JPS6159567B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high frequency switch circuit suitable for the VHF band, particularly for intermediate frequency circuits of multiplex radio equipment.

Multiplex radio equipment requires various switch circuits to enhance its functionality, and for switch circuits in intermediate frequency circuits of such multiplex radio equipment, in addition to the cutoff characteristics of the switch, especially its impedance characteristics are also important. . This is because such intermediate frequency circuits handle signals with a wide frequency band, so when connecting these circuits, certain characteristics such as coaxial lines are required to transfer the signals efficiently and without distortion. It is necessary to use a line having impedance and to match the impedance characteristics at the sending and receiving ends with the characteristic impedance of the line to perform so-called impedance matching. High frequency switch circuits such as those described herein also fall within this scope.

FIGS. 1A and 1B show a block diagram of a conventional high frequency switch circuit and its detailed circuit. 1st
In figures A and B, 1 and 3 are series switch elements, 2, 4 and 6 are parallel switch elements, T ₁ and T ₂ are input and output terminals, respectively;
T ₁₁ and T ₁₃ are control terminals of the series switch element and parallel switch element, respectively. In Fig. 1B, when the negative polarity voltage applied to the terminal _T12 is applied to the terminal _T13 by the switch S, the diode _D1
and D ₃ are conductive; diodes D ₂ , D ₄ , and D ₆ are cut off, and conduction occurs between input terminal T ₁ and output terminal T ₂ ; when switch S is pushed to the control terminal T ₁₁ side, input/output terminal T ₁ and _T2 are cut off, and both terminals _T1 and _T2 have characteristic impedances R2 and _T2 , respectively.
Terminated by R ₆ . In other words, both terminals can have good impedance characteristics regardless of whether the switch element is on or off.

Similarly, Fig. 2 A and B are input terminals, respectively.
This is a circuit that switches signals between T ₄ and output terminal T ₅ or T _6. When switch S is applied to control terminal T ₁₁ , terminals T ₄ and _{T 5} are connected, and terminal T ₆ is terminated with characteristic impedance. be done. Further, when the switch S is turned on to the control terminal _T13 , the terminals _T4 to _T6 are connected and the terminal _T5 is terminated with a characteristic impedance.

Although these circuits have good impedance characteristics at both terminals regardless of whether the switch element is on or off, they have the following drawbacks.

(b) In these circuits, switch elements 2, 6,
Since the element 12 is used for impedance matching, the attenuation characteristic as a switch element is greatly reduced.

(b) When the input and output terminals of terminals T ₁ to _{T 6} are in a conductive state, there is stray capacitance and inductance of the circuit between them, or insertion loss of the switch element, so components must be selected to compensate for these effects. There are restrictions on placement, etc. Moreover, this inevitably results in narrowing the transmission band.

(c) Furthermore, in such a high-frequency switch circuit, the input terminal and output terminal are connected with low loss when conducting, so a defect in the impedance characteristics of the circuit connected to one terminal will directly affect the other terminal. It is also inevitable.

An object of the present invention is to provide a high frequency switch circuit which is simplified, has stable impedance characteristics, and has a wide band.

According to the present invention, there is provided a switch circuit that opens and closes the input terminal (or output terminal) of an amplifier having low input impedance (or low output impedance), the input resistor (or input resistor) connected to the switch input terminal (or switch output terminal). or an output resistor) is connected in series between the other terminal of the input resistor (or output resistor) and the input terminal of the amplifier (or the output terminal of the amplifier), and is connected in series with the amplifier in terms of direct current. n (n
is a positive integer greater than 1), and are connected to the input side (or output side) and ground side of each series switch element via a capacitor, and are connected in series with each other in terms of direct current. n parallel switch elements (n is a positive integer greater than 1) using diodes, and depending on whether or not a common DC current flows through the series switch elements and the amplifier, the series switch is made conductive or cut off. A high frequency switch circuit is characterized in that it has a hand cutter that can change whether the parallel switch is turned on or off, and a means that can change whether the parallel switch is made conductive or cut off depending on whether or not a common DC current flows through the parallel switch elements. Tsutsumi is proposed.

Embodiments of the high frequency switch circuit according to the present invention will be described in detail below with reference to the drawings.

Figure 3A is a high frequency switch circuit with a switch function on the input, and Figure 3B is a detailed circuit diagram in which the block diagram of Figure 3A is extended to a transfer circuit. , is a switch circuit for switchingly connecting the terminal to the input of the amplifier 101. Figure 4A is a high frequency switch circuit with a switch function on the output.
FIG. 4A is a detailed circuit diagram in which the block diagram of FIG.
This is a high frequency switch circuit that is selectively connected to the output terminal _T7 . Although these are all transfer circuits, they can be changed to turn on and off independently, and in that case, there is no problem in terms of impedance characteristics. This makes the conventional circuit extremely complicated, and the circuit loss increases by an integral multiple of the number of branches, so the practical difference is extremely large.

Next, in the block diagram of FIG. 3A, 21 is an input resistor, 23 and 25 are series switch elements, and 2
2 and 24 are parallel switch elements, and 101 is an amplifier. A detailed circuit diagram obtained by transferring and expanding this block diagram is shown in FIG. 3B. In FIG. 3B, each switch element is a diode D ₂₃ ,
D ₂₅ , D ₂₂ and D ₂₄ and has a grounded base transistor TR ₁ as an amplifier with low input impedance and a resistor R ₁ as input resistance.
is used. A switch circuit consisting of the input resistor and series and parallel switch elements is connected to the input terminal of the amplifier 101, and the switch current when the switch circuit becomes conductive is used as the emitter current of the transistor. Figure 3B
In the circuit in , when switch SW ₁ is turned on, the diode in switch circuit 103a
D ₂₄ and D ₂₂ are made conductive, and D ₂₃ and D ₂₅ are cut off. Conversely, in the switch circuit 103b, diodes D ₂₃ and D ₂₅ are made conductive, and D ₂₂ and D ₂₄ are cut off. This switch current finally becomes the emitter current of transistor _TR1 . When the switch SW ₁ is turned to the lower side, each diode becomes conductive and cut off in the exact opposite way, so a transfer switch circuit is formed between the switch circuits 103a and 103b and the input terminal _T3 of the amplifier 101. .

31 and 33 in the block diagram of FIG. 4A.
is a parallel switch element, 32 and 34 are parallel switch elements, 35 is an output resistor, and 102 is an amplifier. Further, in FIG. 4B, diodes D ₃₁ , D ₃₃ , D ₃₂ and D ₃₄ are used as each switch element, an emitter follower or source follower type transistor amplifier TR ₂ is used as a low output impedance amplifier, and a resistor R ₃₅ is used as an output resistance. is used. A switch circuit consisting of series and parallel switch elements is connected to the output terminal of the amplifier 102, and the switch current when each switch circuit becomes conductive is used as the output current of the transistor. That is, in the circuit of FIG. 4B, when switch SW ₂ is turned on, diodes D ₃₂ and D ₃₄ in switch circuit 104a are made conductive, D ₃₁ and D ₃₃ are cut off, and conversely, diodes D ₃₂ and D ₃₄ are made conductive in switch circuit 104b. is blocked
_D31 and _D33 are made conductive and this switch current becomes the output current of transistor _TR2 . When the switch SW ₂ is turned to the lower side, each diode is made conductive and cut off in the opposite manner, so that a transfer switch is formed between the switch circuits 104a and 104b and the output terminal _T5 of the amplifier 102.

The switch circuits shown in FIGS. 3A, B and 4A, B have the following characteristics.

(a) Since the impedance matching elements 21 and 35 are connected in series with the switch circuit, the stray impedance existing in series with the circuit is small compared to the matching element, so its influence is greatly reduced. In other words, the input impedance or output impedance of the switch is resistor R ₂₁ or R _35.
It is approximately determined by.

(b) The signal path of a switch circuit is composed of low impedance circuits except for the output terminal or input terminal, so it has the advantage of being difficult to electrostatically couple with other circuits, especially when it is mounted in a small size and with high density. It will be advantageous.

(c) Since the amplifier 101 or 102 provides a sufficient cutoff ratio between the input and output, the influence of the input/output impedance between the input and output can be completely eliminated.

(d) By appropriately selecting an amplifier, a circuit including this switch can be made lossless or gain-free, greatly increasing the degree of freedom in circuit design. Note that if a negative feedback broadband amplifier is used as an amplifier and the switch is constructed integrally with the amplifier circuit in its output or input circuit, an extremely economical and efficient design becomes possible.

(e) Since the control current of the switch can be used as the power supply current of the amplifier, parts and power consumption can be saved.

(f) Even if multiple inputs or multiple outputs are connected at the same time, the level and impedance will not be affected.

As explained in detail above, the present invention facilitates circuit simplification, stabilization of impedance characteristics, and widening of the band by using an amplifier having input or output impedance sufficiently lower than the input impedance or output impedance. It is characterized by this.

[Brief explanation of the drawing]

1 and 2 show conventional high frequency switch circuits, and FIGS. 3 and 4 show embodiments of the high frequency switch circuit according to the present invention. In the figure, 21 and 35 are input and output resistors, 23, 25, 31, and 33 are series switch elements, 22, 24, 32, and 34 are parallel switch elements, and 101 and 102 are low input and low output impedance amplifiers.

Claims (1)

[Claims] 1 A switch circuit that opens and closes the input terminal (or output terminal) of an amplifier with low input impedance (or low output impedance), and an input resistor (or output resistor) connected to the switch input terminal (or switch output terminal) and a diode connected in series between the other terminal of the input resistor (or output resistor) and the input terminal of the amplifier (or the output terminal of the amplifier), and connected in series with the amplifier in terms of direct current. n series switch elements (n is a positive integer greater than 1) connected via capacitors to the input side (or output end) and ground side of each series switch element, and connected to each other through a DC voltage. n parallel switch elements (n is a positive integer greater than 1) using diodes connected in series to A means to change whether conduction is established or interrupted,
A high frequency switch circuit characterized in that it has means for changing whether the parallel switch is made conductive or cut off depending on whether or not a common direct current is caused to flow through the parallel switch elements.