JPS60174534A - Antenna switch circuit - Google Patents

Abstract

PURPOSE:To prevent transmitter's power and receiver's power from leaking to a receiver and a transmitter respectively by connecting a lambda/4 distribution constant circuit and a tuning circuit including a variable reactance element in series between the transmitter and receiver, and ground, and controlling the variable reactance element. CONSTITUTION:An inductance L2 is connected in parallel to the series circuit of a switching diode D7 having the cathode grounded, a fixed capacitor C1, and an inductance L1, and a choke coil CH1 for stopping a high-frequency signal is connected to the anode of the diode D7, which is fed. On the other hand, a diode D8, capacitor C2, inductance L3 and L4, and choke coil CH2 are provided at the receiver side as well. Then, impedance values of lambda/4 distribution constant circuits 5 and 6 connecting with those tuning circuits 11 and 12 in series are set to zero or infinite when viewed from the sides of the transmiter 3 and receiver 4, and impedance value of lambda/4 distribution constant circuits 1 and 2 connecting with an antenna A are controlled to zero or infinite when viewed from the antenna side.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an antenna changeover switch circuit for a press-talk wireless communication device.

- The simplest antenna switching circuit in a press-talk wireless communication device that uses the same antenna for transmitting and receiving is mechanical relays R and L as shown in Figure 1 (al) or mechanical relays R and L as shown in Figure 1 (b). diode switches D1 and D2 as
It was common to switch between the antenna and the transmitter/receiver by connecting the antenna and the transmitter/receiver. However, with the use of ultra-high frequency bands in recent years, it has become impossible to put the above-mentioned antenna switching circuit into practical use due to the increased insertion loss caused by the deterioration of the isolation W1. Conventionally, as an alternative to this, a switch circuit has been used that uses a λ/4 distributed constant circuit, and when one end is electrically opened or shorted, the impedance at the other end becomes flash or O. Ta. As a concrete example of this, as shown in Fig. 2, first and second λ/4 distributed constant circuits 1 and 2 are connected between antenna A, transmitter 'rX, and receiver R.X. In addition, circuits in which λ/4 distributed constant circuits 5 and 6 and switching diode circuits 7 and 8 are connected in series are connected between these transmitter side 3 and receiver side 4 and the ground, respectively. , the respective diodes D3, 1 of the diode life switch circuits 7 and 8)
4, Ds, and Do are alternately energized to bring them into the ff:ON state or OνF state, thereby connecting the λ
/4 The impedance at the other ends 3 and 4 of the distributed constant circuits 5 and 6 is set to ■ or 0, and the antenna A and transmit +
! ! said first connected between ITX and receivers R and X;
And the impedance of the λ/4 distributed constant circuit of No. 10 2 is set to 0 or ψ to prevent the transmitted wave from flowing into the receiver side, or This prevents received power from leaking to the transmitter side.

However, in the conventional circuit as described above, the terminals of the third and fourth λ/4 distributed constant circuits are opened and shorted by the diode switch circuits 7 and 8, so even in the open state, the diode D3 Due to the stray capacitance existing between the anode and cathode of D6, the antenna is not completely open, and therefore the impedance of the λ/4 distributed constant circuit 5.6 and 1, 2 cannot be completely controlled to O or ■.・There was a limit to the improvement of joist loss and isolation as a switch.

The present invention has been made in order to eliminate the drawbacks of the conventional antenna switch circuit as described above.
In place of the diode switching circuit for opening and shorting the four distributed constant circuit terminals, a tuned circuit including a variable reactance element and a reactance element is used, and by controlling this variable reactance element and changing its reactance value, when the circuit is opened, the tuned circuit is operated as a parallel resonant circuit, that is, the impedance is ``■'', and when short-circuited, it is operated as a series resonant circuit, that is, the impedance is 0, and the impedance seen from the other end of the λ/4 distributed constant circuit (provided) between the antenna and the transmitter or receiver is ``■''. It is an object of the present invention to provide an antenna switch circuit that controls the antenna so that the antenna becomes zero.

The present invention will be described in detail below based on illustrated embodiments.

FIG. 3 is a circuit diagram of an antenna switch section showing one embodiment of the present invention.

In this figure, 11 and 12 are tuning circuits connected in place of the diode switch circuit of the conventional antenna switch circuit shown in FIG. An inductance L2f is connected in parallel to the series circuit of a fixed capacitor Ct and an inductance L1, and a high frequency blocking choke coil CH is connected to the anode of the switching diode.
1i connection to supply current to the switching diode, and the inductance L3. La,
A similar tuning circuit 12 consisting of a capacitor C2 and a diode D8 is also connected to the receiver side.

The tuned circuit configured as described above operates as follows.

That is, FIG. 4a shows the equivalent circuit when the switching diode D7 is energized and conductive, and the same figure shows the equivalent circuit when no current flows, that is, when the switching diode Dy4 is turned off. Now, when the switching diode Dtf becomes conductive, the residual impedance of the diode becomes zero, and the equivalent circuit of this tuned circuit 11 becomes a series-parallel resonant circuit of Lt, L2, and C1, and the impedance zS at this time is Zs=jωLz(j
ωLt+(1/jωCI))/(jω(ht+hz)
+(i/jωCt))...(1).

Therefore, the above equation (
In the case where the numerator of 1) is zero, ωL+ = 1/ωc
I,',ω2=1/ctLs-(21As the currently used frequency f820MHz, the fixed condenser C
If the IO value 'fr is 2pF, then from equation (2), L + -
When 18.8nl-1, the tuned circuit has series resonance.

In other words, when the series circuit of Ll and 01 is co-photographed at 820 M and Hz, the impedance is theoretically zero, and if the value of parallel inductance L2 at this time is finite (if not zero), there will be no effect on this series resonance. .

Next, considering the case where the current to the switching diode D7 is cut off, the floating capacitor between the anode and cathode is considered to be a capacitor CD, which is about 2 pF, and this equivalent circuit is shown in Figure 4 (bl and The impedance Zp in the same figure is Zp=jωLz(jωL1+((1/ct)+(1/
CD) )/j”J/(jω(1,t+L2)+((1
/ct)+(1/Cn))/jω〕・・・・・・・・・
...The condition expressed by (3) that this circuit resonates in parallel as soon as Zp flashes is when the denominator of the above equation (3) is zero, and ω''=1/(L1+L2)(CICD/(C1+CD )
) ...... (4).

= 18.8 n Hf (Substituting into formula 41 gives L2=
1SnH is obtained.

That is, in a series-parallel circuit having the above values, by controlling the diode e-switch D7 to 0N-7OFF l and its capacitance to ■ and 2pF, the frequency f=,820
A series resonant or parallel resonant impedance O or oO can be obtained for MHz.

Therefore, the impedance of the λ/4 distributed constant circuits 5 and 6 connected in series to these tuning circuits 11 and 12 as seen from the transmitter/receiver side 3 and 4 is O' or (1), and the impedance is set to O' or (1), and the impedance is connected to the antenna A. Since the impedance seen from the antenna sides 9 and 10 of the λ/4 distributed constant circuits 1 and 2 can be controlled to 0 or 2, the transmission power can be prevented from flowing into the receiver or It is possible to prevent input from leaking to the transmitter.

This' is λ/4 in the conventional antenna switch circuit.
Unlike the conventional method of opening and shorting the terminals of distributed constant circuits using diodes and switches, this is done using the resonant impedance of the series and parallel resonant circuits, so opening and shorting can be ideally performed as described above. Therefore, performance as an antenna switch, such as reduction of insertion loss or improvement of isolation, can be obtained.

However, there is no necessity that the present invention is limited to the above-described embodiment.9For example, when applied to a Breathtalk radio device with different transmitting and receiving frequencies as shown in FIG. A band f-wave filter BPF with a passband of
If the antenna switch circuit according to the present invention is inserted and connected, only one antenna switch circuit is required according to the present invention.Since this BPF on the receiver side is usually always provided in the receiver, it is sufficient to use it. In this case, the λ/4 distributed constant circuit and the tuning circuit should resonate with the transmitting frequency, and a slight deviation will occur in the receiving frequency, but this is not a problem in practice.

Furthermore, although the diode switches D7 and Dsi were used as the variable reactance elements of the tuning circuits 11 and 12 in the above embodiment, the present invention is not limited to this, and the variable inductance or variable capacitance can be changed by using an active circuit such as a transistor element. It is clear that these funds can be used if this is achieved.

As explained above, the present invention replaces the conventional method of opening and shorting the terminals of the λ/4 distributed constant circuit in an antenna switch circuit using the λ/4 distributed constant circuit by using only a diode switch. This is a tuned circuit including a variable reactance element, and by controlling the value of the variable reactance, switching to series or parallel resonance with respect to the frequency used is performed by changing these impedances, and impedance control of the above-mentioned λ/4 distributed constant circuit. Since it can be ideally implemented, it is extremely effective in reducing loss and improving isolation in antenna switch circuits.

[Brief explanation of the drawing]

1(a), (bl) and FIG. 2 are block diagrams showing an example of a conventional antenna e-switch circuit, FIG. 3 is a block diagram showing one embodiment of the present invention, and FIG. 4(at and (bl)
is an equivalent circuit of the tuning circuits 11 and 12 in FIG. 3, and FIG. 5 is a block diagram showing another embodiment of the present invention. 1.2.5 and 6... λ/4 distributed constant circuit. 11 and 12...Tuning circuit including variable reactance, Dt and D8-...Switching diode, L+, L2. La, La...
・・・・・・Inductance, C1 and C2...
...Fixed capacitor, CD...
・Switching diode capacity, BPF...
...Band P wave device. Patent applicant Toyo Tsushinki Co., Ltd. (α) (b) Figure 1 Figure 21z Conquering country (2) (b) Figure 4

Claims (1)

[Claims] 1. In a radio device that adopts the press-talk method and uses one antenna for both transmission and reception, there is a λ/4 distance between the antenna, the transmitter, and the receiver, respectively. (λ is the wavelength of the frequency used) A distributed constant circuit is provided, and a tuning circuit including a λ/4 distributed constant circuit and a variable reactance element is connected in series between the transmitter side and the receiver side and the ground. By controlling a variable reactance element, the tuned circuit is changed into a parallel resonant circuit and a series resonant circuit with respect to the frequency used, and both ends of the λ/4 distributed constant circuit provided between the antenna and the transmitter and between the antenna and the receiver. An antenna switch circuit characterized by controlling the impedance seen from the antenna. 2. In a press-talk type radio device in which the transmitting and receiving frequencies are different and one antenna is shared for transmitting and receiving, instead of two λ/4 distributed constant circuits and a tuning circuit provided between the antenna and the receiver. Claim 1 characterized in that the receiving frequency is replaced by a band f-wave device whose passband is the receiving frequency.
The antenna switch circuit described.