JPH06197043A - High frequency switch - Google Patents

Abstract

PURPOSE:To reduce an insertion loss at transmission and to improve the isola tion at reception by employing a 2nd diode with a small ON-impedance and connecting its cathode to ground via a parallel circuit comprising a capacitor and a resistor. CONSTITUTION:When the high frequency switch 10 is used to make transmission, a positive voltage is impressed to a control terminal 22. The voltage is impressed to a 1st diode 14 and a 2nd diode 30 as a forward bias voltage respectively to turn on the diodes 14, 30. Thus, a transmission signal from a transmission circuit TX is sent from an antenna ANT. In this case, an ON-impedance of the 2nd diode 30 is as small as 1ohm and a 2nd strip line 26 is connected to ground via the 2nd diode 30 and resonated and the impedance is almost infinite. Thus, the transmission signal is not almost sent to a reception circuit RX and the insertion loss is reduced. On the other hand, when the switch 10 is used to make reception, the diodes 14, 30 are nonconductive and the reception signal is not almost sent to the circuit TX.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention 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 mobile phone.

[0002]

2. Description of the Related Art A high-frequency switch, as shown in FIG.
In digital mobile phones, etc., the connection between the transmission circuit TX and the antenna ANT and the reception circuit RX and the antenna ANT
Used to switch the connection with.

As shown in FIG. 9, a conventional high frequency switch 1 includes an antenna ANT, a transmitting circuit TX and a receiving circuit R.
Connected to X. The anode of the first diode 3 is connected to the transmission circuit TX via the capacitor 2a. The anode of the first diode 3 is grounded via the series circuit of the first strip line 4 and the capacitor 2b. In addition, the first strip line 4 and the capacitor 2
A control terminal 6 is connected via a resistor 5 to an intermediate point of the point b. A control circuit for switching the high frequency switch 1 is connected to the control terminal 6. The cathode of the first diode 3 is connected to the antenna ANT via the capacitor 2c. The receiving circuit RX is connected to the capacitor 2c connected to the antenna ANT via a series circuit of the second strip line 7 and the capacitor 2d. The anode of the second diode 8 is connected to the intermediate point between the second strip line 7 and the capacitor 2d. The cathode of the second diode 8 is grounded.

When transmitting using the high frequency switch 1, a positive voltage is applied to the control terminal 6. This voltage turns on the first diode 3 and the second diode 8. At this time, the capacitors 2a, 2
The direct current component is cut by b, 2c, and 2d, and the voltage applied to the control terminal 6 is applied only to the circuit including the first diode 3 and the second diode 8. When the first diode 3 and the second diode 8 are turned on, the signal from the transmission circuit TX is sent to the antenna ANT, and the signal is sent from the antenna ANT. The transmission signal of the transmission circuit TX is the second
Since the strip line 7 is grounded by the second diode 8 and resonates and its impedance becomes substantially infinite, it is hardly transmitted to the receiving circuit RX side.

On the other hand, at the time of reception, by not applying a voltage to the control terminal 6, the first diode 3 and the second diode 8 are turned off. Therefore, the reception signal is transmitted to the reception circuit RX and is hardly transmitted to the transmission circuit TX side. In this way, the control terminal 6
Transmission and reception can be switched by controlling the voltage applied to.

[0006]

This high frequency switch 1
In order to reduce the insertion loss during transmission,
If a diode having a small resistance when turned on is used as the diode 3 and the second diode 8, the isolation between the transmission circuit TX and the reception circuit RX at the time of reception cannot be sufficiently obtained. On the other hand, in order to obtain sufficient isolation between the transmission circuit TX and the reception circuit RX at the time of reception,
O as the first diode 3 and the second diode 8
If a diode having a small capacitance during FF is used, the insertion loss during transmission will increase.

Therefore, a main object of the present invention is to provide a high frequency switch having a small insertion loss at the time of transmission and a good isolation between a transmission circuit and a reception circuit at the time of reception.

[0008]

The present invention is directed to a transmitter circuit,
A high frequency switch connected to a receiving circuit and an antenna for switching between a transmitting circuit and an antenna and a receiving circuit and an antenna, the anode being connected to the transmitting circuit side and the cathode being connected to the antenna side. 1
, A strip line connected between the antenna and the receiving circuit, and a second diode whose anode is connected to the receiving circuit side and whose cathode is connected to the ground side. The impedance of the diode is several times larger than the impedance on the receiving circuit side.
It is a high-frequency switch using a diode whose impedance at N time is 1Ω or less.

[0009]

Operation: As the first diode, a diode whose OFF-state impedance is several times or more larger than the impedance on the receiving circuit side is used, and further, as the second diode, O
By using a diode having an impedance of 1Ω or less at N time, the insertion loss at the time of transmission becomes small and the isolation between the transmission circuit and the reception circuit at the time of reception becomes good.

[0010]

According to the present invention, it is possible to obtain a high frequency switch having a small insertion loss during transmission and good isolation between the transmission circuit and the reception circuit during reception.

The above-mentioned objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of the embodiments with reference to the drawings.

[0012]

1 is a circuit diagram showing an embodiment of the present invention. The high frequency switch 10 is used for switching transmission / reception of a digital mobile phone or the like. Therefore,
The high frequency switch 10 includes an antenna ANT and a transmission circuit TX.
And the receiving circuit RX. The transmission circuit TX is connected to the anode of the first diode 14 via the capacitor 12. As the first diode 14,
A diode whose impedance at the time of OFF is several times or more larger than the impedance on the receiving circuit TX side of the high frequency switch 10 is used. In this embodiment, as the first diode 14, for example, a diode having an OFF-state capacitance of 0.35 pF is used. The first diode 14 has an electrostatic capacitance of 1 when OFF.
A diode of pF or less is desirable, and a diode of which capacitance when OFF is 0.5 pF or less is more desirable.
A diode having an electrostatic capacitance of 0.35 pF or less is more desirable.

The anode of the first diode 14 is grounded via the first stripline 16 acting as a choke coil and the capacitor 18. Further, the midpoint between the first stripline 16 and the capacitor 18 is
It is connected to the control terminal 22 via the resistor 20.
The same result can be obtained by connecting a resistor instead of the first strip line 16 and the capacitor 18 in the circuit example of FIG. The cathode of the first diode 14 is connected to the antenna ANT via the capacitor 24.

The antenna ANT has a capacitor 2
The second strip line 26 is connected via 4. The second strip line 26 is connected to the receiving circuit RX via a capacitor 28. Further, the midpoint between the second strip line 26 and the capacitor 28 is the second point.
The anode of the diode 30 is connected. As the second diode 30, a diode having an impedance of 1Ω when turned on is used. The second diode 30 has an impedance of 1Ω when turned on.
Smaller diodes may be used. The cathode of the second diode 30 has a capacitor 32 and a resistor 34.
It is grounded through a parallel circuit with.

When transmitting using the high frequency switch 10, a positive voltage is applied to the control terminal 22. The voltage applied to the control terminal 22 is applied to the first diode 14 and the second diode 30 as a forward bias voltage.
And 30 are turned on. Therefore, the transmission circuit T
The transmission signal from X is transmitted from the antenna ANT.
In this case, the impedance when the second diode 30 is ON is as small as 1Ω, and the second strip line 26 is grounded by the second diode 30 to resonate and its impedance becomes almost infinite. The transmission signal is hardly transmitted to the receiving circuit RX side, and the insertion loss becomes small. In addition, when a voltage is applied to the control terminal 22, the current will be
Cut by 2, resistor 20, first diode 14,
It will flow only to the circuit including the second diode 30 and the resistor 34, and will not affect other parts.

In the high frequency switch 10, the second
Of the second diode 30 is grounded via the capacitor 32, the inductance component of the second diode 30 is canceled by the capacitor 32, and the second strip line 26 Becomes closer to the ground potential, and the insertion loss becomes smaller.

On the other hand, when reception is performed using the high frequency switch 10, the voltage application to the control terminal 22 is stopped. Therefore, the first diode 14 and the second diode 14
The diode 30 is turned off. Therefore, the received signal is sent to the receiving circuit RX and hardly transmitted to the transmitting circuit TX. In this case, the first diode 1
Since the capacitance of 4 at the time of OFF is very small, the isolation between the transmission circuit TX and the reception circuit RX is improved.

In the high frequency switch 10, the frequency characteristics between the transmission circuit and the antenna, the frequency characteristics between the antenna and the reception circuit, and the transmission circuit and the reception circuit when the first diode 14 and the second diode 30 are turned on. The frequency characteristics of the first diode 14 and the second diode 30 are shown in FIGS. 2, 3 and 4, respectively.
The frequency characteristics between the transmitting circuit and the antenna, the frequency characteristics between the antenna and the receiving circuit, and the frequency characteristics between the transmitting circuit and the receiving circuit when the switch is turned off are shown in FIGS. 5, 6 and 7, respectively.

As is clear from the frequency characteristics shown in FIGS. 2 to 7, this high-frequency switch 10 has a small insertion loss during transmission and good isolation between the transmission circuit and the reception circuit during reception.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a graph showing frequency characteristics between a transmission circuit and an antenna when the first and second diodes are turned on in the embodiment shown in FIG.

FIG. 3 is a graph showing frequency characteristics between the antenna and the receiving circuit when the first and second diodes are turned on in the embodiment shown in FIG.

FIG. 4 is a graph showing frequency characteristics between the transmission circuit and the reception circuit when the first and second diodes are turned on in the embodiment shown in FIG.

5 is a graph showing frequency characteristics between the transmission circuit and the antenna when the first and second diodes are turned off in the embodiment shown in FIG.

6 is a graph showing frequency characteristics between the antenna and the receiving circuit when the first and second diodes are turned off in the embodiment shown in FIG.

FIG. 7 is a graph showing frequency characteristics between the transmission circuit and the reception circuit when the first and second diodes are turned off in the embodiment shown in FIG.

FIG. 8 is a conceptual diagram showing the operation of a high frequency switch.

FIG. 9 is a circuit diagram showing an example of a conventional high frequency switch.

[Explanation of symbols]

 10 high-frequency switch 14 first diode 16 first stripline 20 resistor 22 control terminal 26 second stripline 30 second diode 32 capacitor 34 resistor TX transmitter circuit RX receiver circuit ANT antenna

Claims (1)

[Claims] 1. A high-frequency switch connected to a transmission circuit, a reception circuit, and an antenna, for switching connection between the transmission circuit and the antenna and connection between the reception circuit and the antenna. A first diode having an anode connected to the antenna and a cathode connected to the antenna, a stripline connected between the antenna and the receiving circuit, and an anode connected to the receiving circuit side and a cathode connected to the ground side A second diode having an impedance at OFF which is several times or more larger than the impedance on the receiving circuit side is used as the first diode, and the impedance at ON is 1Ω or less as the second diode. High frequency switch using the above diode.