JP4390716B2 - Voltage supply circuit, microphone unit and method for adjusting sensitivity of microphone unit - Google Patents

Description

  The present invention relates to a voltage supply circuit, and more particularly to a voltage supply circuit that supplies a voltage to a sensor and a microphone unit using the same when used in a sensor such as a capacitor microphone.

  A technology using a microphone called a condenser microphone is widely used for voice communication in a portable terminal such as a cellular phone. A condenser microphone is a microphone that uses one electrode of a capacitor as a diaphragm, and converts vibrations such as sound as an electric signal by taking out the change as a capacitance.

  FIG. 14 shows a circuit of a capacitor microphone unit 100 using a conventional capacitor microphone. As shown in FIG. 14, the conventional capacitor microphone unit includes a capacitor microphone 101, a JFET (junction field effect transistor) 102, a capacitor 103, resistors 104 and 105, and DC power sources 106 and 108.

  The condenser microphone 101 is a vibration sensor that generates an output signal with respect to sound pressure such as input voice. One electrode of the capacitor microphone 101 is connected to the DC power source 108 via the resistor 104, and the other electrode is grounded. The capacitor microphone 101 is given a specific bias voltage from the DC power supply 108. The output terminal of the capacitor microphone 101 is connected to the gate of the JFET 102. The JFET 102 is an amplifier circuit that amplifies the output signal of the capacitor microphone and generates an amplified signal. The amplified signal generated by the JFET 102 is output via the output terminal 107.

  In the capacitor microphone unit shown in FIG. 14, two DC power sources 106 and 108 are used. However, it is possible to generate a bias voltage to be applied to the capacitor microphone 101 by boosting the voltage supplied from the DC power source 106. It is.

  In such a capacitor microphone unit, manufacturing variations occur when manufacturing the capacitor microphone and the JFET. This manufacturing variation appears as a variation in the distance between the electrodes of the capacitor and a variation in the amplification efficiency of the JFET, which causes the sensitivity to vary from capacitor microphone unit to capacitor microphone unit.

  For this reason, there has been a demand for a capacitor microphone unit that can operate with appropriate sensitivity in response to the variation even when manufacturing variations occur in a sensor device such as a capacitor microphone.

In addition, when it is desired to switch the sensitivity of the capacitor microphone unit with the conventional capacitor microphone unit, two capacitor microphone units having different sensitivity settings are prepared, and the sensitivity is switched by switching the capacitor microphone unit itself. However, in this configuration, a condenser microphone unit must be prepared according to the sensitivity level to be switched. Therefore, a capacitor microphone unit that can select a plurality of sensitivities with one capacitor microphone unit has been desired.
PA acoustic system: Engineering book: 1996 edition

  As described above, conventionally, there is a case where the sensitivity varies for each sensor device, for example, a condenser microphone unit. Also, when variations occur, it is difficult to adjust the sensitivity.

  A voltage supply circuit according to an aspect of the present invention includes a power supply boosting unit, an amplifier that operates using a voltage generated by the power supply boosting unit as a power supply voltage, and supplies a bias voltage to the sensor, and a feedback resistor unit for the amplifier. And an output voltage setting circuit in which a resistance value of the feedback resistor unit is determined in accordance with a set value of the bias voltage of the sensor.

  With such a configuration, it is possible to select a bias voltage to be supplied to a sensor such as a capacitor microphone.

  A microphone unit according to an aspect of the present invention includes a microphone to which a bias voltage is supplied, a power supply boosting unit, an amplifier that operates using the voltage generated by the power supply boosting unit as a power supply voltage, and supplies the bias voltage to the microphone. And an output voltage setting circuit that has a feedback resistance section for the amplifier, and a resistance value of the feedback resistance section is determined in accordance with a setting value of the bias voltage of the microphone.

  With such a configuration, it is possible to reduce variations in sensitivity of the microphone unit.

  According to another aspect of the present invention, there is provided a microphone unit sensitivity adjustment method comprising: inputting a reference sound to a capacitor microphone; comparing the output of the microphone with respect to the reference sound and a reference voltage; A setting value for setting a bias voltage to be biased is output, the setting value is stored, and a feedback resistance value of an amplifier that outputs the bias voltage is determined based on the setting value.

  By performing such a sensitivity adjustment operation, it is possible to reduce variations in sensitivity of the microphone unit.

  It is possible to reduce variations in sensitivity of the microphone unit.

Embodiment 1
Regarding the embodiments described below, a capacitor microphone unit will be described as an example of a microphone unit.

  FIG. 1 is a diagram showing a condenser microphone unit according to Embodiment 1 of the present invention. The capacitor microphone unit according to the first embodiment includes a voltage supply circuit 1, a capacitor microphone 2, an amplifier circuit 3, a capacitor 4, resistors 5 and 6, and a power source 7.

  The voltage supply circuit 1 is a circuit that boosts the voltage supplied from the power supply 7 and supplies a bias voltage to the capacitor microphone 2. This bias voltage is supplied to the capacitor microphone 2 via the resistor 5. Details of the bias voltage output from the voltage supply circuit 1 will be described later. The capacitor microphone 2 is a microphone element (vibration sensor) in which one electrode is a diaphragm. The amplifier circuit 3 is a junction field effect transistor (JFET) in which the output of the capacitor microphone 2 is given to the gate. The JFET 3 is connected between the power source 7 and the ground potential.

  In this condenser microphone unit, the diaphragm of the condenser microphone, which is a vibration sensor, vibrates in accordance with sound or the like. When the diaphragm vibrates, the capacitance changes, so the charge stored in the capacitor microphone 2 changes. Based on this change in charge, the voltage at the node between the resistor 5 and the capacitor microphone 2 changes. This voltage change is applied as an output signal of the capacitor microphone 2 to the gate electrode of the JFET 3 via the capacitor 4. In JFET 3, the output signal of the capacitor microphone is amplified and output from the node between the source of JFET 3 and resistor 6 as the output signal of the capacitor microphone unit.

  Here, the capacitor microphone unit according to the first embodiment applies a first bias voltage (for example, about 24V) to the capacitor microphone 2 and operates, and a second bias voltage (for example, about 12V). And a low sensitivity mode to operate. A mode designation signal for setting this mode is given to the voltage supply circuit 1 from the outside during the operation of the capacitor microphone unit. The voltage supply circuit 1 applies a first or second bias voltage corresponding to the mode designation signal to the capacitor microphone 2.

  In a series of operations, the basic voltage that the voltage supply circuit 1 supplies to the capacitor microphone 2 is determined by the mode designation signal. However, as described above, manufacturing variations occur in the capacitor microphone unit. The voltage supply circuit 1 according to the first embodiment is a voltage supply circuit in which sensitivity adjustment described below is performed in advance, and the first bias voltage and the second bias voltage can be adjusted. The voltage supply circuit 1 will be described below.

  FIG. 2 is a block diagram illustrating a configuration of the voltage supply circuit 1 according to the first embodiment. The voltage supply circuit 1 according to the first embodiment includes a power boosting unit 21, a regulator unit 22, and an output voltage setting unit 23.

  The power booster 21 is a part that boosts and outputs a voltage (for example, 5V) supplied from the power supply 7 to a necessary voltage (for example, about 24V). The power booster 21 can be realized by, for example, a charge pump or a DC-DC converter.

  The regulator unit 22 is a circuit that generates a bias voltage output from the voltage supply circuit 1. The regulator unit 22 includes a reference voltage source 222 and a non-inverting amplifier 221. The reference voltage source 222 is a bandgap voltage source (BGR), for example, and is a circuit that generates and supplies a stable fixed voltage from the voltage of the power supply 7. The non-inverting amplifier 221 is an amplifier that operates using the voltage generated by the power boosting unit 21 as the power supply voltage. The non-inverting input terminal of the non-inverting amplifier 221 is supplied with a stable reference voltage from the BGR 222, and the inverting input terminal is provided with a feedback input via a feedback resistor. The resistance value of the feedback resistor is set by an output voltage setting unit 23 described later.

  The non-inverting amplifier 221 amplifies the voltage given to the non-inverting input terminal and outputs it as a bias voltage. The amplification degree at this time is determined by the resistance value of the feedback resistor. More specifically, it is determined by the ratio of the resistance value of the feedback resistor and the resistance value of the resistor connected between the inverting input terminal of the non-inverting amplifier 221 and the ground potential. Therefore, it can be said that the bias voltage output from the voltage supply circuit 1 is set by the feedback resistance value of the output voltage setting unit 23.

  The output voltage setting unit 23 is a circuit that sets the bias voltage output from the regulator unit 22. The output voltage setting unit 23 sets the bias voltage by changing the feedback resistance value for the amplifier 221. The output voltage setting section 23 is provided with a first feedback resistance section 231 and a second feedback resistance section 232. The first feedback resistor unit 231 is a feedback resistor unit used in the above-described high sensitivity mode, and the second feedback resistor unit 232 is a feedback resistor unit used in the low sensitivity mode. The output voltage setting unit 23 switches between the high sensitivity mode and the low sensitivity mode by selectively using the first or second feedback resistor unit in accordance with the mode designation signal.

  In the voltage supply circuit 1 according to the first embodiment, the BGR 222 generates a reference voltage based on the voltage supplied from the power supply 7 and outputs a voltage obtained by amplifying the reference voltage by the non-inverting amplifier 221 as a bias voltage. At this time, a mode designation signal is given to the output voltage setting unit 23 to select the first feedback resistor unit 231 or the second feedback resistor unit 232. Further, the power supply required by the non-inverting amplifier 221 to output the amplified voltage is generated by the power boosting unit 21. By using the voltage supply circuit 1 having such a configuration, bias voltages in the high sensitivity mode and the low sensitivity mode are generated, and the capacitor microphone unit operates.

  A more detailed configuration of the output voltage setting unit 23 for adjusting the bias voltage described above will be described. The output voltage setting unit 23 according to the first embodiment includes first and second feedback resistance units 231 and 232, first and second selector circuits 233 and 234, a data processing unit 235, and a storage unit 236. . The feedback resistance units 231 and 232 have a plurality of resistors connected in series between the output terminal of the non-inverting amplifier 221 of the regulator unit 22 and the ground potential. In the feedback resistance units 231 and 232 of the first embodiment, eight resistors are connected in series. The feedback resistor units 231 and 232 are connected in parallel to each other with respect to the output of the non-inverting amplifier 221.

  Selector circuits 233 and 234 are connected to the feedback resistance units 231 and 232, respectively. Each selector circuit 233, 234 has seven switches connected to a node between the resistors of the feedback resistor unit. The selector circuits 233 and 234 select any one of the seven switches based on a set value held in a storage unit 236 described later. The node corresponding to the selected switch is connected to the inverting input of the non-inverting amplifier described above.

  The output voltage setting unit 23 includes a storage unit 236 that stores a setting value based on a sensitivity adjustment operation described later. The data processing unit 235 is a circuit that outputs a setting value held in the storage unit 236 and outputs a signal for selecting a switch in the selector circuits 233 and 234 described above. The setting value held in the storage unit 236 corresponds to the setting value for setting the feedback resistance value, and the bias voltage is adjusted. The data processing unit 235 also receives a mode designation signal and outputs a switch control signal for selectively connecting the first feedback resistor unit 231 or the second feedback resistor unit 232 to the amplifier 221.

  In other words, the data processing unit 235 is a circuit that outputs a setting value for mode designation and bias voltage adjustment.

  In the voltage supply circuit of the first embodiment, when the sensitivity adjustment is performed, the first bias voltage value and the second bias voltage value are adjusted, and the setting is stored in the storage unit 236 as the setting value of the feedback resistor. Is done.

  In a normal operation in which the condenser microphone unit is actually used, only the mode designation signal is given to the voltage supply circuit 1. At this time, the output voltage setting unit 23 in the voltage supply circuit 1 outputs the stored setting value together with a signal for selecting the first or second feedback resistor unit from the data processing unit 235. In the selector circuits 233 and 234, a switch corresponding to the set value data is selected, and an arbitrary number (1 to 7) of the eight resistors in the feedback resistor section is connected to the non-inverting amplifier 221. By this operation, the feedback resistance value is set. The non-inverting amplifier 221 determines the amplification degree according to the connected first or second feedback resistor unit and the number of resistors connected to the inverting input terminal in each feedback resistor unit, and outputs a bias voltage.

  With this configuration, the condenser microphone unit according to the first embodiment operates in the high sensitivity mode or the low sensitivity mode. Regarding the sensitivity variation of the capacitor microphone unit, the voltage supply circuit 1 can provide a stable sensitivity by applying a bias voltage adjusted based on the sensitivity adjustment.

Hereinafter, the sensitivity adjustment described above will be described. FIG. 3 is a diagram illustrating a configuration of a sensitivity adjustment device used for sensitivity adjustment of the capacitor microphone unit according to the first embodiment.
This sensitivity adjustment apparatus has a signal generator 31, a speaker 32, a condenser microphone unit 33, and an inspection adjustment machine 34.

  The signal generator 31 is a device that generates a signal having a predetermined frequency, for example, and generates a signal corresponding to a reference sound at the time of sensitivity adjustment. The speaker 32 gives the signal generated by the signal generator 31 to the condenser microphone unit 33 as an actual sound. The capacitor microphone unit 33 is the same as the capacitor microphone unit shown in FIG. The inspection / adjustment unit 34 is a device that measures a signal output from the capacitor microphone unit and outputs a set value to be stored in the voltage supply circuit 1 of the capacitor microphone unit. The inspection adjustment machine 34 includes a comparison circuit 341, a reference circuit 342, an adjustment signal generation circuit 343, and the like.

  In the sensitivity adjustment method of the first embodiment, first, a reference sound serving as a reference is given to the condenser microphone unit 33 from the signal generator 31 and the speaker 32. The condenser microphone unit 33 converts the reference sound into an electric signal and outputs it. The signal output from the capacitor microphone unit 33 is given to one input terminal of the comparison circuit 341 in the inspection adjustment machine 34. A reference voltage is supplied to the other input terminal of the comparison circuit 341 as a comparison target. This reference voltage is stored in the reference circuit 342 as the level of a signal to be output by the capacitor microphone when a reference sound is given. The comparison circuit 341 compares the reference voltage and the output level of the capacitor microphone unit, and outputs the comparison result to the adjustment signal generation circuit 343. The adjustment signal generation circuit 343 determines the voltage width for changing the bias voltage from the difference between the output level of the capacitor microphone unit and the reference voltage level. And the setting value (setting value which sets the feedback resistance value of a feedback resistance part) for setting the voltage which the voltage supply circuit 1 outputs is output. This set value is sent to the output voltage setting unit 23 in the voltage supply circuit 1 and stored in the storage unit 236.

  FIG. 4 is a diagram showing the relationship between the sensitivity of the capacitor microphone unit and the bias voltage. FIG. 5 is a diagram showing the set value output from the adjustment signal generation circuit 343 and the adjustment amount with respect to the bias voltage.

  As described above, the test adjuster 34 determines the voltage width for changing the bias voltage from the difference between the output level of the capacitor microphone unit and the reference voltage. FIG. 4 also shows the relationship between the sensitivity and the adjustment amount.

  For example, when the level of the output signal of the capacitor microphone unit is low and the sensitivity is lower than the set range, the sensitivity increases by increasing the bias voltage for the capacitor microphone. At this time, the voltage width for increasing the bias voltage is also determined according to how much the sensitivity deviates from the set range. When the sensitivity of the capacitor microphone unit is higher than the set range, a voltage width for decreasing the bias voltage of the capacitor microphone unit is determined.

  If the capacitor microphone bias voltage is 24V and the output level of the capacitor microphone unit indicates sensitivity equivalent to the point A in FIG. 4, it is decided to increase the bias voltage by 3V. By increasing the bias voltage by 3 V, the capacitor microphone unit exhibits the sensitivity shown in FIG. 4, point B, and is within the set range. The adjustment signal generation circuit 343 generates data corresponding to the setting for increasing the bias voltage by 3 V in the high sensitivity mode, and sends the data to the storage unit 236 in the voltage supply circuit 1. FIG. 5 is a diagram showing a list of setting values output from the adjustment signal generating circuit 343 in order to indicate such a setting as “the bias voltage +3 V in the high sensitivity mode”. As shown in FIG. 5, this set value is output as 7-bit serial data. The most significant bit (MSB) of the 7-bit data is a bit for indicating the high sensitivity mode or the low sensitivity mode. The 3 bits from the 2nd digit to the 4th digit are sent to the first selector 233. It is a bit for selecting one of the seven switches included. The lower 3 bits of the fifth to seventh digits are bits for selecting one of the seven switches included in the second selector 234 described above. As described above, the feedback resistance value is determined by selecting the switch in the selector circuit, and the bias voltage is set.

  In this embodiment, since the bias voltage can be adjusted to ± 3 V in increments of 1 V in the high sensitivity mode and the low sensitivity mode, the above 7-bit data is used. However, the number of bits of this data is set by voltage setting. The width and range to be performed, the number of sensitivity modes, and the like can be appropriately changed.

  As described above, in the sensitivity adjustment device of the first embodiment, the set value for the voltage supply circuit 1 is determined from the difference between the output of the capacitor microphone unit and the reference voltage. This data is held in the storage unit 236 in the voltage supply circuit 1. As a result, it is possible to obtain a capacitor microphone unit with a small sensitivity difference between units of the capacitor microphone unit.

  Now, referring back to FIG. 2, the detailed configuration of the data processing circuit 235 to which the 7-bit data as described above is given will be described. In the data processing circuit 235, a shift register having seven stages as shown in FIG. 6 is formed. The shift register is supplied with 7-bit serial data and a clock corresponding to the set value from the outside in the sensitivity adjustment operation. Since the shift register sequentially captures the serial data at the falling edge of the clock, it is possible to capture all the 7-bit serial data in 7 clocks. When the 7-bit serial data is taken in, the serial data can be converted into parallel data by looking at the output of each stage of the shift register. In FIG. 6, the output terminals 61 to 67 are the parallel data output terminals.

  Here, the output terminals 62, 63, 64 corresponding to the second to fourth digits are connected to the storage unit for the first selector circuit, and the output terminals 65, 66, 67 corresponding to the fifth to seventh digits are connected. A storage unit for the second selector circuit is connected.

  FIG. 7 is a circuit diagram showing a configuration from the storage unit 236 corresponding to the first selector circuit 233 to the switch in the first selector 233. As shown in FIG. 7, the storage unit 236 in the first embodiment is configured by a fuse element arranged between the shift register and the selector of the data processing circuit. As shown in FIG. 7, the storage unit 236 corresponding to the first selector circuit has three fuse elements 711, 712, 713 and switch elements 721, 722, 723. The fuse and the switch are connected in series between the power line and the ground potential. The switch element is arranged on the ground potential side with respect to the fuse, and high resistances 731, 732, and 733 are connected between the fuse and the ground potential in parallel with the switch element. Data corresponding to the second to fourth digits converted into the parallel data is input to the gates of the switch elements 721, 722, and 723, respectively. That is, they are connected to the parallel data output terminals 62, 63, 64 in FIG. Here, it is assumed that a signal (second digit = 1, third digit, fourth digit = 0) corresponding to the above-described setting “increase the bias voltage by 3 V in the high sensitivity mode” is given. As a result, only the switch element 721 corresponding to the second digit bit is turned on, and the other switch elements 722 and 723 are turned off. At the time of sensitivity adjustment, the fuse cutting voltage VBIAS is applied from the inspection and adjustment machine in this state. Specifically, the power supply line is connected to the fuse cutting voltage VBIAS during sensitivity adjustment. When the fuse cutting voltage VBIAS is applied, an overcurrent flows only in the fuse 711 connected to the switch element 721 in the on state, and the fuse 711 is cut. In the other fuse elements 712 and 713, the switch elements 722 and 723 are in the OFF state, and the overcurrent does not flow because the switch elements 722 and 723 are connected to the ground potential only through the high resistances 732 and 733. When the fuse cutting is completed, the fuse cutting voltage VBIAS is disconnected from the power supply line.

  In the first embodiment, the set value is stored in the blown state of the fuse. Here, the normal operation will be described. During normal operation, the power supply line is connected to the normal circuit power supply VDD, and only the fuse 711 is cut. From the storage unit 236, nodes between the fuse and the high resistance (switch element) are connected to the logic circuit in the first selector circuit 236 (in the example shown in FIG. 7, each of the seven switches in the selector circuit). Gate). In this case, the node between the fuse 711 and the high resistance 731 corresponding to the part where the fuse is blown is at the ground potential (L level), whereas in the part where the fuse is not cut, the fuse 712, A node between 713 and the high resistances 732 and 733 is a power supply potential (H level). For this reason, in the circuit example shown in FIG. 7, an AND gate (the leftmost AND gate in FIG. 7) whose inputs are all at H level outputs H level, thereby selecting a switch of the selector circuit.

  In FIG. 7, only the connection between the storage unit corresponding to the first selector circuit 233 and the first selector circuit is shown, but the storage unit 236 using a fuse is similarly formed for the second selector circuit 234. The set value is stored by cutting the fuse.

  The set value set in the sensitivity adjustment operation in this manner is stored in the output voltage setting unit, and a bias voltage is generated based on this set value.

  As described above in detail, in the present embodiment, the setting value for setting the sensitivity of the capacitor microphone unit is determined by the sensitivity adjustment operation and stored in the voltage supply circuit for the capacitor microphone. Since the voltage supply circuit of the capacitor microphone sets the feedback resistance value based on the set value, it is possible to provide a capacitor microphone unit with no variation in sensitivity. In addition, since the bias voltage is a voltage obtained by amplifying the reference voltage with a non-inverting amplifier, a stable bias voltage with low ripple or the like can be supplied.

Embodiment 2
FIG. 8 is a diagram showing a capacitor microphone unit according to Embodiment 2 of the present invention. In FIG. 8, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In the second embodiment, the configurations of the first feedback resistor portion 831, the second feedback resistor portion 832, the first selector 833, and the second selector 834 are different. In the first embodiment, the feedback resistor units 231 and 232 are configured such that a plurality of resistors are connected in series, and the switch is connected to a node between the resistors. In the feedback resistor units 831 and 832 of the second embodiment, seven resistors are arranged in parallel, and one resistor is connected in series to the seven resistors. One end of this one resistor is connected to the ground potential. The first and second selector circuits 833 and 834 each have seven switches as in the first embodiment, but their connections are different. The seven switch elements are respectively connected to a node between one resistor whose one end is connected to the ground potential and the seven resistors connected in parallel. The other end of the switch is connected to the inverting input terminal of the non-inverting amplifier 221.

  In this embodiment, the resistance values of the seven resistors arranged in parallel are different. As in the first embodiment, the data processing circuit 235 gives a setting value for selecting any one of the seven switches in the selector circuits 833 and 834. That is, in the circuit of the second embodiment, any one of seven resistors having different resistance values is connected to the inverting input terminal of the non-inverting amplifier. As described above, in the second embodiment, the feedback resistance value is set by selecting any one of the resistors having different resistance values and connecting the selected one to the inverting input terminal.

  In the first embodiment, since an arbitrary node between the resistors connected in series is connected, it may be difficult to accurately set the amplification degree of the non-inverting amplifier. For example, in the first embodiment, when the number of resistors between the output of the non-inverting amplifier and the node connected to the inverting input terminal is one, the number of resistors connected from this node to the ground potential is There will be seven. When the number of resistors between the output of the non-inverting amplifier and the node connected to the inverting input terminal is two, the number of resistors connected from this node to the ground potential is six. Since the amplification degree of the amplifier 221 varies depending on the ratio of the feedback resistance value connected to the inverting input and the resistance value connected between the inverting input terminal and the ground potential, in the configuration as in the first embodiment, the amplifier 221 is connected in series. The setting of the resistance value of each individual resistor becomes complicated, and it may be difficult to accurately adjust the bias voltage. On the other hand, in the configuration of the voltage supply circuit 1 according to the second embodiment, it becomes easy to adjust the ratio between the feedback resistance value connected to the inverting input and the resistance value connected between the inverting input terminal and the ground potential. The accuracy for setting the bias voltage is also improved.

Embodiment 3
FIG. 9 is a diagram showing a condenser microphone unit according to Embodiment 3 of the present invention. In FIG. 9, the same components as those of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In the third embodiment, the first feedback resistor unit, the second feedback resistor unit, the first and second selectors are combined into one feedback resistor unit 91 and a selector circuit 92. The feedback resistor 91 has a plurality of resistors connected in series. The selector circuit 92 has a plurality of switches connected between the nodes between the resistors and the inverting input terminal. In the voltage supply circuit 1 of the third embodiment, the feedback resistance value is determined by the combination of switches selected by the selector circuit.

  In the first embodiment, the feedback resistance value is set by selecting one of the seven switches connected to the node between the resistors of the eight resistors. In the third embodiment, a plurality of switches are used. Can be selected. This can be done by changing the correspondence between the set value data set during sensitivity adjustment and the selected switch.

  For example, the number of bits of data set at the time of sensitivity setting is increased to a number of bits corresponding to the number of switches in the selector circuit. When the sensitivity is adjusted, a set value of the number of bits corresponding to the number of switches is stored in accordance with the voltage width to be adjusted in the high sensitivity mode and the low sensitivity mode. During normal operation, the connection between the node between each resistor of the feedback resistor unit and the inverting input terminal is determined for each switch in the selector circuit based on this set value.

  When eight resistors are connected in series as in the first embodiment and seven switches are formed in the selector circuit, there are 128 ways to select the switches. In this case, the setting values stored in the storage unit are the combination data of the switches in the high sensitivity mode and the combination data of the switches in the low sensitivity mode among the combinations. That is, the set value obtained at the time of sensitivity adjustment is 7-bit data corresponding to each switch, and the storage unit 236 stores two types of 7-bit combinations. Thus, by changing the correspondence between the setting value stored in the storage unit and the switch, the feedback resistor unit and the selector circuit are shared in the high sensitivity mode and the low sensitivity mode, and the bias voltage is used as one feedback resistor unit 91 and the selector circuit 92. Can be set.

Embodiment 4
FIG. 10 is a diagram showing a condenser microphone unit according to Embodiment 4 of the present invention. In FIG. 10, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In the fourth embodiment, a log amplifier 1001 is connected to the output of the non-inverting amplifier 221. In the fourth embodiment, the voltage output from the non-inverting amplifier 221 is further amplified by an amplifier called a log amplifier and supplied to the capacitor microphone 2 as a bias voltage. A log amplifier is an amplifier whose output increases exponentially with respect to its input.

  In the fourth embodiment, the log amplifier 1001 includes an operational amplifier, a diode, a bipolar transistor, and a resistor. The output of the non-inverting amplifier 221 is given to the non-inverting input terminal of the operational amplifier via an input resistor. The non-inverting input terminal of the operational amplifier is connected to the ground potential via a resistor. The output of this operational amplifier is fed back to the inverting input terminal via an output resistor, a diode and a bipolar transistor connected in parallel. The log amplifier is supplied with a voltage boosted by a power booster as a power supply voltage.

  It is generally known that the sensitivity of a capacitor microphone unit increases exponentially as the bias voltage for the capacitor microphone unit increases. Therefore, in the fourth embodiment, a log amplifier having almost the same input / output characteristics as those of the capacitor microphone with respect to the bias voltage is used.

  As described above, the output of the log amplifier changes exponentially with respect to the change of its input. For example, in the voltage supply circuit of the first embodiment, the non-inverting amplifier adjusts the bias voltage for the capacitor microphone within a range of ± 3V. However, since the output of the non-inverting amplifier is amplified by the log amplifier in the fourth embodiment, the bias voltage in a range wider than ± 3 V can be adjusted.

In the first embodiment, the storage unit 236 is configured to select any one of the seven switches from the storage unit having three fuse elements. However, other configurations may be used as the storage unit. Is possible. FIG. 11 is a diagram illustrating a case where another circuit is used as the storage unit. In the first embodiment, the storage unit 236 exists between the data processing circuit 235 and the selector circuit 233, but in this modification, the storage unit is provided in parallel with the feedback resistor unit. A fuse is provided in parallel with each of the plurality of resistors of the feedback resistor unit.

  Then, any of the seven fuses is cut according to the voltage width adjusted during the sensitivity adjustment operation. In this manner, a fuse can be provided in parallel with the feedback resistor section, and the fuse can be cut off at the time of sensitivity adjustment to form a memory section. Such a configuration can be applied to any of the second to fourth embodiments. FIG. 12 shows an example in which another modification is applied to the second embodiment. The storage unit shown in FIG. 12 stores a set value by providing a fuse between each feedback resistor and the switch and cutting an arbitrary fuse during sensitivity adjustment.

  In the embodiment, the storage unit is formed using a fuse. However, the storage unit is not limited to the fuse element, and a zener zap, an EEPROM, or the like can be used. Here, the zener zap is an element that operates in the opposite direction to the fuse. When a fuse is blown, it is always memorized that two points are in an “open” state, whereas Zener Zap always memorizes and “shorts” between two points by breakdown. Such a storage unit can be realized, for example, by replacing the fuse of the modification shown in FIG. 11 with a zener zap element as it is.

  FIG. 13 is a circuit diagram showing a configuration when the configuration of the storage unit shown in FIG. 7 in the first embodiment is replaced from a fuse to an EEPROM. When a circuit configured as shown in FIG. 13 is desired to obtain the same output as that of the storage unit of the first embodiment, a high voltage is applied to Vwrite as a write voltage during the sensitivity adjustment operation. Further, an L level signal is applied to the control gate of the EEPROM element 1321, and an H level signal is applied to the control gates of the EEPROM elements 1322 and 1323. As a result, the EEPROM element 1321 is always turned on because electrons of the floating gate are discharged. On the other hand, in the EEPROM elements 1322 and 1323, the electrons of the floating gate are not discharged and remain in the erased state. After the sensitivity adjustment operation is completed, no voltage is applied to the write voltage and the control gate, so that the erased element is always off, and the L level is input only to the leftmost inverter in FIG. As a result, as in the first embodiment, only the leftmost AND gate in FIG. 13 outputs an H level and selects a switch.

  In the embodiment, the power boosting unit 21 outputs a voltage obtained by constantly boosting the power supply voltage regardless of the mode designating signal. However, the mode designating signal is also input to the power boosting unit 21, and the power boosting unit 21. May be configured to generate a voltage required by the amplifier according to the mode.

  As described above in detail, according to the voltage supply circuit of the present invention, it is possible to apply an appropriate voltage based on sensitivity to a sensor such as a capacitor microphone. In addition, it is possible to reduce sensitivity variations for each microphone unit such as a capacitor microphone unit. Further, the present invention is not limited to the configuration shown in the embodiment, and various modifications are possible as in the above-described modifications.

  Furthermore, the voltage supply circuit of the present invention has been described in detail in the embodiment in the case of using a vibration sensor (condenser microphone) as a sensor. However, the use of the voltage supply circuit of the present invention is not limited to the capacitor microphone. . For example, it goes without saying that the present invention is also useful for other sound pressure sensors that detect displacement of capacitance that operates on the same principle as a capacitor microphone, for example, those using a semiconductor element or the like. Therefore, it goes without saying that the microphone unit referred to in the present invention includes other sound pressure sensors that detect displacement of capacitance, such as those using a semiconductor element or the like as a microphone. The voltage supply circuit of the present invention is also very effective for a displacement detection type using a vibration sensor, particularly for a type that detects a change in capacitance. Furthermore, the voltage supply circuit of the present invention can also be applied to other sensors whose output can be changed by a DC bias voltage, such as a temperature sensor and an optical sensor.

It is a figure which shows the capacitor | condenser microphone unit of this invention. FIG. 3 is a diagram illustrating a voltage supply circuit of the capacitor microphone unit according to the first embodiment. It is a figure which shows the sensitivity adjustment apparatus of this invention. It is a figure which shows the relationship between the sensitivity of a capacitor | condenser microphone unit, and bias voltage. It is a figure which shows the setting value which an adjustment signal generation circuit outputs, and the adjustment amount with respect to bias voltage. It is a figure which shows the shift register in a data processing circuit. FIG. 3 is a circuit diagram showing a configuration from a storage unit corresponding to a first selector circuit to a switch in the first selector. 6 is a diagram showing a capacitor microphone unit according to Embodiment 2. FIG. 6 is a diagram showing a capacitor microphone unit according to Embodiment 3. FIG. FIG. 10 is a diagram illustrating a capacitor microphone unit according to a fourth embodiment. It is a figure showing the case where another circuit is used as a memory | storage part. It is a figure showing the case where another circuit is used as a memory | storage part. It is a figure showing the case where another circuit is used as a memory | storage part. It is a figure which shows the conventional capacitor | condenser microphone unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Voltage supply circuit 2 Capacitor microphone 3 Amplification circuit 4 Capacitors 5 and 6 Resistor 7 Power supply 21 Power supply boosting part 22 Regulator part 23 Output voltage setting part 221 Non-inverting amplifier 222 Reference voltage source 231 First feedback resistance part 232 Second feedback Resistance unit 233 First selector circuit 234 Second selector circuit 235 Data processing unit 236 Storage unit 31 Signal generator 32 Speaker 33 Capacitor microphone unit 34 Inspection adjustment machine 341 Comparison circuit 342 Reference circuit 343 Adjustment signal generation circuits 711 and 712 713 Fuse 721, 722, 723 Switch element 731, 732, 733 High resistance 831 First feedback resistor 832 Second feedback resistor 833 First selector circuit 834 Second selector circuit 91 Feedback resistor 92 Selector circuit 1001 Log amplifier 1111 , 1211 First feedback resistor unit and storage unit 1112, 1212 Second feedback resistor unit and storage unit 1113, 1213 First selector circuit 1114, 1214 Second selector circuit

Claims (11)

A power booster;
An amplifier that operates using the voltage generated by the power supply boosting unit as a power supply voltage, and supplies a voltage obtained by non-inverting amplification of the reference voltage to the sensor as a bias voltage ;
It has a feedback resistor section for determining the amplification factor by the resistance ratio of the amplifier in the non-inverting amplifier operation, the resistance ratio and an output voltage setting circuit which is determined in accordance with the set value of the bias voltage of the sensor Voltage supply circuit.   The voltage supply circuit according to claim 1, further comprising a storage unit that holds a setting value of the bias voltage.   The voltage supply circuit according to claim 1, wherein the feedback resistor unit has a resistance value determined by a resistor arbitrarily selected from a plurality of resistors.   The feedback resistor unit includes a plurality of resistors, and the resistance value of the feedback resistor unit is determined by using an arbitrary number of resistors corresponding to a set value of the bias voltage among the plurality of resistors. The voltage supply circuit according to claim 1 or 2, characterized in that   5. The voltage supply circuit according to claim 2, wherein the storage unit holds a set value of the bias voltage with a fuse. 6.   5. The voltage supply circuit according to claim 2, wherein the storage unit holds a set value of the bias voltage by a zener zap. 6. The output voltage setting unit further includes a selector circuit connected to the feedback resistor unit,
A data processing circuit that outputs a selection signal to the selector circuit;
7. The voltage supply circuit according to claim 1, wherein the selector circuit sets a resistance value of the feedback resistor unit based on the selection signal and serves as a feedback resistor of the amplifier. .   The feedback resistor unit includes at least a first feedback resistor unit and a second feedback resistor unit, and based on a mode setting signal input from the outside of the output voltage setting circuit, the first feedback resistor unit or The voltage supply circuit according to claim 1, wherein the second feedback resistor unit is selected as a feedback resistor for the amplifier. A microphone to which a bias voltage is supplied;
A power booster;
An amplifier that operates using the voltage generated by the power supply boosting unit as a power supply voltage and supplies a voltage obtained by non-inverting amplification of a reference voltage to the microphone as a bias voltage ;
Has a feedback resistor section for determining the amplification factor of the amplifier in the non-inverting amplification operation by the resistance ratio has an output voltage setting circuit to which the resistance ratio is determined in accordance with the set value of the bias voltage of the microphone, the Microphone unit.   The microphone unit according to claim 9, further comprising a storage unit that holds a setting value of the bias voltage. A microphone sensitivity adjustment method,
Input a reference sound into the microphone,
Compare the output of the microphone with respect to the reference sound and a reference voltage ,
Based on the comparison result, a setting value for setting a bias voltage to be biased to the microphone is output
The set value is stored, and the resistance ratio of the feedback resistor unit is determined based on the set value ,
A sensitivity adjustment method in which an amplification factor of an amplifier that outputs a voltage obtained by non-inverting amplification of a reference voltage as the bias voltage is determined by the resistance ratio .

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