JPH062346Y2 - RF switch circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to the economicalization of an RF switch circuit used in a video tape recorder or the like.

[Conventional technology]

In a home-use video tape recorder, as shown in FIG. 12, the television signal given from the television antenna to the antenna input terminal 1 is divided into two by the two-distribution circuit 2, and the input terminals IN of the RF switch circuit 3 are respectively supplied. And to the tuner of the video recording / playback circuit 4. When this television signal is viewed on the monitor television, the television signal is transmitted as it is without being attenuated by the RF switch circuit 3, and is supplied to the monitor television from the antenna output terminal 6 via the coupling circuit 5. When playing back a video soft tape, the polarity of the control signal 7 given to the control CTL of the RF switch circuit 3 is inverted by the video recording / playback circuit 4, and the RF switch circuit outputs from the input terminal IN to the output terminal IN. The transmission of the television signal to OUT is blocked, and the television signal 8 obtained by reproducing the video soft tape from the video recording / reproducing circuit 4 is supplied to the antenna output terminal 6 via the coupling circuit 5.

As an example of a conventional RF switch circuit, a high-pass filter type circuit will be described with reference to FIG. 13. Capacitors C _{1 to} C ₅ are sequentially connected in series between an input terminal IN and an output terminal OUT. The input terminal IN is grounded through the coil L ₁ , and the connection point P _{1 of} the capacitors C ₁ and C _{2 and} the connection point of the capacitors C ₂ and C ₃
Connection point of P ₂ , capacitor C ₃ and C ₄ P ₃ , capacitor C ₄ and
The connection point P ₄ of C ₅ is grounded through the coils L ₂ , L ₃ , L ₄ , L ₅ , respectively, and the output terminal OUT is grounded through the coil L ₆ .
The connection points P ₁ , P ₂ , P ₃ are connected to transistors Q ₁ , Q ₂ , Q _{3 respectively.}
Is connected to the collector, the emitter of each transistor is grounded, and the base is connected to the control terminal CTL via resistors R ₁ , R ₂ and R ₃ , respectively.

When watching a normal television, the control signal 6 applied to the control terminal CTL is at a low level (for example, zero volt),
The transistors Q _{1 to} Q ₃ are controlled to be turned off, and the transmission loss frequency characteristic of the RF switch circuit becomes that of a high-pass filter having a cutoff frequency of about 30 MHz, as shown in the actual recording of FIG. 15A. The input television signal is outputted only by suppressing low frequency noise of 30 MHz or less and being attenuated by about 1 dB.

When viewing a video, control signal 6 applied to the control terminal CTL is at a high level, the transistor Q ₁ to Q ₃ is controlled to be turned on. The connection points P ₁ , P ₂ and P ₃ are grounded by a small ON resistance between the collector and emitter of the transistor, respectively, and R
The transmission loss of the F switch circuit becomes large over the entire band, as shown by the solid line in FIG. 15B. In particular, the frequency band of the video signal (in this example, 54-60 MHz and 60-66 M
In North America for Hz), if a TV signal leaks into this band, a beat defect will appear on the TV screen.
It is designed to obtain an attenuation of dB or more.

As another conventional example, a low-pass filter type obtained by replacing the parallel coils L _{1 to} L ₆ of FIG. 13 with parallel capacitors C _{1 to} C ₆ and the series capacitors C _{1 to} C ₅ with series inductance is also used. Various circuits are used, such as a bandpass filter type in which the parallel coils L _{1 to} L ₆ in the figure are replaced with LC parallel resonance circuits, and a series filter type in which the series capacitors C _{1 to} C ₅ are also replaced with LC series resonance circuits. ing.

[Problems to be Solved by the Invention] While the performance of video tape recorders, which have been rapidly spreading in recent years, are becoming more sophisticated, their prices are decreasing more and more. For manufacturers, reducing product costs is one of the important issues that lead to business ups and downs. This invention was made under such a background, and its purpose is RF.
It is an economical switch circuit.

[Means for Solving the Problems]

The first reactance two-terminal circuit Z ₁ is connected between the input terminal and the output terminal, and the first reactance two-terminal circuit Z _1
1 on the input side and the output side, each second input and the output side of the terminal circuit Z _1, respectively second, third reactance 2
It is grounded through the terminal circuits Z ₂ and Z _{3 to} form a π-type LC filter section, and the collectors of the first and second transistors are respectively connected to the input side and the output side of the first reactance 2 terminal circuit Z _1. In an RF switch circuit including a partial circuit in which the emitters of the transistors are grounded and the bases are respectively connected to control terminals via resistors, in the present invention, a fourth circuit is provided between the bases of the first and second transistors. The reactance 2 terminal circuit Z ₄ is connected to the fourth reactance 2
The series circuit of the terminal circuit Z ₄ and the collector capacitances of the first and second transistors is referred to as the first reactance 2 terminal circuit Z.
_By connecting ₁ in parallel, a reactance two-terminal circuit having at least one anti-resonance frequency is formed.

〔Example〕

For the sake of economy, consider a conventional RF switch circuit in which the high-pass filter consisting of π type 5 sections in FIG. 13 is reduced to 4 sections and the transistor Q ₃ is deleted. The transmission loss frequency characteristic of this circuit is shown by the dotted line in FIG. Regarding the characteristics in the transmission state, the loss is reduced as the number of sections is reduced, but there is no particular problem. 66 ± 6 video signal band in transmission blocking state
The loss of MHz becomes 60 dB or less, and the standard value of 70 dB is not satisfied. Therefore, in this device, as shown in FIG.
A coil L ₀ is connected between the bases of the transistors Q ₁ and Q ₂ .
Then, a series circuit of the collector capacitances C _C1 , C _{C2 of the} transistors Q ₁ , Q ₂ and the coil L ₀ is connected in parallel with the capacitor C ₂ and the third circuit is connected.
As shown in the figure, a reactance two-terminal circuit Z ₀ having an antiresonance frequency fa is constructed. The two-terminal circuit Z ₀ has a resonance frequency fr and an anti-resonance frequency fa as shown in the reactance frequency characteristic of FIG. The resonance frequency fr is equal to the resonance frequency of the series circuit composed of C _C1 -L ₀ -C _C2 . The anti-resonance frequency fa is the video signal band 66 ± 6MHz which is going to increase the transmission loss.
, The center frequency of the band is 66 MHz.
If the inductance value of the coil L ₀ is substituted with the sign L ₀ ,
L ₀ is Given in.

Turning on transistors Q ₁ and Q ₂ controlled to ON by an approximate π-type equivalent circuit and showing the main part of FIG. 2, FIG. 5 is obtained. Gi _1, gi ₂ in the figure is a conductance of the input side, g _o1, g _o2 in conductance of the output side, the reciprocal 1
/ Go ₁ and 1 / go ₂ are generally small resistance values.

The transmission loss frequency characteristic of the RF switch circuit of FIG.
As shown by the solid line in FIG, 15 when the transmission state, that the transistor is not inserted coil L ₀ is in the OFF state
It has the same characteristics as the dotted line in FIG. A, but in the transmission blocking state, that is, when the transistor is on, the video signal bandwidth 66 ±
The 6MHz loss is well within the standard value of 70dB. The dotted line in the figure is the characteristic when the coil L ₀ is not inserted and
This is the same as the characteristic shown by the dotted line in FIG. By thus inserting the coil L ₀ to form the two-terminal circuit Z ₀ having the anti-resonance frequency fa and setting the anti-resonance frequency fa in the vicinity of the video signal band, the transmission loss in that band is effective. Be raised to. The circuit of FIG. 2 has one capacitor, transistor, and resistor each reduced compared to the conventional circuit of FIG.

FIG. 2 shows the case where the present invention is applied to a conventional high-pass filter type circuit, but the present invention can also be applied to a conventional low-pass filter type circuit. And characteristics are shown in FIGS. 7 and 8, respectively. A capacitor C ₀ is inserted between the bases of the transistors Q ₁ and Q ₂ ,
A two-terminal circuit having an antiresonance frequency fa is formed by connecting a series circuit of _C1 -C ₀ -C _C2 in parallel with the coil L ₂ , and the antiresonance frequency fa is 96 ± 6 MHz in the video signal band (in Japan). It is set near the middle frequency (96MHz).

The cutoff frequency of the low-pass filter is 22 in Japan.
Selected for frequencies slightly higher than 2MHz.

Circuits and characteristics when the present invention is applied to a conventional bandpass filter type circuit are shown in FIGS. 9 and 10, respectively. In this case, the coil L ₀ is inserted between the bases of the transistors Q ₁ and Q ₂ . The characteristic shown by the dotted line in FIG. 10 is the case where the coil L ₀ is not inserted. Z ₀ of the two-terminal circuit in which the series circuit composed of C _C1 -L ₀ -C _C2 is connected in parallel to the LC series resonance circuit Z _S2 is the first
As shown in FIG. 1, it has two resonance frequencies fr ₁ and fr ₂ and an anti-resonance frequency fa between them. fr ₁ and fr ₂ are equal to the resonance frequency of the series circuit (C _C1 -L ₀ -C _C2 ) and Zs ₂ , respectively.
Note that fr ₂ is near the center frequency of the bandpass filter. The anti-resonance frequency fa is selected around 66 MHz (for North America).

As is apparent from the three embodiments described above, the circuit of the present invention includes at least a π type filter section composed of reactance two-terminal circuits Z ₁ , Z ₂ and Z ₃ , as shown in FIG. A reactance two-terminal circuit Z ₄ is connected between the bases of the transistors Q ₁ and Q ₂ connected to points P ₁ and P _{2 in the} figure. And
By connecting a series circuit composed of C _C1 -Z ₄ -C _C2 in parallel with Z ₁ , a reactance two-terminal circuit Z ₀ having an antiresonance frequency fa is constructed, and an attempt is made to prevent transmission of the antiresonance frequency fa. It can be seen that it is obtained by setting it in the vicinity of the band.

[Effect of device]

According to this invention, it is possible to obtain a transmission loss frequency characteristic almost equal to the conventional one by using a smaller number of filter elements and transistor switches than the conventional one, which leads to the economicalization of the RF switch circuit and the miniaturization thereof.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a generalized main part of the present invention, FIG. 2 is a circuit diagram showing a first embodiment of the present invention, and FIG. 3 is a capacitor C ₂ , a coil L ₀ and a coil of FIG. Transistors Q ₁ , Q ₂
Circuit diagram of an equivalent reactance 2 terminal circuit constructed by
FIG. 4 is a diagram showing a reactance frequency characteristic of the reactance two-terminal circuit Z ₀ of FIG. 3, FIG. 5 is an equivalent circuit diagram of a main part of FIG. 2, and FIG. 6 is a transmission loss of the embodiment of FIG. FIG. 7 is a diagram showing frequency characteristics, FIG. 7 is a circuit diagram showing a second embodiment of the present invention, FIG. 8 is a diagram showing transmission loss frequency characteristics of the embodiment of FIG. 7, and FIG. 9 is a third diagram of the present invention. FIG. 10 is a circuit diagram showing an embodiment, FIG. 10 is a diagram showing a transmission loss frequency characteristic of the embodiment shown in FIG. 9, and FIG. 11 is an LC series resonance circuit Zs ₂ shown in FIG. 9, transistors Q ₁ and Q ₂ and a coil L. Equivalent reactance 2 created with ₀
FIG. 12 is a diagram showing a reactance frequency characteristic of a terminal circuit, FIG. 12 is a block diagram of a video tape recorder, FIG. 13 is a circuit diagram showing an example of a conventional RF switch circuit, and FIG. 14 is another example of a conventional RF switch circuit. FIG. 15 is a diagram showing a transmission loss frequency characteristic of the conventional RF switch circuit shown in FIGS. 13 and 14.

Claims (1)

[Scope of utility model registration request] 1. A first reactance two-terminal circuit Z ₁ is connected between an input terminal and an output terminal, and an input side and an output side of the first reactance two-terminal circuit Z ₁ are respectively second,
It is grounded through the third reactance 2 terminal circuits Z ₂ and Z _{3 to} form a π-type LC filter section, and the first reactance 2 terminal circuit Z _{1 is connected to} the input side and the output side of the first and second transistors, respectively. In an RF switch circuit including a partial circuit in which collectors are connected, emitters of the transistors are grounded, and bases are respectively connected to control terminals via resistors, a fourth circuit is provided between the bases of the first and second transistors. The reactance 2 terminal circuit Z ₄ is connected to the fourth reactance 2
The series circuit of the terminal circuit Z ₄ and the collector capacitances of the first and second transistors is referred to as the first reactance 2 terminal circuit Z.
By connecting in parallel to the _1, RF switch circuit characterized in that it constitutes a reactive two-terminal circuit having at least one anti-resonant frequency.