KR101781555B1 - Read out circuit for microphone sensor - Google Patents

Abstract

The present invention relates to a lead-out circuit for a microphone sensor, the lead-out circuit for a microphone sensor having a first terminal for transmitting a sensing signal corresponding to a change in sound pressure and a second terminal for transmitting a sensor bias voltage, The sensor bias voltage of the buffer, the input capacitor, the feedback capacitor, the sensor bias portion, and the sensor bias portion is transmitted to the second terminal, and is coupled to the feedback capacitor to perform a second filtering on the sensor bias voltage. And a separator for separating the feedback path for the sensing signal fed back to the terminal and the voltage environment of the sensor bias unit.

Description

[0001] READOUT CIRCUIT FOR MICROPHONE SENSOR [0002]

The present invention relates to a lead-out circuit for a microphone sensor, and more particularly, to a lead-out circuit constituting a microphone system using a voltage buffer to improve a signal-to-noise ratio.

Audio microphones are commonly used in a variety of consumer applications such as cellular telephones, digital audio recorders, personal computers, and teleconferencing systems. Electrically conductive microphones (ECM) and micro electro-mechanical systems (MEMS) are examples of sensors used in audio microphones. For ECM microphones, they are used primarily for low-cost applications, and MEMS microphones are used primarily in applications where relatively high quality is required.

Because the ECM microphone is made up of individual components, it takes a lot of steps in the manufacturing process, which is costly and time-consuming. For that reason, ECM microphones have difficulty in providing high quality sound quality and low cost. On the other hand, MEMS microphones have the advantage that a pressure-sensitive diaphragm can be implemented on an integrated circuit, thereby enabling the production of a high-efficiency and low-cost microphone.

In a microphone, a lead-out circuit is connected to a microphone sensor to process a signal output from the microphone sensor and transmit the signal to another component or application. However, when the microphone sensor is a capacitor type, the microphone sensor has a high output impedance, thereby causing a problem in interfacing with the lead-out circuit.

For example, loading by a lead-out circuit can attenuate the output signal of the microphone. Also, the sensitivity of a MEMS microphone implemented on an integrated circuit may have various values depending on fabrication characteristics and fabrication environment, so that the output of the lead-out circuit may differ from one another depending on the microphone sensor. Therefore, in order to keep the output of the lead-out circuit constant to the size required by the system after the lead-out circuit, the function of amplifying or reducing the output of the microphone sensor must be provided.

A conventional lead-out circuit uses a method of amplifying or reducing its output by adjusting the gain of the amplifier. However, when the output of the amplifier is amplified, the noise of the amplifier is also amplified so that the SNR (Signal to Noise Ratio) characteristic of the readout circuit is not improved.

Further, a configuration for controlling the gain of the readout circuit by constituting a feedback circuit with a capacitor in order to suppress the noise of the amplifier can be presented. In this case, however, the capacitance of the capacitor must be adjusted in order to adjust the gain of the readout circuit. As a result, as the gain of the readout circuit increases, the noise of the amplifier also increases, which makes it difficult to adjust the gain while maintaining the SNR characteristics of the readout circuit.

Also, since the noise generated in the charge pump process is included in the bias of the microphone sensor to increase the noise of the microphone sensor, the SNR characteristic of the microphone sensor deteriorates .

On the other hand, in the case of a microphone used in a communication device, a high frequency communication signal flows through the terminals connected to the lead-out circuit and the microphone sensor to be demodulated, thereby deteriorating the performance of the microphone.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a lead-out circuit for a microphone sensor that is easy to provide a constant output in response to the sensitivity of various microphone sensors.

Another object of the present invention is to provide a lead-out circuit for a microphone sensor capable of improving the SNR of a lead-out circuit.

Another object of the present invention is to improve the noise function of the microphone sensor by filtering the noise included in the voltage for biasing the microphone sensor.

Another object of the present invention is to provide a lead-out circuit capable of mitigating performance degradation of a microphone due to high-frequency noise introduced through a terminal to which a microphone sensor and a lead-out circuit are connected.

In order to solve the above problems, a lead-out circuit for a microphone sensor according to the present invention includes a microphone sensor having a first terminal for transmitting a sensing signal corresponding to a change in sound pressure and a second terminal for transmitting a sensor bias voltage A readout circuit comprising: a buffer for outputting the sensing signal transmitted to an input terminal through the first terminal; An input capacitor acting as an input impedance between the first terminal and the input of the buffer and controlling a gain of the readout circuit; A feedback capacitor acting as a feedback impedance between the second terminal and the output terminal of the buffer, and controlling a gain of the readout circuit; A sensor bias unit for providing the sensor bias voltage for driving the microphone sensor and performing first filtering to remove noise mixed with the sensor bias voltage; And a second filter coupled to the feedback capacitor to perform a second filtering on the sensor bias voltage and to feedback from the output terminal of the buffer to the second terminal, A separation unit for separating a feedback path for the sensing signal and a voltage environment of the sensor bias unit; .

In order to solve the above problems, a lead-out circuit for a microphone sensor according to the present invention has a first terminal receiving a sensing signal corresponding to a change in sound pressure and a second terminal for applying a sensor bias voltage A lead-out circuit for a microphone sensor, comprising: a buffer for outputting the sensing signal transmitted to an input terminal through the first terminal; An input capacitor acting as an input impedance between the first terminal and the input terminal of the buffer and controlling a gain of the readout circuit; Pass filter operatively coupled to the input capacitor to isolate the input capacitor and the microphone sensor in a high frequency band filtered by the low pass filter operation and to provide a connection in an operating frequency band that is passed by the low pass filter operation. An input filter unit; A feedback capacitor acting as a feedback impedance between the second terminal and the output terminal of the buffer, and controlling a gain of the readout circuit; A sensor bias unit for providing the sensor bias voltage for driving the microphone sensor and performing first filtering to remove noise mixed with the sensor bias voltage; And a second feedback circuit coupled to the feedback capacitor to perform a second filtering on the sensor bias voltage and to provide feedback on the sensing signal including the feedback capacitor to the second terminal, A separation unit for separating a path and a voltage environment of the sensor bias unit; .

The lead-out circuit for the microphone sensor according to the present invention can improve the interface function of the lead-out circuit by easily providing a constant output corresponding to the sensitivity of various microphone sensors.

Further, the lead-out circuit for the microphone sensor according to the present invention has an effect of improving the SNR characteristic of the lead-out circuit.

In addition, the present invention can improve the noise function of the microphone sensor by filtering the noise included in the voltage for biasing the microphone sensor.

In addition, the present invention can alleviate the performance degradation of the microphone due to the high frequency noise introduced through the terminal to which the microphone sensor and the lead-out circuit are connected.

1 is a circuit diagram showing an embodiment according to a lead-out circuit for a microphone sensor of the present invention.
2 is a circuit diagram showing another embodiment of the lead-out circuit for the microphone sensor of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It is to be understood that the terminology used herein is for the purpose of description and should not be interpreted as limiting the scope of the present invention.

The embodiments described in the present specification and the configurations shown in the drawings are preferred embodiments of the present invention and are not intended to represent all of the technical ideas of the present invention and thus various equivalents and modifications Can be.

1 is a circuit diagram showing an embodiment according to a readout circuit of the present invention.

Referring to FIG. 1, the lead-out circuit 200 of the present invention includes a buffer 210, an input capacitor Cin, a feedback capacitor Cfb, a separator 220, and a sensor bias unit 230.

The microphone sensor 100 senses a change in sound pressure through the sensor bias voltage and generates a sensing signal. More specifically, the microphone sensor 100 may generate a sensing signal through a sensor built in the microphone sensor 100 in response to a sensor bias voltage flowing through the second terminal 20.

Here, the sensor bias voltage is a voltage for biasing the microphone sensor 100 generated from the sensor bias unit 300 to be performed. The sensor bias voltage can be formed in various sizes depending on the performance or environment of the microphone.

The microphone sensor 100 may be a sensor that receives a sound wave or an ultrasonic wave and generates a sensing signal based on the received sound wave or the vibration of the ultrasonic wave. The sensor used in the microphone sensor 100 may be various types of electronic sensors. In the present invention, a capacitor type microphone sensor is exemplified, and a MEMS microphone is exemplified.

The present invention illustrates that the microphone sensor (100) operates in a DC biased manner as a capacitor type. The microphone sensor 100 may include an electrode layer (not shown). Such an electrode layer may have a variable capacitor characteristic in which the interval may vary according to the negative pressure, and the capacitance value varies according to the interval of the changed electrode layer.

Referring to FIG. 1, the microphone sensor 100 includes a capacitor Co whose capacitance is changed when the negative pressure is changed while the sensor bias voltage is applied. Where the capacitor Co is the average capacitance of the microphone sensor 100 and the capacitor Cp may be the parasitic capacitance associated with the fabrication of the microphone sensor 100. Through the above-described configuration, the magnitude of the sensing signal changes according to the magnitude of the sound pressure received by the microphone sensor 100. [ The sensing signal is provided to the lead-out circuit 200 through the first terminal 10.

The lead-out circuit 200 provides a sensor bias voltage for operating the microphone sensor 100, and can remove the noise of the sensing signal and output it to the outside (OUT).

The lead-out circuit 200 further includes an additional input terminal (not shown) for receiving an operating voltage from the outside or an output terminal (not shown) for providing a sensing signal generated by the microphone sensor 100 to the outside can do.

The first terminal 10 may provide the sensing signal provided by the microphone sensor 100 to the lead-out circuit 200 and the second terminal 20 may provide the sensor bias voltage provided by the lead- To the microphone sensor (100).

The first terminal 10 and the second terminal 20 are located between the lead-out circuit 200 and the microphone sensor 100 and are used for physically connecting the lead- May be in the form of a pin.

The readout circuit 200 may include a buffer 210, an input capacitor Cin, a feedback capacitor Cfb, a separation unit 220, and a sensor bias unit 230. The configurations included in the readout circuit 200 may be implemented by being integrated into one chip on the lead-out circuit 200. [

The buffer 210 is composed of an input terminal connected to the first terminal 10 and an output terminal connected to the second terminal 20 and is capable of receiving a sensing signal from the microphone sensor 100. The input capacitor Cin may be connected at one end to a node between the input terminal of the buffer 210 and the first terminal 10. The buffer bias unit 212 may be connected at one end to a node between the input terminal of the buffer 210 and the first terminal 10. The feedback capacitor Cfb may be connected between the output terminal of the buffer 210 and the second terminal 20. The path from the output terminal of the buffer 210 to the second terminal 20 can be regarded as a feedback path to the sensing signal output from the buffer 210.

The buffer 210 can amplify the sensing signal and provide it to the outside (OUT). More specifically, the buffer 210 performs a voltage buffer function for a sensing signal provided from the microphone sensor 100, and a source follower can be exemplified. Therefore, the phase of the sensing signal input to the buffer 210 and the phase of the sensing signal amplified and output from the buffer 210 may be in phase.

The input terminal of the buffer 210 is connected to the first terminal 10, the buffer bias unit 212 and the input capacitor Cin and the output terminal of the buffer 210 is connected to the output terminal of the readout circuit 200 and the feedback capacitor Cfb .

The buffer 210 is driven by a buffer bias voltage applied from the buffer bias unit 212, and a transistor for performing a buffer function may be disposed therein although not shown in FIG.

The input capacitor Cin means a capacitor whose one end is connected to the buffer 210, the first terminal 10 and the buffer bias part 212 and the other end is grounded for the alternating current. The input capacitor Cin may act as an input impedance to the sensing signal provided from the microphone sensor 100. [

The buffer bias unit 212 provides a buffer bias voltage for biasing the buffer 210 using a voltage generated in the voltage source VS1. The buffer bias unit 212 is connected to the buffer bias unit 212 in order to minimize a phenomenon in which a sensing signal provided through the first terminal 10 flows into the buffer bias unit 212 or a leakage current generated from the microphone sensor 100, And may be constituted by an impedance circuit.

The feedback capacitor Cfb is a capacitor whose one end is connected to the output terminal of the buffer 210 and the other end is connected to the second terminal 20 and the separator 220. The feedback capacitor Cfb is located on the feedback path through which the sensing signal provided to the lead-out circuit 200 through the first terminal 10 is fed back through the second terminal 20 via the output of the buffer 210 . The feedback capacitor Cf may serve as a feedback impedance for a sensing signal fed back on a path through which the sensing signal output from the buffer 210 is fed back.

Therefore, it is possible to eliminate the resistance in the feedback path of the sensing signal, thereby minimizing the current consumed in the feedback of the sensing signal.

The feedback capacitor Cfb can control the gain of the readout circuit 200 together with the input capacitor Cin. More specifically, when the capacitance of the feedback capacitor Cfb is C1 and the capacitance of the input capacitor is C2, the gain of the readout circuit 200 can be approximately 1 + C1 / C2. Therefore, the gain of the readout circuit 200 can be controlled by adjusting the capacitances of the feedback capacitor Cfb and the input capacitor Cin. For this, at least one of the feedback capacitor Cfb and the input capacitor Cin is preferably a variable capacitor capable of controlling the magnitude of the capacitance.

The magnitude of the noise generated by the buffer 210 in the readout circuit 200 is determined by the magnitude of the input capacitor Cin and the feedback capacitor Cfb. More specifically, in the feedback configuration for obtaining the gain It can be seen that the noise of the buffer 210 added by the input capacitor Cin is proportional to the capacitance of the input capacitor Cin divided by the capacitance of the feedback capacitor Cfb.

Therefore, as the capacitance of the feedback capacitor Cfb is set to be larger than the capacitance of the input capacitor Cin, the gain of the readout circuit 200 increases, but the noise added thereby decreases relative to the gain, It is possible to provide a lead-out circuit having improved SNR characteristics compared to a circuit.

The separator 220 has one end connected between the second terminal 30 and the feedback capacitor Cfb and the other end connected to the sensor bias unit 230 to receive the input capacitor Cin, Cfb and the voltage environment of the sensor bias unit 230 and perform a second filtering on the sensor bias voltage. The separating unit 220 may include a separating resistor Ri having one end connected between the second terminal 20 and the feedback capacitor Cfb and the other end connected to the sensor bias unit 230.

Since the isolation resistor Ri is set to have a resistance value similar to the sensor filter resistance Rf of the sensor bias unit 230, it can be seen that the isolation resistance Ri is the same within the operating frequency band of the signal. On the other hand, since the feedback path is constituted by a capacitor, it has a relatively low impedance value in comparison with the isolation resistance Ri in the signal operating frequency. Therefore, the feedback path in the signal operating frequency domain can be seen as open when looking at the isolation resistor Ri. As a result, the signal of the feedback path is separated and transmitted from the sensor bias unit 230 without being affected.

That is, the separating unit 220 may be configured to transmit a sensing signal fed back from the sensor bias unit 230 by acting as a high impedance to the feedback path. The sensor bias unit 230 may provide a sensor bias voltage to the microphone sensor 100. A sensor voltage source VS2 for generating a sensor bias voltage, and a sensor filter unit 231 connected between the sensor voltage source VS2 and the separation unit 220 to perform first filtering on the sensor bias voltage have.

The sensor voltage source VS2 generates a sensor bias voltage for driving the microphone sensor 100. [ The sensor voltage source VS2 may include a charge pump circuit for generating the sensor bias voltage. The sensor bias voltage is filtered by noise before it is provided to the microphone sensor 100 because the charge is pumped by the charge pump circuit and a lot of noise is generated.

The sensor filter unit 231 may perform a first filtering on the sensor bias voltage as an RC filter or a low pass filter for the sensor bias voltage generated in the sensor voltage source VS2. The sensor filter unit 231 may include a sensor filter resistor Rf and a filter capacitor Cf coupled to the sensor filter resistor Rf and the sensor filter resistor Rf may include a separator 220 And the sensor voltage source VS2. The filter capacitor Cf may have a configuration in which one end of the filter capacitor Cf is grounded and the other end thereof is connected to the resistor Rf and the separator 220.

And the isolation resistor Ri of the isolation part 220 may be used for additional second filtering with respect to the first filtered sensor bias voltage by the sensor filter part 231. [

One end of the feedback capacitor Cfb is connected to the output terminal of the buffer 210 and one end connected to the buffer 210 of the feedback capacitor Cfb is similar to that of the ground due to the characteristics of the buffer 210 having a very low output impedance. Therefore, the isolation resistor Ri and the feedback capacitor Cfb are coupled to the sensor bias voltage that has passed through the sensor filter unit 231, thereby functioning as an RC filter or a low-pass filter for the second filtering.

That is, the isolation resistor Ri and the feedback capacitor Cfb may perform a second filtering, which is a second filtering on the sensor bias voltage. By performing two filtering operations on the sensor bias voltage, the magnitude of the noise of the sensor bias voltage transmitted to the microphone sensor 100 can be reduced, thereby improving the SNR characteristics of the microphone sensor 100.

2 is a circuit diagram showing another embodiment according to the readout circuit of the present invention. 2, it can be seen that the input filter unit 240 is disposed between the first terminal 10 and the buffer bias unit 212, unlike in FIG. In FIG. 2, the configuration having the same reference numerals as those in FIG. 1 can be understood to perform the same functions as those in FIG. 1 and will not be described here.

In the microphone, the microphone sensor 100 and the lead-out circuit 200 may be physically connected through a plurality of terminals. The microphone sensor 100 and the lead-out circuit 200 are connected through the first terminal 10 and the second terminal 20 in the embodiment of the present invention.

However, since the first terminal 10 and the second terminal 20 are physically connected to the lead-out circuit 200 and the microphone sensor 100, the lead-out circuit 200 and the microphone sensor 100 And may be susceptible to high frequency external noise such as RF noise in a microphone used in a communication device. Particularly, when the communication device operates in the TDMA mode, the TDMA noise generated in the characteristic of the TDMA scheme can be introduced into the first terminal 10 or the second terminal 20.

The input filter 240 may be disposed between the first terminal 10 and the buffer 210 to remove the high frequency noise introduced through the first terminal 10. [

The input filter unit 240 may include an input filter resistor Rf2. The input filter resistor Rf2 may be coupled with the input capacitor Cin to act as a lowpass filter for high frequency noise introduced through the first terminal 10. [ Therefore, the noise characteristic for the RF noise introduced through the first terminal 10 through the input filter resistor Rf2 and the input capacitor Cin can be improved.

At this time, the input filter resistor Rf2 may be an additional noise source for the lead-out circuit 200 since the sensing signal is located on the path provided to the buffer 210. [ Therefore, the resistance value of the input filter resistor Rf2 may be limited to a certain value or less in order to maintain the SNR characteristics according to the configurations of the microphone sensor 100 and the lead-out circuit 200. [ At this time, it is preferable that the resistance value of the input filter resistor Rf2 has a size of 1 k ohm or less.

The input filter resistor Rf2 having such a size causes the frequency characteristic of the input filter 240 to be attenuated only in the carrier frequency band without signal attenuation in the operating frequency band. Thus, by controlling the capacitance of the input capacitor Cin, effective filtering for high frequency noise such as an RF signal becomes possible.

Here, the operating frequency band is an audio frequency band, which may range from 20 Hz to 20 kHz. The high frequency band can be defined as a frequency band ranging from 800 MHz to 2.5 GHz, which is a range of frequencies higher than the operating frequency band.

Demodulation of the carrier frequency is maximized in a combination of a nonlinear element and a capacitor wherein the capacitor of the microphone sensor 100 and the diode (not shown) located on the input side of the lead-out circuit 200 are interconnected in a system configuration. Thus, the input filter resistor Rf2 can effectively attenuate the RF signal, thereby allowing the RF signal to be delivered to the diode at the input side of the lead-out circuit 200 to a minimum. Thus, demodulation of the RF frequency is minimized in the lead-out circuit 200, and deterioration of the sensing function of the microphone sensor 100 is prevented, thereby improving the performance of the microphone.

As described above, the lead-out circuit according to the present invention can easily provide a constant output corresponding to the sensitivity of various microphone sensors.

Further, the readout circuit according to the present invention has an effect of improving the SNR characteristic of the readout circuit.

In addition, the present invention can improve the noise function of the microphone sensor by filtering the noise included in the voltage for biasing the microphone sensor.

In addition, the present invention can alleviate the performance degradation of the microphone due to the high frequency noise introduced through the terminal to which the microphone sensor and the lead-out circuit are connected.

Claims (14)

A lead-out circuit for a microphone sensor having a first terminal for transmitting a sensing signal corresponding to a change in sound pressure and a second terminal for transmitting a sensor bias voltage,
A buffer for outputting the sensing signal transmitted to an input terminal through the first terminal;
An input capacitor acting as an input impedance between the first terminal and the input of the buffer and controlling a gain of the readout circuit;
A feedback capacitor acting as a feedback impedance between the second terminal and the output terminal of the buffer, and controlling a gain of the readout circuit;
A sensor bias unit for providing the sensor bias voltage for driving the microphone sensor and performing first filtering to remove noise mixed with the sensor bias voltage; And
Wherein the first bias voltage of the sensor bias unit is transmitted to the second terminal, the second bias voltage is coupled to the feedback capacitor to perform a second filtering on the sensor bias voltage, And a separation unit for separating the feedback path for the sensing signal and the voltage environment of the sensor bias unit,
Wherein the separation unit performs separation of the voltage environment with respect to the sensing signal fed back by acting as a high impedance to the feedback path. The method according to claim 1,
Wherein at least one of the input capacitor and the feedback capacitor
A lead-out circuit for a microphone sensor comprising a variable capacitor capable of adjusting the magnitude of the capacitance. The apparatus of claim 1, wherein the sensor bias unit
A sensor voltage source for generating the sensor bias voltage; And
A sensor filter unit connected between the sensor voltage source and the isolation unit to perform the first filtering on the sensor bias voltage; For a microphone sensor. The apparatus as claimed in claim 3, wherein the sensor filter unit
A sensor filter resistor carrying the sensor bias voltage of the sensor voltage source and a sensor filter capacitor whose one end is coupled to the sensor filter resistor. The apparatus of claim 1, wherein the separator
And a separation resistor having one end connected to a node between the second terminal and the feedback capacitor and the other end connected to the sensor bias portion. 6. The method of claim 5,
Wherein the second filter is coupled to the feedback capacitor to remove noise of the sensor bias voltage provided to the second terminal in the sensor bias portion. delete A lead-out circuit for a microphone sensor having a first terminal receiving a sensing signal corresponding to a change in sound pressure and a second terminal for applying a sensor bias voltage,
A buffer for outputting the sensing signal transmitted to an input terminal through the first terminal;
An input capacitor acting as an input impedance between the first terminal and the input terminal of the buffer and controlling a gain of the readout circuit;
Pass filter operatively coupled to the input capacitor to isolate the input capacitor and the microphone sensor in a high frequency band filtered by the low pass filter operation and to provide a connection in an operating frequency band that is passed by the low pass filter operation. An input filter unit;
A feedback capacitor acting as a feedback impedance between the second terminal and the output terminal of the buffer, and controlling a gain of the readout circuit;
A sensor bias unit for providing the sensor bias voltage for driving the microphone sensor and performing first filtering to remove noise mixed with the sensor bias voltage; And
And a second feedback circuit coupled to the feedback capacitor to perform a second filtering on the sensor bias voltage and to provide a feedback path for the sensing signal comprising the feedback capacitor to the second terminal, And a separation unit for separating the voltage environment of the sensor bias unit,
Wherein the separation unit performs separation of the voltage environment with respect to the sensing signal fed back by acting as a high impedance to the feedback path. 9. The apparatus of claim 8, wherein the input filter section
Wherein the input filter resistor is a resistor coupled to the input capacitor to perform a low pass filter operation on noise introduced through the first terminal. 9. The apparatus of claim 8, wherein the sensor bias portion
A sensor voltage source for generating the sensor bias voltage; And
A sensor filter unit connected between the sensor voltage source and the isolation unit to perform the first filtering on the sensor bias voltage; For a microphone sensor. 11. The apparatus of claim 10, wherein the sensor filter portion
A sensor filter resistor carrying the sensor bias voltage of the sensor voltage source and a filter capacitor whose one end is coupled to the sensor filter resistor. 9. The apparatus of claim 8, wherein the separator
And a separation resistor having one end connected to a node between the second terminal and the feedback capacitor and the other end connected to the sensor bias portion. 13. The method of claim 12,
Wherein the second filter is coupled to the feedback capacitor to remove noise of the sensor bias voltage provided to the second terminal in the sensor bias portion. delete

Images