JPH0129870Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The invention uses a switching diode to select one reception signal from a plurality of antenna circuits, and conversely to send a transmission signal to one of them. This invention relates to an antenna switching circuit.

[Conventional technology]

FIG. 3 shows this type of conventional receiving antenna switching circuit, in which a switching signal is applied to a switching diode (any one of D11 to D13) depending on the selected position of the selector switch S11.
is turned on. Then, the selected terminal (J11
- J13), the received signal of the associated antenna circuit is supplied to the receiving circuit.

[The problem that the invention attempts to solve]

However, in this circuit, terminals J11 to J1
The terminal impedance of the remaining two terminals that are not selected among the three terminals is the switch diode D11.
~D13 and the changeover switch S11 open the switch. Therefore, when the terminals J11 to J13 are each connected to the antenna through an amplifier, external vibrations are generated in the amplifier, which may interfere with the receiving circuit. Incidentally, even if it is attempted to connect a resistor between each switching contact of the switching switch S11 and the ground, if the resistance value is set small enough to avoid such a phenomenon, the matching state of the receiving circuit will be affected.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an antenna switching circuit in which unselected antenna circuits are terminated.

[Means for solving problems]

In order to achieve this objective, the present invention adopts the basic configuration of the antenna switching circuit as shown in FIG. 1a. In the figure, J1 and J2 are terminals connected to the antenna circuit to be selected, for example, the antenna itself or a circuit including an amplifier. J3
is a transmitting/receiving circuit that receives signals from terminals J1 or J2 or sends signals to these terminals. J4 and J5 are terminals to which switching signals inverted from L level to H level are respectively applied. B1 and B2 are diode pair D1,
D2: A bias circuit that applies bias voltages to D3 and D4 in the forward and reverse directions at a level lower than that of the switching signal, and includes an internal resistor with a resistance value large enough not to affect the matching state of the transmitter/receiver circuit. I'm here. Ro is a terminating resistor that brings the impedance seen from the terminal J1 or J2 toward the associated antenna circuit into a matching state or sufficiently small. Z1 is an impedance element that exhibits a value sufficiently larger than the matching impedance of the transmitting/receiving circuit connected to the terminal J3 with respect to the input high frequency transmitting/receiving signal.

If there are two or more n antenna circuits to be selected, n-1 switching circuits according to FIG. 1a are connected in a tournament manner. For example, in the case of four switching circuits, three switching circuits 1 to 3 shown in FIG. 1a are connected as shown in FIG. 1b. That is, the selected antenna circuit is connected to the respective terminals J1 and J2 of the switching circuits 1 and 2, and the selected reception signal or the transmission/reception signal of the transmission signal to be transmitted is supplied to the terminal J3 of the switching circuit 3. In the case of three switching circuits, two such switching circuits 5 and 6 are used, as shown in FIG. 1c.

[Effect]

The operation of the antenna switching circuit shown in FIG. 1a will first be explained for reception. When the output of the receiving antenna circuit at terminal J1 is supplied to the receiving circuit at terminal J3, terminal J4 is set to L level, for example, ground potential, and terminal J5 is set to H level, for example, a switching signal of positive potential. This causes the diode D
1 is on, diode D2 is off, diode D
3 is off and diode D4 is on. At this time, the received signal from terminal J1 is transmitted through high impedance element Z1 or diode D3.
coupling capacitor C without flowing into
1, and is supplied to terminal J3 through C2. on the other hand,
The output end of the receiving antenna circuit connected to terminal J2 is radio-frequency terminated through coupling capacitor C3 and diode D4. Terminal J2
When selecting the output of the receiving antenna circuit, instead, terminal J4 is set to positive potential and terminal J5 is set to ground potential. Diode D1 is off, diode D
2 is on, diode D3 is on, diode D
4 is off. The received signal from terminal J2 is supplied to terminal J3 through diode D3, and
The output terminal of the receiving antenna circuit of No. 1 is a diode D2.
through and terminated with a resistor Ro.

Depending on how the circuit potential is applied, the H level of the switching signal corresponds to the ground potential, and the L level of the switching signal corresponds to the negative potential. When applied as a transmitting antenna switching circuit, a transmitting circuit is connected to terminal J3, and a transmitting antenna circuit including the transmitting antenna itself or an amplifier etc. is connected to terminals J1 and J2.
A resistor Ro terminates the input end of the unselected transmitting antenna circuit. Regarding FIG. 1b, the control terminals J4 and J5, which belong to the received signal to be selected among the four receiving circuits, are each set to H level.
For example, when outputting the received signal at the terminal J1 of the switching circuit 1 to the final output terminal J3 of the switching circuit 3, the terminal J5 of the switching circuit 1 and the terminal J5 of the switching circuit 3 are set to H level. At this time, by setting the terminal J4 or J5 of the switching circuit 2 to H level, the terminals J1 and J2 of this circuit can also be terminated. Regarding FIG. 1c, for example, when selecting the received signal of a single terminal J2, the terminal J4 of the switching circuit 6 is set to H level. Also, for termination, terminal J4 of switching circuit 5
Or set J5 to H level as well.

[Example of idea]

Figure 2 shows an embodiment of the antenna switching circuit based on the basic circuit configuration of Figure 1a.
The same parts are indicated by the same symbols. In the figure, an inductance L1 and a resistor R5 constitute the impedance element Z1 of FIG. 1a, and a series resistor R5 is connected so that the value of the inductance L1 can be small. capacitors C6 and C7
constitutes a coupling capacitor C2, which is divided to prevent interference due to the transition capacitance of diodes D1 and D3. R6 and R7
correspond to the terminating resistor Ro, and are similarly divided to prevent interference. The respective resistors R6 and R7 are made to either precisely match the impedance seen by the antenna circuit connected to the terminals J1 and J2, or to be of a sufficiently small value so as not to cause interference as described above. The resistor R8 is the resistor R6, R
7 is inserted in series with these so that even if the resistance value is small, the current level of the switching signal applied to the terminal J5 does not have to be increased. C
8 is the resistance R at high frequency when the resistance R8 is inserted.
This is a decoupling capacitor that makes the common connection point of 7 and R8 a reference potential. L2 is a resistor R6,
This is an inductance that exhibits a large impedance at high frequencies with respect to R7 and capacitor C8.

A flip-flop circuit 9 follows terminals J4 and J5, and each time a trigger pulse is input to this,
A switching signal is alternately supplied to terminals J4 and J5, one at H level and the other at L level, as shown in Fig. 1a.
Terminal J1 or J2 is selected with the same effect as .

[Effects of the Invention] As described above, according to the present invention, the terminal of the antenna switching circuit for the antenna circuit not selected among the plurality of antenna circuits can be terminated with a small resistance independently of the transmitting/receiving circuit. This avoids the problem of parasitic vibrations occurring in unselected antenna circuits and causing interference to the transmitter/receiver circuit.

[Brief explanation of the drawing]

1a to 1c show the basic configuration of an antenna switching circuit according to the present invention, FIG. 2 shows an embodiment of the antenna switching circuit of FIG. 1a, and FIG. 3 shows a conventional antenna switching circuit. Z1... Impedance element, B1, B2...
bias circuit.

Claims (1)

[Scope of utility model registration request] A coupling capacitor C1 connected to the first antenna circuit and a first pair of switching diodes D1, D2 followed by an anode to this capacitor.
, a bias circuit B1 that forward biases these diodes through internal resistance, and a coupling capacitor C3 connected to the second antenna circuit.
a second pair of switching diodes D3, D4 whose cathodes follow this capacitor; a bias circuit B2 which biases these diodes in the opposite direction through an internal resistor; and one of said first pair of diodes D1. an impedance element Z1 to which a switching signal is applied, which is connected to the cathode of D3 and the anode of one of the diodes D3 of the second pair, and a coupling capacitor C to which the transmitting/receiving circuit is connected.
2, and a terminating resistor Ro to which a switching signal is applied, which is connected to the cathode of the other diode D2 of the first pair and the anode of the other D4 of the second pair of diodes.