CN107167649A - A kind of electret microphone current testing circuit and its method of testing - Google Patents
A kind of electret microphone current testing circuit and its method of testing Download PDFInfo
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Abstract
The invention discloses a kind of electret microphone current testing circuit, including dc source, digital regulation resistance, first analog switch, calibrating resistance, electret microphone, signal condition part, second analog switch, the full width modulating part of numeral and high-performance AC coupling data capture card, the dc source, digital regulation resistance, analog switch, calibrating resistance and electret microphone constitute loop, the signal condition part is by the first amplifier, second amplifier and the 3rd amplifier are constituted, described the first amplifier and the second amplifier is connected by the full width modulating part of the second analog switch and numeral, the full width modulating part of numeral and the 3rd amplifier are connected with high-performance AC coupling data capture card.The invention also provides a kind of method of testing of electret microphone current testing circuit, by calculating the actual Res values of circuit and calculating microphone current, solve current electret microphone current test method and there is the problem of test result is not accurate.
Description
[ technical field ] A method for producing a semiconductor device
The invention relates to the technical field of microphone current testing, in particular to an electret microphone current testing circuit and a testing method thereof.
[ background of the invention ]
The electret microphone is a capacitance type sound-electricity transducer, which is composed of sound-electricity conversion and impedance conversion. The acoustoelectric conversion part is a capacitor formed by an electret material film and a metal plate, which are separated by a thin insulating ring, and the key element is the electret material film which adopts a pre-polarization method to permanently store electric charges in the electret material. When the acoustic wave acts on the electret film, the capacitance is changed, and because the capacitance between the electret film and the metal polar plate is small and is only dozens of picofarads, the low-frequency output impedance of the electret film can reach dozens of mega or even hundreds of mega ohms. Such high output impedance cannot be directly connected to the audio amplifier circuit, and a dedicated fet is required as an impedance transformer, i.e., an impedance conversion part of the electret microphone. Generally, the characteristics of the junction field effect transistor that the input impedance is high and the output impedance is low are utilized, and the normal operation of the field effect transistor needs to consume a part of current, namely the current parameter index of the electret microphone, which is generally required to be less than or equal to 0.5mA (500 uA). The excessive microphone working current means that the battery is not durable for the handheld device, so that the parameter needs to be strictly controlled in practical production.
The operating current of an electret microphone refers to the current consumed by the microphone when the microphone is operating under rated conditions. The conventional electret microphone current testing methods include the following two methods: firstly, as shown in fig. 1, a circuit measures the microphone current through a series-connection ammeter, the method has the defect that the requirement of automatic test cannot be met, the current value needs to be read manually, the connected ammeter has certain internal resistance, and certain errors are introduced in the microphone frequency response test; secondly, as shown in FIG. 2, the circuit is formed by connecting a sampling resistor (with a common resistance value) in series<100 omega) is adopted, and voltage V at two ends of r is collectedrThe current is calculated, the differential circuit is influenced by temperature drift, operational amplifier DC offset voltage and other factors, and V is generated due to the small resistance of the sampling resistorrThe amplified offset voltage (in the level of tens of mV) has no great difference relative to the amplified offset voltage (in the level of mV), and the offset voltage of the operational amplifier can change along with different working voltages, which can directly influence the accuracy of the microphone current test. The measurement error can be properly reduced by selecting a high-performance dynamic balance operational amplifier, but the high cost investment cannot be qualitatively improved. Similarly, if the circuit has no C2 capacitor, the microphone frequency response test has errors, the problem of microphone frequency response test can be effectively solved by introducing the AC coupling capacitor C2, but the charging time can affect the microphone test speed, and the cyclic charging and discharging process can cause oscillation to affect the microphoneAnd (5) testing the wind frequency response. In order to solve the problem of inaccurate test result of the conventional electret microphone current test method, it is necessary to provide an electret microphone current test circuit and a test method thereof.
[ summary of the invention ]
The invention aims to overcome the defects of the prior art, provides an electret microphone current test circuit and a test method thereof for a data acquisition card system for acquiring alternating current signals, and aims to solve the technical problem that the traditional electret microphone current test method in the prior art is inaccurate in test result.
In order to achieve the purpose, the invention provides an electret microphone current testing circuit, which comprises a direct-current power supply, a digital potentiometer, a first analog switch, a calibration resistor, an electret microphone, a signal conditioning part, a second analog switch, a digital full-amplitude modulation part and a high-performance alternating-current coupling data acquisition card, wherein the direct-current power supply, the digital potentiometer, the analog switch, the calibration resistor and the electret microphone form a loop, a node A is arranged between the direct-current power supply and the digital potentiometer, a node B is arranged between the digital potentiometer and the first analog switch, the signal conditioning part comprises a first operational amplifier, a second operational amplifier and a third operational amplifier, the first operational amplifier is connected with the node A, the second operational amplifier is connected with the node B, the input end of the third operational amplifier is connected with the node B through a DC blocking capacitor C1, the first operational amplifier and the second operational amplifier are connected with the digital full-amplitude modulation part through the second analog switch, the digital full-amplitude modulation part is connected with the high-performance alternating-current coupling data acquisition card through a blocking capacitor C2, and the output end of the third operational amplifier is connected with the high-performance alternating-current coupling data acquisition card through a blocking capacitor C3.
Preferably, the first analog switch comprises an input terminal, an output terminal 1 and an output terminal 2, one end of the digital potentiometer is connected with the positive pole of the direct current power supply, the other end of the digital potentiometer is connected with the input terminal of the analog switch, the output terminal 1 of the analog switch is connected with the electret microphone, the output terminal 2 of the analog switch is connected with the calibration resistor, the other ends of the electret microphone and the calibration resistor are both connected with the negative pole of the direct current power supply, and the negative pole of the direct current power supply is connected with the ground.
Preferably, the second analog switch comprises a 3 input terminal, a 4 input terminal and an output terminal, the input terminal of the first operational amplifier is connected with the node a, the output terminal of the first operational amplifier is connected with the 3 input terminal of the second analog switch, the input terminal of the second operational amplifier is connected with the node B, the output terminal of the second operational amplifier is connected with the 4 input terminal of the second analog switch, and the output terminal of the second analog switch is connected with the input terminal of the full-width modulation part.
Preferably, the magnitude of the current-limiting resistor of the digital potentiometer is controlled and adjusted by upper computer software.
Preferably, the current limiting resistance of the digital potentiometer is adjusted within the range of 0-20k omega.
The invention also provides a test method of the electret microphone current test circuit, which comprises two parts of calculating the actual Res value of the circuit and calculating the microphone current, and comprises the following specific steps:
s1, calculating the actual Res value of the line:
s1.1, setting the voltage of a direct-current power supply, and setting the resistance value of a digital potentiometer through upper computer software;
s1.2, the analog switch is switched to the 2 output terminal, and the voltage values at the two positions of the node A and the node B are respectively V acquired through a high-performance AC coupling data acquisition cardA、VB；
S1.3, the calibration resistor is a known accurate resistor, the resistance value is r, and the voltage value V is obtained according to the known node BBAnd the resistance r of the calibration resistor, and the actual Res value of the circuit is calculated according to a calculation formula;
s2, calculating the microphone current:
s2.1, the analog switch is switched to the output terminal 1, and the voltage values at the node A and the node B are collected again through a high-performance AC coupling data acquisition card and are respectively VA`、VB`；
S2.2, testing according to ohm law, kirchhoff current law and a calculation formula to obtain electret microphone current Imic；
S2.3, judging whether the electret microphone current test meets the frequency requirement, and if so, ending the test; if not, returning to the step S2.1 again, and continuously acquiring the voltage values at the two positions of the node A and the node B.
Preferably, in step S1.3, the actual Res value of the line includes a resistance value set by the digital potentiometer, and equivalent internal resistances of the line and the peripheral circuit, and the calculation formula of the actual Res value of the line is as follows:wherein,
preferably, the electret microphone current I in step S2.2 ismicThe calculation formula of (2) is as follows:
the invention has the beneficial effects that: compared with the prior art, the invention provides an electret microphone current test circuit and a test method thereof based on a data acquisition card system for acquiring alternating current signals, wherein the test circuit comprises the accurate acquisition of microphone voltage and the accurate calculation of a microphone current-limiting resistor, the microphone voltage acquisition is realized by dialing an analog switch to an output terminal 1, the alternating current-direct current conversion of the microphone direct current voltage is realized through a digital full-amplitude modulation part, and the data acquisition is completed by using a high-performance alternating current coupling data acquisition card; the microphone current-limiting resistor acquires voltages at two ends of the current-limiting resistor by dialing the analog switch to the output terminal 2, knowing the resistance value of the precise resistor r, and calculating the accurate resistance value of the current-limiting resistor by a voltage division principle.
The features and advantages of the present invention will be described in detail by embodiments in conjunction with the accompanying drawings.
[ description of the drawings ]
FIG. 1 is a circuit diagram of a conventional electret microphone current test circuit;
FIG. 2 is a circuit diagram of another conventional electret microphone current test circuit;
FIG. 3 is a circuit diagram of an electret microphone current test circuit according to an embodiment of the invention;
FIG. 4 is a flow chart of the calculation of the actual Res value of the line according to the embodiment of the present invention;
fig. 5 is a flow chart of the microphone current calculation according to the embodiment of the present invention.
[ detailed description ] embodiments
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood, however, that the description herein of specific embodiments is only intended to illustrate the invention and not to limit the scope of the invention. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present invention.
Referring to fig. 3, an embodiment of the present invention provides a digital full-width modulation system including a dc power supply 1, a digital potentiometer 2, a first analog switch 3, a calibration resistor 4, an electret microphone 5, a signal conditioning part 6, a second analog switch 7, a digital full-width modulation part 8, and a high performance ac-coupled data acquisition card 9, where the dc power supply 1, the digital potentiometer 2, the analog switch 3, the calibration resistor 4, and the electret microphone 5 form a loop, a node a is disposed between the dc power supply 1 and the digital potentiometer 2, a node B is disposed between the digital potentiometer 2 and the first analog switch 3, the signal conditioning part 6 is composed of a first operational amplifier 61, a second operational amplifier 62, and a third operational amplifier 63, the first operational amplifier 61 is connected to the node a, the second operational amplifier 62 is connected to the node B, an input end of the third operational amplifier 63 is connected to the node B through a dc blocking capacitor C1, and the first operational amplifier 61 and the second operational amplifier 62 are connected to the digital full-width modulation part 8 through the second analog switch 7 And the digital full-amplitude modulation part 8 is connected with the high-performance AC coupling data acquisition card 9 through a blocking capacitor C2, and the output end of the third operational amplifier 63 is connected with the high-performance AC coupling data acquisition card 9 through a blocking capacitor C3.
Further, the first analog switch 3 include input terminal, 1 output terminal and 2 output terminals, one end of digital potentiometer 2 be connected with dc power supply 1's positive pole, the other end is connected with analog switch 3's input terminal, analog switch 3's 1 output terminal be connected with electret microphone 5, 2 output terminal be connected with calibration resistance 4, electret microphone 5 and calibration resistance 4's the other end all be connected with dc power supply 1's negative pole, dc power supply 1's negative pole ground connection.
Further, the second analog switch 7 includes a 3 input terminal, a 4 input terminal and an output terminal, the input terminal of the first operational amplifier 61 is connected to the node a, the output terminal is connected to the 3 input terminal of the second analog switch 7, the input terminal of the second operational amplifier 62 is connected to the node B, the output terminal of the second operational amplifier 62 is connected to the 4 input terminal of the second analog switch 7, and the output terminal of the second analog switch 7 is connected to the input terminal of the full-width modulation part 8.
Specifically, a dc blocking capacitor C1 is further connected between the input terminal of the third operational amplifier 63 and the node B, wherein Vout is a microphone frequency response test circuit, which is not described in detail herein.
In the embodiment of the invention, the size of the current-limiting resistor of the digital potentiometer 2 is controlled and adjusted by upper computer software, and the adjustment range of the current-limiting resistor of the digital potentiometer 2 is 0-20k omega. The random setting of the 0-20k omega current-limiting resistor can be realized through upper computer software, and the problem that some manufacturers can only provide a plurality of commonly used resistance values for users to select and use at present is solved.
The invention abandons the traditional direct current collection, uses the digital full-amplitude modulation part 7 to carry out digital full-amplitude alternating current modulation on the collected voltage, and combines the high-performance alternating current coupling data acquisition card 9 to finish the reading of signals. The influence of the stability, the temperature coefficient and the like of a pressure control element on the common direct current acquisition is large, and the accurate direct current acquisition has key factors of high cost, complex circuit and the like. Industrial-grade dc acquisition cards are also expensive. Therefore, only the high-performance AC coupling data acquisition card 9 is used in the invention, the precision is ensured, and the electret microphone current test is completed by using a simple and low-cost circuit.
Referring to fig. 4 and 5, an embodiment of the present invention further provides a testing method for an electret microphone current testing circuit, including two parts of calculating an actual Res value of a line and calculating a microphone current, which includes the following specific steps:
s1, calculating the actual Res value of the line:
s1.1, setting the voltage of the direct current power supply 1, and setting the resistance value of the digital potentiometer 2 through upper computer software.
S1.2, the analog switch 3 is dialed to the output terminal 2, and the voltage values at the node A and the node B are respectively V acquired through a high-performance AC coupling data acquisition card 9A、VB。
S1.3, the calibration resistor 4 is a known accurate resistor with a resistance value r according to a known node B voltage value VBAnd calibrating the resistance r of the resistor 4, and calculating the actual Res value of the circuit according to a calculation formula, wherein the actual Res value of the circuit comprises a numberThe resistance value set by the word potentiometer 2, the equivalent internal resistance of the flowing circuit and the peripheral circuit, and the calculation formula of the actual Res value of the circuit is as follows:wherein,
s2, calculating the microphone current:
s2.1, the analog switch 3 is dialed to the output terminal 1, and the voltage values at the node A and the node B are collected again through the high-performance AC coupling data acquisition card 9 and are respectively VA`、VB`。
S2.2, testing according to ohm law, kirchhoff current law and a calculation formula to obtain electret microphone current ImicElectret microphone current ImicThe calculation formula of (2) is as follows:
s2.3, judging whether the electret microphone current test meets the frequency requirement, and if so, ending the test; if not, returning to the step S2.1 again, and continuously acquiring the voltage values at the two positions of the node A and the node B.
The invention discloses a testing method of an electret microphone current testing circuit, which well solves the problem that the testing result of the traditional electret microphone current testing method is inaccurate, and the current limiting resistance (including the resistance value set by a digital potentiometer, the equivalent internal resistance of a flowing line and a peripheral circuit) of a microphone removing part in the whole circuit can be calculated by selecting an accurate resistor r and acquiring the voltage (V level) at a circuit A, B.
According to Kirchhoff's Current Law (KCL), for a node B, the sum of the currents flowing out is equal to the sum of the currents flowing in, so that when a switch is turned to 1, the current of a microphone is equal to the current flowing through a current-limiting resistor, and then the calculation is carried out by combining ohm's theorem.
For direct current voltage (including V)A、VB、VA`、VBAnd the invention adopts a digital full-amplitude modulation method to complete signal AC/DC conversion, and then inputs the converted signal into an AC coupling data acquisition card to carry out data calculation and analysis. If the DC signal is VDThe signal is picked up by a high-performance AC coupling data acquisition card 9, and the effective value V of the signal is calculatedRMSThen, the DC voltage V can be calculated by the following formulaD：Thus a DC voltage signal VAAfter being modulated into sine waves with a certain frequency by the digital full-amplitude modulation part 8, the signals are picked up by the high-performance AC coupling data acquisition card 9, the effective value of the signals is calculated, and the effective value is obtainedCan obtain VAThe value is obtained. By analogy, V can be obtainedB、VA`、VBThe value of the voltage.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents or improvements made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (8)
1. The utility model provides an electret microphone current test circuit which characterized in that: the high-performance AC coupling digital microphone comprises a DC power supply (1), a digital potentiometer (2), a first analog switch (3), a calibration resistor (4), an electret microphone (5), a signal conditioning part (6), a second analog switch (7), a digital full-amplitude modulation part (8) and a high-performance AC coupling data acquisition card (9), wherein the DC power supply (1), the digital potentiometer (2), the analog switch (3), the calibration resistor (4) and the electret microphone (5) form a loop, a node A is arranged between the DC power supply (1) and the digital potentiometer (2), a node B is arranged between the digital potentiometer (2) and the first analog switch (3), the signal conditioning part (6) consists of a first operational amplifier (61), a second operational amplifier (62) and a third operational amplifier (63), the first operational amplifier (61) is connected with the node A, the second operational amplifier (62) is connected with the node B, the input end of a third operational amplifier (63) is connected with a node B through a blocking capacitor C1, the first operational amplifier (61) and the second operational amplifier (62) are connected with a digital full-amplitude modulation part (8) through a second analog switch (7), the digital full-amplitude modulation part (8) is connected with a high-performance AC coupling data acquisition card (9) through a blocking capacitor C2, and the output end of the third operational amplifier (63) is connected with the high-performance AC coupling data acquisition card (9) through a blocking capacitor C3.
2. An electret microphone current test circuit as claimed in claim 1, wherein: first analog switch (3) include input terminal, 1 output terminal and 2 output terminal, the one end of digital potentiometer (2) be connected with DC power supply (1) positive pole, the other end is connected with analog switch (3) input terminal, analog switch (3) 1 output terminal be connected with electret microphone (5), 2 output terminal are connected with calibration resistance (4), the other end of electret microphone (5) and calibration resistance (4) all be connected with DC power supply (1) negative pole, DC power supply (1) negative pole ground connection connect.
3. An electret microphone current test circuit as claimed in claim 1, wherein: the second analog switch (7) comprises a 3 input terminal, a 4 input terminal and an output terminal, the input end of the first operational amplifier (61) is connected with the node A, the output end of the first operational amplifier is connected with the 3 input terminal of the second analog switch (7), the input end of the second operational amplifier (62) is connected with the node B, the output end of the second operational amplifier (62) is connected with the 4 input terminal of the second analog switch (7), and the output terminal of the second analog switch (7) is connected with the input end of the full-width modulation part (8).
4. An electret microphone current test circuit as claimed in claim 1, wherein: the size of the current-limiting resistor of the digital potentiometer (2) is controlled and adjusted by upper computer software.
5. An electret microphone current test circuit as claimed in claim 4, wherein: the current limiting resistance of the digital potentiometer (2) is adjusted within the range of 0-20k omega.
6. A test method of an electret microphone current test circuit is characterized in that: the method comprises two parts of calculating the actual Res value of a line and calculating the current of a microphone, and comprises the following specific steps:
s1, calculating the actual Res value of the line:
s1.1, setting the voltage of a direct current power supply (1), and setting the resistance value of a digital potentiometer (2) through upper computer software;
s1.2, the analog switch (3) is dialed to the output terminal 2, and the voltage values at the node A and the node B are respectively V acquired through a high-performance AC coupling data acquisition card (9)A、VB；
S1.3, the calibration resistor (4) is a known accurate resistor with a resistance value r according to a known node B voltage value VBAnd the resistance r of the calibration resistor (4), and the actual Res value of the circuit is calculated according to a calculation formula;
s2, calculating the microphone current:
s2.1, the analog switch (3) is dialed to the output terminal 1, and the voltage values at the node A and the node B are collected again through a high-performance AC coupling data acquisition card (9) and are respectively VA`、VB`；
S2.2, testing according to ohm law, kirchhoff current law and a calculation formula to obtain electret microphone current Imic；
S2.3, judging whether the electret microphone current test meets the frequency requirement, and if so, ending the test;
if not, returning to the step S2.1 again, and continuously acquiring the voltage values at the two positions of the node A and the node B.
7. The electret microphone electric of claim 6A method of testing a flow test circuit, comprising: the actual Res value of the line in the step S1.3 includes the resistance value set by the digital potentiometer (2), the equivalent internal resistance of the flowing line and the peripheral circuit, and the calculation formula of the actual Res value of the line is as follows:wherein,
8. the method of claim 6, wherein the testing method comprises the following steps: the electret microphone current I in the step S2.2micThe calculation formula of (2) is as follows:
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| CN113543007A (en) * | 2021-07-06 | 2021-10-22 | 昆山鑫润利自动化科技有限公司 | Flexible circuit board microphone sensitivity simulation test circuit |
| CN113543007B (en) * | 2021-07-06 | 2023-11-10 | 昆山鑫润利自动化科技有限公司 | Flexible circuit board microphone sensitivity analog test circuit |
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Address after: 310000 No. 10, Xianqiao Road, Zhongtai street, Yuhang District, Hangzhou City, Zhejiang Province Applicant after: Hangzhou Zhaohua Electronics Co.,Ltd. Address before: 310000 building 1-3, No. 31-1, Xianxing Road, Xianlin street, Yuhang District, Hangzhou City, Zhejiang Province Applicant before: CRY SOUND CO.,LTD. |
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