JPS5855700B2 - antenna switching device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an antenna switching device suitable for radio equipment in the 400 MHz band to 800 MHz band.

In radio equipment, antenna switching devices have been used for a long time when the antenna is shared for transmitting and receiving, but recently solid-state antenna switching devices using switching diodes have been widely used. .

FIG. 1 is a circuit diagram showing an example of a conventional antenna switching device of this type. In the figure, 1 is an antenna for both transmitting and receiving, 2 is a transmitting output terminal, 3 is a receiving input terminal, and 4 and 5 are a transmitting side and a receiving side, respectively. 6 and 7 are coupling capacitors on the transmitting side and receiving side, respectively; 8 is a radio frequency choke coil (RFC) inserted in the circuit that biases the transmitting side switching diode 4; 9 is a switching diode on the side;
is a resistor for setting the bias current, 10 is a bypass capacitor, 11 is a power supply terminal for supplying the bias voltage, 12 is a bypass capacitor connected in series with the switching diode 5 on the receiving side, and 13 is a bias voltage for the switching diode 5 on the receiving side. A power supply terminal for supplying voltage, 14 a reception-side impedance matching coil, and 15 and 16 impedance matching capacitors.

With the above configuration, when transmitting, the transmitting side bias power supply terminal 11
Apply a positive DC voltage to the receiving side bias power supply terminal 13.
When grounded, both switching diodes 4 and 5 are biased in the forward direction, and a forward current determined by the resistor 9 flows, resulting in a low resistance of less than ■Ω (usually about 0.1Ω to 0.5Ω), equivalently creating a short-circuit state. It can be considered as

Therefore, the receiving terminal B of the coil 14 is grounded in terms of high frequency, and the coil 14 and the capacitor 15 form a parallel resonant circuit.

If this resonant frequency is made to match the transmitting frequency of the radio, the impedance when looking at the receiving side from connection point A of antenna 1 will be the impedance of antenna 1 (usually about 50Ω).
The value will be much larger than that.

In this state, the transmission output supplied from the transmission output terminal 2 toward the antenna 1 passes through the coupling capacitor 6 and the switching diode 4, and is radiated from the antenna 1 with almost no loss.

On the other hand, at this time, the switching diode 5 is connected to the receiving input side.
conducts and is short-circuited to ground at high frequencies, but an amplitude-limiting diode is installed at the entrance of the receiving stage to prevent leakage power from transmitting power from destroying the small-signal transistor in the first stage of the receiving stage. is provided.

(Not shown in the figure) Next, during reception, when a positive DC voltage is applied to the receiving bias power terminal 13 and the transmitting bias power terminal 11 is grounded, both switching diodes 4 and 5 are reverse biased and cut off. However, it merely exhibits a small junction capacitance of less than a few F.

The parallel capacitance of the capacitor 15, the coil 14, and the capacitor 16 with the junction capacitance of the diode 5 forms a low-pass filter having a characteristic impedance equal to the characteristic impedance of the antenna 1 (usually about 50Ω).

Therefore, the impedance of the received input signal coming from the antenna 1 when viewed from the connection point A to the transmitter side is extremely high due to the junction capacitance of the switching diode 4 being connected in series. 7 and is supplied to the receiving stage.

The operation of the conventional antenna switching device using switching diodes is as described above.
Although it operates satisfactorily in the Hz band, the following problems arise when the frequency reaches the 400 MHz band or higher.

That is, (1) since the individual components are wired using lead wires, the parasitic inductance of the lead wires of the switching diodes 4 and 5 and the capacitor 11.16
Due to the influence of parasitic inductance of the coil 14, parasitic capacitance of the coil 14, etc., the reproducibility of characteristics during assembly is poor, resulting in poor mass productivity.

(2) When the switching diode 4 is reverse biased, the actance value of the junction capacitance approaches the characteristic impedance value (usually 50Ω) on the receiving side, and the loss to the received input signal increases, resulting in a decrease in receiving sensitivity.

This invention was made in view of the above points.
The present invention aims to provide a solid-state antenna switching device that can be used in frequency bands from 00 MHz to 800 MHz.

FIG. 2 is a circuit diagram showing a basic configuration example of the present invention. In the figure, 17 and 18 are switching diodes connected in series with a plurality of switching diodes with small parasitic interfaces connected to the transmitting side and the receiving side, respectively. Element 19 is a strip line which is inserted into the receiving input path from antenna 1, has a characteristic impedance equal to that of the antenna, and has a wavelength of 1/4 at the operating frequency.

Now, it is clear that in the switching elements 1γ and 18, a plurality of switching diodes are connected in series, and the junction capacitance exhibited at the time of cut-off can be effectively reduced. This makes it unsuitable for use in high frequency bands.

FIG. 3 shows an example of the configuration of a switching element used in the antenna switching device of the present invention, and FIG. 3a is a top view thereof, and FIG. .

As shown in the figure, first, second and third metallized electrodes 21 are electrically insulated from each other on the surface of an insulating substrate 20,
22 and 23 are formed.

In particular, the first and second electrodes 21 and 22 at both ends are formed from the top surface of the substrate 20, via the side surfaces, to the bottom surface, respectively.

Then, the first and third metallized electrodes 21 and 2
Above each switching diode chip 2
One electrode of each diode is fused with a suitable solder, and then the other electrode of each diode and the third and second metallized electrodes are connected with a thin wire 25 such as a gold wire.

A key-shaped notch 26 provided in the third metallized electrode 23 allows solder to pass through the gold wire 25 when the diode chip 24 is fused.
This is to prevent the liquid from flowing into the bonding part.

When the above assembly is completed, the switching element is completed by covering the side of the diode where the chip 24 is present with a suitable cap or resin.

In this switching element, parasitic inductance is mainly caused by the thin bonding wires 25, but by arranging several thin bonding wires 25 in parallel, the parasitic inductance can be made extremely small.

Therefore, by using such switching elements 17 and 18 as shown in FIG. 2, the above-mentioned problems of the conventional device can be solved.

Next, the strip line 19 is used in place of the low-pass filter consisting of the coil 14 and capacitors 15 and 16 in the conventional device shown in FIG. 1, and has the same characteristic impedance as the antenna 1 as described above. , has a length of 1/4 wavelength at the operating frequency, so when the switching element 18 becomes conductive during transmission and point B is grounded at high frequency, the impedance when looking at the receiving side from point A becomes infinite, and the receiving side becomes infinite. Sometimes, the impedance seen from point A on the transmitting side is extremely large, so the impedance seen from point A on the receiving side is approximately the above characteristic impedance, and the received input signal from the antenna is transmitted to the receiving stage without loss.

As detailed above, in the antenna switching device of the present invention, the first and second metallized electrodes are provided at both ends of the insulating plate so as to wrap around these ends, and the first and second metallized electrodes are provided on the upper surface of the insulating plate. At least one third metallized electrode is provided sandwiched between the electrodes and insulated from each other, a diode chip is fixed to each of the first and third metallized electrodes by contacting one of the electrodes, and the other electrode is fixed to the metallized electrode. Since the switching element is connected to the third and second metallized electrodes by thin wires, the parasitic capacitance and parasitic inductance of the switching element can be extremely small, and if this antenna switching device can be used in a higher frequency range, Close.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a conventional antenna switching device.
FIG. 2 is a circuit diagram showing a basic configuration example of the present invention, FIG. 3 is a configuration example of a switching element used in the antenna switching device of this invention, FIG. 3a is a top view thereof, and FIG. Figure 3a
FIG. 2 is a cross-sectional view taken along line BB of In the figure, 1 is an antenna, 2 is a transmission output terminal, 3 is a reception input terminal, 17 and 18 are switching elements, 20 is an insulating substrate,
2L22 and 23 are first, second and third electrodes, 24 is a diode chip, and 25 is a thin metal wire. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. In an antenna that switches the same antenna for transmission and reception, first and second metallized electrodes are formed at both ends of an electrically insulating substrate, respectively, extending from the top surface to the side end surface to the bottom surface, and the above-mentioned insulating substrate. at least one third metallized electrode formed insulated between the first and second metallized electrodes on the upper surface;
and a diode chip that is fixed with one electrode in contact with the third metallized electrode, and the other electrode of the diode chip that is composed of a plurality of pieces and is fixed to the first and third metallized electrodes, respectively. A switching element having a group of fine metal wires connected to the third and second metallized electrodes is connected between the antenna and the transmission output terminal, and between the connection point of the antenna and the reception input terminal and the ground point, respectively. An antenna switching device characterized in that the diode chips of these switching elements are connected to each other and are both in a conductive state during transmission and a cutoff state during reception.