KR100993680B1 - Amplifier circuit with noise filter and noise filter - Google Patents

Abstract

In the noise filter LPF using the junction capacitance of the diode, the cutoff frequency of the LPF is determined by the capacitance value and the resistance value of the junction capacitance. However, in order to obtain sufficient RFI rejection characteristics, a cutoff frequency of 5 MHz or less is required, and either the capacitance value or the resistance value needs to be increased. However, if the capacitance value is increased, the chip size is enlarged. If the resistance value is increased, the input loss increases. A ladder type LPF is formed by a first capacitor comprising a transistor in which two terminals of the three terminals are diode-connected, and a second capacitor in which a pn junction capacitor and an insulating capacitor are connected in parallel. Since the pn junction capacitance formed in the semiconductor layer and the insulating capacitance formed on the surface thereof are superimposed in parallel and connected in parallel, an increase in the occupied area can be avoided even when the capacitance value is increased. In addition, since the first capacitance has a snapback characteristic, it is possible to protect the second capacitance having an insulation capacitance from ESD, to have a small and high-performance RFI removal characteristic, and to realize high EDS.

First capacitance, second capacitance, pn junction capacitance, insulation capacitance, insulating film, conductive layer

Description

Noise filter and amplifier circuit with built-in noise filter {NOISE FILTER AND AMPLIFIER CIRCUIT WITH THE SAME}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise filter and an amplifier circuit with a built-in noise filter. More particularly, the present invention relates to a noise filter and an amplifier circuit with a built-in noise filter for realizing improvements in RFI (Radio Frequency Interference).

An amplifier element is used to perform impedance conversion and amplification of an electret condenser microphone (ECM). The amplifier element is composed of, for example, a junction field effect transistor (hereinafter referred to as J-FET) or an amplifying integrated circuit element.

By the way, when the ECM is mounted on, for example, a cellular phone, radio wave propagation of the radio frequency of the cellular phone affects the wiring and related components and is detected as noise of the ECM.

Therefore, various noise filters are used to prevent leakage or intrusion of noise through wiring such as signals and to improve RFI (see Patent Document 1 and Patent Document 2, for example).

FIG. 5 is a circuit diagram showing conventional noise filters 510 and 511 connected to an amplification integrated circuit element for impedance conversion. The noise filters 510 and 511 are, for example, low-pass filter (LPF) type electro-magnetic interference (EMI) filters for preventing electromagnetic interference.

In the noise filter 510 shown in Fig. 5A, two capacitors C11 and C12 are connected in parallel, and a resistor R is connected in series between one end of the high voltage side of the two capacitors C11 and C12. The input terminal Vi 'of the noise filter 510 is connected to a power supply, and the output terminal Vo' is connected to an amplifying integrated circuit element (not shown).

This circuit is an LPF in which two capacitors C11 and C12 are connected in a ladder shape and a resistor R is connected therebetween. By connecting this to an amplifier integrated circuit element, foreign RF noise is cut off by the LPF, thereby amplifying integrated circuit elements. Since the influence on the surface can be made very small, the RFI of the ECM can be improved.

In addition, in the noise filter 511 shown in FIG. 5B, diodes D1 and D2 are connected instead of the above capacitors C11 and C12, and the junction capacitances C21 and C22 of the diodes D1 and D2 are shown in FIG. LPF used as the capacity C11 and C12 shown to A).

The LPF can be integrated on the same chip as the amplification integrated circuit device or the amplification integrated circuit device and the J-FET or p-channel MOSFET (Metal 0xide Semiconductor Field Effect Transistor) used for impedance conversion. In view of an electrostatic discharge (ESD) or a manufacturing process, it is common to use the junction capacitances of the diodes D1 and D2 as shown in Fig. 5B.

[Patent Document 1] Japanese Unexamined Patent Publication No. 2007-267168

[Patent Document 2] Japanese Patent Publication No. 2006-514497

FIG. 6 is a circuit diagram showing an example in the case where the noise filter 511 shown in FIG. 5B is connected to the amplifying integrated circuit element 550.

The input terminal IN of the amplified integrated circuit device 550 is connected to one end of the ECM 560. In the noise filter 511, the output terminal Vo ′ on the high voltage side and the output terminal GND on the low voltage side are connected in parallel with the amplifying integrated circuit element 550. Therefore, the noise filter 511 and the amplifier integrated circuit element 550 can be integrated in one chip.

By the way, in the noise filter 511 using diodes D1 and D2, the cutoff frequency fc of the LPF is determined by the junction capacitances C21 and C22 of the diodes D1 and D2 and the resistance value of the resistor R. However, in order to sufficiently improve RFI, it is necessary to lower the cutoff frequency fc of the filter, for which the capacitance value or the resistance value must be increased.

However, increasing the capacitance has a problem in that the chip size of the noise filter 511 or the amplification integrated circuit device incorporating this and the amplification integrated circuit device 550 is enlarged.

In addition, when the resistance value of the resistor R is increased, the voltage applied to the amplified integrated circuit element 550 is also reduced due to the voltage drop output from the noise filter 511, so that the problem of output reduction from the EMC 560 is caused. (Output loss) occurs.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems. Firstly, a first capacitance comprising a junction capacitance of a transistor in which two terminals of three terminals are diode-connected, a second capacitance formed by connecting a pn junction capacitance and an insulation capacitance in parallel, A resistor is provided, the high voltage side of the first capacitor is input, the high voltage side of the second capacitor is output, the resistor is connected between the first capacitor and the second capacitor, and the first capacitor is connected. And the GND connection of the low voltage side of the second capacitor.

Secondly, a first capacitor comprising a junction capacitance of a transistor in which two terminals of the three terminals are diode-connected, a second capacitor formed by connecting a pn junction capacitor and an insulation capacitor in parallel, and a resistor, and have a high voltage of the first capacitor. The side is input, the high voltage side of the second capacitor is output, the resistor is connected between the first capacitor and the second capacitor, and the low voltage side of the first capacitor and the second capacitor is connected to GND. This is solved by providing an amplifier element connected to the output of one noise filter.

Third, one conductive semiconductor layer constituting one chip, a noise filter provided in the one conductive semiconductor layer, and an amplifier element provided in the one conductive semiconductor layer, the noise filter comprises two of three terminals. A first capacitor comprising a junction capacitance of a transistor having diode-connected terminals, a second capacitor formed by connecting a pn junction capacitance and an insulation capacitor in parallel, and a resistor; and the noise filter includes a high voltage side of the first capacitor. An input, the high voltage side of the second capacitor being an output, the resistor connected between the first capacitor and the second capacitor, the GND connection of the low voltage side of the first capacitor and the second capacitor, The amplifier element is solved by being connected to the output of the noise filter.

According to the present invention, firstly, it is possible to provide a noise filter having a small and high capacitance value. That is, by setting one capacitance (second capacitance) as a capacitance in which the pn junction capacitance and the insulation capacitance are connected in parallel, a high capacitance value is obtained without increasing the size as the noise filter.

Second, a high ESD effect is obtained by using the junction capacitance of the transistor having diode-connected terminals as the first capacitance. Although the second capacitance has a problem that the insulation capacitance is particularly weak in ESD, the second capacitance can be protected by the snapback characteristic of the first capacitance and the resistance inserted between the first capacitance and the second capacitance.

Third, the amplification integrated circuit device incorporating the amplification integrated circuit device and the noise filter integrated on the same chip can realize a high RFI elimination characteristic at the same chip size as compared with the conventional structure.

In addition, if the RFI removal characteristic equivalent to the conventional structure is maintained, the chip size can be reduced, and the cost can be reduced.

That is, it is possible to provide an amplification integrated circuit device with a built-in noise filter having a small size, good RFI removal characteristics, and a high ESD effect.

An embodiment of the present invention will be described with reference to FIGS. 1 to 3.

1 is a circuit diagram showing the noise filter 100 of the present embodiment.

The noise filter 100 includes a first capacitor 10, a second capacitor 20, and a resistor 30.

The first capacitor 10 is a junction capacitor of a transistor in which two terminals of the three terminals are diode-connected. Specifically, the transistor is, for example, a MOSFET (Metal 0xide Semiconductor Field Effect Transistor) having a source S, a drain D, a gate G, and a back gate BG connected to the source S. The diode is connected to the source S and the gate G, and the anode is provided. Let A be. The drain D becomes the cathode K and becomes the input terminal Vi of the noise filter 100.

The anode A is connected to the low voltage side GND, the cathode K is connected to the high voltage side (power supply VDD via the load resistor R _L ), and since reverse bias is applied, it operates as a capacitor rather than a diode (see FIG. 2). ).

The second capacitor 20 is a parallel connection between the pn junction capacitor 20a and the insulating capacitor 20b. One end is the anode A, the other end is the cathode K, and the output terminal Vo of the noise filter 100. The anode A is connected to the low voltage side GND, the cathode K is connected to the high voltage side (resistance 30 and the power supply VDD via the load resistor R _L ), and a reverse bias is applied, so that the pn junction capacitance 20a is applied. Acts as a capacitor, not a diode (see FIG. 2).

A resistor 30 is connected in series between the cathode K (high voltage side) of both the first capacitor 10 and the second capacitor 20 to form an n-type noise filter 100.

The noise filter 100 is, for example, an electromagnetic interference (EMI) filter for preventing electromagnetic interference, hereinafter referred to as an EMI filter 100.

FIG. 2 is a circuit diagram showing an amplifier circuit 200 (hereinafter referred to as an EMI filter built-in amplifier circuit 200) incorporating the EMI filter 100 shown in FIG.

The amplifier element 201 is formed of, for example, an amplified integrated circuit element, a J-FET, etc., and the first terminal IN (Gate) is connected to one end of the electret condenser microphone (ECM) 250, and the second terminal is provided. OUT (Drain) is connected to the output terminal Vo side of the EMI filter 100. In addition, the third terminal GND (Source) is connected to GND.

The amplifier circuit with built-in EMI filter of this embodiment is an integrated circuit element which integrated the EMI filter 100 and the amplifier element 201 in one chip in this way.

The ECM 250 arrange | positions a vibration membrane (vibration plate) and the electrode which opposes it in a case, and the movement of a vibration membrane by sound is taken out as a change of the electrostatic capacitance between a vibration membrane and an electrode. The vibrating membrane is made of, for example, a polymer material, and charges the vibrating membrane by the electret effect.

One end (cathode K (input terminal Vi) of the first capacitor 10) of the amplifier circuit 200 with the EMI filter is connected to the power supply VDD through the load resistor _RL . The other end of the amplifier circuit 200 having the EMI filter (the anode A of the first capacitor 10, the anode A of the second capacitor, and the third terminal GND of the amplifier circuit 201) is connected to GND.

The current flowing through the second terminal OUT of the amplifier circuit 201 is sufficiently low compared to the cutoff frequency of the EMI filter 100 (for example, 100 Hz), and passes through the EMI filter 100 as it is. It becomes the output current of the amplifier circuit 200 with a filter. As the current flows to the load resistor R _L, and a potential difference occurs across the load resistance R _L, the change in the potential difference (AC min) is outputted as VOUT.

When unnecessary high frequency signals (RF noise) are propagated from the VDD or the load resistor R _L side to the EMI filter 100, the load resistor R _L and the EMI filter 100 operate as the secondary LPF, and the first capacitance 10 ), The RF noise escapes through the second capacitor 20, and thus exhibits a blocking characteristic of up to -12 dB / OCT.

Thereby, the high frequency signal of a radio frequency can be prevented from being input to the amplifier element 201.

Although described later in detail, the second capacitor 20 of the present embodiment has a pn junction capacitor 20a formed in the semiconductor layer, and an insulating capacitor 20b having an insulating film as a dielectric on the semiconductor layer and a conductive material disposed thereon. ) Are overlapped and arranged in parallel. Therefore, the capacitance value can be increased without increasing the size of the EMI filter 100. Therefore, it is possible to prevent an increase in the chip size of the amplifier circuit 200 with the built-in EMI filter and to improve the RFI elimination characteristics.

On the other hand, the insulating capacitor 20b is weak in electrostatic discharge (ESD) because the insulating film is used as the dielectric. However, in the present embodiment, a MOSFET in which two terminals are diode-connected is used as the first capacitor 10. Thereby, the static electricity can be sufficiently discharged in the first capacitor 10, and the static electricity applied to the second capacitor 20 can be greatly attenuated.

3 is a schematic diagram showing the current I-voltage V characteristics of the MOSFET which is the first capacitor 10. Thus, since the MOSFET is a diode connection, it has a snapback characteristic and is resistant to ESD. Therefore, by designing the breakdown voltage of the MOSFET below the voltage V _SB to snap back, the static electricity can be sufficiently absorbed and the second capacitor 20 and the amplifier element 201 can be protected from ESD.

4 is a cross-sectional view illustrating the structure of a portion of the second capacitor 20 of the EMI filter built-in amplifier circuit 200 of the present embodiment. Here, the p-type semiconductor substrate is described as an example.

The second capacitor 20 is composed of a pn junction capacitor 20a and an insulating capacitor 20b. The pn junction capacitance 20a is formed with an n-type semiconductor region 22 in which n-type (n + -type) impurities are diffused on the surface of the p-type semiconductor layer 11, and formed on the surface of the p-type semiconductor layer 11. The insulating film 23 is formed. On the p-type semiconductor layer 11, a first capacitor electrode (cathode electrode) 25 is formed in contact with the n-type semiconductor region 22 through an opening formed in the insulating film 23. The first capacitor electrode 25 becomes the output terminal Vo of the EMI filter 100 and is connected to the resistance electrode of the resistor 30 and the drain electrode of the amplifier element 201.

On the surface of the p-type semiconductor layer 11, another GND contact region 28 formed by a high concentration of p-type (p + type) impurity region is formed, and the second capacitor electrode (anode) is formed through the opening formed in the insulating film 23. Electrode) 26.

The pn junction capacitance 20a is formed by the pn junction of the p-type semiconductor layer 11 and the n-type semiconductor region 22.

In addition, a conductive layer (for example, polysilicon) 24 is disposed on the insulating film 23 on the surface of the p-type semiconductor layer 11. The polysilicon 24 is covered with the insulating film 23 again, and one end of the polysilicon 24 is in contact with the third capacitor electrode 27 formed thereon. The second capacitor electrode 26 and the third capacitor electrode 27 are connected, and a GND potential is applied. As a result, an insulating capacitor 20b having the insulating film 23 as a dielectric, the first capacitor electrode 25 as a cathode electrode, and the third capacitor electrode 27 as an anode electrode is configured.

By the parallel connection of the pn junction capacitance 20a and the insulation capacitance 20b, the capacitance value can be increased in comparison with the conventional structure (capacity C12 in FIG. 5A and capacitance C22 in FIG. 5B). Can be.

In addition, the insulating capacitor 20b is formed to substantially overlap with the pn junction capacitor 20a formed in the p-type semiconductor layer 11. In other words, the second capacitor 20 has a structure in which the capacitance value is increased by the parallel connection of the pn junction capacitor 20a and the insulating capacitor 20b, and the increase in the occupied area can be prevented.

1 is a circuit diagram illustrating a noise filter of the present embodiment.

Fig. 2 is a circuit diagram illustrating an amplifier circuit with a built-in noise filter of this embodiment.

Fig. 3 is a characteristic diagram illustrating the noise filter of this embodiment.

4 is a cross-sectional view illustrating a second capacitance of the amplifier circuit with a built-in noise filter of this embodiment.

5 is a circuit diagram illustrating a conventional noise filter.

6 is a circuit diagram illustrating an amplifier circuit incorporating a conventional noise filter.

<Explanation of symbols for main parts of the drawings>

10: first dose

11: p-type semiconductor layer

20: second dose

20a: pn junction capacity

20b: insulation capacity

22: n-type semiconductor region

23: insulating film

24: conductive layer

25: first capacitor electrode

26: second capacitor electrode

27: third capacitor electrode

28: GND contact area

30: resistance

100: noise filter

200: amplifier circuit with built-in noise filter

201: Amplifier element (J-FET)

250: ECM

510, 511: noise filter

550 amplified integrated circuit device

C11, C12: Capacity

C21, C22: junction capacity

Vi, Vi ', IN: Input terminal

Vo, Vo ': Output terminal

R: resistance

D1, D2: Diode

Claims (5)

A first capacitor comprising a junction capacitance of a transistor in which two terminals of the three terminals are diode-connected, a second capacitance formed by connecting the pn junction capacitance and the insulation capacitance in parallel; With resistance, The high voltage side of the first capacitor is input, the high voltage side of the second capacitor is output, and the resistor is connected between the first capacitor and the second capacitor, A noise filter comprising a GND connection between the low voltage side of the first capacitor and the second capacitor. A first capacitor comprising a junction capacitance of a transistor in which two terminals of the three terminals are diode-connected, a second capacitor formed by connecting the pn junction capacitance and the insulation capacitance in parallel, and a resistance; The high voltage side of the first capacitor is input, the high voltage side of the second capacitor is output, and the resistor is connected between the first capacitor and the second capacitor, Amplifier element connected to the output of the noise filter which GND-connected the low voltage side of the said 1st capacitor | capacitance and the said 2nd capacitor | capacitance An amplifier circuit with a built-in noise filter, characterized in that it comprises a. One conductive semiconductor layer constituting one chip; A noise filter provided in the one conductive semiconductor layer; An amplifier device provided in the one conductive semiconductor layer, The noise filter includes a first capacitor comprising a junction capacitance of a transistor in which two terminals of the three terminals are diode-connected, a second capacitor formed by connecting a pn junction capacitor and an insulation capacitor in parallel, and a resistance; The noise filter uses the high voltage side of the first capacitor as an input, the high voltage side of the second capacitor as an output, connects the resistor between the first capacitor and the second capacitor, and the first capacitor. And a GND connection of the low voltage side of the second capacitor, And the amplifier element is connected to the output of the noise filter. The method of claim 3, The second capacitor includes a reverse conductive semiconductor region formed on the surface of the one conductive semiconductor layer, an insulating film formed on the one conductive semiconductor layer, and a conductive layer formed on the insulating film. And the pn junction capacitance is formed by the semiconductor semiconductor layer and the reverse conductive semiconductor region, and the insulation capacitance is formed by the reverse conductive semiconductor region, the insulating film, and the conductive layer. The method of claim 4, wherein At least a portion of the pn junction capacitance and the insulation capacitance overlap each other.

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