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DESCRIPTION JP2009225100

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DESCRIPTION JP2009225100
To integrate a capacitor and realize a high ESD withstand voltage. A semiconductor integrated
circuit according to one aspect of the present invention is a semiconductor integrated circuit for
a capacitor and a microphone, and a resistor connected in series between the drain of an output
transistor MN1 and a terminal B. R5, a resistor R6, a terminal C connected to the source of the
output transistor MN1, a capacitor C1 provided between a connection point n4 of the resistors
R5 and R6 and the terminal C, and a capacitor C1 in parallel And a diode D3. [Selected figure]
Figure 1
Semiconductor integrated circuit and capacitor microphone
[0001]
The present invention relates to a semiconductor integrated circuit and a condenser microphone,
and more particularly to a semiconductor integrated circuit mounted on a condenser microphone
and a condenser microphone using the same.
[0002]
In condenser microphones, the component mounting area is reduced as the microphones are
miniaturized.
Therefore, the reduction of mounted components is desired, and the integration of capacitors for
high frequency cutting is desired. However, the integration of the capacitors causes a problem of
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a decrease in the ESD withstand voltage. In general, a withstand voltage of 8 kV is required for
the microphone in an ESD test (IEC 61000-4-2), and it is desired to perform integration while
securing the ESD withstand voltage of the microphone.
[0003]
FIG. 9 shows the configuration of the conventional example described in Patent Document 1. As
shown in FIG. In FIG. 9, a terminal A is a device input terminal, one of which is connected to the
gate of the output transistor MN1 via the resistors R1 and R2, and the other one of which is
connected to the diaphragm C3 of the condenser microphone 2. Terminal B is an output / power
supply terminal sharing the power supply terminal and the output terminal. One of the terminals
B is connected to the drain of the output transistor MN1 and the other is connected to the
terminal E of the condenser microphone 2. The terminal E is connected to the power supply VDD
via the load resistor RL. Further, the terminal E is connected to the output terminal VOUT of the
AC signal.
[0004]
The resistors R1 and R2 and the diodes D1 and D2 in the device are protection circuits, and can
be eliminated if unnecessary. The resistor R3 is a pull-down resistor for determining the input
impedance of the device, and a resistor of several hundreds of MΩ to several tens of GΩ is
usually used. The resistor R4 is a source resistor and is used to adjust the gain. The resistor R4
can be deleted if it is unnecessary.
[0005]
The voltage input to the diaphragm C3 of the condenser microphone 2 is input to the gate of the
output transistor MN1 to amplify the current and then output from the output terminal VOUT.
Thereby, the input signal is amplified and impedance conversion is performed. Capacitors C1 and
C2 are disposed as ground capacitors between the terminal B and the drain of the output
transistor MN1 in order to remove RF noise (800 MHz to 2 GHz). These capacitors C1 and C2
function as a filter function for the RF signal to reduce RF noise.
[0006]
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In the conventional example described in Patent Document 1, miniaturization is realized by
integrating the capacitors C1 and C2. In the conventional example, capacitors 10 pF and 33 pF
are used as the capacitors C1 and C2. However, in general, it is difficult to increase the size of a
capacitance integrated in a semiconductor, and when realizing capacitances of 10 pF and 33 pF,
the size of a chip increases.
[0007]
It is possible to make the chip smaller if it is a capacitive element with a large unit capacitance
like a gate capacitance, but when the unit capacitance is large, it tends to be weak to ESD, and it
is difficult to achieve the required ESD level Become. For this reason, the integration of the
microphone for miniaturization and the ESD resistance are contradictory, and it is difficult to
realize these in the circuit of the conventional example. Registered Utility Model No. 3081106
[0008]
As described above, it is difficult to integrate capacitors to reduce the chip size and to realize a
high ESD withstand voltage.
[0009]
A semiconductor integrated circuit according to an aspect of the present invention is a
semiconductor integrated circuit for a capacitor and a microphone, comprising: a first resistor
and a second resistor serially connected between a drain of an output transistor and an output
terminal; A power supply terminal connected to the source of the output transistor, a first
capacitor provided between a connection point of the first resistor and the second resistor, and
the power supply terminal, and a parallel connection with the first capacitor And a first diode.
Thus, the set of the first capacitor and the first diode is disposed as a part of the protection
circuit between the connection point of the first resistor and the second resistor and the power
supply terminal. Thereby, the high frequency component of the ESD current is discharged
through the first capacitor and the low frequency component is discharged through the first
diode.
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[0010]
Further, the first resistor and the second resistor are disposed to be symmetrical with respect to
the first capacitor and the first diode, respectively. By providing the first resistor on the output
capacitor side of the first capacitor and the first diode, the impedance on the internal circuit side
can be made higher than that of the first capacitor and the first diode, thereby protecting the
internal circuit from ESD current can do. In addition, by providing the second resistor on the
output terminal side of the first capacitor and the first diode, it is possible to increase the time
constant of the entire circuit and to lengthen the ESD discharge time. It is possible to protect
Furthermore, the first resistor, the second resistor, the first capacitor, and the first diode
constitute a T-type low pass filter, which removes the RF noise of the power supply and provides
a low noise, high ESD withstand voltage capacitor microphone Can realize a semiconductor
integrated circuit.
[0011]
According to the present invention, it is possible to propose a semiconductor integrated circuit
and a capacitor microphone which can integrate capacitors and realize a high ESD withstand
voltage.
[0012]
Embodiment 1
A condenser microphone using the semiconductor integrated circuit according to the first
embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. FIG.
1 is a diagram showing the configuration of a semiconductor integrated circuit 10 according to
the present embodiment. FIG. 2 is a diagram showing the configuration of a condenser
microphone 20 using the semiconductor integrated circuit 10 shown in FIG. As shown in FIG. 1,
the semiconductor integrated circuit 10 according to the present embodiment includes an output
transistor MN1, a capacitor C1, diodes D1, D2, D3, and resistors R1, R2, R3, R4, R5, R6.
[0013]
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As shown in FIG. 2, the terminal A which is the input terminal of the semiconductor integrated
circuit 10 is connected to the diaphragm C3 of the condenser microphone 20. Terminal B is
connected to terminal E of condenser microphone 20. In the present embodiment, the terminal B
is a power supply / output terminal sharing the power supply terminal and the output terminal.
The terminal E is connected to the power supply VDD via a load resistor RL. Further, the terminal
E is connected to the output terminal VOUT of the AC signal. The terminal C is connected to the
terminal D of the condenser microphone 20, and the terminal D is connected to the ground
power supply GND. The terminal C is a power supply terminal connected to the ground power
supply GND. Thus, in the present invention, no external component is required other than the
load resistor RL. Therefore, the condenser microphone 20 can be miniaturized.
[0014]
As shown in FIG. 1, resistors R1 and R2 are connected in series between the terminal A of the
semiconductor integrated circuit 10 and the gate of the output transistor MN1. For example, a
field effect transistor (FET) is used as the output transistor MN1. A diode D1 is provided in the
reverse direction between the connection point n1 of the resistor R1 and the resistor R2 and the
terminal C. Further, a diode D2 is provided in the forward direction between a terminal C and a
connection point n2 between the resistor R1 and the resistor R2. The resistors R1 and R2 and the
diodes D1 and D2 are protection circuits, and can be eliminated if not required.
[0015]
A resistor R3 is provided between a terminal C and a connection point n3 between the resistor
R2 and the gate of the output transistor MN1. The resistor R3 is a pull-down resistor for
determining the input impedance of the device, and a resistor of several hundreds of MΩ to
several tens of GΩ is usually used. The source of the output transistor MN1 is connected to the
terminal C via the resistor R4. The resistor R4 is a source resistor and is used to adjust the gain.
The resistor R4 can be deleted if it is unnecessary. The back gate of the output transistor MN1 is
connected to the terminal C.
[0016]
The drain of the output transistor MN1 is connected to the terminal B via the resistors R5 and
R6. The resistors R5 and R6 are connected in series. Diffusion resistors or polysilicon resistors
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can be used as the resistors R5 and R6. A capacitor C1 is provided between a connection point
n4 between the resistor R5 and the resistor R6 and a terminal C connected to the ground power
supply GND. As the capacitor C1, a MOS capacitance, an MIM capacitance, an MIP (metalinsulator-poly) capacitance or the like is used.
[0017]
In addition, a diode D3 is connected in the reverse direction between a connection point n5
between the resistor R5 and the resistor R6 and a terminal C connected to the ground power
supply GND. That is, the diode D3 is connected in parallel to the capacitor C1. A PN junction
diode or P-MOS or N-MOS can be used as the diode D3.
[0018]
The voltage input to the diaphragm C3 of the condenser microphone 20 is input to the gate of
the output transistor MN1, and after current amplification, is output from the output terminal
VOUT. Thereby, the input signal can be amplified and impedance conversion can be performed.
[0019]
In the semiconductor integrated circuit 10 according to the first embodiment, as a part of the
ESD protection circuit, a set of the capacitor C1 and the diode D3 is a terminal C connected to the
connection point of the resistor R5 and the resistor R6 and the ground power supply GND. It is
provided between. Thereby, the high frequency component of the ESD current flows through the
capacitor C1, and the low frequency component flows through the diode D3 to the ground power
supply GND.
[0020]
Further, in the semiconductor integrated circuit 10, the resistors R5 and R6 are disposed so as to
be symmetrical with respect to the capacitor C1 and the diode D3, respectively. That is, the
resistor R5 is disposed on the side of the output transistor MN1 of the connection point n4 to
which the capacitor C1 is connected, and the resistor R6 is disposed on the terminal B side of the
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connection point n5 to which the diode D3 is connected.
[0021]
By providing the resistor R5 on the side of the output transistor MN1 of the connection point n4,
the impedance on the internal circuit side can be made higher than that of the capacitor and the
diode. This can protect the internal circuit from the ESD current. Further, by providing the
resistor R6 on the side of the terminal B connected to the power supply VDD at the connection
point n5, the time constant of the pulse current of ESD can be increased, and the discharge time
can be extended. As a result, it is possible to prevent the destruction of the capacitor C1 and the
diode D3 due to the over current.
[0022]
Furthermore, these two resistors R5 and R6, the capacitor C1, and the diode D3 also function as
a T-type low pass filter. Therefore, signals of 800 MHz to 2 GHz can be attenuated relatively
easily, and RF noise (800 MHz to 2 GHz) of the power supply VDD can be removed. On the other
hand, no deterioration occurs to the signal of -20 kHz which is an audio signal. As a result, a low
noise, high ESD withstand capacitor microphone 20 can be realized.
[0023]
Here, a simulation using the circuit according to the present embodiment shown in FIG. 3 will be
described. As shown in FIG. 3, simulation of the ESD withstand voltage for a circuit using a diode
with a resistor R5 = R6 = 150Ω, a capacitor C1 = 20pF, a diode D3 with a breakdown voltage of
8V and an ON resistance of 0.2Ω at break is shown. went. Here, in the ESD test IEC 61000-4-2,
the drain voltage (Vdrain) applied to the drain terminal at 8 kV was simulated. In addition, as a
load resistance, 1 MΩ which is sufficiently large as compared to the output resistance used for
the capacitor microphone is used as the output resistance.
[0024]
The simulation results are shown in FIG. As a comparison, the same simulation was performed
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for the circuit of only the capacitor of the conventional example. As shown in FIG. 4, it can be
seen that the peak voltage is about 1.7 kV in the circuit consisting only of the conventional
capacitor, and this voltage is applied to the drain end and the capacitor end. From this, it can be
easily estimated that the ESD withstand voltage is low in the conventional circuit.
[0025]
On the other hand, in the circuit according to the first embodiment, the peak voltage is 12 V, and
the voltage applied to the drain end and the capacitor end is significantly reduced. This greatly
improves the ESD characteristics. The peak current is determined by the breakdown voltage of
the diode and the parasitic resistance, and the peak voltage applied to the drain end and the
capacitor end can be further reduced by designing these values small.
[0026]
Further, FIG. 5 shows a simulation result of the high frequency pass characteristics. As shown in
FIG. 5, in the conventional example, -8 dB at 800 MHz and -17 dB at 2 GHz. On the other hand, in
the circuit according to the first embodiment, it is -33 dB at 800 MHz and -40 dB at 2 GHz, which
is effective for removing high frequency noise.
[0027]
In the conventional circuit, the incorporation of a capacitor for reducing RF noise causes an
increase in chip area and a deterioration in the ESD withstand voltage, which is difficult to
realize. However, by using the semiconductor integrated circuit 10 according to the present
invention, it is possible to reduce RF noise while maintaining a high ESD withstand voltage, and it
is possible to integrate parts that have conventionally been externally attached. is there.
[0028]
Second Embodiment A semiconductor integrated circuit 11 according to a second embodiment of
the present invention will be described with reference to FIG. FIG. 6 is a diagram showing the
configuration of the semiconductor integrated circuit 11 according to the present embodiment.
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In FIG. 6, the same components as in FIG. 1 are assigned the same reference numerals and
descriptions thereof will be omitted as appropriate.
[0029]
As shown in FIG. 6, in the semiconductor integrated circuit 11 according to the present
embodiment, the drain of the output transistor MN1 is connected to the terminal B via the
resistors R5, R6, and R7. The resistors R5, R6 and R7 are connected in series. A capacitor C1 is
provided between a terminal C and a connection point n4 between the resistors R5 and R6.
Further, between the connection point n5 between the resistor R5 and the resistor R6 and the
terminal C, a diode D3 is connected in the reverse direction. That is, the diode D3 is connected in
parallel to the capacitor C1.
[0030]
A capacitor C2 is provided between a terminal C and a connection point n6 between the resistor
R6 and the resistor R7. Further, between the connection point n8 between the resistor R6 and
the resistor R7 and the terminal C, a diode D4 is connected in the reverse direction. That is, the
diode D4 is connected in parallel with the capacitor C2. As shown in FIG. 2, the terminal C is
connected to the ground power supply GND via the terminal D of the condenser microphone 20.
[0031]
As described above, in the semiconductor integrated circuit 10 according to the second
embodiment, a set of the capacitor C1 and the diode D3 as a part of the ESD protection circuit is
a terminal connected to the connection point of the resistor R5 and the resistor R6 and the
ground power supply GND. It is provided between C and C. Furthermore, a set of the capacitor C2
and the diode D4 is provided between the connection point of the resistor R6 and the resistor R7
and the terminal C connected to the ground power supply GND. As described above, the twostage set of the capacitor and the diode can improve the pass characteristic of the RF noise.
[0032]
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FIG. 7 shows a simulation result of high frequency pass characteristics when the circuit
according to the present embodiment is used. As shown in FIG. 7, in the conventional example, -8
dB at 800 MHz and -17 dB at 2 GHz. On the other hand, the circuit according to the second
embodiment has -52 dB at 800 MHz and -72 dB at 2 GHz, which makes it possible to further
remove high frequency noise.
[0033]
Further, by forming the set of the capacitor and the diode in two stages, the peak voltage due to
the ESD can be reduced to 8 V which is substantially equivalent to the breakdown voltage of the
diodes D3 and D4, and the ESD protection capability can be further improved. From the above
results, high ESD withstand voltage and low RF noise can be realized.
[0034]
Third Embodiment A semiconductor integrated circuit 12 according to a third embodiment of the
present invention will be described with reference to FIG. FIG. 8 is a diagram showing the
configuration of the semiconductor integrated circuit 12 according to the present embodiment.
In FIG. 8, the same components as in FIG. 1 will be assigned the same reference numerals and
descriptions thereof will be omitted as appropriate.
[0035]
As shown in FIG. 8, in the semiconductor integrated circuit 12 according to the present
embodiment, the resistor R5 shown in FIG. 1 is replaced with an inductance L1. Thus, even when
the inductance L1 is provided between the gate of the output transistor MN1 and the connection
point n4, the same effect as that of the first embodiment can be expected. For example, a spiral
inductor can be used as the inductance L1. The inductance L1 increases the wiring resistance,
and is designed to have the same resistance as the resistance R5. Since the inductance L1 works
as a metal resistance, the impedance can be increased by the same principle as the resistance R5,
and the internal circuit can be protected from the ESD current.
[0036]
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In addition, since the inductance L1 has a low Q value for high frequency components of noise, it
causes dielectric loss. As a result, it is possible to remove RF noise and realize a low noise
condenser microphone in order to deteriorate the pass characteristic at 800 MHz to 2 GHz.
[0037]
As described above, according to the present invention, in a semiconductor integrated circuit for
a capacitor and a microphone, a capacitor can be incorporated to realize miniaturization of the
capacitor and the microphone, and to realize a high ESD withstand voltage. it can.
[0038]
FIG. 1 is a diagram showing a configuration of a semiconductor integrated circuit according to a
first embodiment.
FIG. 1 is a diagram showing a configuration of a condenser microphone using a semiconductor
integrated circuit according to a first embodiment. It is a figure which shows the structure of the
semiconductor integrated circuit which implemented the ESD simulation. It is a graph which
shows the simulation result of ESD of the semiconductor integrated circuit shown in FIG. It is a
graph which shows the simulation result of the high frequency pass characteristic of the
semiconductor integrated circuit shown in FIG. FIG. 7 is a diagram showing a configuration of a
semiconductor integrated circuit according to a second embodiment. 15 is a graph showing
simulation results of high frequency pass characteristics of the semiconductor integrated circuit
according to the second embodiment. FIG. 7 is a diagram showing a configuration of a
semiconductor integrated circuit according to a third embodiment. It is a figure which shows the
structure of the conventional condenser microphone.
Explanation of sign
[0039]
10, 11, 12 semiconductor integrated circuit 20 capacitor microphone C1, C2 capacitor R1, R2,
R3, R4, R5, R6 resistance D1, D2, D3, D4 diode MN1 output transistor RL load resistance L1
inductance
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