JP2011193144A - Signal processing device, digital output microphone unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stabilize fluctuation of digital output to ambient temperature change within a wide temperature range. <P>SOLUTION: In a signal processing device (13) which converts analog electric signals converted from sound by a microphone (1) to digital signals, and outputs them, the device is provided with a preamplifier (15) for amplifying the analog electric signals output from the microphone (1), an analog-digital convertor (12) for comparing the analog electric signals output from the preamplifier (15) with a reference voltage (Vref) for converting the signals from analog to digital, and a reference voltage generation circuit (14) for generating the reference voltage (Vref) and supplying the voltage to the analog-digital convertor (12). The reference voltage generation circuit (14) is provided with an element having a higher temperature dependency in terms of an electric property, compared to other electric circuit elements among electric circuit elements constituting the signal processing device (13), and generates a reference voltage (Vref) corresponding to the voltage between both terminals of the element. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a signal processing apparatus and a digital output microphone unit including the same.

  A microphone is a sensor that converts sound (elastic wave propagating through an elastic body) into an analog electric signal, and is classified into a piezoelectric type, an electrodynamic type, an electrostatic type, and the like depending on the conversion method. In portable devices such as mobile phones and IC recorders that are required to be small and thin, electrostatic ECM (Electret Condenser Microphone) and MEMS (Micro Electro Mechanical Systems) microphones are generally employed. .

  By the way, it is known as one of the characteristics of the microphone that it is vulnerable to ambient temperature changes. For example, when a sound pressure level of 94 dB SPL (Sound Pressure Level) equivalent to that of normal conversation is collected in the ECM, the voltage level of the analog electric signal output from the ECM is at room temperature (about 20 ° C.). Although stable at about 20 mVpp (Peak to Peak), fluctuations of about 15 to 30 mVpp (Peak to Peak) occur over a wide range of temperature changes from -40 ° C to 90 ° C. As described above, when collecting and reproducing a normal conversation, there is a problem that the volume of the sound fluctuates according to the ambient temperature change.

  In order to improve the acoustic characteristics of the microphone with respect to ambient temperature changes, for example, techniques described in Patent Documents 1 and 2 have been proposed.

  Patent Document 1 discloses an ECM configured by laminating three members, an electric circuit board, a back electrode board, and a diaphragm support frame, in which an electrode film, an electret layer, a diaphragm, and the like are integrated. In this way, by using the same material for the three members, the acoustic characteristics are improved with respect to ambient temperature changes.

  Patent Document 2 discloses a microphone unit that incorporates a thermistor and adjusts an output level following a change in ambient temperature. FIG. 18 is a circuit diagram showing the configuration of the conventional microphone unit shown in FIGS. A microphone unit 50 shown in FIG. 18 includes a microphone 51 and a preamplifier 52 including an operational amplifier 53. The output of the microphone 51 is connected to the non-inverting input terminal of the operational amplifier 53. The output of the operational amplifier 53 is connected to an output terminal 55 for extracting an audio signal, and is also connected to an inverting input terminal of the operational amplifier 53 via a feedback resistor 56. The inverting input terminal of the operational amplifier 53 is connected to a predetermined terminal 59 via a variable resistor 58 for determining the gain of the preamplifier 52 as with the feedback resistor 56. In addition to the basic configuration of the microphone unit 50, a signal line from the thermistor 57 is connected to both ends of the feedback resistor 56, whereby the operational amplifier 53 for determining the gain (amplification factor) of the preamplifier 52 is connected. A feedback resistance element is configured. With this configuration, when the ambient temperature increases, the resistance value of the thermistor 57 connected in parallel to the feedback resistor 56 decreases, and the gain of the preamplifier 52 is automatically adjusted so as to suppress the increase in sensitivity of the microphone unit 50 due to the temperature increase. Adjusted. On the other hand, when the ambient temperature decreases, the resistance value of the thermistor 57 increases, and the gain of the preamplifier 52 is automatically adjusted so as to suppress the sensitivity decrease of the microphone unit 50 due to the temperature decrease. Note that the initial sensitivity of the microphone unit 50 is adjusted in advance in the manufacturing stage or the like so as to be within the specified sensitivity range at room temperature by the variable resistor 58. The temperature characteristics of the microphone unit 50 are adjusted by the resistance values of the variable resistor 58 and the thermistor 57.

JP 2002-345087 A JP 2008-256433 A

  By the way, the techniques described in Patent Documents 1 and 2 have the following problems.

  In the technique described in Patent Document 1, it is expected to improve acoustic characteristics against changes in ambient temperature by using the same material for the three members of the electric circuit board, the back electrode board, and the diaphragm support frame. However, it is not clear how much it has actually been improved, and there is a problem of lack of concreteness and feasibility. Further, when the same material is used for the three members, the analog electric signal output from the ECM still changes with respect to the ambient temperature change. However, Patent Document 1 discloses that the temperature characteristics of the analog electric signal are improved. There is no description or suggestion of a specific configuration for this purpose.

  In the technique described in Patent Document 2, variations in initial sensitivity and temperature characteristics of the microphone itself due to the manufacturing process, and the resistance values of the feedback resistor 56, the thermistor 57, and the variable resistor 58 that determine the gain of the preamplifier 52 are obtained. It is considered that variation in temperature characteristics occurs with respect to the output (analog electric signal) of the microphone unit 50 mainly due to two factors, variation.

  Here, in Patent Document 2, a variable resistor 58 is built in the microphone unit 50 in advance in consideration of the variation of the microphone itself caused by the manufacturing process, and the initial sensitivity of the microphone unit 50 is a specified sensitivity at normal temperature in the manufacturing stage. It is adjusted in advance by the variable resistor 58 so as to be within the range. However, the adjustment of the initial sensitivity is complicated, and there is a problem that the manufacturing cost is increased by the steps required for the adjustment.

  Further, in Patent Document 2, in order to adjust the gain of the preamplifier 52 in order to improve the temperature characteristic of the output (analog electric signal) of the microphone unit 50, two or more types of resistors (feedback resistor 56, thermistor 57) that are not of the same type are used. The variable resistor 58) is built in the microphone unit 50. Since these resistors have individual temperature characteristic variations, there is a problem that uniform adjustment is difficult and difficult for the gain of the preamplifier 52 and the temperature characteristic of the output of the microphone unit 50. . Furthermore, if the peripheral circuit including the preamplifier 52 of the microphone unit 50 is integrated, the temperature characteristics of two or more types of resistors that are not of the same type in the integrated circuit vary significantly. It becomes even more prominent.

  Furthermore, neither Patent Documents 1 and 2 describe nor suggest that a microphone unit including a microphone is miniaturized and digitized. Conventionally, including the inventions described in Patent Documents 1 and 2, since the microphone unit is generally composed of discrete components, it has been difficult to reduce the size of the microphone unit. In particular, when a digital output microphone unit equipped with an analog-digital converter is manufactured, the number of new parts increases for digitization, so that it is more difficult to reduce the size of the digital output microphone unit.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a digital output microphone unit that stabilizes fluctuations in digital output with respect to ambient temperature changes within a wide temperature range.

In order to solve the above problems, a signal processing device according to the present invention is a signal processing device that performs analog-digital conversion of an analog electrical signal converted from sound by a microphone into a digital electrical signal, and outputs the digital electrical signal. A preamplifier for amplifying the output analog electrical signal; an analog-to-digital converter for converting the analog electrical signal output from the preamplifier to a digital electrical signal by comparing with a reference voltage; and generating the reference voltage to generate the analog A reference voltage generating circuit for supplying to the digital converter, wherein the reference voltage generating circuit is a temperature of its electrical properties compared to other electric circuit elements among the electric circuit elements constituting the signal processing device. Equipped with highly dependent elements (hereinafter referred to as high temperature dependent elements), based on the voltage across both terminals of the high temperature dependent elements Generating a reference voltage, it is intended.
According to this configuration, when the reference voltage generated by the reference voltage generation circuit has a temperature characteristic having temperature dependency similar to the temperature characteristic of the microphone, the analog-digital converter outputs the analog electric signal output from the preamplifier. Since the signal is compared with this reference voltage, even if the magnitude of the analog electrical signal converted from sound by the microphone changes depending on the ambient temperature change, this reference voltage will change to the magnitude of the analog electrical signal. Follow and change. For this reason, changes due to temperature in the magnitude of the analog electrical signal are canceled out by changes in the reference voltage generated by the reference voltage generation circuit, and the output level of the digital output microphone unit when the ambient temperature changes is stabilized. Can be made. In addition, since an element having a relatively high temperature dependency as compared with other electric circuit elements constituting the signal processing device is employed, it is easy to give the reference voltage temperature characteristics. Further, the reference voltage generation circuit does not have to be configured by combining different types of elements in addition to the high temperature dependent element. For this reason, it is only necessary to consider the manufacturing variation of the high temperature dependent element, and it is easy to generate a desired reference voltage having a temperature characteristic that cancels the temperature characteristic of the analog electric signal output from the microphone. Become.

  In the above signal processing device, the high temperature dependent element is a diode, and the reference voltage generation circuit is configured by connecting a current source and the diode in series between a power supply terminal and a ground terminal, The reference voltage may be generated based on a voltage at a connection point between a power supply terminal and the diode.

  According to this configuration, the temperature characteristic of the diode is approximated as a linear line similarly to the temperature characteristic of the microphone, and the forward voltage of the diode is stable at about 0.7 V. Therefore, output from the microphone is achieved by using the diode. Therefore, it is possible to easily generate a reference voltage having a temperature characteristic that cancels the temperature characteristic of the analog electric signal. Further, it is possible to manufacture the reference voltage generation circuit with a small number of parts.

In the above signal processing device, the high temperature dependent element is a resistor having a positive or negative temperature coefficient, and the reference voltage generating circuit includes a current source and the resistor in series between a power supply terminal and a ground terminal. The reference voltage may be generated based on a voltage at a connection point between the power supply terminal and the resistor.
According to this configuration, the reference voltage can be easily given temperature characteristics as in the case of the diode, and the reference voltage generation circuit can be manufactured with a small number of components.

In the above signal processing device, the preamplifier, the analog-digital converter, and the reference voltage generation circuit may be integrated.
According to this configuration, a very small and accurate digital output microphone unit can be realized.

  The digital output microphone unit according to the present invention includes a microphone that converts sound into an analog electrical signal, a preamplifier that amplifies the analog electrical signal output from the microphone, and an analog electrical signal output from the preamplifier as a reference voltage. An analog-to-digital converter that converts the signal into a digital electric signal, and a reference voltage generation circuit that generates the reference voltage and supplies the reference voltage to the analog-to-digital converter, and the reference voltage generation circuit includes: Among the electric circuit elements constituting the signal processing device, the electric circuit element includes an element having a higher temperature dependency of its electrical properties than the other electric circuit elements (hereinafter referred to as a high temperature dependent element). A reference voltage corresponding to the voltage between both terminals is generated.

  In the above digital output microphone unit, the microphone may be an ECM (Electret Condenser Microphone).

  According to this configuration, an ECM unit with a temperature compensation function can be realized.

  In the digital output microphone unit, the microphone may be a MEMS (Micro Electro Mechanical Systems) microphone.

According to this configuration, a MEMS microphone unit with a temperature compensation function can be realized.
In the digital output microphone unit, the analog-digital converter may be a delta-sigma modulation type analog-digital converter.
According to this configuration, it is possible to provide a high-quality digital output microphone unit with low noise.

In the digital output microphone unit, the digital electric signal may be converted into a PDM (Pulse Density Modulation) method and output to the outside.
According to this configuration, it is not necessary to provide a DSP for audio signal processing in the digital output microphone unit, and a small digital output microphone unit can be realized. Furthermore, since the signal output from the digital output microphone unit is a digital electric signal, it is difficult to be affected by disturbance noise, and location-free can be realized in a set product on which the digital output microphone unit is mounted.

  According to the present invention, it is possible to realize a digital output microphone unit that stabilizes a digital output level against a change in ambient temperature within a wide temperature range.

It is a circuit diagram which shows the structure of the digital output microphone unit which concerns on the 1st Embodiment of this invention. It is a circuit diagram which shows the structure of a delta-sigma modulation type | mold analog-digital converter. It is a circuit diagram which shows the structure of the reference voltage generation circuit in the digital output microphone unit of FIG. 2 is a graph showing temperature characteristics of an ECM output signal having a positive temperature coefficient in the digital output microphone unit of FIG. 1. 2 is a graph showing temperature characteristics of an anode-cathode voltage of a diode in the digital output microphone unit of FIG. 1. It is a graph which shows the temperature characteristic of the output level of the digital output microphone unit of FIG. It is a circuit diagram which shows the structure of the reference voltage generation circuit in the digital output microphone unit which concerns on the 2nd Embodiment of this invention. It is a circuit diagram which shows the structure of the reference voltage generation circuit in the digital output microphone unit which concerns on the 3rd Embodiment of this invention. It is a graph which shows the temperature characteristic of resistance which has a positive temperature coefficient in the digital output microphone unit which concerns on the 3rd Embodiment of this invention. It is a circuit diagram which shows the structure of the reference voltage generation circuit in the digital output microphone unit which concerns on the 4th Embodiment of this invention. It is a graph which shows the temperature characteristic of resistance which has a negative temperature coefficient in the digital output microphone unit which concerns on the 4th Embodiment of this invention. It is a graph which shows the temperature characteristic of ECM which has a negative temperature coefficient in the digital output microphone unit which concerns on the 5th Embodiment of this invention. It is a circuit diagram which shows the structure of the reference voltage generation circuit in the digital output microphone unit which concerns on the 5th Embodiment of this invention. It is a graph which shows the temperature characteristic of the output level of the digital output microphone unit which concerns on the 5th Embodiment of this invention. It is a circuit diagram which shows the structure of the reference voltage generation circuit in the digital output microphone unit which concerns on the 6th Embodiment of this invention. It is a circuit diagram which shows the structure of the reference voltage generation circuit in the digital output microphone unit which concerns on the 7th Embodiment of this invention. It is a circuit diagram which shows the structure of the reference voltage generation circuit in the digital output microphone unit which concerns on the 8th Embodiment of this invention. It is a circuit diagram which shows the structure of the conventional analog output microphone unit.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same referential mark is attached | subjected to the element which is the same or it corresponds through all the figures below, and the overlapping description is abbreviate | omitted.
(First embodiment)
Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings.

[Concept of the present invention]
The present invention includes a microphone, a preamplifier, and an analog-digital converter. An analog electrical signal output from the microphone is input to the analog-digital converter via the preamplifier, and the analog-digital conversion is performed. The digital output microphone unit that converts it into a digital electric signal by the device is the application target. Here, the digital electrical signal output from the digital output microphone unit has the same temperature characteristics as the analog electrical signal output from the conventional analog output microphone unit. Therefore, the present inventor has considered that a temperature characteristic having a temperature dependence opposite to the original temperature characteristic is created inside the digital output microphone unit and used to cancel the original temperature characteristic. Specifically, the reference voltage compared with the analog electric signal having the temperature characteristic in the analog-digital converter is considered to have a temperature characteristic having the same temperature dependence as the temperature characteristic of the analog electric signal. “Having opposite temperature dependence” means “the sign of the temperature coefficient is opposite”, and “similar temperature dependence” means “the sign of the temperature coefficient is the same”. To do.

  Here, the basic principle of the analog-digital converter is that the analog electric signal is quantized by comparing the reference voltage of the analog-digital converter and the analog electric signal input to the analog-digital converter. Is to do. If this analog-digital conversion process is simplified, it can be expressed by the following equation.

Dcode = (Vin / Vref) × 2 ^N (1)
Dcode is a digital output code, Vin is an input voltage (analog electrical signal), Vref is a reference voltage of the analog-digital converter, and N is a conversion bit number (conversion resolution). Here, for example, when Vin = 1V, Vref = 1V, and N = 5, the digital output code Dcode outputs “11111” in full scale. When Vin = 0.5V, Vref = 1V, and N = 5, the digital output code Dcode outputs “01111” of ½ full scale. That is, when the reference voltage Vref is constant, it can be seen that the digital output code Dcode varies greatly according to the variation of the input voltage Vin.

  Therefore, even if the magnitude of the analog electric signal input from the microphone to the analog-to-digital converter via the preamplifier changes due to a change in ambient temperature, the temperature change of the analog electric signal input to the analog-to-digital converter. A reference voltage that follows the change due to is generated, and the reference voltage is used as the reference voltage of the analog-digital converter. As a result, the digital output code Dcode is stabilized without depending on the ambient temperature change.

  In addition, compared with other electric circuit elements constituting the digital output microphone unit, an element (hereinafter referred to as a high temperature dependent element) having a higher temperature dependence of its electrical properties (electrical resistance, resistivity, conductivity, etc.) A reference voltage corresponding to the voltage between both terminals of the element is generated. By adopting this high temperature dependent element, it becomes easy to give temperature characteristics to the reference voltage of the analog-digital converter. Further, it is sufficient to use only the high temperature dependent element when generating the reference voltage, and there is no need to combine different types of electric circuit elements as in the thermistor 57 and the feedback resistor 56 shown in FIG. . For this reason, it is only necessary to consider the manufacturing variation of the high temperature dependent element, and it becomes easy to generate a desired reference voltage that follows the change of the analog electric signal output from the microphone due to the temperature.

  Examples of the high temperature-dependent element include a diode (including a diode-connected MOSFET and a bipolar transistor) described later, and a resistor (polysilicon resistor, diffused resistor, etc.) having a positive or negative temperature coefficient. The temperature characteristic of the diode is approximated as a linear line having a positive or negative temperature coefficient similar to the temperature characteristic of the microphone, and the forward voltage of the diode is stable at about 0.7 V at room temperature. For example, it becomes easy to generate a reference voltage that follows changes in temperature of an analog electrical signal output from a microphone. It is also possible to manufacture the reference voltage generation circuit with a small number of parts. The same can be said when a resistor approximating the temperature characteristic of the diode is used.

[Configuration of digital output microphone unit]
FIG. 1 is a circuit diagram showing a configuration of a digital output microphone unit according to the first embodiment of the present invention.

  The digital output microphone unit 100 shown in FIG. 1 includes a microphone 1, a preamplifier 15, an analog-digital converter 12, and a reference voltage generator in a casing 18 provided with an opening 11 for collecting ambient sounds. The circuit 14 is configured in combination. The digital output microphone unit 100 includes at least a power supply terminal 2, a ground terminal 9, and a digital output terminal 16 as external terminals.

  The microphone 1 is a sound detection sensor that converts sound collected from the opening 11 (elastic wave propagating through an elastic body) into an analog electric signal. The microphone 1 is preferably an electrostatic ECM (Electret Condenser Microphone) or MEMS (Micro Electro Mechanical Systems) microphone in consideration of miniaturization of the digital output microphone unit 100 and integration of an integrated circuit. It may be a mold or an electrodynamic type.

  The preamplifier 15 is an amplifier that receives an analog electrical signal output from the microphone 1 and amplifies the analog electrical signal with a predetermined amplification factor in order to adjust the sound quality, volume, and the like.

  The analog-digital converter 12 receives the analog electric signal output from the preamplifier 15 and converts the analog electric signal into a digital electric signal based on a comparison between the analog electric signal and a reference voltage Vref described later. An output of the analog-digital converter 12 is connected to a digital output terminal 16, and a digital electric signal is output to the outside through the digital output terminal 16. The analog-digital converter 12 is provided with a reference voltage input terminal 17 to which the reference voltage Vref generated by the reference voltage generation circuit 14 is applied.

  The analog-to-digital converter 12 is preferably a delta-sigma modulation type capable of obtaining a high resolution. FIG. 2 is a circuit diagram showing a configuration of a delta-sigma modulation type analog-digital converter.

  The analog-digital converter 12 shown in the figure includes a delta-sigma modulator composed of a subtractor 121, an integrator 122, a comparator (quantizer) 123, a delay unit 124, and a digital-analog converter 125, and a digital And a filter 126.

  As a modulation operation of the above delta sigma modulator, first, an analog electric signal is input to the subtractor 121 together with the output at the previous time of the digital-analog converter 125. The subtractor 121 calculates a difference between the analog electric signal and the output of the digital-analog converter 125 and inputs the difference to the integrator 122. The integrator 122 inputs the result of adding the output of the subtractor 121 and the data at the previous time of the output to the comparator 123. The comparator 123 compares the output of the integrator 122 and the reference voltage Vref applied to the reference voltage input terminal 17 to generate a digital electric signal. The digital electrical signal output from the comparator 123 is oversampled by a latch circuit (not shown) and the like and then input to the digital filter 126 and is fed back to the subtractor 121 via the delay device 124 and the digital-analog converter 125. Entered. The digital filter 126 performs an averaging process and decimation of the sampling frequency to improve the resolution of the oversampled digital electrical signal.

  In particular, the analog-to-digital converter 12 can achieve a high signal-to-noise ratio with low power consumption by using a 4th order delta-sigma modulation type with a clock frequency of 1 M to 4 MHz and an oversampling rate of 50 to 64 times. The high-quality digital output microphone unit 100 can be realized. The analog-to-digital converter 12 is not limited to the delta-sigma modulation type, and any analog-to-digital converter may be used as long as the analog electric signal output from the preamplifier 15 is compared with the reference voltage Vref. For example, a successive approximation type, a flash type, or a pipeline type may be used.

  The digital electric signal output from the analog-digital converter 12 is preferably output to the outside from the digital output terminal 16 after being converted into a PDM (Pulse Density Modulation) format. As a result, a DSP (Digital Signal Processor) connected to the digital output terminal 16 for audio signal processing can convert a digital electric signal in the PDM format into an arbitrary audio interface format. Alternatively, a digital electric signal may be output from the digital output terminal 16 according to the audio interface format by taking the DSP into the housing 18.

  Note that the preamplifier 15, the analog-digital converter 12, and the reference voltage generation circuit 14 are preferably configured as an integrated circuit signal processing device 13 instead of being configured as discrete components. Thereby, the power supply terminal 2 and the ground terminal 9 can be shared among the preamplifier 15, the analog-digital converter 12, and the reference voltage generation circuit 14, and further miniaturization of the digital output microphone unit 100 can be realized. .

[Configuration of reference voltage generation circuit]
FIG. 3 is a circuit diagram showing a configuration of a reference voltage generation circuit in the digital output microphone unit of FIG.

  The reference voltage generation circuit 14 shown in the figure includes a current source 19 and a diode 25 connected in series between a power supply 27 and a ground terminal, and an inverting amplifier 23 to which a voltage at a connection point between the current source 19 and the diode 25 is input. And is composed of.

  The current source 19 is connected at its input side to the power supply 27 and supplies a forward current to the diode 25. Note that the current value of the current source 19 preferably does not change due to changes in temperature and power supply voltage.

  The diode 25 has its cathode side connected to the ground terminal and its anode side connected to the inverting input terminal of the operational amplifier 26 via the output of the current source 19 and the input resistor 20. That is, the anode-cathode voltage of the diode 25 is applied to the inverting input terminal of the operational amplifier 26.

  The output terminal of the operational amplifier 26 is connected to the reference voltage output terminal 22 and is connected to the inverting input terminal of the operational amplifier 26 via the feedback resistor 21 that determines the gain of the inverting amplifier 23. The input resistor 20 and the feedback resistor 21 are preferably manufactured using the same type of manufacturing process technology. As a result, variations in resistance values of the input resistor 20 and the feedback resistor 21 can be reduced, and variations in gain of the inverting amplifier 23 can be reduced. The non-inverting input terminal of the operational amplifier 26 is connected to the power source 24 and controls the output voltage of the inverting amplifier 23. It is preferable that the voltage value of the power supply 24 does not change due to changes in temperature and power supply voltage.

With the above configuration, the slope of the temperature characteristic of the reference voltage Vref generated by the reference voltage generation circuit 14 is adjusted using the slope (mV / ° C.) of the temperature characteristic of the anode-cathode voltage of the diode 25. It becomes possible.
[Example of temperature characteristic compensation]
FIG. 4 is a graph showing temperature characteristics of an ECM output signal (analog electrical signal) having a positive temperature coefficient in the digital output microphone unit shown in FIG. The graph is obtained when the ECM collects a sound corresponding to 94 dB SPL (Sound Pressure Level).

  According to the figure, the voltage level of the output signal of the ECM is about 20 mVpp (Peak to Peak) at 27 ° C., but decreases to about 16 mVpp (Peak to Peak) at −40 ° C., and about 25 mVpp at 90 ° C. It can be seen that the number has increased. As described above, the temperature characteristic of the ECM is approximated as a linear line (or a linear curve) having a positive slope.

  FIG. 5 is a graph showing temperature characteristics of the anode-cathode voltage of the diode in the digital output microphone unit shown in FIG.

  According to the figure, it can be seen that the slope of the anode-cathode voltage with respect to the temperature change is about −2 (mV / ° C.). Here, when the gain of the inverting amplifier 23, that is, the ratio between the input resistor 20 and the feedback resistor 21 is set to “1”, for example, the gradient of the temperature characteristic of the output voltage (reference voltage Vref) of the reference voltage generation circuit 14 is about +2. (MV / ° C.). Therefore, similar to the temperature characteristic of the microphone shown in FIG. 4, the temperature characteristic of the reference voltage Vref is approximated as a linear line having a positive slope. Note that the ratio between the input resistor 20 and the feedback resistor 21 for determining the gain may be determined so as to correspond to the temperature change of the analog electric signal output from the microphone 1.

  FIG. 6 is a graph showing the temperature characteristics of the output level (digital electric signal) of the digital output microphone unit shown in FIG. Note that the graph is obtained when an ECM having a positive temperature coefficient collects 94 dB SPL equivalent. The broken line indicates the output level when the reference voltage Vref is assumed to be constant, and the solid line indicates the output level when the reference voltage Vref is generated based on the anode-cathode voltage of the diode 25.

As can be seen from the figure, when the reference voltage Vref is assumed to be constant, the output level changes by about 4 dB in a wide temperature range of −40 ° C. to 90 ° C. On the other hand, when the reference voltage Vref is generated based on the anode-cathode voltage of the diode 25, the output level is stabilized to a value close to −26 dBFS within the same wide temperature range as described above (temperature characteristic compensation is performed). I understand).
(Second Embodiment)
Hereinafter, a digital output microphone unit according to a second embodiment of the present invention will be described. Note that, as in the first embodiment, the second embodiment is applied to the case where the microphone 1 has a positive temperature coefficient as shown in FIG. The only difference from the digital output microphone unit 100 according to the first embodiment is the configuration of the reference voltage generation circuit 14.

  FIG. 7 is a circuit diagram showing a configuration of a reference voltage generation circuit in the digital output microphone unit according to the second embodiment of the present invention.

  7 includes a diode 25 and a current source 19 connected in series between a power supply 27 and a ground terminal, and a non-inverted input of a voltage at a connection point between the diode 25 and the current source 19. And an amplifier 28.

  The diode 25 has an anode side connected to the power source 27 and a cathode side connected to the input of the current source 19. The voltage at the connection point between the diode 25 and the current source 19 is connected to the inverting input terminal of the operational amplifier 26.

  The output terminal of the operational amplifier 26 is connected to the reference voltage output terminal 22 and is connected to the inverting input terminal of the operational amplifier 26 via a feedback resistor 29 that determines a gain (amplification factor). The inverting input terminal of the operational amplifier 26 is connected to the power source 24 via a resistor 30 that determines the gain of the non-inverting amplifier 28. The feedback resistor 29 and the resistor 30 can be manufactured using the same manufacturing process technology of the same type, so that variations in the resistance values of the feedback resistor 29 and the resistor 30 can be reduced, and gain variations in the non-inverting amplifier 28 can be reduced. Can be reduced. Further, it is preferable that the voltage value of the power supply 24 does not change due to changes in temperature and power supply voltage.

With the above configuration, the slope of the temperature characteristic of the output voltage (reference voltage Vref) of the reference voltage generation circuit 14 is controlled using the slope (mV / ° C.) of the temperature characteristic of the anode-cathode voltage of the diode 25. It becomes possible to do. As in the first embodiment, fluctuations in the output level (digital electrical signal) of the digital output microphone unit 100 with respect to ambient temperature changes can be compensated for within a wide temperature range. The gain of the non-inverting amplifier 28 (that is, the ratio of the feedback resistor 29 and the resistor 30) is set to the output of the microphone 1 so that the temperature characteristic of the anode-cathode voltage of the diode 25 is preserved in the output voltage. What is necessary is just to determine so that it may respond to the temperature change of a signal (analog electric signal).
(Third embodiment)
Hereinafter, a digital output microphone unit according to a third embodiment of the present invention will be described. Note that, as in the first and second embodiments, the third embodiment is applied to the case where the microphone 1 has a positive temperature coefficient as shown in FIG. The only difference from the digital output microphone unit 100 according to the first and second embodiments is the configuration of the reference voltage generation circuit 14.

  FIG. 8 is a circuit diagram showing a configuration of a reference voltage generation circuit in the digital output microphone unit according to the third embodiment of the present invention. FIG. 9 is a graph showing a temperature characteristic of a resistor having a positive temperature coefficient in the digital output microphone unit according to the third embodiment of the present invention.

  The reference voltage generation circuit 14 shown in FIG. 8 includes a current source 19 and a resistor 31 having a positive temperature coefficient as shown in FIG. And a non-inverting amplifier 28 to which the voltage at the connection point of the resistor 31 is input.

  The resistor 31 is, for example, a polysilicon resistor or a diffused resistor. One terminal is connected to the ground terminal, and the other terminal is connected to the output of the current source 19 and the non-inverting input terminal of the operational amplifier 26. The output terminal of the operational amplifier 26 is connected to the inverting input terminal of the operational amplifier 26 via a feedback resistor 29 that determines the gain (amplification factor). The inverting input terminal of the operational amplifier 26 is connected to the power supply 24 via a resistor 30 that determines the gain of the non-inverting amplifier 28.

With the above configuration, the inclination of the temperature characteristic of the resistor 31 similar to the temperature characteristic (primary line) of the microphone 1 (mV / ° C.) is used to increase or decrease the inclination of the temperature characteristic of the output voltage of the reference voltage generation circuit 14. It becomes possible to adjust. As in the first embodiment, fluctuations in the output level (digital electrical signal) of the digital output microphone unit 100 with respect to ambient temperature changes can be compensated for within a wide temperature range. The gain of the non-inverting amplifier 28 (that is, the ratio of the feedback resistor 29 and the resistor 30) is set to the output signal of the microphone 1 so that the temperature characteristic of the resistor 31 having a positive temperature coefficient is stored in the output voltage. What is necessary is just to determine so that it may respond to the temperature change of an analog electric signal.
(Fourth embodiment)
Hereinafter, a digital output microphone unit according to a fourth embodiment of the present invention will be described. In the fourth embodiment, as in the first to third embodiments, the case where the microphone 1 has a positive temperature coefficient as shown in FIG. 4 is applied. The only difference from the digital output microphone unit 100 according to the first to third embodiments is the configuration of the reference voltage generation circuit 14.

  FIG. 10 is a circuit diagram showing a configuration of the reference voltage generation circuit 14 in the digital output microphone unit according to the fourth embodiment of the present invention. FIG. 11 is a graph showing a temperature characteristic of a resistor having a negative temperature coefficient in the digital output microphone unit according to the fourth embodiment of the present invention.

  A reference voltage generation circuit 14 shown in FIG. 10 includes a current source 19 connected in series between a power supply 27 and a ground terminal, a resistor 32 having a negative temperature coefficient as shown in FIG. The operational amplifier 33 is supplied with the voltage at the connection point 32, and the inverting amplifier 23 is supplied with the output of the operational amplifier 33.

  The resistor 32 is, for example, a polysilicon resistor or a diffused resistor. One terminal is connected to the ground terminal, and the other terminal is connected to the output of the current source 19 and the non-inverting input terminal of the operational amplifier 33. The output terminal of the operational amplifier 33 is connected to the inverting input terminal of the operational amplifier 33. The operational amplifier 33 functions as a backflow prevention buffer (voltage follower) having a gain of “1”. The output terminal of the operational amplifier 33 is connected to the inverting input terminal of the operational amplifier 26 through the input resistor 20. The output terminal of the operational amplifier 26 is connected to the inverting input terminal of the operational amplifier 26 via the feedback resistor 21 that determines the gain of the inverting amplifier 23.

With the above configuration, the temperature of the output voltage of the reference voltage generation circuit 14 is obtained using the gradient (mV / ° C.) of the temperature characteristic of the resistor 32 having a negative temperature coefficient similar to the temperature characteristic (primary line) of the microphone 1. It becomes possible to control the magnitude of the slope of the characteristic. As in the first embodiment, fluctuations in the output level (digital electrical signal) of the digital output microphone unit 100 with respect to ambient temperature changes can be compensated for within a wide temperature range. Note that the gain of the inverting amplifier 23 (that is, the ratio between the input resistor 20 and the feedback resistor 21) is set to the output signal of the microphone 1 so that the temperature characteristic of the resistor 32 having a negative temperature coefficient is stored in the output voltage. What is necessary is just to determine so that it may respond to the temperature change of an analog electric signal.
(Fifth embodiment)
Hereinafter, a digital output microphone unit according to a fifth embodiment of the present invention will be described.

  In the first to fourth embodiments, the case where the microphone 1 has a positive temperature coefficient as shown in FIG. On the other hand, in the fifth embodiment, the case where the microphone 1 has a negative temperature coefficient as shown in FIG.

  FIG. 12 is a graph showing temperature characteristics of an ECM output signal (analog electric signal) in the digital output microphone unit according to the fifth embodiment of the present invention. The graph is obtained when an ECM having a negative temperature coefficient collects a sound equivalent to 94 dB SPL.

  As shown in the figure, the voltage level of the output signal of the ECM is about 20 mVpp at 27 ° C., but increases to about 25 mVpp at −40 ° C. and decreases to about 16 mVpp at 90 ° C.

  FIG. 13 is a circuit diagram showing a configuration of a reference voltage generation circuit in the digital output microphone unit according to the fifth embodiment of the present invention.

  The reference voltage generation circuit 14 includes a current source 19 and a diode 25 and a non-inverting amplifier 28 that are connected in series between a power supply 27 and a ground terminal.

  The diode 25 has a cathode connected to the ground terminal and an anode connected to the output of the current source 19 and the non-inverting input terminal of the operational amplifier 26. The output terminal of the operational amplifier 26 is connected to the inverting input terminal of the operational amplifier 26 via a feedback resistor 29 that determines the gain (amplification factor) of the non-inverting amplifier 28. The inverting input terminal of the operational amplifier 26 is connected to the power supply 24 via a resistor 30 that determines the gain of the non-inverting amplifier 28.

  With the above configuration, it is possible to adjust the magnitude of the slope of the temperature characteristic of the output voltage of the reference voltage generation circuit 14 using the slope (mV / ° C.) of the temperature characteristic of the anode-cathode voltage of the diode 25. Become. As in the first embodiment, fluctuations in the output level (digital electrical signal) of the digital output microphone unit 100 with respect to ambient temperature changes can be compensated for within a wide temperature range. The gain of the non-inverting amplifier 28 (that is, the ratio of the feedback resistor 29 and the resistor 30) is set to the output signal of the microphone 1 so that the temperature characteristic of the anode-cathode voltage of the diode 25 is preserved in the output voltage. What is necessary is just to determine so that it may respond to the temperature change of an analog electric signal.

  FIG. 14 is a graph showing the temperature characteristics of the output level (digital electric signal) of the digital output microphone unit according to the fifth embodiment of the present invention. The graph is obtained when the ECM collects 94 dB SPL equivalent. The broken line indicates the output level when the reference voltage Vref is constant, and the solid line indicates the output level when the reference voltage Vref is generated based on the anode-cathode voltage of the diode 25.

From the figure, it is understood that when the reference voltage Vref is constant, the output level changes by about 4 dB in the temperature range of −40 ° C. to 90 ° C. On the other hand, when the reference voltage Vref is generated based on the anode-cathode voltage of the diode 25, it can be seen that the output level is stabilized to a value close to −26 dBFS in the same temperature range as in the above case.
(Sixth embodiment)
Hereinafter, a digital output microphone unit according to a sixth embodiment of the present invention will be described. In the sixth embodiment, as in the fifth embodiment, the case where the microphone 1 has a negative temperature coefficient as shown in FIG. 12 is applied. The only difference from the digital output microphone unit 100 according to the fifth embodiment is the configuration of the reference voltage generation circuit 14.

  FIG. 15 is a circuit diagram showing a configuration of a reference voltage generation circuit in the digital output microphone unit according to the sixth embodiment of the present invention.

  The reference voltage generation circuit 14 shown in FIG. 15 includes a diode 25 and a current source 19 connected in series between a power supply 27 and a ground terminal, and an inverting amplifier 23.

  The diode 25 has an anode connected to a power source 27 and a cathode connected to the input of the current source 19 and the inverting input terminal of the operational amplifier 26 via the input resistor 20. The output terminal of the operational amplifier 26 is connected to the inverting input terminal of the operational amplifier 26 via the feedback resistor 21 that determines the gain of the inverting amplifier 23.

With the above configuration, it is possible to control the magnitude of the slope of the temperature characteristic of the output voltage of the reference voltage generation circuit 14 using the slope (mV / ° C.) of the temperature characteristic of the anode-cathode voltage of the diode 25. Become. As in the fifth embodiment, it is possible to compensate for fluctuations in the output level (digital electric signal) of the digital output microphone unit 100 with respect to ambient temperature changes within a wide temperature range. Note that the gain of the inverting amplifier 23 (that is, the ratio between the input resistor 20 and the feedback resistor 21) is set to the output signal of the microphone 1 so that the temperature characteristic of the resistor 32 having a negative temperature coefficient is stored in the output voltage. What is necessary is just to determine so that it may respond to the temperature change of an analog electric signal.
(Seventh embodiment)
Hereinafter, a digital output microphone unit according to a seventh embodiment of the present invention will be described. In the seventh embodiment, as in the fifth and sixth embodiments, the case where the microphone 1 has a negative temperature coefficient as shown in FIG. 12 is applied. Note that the only difference from the digital output microphone unit 100 according to the fifth and sixth embodiments is the configuration of the reference voltage generation circuit 14.

  FIG. 16 is a circuit diagram showing a configuration of a reference voltage generation circuit in the digital output microphone unit according to the seventh embodiment of the present invention.

  A reference voltage generation circuit 14 shown in FIG. 16 includes a current source 19 connected in series between a power supply 27 and a ground terminal, a resistor 31 having a positive temperature coefficient as shown in FIG. 9, an inverting amplifier 23, It is constituted by.

  The resistor 31 has one terminal connected to the ground terminal and the other terminal connected to the output of the current source 19 and the non-inverting input terminal of the operational amplifier 33. The output terminal of the operational amplifier 33 is connected to the inverting input terminal of the operational amplifier 33. The operational amplifier 33 functions as a backflow prevention buffer (voltage follower) having a gain of “1”. The output terminal of the operational amplifier 33 is connected to the inverting input terminal of the operational amplifier 26 through the input resistor 20. The output terminal of the operational amplifier 26 is connected to the inverting input terminal of the operational amplifier 26 via the feedback resistor 21 that determines the gain of the inverting amplifier 23.

With the above configuration, it is possible to control the magnitude of the slope of the temperature characteristic of the output voltage of the reference voltage generation circuit 14 using the slope (mV / ° C.) of the temperature characteristic of the resistor 31 having a positive temperature coefficient. Become. As in the fifth embodiment, it is possible to compensate for fluctuations in the output level (digital electric signal) of the digital output microphone unit 100 with respect to ambient temperature changes within a wide temperature range. Note that the gain of the inverting amplifier 23 (that is, the ratio between the input resistor 20 and the feedback resistor 21) is set to the output signal of the microphone 1 so that the temperature characteristic of the resistor 32 having a positive temperature coefficient is stored in the output voltage. What is necessary is just to determine so that it may respond to the temperature change of an analog electric signal.
(Eighth embodiment)
Hereinafter, a digital output microphone unit according to an eighth embodiment of the present invention will be described. In the eighth embodiment, as in the fifth to seventh embodiments, the case where the microphone 1 has a negative temperature coefficient as shown in FIG. 12 is applied. The only difference from the digital output microphone unit 100 according to the fifth to seventh embodiments is the configuration of the reference voltage generation circuit 14.

  FIG. 17 is a circuit diagram showing a configuration of a reference voltage generation circuit in the digital output microphone unit according to the eighth embodiment of the present invention.

  A reference voltage generation circuit 14 shown in FIG. 17 includes a current source 19 connected in series between a power supply 27 and a ground terminal, a resistor 32 having a negative temperature coefficient as shown in FIG. , Is composed of.

  The resistor 32 has one terminal connected to the ground terminal and the other terminal connected to the output of the current source 19 and the non-inverting input terminal of the operational amplifier 26. The output terminal of the operational amplifier 26 is connected to the inverting input terminal of the operational amplifier 26 via a feedback resistor 29 that determines the gain (amplification factor). The inverting input terminal of the operational amplifier 26 is connected to the power supply 24 via a resistor 30 that determines the gain of the non-inverting amplifier 28.

  With the above configuration, it is possible to control the magnitude of the slope of the temperature characteristic of the output voltage of the reference voltage generation circuit 14 using the slope (mV / ° C.) of the temperature characteristic of the resistor 32 having a negative temperature coefficient. Become. As in the fifth embodiment, it is possible to compensate for fluctuations in the output level (digital electric signal) of the digital output microphone unit 100 with respect to ambient temperature changes within a wide temperature range. Note that the gain of the inverting amplifier 23 (that is, the ratio of the feedback resistor 21 and the resistor 30) is set to the output signal (analogue) of the microphone 1 so that the temperature characteristic of the resistor 31 having a negative temperature coefficient is stored in the output voltage. What is necessary is just to determine so that it may respond to the temperature change of an electrical signal.

  From the above description, many modifications and other embodiments of the present invention are obvious to one skilled in the art. Accordingly, the foregoing description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of the structure and / or function may be substantially changed without departing from the spirit of the invention.

  The present invention is beneficial for a digital output microphone unit that needs to stabilize digital output level fluctuations with respect to ambient temperature changes within a wide temperature range.

DESCRIPTION OF SYMBOLS 100 ... Digital output microphone unit 11 ... Opening part 12 ... Analog-digital converter 121 ... Subtractor 122 ... Integrator 123 ... Comparator 124 ... Delay device 125 ... Analog converter 125 ... Digital filter 13 ... Signal processing device 14 ... Reference voltage Generation circuit 15 ... preamplifier 16 ... digital output terminal 17 ... reference voltage input terminal 18 ... housing 19 ... current source 2 ... power supply terminal 9 ... ground terminal 20 ... input resistor 21 ... feedback resistor 22 ... reference voltage output terminal 23 ... inverting amplifier 24 ... power source 25 ... diode 26 ... operational amplifier 27 ... power source 28 ... non-inverting amplifier 29 ... feedback resistor 30 ... resistor 31 ... resistor 32 having a positive temperature coefficient ... resistor 33 having a negative temperature coefficient ... operational amplifier

Claims (9)

A signal processing apparatus for converting an analog electric signal converted from sound by a microphone into a digital electric signal by analog-to-digital conversion and outputting the digital electric signal,
A preamplifier for amplifying an analog electrical signal output from the microphone;
An analog-to-digital converter that compares the analog electrical signal output from the preamplifier with a reference voltage and converts the analog electrical signal into a digital electrical signal;
A reference voltage generation circuit that generates the reference voltage and supplies the reference voltage to the analog-to-digital converter,
The reference voltage generation circuit includes an element (hereinafter referred to as a high temperature-dependent element) whose electric property is higher in temperature than other electric circuit elements among the electric circuit elements constituting the signal processing device. A signal processing device that generates a reference voltage based on a voltage between both terminals of the high temperature dependent element. The high temperature dependent element is a diode;
The reference voltage generation circuit includes a current source and the diode connected in series between a power supply terminal and a ground terminal, and the reference voltage is generated based on a voltage at a connection point between the power supply terminal and the diode. The signal processing device according to claim 1, wherein the signal processing device is generated. The high temperature dependent element is a resistor having a positive or negative temperature coefficient;
The reference voltage generation circuit includes a current source and the resistor connected in series between a power supply terminal and a ground terminal, and the reference voltage is generated based on a voltage at a connection point between the power supply terminal and the resistor. The signal processing device according to claim 1, wherein the signal processing device is generated.   The signal processing apparatus according to claim 1, wherein the preamplifier, the analog-digital converter, and the reference voltage generation circuit are integrated. A microphone that converts sound into an analog electrical signal;
A preamplifier for amplifying an analog electrical signal output from the microphone;
An analog-to-digital converter that compares the analog electrical signal output from the preamplifier with a reference voltage and converts the analog electrical signal into a digital electrical signal;
A reference voltage generation circuit that generates the reference voltage and supplies the reference voltage to the analog-to-digital converter,
The reference voltage generation circuit includes:
Among the electric circuit elements constituting the signal processing device, the electric circuit element includes an element whose electrical property is higher in temperature dependency than the other electric circuit elements (hereinafter referred to as a high temperature dependent element), and the high temperature dependent element Digital output microphone unit that generates a reference voltage according to the voltage between both terminals.   The digital output microphone unit according to claim 5, wherein the microphone is an ECM (Electret Condenser Microphone).   The digital output microphone unit according to claim 5, wherein the microphone is a MEMS (Micro Electro Mechanical Systems) microphone.   6. The digital output microphone unit according to claim 5, wherein the analog-to-digital converter is a delta-sigma modulation type analog-to-digital converter.   6. The digital output microphone unit according to claim 5, wherein the digital electric signal is converted into a PDM (Pulse Density Modulation) method and output to the outside.

Images