JPH11154804A - High frequency circuit device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a high frequency circuit small in size and low in cost by introducing a phase inverting circuit to the high frequency circuit. SOLUTION: In this high frequency circuit connected to a transmission reception common use antenna, a transmission circuit (Tx) and a reception circuit (Rx) and for leading a reception signal from the antenna to the reception circuit only and leading a transmission signal from the transmission circuit to the antenna only, surface acoustic wave filters 1, 4 where an absolute value of a reflection coefficient at a transmission signal frequency band is 0.8 or over and phase inverting circuits 2, 5 are placed between the antenna and the reception circuit respectively, in such a way that the phase inverting circuits connect directly to the antenna, and high frequency switches 3, 6 are placed between the antenna and the transmission circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a duplexer for a mobile communication terminal, comprising a surface acoustic wave filter and a high-frequency switch. The high-frequency circuit device of the present invention is mainly used for a duplexer of a so-called dual-band mobile radio terminal.

[0002]

2. Description of the Related Art In recent years, development of mobile communication terminals represented by small and lightweight portable telephones has been progressing at a rapid pace. Since a mobile phone transmits and receives a transmission signal and a reception signal using a single antenna, means for separating the transmission signal and the reception signal is essential. Analog system (FDMA: Fr
In the case of frequency division multiple access, a duplexer composed of a dielectric resonator or a surface acoustic wave element is used, and a digital system (TDMA: T) is used.
In the case of ime division multiple access, an antenna switch circuit using a high-frequency switch or a duplexer has been used.

[0003]

With the spread of mobile communication, in addition to the 800 MHz band frequency originally developed,
A frequency band near 2 GHz has been put to practical use.

[0004] More recently, the proliferation of users has limited the subscriber capacity of a single system, so that two or more systems (eg, 800 MHz GS in Europe).
There is an urgent need to develop a so-called dual-band terminal that enables the sharing of a 1.9 GHz band PCN (Personal Communication System) with an M (Grobal Communication System). In a dual-band terminal, the baseband circuit and the like can be shared, but the RF unit, especially the duplexer, cannot be shared. The present invention provides means for realizing a duplexer for a dual-band terminal at a smaller size, lighter weight, and lower cost than a conventional duplexer or an antenna switch circuit.

[0005]

Means for applying an ON / OFF type having a simpler structure than a conventional SPDT (Single Pole Dual Throw) type to a transmitting high frequency switch will be described below. When a duplexer is configured by connecting an ON / OFF type high-frequency switch and a surface acoustic wave filter for reception in parallel, the impedance when the surface acoustic wave filter for reception is viewed from the parallel connection point in the transmission band becomes substantially open. Need to be. This is to minimize an increase in loss (parallel connection loss) due to parallel connection. In the present invention, a receiving surface acoustic wave filter having an absolute value of a reflection coefficient of an input terminal pair in a transmission band of 0.8 or more, and a phase rotation circuit connected to the input terminal pair of the receiving surface acoustic wave filter, It is proposed that the impedance when the surface acoustic wave filter for reception is viewed from the parallel connection point be substantially opened. Here, the impedance is substantially open when the absolute value of the reflection coefficient is equal to 0.
8 or more, the phase of the reflection coefficient is approximately 0 in the transmission band.
It shows that it becomes a degree. If the above general opening condition is satisfied, the parallel connection loss can be suppressed to 0.5 dB or less. By the above means, a duplexer in which an ON / OFF type high frequency switch and a surface acoustic wave filter for reception are connected in parallel can be realized.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. Note that, for simplicity of explanation,
GSM (transmission: 890-91) is used as the first transmission / reception band.
5 MHz, reception: 935-960 MHz) A PCN (transmission: 1710-17) is used as the second transmission / reception band.
(85 MHz, reception: 1805-1880 MHz) A system will be described as a specific example.

FIG. 1 is a block diagram showing a first embodiment of the present invention, and shows a configuration example of a duplexer for sharing both the GSM and PCN systems. A GSM receiving surface acoustic wave having a necessary attenuation characteristic in a system with a GSM reception band as a pass band and an absolute value of a reflection coefficient of a filter as viewed from an input side in a GSM transmission band of 0.8 or more. Filter 1 is introduced. For the input terminal pair,
One terminal pair of a phase rotation circuit 2 for making the input impedance of the surface acoustic wave filter 1 substantially open in a GSM transmission band is connected. The other terminal pair of the phase rotation circuit 2 is connected to an ON / OFF type high frequency switch 3 at a parallel connection point A. With the PCN reception band as the pass band, it has the attenuation characteristics necessary for the system and
The surface acoustic wave filter 4 for PCN reception in which the absolute value of the reflection coefficient of the filter as viewed from the input side in the N transmission band is 0.8 or more is introduced. One terminal pair of a phase rotation circuit 5 for making input impedance substantially open in the transmission band of the PCN of the surface acoustic wave filter 4 is connected to the input terminal pair. The other terminal pair of the phase rotation circuit 5 is connected to an ON / OFF type high-frequency switch 6 at a parallel connection point B. A low-pass filter (LPF) 7 that connects the transmission band of the PCN to a pass band and attenuates harmonic components of a transmission signal is connected to a stage subsequent to the high-frequency switch 6. Between the parallel connection point A and the parallel connection point C, the GSM transmission / reception band is a pass band, the PCN transmission / reception band is an attenuation band, and the input impedance in the PCN transmission / reception band viewed from the parallel connection point C side is substantially open. A low-pass filter (LPF) 8 between the parallel connection point B and the parallel connection point C has a transmission / reception band of PCN as a pass band, a transmission / reception band of GSM as an attenuation band, and from the parallel connection point C side. PC I saw
A high-pass filter (HPF) 9 whose input impedance in the N transmission / reception band is substantially open is connected. That is, the filters 8 and 9 form a duplexer having A, B and C as a terminal pair. The parallel connection point C is connected to the antenna.

[0008] The operation of the duplexer having the above configuration at the time of dual band will be described. ON when transmitting GSM
Only the / OFF type high frequency switch 3 is turned on. GS
The transmission signal arriving from the M transmission circuit passes through the ON / OFF type high frequency switch 3 and reaches the parallel connection point A.
Since the impedance in the GSM transmission band when the GSM receiving circuit side is viewed from the parallel connection point A is substantially open,
The GSM transmission signal passes through the low-pass filter (LPF) 8 without going to the GSM receiving circuit side, and is connected to the parallel connection point C.
To reach. When the transmission / reception circuit side of the PCN is viewed from the parallel connection point C, the impedance is a high-pass filter (HPF).
9, the antenna is radiated from the antenna without wrapping around the transmitting / receiving circuit side of the PCN.

At the time of PCN transmission, only the ON / OFF high-frequency switch 6 is turned ON. The transmission signal arriving from the PCN transmission circuit is turned on / off by a high-frequency switch 6.
And reaches the parallel connection point B. Since the impedance in the PCN transmission band when the PCN receiving circuit side is viewed from the parallel connection point B is substantially open, the PCN transmission signal does not sneak to the PCN receiving circuit side, and the high-pass filter ( (HPF) 9 and reaches the parallel connection point C.
Since the impedance of the GSM transmission / reception circuit side viewed from the parallel connection point C is substantially open due to the low-pass filter (LPF) 8, it is radiated from the antenna without going around the GSM transmission / reception circuit side.

When the high-frequency switches 3 and 6 of the ON / OFF type are turned off at the time of reception, the impedance when each transmission circuit side is viewed from the parallel connection points A and B is substantially open. Therefore, the received waves of both the GSM and PCN bands reaching the antenna are split by the low-pass filter (LPF) 8 and the high-pass filter (HPF) 9, and the GSM received signal is connected to the parallel connection point A and the PCN received signal is received. The signal reaches the parallel connection point B, and does not go to each transmission circuit side.
The light passes through the surface acoustic wave filter 1 or the surface acoustic wave filter 4. The received signal is supplied to each receiving circuit after unnecessary components are removed by a filter. Note that, for a GSM transmission signal, the low-pass filter 8 suppresses a harmonic component included in the transmission signal, so that a low-pass filter is not required in a stage preceding the ON / OFF type high-frequency switch 3. .

Next, the superiority of the present invention will be described with reference to FIGS. FIG. 2 is a diagram showing a configuration of the present invention in which a portion between the parallel connection point A of FIG. 1 and each terminal of the transmission / reception circuit is extracted.
Shows a configuration example according to the prior art. In each of the figures, a low-pass filter for suppressing a harmonic component of a transmission signal is omitted for simplicity. As is apparent from a comparison between FIG. 2 and FIG. 3, in the configuration of the related art, in order to eliminate the influence of the receiving circuit at the time of transmission, the high-frequency switch 3 has a so-called SPDT (Single Polt) having an output of 2 with respect to the input 1.
e Dual Throw) type switch is required. On the other hand, in the configuration of the present invention in which the phase rotation circuit 2 is introduced, since the impedance of the reception filter 1 is substantially open at the transmission frequency, a simple ON / OFF type high frequency switch can be applied. To configure an SPDT type switch, at least two or more transistors, FETs or diodes are required, but an ON / OFF type switch can be configured with at least one transistor, FET or diode. Therefore, the size of the ON / OFF switch can be reduced and the price can be reduced as compared with the SPDT switch.

Next, the block diagram of the dual-band duplexer shown in FIG. 1 will be described with reference to FIG. 4 using a more detailed circuit diagram. Inductance 22 and capacitance 21,
23 constitutes a phase rotation circuit (corresponding to the phase rotation circuit 2 in FIG. 1), is connected to the surface acoustic wave filter 1, and a PIN diode 27 has a bias circuit composed of an inductance 30 and a capacitor 28 and a DC blocking capacitor 29. , 31 are connected in parallel at a parallel connection point A. If the bias circuit composed of the inductance 30 and the capacitance 28 is set to a constant so as to cause parallel resonance at the GSM transmission frequency,
It is possible to avoid the influence of the bias circuit on the transmission signal frequency. Similarly, the inductance 42 and the capacitance 4
1, 43 constitute a phase rotation circuit (corresponding to the phase rotation circuit 5 of FIG. 1), which is connected to the surface acoustic wave filter 4,
A low-pass filter (corresponding to the low-pass filter 7 in FIG. 1) and a DC cutoff, which are constituted by a bias circuit composed of an inductance 50 and a capacitance 48 in a diode 47 and an inductance 51 and a capacitance 52 (some capacitances 48 also contribute). Are connected in parallel at a parallel connection point B. Between the parallel connection point A and the parallel connection point C, the transmission / reception band of GSM is used as a pass band, the transmission / reception band of PCN is used as an attenuation band, and the PC viewed from the parallel connection point C is used.
A low-pass filter composed of the inductance 25 and the capacitances 24 and 26 that makes the input impedance in the N transmission / reception band substantially open is formed. Between the parallel connection point B and the parallel connection point C, the transmission / reception band of the PCN is set as a pass band,
A high-pass filter composed of inductances 44 and 46 and a capacitor 45 that makes the transmission / reception band of GSM an attenuation band and makes the input impedance in the transmission / reception band of PCN viewed from the parallel connection point C substantially open. The parallel connection point C is generally a connection point with the antenna. Inductance 30 and capacitance 29 that constitute the bias circuit in the figure
Of the high-frequency switch by taking out a pair of bias terminals (Vcnt1 and Vcnt2) from the connection point of (1) and the connection point of the inductance 50 and the capacitance 49 and applying a switch control voltage.
It is possible to control OFF.

FIG. 4 shows an example in which the bias circuits 28, 29, 30, 48, 49, and 50 of the high-frequency switch are constituted by lumped constant circuits which are in parallel resonance at the transmission signal frequency. It is obvious that the influence of the bias terminal pair can be avoided even if a distributed constant line having an electric length of about 1/4 of the wavelength of the transmission signal frequency is used.

FIG. 4 shows an example in which the circuit is constituted by a lumped constant circuit. The phase rotation circuit for making the input impedance in the transmission band of the surface acoustic wave filter substantially open is constituted by a distributed constant circuit having an optimum length. It is also possible.

With the above configuration, a duplexer for dual band using two transmission / reception bands can be realized at a small size and at a low price. Further, it is apparent that a triple-band duplexer using three or more transmission / reception bands can be dealt with by extending the configuration of the present invention.

[0016]

According to the structure of the present invention, since the input impedance on the receiving circuit side as viewed from the parallel connection point is substantially open, a high-frequency switch having a simple structure comprising at least one PIN diode and a bias circuit is provided on the transmitting side. It can be used, and downsizing and cost reduction can be achieved.

[Brief description of the drawings]

FIG. 1 is a block diagram of a dual-band duplexer.

FIG. 2 is a configuration diagram (main parts) of a duplexer according to the present invention.

FIG. 3 is a configuration diagram (main parts) of a duplexer according to a conventional technique.

FIG. 4 is an example of a circuit configuration of a dual-band duplexer.

[Explanation of symbols]

1,4 ... surface acoustic wave filter, 2,5 ... phase rotation circuit,
3, 6 high frequency switch, 7, 8 low pass filter,
9 high-pass filter, 21, 23, 24, 26, 2
8, 29, 31, 41, 43, 45, 48, 49, 5
2, 53 ... capacity, 22, 25, 30, 42, 44, 4
6, 50, 51 ... inductance, 27, 47 ... PIN
diode.

Continued on the front page (72) Inventor Kazuyuki Sakiyama 1 Kitano, Makino, Mizusawa-shi, Iwate Prefecture Hitachi Media Electronics Co., Ltd.

Claims (10)

[Claims] 1. A surface acoustic wave filter wherein a reception signal band is a pass band, a transmission signal band is a stop band, and an absolute value of a reflection coefficient in a transmission signal band viewed from an input terminal pair is 0.8 or more. A phase rotation circuit for making the input impedance of the surface acoustic wave filter in a transmission signal band substantially open, and a bias circuit capable of switching a passage loss in the transmission signal band depending on the presence or absence of an applied voltage from an external circuit. A high-frequency switch, one terminal pair of the phase rotation circuit is connected to an input terminal pair of the surface acoustic wave filter, and the other terminal pair of the phase rotation circuit is connected to an output terminal pair of the high-frequency switch. A high-frequency circuit device comprising: 2. The high-frequency circuit device according to claim 1, wherein said phase rotation circuit is constituted by a lumped constant element including an inductance element and a capacitance element. 3. The high-frequency circuit device according to claim 1, wherein said bias circuit comprises a lumped constant element including an inductance element and a capacitance element. 4. The high-frequency circuit device according to claim 1, wherein said phase rotation circuit is a distributed constant circuit. 5. The high-frequency circuit device according to claim 1, wherein said bias circuit includes a distributed constant line having an electrical length of a quarter wavelength of a signal. 6. The first reception signal band is a pass band, the first transmission signal band is a stop band, and the absolute value of the reflection coefficient in the first transmission signal band viewed from the input terminal pair is 0.
A first surface acoustic wave filter that is equal to or greater than 8, a first phase rotation circuit for making the input impedance of the first surface acoustic wave filter in a first transmission signal band substantially open, and a first transmission A first high-frequency switch including a bias circuit capable of switching a pass loss in a signal band depending on the presence or absence of an applied voltage from an external circuit; a second reception signal band is a pass band, and a second transmission signal band is A second surface acoustic wave filter that is a stop band and has an absolute value of a reflection coefficient of 0.8 or more in a second transmission signal band as viewed from the input terminal pair; and a second surface acoustic wave filter of the second surface acoustic wave filter. A second phase rotation circuit for making the input impedance in the transmission signal band substantially open, and switching a pass loss in the second transmission signal band depending on the presence or absence of an applied voltage from an external circuit. A second high-frequency switch having a bias circuit that can be used, a first reception signal band and a first transmission signal band are pass bands, and a second reception signal band and a second transmission signal band are stop bands. And a low-pass filter in which the second reception signal band and the second transmission signal band are pass bands, and the first reception signal band and the first transmission signal band are stop bands. One terminal pair of the first phase rotation circuit is connected to an input terminal pair of the first surface acoustic wave filter, and the other terminal pair of the first phase rotation circuit and the An output terminal pair of the first high-frequency switch and one terminal pair of the low-pass filter are connected to each other, and one terminal pair of the second phase rotation circuit is connected to an input terminal pair of the second surface acoustic wave filter. And the other of the second phase rotation circuit A terminal pair, an output terminal pair of the second high-frequency switch, and one terminal pair of the high-pass filter are connected to each other, and the other terminal pair of the low-pass filter and the other terminal of the high-pass filter A high-frequency circuit device wherein a pair is connected. 7. The high-frequency device according to claim 2, wherein the first phase rotation circuit or the second phase rotation circuit is formed by a lumped constant element including an inductance element and a capacitance element. Circuit device. 8. The high-frequency circuit device according to claim 2, wherein said first bias circuit or said second bias circuit is constituted by a lumped constant element including an inductance element and a capacitance element. 9. The high-frequency circuit device according to claim 2, wherein said first phase rotation circuit or said second phase rotation circuit is a distributed constant circuit. 10. The first bias circuit or the second bias circuit.
3. The high-frequency circuit device according to claim 2, wherein the bias circuit includes a distributed constant line having an electrical length of a quarter wavelength of the signal.