JP2001127663A - Static electricity protection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a static electricity protection circuit that can protect a circuit network in a circuit module from static electricity without affecting adversely miniaturization and weight reduction of a mobile communication unit. SOLUTION: In an antenna switch 20 to which the static electricity protection circuit 20 is applied, the static electricity protection circuit 20a built in the antenna switch 20 comprises a capacitor C0 that is connected between an antenna terminal ANT, to which an antenna is electrically connected, and an input output terminal J of a switch circuit 20b and of an inductor L0 connected between the antenna terminal of the capacitor C0 and a case grounding FG. The inductor L0 and the capacitor C0 block intrusion of AC and DC components of at least a frequency lower than a communication frequency of the mobile phone. Since the static electricity intruding from the antenna escapes to the case grounding FG at the pre-stage of the switch circuit 20b, the static electricity can be blocked against the switch circuit 20b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic protection circuit for protecting a circuit module connected to an antenna of a mobile communication device, for example, a portable telephone, a simplified portable telephone or the like from static electricity.

[0002]

2. Description of the Related Art In recent years, mobile communication devices typified by portable telephones and simplified portable telephones (so-called PHS) have been remarkably reduced in size and size, and many of them do not feel uncomfortable even when they are carried in pockets such as clothes. It has been improved. For this reason, the style of carrying a mobile phone or the like in a clothes pocket or handbag has become a common practice for its users. I can see it often.

[0003] By the way, static electricity tends to be generated when synthetic fibers are combined with a dry atmosphere. Therefore, especially when clothes and the like rub against each other in the season when the air is easy to dry (autumn and winter) or when getting off the car seat. It is known from everyday experience that static electricity occurs in such as. Since the voltage of the static electricity generated in such a case reaches as much as ten and several kV, if the static electricity jumps directly into an antenna of a mobile phone or the like put in a pocket of clothes or the like, it may lead to a failure cause of the mobile phone or the like. . That is, the static electricity that has entered the mobile phone or the like from the antenna can degrade the performance of the internal circuit module.

To solve such a problem, there is an electrostatic protection circuit disclosed in Japanese Patent Application Laid-Open No. Hei 6-112850. In this static electricity protection circuit, a (1/4) wavelength resonator of the operating frequency is inserted between the antenna and the circuit module (transmission high-frequency amplifier circuit),
The (1/4) wavelength resonator has almost infinite impedance for the signal of the operating frequency and does not affect the circuit module. Even if a high voltage due to static electricity is applied, the charge flows through the (1/4) wavelength resonator to the ground side, thereby preventing damage to the circuit module.

[0005]

However, according to the electrostatic protection circuit disclosed in Japanese Patent Application Laid-Open No. Hei 6-112850, the (1/4) wavelength resonator uses a lossless distributed constant line (for example, a microstrip line). ) And a variable capacitor connected in parallel thereto. For this reason, it is necessary to secure a space for providing a (1/4) wavelength resonator composed of these components. There is a problem that hinders the conversion.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a circuit in a circuit module with static electricity without hindering reduction in size and weight of a mobile communication device. It is an object of the present invention to provide an electrostatic protection circuit capable of protecting from a static electricity.

[0007]

According to a first aspect of the present invention, there is provided an electrostatic protection circuit for protecting a circuit network in a circuit module connected to an antenna of a mobile communication device from static electricity. A capacitor connected between an antenna connection side where the antenna is connected to the circuit module and a signal input / output terminal to which a communication signal is input or output to the circuit network, and a capacitor built in the circuit module; An inductor that is connected between one end of the capacitor connected to the antenna connection side and ground and that is built in the circuit module, and that the inductor and the capacitor reduce a communication frequency of the mobile communication device. It is also a technical feature that at least a low frequency AC component and a DC component are blocked from passing.

Further, in the electrostatic protection circuit according to a second aspect, in the first aspect, the ground is technically characterized in that the ground is insulated DC from the ground of the circuit network.

Further, in the electrostatic protection circuit according to the third aspect,
A technical feature according to claim 1 or 2, wherein the inductor and the capacitor constitute at least a part of a bandpass filter that allows a communication signal of the mobile communication device to pass.

Further, in the electrostatic protection circuit according to a fourth aspect, the circuit module according to any one of the first to third aspects, wherein the circuit module is formed of a multilayer substrate, and at least one of the inductor and the capacitor is connected to the multilayer substrate. It is a technical feature that it is constituted by a laminated structure using a substrate.

According to the first aspect of the present invention, a capacitor connected between an antenna connection side of a circuit module connected to an antenna of a mobile communication device and a signal input / output terminal of a circuit network in the circuit module; An inductor connected between one end of the capacitor on the antenna connection side and the ground is incorporated in the circuit module, and the inductor and the capacitor allow the AC component and the DC having a frequency lower than the communication frequency of the mobile communication device to be at least lower. Block the passage of components. That is, a high-pass filter that blocks the passage of the AC component and the DC component at least lower than the communication frequency by the inductor and the capacitor built in the circuit module is configured. As a result, even if static electricity enters the circuit module from the antenna, the DC component of the static electricity and the AC component having a frequency lower than the communication frequency are reduced.
The inductor allows the circuit module to escape to the ground side, and the capacitor prevents the circuit module from entering the circuit network side.

According to the second aspect of the present invention, since the ground to which the inductor is connected is insulated in a DC manner from the ground of the circuit network, the DC component of the static electricity escaping through the inductor and the AC having a lower frequency than the communication frequency. Components can be prevented from wrapping around the network through the ground of the network.

According to the third aspect of the present invention, since the inductor and the capacitor incorporated in the circuit module constitute at least a part of the band-pass filter that allows the communication signal of the mobile communication device to pass, the band-pass filter is provided. Accordingly, it is possible to prevent the passage of the AC component having a frequency higher than the communication frequency.

According to the fourth aspect of the present invention, at least one of the inductor and the capacitor incorporated in the circuit module is constituted by a laminated structure of a multilayer substrate constituting the circuit module. Therefore, these inductors and capacitors are added. This can suppress an increase in the size of the circuit module itself.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment in which the electrostatic protection circuit of the present invention is applied to an antenna switch of a portable telephone will be described below with reference to FIGS. First, the configuration of a mobile phone to which the antenna switch 20 is applied will be described with reference to FIG. The mobile phone illustrated in FIG. 2 uses a communication frequency band of 880 to 915 MHz, and its wireless unit mainly includes a transmitting unit 60, a receiving unit 70, an antenna 80, an antenna switch 20, and the like. Although not shown in FIG. 2, in addition to the wireless unit, the mobile phone includes a control unit composed of a digital circuit centered on a microcomputer, a power supply unit composed of a secondary battery, a power supply circuit, and the like. Having.

The transmitting section 60 has a radio transmission frequency (880-800).
A voltage-controlled oscillator (hereinafter referred to as “transmission VCO”) 62 capable of generating a high frequency of 915 MHz band),
A mixer 63 for mixing and outputting a high-frequency signal generated from the CO 62 and a source signal input from a modulator or the like, a transmission amplifier 66 for amplifying the power of the mixer output, and a transmission amplifier 66
A low-pass filter (hereinafter referred to as “LP”) that removes a frequency component higher than the radio transmission frequency (915 MHz band) from the output of
F ". ) 68 and a balun 64 for performing balanced / unbalanced input / output conversion with respect to a transmission amplifier 66 having input / output balanced lines. The high-frequency signal output from the transmission unit 60 is distributed to the antenna 80 via the antenna switch 20 and is radiated from the antenna 80 to space.

The receiving section 70 receives a high-frequency signal received by the antenna 80 via the antenna switch 20, and allows a band-pass filter (hereinafter, referred to as "BPF") 71 that allows passage of necessary frequency components, and outputs an output signal of the BPF 71. A receiving amplifier 73 for amplifying, a voltage-controlled oscillator (hereinafter referred to as “receiving VCO”) 76 capable of generating a high frequency shifted from the output of the receiving amplifier 73 by a predetermined frequency from a wireless receiving frequency (925-960 MHz band), and 76. High frequency signal generated from receiving VCO 76 and receiving amplifier 7
And a balun 7 for performing balanced / unbalanced input / output conversion with respect to the mixer 78 for mixing a signal wave of a predetermined frequency to the demodulator by mixing with the output of the mixer 3
4 The signal wave converted to a predetermined frequency by the receiving unit 70 is input to a demodulator or the like and demodulated into a voice band signal, a digital signal, or the like.

As described above, the antenna switch 20 including the electrostatic protection circuit according to the present embodiment sends the high-frequency signal received by the antenna 80 to the receiving unit 70 without giving it to the transmitting unit 60 side, Without giving the high frequency signal transmitted by 60 to the receiving unit 70 side,
It has a function of distributing high-frequency signals passing through a transmission path, which is sent to the antenna 80 and radiated into the air.

Next, the configuration of the antenna switch 20 is shown in FIG.
This will be described with reference to FIGS. As shown in FIG.
The antenna switch 20 includes an electrostatic protection circuit 20a and a switch circuit 20b. The electrostatic protection circuit 20a includes a capacitor C0 connected between an antenna terminal ANT (antenna connection side) to which the antenna 80 is electrically connected and the input / output terminal J of the switch circuit 20b, and an antenna terminal ANT of the capacitor C0. And an inductor L0 connected between one end and the housing ground FG, and discharges static electricity invading from the antenna 80 side to the housing ground FG side in front of the switch circuit 20b as a circuit network. And attempts to prevent it from entering the switch circuit 20b.

That is, since it is known that most of the frequency component of static electricity is a DC component or an AC component having a relatively low frequency, a high-pass filter (hereinafter "HPF") is formed by the inductor L0 and the capacitor C0. ) Prevents static electricity from penetrating into the subsequent switch circuit 20b. Here, the inductor L0 is connected to the antenna 8 more than the capacitor C0.
By locating on the 0 side, a configuration is adopted in which static electricity that has entered from the antenna 80 side is released to the housing ground FG side on the antenna 80 side from the capacitor C0. As a result, compared with the HPF in which the capacitor C0 is located closer to the antenna 80 than the inductor L0, no static energy is stored in the capacitor C0, and thus the destruction of the capacitor C0 due to static electricity can be prevented. The housing ground FG is connected to a ground of a switch circuit 20b to be described later.
That is, it is DC-insulated from the signal ground SG. As a result, the static electricity that escaped through the inductor L0 is transferred to the switch circuit 20 via the housing ground FG of the static electricity protection circuit 20a.
It can be prevented from going around to the b side. Therefore, there is also an effect that the switch circuit 20b in the antenna switch 20 can be more reliably protected from static electricity.

The frequency fCL at which the attenuation by the HPF composed of the inductor L0 and the capacitor C0 reaches 3 dB (hereinafter referred to as "low-frequency cutoff frequency") is, for example, 90 when the communication frequency of the portable telephone is 915 MHz.
It is set to around MHz (see FIG. 10A). By setting the low-frequency cutoff frequency fCL by the HPF to less than half or less than 1/10 of the communication frequency, the HPF, that is, the static electricity protection circuit 2 is designed at the time of design or product trial production.
If the low cutoff frequency fCL of 0a is set, it is not necessary to individually adjust the frequency during mass production of the product. As a result, it is not necessary to use a component having an adjustable mechanism, for example, a variable capacitor for the capacitor C0, so that it is possible to prevent the antenna switch 20 from being enlarged by the electrostatic protection circuit 20a and to prevent an increase in the number of adjustment points.
Therefore, the switch circuit 2 can be used without hindering the reduction in size and weight of the mobile phone and without increasing the number of adjustment steps.
0b can be protected from static electricity.

As shown in FIG. 1, the switch circuit 20b
Is composed of circuit elements of coupling capacitors C1, C3, C4, a bypass capacitor C2, a choke coil L1, an inductor L2, and high-frequency switching diodes D1, D2. That is, the terminal T connected to the transmitting unit 70
As for the transmission path between X and the terminal J connected to the electrostatic protection circuit 20a, the coupling capacitor C1 connected to the terminal TX can be obtained by applying a control voltage to the terminal VCNT.
To the coupling capacitor C3 connected to the terminal J are AC-established via the high-frequency switching diode D1, and the high-frequency switching diode D2 side of the inductor L2 connected to the coupling capacitor C3 has a low impedance also in the AC. Thus, the circuit elements of the coupling capacitors C1 and C3, the inductor L2, and the high-frequency switching diodes D1 and D2 are connected. On the other hand, regarding the transmission path between the terminal RX connected to the receiving unit 60 and the terminal J connected to the electrostatic protection circuit 20a, the terminal V
When the control voltage applied to the CNT is cut off, the high frequency switching diode D2 side of the inductor L2 connected to the coupling capacitor C3 has a high impedance, so that the coupling capacitor C3 is connected to the terminal RX via the inductor L2. The coupling capacitors C1, C3, C4, the inductor L2, the high-frequency switching diode are connected so that the coupling capacitor C4 is established in an AC manner and the transmission path from the coupling capacitor C1 to the coupling capacitor C3 is cut off by the high-frequency switching diode D1. The circuit elements D1 and D2 are connected. The choke coil L1 is an inductor for preventing a high-frequency signal from flowing into the terminal VCNT, and the bypass capacitor C2 is a capacitor for releasing the high-frequency signal that has jumped to the terminal VCNT to the signal ground SG.

By configuring the switch circuit 20b in this way, when a control voltage is applied to the terminal VCNT,
When a forward voltage is applied to the high-frequency switching diodes D1 and D2 via the choke coil L1, a transmission path from the terminal TX to the coupling capacitor C1, the high-frequency switching diode D1 and the coupling capacitor C3 is AC-established. One end of the inductor L2 on the side of the high-frequency switching diode D2 is also connected to the signal ground SG in an AC manner.
The high frequency signal of 0 is radiated to the space from the antenna 80 connected to the antenna terminal ANT via the coupling capacitor C3 and the electrostatic protection circuit 20a without being guided to the terminal RX side.

On the other hand, when the control voltage applied to the terminal VCNT is cut off, the forward voltage of the high-frequency switching diodes D1 and D2 applied via the choke coil L1 is cut off. Since the transmission path to the capacitor C1, the high-frequency switching diode D1, and the coupling capacitor C3 is cut off in an AC manner, and one end of the inductor L2 on the high-frequency switching diode D2 side has a high impedance, the received signal input from the terminal J is Is transmitted to the receiving unit 60 connected to the terminal RX via the coupling capacitor C3, the inductor L2 and the coupling capacitor C4 without being guided to the terminal TX side.

Accordingly, the high-frequency switching diodes D1 and D1 for establishing or blocking the transmission path from the terminal TX to the terminal J and the transmission path from the terminal J to the terminal RX.
2 is essential for the switch circuit 20b, and the high-frequency switching diodes D1 and D2 are made of semiconductor.
Therefore, it is extremely weak to a high voltage of more than ten kV due to static electricity, and application of static electricity often leads to deterioration of reverse characteristics and destruction of the element itself. Therefore, by disposing the above-described static electricity protection circuit 20a at a stage before the antenna terminal ANT of the switch circuit 20b, static electricity jumping from the antenna 80 of the mobile phone can be transmitted to the antenna terminal AN.
Even if the antenna switch 20 enters the antenna switch 20 via the T, the DC component of the static electricity and the AC component of a predetermined frequency or less are converted into the housing ground FG by the inductor L0 of the static electricity protection circuit 20a.
And the capacitor C0 can prevent intrusion into the switch circuit 20b. Therefore, in the present embodiment, there is an effect that the switch circuit 20b in the antenna switch 20 can be protected from static electricity without hindering reduction in size and weight of the mobile phone.

Here, an example in which the antenna switch 20 is mounted on a multilayer substrate will be described with reference to FIGS. FIG.
As shown in FIG. 1, the antenna switch 20 has, for example, a 14-layer glass ceramic substrate (hereinafter, referred to as “substrate”) 2.
2, 23, 24, 25, 26, 27, 28, 29, 3,
It has a ceramic laminated structure in which 0, 31, 32, 33, 34 and 35 are laminated, and is formed, for example, by laminating dielectric ceramic sheets and sintering them at a low temperature. FIGS. 4 and 5 show a state where the laminated structure is developed.

As shown in FIGS. 4 and 5, the substrate constituting the antenna switch 20 includes capacitors C1, C3,
The wiring pattern 22a, the ground pattern 22b, and the like are arranged in this order from the surface on which components such as C4 and inductors L0 and L1 are mounted.
The substrate 22 forming the substrate 22c is located under the substrate 22.
Via holes 41, 42, 43, 44, 45, 4 from
Substrate 2 for forming 6, 47, 48, 49, 50, 51
3 and 24 are respectively located. A substrate 25 for forming a solid earth pattern 25a is located below the substrate 24, and via holes 41, 42, 43, 44, 45, 46, 47, 4 from the substrates 22, 23, 24, 25 are located thereunder.
The substrate 26 on which the patterns 8, 49 and 51 are formed, and the substrates 27 and 28 on which the patterns 27a and 28a of the inductor L2 are formed, respectively, are located. And the substrate 2
8, substrates 22, 23, 24, 25, 26, 27, 2
Via holes 41, 42, 43, 44, 45 from 8,
Substrates 29, 30, 31, 32 forming 46, 47, 48, 49, 51, 52, 53, etc .;
Substrate 3 on which an electrode pattern 33a and a solid earth pattern 34a also serving as a counter electrode thereof are formed.
3 and 34 are located respectively, and the substrate 35 is located at the lowermost layer. The substrates 22, 23, 24, 25, 26, 27,
Via holes 41, 42, 43, 44, 45 formed in 28, 29, 30, 31, 32, 33, 34, 35,
46, 47, 48, 49, 50, 51, 52 and 53 are indicated by black circles and broken lines in FIGS.

Since it is necessary to mount the antenna switch 20 on the substrate constituting the mobile phone, the electrodes 35a, 35b, 35c, 35d, 35
e, 35f, 35g, 35h, 35i, and 35j are provided, and the shape around the plane is formed to be uneven. The electrode section 35a is connected to the terminal TX, the electrode sections 35b and 35.
d, 35f, 35h, 35i, 35j are signal ground SG or housing ground FG, electrode 35c is terminal RX, electrode 3
5e is a terminal VCNT, and the electrode portion 35g is an antenna terminal ANT.
Corresponding to each. The planar shapes of the substrates 32, 33, and 34 are adapted to the planar shape of the substrate 35, so that the internal wirings 23a, 30a, 32a, 32c, 32d, 32f, and 32f connected to these electrode portions 35a to 35j.
32g, 32h, 32i, 32j, etc. are possible.

As shown in FIGS. 4 and 5, the inductor L2 and the capacitor C2 are formed in a multilayer structure with a multi-layer substrate, but the inductor L0 and the capacitor C0 also have the inductor L2 and the capacitor C2.
In the same manner as described above, it may be configured by laminating with a multilayer substrate. As a result, the size of the antenna switch 20 itself due to the addition of the inductor L0 and the capacitor C0 can be suppressed. Therefore, there is an effect that the switch circuit 20b can be protected from static electricity without hindering reduction in size and weight of the mobile phone. Further, since the laminated structure of the antenna switch 20 is a glass ceramic substrate formed by firing at a low temperature, it can be fired at a relatively low temperature. This makes it possible to use silver, copper, or the like having a low conductor resistance for the pattern. Therefore, there is no need to use palladium, tungsten, or the like that has low conductor resistance and can withstand high temperatures, and thus has the effect of reducing the manufacturing cost of the antenna switch 20.

Next, a description will be given of the measurement results when static electricity is applied to the antenna terminal ANT of the antenna switch 20 by the static electricity tester with reference to FIGS. 1 and 6 to 8. As shown in FIG. 6, the application of static electricity to the antenna switch 20 is performed by a measurement system 100 that complies with IEC1000-4-2: 1995 (published in the basic EMC publication of electrostatic discharge immunity test). That is, the plane 102 is connected to the ground plane 101 connected to the ground G via the 1 MΩ resistor 103, the jig 110 having the antenna switch 20 mounted thereon is placed on the plane 102, and the input terminal 110 a is connected to the input terminal 110 a. ± 16k with electrostatic gun 105
V static electricity is applied a predetermined number of times. Plane 1
02 is equivalent to the housing ground FG of the mobile phone,
Is equivalent to a human body. The antenna terminal ANT of the antenna switch 20 attached to the jig 110
Is connected to the input terminal 110a of the jig 110 and the terminal T
X or the terminal RX is connected to the output terminal 110 b of the jig 110.

First, a voltage leaked to the terminal TX or the terminal RX when static electricity was applied to the antenna terminal ANT of the antenna switch 20 was measured. That is, the measurement system 100
In the above, aerial discharge by static electricity of ± 16 kV was performed about 30 times between the tip of the input terminal 110a of the jig 110 and the electrostatic gun 105, and the voltage leaked from the output terminal 110b at that time was measured by an oscilloscope or the like ( The number of samples is 28).

As a result, the average value of the voltage leaking from the terminal TX or the terminal RX is 128 V in the case where the static electricity protection circuit 20a is provided,
It was found that the voltage was 288 V for those having no. Accordingly, in the antenna switch 20 including the static electricity protection circuit 20a, a part of the static electricity that has entered the antenna terminal ANT can be released to the housing ground FG side by the static electricity protection circuit 20a. Was confirmed to be less than 150 V which is a minimum voltage at which a general semiconductor can be damaged by static electricity. On the other hand, when the static electricity protection circuit 20a is not provided, since the voltage is 288 V, a semiconductor such as a high-frequency switching diode in an antenna switch or a semiconductor in another circuit module that can be connected to a stage subsequent to the terminal TX or the terminal RX is used. It was also found that it could be destroyed by static electricity.

Further, as shown in FIGS. 7 and 8, it was confirmed how the application of such static electricity affects the passing characteristics of the antenna switch 20. That is, the measurement was performed with a spectrum analyzer centering on the insertion loss of 900 MHz of the antenna switch 20 and the like before and after the application of the static electricity. In FIGS. 7 and 8, (A) shows a state before applying static electricity, and FIG. 8 (B) shows a state after applying static electricity. The measurement range is 800 MHz to 1000 MHz. As can be seen from FIGS. 7A and 7B, in the antenna switch 20 including the static electricity protection circuit 20a, the insertion loss does not change before and after the application of static electricity. On the other hand, from FIGS. 8A and 8B, it can be seen from FIG. 8A that the antenna switch without the static electricity protection circuit 20a has 0.2% more static electricity after applying static electricity than before applying static electricity.
It can be seen that the insertion loss is increased by about 6 dB. This is presumed to be due to the fact that the static electricity applied from the antenna terminal ANT caused the destruction of the high-frequency switching diode in the antenna switch or the deterioration of the reverse characteristics in the case where the static electricity protection circuit 20a was not provided as described above. . Accordingly, in the antenna switch 20 including the static electricity protection circuit 20a, the static electricity protection circuit 20
It was confirmed that a protected the high-frequency switching diodes D1 and D2 in the antenna switch 20.

Next, a modification of the static electricity protection circuit 20a constituting the antenna switch 20 will be described with reference to FIG. 9, and the frequency distribution characteristics of the static electricity signal level when static electricity is applied to the static electricity protection circuit 20a 500 times will be described with reference to FIG. ~
This will be described with reference to FIG. As shown in FIG. 9, as a modification of the static electricity protection circuit 20a, the static electricity protection circuit 20a
The static electricity protection circuit 40a in which the inductor L0 and the capacitor C0 constitute at least a part of the BPF that allows the communication frequency of the mobile phone to pass therethrough. That is, the inductor L21 and the capacitor C20 constituting the static electricity protection circuit 40a correspond to the inductor L0 and the capacitor C0 constituting the static electricity protection circuit 20a, respectively, to form an HPF, and the capacitors C21, C
23. A BPF is formed as a whole by adding an LPF formed by the inductor L20. As a result, the BPF can also prevent the passage of an AC component having a frequency higher than the communication frequency. Therefore, there is an effect that the switch circuit 20b in the antenna switch 20 can be protected from static electricity having an AC component having a frequency higher than the communication frequency without hindering reduction in size and weight of the mobile phone.

For example, when the communication frequency of the portable telephone is 915 MHz, the low cutoff frequency fCL of the BPF by the electrostatic protection circuit 40a is set to about 90 MHz, and the frequency at which the attenuation by the LPF reaches 3 dB (hereinafter referred to as "high band"). FCH is set to about 1.3 GHz (see FIG. 10B). By setting the low-frequency cutoff frequency fCL and the high-frequency cutoff frequency fCH by the BPF with a margin more than the communication frequency bandwidth, the low-frequency cutoff frequency fCL and the high-frequency If the cutoff frequency fCH is set, it is not necessary to individually adjust the frequency during mass production of the product.
This eliminates the need to use a component having an adjustable mechanism, such as a variable capacitor, for the capacitors C20, C21, and C23, and thus suppresses the enlargement of the antenna switch 40 due to the static electricity protection circuit 40a, similarly to the static electricity protection circuit 20a. In addition, it is possible to prevent an increase in the number of adjustment points.

The static electricity protection circuit 40 thus configured
In order to compare the static electricity blocking capability of the static electricity protection circuit 20a with the static electricity protection circuit 20a, the static electricity protection circuits 20a and 40a are charged with 500 static electricity.
The frequency distribution characteristic of the static signal level when the voltage was applied once was measured. This measurement is performed by a spectrum analyzer via a 40 dB attenuator.
a is connected to the antenna terminal ANT of the static electricity protection circuit 20a or 40a, and air discharge due to static electricity of +3 kV is applied to the antenna terminal ANT.
The results are shown in FIGS. 11 and 12, which are stored and recorded by a spectrum analyzer. In both figures, (B) shows the static electricity protection circuit 20.
a or aerial discharge directly by +3 kV static electricity without passing through the static electricity protection circuit 40a.

The measurement results shown in FIG. 11A are the frequency distribution characteristics of the static electricity signal level when static electricity is applied to the static electricity protection circuit 20a alone. This and FIG. 11 (B)
And 0 Hz, that is, DC component and several hundred Hz
In addition to the fact that the AC component of
It can be seen that the AC component up to about 0 MHz is attenuated by about 10 dB. That is, H by the static electricity protection circuit 20a
It was also confirmed in this measurement that the effect of PF appeared. The measurement results shown in FIG. 12A are the frequency distribution characteristics of the static signal level when static electricity is applied to the static electricity protection circuit 40a alone. This and FIG.
11B, the DC component and the AC component of several hundred Hz are attenuated by about 40 dB, as in the result obtained by the electrostatic protection circuit 20a (FIG. 11A). Further, according to the static electricity protection circuit 40a, it can be seen that the AC component having a frequency from 2 MHz to 300 MHz is attenuated as compared with the result of the static electricity protection circuit 20a (FIG. 11A). This indicates that the BPF formed by the static electricity protection circuit 40a has a larger insertion loss than the HPF formed by the static electricity protection circuit 20a, and it has been confirmed that the passage of static electricity can be prevented accordingly.

As described above, according to the antenna switch 20 to which the static electricity protection circuit 20a according to the present embodiment is applied, the static electricity protection circuit 20a built in the antenna switch 20 includes the antenna to which the antenna 80 is electrically connected. Terminal ANT (antenna connection side) and switch circuit 20
b connected to the input / output terminal J
And an inductor L0 connected between one end of the capacitor C0 and the antenna ground FG on the antenna terminal ANT side.
And the inductor L0 and the capacitor C0 prevent passage of AC and DC components at least lower than the communication frequency of the mobile phone. Thus, static electricity that has entered from the antenna 80 side can escape to the case grounding FG side before the switch circuit 20b, so that there is an effect that static electricity that enters the switch circuit 20b can be prevented.

[0039]

According to the first aspect of the present invention, a capacitor connected between an antenna connection side of a circuit module connected to an antenna of a mobile communication device and a signal input / output terminal of a circuit network in the circuit module is provided. An inductor connected between one end of this capacitor on the antenna connection side and the ground is incorporated in the circuit module, and the inductor and the capacitor allow an AC component having a frequency at least lower than the communication frequency of the mobile communication device. And block the passage of DC components. That is, a high-pass filter that blocks the passage of the AC component and the DC component at least lower than the communication frequency by the inductor and the capacitor built in the circuit module is configured. As a result, even if static electricity enters the circuit module from the antenna, the DC component of the static electricity and the AC component having a lower frequency than the communication frequency are released to the ground side by the inductor and the capacitor enters the circuit network side of the circuit module by the capacitor. To block. Therefore, there is an effect that the circuit network in the circuit module can be protected from static electricity without hindering reduction in size and weight of the mobile communication device.

According to the second aspect of the present invention, since the ground to which the inductor is connected is insulated from the ground of the circuit network in a DC manner, the DC component of the static electricity escaping through the inductor and the AC of a frequency lower than the communication frequency are reduced. Components can be prevented from wrapping around the network through the ground of the network. Therefore, there is an effect that the circuit network in the circuit module can be more reliably protected from static electricity without hindering reduction in size and weight of the mobile communication device.

According to the third aspect of the present invention, since the inductor and the capacitor incorporated in the circuit module constitute at least a part of the band-pass filter that allows the communication signal of the mobile communication device to pass, the band-pass filter is provided. Accordingly, it is possible to prevent the passage of the AC component having a frequency higher than the communication frequency. Therefore, there is an effect that the circuit network in the circuit module can be protected from static electricity having an AC component having a frequency higher than the communication frequency without hindering the reduction in size and weight of the mobile communication device.

According to the fourth aspect of the present invention, at least one of the inductor and the capacitor incorporated in the circuit module is constituted by a laminated structure of a multilayer substrate constituting the circuit module. This can suppress an increase in the size of the circuit module itself. Therefore, there is an effect that the circuit network in the circuit module can be protected from static electricity without hindering reduction in size and weight of the mobile communication device.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an antenna switch to which an electrostatic protection circuit according to an embodiment of the present invention is applied.

FIG. 2 is a block diagram showing a circuit configuration of a mobile phone using the antenna switch according to the embodiment.

FIG. 3 is a schematic cross-sectional view illustrating a stacked state of the antenna switch according to the embodiment.

FIG. 4 is a perspective view showing an expanded state of each layer of the antenna switch according to the embodiment.

FIG. 5 is a perspective view showing an expanded state of each layer of the antenna switch according to the embodiment.

FIG. 6 is a schematic diagram showing a measurement system when static electricity is applied to the antenna switch according to the embodiment.

FIG. 7A is a characteristic diagram showing a transmission characteristic of the antenna switch according to the present embodiment. FIG.
(B) is after the application of static electricity.

8A and 8B are characteristic diagrams showing the pass characteristics of an antenna switch having no static electricity protection circuit. FIG. 8A is a diagram before the static electricity is applied, and FIG. 8B is a diagram after the static electricity is applied.

FIG. 9 is a modification example of the electrostatic protection circuit according to the embodiment;
FIG. 3 is a circuit diagram when a BPF is configured.

FIG. 10A is a characteristic diagram showing a pass characteristic of the electrostatic protection circuit according to the present embodiment. FIG.
(B) BPF.

FIG. 11 is a characteristic diagram of a frequency distribution characteristic of an electrostatic signal level measured by a spectrum analyzer when static electricity is applied to the electrostatic protection circuit according to the present embodiment.
1 (A) is for HPF, FIG. 11 (B) is directly connected (no HPF)
belongs to.

FIG. 12 is a characteristic diagram of a frequency distribution characteristic of an electrostatic signal level measured by a spectrum analyzer when static electricity is applied to the electrostatic protection circuit according to the present embodiment.
2 (A) is for BPF, Fig. 12 (B) directly connected (no BPF)
belongs to.

[Explanation of symbols]

Reference Signs List 20 antenna switch (circuit module) 20a electrostatic protection circuit (HPF) 20b switch circuit (circuit network) 21, 22, 23, 24, 25, 26, 27, 28, 2
9, 30, 31, 32, 33, 34 Glass ceramic substrate (multilayer substrate) 40a Static electricity protection circuit (BPF) 60 Transmitter 70 Receiver 80 Antenna L0 Inductor C0 Capacitor ANT Antenna terminal J terminal (signal input / output terminal) FG housing Body ground (ground) SG Signal ground (network ground)

Claims (4)

[Claims] 1. An electrostatic protection circuit for protecting a circuit network in a circuit module connected to an antenna of a mobile communication device from static electricity, comprising: an antenna connection side where the antenna is connected to the circuit module; Connected between a signal input / output terminal through which a communication signal is input or output, and a capacitor built in the circuit module, and connected between one end of the capacitor connected to the antenna connection side and ground. And an inductor built in the circuit module, wherein the inductor and the capacitor block the passage of an AC component and a DC component at least lower than a communication frequency of the mobile communication device. Static electricity protection circuit. 2. The static electricity protection circuit according to claim 1, wherein the ground is DC-insulated from the ground of the network. 3. The static electricity protection circuit according to claim 1, wherein the inductor and the capacitor constitute at least a part of a band-pass filter that allows a communication signal of the mobile communication device to pass. . 4. The circuit module according to claim 1, wherein the circuit module includes a multilayer substrate, and at least one of the inductor and the capacitor includes a multilayer structure including the multilayer substrate. Static electricity protection circuit described in the section.