JP2003243944A - High input impedance amplifier, and semiconductor integrated circuit for electret condenser microphone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the size of a semiconductor device by forming a resistive element (106) with a large area and a resistance of several hundreds M (mega) ohms to several G (giga) ohms having been externally mounted on an IC (101) for an electret condenser microphone ECM into an integrated circuit. <P>SOLUTION: The IC for an electret condenser microphone (ECM) is provided with a J-FET (2) having a gate (5), a source (7), and a drain (8), a microphone capacitor (2) acting as an input element, and a capacitor (9) placed between the source (7) and the drain (8), a Schottky barrier diode (6) with a small area is provided between the microphone capacitor (2) and the gate (5). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high input impedance amplifier and a resistance element in an IC for an electret condenser microphone using the high input impedance amplifier.

[0002]

2. Description of the Related Art In recent years, mobile phones have become smaller and smaller. Electret condenser microphones (hereinafter referred to as ECMs) are generally used as microphones on the transmitting side of mobile phones, and with the demand for miniaturization of mobile phones, the ECM itself is naturally made smaller and particularly thin. Has been requested.

FIG. 7 shows an IC for a conventional electret condenser microphone (hereinafter referred to as an ECM IC (10
It is a circuit diagram showing (1). IC for ECM (1
01) is a microphone condenser (10
2) and an impedance conversion circuit (103) for transmitting an audio signal voltage generated by a change in the electrostatic capacitance of the microphone capacitor (102) due to the audio signal.

The microphone capacitor (102) is constructed with an electret layer between a diaphragm vibrating by a voice signal and a capacitance electrode plate facing the diaphragm. The impedance conversion circuit (103) is a junction field effect transistor (hereinafter, referred to as J-FET (104)) in which one end of the microphone capacitor (102) is connected to the gate.
And a resistance element (106) connected between the gate (105) of the J-FET (104) and the ground. A capacitor (109) for suppressing RF (high frequency) burst noise is connected between the source (107) and the drain (108) of the J-FET (104). Further, the J-FET (104) constitutes a source ground circuit.

[0005]

The above-mentioned IC for ECM
At (101), a leak current I as shown in FIG. 7 is generated from the drain (108) side. This leak current I is P in the J-FET (104) at the time of reverse bias.
It is generated from the N-junction, the gate voltage is kept at the GND potential, and this leakage current I is determined by the J-FET (10
4) One issue is how to make it flow out from the inside. Therefore, the impedance conversion circuit (103) can prevent the rise of the gate voltage due to the outflow of the leak current I if the input impedance (of the leak current I flowing into the impedance conversion circuit) is low. Further, since the IC (101) for ECM is used as a microphone of a mobile phone, the shorter the time (so-called “rise time”) from detecting a signal until communication becomes possible, the better the performance of the mobile phone. Can be said to be However, this rise time is determined by the product (time constant) of the capacitance of the input section and the input resistance in the impedance conversion circuit (103), and the lower the time constant, the shorter the rise time.

On the other hand, in consideration of the low frequency characteristic, 100
In order to input a low-frequency audio signal of Hz or higher, it is preferable that the impedance is high because of the HPF (high-pass filter) configuration of the capacitance of the microphone and the input resistance.

Therefore, these two requirements (measuring low impedance for leak current I, shortening so-called "rise time", and realizing high impedance for low-frequency characteristics) are met. Therefore, the resistance value of the resistance element (106) needs to be several hundreds M (mega) to several G (giga) Ω.

Under the above circumstances, the J-FET is
(104), resistance element (106), capacitor (10
It has been difficult so far to install 9) and the like in the same semiconductor device chip to form an IC. This is because the resistance element (106) element having several hundreds M (mega) to several G (giga) Ω has a very large element area. Therefore,
Resistance element (106) of several hundred M (mega) to several G (giga) Ω
In the case of connecting with, there is no choice but to install it outside the J-FET (104). This cannot sufficiently meet the recent needs for downsizing (particularly ICs). Further, when the area of the resistance element (106) itself becomes large, there is also a drawback that the parasitic capacitance increases accordingly. For example,
One side of a semiconductor chip having a J-FET inside is 0.6
Although it is a square of about 5 to 0.70 mm, it is several hundred M
(Mega) to several G (giga) Ω Resistance element (10
6) is a rectangle having a short side of about 0.50 mm and a long side of about 1.0 mm. This is about 1.5 times the area of a semiconductor chip.

Therefore, the present invention has been made in view of the above-mentioned drawbacks, and provides a high resistance element of several hundreds M (mega) to several G (giga) Ω between the gate (105) and the source (107). By using a Schottky barrier diode,
Realized IC.

[0010]

A high input impedance amplifier of the present invention is an impedance conversion circuit for impedance-converting or amplifying an input signal, wherein an impedance conversion element and an input terminal of the impedance conversion element are biased to a DC voltage. And a Schottky barrier diode.

[0011]

DETAILED DESCRIPTION OF THE INVENTION A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an IC for an electret condenser microphone (hereinafter, referred to as an IC for ECM (1)) according to a first embodiment of the present invention.

The IC for the ECM (1) is a microphone capacitor (2) to which a voice signal is input, and an impedance conversion circuit (impedance conversion circuit for impedance-converting a signal voltage generated by a change in the capacitance of the microphone capacitor (2) due to the voice signal. 3).

The microphone capacitor (2) is constructed with an electret layer between a diaphragm vibrating by a voice signal and a capacitance electrode plate facing the diaphragm. Further, the impedance conversion circuit (3) includes a junction field effect transistor (hereinafter, referred to as J-FET (4)) in which one end of the microphone capacitor (2) is connected to the gate, and a J-FET.
It is composed of a gate (5) of (4) and a Schottky barrier diode (6) connected between the ground. J
A capacitor (9) for suppressing RF burst noise is connected between the source (7) and drain (8) of the -FET (4). The J-FET (4) constitutes a source ground circuit. The J-FET (4) has a function of amplifying an input signal.

A feature of the present invention is that the resistance element (10
Instead of 6), a Schottky barrier diode (6) is adopted as a high resistance element. The Schottky barrier diode (6) is a junction diode formed of a metal and a semiconductor and has a higher resistance than an ordinary PN junction diode. This makes it possible to form the high resistance element with a small element area.

In the present invention, in addition to the above configuration, the cathode side of the Schottky barrier diode (6) and the J-FET.
The case where the source side (7) of (4) is connected and the integrated wiring is grounded is also included.

FIG. 2 is a diagram showing the VI (voltage / current) characteristics of the Schottky barrier diode (6). In this figure, the horizontal axis represents voltage (V) and the vertical axis represents current (μA). Normally, the Schottky barrier diode (6) has a voltage of 0.
It rises so that the current becomes 10 (μA) with respect to 35 (V). In the present invention, the Schottky barrier diode (6) is used within a low voltage range of about 0.1 to 0.2 (V). Current flowing in this voltage range is 700p
(Pico) to 30 n (nano) (A). The resistance value of the Schottky barrier diode (6) at this time is 7 to 14
It becomes 3M (mega) (Ω). The Schottky barrier diode (6) operates within a low voltage range of about 0.1 to 0.2 (V) until the current of the Schottky barrier diode (6) rises and the curve showing its characteristics becomes steep. ECM shown in FIG.
In the IC for (1), the amplitude of the AC signal input via the microphone capacitor (2) falls within such a low voltage range. Therefore, a low voltage and a low current as shown in FIG. 2 can be realized, and as a result, a high resistance value suitable for the impedance conversion circuit can be realized.

FIG. 3 shows an ECM (1) incorporating a Schottky barrier diode (6) inside a semiconductor chip.
FIG. 3 is a plan view of an IC for use in a computer. (10) is a semiconductor chip,
(11) represents other elements. As shown in FIG. 3, the square source (7), the gate (5), and the drain (8) are respectively arranged at three locations among the four corners in the square semiconductor chip (10). Then, the capacitors (9) are arranged in the remaining corners. The capacitor (9) is composed of a plurality of areas, and has a specification such that the required number of capacitors (9) can be used according to the application in response to user's demand. The present invention has disclosed a mode in which the capacitance value of the capacitor (9) can be changed according to the demand from the user side. However, the present invention is not limited to these, and includes an IC using a capacitor (9) having a fixed capacitance value. The other element (11) is, for example, a resistance element necessary for the inside of about several hundred Ω, a diode for preventing electrostatic breakdown, or the like.

The arrangement of the J-FET (2), gate (5), source (7), drain (8) pads, capacitor (9) and other elements (11) shown in FIG. 3 is an example. Is only shown and is not limited to the above contents.

Next, the internal dimensions of the IC package in FIG. 3 will be described. One side of the semiconductor chip (10) is 0.
It has a width of about 65 to 0.70 mm and forms a square. Similarly, each side of the source (7), the gate (5), and the drain (8) has a length of about 0.13 mm, and each of these also forms a square. Further, the Schottky barrier diode (6) has a side of about 50 μm and is in the shape of a square.
As the capacitor (9), in the example disclosed in FIG. 3, four capacitors are arranged in parallel at equal intervals. As a result, when these four capacitors (9) are viewed as one body, they form a square as a whole, and one side thereof is about 0.3 to 0.4 mm.

A feature of the present invention is to utilize the voltage / current characteristics of the Schottky barrier diode (6) and the small area of the Schottky barrier diode (6) element. That is, of the characteristics of the Schottky barrier diode (6), the J-FET is used in a range that exhibits a high resistance value.
By installing (2), the gate (5), the source (7), and the drain (8) in the same semiconductor chip, the IC
The size of the entire IC for ECM (1) has been reduced.

From the above, the area of the Schottky barrier diode (6) is only about 0.5 to 0.6% of the area of the square semiconductor chip (10), and the area within the same semiconductor chip (10) is small. It is possible to integrate the J-FET (2), the source (7), the gate (5), the drain (8), the capacitor (9), and the Schottky barrier diode (6) into an IC. The microphone capacitor (2) may be provided inside the IC or outside the IC.

FIG. 4 is a diagram showing an electret condenser microphone according to the second embodiment of the present invention. In the figure, the same components as in FIG.
The same reference numerals are given and the description thereof is omitted. In this embodiment, the drain-grounded (source follower) J-FET (2) and the Schottky barrier diode (6) are connected. At this time, a fixed current source (11) may be connected between the source (7) and earth ground.

FIG. 5 is a diagram showing an electret condenser microphone according to the third embodiment of the present invention. In the figure, the same components as in FIG.
The same reference numerals are given and the description thereof is omitted. In the present embodiment, the differential input terminal of the differential amplifier circuit (12) and the Schottky barrier diode (6) are connected. At this time, the J-FET (1
A fixed current source (11) may be connected between both sources (7) of (3) and (14) and earth ground. This operation amplification circuit (12) includes a pair of J-FETs (13), (1
4), but a pair of operating bipolar transistors may be used instead.

FIG. 6 is a diagram showing an electret condenser microphone according to a fourth embodiment of the present invention. In the figure, the same components as in FIG.
The same reference numerals are given and the description thereof is omitted. In this embodiment, the bipolar transistor (15) and the Schottky barrier diode (6) are connected. In FIG.
Although the grounded collector (emitter follower) is disclosed, there is no problem even if grounded emitter or base is used. (Also, the fixed current source (11) may be connected to any terminal of the base, the emitter, and the collector.) In FIG. 6, the collector-grounded bipolar transistor (15).
, A fixed current source (11) is connected between the emitter and the power supply. Although the PNP type bipolar transistor (15) is disclosed in FIG. 6, it may be an NPN type bipolar transistor (15).

[0025]

As described above, according to the present invention, since the Schottky barrier diode (6) is used as the high resistance element used in the impedance conversion circuit (3), the element area can be greatly reduced, It becomes possible to integrate it on a semiconductor chip.

[Brief description of drawings]

FIG. 1 is a diagram showing an IC for an electret condenser microphone according to a first embodiment of the present invention.

FIG. 2 is a diagram showing VI characteristics of the Schottky barrier diode according to the first embodiment of the present invention.

FIG. 3 is a plan view of an IC of the electret condenser microphone according to the first embodiment of the present invention.

FIG. 4 is a diagram showing an IC of an electret condenser microphone according to a second embodiment of the present invention.

FIG. 5 is a diagram showing an IC of an electret condenser microphone according to a third embodiment of the present invention.

FIG. 6 is a diagram showing an IC of an electret condenser microphone according to a fourth embodiment of the present invention.

FIG. 7 is a circuit diagram showing a conventional J-FET.

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Claims (6)

[Claims] 1. An impedance conversion circuit for impedance-converting or amplifying an input signal, comprising: an impedance conversion element; and a Schottky barrier diode for biasing an input terminal of the impedance conversion element to a DC voltage. High input impedance amplifier. 2. The high input impedance amplifier according to claim 1, wherein the impedance conversion element and the Schottky barrier diode are integrated on the same semiconductor chip. 3. The high input impedance amplifier according to claim 1, wherein the impedance conversion element is one of a field effect transistor, a bipolar transistor, and a differential amplifier circuit. 4. An input terminal to which an audio signal is input, an impedance conversion element for impedance-converting or amplifying a signal voltage generated by the signal, and a Schottky barrier diode for biasing the input terminal of the impedance conversion element to a DC voltage. And a semiconductor integrated circuit for an electret condenser microphone. 5. The semiconductor integrated circuit for an electret condenser microphone according to claim 4, wherein the impedance conversion element and the Schottky barrier diode are integrated on the same semiconductor chip. 6. The semiconductor integrated circuit for an electret condenser microphone according to claim 3, wherein the impedance conversion element is one of a field effect transistor, a bipolar transistor, and a differential amplifier circuit.