JPH05110356A - High frequency circuit having antenna - Google Patents

Abstract

PURPOSE:To improve the surge immunity by connecting a stub between a ground and a high frequency signal transmission line between an antenna circuit and a coupling capacitor and specifying the length of the stub. CONSTITUTION:A reception side circuit consists of a reception high frequency circuit 3 connecting to an antenna circuit section comprising an antenna 1 and a duplexer 2, a low frequency amplifier 5, a speaker 6 and a stub 7 comprising a strip line. Then the length L of the stub 7 connected between a ground and a main transmission line 8 located between the antenna circuit section and a coupling capacitor 9 of the reception high frequency circuit 3 is selected so that the relation of L=(1/4)lambda=(1/4)X(C/f) is almost satisfied, where f is a frequency of a high frequency signal, that is, a frequency of a carrier signal, lambdais a wavelength of the high frequency signal and C is the velocity of light. Since a surge flows to ground through the stub 7, the high frequency amplifier is protected from the surge and the loss in the high frequency signal is suppressed to improve the surge immunity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency circuit having an antenna for a mobile phone or the like.

[0002]

2. Description of the Related Art A mobile phone includes a receiving side circuit and a transmitting side circuit, which are connected to an antenna through a switch (hereinafter referred to as a duplexer).

[0003]

By the way, when a small mobile phone is put in or taken out of a pocket of clothes, static electricity is generated due to friction between the clothes and the mobile phone, and this enters the inside of the main body of the mobile phone from the antenna. Sometimes. In addition, when it is dry such as in winter, the human body becomes charged due to static electricity generated by friction between the human body and clothes, and when the human body contacts the antenna, a voltage based on the charge enters the mobile phone. The voltage based on static electricity reaches 2 to 10 kV and may damage the semiconductor element (transistor) of the high frequency amplifier connected to the antenna circuit. To protect high frequency circuits from static electricity and external surges, surge absorbing elements such as varistors and arresters may be connected to the antenna circuit, but these surge absorbing elements are relatively large and hinder the miniaturization of mobile phones. .. In addition, since mobile phones handle extremely high frequencies, it is difficult to achieve impedance matching with ordinary surge absorbing elements. Such problems also occur in other transmitting and / or receiving devices similar to mobile phones.

Therefore, it is an object of the present invention to provide a high frequency circuit for transmission or reception which is improved in surge resistance.

[0005]

The present invention for achieving the above object provides an antenna circuit, a coupling capacitor connected to the antenna circuit, a matching circuit connected to the coupling capacitor, and the matching circuit. In a receiving high-frequency circuit including a connected high-frequency amplifier, a stub is connected between a high-frequency signal transmission line between the antenna circuit and the coupling capacitor and a ground, and a length L of the stub is L. = (1/4) λ = (1/4) × (C / f) (where λ is the wavelength of the transmission signal, C is the speed of light, and f is the frequency of the transmission signal). The present invention relates to a receiving high frequency circuit. Another invention of the present application is a high frequency amplifier for amplifying a transmission signal, a coupling capacitor connected to an output transmission path of the high frequency amplifier, a matching circuit connected to an output side of the coupling capacitor, and In a transmission high frequency circuit including an antenna circuit connected to a matching circuit, a stub is connected between a high frequency signal transmission line between the coupling capacitor and the matching circuit and a ground, and a length L of the stub is , L = (1 /
4) For transmission set to substantially satisfy λ = (1/4) × (C / f) (where λ is the wavelength of the transmission signal, C is the speed of light, and f is the frequency of the transmission signal). It relates to high frequency circuits.

[0006]

[Operation] The coupling capacitor in the receiving high frequency circuit is
The direct current component is cut off, and the alternating current component (for example, a high frequency signal of carrier frequency f) is passed. The matching circuit performs impedance conversion so that the characteristic impedance of the transmission path including the antenna circuit matches the characteristic impedance of the high frequency amplifier. The stub is a side path of the main transmission line and acts as a reactance element. In the present invention, since the stub is connected between the main transmission line and the ground, it works as a short stub. Since the tip of the stub is connected to the ground, the DC potential of the main transmission line to which the stub is connected is ground (zero). When the frequency (for example, carrier frequency) of the high frequency signal flowing in the main transmission line is f, the length L of the stub is L
When = (1/4) λ = (1/4) × (C / f), the impedance of the stub becomes maximum with respect to the high frequency signal of the frequency f, and the attenuation amount becomes minimum. Therefore, if the stub is formed so as to satisfy the above condition, the leakage of the high frequency signal can be prevented and the direct current can be bypassed. The electrostatic surge can be thought of as direct current, so it flows through the stub to ground. Thereby, the high frequency amplifier can be protected from static electricity.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a mobile phone according to an embodiment of the present invention will be described with reference to FIGS. The receiving side circuit of the mobile phone of FIG. 1 includes a receiving high-frequency circuit 3 connected to an antenna circuit portion including an antenna 1 and a duplexer 2, a demodulation circuit 4, a low-frequency amplifier 5, a speaker 6, and a strip line. And a stub 7 consisting of. The receiving high-frequency circuit 3 is configured by sequentially connecting a coupling capacitor 9, a matching circuit 10, and a high-frequency amplifier 11 which are connected in series to the output main transmission line 8 of the duplexer 2. The stub 7 is connected between the main transmission line 8 and the ground (earth) and functions as a short stub. The length L of the stub 7 is L = (1/4) λ = (1 /
4) × (C / f) is set to be substantially satisfied. However, here, λ is the wavelength of the high frequency signal, and C is the speed of light. Demodulation circuit 4 is shown as including an intermediate frequency converter, an intermediate frequency amplifier, and a demodulator. The demodulated signal reaches the speaker 6 via the low frequency amplifier 5 and is converted into voice.

The transmitting side circuit includes a microphone 12, a low frequency amplifier 13, a modulating circuit 14, and a transmitting high frequency circuit 1.
5 and a stub 16. The sound input to the microphone 12 is converted into an electric signal and sent to the modulation circuit 14 via the low frequency amplifier 13. Modulation circuit 14 is shown as including a carrier oscillator, FM modulator, and the like. The transmission high frequency circuit 15 includes a high frequency amplifier 17 connected to the modulation circuit 14, a coupling capacitor 19 connected in series to the output transmission line 18, and a matching circuit connected between the coupling capacitor 19 and the duplexer 2. It consists of 20 and.

The stub 16 according to the present invention is connected between the main transmission line 18 on the output side of the coupling capacitor 19 and the ground. The length L of this stub 16 is also L as in the receiving side.
= (1/4) λ = (1/4) × (C / f) is substantially satisfied.

FIG. 2 shows the receiving high-frequency circuit 3 of FIG. 1 in principle. The matching circuit 10 has two impedance elements Z1.
, Z2 and one capacitor C1. The high frequency amplifier 11 includes a transistor Q1, which is an FET, impedance elements Z3, Z4, etc., and amplifies the high frequency signal received by the antenna 1. Since the stub 7 composed of the λ / 4 strip line is connected between the main transmission line 8 and the ground, even if a surge such as static electricity is input from the antenna, it flows to the ground through the stub 7 and the transistor Q1 or the like is discharged. Destruction is prevented.

FIG. 3 shows the transmitting high-frequency circuit 15 in principle. The high frequency amplifier 17 is a transistor Q composed of an FET
2, including an impedance element Z5, a capacitor C2, etc., for power amplification of a high frequency signal. The matching circuit 20 comprises impedance elements Z6 and Z7 and a capacitor C3. A surge such as static electricity entering from the side of the duplexer 2 flows to the ground through the stub 16 and protects the transistor Q2.

[0012]

As is apparent from the above, in both the high frequency circuit for reception of claim 1 and the high frequency circuit for transmission of claim 2, the surge flows to the ground through the stub, so that the high frequency amplifier is protected from the surge. be able to.
Further, since the stub is set to have a length of λ / 4 and has a high impedance for a high frequency signal, it is possible to suppress the loss of the high frequency signal and improve the surge resistance.

[Brief description of drawings]

FIG. 1 is a block diagram showing in principle a mobile phone according to an embodiment of the present invention.

FIG. 2 is a diagram showing a high frequency circuit on the receiving side of FIG.

FIG. 3 is a diagram showing a high frequency circuit on the transmitting side of FIG.

[Explanation of symbols]

 1 Antenna 7 Stub 8 Main Transmission Line 9 Coupling Capacitor 10 Matching Circuit 11 High Frequency Amplifier

Claims (2)

[Claims] 1. A receiving high-frequency circuit including an antenna circuit, a coupling capacitor connected to the antenna circuit, a matching circuit connected to the coupling capacitor, and a high-frequency amplifier connected to the matching circuit, A stub is connected between the high-frequency signal transmission line between the antenna circuit and the coupling capacitor and the ground, and the length L of the stub is L = (1/4) λ = (1/4) × ( C / f) (where λ is the wavelength of the transmission signal, C is the speed of light, and f is the frequency of the transmission signal). 2. A high frequency amplifier for amplifying a transmission signal, a coupling capacitor connected to an output transmission line of the high frequency amplifier, a matching circuit connected to an output side of the coupling capacitor, and a matching circuit connected to the matching circuit. In the high frequency circuit for transmission including the antenna circuit, the stub is connected between the high frequency signal transmission line between the coupling capacitor and the matching circuit and the ground, and the length L of the stub is L = ( 1/4) λ = (1/4) × (C / f) (where λ is the wavelength of the transmission signal, C is the speed of light, and f is the frequency of the transmission signal). A high-frequency circuit for transmission, characterized in that