JPH11340872A - Antenna switching circuit having provision for dual band - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an antenna switching circuit having provision for dual band, that stably selects a transmission wave at a prescribed transmission frequency band and transmits the selected wave from an antenna, when coping with two different transmission frequency bands. SOLUTION: This circuit is provided with an antenna terminal ANT which is connected to a reception/transmission antenna, a transmission signal terminal TX connecting to a transmission system circuit TX and to which a transmission signal is fed, a 1st reception signal terminal RX1 and a 2nd reception signal terminal RX2, from which a reception signal is fed to a reception system circuit RX to switch the transmission reception operation of the antenna. Then switching elements D1, D2 are placed between one terminal of two strip lines SL, that provide a high impedance to 1st and 2nd transmission signals and a point of a ground level, and a resonance circuit X that provides high impedance for each transmission frequency band is provided between the switching elements D1, D2 and the point of the ground potential.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dual-band antenna switching circuit used in a dual-band portable communication device for transmitting and receiving signals in different frequency bands.

[0002]

2. Description of the Related Art As shown in FIG. 10, an antenna switching circuit used in a portable communication device or the like transmits and receives a transmission circuit TX and a reception circuit RX with the same antenna ANT. It is used for the purpose of switching the connection between the receiver and the receiving circuit RX.

[0003] In recent years, there has been a demand for portable communication devices that can perform transmission and reception operations in two different frequency bands due to services using communication systems with different frequency bands.

Conventionally, a dual-band compatible antenna switching circuit has a circuit configuration as shown in FIG.

[0005] An antenna terminal ANT to which an antenna for performing reception and transmission is connected, a transmission signal terminal TX connected to a transmission system circuit, and two reception signal terminals RX1 and RX2 connected to the reception system circuit. I was Note that transmission signals in different frequency bands are supplied to the transmission signal terminal TX from the transmission circuit side.

A transmission / reception signal line (transmission signal terminal TX)
And a first reception signal terminal RX1) and a first connection point S branched from the first reception signal terminal RX1 to the antenna terminal ANT.
A second connection point D to which the second reception signal terminal RX2 is connected is provided between the first reception signal terminal RX1 and the first reception signal terminal RX1. still,
In order to clearly distinguish the first connection point S and the second connection point D, the first connection point is simply called the connection point S, and the second connection point D is called the branch point.

[0007] Then, a connection point S with the antenna terminal ANT.
A first strip line SL2 corresponding to a λ / 4 wavelength in the transmission frequency band of the second transmission signal ft2 is disposed between the first strip line SL2 and the branch point D. Then, a coupling capacitor C4 is arranged between the first strip line SL2 and the end on the first reception signal terminal RX1 side. at the same time,
On the reception signal terminal RX1 side of the first strip line SL2, a first switch element D2 such as a diode is arranged between the first strip line SL2 and the ground potential. The cathode side of the diode D2 is grounded at a high frequency via a capacitor or the like.

[0008] For example, a frequency switching control terminal CONT2 is connected to a cathode side of a diode D2 as a first switch element via a strip line SL4 for generating a predetermined inductance component.

The first strip line SL3 and the coupling capacitor C5 are arranged between the branch point D and the second reception signal terminal RX2. A second switching element D3 such as a diode is arranged between the strip line SL3 and the reception signal terminal RX2 between the strip line SL3 and the ground potential. Note that the cathode side of the diode D3 is
High frequency grounded.

[0010] The strip line SL3 has the first transmission signal ft together with the strip line SL2 (having a line length corresponding to the frequency band of the second transmission signal).
The length is set to correspond to λ / 4 wavelength of one transmission frequency band.

An anode of the diode D1 is connected between the transmission signal terminal TX to which the transmission signal is supplied and the connection point S via a capacitor C1 from the transmission signal terminal TX. Then, the capacitor C1 and the diode D1
A strip line SL1 whose one end is grounded at a high frequency and generates a predetermined inductance component is disposed between the first and second lines. A frequency switching control terminal CONT1 is connected to a ground-side end of the strip line SL1 via a resistor R1.
Are formed.

In the antenna switching circuit thus configured, the transmission signal ft1 in the first transmission signal frequency band
Is supplied, an H level (positive voltage) is applied to each of the frequency control terminals CONT1 and CONT2.
Thereby, the resistor R1, the strip line SL1, the diode D1, the strip line SL2, and the strip line SL
A current flows to the ground potential via the line 3. That is, the diodes D1 and D3 are turned on, and the diode D2 is turned off.

Therefore, the strip line SL2 and the strip line SL3 operate as an integrated strip line, and one end thereof is grounded. Therefore, as described above, the strip line SL2 and the strip line SL3 have the line length of λ / λ of the first transmission signal ft1.
4, the reception signal terminals RX1 and RX2 are viewed from the cathode of the diode D1.
The state becomes a high impedance state, and the first transmission signal ft1 is hardly transmitted to the receiving system circuit, and is led to the antenna terminal ANT via the capacitor C2.

When the transmission signal ft2 of the second transmission signal frequency band is supplied, the frequency control terminal CONT1 receives H
Level (positive voltage) is applied, and L is applied to the frequency control terminal CONT2.
Add level (ground level). Thereby, the resistor R1, the strip line SL1, the diode D1, the strip line SL2, the diode D2, and the strip line SL
4. A current flows to the ground potential via the diode D3, and at the same time, the resistor R1, the strip line SL1, the diode D1, the strip line SL2, and the strip line SL
3. A current flows to the ground potential via the diode D3. That is, the diodes D1 to D3 are turned on.

However, since the diode D2 is in the ON state, one end of the strip line SL2 is grounded at a high frequency, and the line length of the strip line SL2 is λ / 4 of the second transmission signal ft2 as described above. When the reception signal terminal RX is viewed from the cathode of the diode D1, the transmission signal ft1 is hardly transmitted to the reception circuit, and the antenna terminal ANT is transmitted via the capacitor C2. Is derived.

On the other hand, at the time of reception, both the frequency control terminals CONT1 and CONT2 are set to LOW (ground potential). For this reason, the diodes D1 to D3 are all in a high impedance state, and the reception signals fr1 and fr2 (fr1> fr2) received from the antenna terminal ANT are not led out to the transmission signal terminal TX, and the capacitor C2, the strip line SL2, and the capacitor Received signal terminal R via C4
X1 and the received signal RX via the capacitor C2, the strip line SL2, the strip line SL3, and the capacitor C5.
2, respectively.

Incidentally, at the subsequent stage of the first reception signal terminal RX1,
If a high-pass filter that passes the frequency band of the reception signal fr1 is connected, and at the same time, a low-pass filter that passes the frequency band of the reception signal fr2 is connected downstream of the second reception signal terminal RX2, two types of frequencies can be obtained. The received signal of the band can be selectively extracted.

[0018]

In order to transmit a transmission signal formed by the above-mentioned transmission system circuit from an antenna,
A signal having a large output level (having a large amplitude) is obtained.

In this circuit configuration, for example, when the frequency control terminal CONT1 and the frequency control terminal CONT2 are set to the H level and the first transmission signal ft1 is transmitted from the antenna, the switching element is a switching element that normally operates in the OFF state. There is a problem that D2 is rectified only in the positive cycle by the AC signal and flows to the ground potential. As a result, distortion (spurious) occurs in the first transmission signal ft1.

Further, since the strip line SL2 does not have a λ / 4 wavelength in the frequency band of the first transmission signal ft1, that is, the strip line SL2 does not have a high impedance with respect to the transmission signal ft1. As a result, the transmission signal ft1 having spurious signals is transmitted from the antenna terminal ANT via the capacitor C2.

In order to suppress the spurious component, a low-pass filter, a trap circuit, and the like are connected to the antenna terminal AN.
It is conceivable to provide it before T. However, if a low-pass filter, a trap circuit, or the like is provided, the circuit configuration is inevitably increased in size, and at the same time, cost reduction cannot be achieved, and the problem of signal attenuation of transmission and reception signals is achieved.

As a result, a transmission signal of a predetermined frequency is not stably derived from the antenna, and spurious components may adversely affect surrounding communication equipment.

The present invention has been devised in view of the above-described problems, and has as its object to suppress spurious components even when a transmission signal having a large signal level is supplied to a transmission signal terminal, thereby achieving stable transmission. An object of the present invention is to provide a dual band compatible antenna switching circuit capable of leading a signal to an antenna terminal.

[0024]

The present invention provides an antenna terminal to which an antenna for transmitting and receiving is connected, a transmission signal terminal to which a transmission circuit is connected, and first and second terminals to which a reception circuit is connected. A second reception signal terminal, wherein the antenna terminal, the transmission signal terminal, and the first reception signal terminal are connected to each other at a first connection point, and the second reception signal terminal is connected to the first connection point. And a first connection point between the first reception signal terminal and the first reception signal terminal, and a first connection point corresponding to a λ / 4 wavelength of a first transmission frequency band between the first and second connection points. A strip line and a first switch element for grounding one end of the strip line to the ground potential side are provided between the second connection point and the second reception signal terminal together with the first strip line. The second strip corresponding to the λ / 4 wavelength of the transmission frequency band No. 2 And a second switching element for grounding one end of the strip line and the strip line to a ground potential, and a resonance circuit between at least one of the first and second switching elements and a ground potential. The dual-band antenna switching circuit is characterized in that the in-piece dance between the switching element and the ground potential is increased to reduce the voltage applied to the switching element.

[0025]

As described above, according to the present invention, for example, the strip line SL4 and the frequency control terminal CO of the circuit configuration shown in FIG.
A capacitor C7, one of which is grounded, is arranged between the capacitor C1 and NT2, and the capacitor C6, the strip line SL4, and the capacitor C7 form a resonance circuit. Therefore, the impedance at the capacitor C7 of this resonance circuit can be increased. Thus, the voltage applied to the diode D2 is reduced, and the flowing current is minimized, so that the occurrence of spurious is reduced.

That is, a transmission signal of a large level (large amplitude)
Signal is applied to the diode in the OFF state, the impedance between the cathode of the diode and the ground potential is large, so the voltage applied to both ends of the diode is reduced, and the signal having a large amplitude is not rectified.
Therefore, distortion of the transmission signal is reduced, and spurious components can be effectively suppressed.

Accordingly, a predetermined signal can be led out to the antenna terminal in a stable state.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A dual-band antenna switching circuit according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing a configuration of a dual band antenna switching circuit according to the present invention. The same parts as those in the conventional circuit diagram will be described with the same reference numerals.

In the figure, ANT is an antenna terminal to which an antenna is connected, TX is a transmission signal terminal, and R
X1 and RX2 are reception signal terminals, respectively. In other words, the transmission signal f of two different frequency bands is provided to the transmission signal terminal TX.
t1 and ft2 are supplied from the transmission circuit, and a signal received from the antenna is derived to the first reception signal terminal RX1 and the second reception signal terminal. It should be noted that a pass band filter (high-pass filter, low-pass filter) corresponding to two reception frequency bands is connected to a stage subsequent to each reception terminal. Therefore, a pass band filter (high pass filter, low pass filter) of the first reception signal terminal is connected. In addition, the transmission / reception signal line, that is, the transmission signal terminal TX and the first
Between the antenna terminal ANT and the reception signal terminal RX1.
And a branch point D branching to the second reception signal terminal RX2 is provided between the connection point S and the first reception signal terminal RX1.

Then, a connection point S with the antenna terminal ANT
A first strip line S corresponding to a λ / 4 wavelength of the transmission frequency band of the first transmission signal ft1 between the first strip line S and the branch point D.
L2 is arranged. Also, the first strip line S
A first switch element D2 such as a diode is arranged between the first reception signal terminal RX1 side of L2 and the branch point D. The anode side of the diode D2 serving as the first switching element is connected to one end of the strip line SL2, and the cathode side of the diode D2 is grounded.

The branch point D and the second reception signal terminal RX
2, a second strip line SL3 and a capacitor C5 are arranged to correspond to the λ / 4 wavelength of the transmission frequency band of the second transmission signal ft2 together with the first strip line SL2. . Further, a second switch element D3 such as a diode is arranged between the second strip line SL3 and the capacitor C5. The anode side of the diode D3, which is the second switching element, is connected to one end of the strip line SL3, and the cathode side of the diode D3 is grounded.

Between the transmission signal terminal TX to which the transmission signal is supplied and the connection point S, the anode side of the diode D1 is connected from the transmission signal terminal TX via a capacitor C1. It is connected to the ground potential through the strip line SL1 to be generated and the capacitor C3.

A frequency switching control terminal CONT1 is formed between the strip line SL1 and the capacitor C3 via a resistor R1.

In the above circuit configuration, a resonance circuit (shown by a dotted line in the figure) is added to the cathode side (ground side) of either the first switch element D2 or the second switch element D3. is there. In the figure, a resonance circuit including a strip line SL4 and a capacitor C6 is added to the first switch element D2 side.

The above-described resonance circuit X has two transmission signals ft
Between 1 and ft2, a signal of a lower frequency, for example, a frequency band of the transmission signal ft1 is set to be close to the resonance frequency.

More specifically, the circuit constant of the resonance circuit X can be set, for example, by adjusting the capacitance values of the capacitors C6 and C7 and, if necessary, by adjusting the inductance component of the strip line SL4. . That is,
In the frequency band of the transmission signal ft1, the resonance circuit X has a high impedance.

For example, in the circuit configuration of FIG. 1, the transmission signal ft1 in the first transmission signal frequency band is transmitted to the antenna terminal AN.
When transmitting from T, the frequency control terminals CONT1 and CONT2 are set to H level (positive voltage), respectively. As a result, a current flows to the ground potential via the resistor R1, the strip line SL1, the diode D1, the strip line SL2, the strip line SL3, and the diode D3.

Thus, the diodes D1 and D3 are turned on, and the diode D2 is turned off.

Therefore, the strip line SL2 and the strip line SL3 operate as an integrated strip line, and one end thereof is grounded. The strip line SL2 and the strip line SL3 determine the line length of the integrated strip line by the first transmission signal ft.
1 is set to a length corresponding to λ / 4, and when the reception signal terminal RX is viewed from the cathode of the diode D1, a high impedance state is established, the transmission signal ft1 is hardly transmitted to the reception system circuit, and the capacitor C2 Through the antenna terminal ANT.

When transmitting the transmission signal ft2 of the second transmission signal frequency band from the antenna terminal ANT, the frequency control terminal CONT1 is set to H level (positive voltage), and the frequency control terminal CONT2 is set to LOW (ground potential). I do. As a result, a current flows to the ground potential via the resistor R1, the strip line SL1, the diode D1, the strip line SL2, the diode D2, the strip line SL4, and the capacitor C7. As a result, the diodes D1 and D2 are turned on. Further, a resistor R1, a strip line SL1, a diode D1, and a strip line S
A current flows to ground potential via L2, strip line SL3, and diode D3. As a result, the diode D3 is also turned on. That is, all of the diodes D1 to D3 are turned on.

At this time, since the line length of the strip line SL2 whose one end is grounded via the diode D2 is set to a length corresponding to λ / 4 of the second transmission signal ft2, the cathode of the diode D1 is set. Looking at the reception signal terminal RX, the state becomes high impedance, and the transmission signal ft1
Is hardly transmitted to the receiving circuit, and the capacitor C2
Through the antenna terminal ANT.

At the time of reception, both the frequency control terminals CONT1 and CONT2 are set to LOW (ground potential). As a result, the diodes D1 to D3 are all in a high impedance state, and the reception signals fr1 and fr2 received from the antenna terminal ANT are not led out to the transmission signal terminal TX. That is, the received signals fr1 and fr2 (fr1
> Fr2) is a capacitor C2, a strip line SL
2. While being derived from the reception signal terminal RX1 via the capacitor C4, the capacitor C2 and the strip line S
L2, the strip line SL3, and the received signal RX2 via the capacitor C5.

As described above, a high-pass filter that passes the frequency band of the reception signal fr1 is connected to the subsequent stage of the first reception signal terminal RX1, and the second reception signal terminal RX1
By connecting a low-pass filter that passes the frequency band of the reception signal fr2 to the second stage, it is possible to select and extract the reception signals of the two types of frequency bands.

As described in the problem to be solved by the above-described invention, when transmitting the first transmission signal ft1, the first switch element D2 is turned off.
However, when the amplitude of the first transmission signal ft1 increases,
Since the diode D2 is grounded in an AC manner despite the OFF state, an AC rectifying action occurs,
As a result, distortion occurs in the first transmission signal ft1.

However, in the present invention, a resonance circuit X having a high impedance in the frequency band of the first transmission signal ft1 is added to the cathode side of the diode D2.

That is, when the reception signal terminal RX is viewed from the cathode of the diode D1, the first transmission signal ft is formed by the integration of the strip line SL2 and the strip line SL3.
1 and at the same time, due to the presence of the resonance circuit X having a high impedance with respect to the first transmission signal ft1 arranged at the ground potential AC grounded from one end of the strip line SL2. A very stable signal state can be transmitted from the antenna terminal ANT without being short-circuited to the receiving system circuit or the ground potential.

As shown in FIG. 2, the inventor fixed the capacitor C7 constituting the resonance circuit X at 47 pF and measured the impedance when the capacitor C6 was used as a parameter. The result is shown in FIG. That is, the capacitor C6
= 3 pF, the impedance becomes maximum around the frequency of 900 MHz, and as shown in FIG. 4, the harmonic distortion of the capacitor C6 = 2.5 pF and 3P is about 75 dBc in a wide frequency range. It can be seen that the level of is low.

The capacitor C constituting the resonance circuit X
6 was fixed to 3 pF, and the impedance was measured when the capacitor C7 was used as a parameter. The result is shown in FIG.

As shown in FIG.
In the vicinity of 0 MHz, the impedance becomes maximum when the capacitor C7 = 50 pF. As shown in FIG. 6, the harmonic distortion is measured.
Good harmonic distortion at 7P, capacitor C7 = 20p
It can be seen that at about F, the harmonic distortion is reduced to 60 dBc or less.

From these results, it is sufficient to set the capacitors C6 and C7 so that the harmonic distortion has the maximum impedance of the resonance circuit X including the strip line SL4, the capacitor C6, and the capacitor C7.

At this time, the voltage applied to both ends of the diode D2 is minimized, and the distortion is also minimized.

In the above example, the impedance of the resonance circuit X is increased by optimizing the capacitors C6 and C7. However, as shown in FIG. 7, the strip line SL4 is a variable inductance element, The inductance component may be adjusted so that the impedance of the resonance circuit X is maximized.

Further, as shown in FIG. 8, the impedance may be maximized by the parallel circuit of the strip line SL4 and the capacitor C6, and the frequency control terminal CONT2 may be arranged via the strip line SL5. As shown, a configuration in which the strip line SL5 is replaced with a resistor R2 or the like may be used.

The above description has been given of the example in which the first and second switching elements are used as the diodes D2 and D3.
The diode may be a PN junction type diode or a PIN junction type diode. Further, as the switching element, a transistor or an EFT (field effect transistor) may be used in addition to the diode described above.

In the figure, the first switching element D1 at one end of the strip line SL2 is provided to suppress AC grounding only for the first transmission signal ft1, which is the lower frequency band of the two frequency bands. The resonance circuit X is added to, for example, in order to suppress the AC grounding for the second transmission signal ft2 which is a high frequency band, for example,
The resonance circuit X may be added to the second switching element D3 on one end side of the strip line SL3. Also in this case, the circuit constant of the resonance circuit X may be set in consideration of the frequency band of the second transmission signal ft2 so as to have a resonance frequency corresponding thereto.

[0057]

As described above, according to the present invention, as an antenna switching circuit of a dual band communication device, spurious noise generated from the antenna can be suppressed even when the transmission circuit has a high power.

That is, it is not necessary to provide a low-pass filter or a trap circuit for suppressing the spurious level in front of the antenna terminal, so that signal loss does not occur and the size can be reduced.

Therefore, transmission signals of different frequency bands are
An extremely stable high-level transmission signal can be selectively transmitted from the antenna.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a dual band antenna switching circuit according to the present invention.

FIG. 2 is a circuit diagram of a portion X of a resonance circuit X in the circuit of FIG.

FIG. 3 is a characteristic diagram showing impedance characteristics when a capacitor C7 constituting the resonance circuit X is fixed and the capacitor C6 is used as a parameter.

FIG. 4 is a characteristic diagram showing harmonic distortion characteristics in FIG.

FIG. 5 is a characteristic diagram showing impedance characteristics when a capacitor C6 constituting the resonance circuit X is fixed and a capacitor C7 is used as a parameter.

6 is a characteristic diagram showing harmonic distortion characteristics in FIG.

FIG. 7 is another circuit diagram of a portion X of a resonance circuit X used for a dual band compatible antenna switching circuit.

FIG. 8 is another circuit diagram of a portion X of a resonance circuit X used for a dual band antenna switching circuit.

FIG. 9 is another circuit diagram of a portion X of a resonance circuit X used for a dual-band compatible antenna switching circuit.

FIG. 10 is a circuit diagram illustrating an operation of an antenna switching circuit used in a mobile communication device or the like.

FIG. 11 is a circuit diagram showing a configuration of a conventional dual-band compatible antenna switching circuit.

[Explanation of symbols]

 D2 first switch element D3 second switch element D1 diode SL1 to SL5 strip line TX transmission signal terminal RX1 first reception signal terminal RX2 second ANT ... antenna terminal S ... connection point D ... branch point X ... resonance circuit C6, C7 ... capacitor

Claims (1)

[Claims] An antenna terminal to which an antenna for transmitting and receiving is connected, a transmission signal terminal to which a transmission system circuit is connected,
A first receiving signal terminal to which a receiving system circuit is connected; a first connecting point connecting the antenna terminal, the transmitting signal terminal, and the first receiving signal terminal to each other; Are connected at a second connection point between the first connection point and the first reception signal terminal, and a first transmission frequency band of the first transmission frequency band is provided between the first and second connection points. a first strip line corresponding to λ / 4 wavelength and a first switch element for grounding one end of the strip line to the ground potential side, between the second connection point and the second reception signal terminal; Along with the first strip line, a second strip line corresponding to a λ / 4 wavelength of a second transmission frequency band and a second switch element for grounding one end of the strip line to a ground potential are arranged respectively. The first and second switching elements A resonance circuit is arranged between at least one of the terminals and the ground potential, the in-piece dance between the switching element and the ground potential is increased, and the voltage applied to the switching element is reduced. Dual-band compatible antenna switching circuit.