JP2001016130A - High frequency switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high frequency switch, which can be miniaturized, by improving isolation between an antenna and a transmission circuit and minimizing the number of parts. SOLUTION: Concerning this high frequency switch, a parallel circuit is formed by connecting an inductor 11 and a capacitor 4, which is connected to the cathode of a first diode 1 for limitation from an antenna ANT to the transmission circuit to the said first diode and a transmission/reception switching signal to be the forward bias voltage of first and second diodes 1 and 3 is supplied to the node of the inductor 11 and the capacitor 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high-frequency switch, and more particularly to a high-frequency switch for switching a signal path in a high-frequency circuit such as a digital portable telephone.

[0002]

2. Description of the Related Art A high-frequency switch is used for switching the connection between a transmission circuit TX and an antenna ANT and the connection between a reception circuit RX and an antenna ANT in a portable telephone or a mobile communication device.

In a conventional high-frequency switch 20, as shown in FIG. 3, a transmission circuit TX is connected to an antenna ANT via a capacitor 25 and a first diode 21. At the same time, the antenna ANT is connected to the receiving circuit RX via the strip line 22 and the capacitor 28.

On the transmitting circuit TX side, a control terminal V is connected to a midpoint between the capacitor 25 and the anode of the first diode 21 via an inductor element 24 and a resistor 29.
T is connected. Incidentally, the inductor element 24, the resistor 2
9 is grounded via a capacitor 26.

On the receiving circuit RX side, a second diode 23 is connected to an intermediate point between the strip line 22 and the capacitor 28. The anode is connected between the strip line 22 and the capacitor 28, and the cathode is grounded.

Here, capacitors 25, 26, 27, 2
Reference numeral 8 denotes a bypass capacitor for cutting a DC component, for example, preventing a control current (transmission / reception switching signal) supplied from the control terminal VT from leaking to the transmission circuit TX, the reception circuit RX, the antenna circuit ANT, and the ground. Things.

In the above-described high-frequency switch 20, when performing a transmission operation, a positive voltage is applied to the control terminal VT.
This voltage applies a forward bias to the first diode 21, the strip line 22, and the second diode 23, and the first diode 21 and the second diode 23 are turned on.

When the first diode 21 is turned on, the transmission signal from the transmission circuit TX is transmitted to the antenna AN.
Sent to T. Also, one end of the strip line 22 is grounded via the second diode 23, and is set to have a length of 1/4 wavelength with respect to the transmission signal,
Since the impedance resonates and the impedance becomes infinite with respect to the frequency of the transmission signal, the impedance is not transmitted to the reception circuit RX.

In the high-frequency switch 20, when receiving, no voltage is applied to the control terminal VT. As a result, the first diode 21 and the second diode 23 are turned off. Therefore, the reception signal is transmitted from the antenna ANT to the reception circuit RX, and is not transmitted to the transmission circuit TX.

As described above, transmission and reception can be switched by controlling the voltage applied to the control terminal VT.

However, in a diode used for a high-frequency switch, the first and second diodes are turned off when the diode is turned off.
Are present in the diodes 21 and 23, and are not completely insulated. First and second diodes 2
When the switches 1 and 23 are in the OFF state, the conduction between the antenna ANT and the receiving circuit RX is established. At this time, the first diode 21 has a capacitance component as described above.
When the transmission circuit TX is viewed from the antenna ANT, isolation cannot be obtained. For this reason, the received signal leaks to the transmitting circuit TX side, and the insertion loss between the antenna ANT and the receiving circuit RX increases. Thus, because of the capacitance that exists in the diode,
The performance of the high frequency switch is reduced.

Such a transmitting circuit TX and an antenna ANT
As a structure for improving the isolation between
Has been proposed.

In FIG. 4, a series circuit including an inductor element 31 and a capacitor 32 is provided in parallel with the first diode 21.

Then, the first diode 2 in the OFF state
A resonance circuit is formed by the capacitance component of No. 1 and the inductor element 31 and the capacitor 32, and the constants of the inductor element 31 and the capacitor 32 are determined so that the impedance becomes infinite with respect to the reception frequency of the reception signal. .

In FIGS. 3 and 4, the inductance element 24 connected between the capacitor 25 and the first diode 21 cuts an AC component, and flows from the transmission circuit TX to the antenna ANT. The transmission signal is prevented from flowing to the control terminal VT side, and the insertion loss is reduced. In FIG. 4, the capacitor 32 is a DC component blocking capacitor that allows a control current supplied from the control terminal VT to flow stably through the first diode 21.

[0016]

However, the above problem is that the control terminal VT is connected between the transmission circuit TX and the antenna ANT via the inductance element 24. That is, as a result of improving the characteristics from the high-frequency switch 20 of FIG. 3 to the high-frequency switch 30 of FIG.
Only the resonance circuit of C is added, and the number of components constituting the high-frequency switch circuit is merely increased.

[0017] For this reason, it has been difficult to reduce the size with an increase in the number of components constituting the circuit in order to improve the characteristics.

The present invention has been devised in view of the above-mentioned problems, and has as its object to improve the isolation between a transmitting circuit and an antenna, and to reduce the number of parts and to reduce the size. To provide a simple high-frequency switch.

[0019]

According to the present invention, there is provided a first diode having an anode connected to a transmission circuit and a cathode connected to an antenna, a strip line connected between the antenna and the reception circuit, An anode is connected between the strip line and the receiving circuit, a second diode having a cathode connected to the ground, an inductor and a capacitor connected in series, and the inductor is an anode of the first diode; A resonance circuit in which the capacitor is connected to a cathode of a first diode, and a transmission / reception switching signal serving as a forward bias voltage of the first and second diodes is provided at a connection point between the inductor and the capacitor. A high-frequency switch characterized by being supplied.

It is preferable that the inductor has an inductance value of 30 nH or more.

[0021]

According to the present invention, a series circuit comprising an inductor and a capacitor is connected in parallel with the first diode. That is, a parallel resonance circuit is formed by the capacitance of the first diode in the OFF state, the inductor, and the capacitor.

By setting the impedance of the parallel resonance circuit to infinity with respect to the frequency of the reception signal, the isolation between the transmission circuit and the antenna can be improved. As a result, the reception signal is transmitted to the transmission circuit TX. It is possible to completely prevent the signal from flowing and reduce the insertion loss of the received signal.

A control current for controlling ON and OFF of the first diode and the second diode is supplied between the inductor and the capacitor.

Therefore, the transmission / reception switching signal (control current)
Is supplied from the anode side of the first diode via the inductor element, and becomes a forward bias of the first diode and the second diode.

Then, when the transmission signal is supplied to the antenna, the transmission signal does not flow into the control terminal due to the presence of the inductor element having an AC blocking function.
Thereby, the insertion loss of the transmission signal is reduced.

In order to prevent the transmission signal from flowing into the control terminal, the inductance value of the inductor element is set to a value of 30 nH or more.

At the same time, the frequency of the received signal, OF
The inductance value and the value of the capacitor are selected in consideration of the capacitance component of the first diode in the F state.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a high-frequency switch according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram showing one embodiment of the high-frequency switch of the present invention.

This high-frequency switch 10 is connected to an antenna, a receiving circuit, and a transmitting circuit that constitute a digital cellular phone and a mobile communication device. In the figure, terminal TX
Is connected to the terminal ANT, the antenna is connected to the terminal ANT, and the receiving circuit is connected to the terminal RX. For convenience, an antenna is referred to as an antenna ANT, a receiving circuit as a receiving circuit RX, and a transmitting circuit as a receiving circuit TX.

The transmission circuit TX is connected via a capacitor 5
Connected to the anode of the first diode 1 and
Of the diode 1 is connected to the antenna ANT. The antenna ANT is connected to the receiving circuit RX via the strip line 2 and the capacitor 8.

The above is the path of the transmission signal of the predetermined frequency and the reception signal of the predetermined frequency. In the GSM communication system, the path is for a transmission signal and a reception signal of a predetermined frequency. GS
In the M communication system, the frequency band of the transmission signal is 880 to 91
5 MHz, and the frequency band of the received signal is 920 to 96
0 MHz.

The anode of the first diode 1 is
One end of the inductor element 11 is connected, and the other end of the inductor element 11 is connected to one end of the capacitor 4.

The other end of the capacitor 4 is connected to the cathode of the first diode 1. That is, a series circuit connecting the inductor element 11 and the capacitor 4 is:
The first diode 1 is connected in parallel.

Further, a connection point between the inductor element 11 and the capacitor 4 is grounded via a resistor 12 and a capacitor 6 to ground. At the same time, a connection point between the resistor 12 and the capacitor 6 has a control terminal VT to which a transmission / reception switching signal (hereinafter, control current) is supplied.

The strip line 2 and the capacitor 8
Is connected to the anode of the second diode 3, and the cathode of the second diode 3 is grounded to the ground potential.

The capacitors 4 and 5 in the above-described configuration are mainly bypass capacitors for blocking a DC component, and the inductor element 11 is an inductor which forms a parallel resonance circuit together with the first diode 1 to block a reception signal of a predetermined frequency. Component, and at the same time, an inductance component for alternating-current cutoff for preventing a transmission signal transmitted from the transmission circuit TX from leaking to the control terminal VT side.

The resistor 12 is a resistor for limiting a control current from the control terminal VT.

In particular, in the series circuit including the inductor element 11 and the capacitor 4 described above, the inductor element 1
1 requires a value of 30 nH or more from two functions, namely, an inductance component of a parallel circuit and an inductance component for AC cutoff. Note that the inductor element 11 is 30 n
If it is less than H, the transmission signal sent from the transmission circuit TX leaks to the ground potential via the resistor 12, the control terminal VT and the capacitor 6. In such a case, the insertion loss of the transmission signal increases.

Further, the inductor element 11 has the above-mentioned 30
The first diode 1 having a value of nH or more and in an OFF state
In consideration of the capacitance component of the capacitor 4 and the capacitor 4, the resonance circuit is set so that the frequency of the received signal (for example, the frequency band in GSM becomes infinite with respect to 920 to 960 MHz. When the capacitance component of the first diode 1 is, for example, 0.5 pF, the inductor element 11 is set to 50 nH.
As described above, if the capacitor 4 is set to 0.2 to 0.5 pF, the impedance can be made infinite for frequencies of 920 to 960 MHz.

In the high-frequency switch 10 having such a configuration, when transmitting a transmission signal from the transmission circuit TX to the antenna ANT, a positive voltage is applied to the control terminal VT. Since the DC limiting capacitors 4 to 8 exist, the control terminal V
The voltage supplied from T is a resistor 12 and an inductor element 1
1, the first diode 1, the strip line 2, the second diode 3, and a voltage applied between the ground potential. That is, the voltage is forward-biased with respect to the first diode 1 and the second diode 3, and the first diode 1 and the second diode 3 are turned on.

Here, since the second diode 3 is turned on, the end of the strip line 2 on the receiving circuit side is grounded to the ground potential. Then, the strip line 2 is transmitted to a transmission signal (frequency 880 to 915 MHz).
In contrast, by setting a short stub (infinite impedance), the transmission signal is cut off by the strip line 2 and does not leak to the reception circuit RX. Therefore, the transmission signal from the transmission circuit TX is guided to the antenna ANT without insertion loss.

When transmitting a reception signal received by the antenna ANT to the reception circuit RX, no voltage is applied to the control terminal VT. Thus, the first diode 1 and the second diode 3 are turned off since no forward bias voltage is applied. Here, the first diode 1
In the OFF state, the first diode 1 itself has a capacitance component. Then, as described above, the capacitance component, the inductance component of the inductor element 11, and the capacitance component of the capacitor 4 make LC
Thus, a resonance circuit is formed. Since the anti-resonance frequency of the LC resonance circuit is set to be equal to the frequency of the reception signal, the isolation between the antenna ANT and the transmission circuit TX is improved, and the reception signal is transmitted to the transmission circuit Tx.
It will not leak to the X side. Since the strip line 2 operates simply as a transmission line, the received signal is sent to the receiving circuit RX without insertion loss.

The present inventor has designed a first diode 21 for preventing the reception signal shown in FIG. 3 from leaking to the transmission circuit TX side, a first diode 1, an inductor element 11, and a capacitor 4 shown in FIG. Assuming a parallel resonance circuit in which ANT is connected, the transmission loss characteristic from the ANT to the transmission terminal in the receiving state (VT = 0 V) is represented by F ₁ (for example, 880 to 91).
5 MHz).

For example, FIG. 2A shows a measuring circuit assuming the high-frequency switch of the present invention, FIG. 2B shows a characteristic diagram, and FIG. 5A shows a conventional high-frequency switch 2 shown in FIG.
FIG. 5B shows a measurement circuit assuming 0, and shows a characteristic diagram of FIG. The receiving circuit is connected to 50Ω on the assumption that it is connected to a measuring instrument.

That is, in the conventional high-frequency switch, -18
With respect to the pass loss of about db, the high-frequency switch of the present invention has a pass loss of about -28 db. That is, the isolation is greatly improved as compared with the related art.

In the present invention, the control current from the control terminal VT is supplied to the connection between the inductor element 11 and the capacitor 4. The inductor element 11 having the inductance value of 30 nH or more prevents the transmission signal from flowing to the control terminal VT when the control terminal VT is viewed from the transmission circuit TX side. Thereby, the insertion loss of the transmission signal can be improved.

As described above, the inductor element 11 and the capacitor 4 constituting the resonance circuit together with the first diode 1 prevent the transmission signal from leaking to the control terminal VT during transmission. At the time of reception, the whole resonance circuit prevents the reception signal from leaking to the transmission circuit TX side and the control terminal VT side. The control current from the control terminal VT is controlled so that the first diode 1 is biased in the forward direction.

As described above, according to the present invention, at the time of reception, the inductor element 11 and the capacitor 4 improve the isolation when the transmission circuit TX is viewed from the antenna ANT.
When transmitting, the control current is changed to the first and second diodes 1,
3 also serves as a stable supply element.

For this reason, as in the prior art, the inductor element 31 forming a parallel circuit with the first diode 21
In addition, the inductor element 24 for preventing the transmission signal from flowing to the control terminal can be shared, and the number of circuit components can be reduced. Moreover, since the element that can be reduced is usually an inductor element requiring a relatively large area on the circuit board, it can contribute to downsizing of the high-frequency switch itself.

[0050]

As described above, according to the present invention, the isolation between the transmission circuit and the antenna can be improved. As a result, the reception signal can be completely prevented from flowing to the transmission circuit TX, and the reception signal can be inserted. Loss reduction can be prevented. Further, the number of components of the electronic component element can be reduced and can be stably supplied as a forward bias of the first diode and the second diode.

Thus, a small high-frequency switch with stable isolation characteristics and stable diode switching operation can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a high-frequency switch according to the present invention.

FIGS. 2A and 2B are diagrams showing a passage loss of a reception signal of a first diode of the high-frequency switch shown in FIG. 1, wherein FIG. 2A is a measurement circuit diagram and FIG. 2B is a characteristic diagram.

FIG. 3 is a circuit diagram showing one embodiment of a conventional high-frequency switch.

FIG. 4 is a circuit diagram showing another embodiment of the conventional high-frequency switch.

FIGS. 5A and 5B are diagrams showing a passage loss of a reception signal of a first diode of the high-frequency switch shown in FIG. 3, wherein FIG. 5A is a measurement circuit diagram and FIG. 5B is a characteristic diagram.

[Explanation of symbols]

 10, 20, 30 ... high frequency switch 1, 21 ... first diode 3, 23 ... second diode 2, 22 ... strip line 11, 31, ... inductor element 32, 4, ... ... Capacitor VT ... Control terminal TX ... Transmit circuit RX ... Receive circuit ANT ... Antenna

Claims (1)

[Claims] 1. A first diode having an anode connected to a transmission circuit and a cathode connected to an antenna, a stripline connected between the antenna and a reception circuit, and an anode connected to the stripline and the reception circuit. A second diode connected between the first diode and a circuit; a cathode connected to ground; and an inductor and a capacitor connected in series, the inductor being connected to the anode of the first diode, and the capacitor being connected to the first diode. A resonance circuit connected to the cathode of the diode, wherein a transmission / reception switching signal serving as a forward bias voltage of the first and second diodes is supplied to a connection point between the inductor and the capacitor. A high frequency switch characterized by the above.