JPH08237166A - Antenna multicoupler with built-in rf switch - Google Patents

Abstract

PURPOSE: To make the antenna multicoupler with built-in RF switch. CONSTITUTION: An antenna changeover circuit 4 comprising an antenna changeover circuit consisting of diodes D1, D2 and a λ/4 phase shift circuit 41 and comprising a parallel resonance circuit 42 is provided among an antenna terminal ant, a transmission filter 2 and a reception filter 3, and a control signal received from a control terminal CONT is used to select the connection between an antenna ANT and the transmission filter 2 or select the connection between the antenna ANT and the reception filter 3. The parallel resonance circuit 42 is made up of a resonance circuit comprising a capacitor CRF and a coil LRF having a resonance point for a transmission frequency band and the circuit to block a transmission signal is made small by employing a lamination chip capacitor and an air-core coil thereby making the size of the antenna multicoupler with built-in RF switch.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antenna with a built-in RF switch, in which an antenna is connected to a transmitting filter and a receiving filter by an RF switch, and one antenna is shared by the transmitting antenna and the receiving antenna. It is related to vessels.

[0002]

2. Description of the Related Art Conventionally, an antenna duplexer is known in which one antenna is shared by a transmitting antenna and a receiving antenna.

FIG. 3 is a block diagram showing an example of a conventional antenna duplexer. Antenna duplexer 100 shown in FIG.
Is between the antenna terminal ant connected to the antenna 101 and the transmission terminal Tx connected to the transmission circuit 102.
A transmission filter 100A including a (Band Elimination Filter) is provided, and the antenna terminal ANT and the reception circuit 1 are provided.
BPF (Band Pass) between the receiving terminals Rx connected to
A receiving filter 100B including a filter) is provided. The transmission filter 100A and the reception filter 100B are, for example, dielectric filters.

Further, there is known an RF switch which is provided between one antenna and a transmission / reception circuit and which switches the connection between the antenna and the transmission circuit or the reception circuit to share the antenna for transmission and reception.

FIG. 4 is a circuit configuration diagram of a conventional RF switch. The RF switch 104 shown in the figure has two FEs.
The semiconductor switches 105 and 106 made of T (Field Effect Transistor) are used. Tx terminal, Rx
The terminal and the ant terminal are a transmission circuit (not shown),
A terminal to which a receiving circuit (not shown) and the antenna 101 are connected.

The terminal V is a terminal for supplying drive power (DC power supply) for the FETs 105 and 106, and a control terminal G1.
G2 is the ON / OFF of FET105 and FET106, respectively.
This is a terminal to which a control signal for controlling OFF (opening / closing) is input. Further, the capacitor C connects the FETs 105 and 106 and the terminal ant in an alternating current manner, and cuts off the output of the driving power input from the terminal V to the terminal ant side. Further, the choke coil RFC is FET10.
5, 106 and power supply terminal V are connected in a direct current manner, and FET1
The transmission signal output from 05 is prevented from flowing out to the power supply terminal V side.

Control signals S1 and S2, which are pulse train signals having mutually inverted phases, are input to the control terminals G1 and G2, respectively, and the FET 10 is driven by these control signals S1 and S2.
Antenna terminal a by turning on and off 5, 106 alternately
The connection between nt (that is, the antenna 101) and the terminal Tx (that is, the transmission circuit) or the terminal Rx (that is, the reception circuit) is alternately switched.

[0008]

In the conventional antenna duplexer 100, the output end of the transmission filter 100A and the input end of the reception filter 100B are directly connected to the antenna terminal ant and transmitted through the transmission filter 100A. Since the signal flows into the receiving circuit 103 via the receiving filter 100B and the received signal received by the antenna 101 flows into the transmitting circuit 102 via the transmitting filter 100A, in order to prevent this, the transmitting filter 100A and As the filter characteristics of the reception filter 100B, a sufficient amount of attenuation is required in the partner band (reception band for the filter 100A and transmission band for the filter 100B).

However, in the filter design of the transmission filter 100A and the reception filter 100B, when the filter design is performed by giving priority to the attenuation characteristic in the other band, the loss (insertion loss) in the pass band becomes large and the low in the pass band. It is difficult to apply a conventional antenna duplexer to a wireless device that requires loss.

In order to solve this problem, the antenna terminal a
nt, transmission filter 100A, and reception filter 10
RF switch 104 is provided between 0B, and this RF switch causes antenna terminal ant and transmission filter 100A.
Alternatively, a method of alternately switching the connection with the reception filter 100B can be considered.

However, if such a method is adopted, the size of the antenna duplexer is increased due to the increase in the number of switch circuits. Therefore, it is desirable that the switch circuit be composed of components as small as possible.

By the way, the choke coil RFC provided at the power supply terminal V of the RF switch 104 prevents an inflow of a high power transmission signal to the power supply terminal side, so that the inductance value at which the impedance becomes 1 kΩ or more at least in the transmission band. Required.

For example, in an antenna duplexer for a communication device having a transmission band in the 900 MHz band, it is necessary to configure the choke coil RFC with an air core coil having an inductance value of 200 nH or more or a laminated type chip inductor.

However, if the choke coil RFC is composed of an air-core coil, it becomes very large and it is difficult to miniaturize the switch circuit. On the other hand, if the choke coil RFC is composed of a chip conductor, it will be smaller than the air-core coil, but at the same time, the cost of parts will be high, and the cost reduction of the antenna duplexer will be violated.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an antenna duplexer having a built-in RF switch which is relatively inexpensive and can be miniaturized.

[0016]

The present invention is directed to an antenna terminal to which an antenna is connected, a receiving terminal to which a receiving circuit is connected, a transmitting terminal to which a transmitting circuit is connected, and a received signal received by the antenna. To a predetermined reception band and output to the reception circuit, a transmission filter that limits the transmission signal input from the transmission circuit to a predetermined transmission band and outputs to the antenna, the antenna terminal And an RF switch unit interposed between the transmission filter and the reception filter and switchingly connecting the antenna to the output end of the transmission filter and the input end of the reception filter, and switching control of the RF switch unit. And a control terminal to which a control signal for receiving the control signal is input, and the RF switch means is switched by the control signal to set the antenna for transmission and reception. An antenna duplexer with a built-in RF switch shared with an antenna, wherein a parallel resonance circuit of a capacitor and a coil having a resonance point in the transmission band is provided between the control terminal and the RF switch means. .

[0017]

According to the present invention, the antenna duplexer is used by connecting the antenna for both transmission and reception to the antenna terminal and connecting the reception circuit and the transmission circuit to the reception terminal and the transmission terminal, respectively. The connection of the RF switch means is alternately switched by the switching control signal inputted from the control terminal, whereby the antenna is switched and connected to the transmitting circuit and the receiving circuit alternately in a time division manner and shared for transmission and reception.

The resonance circuit provided between the control terminal and the RF switch means has a resonance point in a predetermined transmission band (has a high impedance with respect to the transmission frequency in the transmission band) and is output from the transmission filter. It prevents the transmission signal from flowing out to the control terminal side.

Since the high-frequency blocking circuit for blocking high-frequency signals is composed of a parallel resonant circuit of a capacitor and a coil, the element values of the capacitor and coil are small, and the chip capacitor and the small air-core coil form a choke coil. The circuit element can be downsized as compared with the case where it is configured by a single body.

[0020]

1 is a circuit configuration diagram of an embodiment of an antenna duplexer according to the present invention. The antenna duplexer 1 is used in a two-way wireless communication device such as a mobile phone.

The antenna duplexer 1 includes a transmission filter 2,
It is composed of a receiving filter 3 and an antenna switching circuit 4 using a diode switch.

The antenna duplexer 1 includes an antenna terminal ant to which the antenna ANT is connected, a transmission terminal Tx to which a transmission circuit (not shown) is connected, a transmission terminal Rx to which a reception circuit (not shown) is connected, and the above antenna. A control terminal CONT to which a control signal for controlling the connection between the ANT and the transmission filter 2 and the reception filter 3 is input is provided.

The transmission filter 2 is a filter composed of an LPF (Low Pass Filter) that limits the transmission signal from the transmission circuit input from the transmission terminal Tx to a predetermined transmission band, and its input end is connected to the transmission terminal Tx. Has been done. The transmission filter 2 is composed of, for example, a dielectric filter in which a plurality of dielectric coaxial resonators are cascade-coupled via a capacitor. The transmission filter 2 is a BEF (Band Elimination Fil) formed by cascading a series circuit of a capacitor and a dielectric coaxial resonator via an inductance formed by a transmission line.
ter).

The transmission filter 2 can be constituted by an LPF or BEF using a strip line instead of the dielectric coaxial resonator, but it has a high Q value (sharpness), a low pass band loss, and the like. Considering this, it is desirable to use a dielectric filter.

The reception filter 3 limits the reception signal received by the antenna ANT to a signal in a predetermined reception band B.
It is a filter made of PF, and its output end is connected to the reception terminal Rx. The reception filter 3 is composed of, for example, a SAW filter. The transmission filter 2 can also be formed of a dielectric filter, but in consideration of the size reduction and weight reduction of the antenna duplexer 1, a small and lightweight SAW is used.
It is desirable to use a filter.

The antenna switching circuit 4 is an RF switch circuit (RF switch means) composed of diodes D1 and D2 composed of two pin diodes and a λ / 4 phase circuit 41, and a parallel resonant circuit for blocking high frequency signals in the transmission band. Four
2 and a resistor R that limits the control current flowing through the antenna switching circuit 4 and are connected as follows.

That is, the diode D1, the λ / 4 phase circuit 41 and the diode D2 are serially connected in this order, the anode of the diode D1 is connected to the output end of the transmission filter 2 via the coupling capacitor C2, and the parallel resonant circuit is connected. It is connected to the control terminal CONT via 42 and the resistor R, and the cathode of the diode D2 is grounded. The cathode of the diode D1 is connected to the antenna terminal ant via the coupling capacitor C1, and the diode D2
The anode of is connected to the input end of the receiving filter 3 via the coupling capacitor C3.

The λ / 4 phase circuit 41 includes the transmission filter 2
It blocks the inflow of the transmission signal output from the receiving filter 3 side, and is constituted by, for example, a 1/4 wavelength transmission line. In the λ / 4 phase circuit 41, the diode D2 is O
In the N state, the line constant is set so that the impedance seen from the input end to the diode D2 side becomes large in the frequency band (transmission band) to be blocked.

The parallel resonance circuit 42 comprises a parallel circuit of a capacitor C _RF and a coil L _RF, and its resonance point is set within the transmission band. For example, when the transmission band is set near 900 MHz, the circuit constants of the capacitor C _RF and the coil L _RF are set to C _RF = 3 pF and L _RF = 10 nH so that the resonance point becomes 900 MHz, for example. There is.

Since the circuit constants of the parallel resonant circuit 42 are small as described above, the capacitor C _RF is composed of a laminated chip capacitor or a plate capacitor, and the coil L _RF is composed of an air-core coil. As shown in FIG. 2, the plate-shaped capacitor is one in which silver electrodes 5 and 6 are formed on the front and back surfaces of a plate-shaped ceramic 5 having a high dielectric constant.

When a circuit for blocking high frequency signals (hereinafter referred to as an RFC circuit) is composed of a choke coil composed of an air-core coil as in the conventional case, the inductance value is 200n.
Although an air-core coil of H or more is required, the inductance value of the coil L _RF is 1 with respect to the choke coil in this embodiment.
Since it is / 20 or less, the size of the coil L _RF can be remarkably reduced. For example, if the coil diameters are the same,
The coil length (the number of turns) of the coil L _RF is 1/20 or less of that of the choke coil.

In this embodiment, since the RFC circuit is composed of the parallel resonant circuit 42, an extra capacitor C _RF is required as a circuit element compared to the structure of the choke coil, but a laminated capacitor of several pF. Since the plate-shaped capacitor is a rectangular parallelepiped of about 1 mm square and is extremely small, the size of the parallel resonant circuit 42 composed of the multilayer capacitor or the plate-shaped capacitor and the air-core coil is not significantly larger than that of a single choke coil including the air-core coil. Absent.

Further, when the transmission band is different, and when the RFC circuit is composed of a choke coil of an air-core coil, the size of the choke coil changes according to the inductance value. However, as in this embodiment, the RFC circuit is a parallel resonance circuit. When configured with 42, the size can be made substantially constant, which also contributes to standardization of the size of the antenna duplexer 1.

For example, when the transmission band is near 1500 MHz and the resonance point is 1500 MHz, the inductance value of the choke coil is 120 nH or more, so that the coil length of the choke coil is 1 / 1.7 as compared with the case where the resonance point is 900 MHz. However, since the circuit constants of the parallel resonance circuit 42 are C _RF = 1 pF and L _RF = 10 nH, the size of each element of the multilayer capacitor or plate capacitor and the air-core coil hardly changes.

The diodes D1 and D2 are connected to the antenna ANT.
Is a switch circuit that controls the connection between the transmission filter 2 and the reception filter 3, and ON / OFF (opening / closing) is controlled by a control signal input from the control terminal CONT.

The control signal is composed of a pulse train signal in which a high level and a low level are alternately inverted in a predetermined cycle, and the antenna ANT operates as a transmitting antenna and a receiving antenna depending on the level of the control signal as described below. Is switched to. By switching the antenna ANT between the transmitting antenna and the receiving antenna in a time division manner, the antenna ANT is shared for transmission and reception, and bidirectional communication is possible.

(1) When the control signal is at high level When the control terminal CONT goes to high level, the coil L _RF of the parallel resonance circuit 42, the diode D1, and the λ / 4 phase circuit 4
A forward current flows through the diode 1 and the diode D2, and the diodes D1 and D2 are turned on (closed). Diode D
When 1 is turned on, the transmission filter 2 and the antenna terminal ant are circuit-connected, and the transmission signal output from the transmission circuit via the transmission filter 2 is diode D1.
And is guided to the antenna ANT via the capacitor C1,
It is radiated in the air.

The transmission signal is blocked by the λ / 4 phase circuit 41 and does not flow to the ground via the diode D2. Further, the transmission signal is blocked by the parallel resonance circuit 42 and does not flow out to the control terminal CONT side.
Further, the reception signal received by the antenna ANT passes through the λ / 4 phase circuit 41, flows out to the ground through the diode D2, and is not guided to the reception filter 3 side.

Therefore, when the control signal is at the high level, the antenna ANT operates as a transmitting antenna.

(2) When the control signal is low level When the control terminal CONT becomes low level, the diode D
1, D2 are reverse biased and diodes D1, D2 are O
The FF state (open state) is entered. Diodes D1 and D2 are O
In the FF state, the transmission filter 2 and the antenna terminal a
The circuit between nt is blocked, and the transmission signal output from the transmission circuit via the transmission filter 2 is not guided to the antenna ANT. Further, the transmission signal is blocked by the parallel resonance circuit 42 and does not flow out to the control terminal CONT side.

On the other hand, the received signal received by the antenna ANT passes through the λ / 4 phase circuit 41 and is guided to the receiving filter 3 side without flowing out to the ground through the diode D2. Therefore, when the control signal is low level, the antenna ANT operates as a receiving antenna.

As described above, since the RFC circuit is composed of the parallel resonance circuit 42 of the laminated chip capacitors or the plate capacitors and the air-core coil, the RFC circuit is configured as compared with the case of the single choke coil. It can be small and inexpensive.

[0043]

As described above, according to the present invention,
RF switch means is provided between the antenna terminal to which the antenna is connected, the transmission filter connected to the transmission terminal, and the reception filter connected to the reception terminal, and the RF switch means is provided by a control signal input from the control terminal. R to share the antenna for transmission and reception by switching the connection of
An F-switch built-in antenna duplexer, which is provided with a parallel resonance circuit of a capacitor and a coil having a resonance point in the transmission band, interposed between the control terminal and the RF switch means to the transmission signal control terminal side. Since the outflow of the transmission signal is prevented, the reactance value of each circuit element becomes smaller than that in the case where this transmission signal prevention circuit is composed of a conventional choke coil, and the transmission signal prevention circuit is downsized and the RF switch. It is possible to reduce the size and cost of the built-in antenna duplexer.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an embodiment of an antenna duplexer with a built-in RF switch according to the present invention.

FIG. 2 is a perspective view showing a structure of a plate capacitor.

FIG. 3 is a block diagram of a conventional antenna duplexer.

FIG. 4 is a circuit configuration diagram of a conventional RF switch.

[Explanation of symbols]

1 Antenna Duplexer 2 Transmission Filter 3 Reception Filter 4 Antenna Switching Circuit 41 λ / 4 Phase Circuit 42 Parallel Resonance Circuit (RFC Circuit) 5 Ceramics 6, 7 Electrode ANT Antenna ant Antenna Terminal C1, C2, C3, C _RF Capacitor D1, D2 Diode L _RF coil Rx receiving terminal Tx transmitting terminal

Claims (1)

[Claims] 1. An antenna terminal to which an antenna is connected,
A reception terminal to which a reception circuit is connected, a transmission terminal to which a transmission circuit is connected, a reception filter for limiting a reception signal received by the antenna to a predetermined reception band and outputting the reception signal to the reception circuit, and the transmission A transmission filter that limits the transmission signal input from the circuit to a predetermined transmission band and outputs the transmission signal to the antenna, and is provided between the antenna terminal and the transmission filter and the reception filter. RF switch means for switching and connecting the output end and the input end of the receiving filter, and a control terminal to which a control signal for performing switching control of the RF switch means is provided, and the RF switch means is provided by the control signal. An antenna duplexer with a built-in RF switch for switching the antenna to a transmitting antenna and a receiving antenna by switching Having excitation point, RF switch built-in antenna duplexer, wherein a parallel resonance circuit of the capacitor and the coil, is interposed between said control terminal and said RF switch means.