end 8a of switch 8 is electrically connected to input terminal 10a of microphone 10 via output terminal 20b and line L1, a second end 8b is electrically connected to input terminal 20a, and a third end 8c is electrically connected to boost circuit 30. Switch 8 switches to the first connection state by connecting the first end 8a to the third end 8c, and switches to the second connection state by connecting the first end 8a to the second end 8b.

[0025] In the first connection state, the voltage boosted from power supply voltage VDD by boost circuit 30 can be transmitted to vibration electrode 12a of transducer 12 via line L23, switch 8, line L24, output terminal 20b, line L1, input terminal 10a, and line L11. That is, preamplifier 20 can supply a voltage higher than power supply voltage VDD as a bias voltage to microphone 10 by switching to the first connection state with switch 8.

[0026] In the second connection state, the power supply voltage VDD received at the input terminal 20a can be transmitted to the vibrating electrode 12a of the transducer 12 via the line L21, the switch 8, the line L24, the output terminal 20b, the line L1, the input terminal 10a, and the line L11. That is, the preamplifier 20 can supply the power supply voltage VDD as a bias voltage to the microphone 10 by switching to the second connection state with the switch 8.

[0027] The amplifier circuit 5 is electrically connected between the output terminal 10b of the microphone 10, the comparison circuit 6, and the switch 7. The amplifier circuit 5 operates using the power supply voltage VDD and the ground voltage GND. The amplifier circuit 5 amplifies the signal output from the microphone 10.

[0028] For the amplifier circuit 5, the input node 5a is electrically connected to the output terminal 10b of the microphone 10 via the line L25, the input terminal 20c, and the line L2. For the amplifier circuit 5, the output node 5b is electrically connected to the switch 7 via the line L25 and is also electrically connected to the comparison circuit 6 via the lines L25 and L26. The line L26 is electrically connected between the node N2 and the switch 7. The node N2 is the node between the output node 5b of the amplifier circuit 5 on the line L25 and the switch 7.

[0029] The comparison circuit 6 is electrically connected between the output terminal 10b of the microphone 10 and the switch 7 and can be electrically connected, for example, between the amplifier circuit 5 and the switch 7. The comparison circuit 6 is arranged on the line L26 that bypasses the line L25. The comparison circuit 6 operates using the power supply voltage VDD and the ground voltage GND. The comparison circuit 6 receives the signal output from the microphone 10 and amplified by the amplifier circuit 5, compares the level of that signal with a threshold level, and outputs a signal of the comparison result. The threshold level is set to a desired value according to the level of the signal at which the microphone module 100 should switch the operation mode to the first mode of amplifying the signal from the microphone when voice input is performed to the microphone 10.

[0030] The comparison circuit 6 has an input node 6a electrically connected to the output terminal 10b of the microphone 10 via the node N2, the amplifier circuit 5, the input terminal 20c, and the line L2, and an output node 6b electrically connected to the switch 7.

[0031] The switch 7 is electrically connected between the amplifier circuit 5 and the comparison circuit 6 and the output terminal 20d. The switch 7 switches between a third connection state and a fourth connection state. The third connection state is a state in which the amplifier circuit 5 and the output terminal 20d are connected. The fourth connection state is a state in which the comparison circuit 6 and the output terminal 20d are connected. In the fourth connection state, the amplifier circuit 5 may be connected to the output terminal 20d via the comparison circuit 6.

[0032] The switch 7 has a first end 7a electrically connected to the output terminal 20d, a second end 7b electrically connected to the output node 5b of the amplifier circuit 5 via the node N2, and a third end 7c electrically connected to the output node 6b of the comparison circuit 6. The switch 7 switches to the third connection state by connecting the first end 7a to the second end 7b, and switches to the fourth connection state by connecting the first end 7a to the third end 7c.

[0033] In the third connection state, the comparison circuit 6 is electrically disconnected from the path from the input terminal 20c to the output terminal 20d, and the signal amplified by the amplifier circuit 5 can be transmitted to the output terminal 20d without passing through the comparison circuit 6. That is, the preamplifier 20 can output the signal amplified by the amplifier circuit 5 as the output signal OUT by switching the switch 7 to the third connection state.

[0034] In the fourth connection state, the comparison circuit 6 is electrically inserted into the path from the input terminal 20c to the output terminal 20d, the signal amplified by the amplifier circuit 5 is input to the comparison circuit 6, and the level of the signal and the threshold level are compared in the comparison circuit 6. Then, the signal indicating the result of the comparison in the comparison circuit 6 can be transmitted to the output terminal 20d. That is, the preamplifier 20 can output the signal of the comparison result of the comparison circuit 6 as the output signal OUT by switching the switch 7 to the fourth connection state.

[0035] The microphone module 100 has, as its operation modes, a first mode and a second mode as shown in FIG. 2. FIG. 2 is a diagram showing the operation modes of the microphone module 100, where FIG. 2(a) shows the first mode and FIG. 2(b) shows the second mode.

[0036] The first mode is a normal operation mode in which voice processing is performed by the preamplifier 20, and the second mode is an operation mode in the standby state. In the first mode, the signal from the microphone 10 is amplified as a voice signal by the preamplifier 20, while in the second mode, it is detected by the preamplifier 20 whether the signal from the microphone 10 exceeds a predetermined level. Therefore, in the first mode, the signal from the microphone 10 is required to have a signal strength that can ensure the signal-to-noise ratio as a voice signal, while in the second mode, the signal from the microphone 10 is required to have a signal strength that can detect whether it exceeds a predetermined level. That is, the signal strength required for the signal from the microphone 10 in the second mode is smaller than the signal strength required for the signal from the microphone 10 in the first mode.

[0037] For this reason, as shown in FIG. 2(a), in the first mode, the preamplifier 20 is switched to the first connection state by the switch 8 and to the third connection state by the switch 7. Thereby, in the first mode, the voltage boosted by the boost circuit 30 is supplied to the microphone 10 as a bias voltage, and the signal from the microphone 10 can be supplied to the preamplifier 20 with a signal strength corresponding to the first mode. Also, the signal from the microphone 10 is amplified by the amplifier circuit 5, and the amplified signal can be output as an output signal OUT from the output terminal 20d to the subsequent circuit without passing through the comparison circuit 6.

[0038] As shown in Fig. 2(b), in the second mode, the preamplifier 20 switches to the second connection state with switch 8 and to the fourth connection state with switch 7. As a result, in the second mode, the power supply voltage VDD is supplied to the microphone 10 as a bias voltage, and a signal can be supplied from the microphone 10 to the preamplifier 20 at a signal strength corresponding to the second mode. Also, a signal from the microphone 10 is amplified by the amplifier circuit 5, the level of the amplified signal is compared with a threshold level by the comparison circuit 6, and the signal of the comparison result can be output as an output signal OUT from the output terminal 20d to the subsequent circuit.

[0039] That is, in the second mode, since the preamplifier 20 supplies a lower voltage than in the first mode to the microphone 10 as a bias voltage, the power consumption of the preamplifier 20 can be easily reduced.

[0040] In the second mode, since the voltage boosted by the boost circuit 30 is not used as a bias voltage, the boost circuit 30 can be stopped. For this reason, the preamplifier 20 may keep the switch 9 in the on state to operate the boost circuit 30 in the first mode shown in Fig. 2(a), and keep the switch 9 in the off state to stop the boost circuit 30 in the second mode shown in Fig. 2(b). Thereby, in the second mode, the power consumption of the preamplifier 20 can be more easily reduced than in the first mode.

[0041] In the second mode, the driving force of the amplifier circuit 5 may be sufficient to transmit the signal. For this reason, the preamplifier 20 operates the amplifier circuit 5 with a first driving force in the first mode shown in Fig. 2(a), and operates the amplifier circuit 5 with a second driving force in the second mode shown in Fig. 2(b). The second driving force is a driving force smaller than the first driving force. For example, when the amplifier circuit 5 has a variable current source, the preamplifier 20 may supply a first driving current from the variable current source in the first mode, and supply a second driving current lower than the first driving current from the variable current source in the second mode. Thereby, in the second mode, the power consumption of the preamplifier 20 can be more easily reduced than in the first mode.

[0042] Also, the microphone module 100 can transition the operation mode of the preamplifier 20 between the first mode and the second mode in response to a predetermined condition being satisfied. The microphone module 100 may perform a transition of the operation mode as shown in, for example, FIG. 3. FIG. 3 is a flowchart showing the operation of the microphone module 100.

[0043] When activated, the microphone module 100 operates in the first mode (S1). For example, when the microphone module 100 is activated, the preamplifier 20 is switched to the second connection state by the switch 8 and to the fourth connection state by the switch 7. Alternatively, in response to the activation of the microphone module 100, the preamplifier 20 is switched to the second connection state by the switch 8 and to the fourth connection state by the switch 7. Thereby, the voltage boosted by the boost circuit 30 is supplied from the preamplifier 20 to the microphone 10 as a bias voltage, and a signal can be supplied from the microphone 10 to the preamplifier 20 with a signal intensity corresponding to the first mode.

[0044] The microphone module 100 determines whether the signal level from the microphone 10 is below the threshold level (S2). The threshold level corresponds to the lower limit of the signal level generated by the microphone 10 when voice input is performed to the microphone 10. If the signal level exceeds the threshold level (No in S2), the microphone module 100 returns the process to S1.

[0045] When the signal level becomes below the threshold level (Yes in S2), the microphone module 100 measures the duration during which the signal level remains continuously below the threshold level. If the duration is less than the threshold time (No in S3), the microphone module 100 returns the process to S1. The threshold time corresponds to the lower limit of the time during which the signal level becomes less than the threshold level when no voice input is performed to the microphone 10.

[0046] When the duration is equal to or longer than the threshold time (Yes in S3), assuming that the microphone module 100 enters a standby state where no voice input is performed to the microphone 10, the operation mode is switched from the first mode to the second mode (S4). That is, the preamplifier 20 switches to the second connection state with the switch 8 and switches to the fourth connection state with the switch 7. Thereby, the microphone module 100 operates in the second mode (S5), the power supply voltage VDD is supplied from the preamplifier 20 to the microphone 10 as a bias voltage, and a signal can be supplied from the microphone 10 to the preamplifier 20 with a signal intensity corresponding to the second mode.

[0047] The microphone module 100 determines whether or not the signal level from the microphone 10 is equal to or lower than the threshold level (S6). If the signal level is equal to or lower than the threshold level (Yes in S6), the microphone module 100 returns the process to S5.

[0048] When the signal level exceeds the threshold level (No in S6), assuming that voice input is performed to the microphone 10, the microphone module 100 switches the operation mode from the second mode to the first mode (S7). That is, the preamplifier 20 switches to the first connection state with the switch 8 and switches to the third connection state with the switch 7. Thereby, the microphone module 100 operates in the first mode (S1), the voltage boosted by the boost circuit 30 is supplied from the preamplifier 20 to the microphone 10 as a bias voltage, and a signal can be supplied from the microphone 10 to the preamplifier 20 with a signal intensity corresponding to the first mode. Then, the operations after S2 are performed.

[0049] As described above, in the present embodiment, the preamplifier 20 of the microphone module 100 is configured to be able to switch the bias voltage to be supplied to the microphone between the boosted voltage and the power supply voltage VDD before boosting. For example, in the first mode in which voice processing is performed by the preamplifier 20, the bias voltage to be supplied to the microphone is the boosted voltage, and in the second mode which is the standby state, the bias voltage to be supplied to the microphone is the power supply voltage VDD before boosting. Thereby, the power consumption of the preamplifier 20 can be reduced according to the operation mode.

[0050] As a first modification example of the embodiment, in the microphone module 200, as shown in FIG. 4, a control logic circuit (control circuit) 240 for transition of the operation mode may be provided in the preamplifier 220. FIG. 4 is a diagram showing the configuration of the microphone module 200 according to the first modification example of the embodiment. The preamplifier 220 further has a control logic circuit 240. The control logic circuit 240 is electrically connected between the comparison circuit 6, the switch 8, the amplifier circuit 5, the switch 9, and the switch 7. The control logic circuit 240 has a timer 241 and can measure time with the timer 241. The control logic circuit 240 can receive the comparison result signal of the comparison circuit 6, measure time with the timer 241, and control the switch 8, the amplifier circuit 5, the switch 9, and the switch 7 respectively.

[0051] The input node 240a of the control logic circuit 240 is electrically connected to the output node 6b of the comparison circuit 6 via the node N3. The node N3 is a node between the comparison circuit 6 and the switch 7 on the line L26. The output node 240b of the control logic circuit 240 is electrically connected to the control node 8d of the switch 8, the control node 7d of the switch 7, the control node 9c of the switch 9, and the control node 5c of the amplifier circuit 5.

[0052] In the first mode, the switch 8 switches to the first connection state according to the control signal received at the control node 8d from the control logic circuit 240. The switch 7 switches to the third connection state according to the control signal received at the control node 7d from the control logic circuit 240. The switch 9 is maintained in the on state according to the control signal received at the control node 9c from the control logic circuit 240. The amplifier circuit 5 operates with the first driving force according to the control signal received at the control node 5c from the control logic circuit 240.

[0053] In the second mode, switch 8 switches to the second connection state according to the control signal received at control node 8d from the control logic circuit 240. Switch 7 switches to the fourth connection state according to the control signal received at control node 7d from the control logic circuit 240. Switch 9 is maintained in the off state according to the control signal received at control node 9c from the control logic circuit 240. Amplifier circuit 5 operates with the second driving force according to the control signal received at control node 5c from the control logic circuit 240.

[0054] Also, the control logic circuit 240 can control the transition of the operation modes illustrated in FIG. 3. When operating in the first mode (S1), the control logic circuit 240 can control switch 8 to switch to the first connection state and control switch 7 to switch to the third connection state.

[0055] The control logic circuit 240 determines whether the signal level from the microphone 10 is equal to or lower than the threshold level according to the comparison result signal of the comparison circuit 6 (S2). If the signal level exceeds the threshold level (No in S2), the control logic circuit 240 returns the process to S1. When the signal level becomes equal to or lower than the threshold level (Yes in S2), the control logic circuit 240 measures the duration during which the signal level remains continuously equal to or lower than the threshold level with the timer 241. If the duration is less than the threshold time (No in S3), the control logic circuit 240 returns the process to S1. When the duration becomes equal to or longer than the threshold time (Yes in S3), the control logic circuit 240 switches the operation mode from the first mode to the second mode (S4). That is, the control logic circuit 240 controls switch 8 to switch to the second connection state and controls switch 7 to switch to the fourth connection state. Thereby, the microphone module 200 operates in the second mode (S5).

[0056] The control logic circuit 240 determines whether the signal level from the microphone 10 is below the threshold level according to the comparison result signal of the comparison circuit 6 (S6). If the signal level is below the threshold level (Yes in S6), the control logic circuit 240 returns the process to S5. When the signal level exceeds the threshold level (No in S6), the control logic circuit 240 switches the operation mode from the second mode to the first mode (S7). That is, the control logic circuit 240 controls the switch 8 to switch to the first connection state and controls the switch 7 to switch to the third connection state.

[0057] In this way, in the microphone module 200, the control for the transition of the operation mode is performed in the preamplifier 20. Thereby, the circuit to be operated at the subsequent stage of the preamplifier 20 can be restricted according to the operation mode. As a result, the power consumption of the entire microphone module 200 can be reduced according to the operation mode.

[0058] Alternatively, as a second modification of the embodiment, in the microphone module 300, the preamplifier 320 may have a configuration in which the switch 7 is omitted as shown in FIG. 5. FIG. 5 is a diagram showing the configuration of the microphone module 300 according to the second modification of the embodiment. The preamplifier 320 omits the switch 7 (see FIG. 4) and further has an output terminal 20f. The output terminal 20f is electrically connected to the output node 6b of the comparison circuit 6 via the line L26. Thereby, the preamplifier 320 can output the comparison result signal DETECT of the comparison circuit 6 to the subsequent stage circuit in each of the first mode and the second mode.

[0059] In this way, in the microphone module 300, the preamplifier 320 has a configuration in which the switch 7 is omitted. Thereby, since the power for operating the switch 7 can be reduced, the power consumption of the preamplifier 20 can be further reduced.

[0060] Alternatively, as a third modification of the embodiment, in the microphone module 400, as shown in FIG. 6, a control logic circuit (control circuit) 240 for transition of the operation mode may be provided after the preamplifier 420. FIG. 6 is a diagram showing the configuration of the microphone module 400 according to the third modification of the embodiment.

[0061] The microphone module 400 includes, in addition to the microphone 10 and the preamplifier 420, an ASIC circuit block 450 and a signal processing circuit (Signal Processor) block 460. The preamplifier 420 has an input terminal 20g in addition to the configuration shown in FIG. 5, with the control logic circuit 240 omitted. The input terminal 20g is a control terminal for receiving a control signal and is electrically connected to the control node 8d of the switch 8, the control node 9c of the switch 9, and the control node 5c of the amplifier circuit 5.

[0062] The ASIC circuit block 450 includes an input terminal 450a, an input terminal 450b, an output terminal 450c, an output terminal 450d, an analog-to-digital converter (ADC) circuit 451, and a control logic circuit 240. The input terminal 450a is electrically connected to the output terminal 20f of the preamplifier 420 and receives the comparison result signal DETECT of the comparison circuit 6. The input terminal 450b is electrically connected to the output terminal 20d of the preamplifier 420 and receives the signal OUT amplified by the amplifier circuit 5. The analog-to-digital converter circuit 451 has its input node 451a electrically connected to the input terminal 450b, and its output node 451b electrically connected to the input node 240c and the output terminal 450d of the control logic circuit 240. The output terminal 450d is electrically connected to the input terminal 460b of the signal processing circuit block 460. Thereby, the signal OUT (analog signal) amplified by the amplifier circuit 5 can be converted into a digital signal by the analog-to-digital converter circuit 451 and the digital signal can be processed by the signal processing circuit block 460.

[0063] In the control logic circuit 240, an input node 240a is connected to an input terminal 450a, and an output node 240b is electrically connected to an output terminal 450c. The output terminal 450c is electrically connected to an input terminal 20g of the preamplifier 420 and an input terminal 460a of the signal processing circuit block 460.

[0064] In the first mode, the switch 8 switches to the first connection state according to a control signal received at the control node 8d from the control logic circuit 240 via the output terminal 450c and the input terminal 20g. The switch 9 is maintained in the on state according to a control signal received at the control node 9c from the control logic circuit 240 via the output terminal 450c and the input terminal 20g. The amplifier circuit 5 operates with a first driving force according to a control signal received at the control node 5c from the control logic circuit 240 via the output terminal 450c and the input terminal 20g.

[0065] In the second mode, the switch 8 switches to the second connection state according to a control signal received at the control node 8d from the control logic circuit 240 via the output terminal 450c and the input terminal 20g. The switch 9 is maintained in the off state according to a control signal received at the control node 9c from the control logic circuit 240 via the output terminal 450c and the input terminal 20g. The amplifier circuit 5 operates with a second driving force according to a control signal received at the control node 5c from the control logic circuit 240 via the output terminal 450c and the input terminal 20g.

[0066] Also, the control logic circuit 240 can control the transition of the operation mode illustrated in FIG. 3, which is the same as the first modification.

[0067] In this way, in the microphone module 400, the control for the transition of the operation mode is performed at the subsequent stage of the preamplifier 420. Thereby, the circuit that operates the preamplifier 20 can be restricted according to the operation mode. As a result, the power consumption of the entire microphone module 400 can be reduced according to the operation mode.

[0068] As described above, embodiments of the present invention have been explained. However, the above embodiments are presented as examples and are not intended to limit the scope of the invention. The above novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments are included in the scope and gist of the invention and are included in the invention described in the claims and the equivalent scope thereof.

Explanation of Reference Numerals

[0069] 5 Amplification circuit 6 Comparison circuit 7 Switch 8 Switch 9 Switch 10 Microphone 20, 220, 320, 420 Preamplifier 30 Boost circuit 100, 200, 300, 400 Microphone module 240 Control logic circuit

Claims

1. A capacitive microphone, a preamplifier connected to the microphone, comprising: the preamplifier has an external power supply terminal for receiving a first voltage from the outside, a boost circuit that boosts the first voltage received at the external power supply terminal to generate a second voltage, a first switch that switches between a first connection state in which the boost circuit and one end of the microphone are connected and a second connection state in which the external power supply terminal and one end of the microphone are connected, an output terminal, an amplifier circuit connected to the other end of the microphone, a comparison circuit connectable to the other end of the microphone, a second switch that switches between a third connection state in which the amplifier circuit and the output terminal are connected and a fourth connection state in which the comparison circuit and the output terminal are connected, and has a microphone module.

2. In the first mode, the preamplifier switches to the first connection state with the first switch and switches to the third connection state with the second switch. In the second mode, the preamplifier switches to the second connection state with the first switch and switches to the fourth connection state with the second switch. The microphone module according to claim 1.

3. In the first mode, the preamplifier operates the boost circuit, and in the second mode, the preamplifier stops the boost circuit. The microphone module according to claim 2.

4. In the first mode, the preamplifier operates the amplifier circuit with a first driving force, and in the second mode, the preamplifier operates the amplifier circuit with a second driving force smaller than the first driving force. The microphone module according to claim 2.

5. The first mode is a mode for amplifying a signal output from the microphone, and the second mode is a mode for detecting whether a signal output from the microphone exceeds a predetermined level. The microphone module according to claim 2.

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