KR100706441B1 - Electret Condenser Microphone - Google Patents

Abstract

The present invention relates to an electret condenser microphone having a series of circuits inside the condenser microphone to enhance static electricity protection, block noise, and stabilize the bias.

The present invention can further block the TDMA noise by implementing an RC circuit using a varistor having a series resistor and a capacitor component inside the electret condenser microphone, and also by installing two TVS (Transient Voltage Suppressor) diodes. Or electrostatic protection effect during contact ESD test, and when applying the electrostatic protection and noise blocking electret condenser microphone to the mobile terminal, it can block the RF noise in various mobile communication frequency bands as well as the maximum power This allows you to reduce the TDMA noise level during a call.

In addition, in the electret condenser microphone of the present invention, by using the internal analog grounding, it is possible to separate the microphone substrate PCB (Artwork) or other components, and the bias stabilization unit can stabilize the bias voltage so that the operation stability is improved. By providing a WCDMA noise canceling unit, it is possible to remove noise induced in MCDMA to remove noise up to the WCDMA band (2.1 GHz).

Mobile Terminals, Static Protection, TDMA Noise, Condenser Microphones, Diaphragms, Back-Electrets, Spacers, FETs, Chip Capacitors

Description

Electret Condenser Microphone

1 is a schematic view showing a conventional condenser microphone.

2 is a view showing an electret condenser microphone used in a mobile communication terminal according to the present invention.

3 is an internal circuit diagram of an electret condenser microphone according to the present invention;

4 is a view for explaining the relationship between the capacitance and the amount of charge formed by the back- electret and the diaphragm in the electret condenser microphone according to the present invention.

5 is a diagram showing a detailed configuration of a diaphragm in FIG.

FIG. 6 is a diagram showing a detailed configuration of a back electret in FIG. 2; FIG.

7 is a diagram showing a detailed connection state of the FET in FIG.

8 is a graph showing the frequency response characteristics of the electret condenser microphone according to the present invention.

9 is a graph showing the polar pattern of the electret condenser microphone according to the present invention;

10 is a graph showing the FET gain characteristics according to the bias voltage and current consumption of the electret condenser microphone according to the present invention.

11 is a graph showing the FET gain characteristics according to the load storage and current consumption of the electret condenser microphone according to the present invention.

Fig. 12A is a diagram showing gain characteristics when the maximum transmit power level is used in a conventional electret condenser microphone.

Fig. 12B is a diagram showing gain characteristics when using the maximum transmit power level in the electret condenser microphone according to the present invention.

13 shows WCDMA noise characteristics in an electret condenser microphone according to the present invention;

Explanation of symbols on the main parts of the drawings

20: PCB substrate 21: MLCC

22: FET 23: series resistor

24: varistor 25: TVS diode

26: WCDMA noise prevention unit 27: bias stabilizer

30: diaphragm 40: back electret

50: spacer 60: first base

70: second base 80: case

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a condenser microphone used in a mobile communication terminal. In particular, a series of circuits are provided inside the condenser microphone to enhance electro-static discharge protection, to block noise, and to stabilize a bias. The present invention relates to an electret condenser microphone.

In general, a condenser microphone used in a mobile communication terminal such as a smart phone, PDA, CDMA terminal, GSM terminal, etc. receives a FET (Field-Effect Transistor) after a series of sounds are received according to the amount of charge that varies with sound pressure. It is supplied to the baseband codec in a differential type (a type having both a positive terminal and a negative terminal).

However, in the condenser microphone described above, the body of the enclosed portion is formed by one terminal of the differential, not the ground, and thus, the power supply line and the ground source when connected to the mechanism of the mobile communication terminal. There is a problem that noise is introduced into the microphone due to contact with the microphone.

In addition, the conventional condenser microphone has a multi-layer ceramic capacity (MLCC) 11 and a field effect transistor (FET) 12, which are chip capacitors, on an internal PCB substrate 10, as shown in FIG. Since it is composed of only, there is a problem in that it is also vulnerable in electro-static discharge protection, and the bias is not stabilized by the introduction of external noise and thus does not provide good characteristics.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object thereof is to further implement an RC circuit by using a varistor having a series resistor and a capacitor component in an electret condenser microphone to block TDMA noise, A TVS (Transient Voltage Suppressor) diode is installed to provide electrostatic protection for wireless or contact ESD tests.

Another object of the present invention is to apply an electrostatic condenser microphone for electrostatic protection and noise blocking to a mobile communication terminal to block RF noise in GSM frequency bands, DCS and PCS frequency bands, and also to increase the TDMA noise level when talking at the maximum power level. To reduce the

It is still another object of the present invention to provide good driving by stabilizing a bias applied as a driving power source by providing a bias stabilizing portion in an electret condenser microphone.

Another object of the present invention is to remove the WCDMA band noise by providing a WCDMA noise suppression unit in the electret condenser microphone.

A feature of the present invention for solving the above object is a FET for impedance matching the electrical signal generated by the signal generation means disposed between the gate terminal and the source terminal on the PCB substrate, and the FET An electret condenser microphone having a chip capacitor arranged in parallel between a drain terminal and a source terminal of the circuit, comprising: a series resistor disposed at each terminal of the chip capacitor and a varistor disposed in parallel with the series resistor; RC circuitry to perform a TDMA noise isolation function; Two TVS diodes connected in parallel to the varistor to perform an electrostatic protection function; A WCDMA noise canceling unit configured to arrange capacitors in parallel between resistors and capacitors arranged in series at both ends of the two TVS diodes connected in series to remove WCDMA noise; And a bias stabilizer for stabilizing a bias voltage applied for driving the signal generation means and the FET.

delete

delete

In addition, the bias stabilizing unit inputs a bias on / off control signal to a base of the first transistor connected to the emitter follower, and arranges a forward diode composed of a second transistor in series with the first transistor, and the first transistor. And a forward diode comprising a third transistor in parallel between the and second transistors, and a capacitor in parallel between the third transistor and the first transistor.

In addition, the above-described electrostatic condenser microphone capable of protecting the static electricity and blocking noise may form one contact between the two TVS diodes and connect the contact point and the microphone outer case to implement analog ground.

In this case, the microphone outer case is characterized in that the case is gold-coated to enhance the grounding function.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The electret condenser microphone used in the mobile communication terminal according to the present invention includes a diaphragm 30 serving as a diaphragm vibrating according to sound pressure, as shown in FIG. Forming a space for forming an electrostatic field between the back- electret 40 and the diaphragm 30 and the back electret 40 The main body comprises a spacer 50 using a polymer PET film and an FET 22 having an internal resistance value of about 100 kW, which is used to transmit a signal when a signal is generated.

On the PCB substrate 20 inside the electret condenser microphone described above, a series resistor other than the MLCC 21 and the FET 22 is shown, as shown in FIG. 2B and the accompanying FIG. 3. (23) and a varistor (Varistor) (24) with a capacitor component is implemented, and two TVS (Transient Voltage Suppressor) diodes (25) are installed (shunt) to enhance the static protection In addition, a WCDMA noise prevention unit 26 is provided to prevent WCDMA band noise, and a bias stabilizer 27 is provided to stabilize the bias voltage.

In addition, in the above-described electret condenser microphone, as shown in FIG. 4A, a voice signal is converted into an electrical signal by a change in capacitance formed by the back- electret 40 and the diaphragm 30. As a kind of converter, the amount of charge formed between the diaphragm 30 and the back electret 40 is constant according to the principle of using 'Q = CV (Q: charge amount, C: capacitance, V: voltage)'. do.

At this time, as shown in (b) and (c) of FIG. 4, when the diaphragm 30 vibrates, the capacitance changes, but the strength of the electrostatic field formed between the diaphragm 30 and the back electret 40 and Since the amount of charge is constant, the voltage value changes as the capacitance changes.

That is, when the diaphragm 30 approaches the back electret 40, the capacitance increases (Q (schedule) = C ↑ V ↓), and when the diaphragm 30 moves away from the back electret 40 The capacitance becomes smaller (Q (constant) = C ↓ V ↑).

In addition, the diaphragm 30 serves as a diaphragm vibrating according to a sound pressure, and forms an electrode together with the back electret 40 to serve as an electrode for forming an electrostatic field, and as a diaphragm, a back electret ( 40) and a voltage signal is generated by adjusting the capacitance value of the formed electrostatic field, and in order to use it as an electrode for forming the electrostatic field, as shown in FIG. 5, gold (Sputtering) is applied to the PET film film using a sputtering technique. Au) particles are coded on the film surface.

In addition, the back electret 40 may form an electrode together with the diaphragm 30 and at the same time form a semi-permanent electrostatic field, as shown in FIG. 6, a polymer FEP film (Fluorinated Ethylene) on a metal plate. It is a device made to contain electric charge by laminating propylene copolymer film, and it has air holes on both sides of the metal plate so that the diaphragm 30 can vibrate. It is the device that has the greatest influence on the characteristics.

Next, the spacer 50 is a device for forming a space for forming an electrostatic field between the diaphragm 30 and the back electret 40, and uses a polymer PET film, and the first base 60 Is formed of a polymer material to maintain the structure of the condenser microphone and to fix the back electret 40, and also prevent the short circuit of the signal voltage flowing through the case 80 and the second base 70. Give it.

Here, the second base 70 is a device that serves as a conductor to transfer the electrical signal generated by the back- electret 40 and the diaphragm 30 to the PCB substrate 20, gold (Au) coding on brass The electrical resistance is lowered by the treatment, and is in contact with the back- electret 40 and the PCB substrate 20 in the first base 60.

In addition, the PCB substrate 20 forms a series of circuits and transmits the electrical signals transmitted through the second base 70 to the gate terminals of the FET 22, and the '+' terminal MIC_P and the '-' terminal. (MIC_N) is formed to connect a signal to an external terminal, and a control terminal (BC) serves to input a bias control signal from the outside.

In addition, the FET 22 matches the impedance with the external circuit and transfers the signal generated from the condenser microphone to the next stage. This is because the input impedance of the condenser microphone has an internal resistance of about 100 Hz when the signal is generated. As shown in FIG. 7, the drain terminal D is connected to the '+' terminal MIC_P of the microphone and the source terminal S is connected to the '-' of the microphone as shown in FIG. 7. 'It is connected to terminal MIC_N.

The case 80 forming the outer shape of the condenser microphone described above is connected to the '-' terminal to function as an analog ground (AGND). For this purpose, the case 80 is coated with gold to enhance the grounding function. Through the curling process, which is the final stage of the microphone process, the sound from the outside except for the sound hall is introduced into the microphone (if the external sound is introduced, it causes a bad frequency).

In addition, the MLCC 21, which is a chip capacitor, is a device bonded on the PCB substrate 20 to block RF noise. The MLCC 21 is disposed in parallel across the source and drain terminals of the FET 22. The resonant filter determines the capacitor capacitance value for filtering according to the frequency band of the mobile communication terminal. For example, a chip capacitor having a capacitance value of 33 GHz is used for a terminal having a 900 MHz frequency band, and a chip capacitor having a capacitance value of 10 GHz is used for a terminal having a 1.8 GHz frequency band.

As described above, the electret condenser microphone (ECM) according to the present invention has a frequency response characteristic having a gain of about -42 dB up to a 3 kHz frequency as shown in the graph shown in FIG. Pattern) has the same characteristics as the graph shown in FIG. 9, which all exhibits characteristics in omni-directional microphones.

FIG. 10 is a graph illustrating FET gain characteristics according to bias voltage and current consumption, and FIG. 11 is a graph illustrating FET gain characteristics according to load storage and current consumption.

Meanwhile, when the electret condenser microphone according to the present invention is described in more detail, it has a circuit configuration as shown in FIG. 3, wherein the FET 22 and the GSM frequency band (800 MHz or 900 MHz) are provided inside the ECM case 80. And a capacitor, which is an MLCC (21), is disposed in parallel across the source terminal (S) and the drain terminal (D) of the FET 22 to block RF noise of the DCS and PCS frequency bands, and the GSM frequency band and the DCS, PCS. In order to block TDMA noise when talking at the maximum power level in the frequency band, a varistor 24 having a series resistor 23 and a shunt capacitor component is connected, and two TVS diodes 25 are connected to the output terminal. It provides electrostatic protection for Air or Contact electrostatic testing. A bias stabilizer 27 includes a WCDMA noise prevention part 26 configured to be connected to a resistor and a capacitor to remove WCDMA band (2.1 GHz) noise, and is connected to a transistor Q2 to Q4 and a capacitor. It provides a function to stabilize the bias voltage of the microphone.

In addition, in the bias stabilization unit 27, an emitter follower circuit is formed of the transistor Q2, but a control signal for controlling bias on / off is connected by connecting a control terminal BC to the base terminal. Input bias to control the bias on / off, and configure the forward diode by the transistor (Q3) to ensure a stable supply of the bias voltage (Vdd), the capacitor between the transistor (Q3) and the transistor (Q4) has a bypass function And the forward diode was blocked by the transistor Q4 to block backflow noise, and the reason why the forward diode was formed by the transistors Q3 and Q4 is to compensate for the fact that the voltage drop of the general diode is too large. will be. In addition, the WCDMA noise canceling unit 26 can remove quad-band noise by removing the noise induced in the WCDMA. In order to remove the noise induced in the WCDMA band, the frequency at which a human can listen is approximately 20 to 20,000 Hz, but most humans The frequency accepted by the cochlea is less than 5KHz, so the cutoff frequency is set to 5KHz. The formula using this is "Cutoff frequency = 1 / 2πRC".

As described above, the condenser microphone using the conventional differential type does not use internal grounding, and as the two pins of the '+' and '-' terminals of the microphone enter the input of the baseband codec, There is a problem to be configured externally, even if the circuit configuration in the PCB substrate (Artwork) or the line configuration of the microphone, even if the circuit does not see the effect of the electrostatic protection, but in the present invention is configured inside the condenser microphone, the internal ground As it is used as the analog ground (AGND), it has the effect of isolating the line from the condenser microphone to the codec, thereby having an electrostatic protection effect.

In addition, the gain characteristics when the maximum transmission power level is used in the DCS frequency band and the GSM frequency band of the electret condenser microphone are as shown in the graphs shown in FIGS. 12A and 12B, and FIG. 12A uses a conventional electret condenser microphone. Fig. 12B shows gain characteristics when the electret condenser microphone for electrostatic protection and TDMA noise isolation according to the present invention is used. Here, (a) is the case of DCS frequency band, (b) is the case of GSM frequency band, and (c) is a table comparing the case of DCS frequency band and the case of GSM frequency band, respectively.

13 is a graph illustrating the WCDMA noise characteristics of the electret condenser microphone according to the present invention. When the WCDMA noise canceller 26 is not applied, FIG. When the WCDMA noise canceling section 26 is applied, the same characteristics will be obtained as shown in Fig. 13B, and Fig. 13C is a table showing the characteristic values in the WCDMA mode.

In addition, the embodiments according to the present invention are not limited to the above-described embodiments, and various alternatives, modifications, and changes can be made within the scope apparent to those skilled in the art.

As described above, the present invention can further block the TDMA noise by additionally implementing an RC circuit using a varistor having a series resistor and a capacitor component inside the electret condenser microphone, and further, two TVS (Transient Voltage Suppressor) diodes. It can be installed to have static protection effect during wireless or contact ESD test.

In addition, when the electret condenser microphone of the present invention is applied to a mobile communication terminal, it is possible to cut off the RF noise of the GSM frequency band, the DCS, and the PCS frequency band. Can be reduced.

Further, in the electret condenser microphone of the present invention, internal analog grounding is used, thereby allowing the microphone PCB fabrication or separation between other components.

In addition, in the electret condenser microphone of the present invention, by providing a bias stabilizing part, the bias voltage can be stabilized, and thus, operation stability can be satisfactorily secured.

In addition, the electret condenser microphone of the present invention includes a WCDMA noise canceling unit, thereby removing noise induced by MCDMA, thereby removing noise up to the WCDMA band (2.1 GHz).

Claims (6)

On the PCB substrate, an FET for impedance matching and transferring the electrical signal generated by the signal generating means disposed between the gate terminal and the source terminal, and a chip capacitor disposed in parallel between the drain terminal and the source terminal of the FET In the electret condenser microphone, An RC circuit configured to arrange a series resistor on each terminal of the chip capacitor and to arrange a varistor in parallel with the series resistor to perform a TDMA noise blocking function; Two TVS diodes connected in parallel to the varistor to perform an electrostatic protection function; A WCDMA noise canceling unit configured to arrange capacitors in parallel between resistors and capacitors arranged in series at both ends of the two TVS diodes connected in series to remove WCDMA noise; And a bias stabilizer for stabilizing a bias voltage applied for driving the signal generation means and the FET. delete delete The method of claim 1, The bias stabilizing unit inputs a bias on / off control signal to a base of a first transistor connected to an emitter follower, and arranges a forward diode made of a second transistor in series with the first transistor, and the first transistor and the first transistor. And a capacitor arranged in parallel between two transistors and a capacitor disposed in parallel between the third and first transistors. The method of claim 1, An electret condenser microphone, comprising: forming one contact point between the two TVS diodes and connecting the contact point and the microphone outer case to implement analog ground. The method of claim 5, The microphone outer case is an electret condenser microphone, characterized in that the case coated with gold to enhance the grounding function.

Images