JP3377801B2 - High frequency signal switching circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency signal switching circuit for a trunk type optical receiver in a transmission line for cable television broadcasting.

[0002]

2. Description of the Related Art In recent years, the CATV system is an urban CAT.
It is desired to expand the service area and improve the image quality, as typified by V. Introducing an optical transmitter / receiver in the transmission line of each facility, and an optical receiver incorporating a coaxial transmission line as a backup for the optical transmission line. Is being introduced.

A conventional high-frequency signal switching circuit will be described below with reference to the drawings. FIG. 2 is a perspective view showing the structure of the trunk type optical receiver. In this figure, the optical receiver unit
27 and 28 are composed of a photoelectric conversion circuit, a high frequency amplifier circuit, and the like. The main chassis unit 30 is composed of a high frequency signal switching circuit, an output level adjusting circuit and the like. A power supply and signal input / output terminal 29 is provided on the bottom surface of each of the light receiving units 27 and 28 so as to project therefrom. Also, on the upper part of the main chassis unit 30 , the power supply and signal input / output terminals 3
One concave portion is provided. Moreover, the optical receiving units 27,
8 and the main chassis unit 30 is connected via a power and input and output terminals 29, 31, Ru built into aluminum die-cast casing 26.

FIG. 3 is a circuit diagram showing a conventional high-frequency signal switching circuit in the main chassis unit. In the figure, an input terminal 1 is a terminal for detecting an optical input signal, and is connected to the inverting input terminal of the first differential amplifier 2. Differential amplifier 2
Has a load resistor 3 connected between the output terminal and the power supply. The optical signal input terminal 4 of the other optical receiving unit is connected to the inverting input terminal of the second differential amplifier 5. Differential amplifier 5
A load resistor 6 is connected to the output end of the power supply and the power supply. Also, resistors 7 and 8 are connected in series between the power supply and the ground terminal,
The middle point is connected as a reference voltage terminal to the non-inverting input terminals of the first and second differential amplifiers 2 and 5. The terminal 11 is an input terminal for a DC power supply.

The output terminals of the first and second differential amplifiers 2 and 5 are connected to the NAND circuit 12. The NAND circuit 12 obtains an inverted signal of the logical product, and its output terminal is connected to the base of the transistor 14 via the resistor 13.
The emitter of the transistor 14 is grounded, and the collector is connected to the power supply terminal 11 via the relay coil of the high frequency relay 15. A diode 16 for absorbing surge current is connected between the collector of the transistor 14 and the power supply terminal 11. High frequency relay 15 is normally closed (NC)
It has a terminal, a normally open (NO) terminal, and a common terminal, and is connected to the input terminals 17 and 18 and the output terminal 19, respectively. The input terminal 17 is an input terminal for a first high frequency signal obtained by photoelectrically converting a signal from the optical transmission line, the input terminal 18 is a second input terminal for inputting a high frequency signal from the coaxial transmission line, and the output terminal 19 is This is a terminal for selecting and outputting one of the high frequency signals .

The operation of the high-frequency signal switching circuit configured as above will be described. Here, it is assumed that the voltage of the optical input signal detection terminal changes to the L or H level depending on the presence or absence of the optical input signal. First, when an optical input signal obtained by directly brightness-modulating an AM-FDM signal is input to one of the optical receiving units, for example, the first optical input signal detection terminal 1 outputs the first differential amplifier 2 An L level voltage is supplied to the inverting input terminal. Since the midpoint voltage of the resistors 7 and 8 is applied to the non-inverting input terminal, the output of the first differential amplifier 2 becomes H level . Similarly, when the L-level voltage is supplied to the second optical input signal detection terminal 4 as well, the H-level signal is similarly output from the second differential amplifier 5. These outputs are input to the NAND circuit 12, and an L level signal is input to the resistor 13
Is supplied to the transistor 14 via. Therefore, the transistor 14 is turned off, and the photoelectrically converted first high frequency signal is output from the input terminal 17 through the high frequency relay 15 to the output terminal 19.

Next, when the first optical input signal is turned off, the output of the optical input signal detecting terminal 1 becomes H level, and the output of the first differential amplifier 2 is inverted and becomes L level. Therefore, the NAND circuit 12 outputs an H level signal and the transistor 14 is turned on. Therefore, the high frequency relay 15 is NC
The second high-frequency signal switched from the terminal to the NO terminal side and supplied in the coaxial system receives the input terminal 18 and the high-frequency relay 15.
Is output from the output terminal 19 via.

As described above, when the L level voltage is simultaneously input from the first and second optical input signal detecting terminals 1 and 4,
The NAND circuit 12 outputs the L level, the transistor 14 is turned off, and the first high frequency signal is output. Further, when an H level voltage is input from either one or both, the transistor 14 is turned on and the high frequency relay 1
The contact point 5 is switched, the second high frequency signal of the coaxial system is output from the device, and the high frequency signal can be switched according to the presence or absence of the optical input signal.

[0009]

However, in such a structure, when the optical input signal alone is received, the high
The question that the position of the contact of the frequency signal switching circuit cannot be regulated
There is a point. In order to confirm the operation of the high-frequency signal switching circuit, the main chassis unit is assembled in an aluminum die-cast case and then the optical receiver unit is fitted and the optical fiber cable is connected to the optical receiver unit, or the main chassis unit is cased. Then, a voltage of L or H level must be externally applied to the optical input signal detection terminal using a jig. Therefore, there is a problem that the work of confirming the circuit operation becomes complicated.

The present invention has been made in view of the above conventional problems, and an object of the present invention is to provide a high-frequency signal switching circuit whose operation can be confirmed with a simple circuit configuration.

[0011]

According to a first aspect of the present invention, an optical input signal is photoelectrically converted into a high frequency signal and another high frequency signal.
A high-frequency relay switch that selectively switches between the wave signal and
First control signal generating means for outputting a first switching control signal for switching control of the high-frequency relay switch according to the presence or absence of a plurality of high-frequency signals, and a second control signal for switching the high-frequency relay switch to a predetermined terminal. In a high frequency signal switching circuit having a second control signal generating means for outputting a switching control signal, the first switching control means has a differential amplifier for detecting the presence or absence of a plurality of high frequency signals, and a differential amplifier. The second control signal generating means includes a switch means for fixing the output of the logical sum circuit to a predetermined value.

According to the invention of claim 2 of the present application, the optical input signal is an optical signal.
The first high-frequency signal that has been converted into electricity and the second high-frequency signal
A high-frequency relay switch, a first control signal generating means for outputting a first switching control signal for switching control of the high-frequency relay switch according to the presence or absence of a plurality of high-frequency signals, and a high-frequency relay switch. In a high-frequency signal switching circuit for outputting a second switching control signal for switching to a predetermined terminal, the first switching control means includes first and second high-frequency signals. And first and second differential amplifiers for respectively detecting the presence and absence of the output of the first and second differential amplifiers, the outputs of the first and second differential amplifiers are respectively connected to the anodes, and the cathodes of the first and second differential amplifiers are commonly connected. A switching transistor having a base connected to the cathode common connection end of the diode and being energized by the output of the diode. Is characterized in that the cathode common connection end to include switching means connected between the ground terminal.

[0013]

According to the present invention having such characteristics, a logical sum condition is satisfied unless a plurality of optical input signals are detected by the differential amplifier and no signal is obtained at at least one optical input signal detection terminal. The high frequency relay is driven, and the output is switched. The input level of the transistor is fixed at a predetermined value by operating the switching means irrespective of these optical input signals, and the high frequency signal is switched.

[0014]

1 is a circuit diagram of a high frequency signal switching circuit according to an embodiment of the present invention. In the figure, optical input signal detection terminals 1 and 4, first and second differential amplifiers 2 and 5, resistors 3 and
6 to 8 are the same as the above-mentioned conventional example. In this embodiment,
The inverting input terminals and non-inverting input terminals of the first and second differential amplifiers 2 and 5 are reversed from those of the conventional example of FIG. The outputs of the first and second differential amplifiers 2 and 5 are diode 2 respectively.
1, 22 are connected to the anode ends. Diode 21,
The cathodes of 22 are commonly connected and connected to the base of the transistor 14 via the resistor 23. The common connection end of the cathode is grounded via the resistor 24 and the switch 25. The diodes 21 and 22 and the resistors 3 and 6 form a logical sum circuit.

Next, the operation of the high frequency signal switching circuit of this embodiment will be described. The optical input signal detection terminal is set to the L or H level depending on the presence or absence of the optical input signal . First, when an optical input signal in which the AM-FDM signal is directly brightness-modulated is input to the optical receiving unit, the first optical input signal detection terminal 1 outputs an L level signal to the non-inverting input terminal of the first differential amplifier 2. Is supplied. Resistors 7 and 8 at the inverting input terminal
Since the midpoint voltage is applied, the first differential amplifier 2
Output becomes L level . Similarly, when an L level voltage is also input to the second optical input signal detection terminal 4 , its output becomes L level. These outputs are diode 2 respectively.
The signal of L level is mixed through
Is supplied to the transistor 14 via. Therefore, the transistor 14 is turned off, and the photoelectrically converted first high-frequency signal is output from the input terminal 17 from the output terminal 19 via the NC terminal and the common terminal of the high-frequency relay 15.

Next, when the first optical input signal is turned off, an H level voltage is supplied to the non-inverting input terminal of the first differential amplifier 2 and its output becomes H level. Therefore, an H level signal is output from the common terminal of the diodes 21 and 22, and the transistor 14 is turned on. Therefore, the relay coil of the high frequency relay 15 is driven to switch the contact from the NC terminal to the NO terminal side . Therefore, the coaxial high frequency signal input to the input terminal 18 is output from the output terminal 19.

When the switch 25 is short-circuited in this state, the base voltage of the transistor 14 drops. If the values of the resistors 6, 23 and 24 are set so that the base voltage at this time becomes VBE or less, the transistor 14 is forcibly turned off, the high frequency relay 15 is not driven, and the contact is on the NC terminal side. The first high frequency signal is switched and output from the output terminal 19.

As described above, in this embodiment, each differential amplifier is
The outputs of 2 , 5 are mixed through diodes 21 , 22 and mixed .
Switch to the switching transistor 14
And force off 25, so that wear <br/> by turning off the high frequency relay 15. Therefore, the contact of the high frequency relay 15 can be easily switched from the NO terminal to the NC terminal side even if the optical input signal is not supplied. In this example,
The resistor 24 may be omitted, and the switch 25 may be directly connected to the base of the transistor 14. Switch 2
5 may be provided between the input / output terminal of each differential amplifier 2 , 5 and the ground terminal. It is also possible to forcibly turn off the output of the conventional NAND circuit.

[0019]

As described in detail above, according to the present invention, it is possible to switch the high frequency relay regardless of the presence or absence of the optical input signal. Therefore, the malfunction of the optical independent function
There is ensured the prevention, confirmation of circuit operation without using a jig voltage switching or connecting the optical fiber cable can, it is possible to improve the assembling workability during assembly, also easily performed that repair and inspection The effect of being able to do is obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a high frequency signal switching circuit according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a structure of a trunk type optical receiver.

FIG. 3 is a circuit diagram of a conventional high frequency signal switching circuit.

[Explanation of symbols]

1,4 Optical input signal detection terminal 2,5 differential amplifier 3,6,7,8,23,24 Resistance 14 transistors 15 High frequency relay 16,21,22 diode 25 switch

Continuation of the front page (56) Reference JP-A-4-61428 (JP, A) Actual development 3-115440 (JP, U) Actual development 1-172188 (JP, U) (58) Fields investigated (Int .Cl. ⁷ , DB name) H03K 17/00 H04B 1/00

Claims (2)

(57) [Claims] 1. A high frequency signal obtained by photoelectrically converting an optical input signal.
And a high- frequency relay switch for selectively switching between other high-frequency signals, and a first control for outputting a first switching control signal for switching control of the high-frequency relay switch according to the presence or absence of the plurality of high-frequency signals. A high-frequency signal switching circuit having a signal generating means and a second control signal generating means for outputting a second switching control signal for switching the high-frequency relay switch to a predetermined terminal. Includes a differential amplifier that detects the presence or absence of each of the plurality of high-frequency signals, and a logical sum circuit that performs a logical sum of the outputs of the differential amplifiers. A high-frequency signal switching circuit including switching means for fixing the output of the summing circuit to a predetermined value. 2. A first high-frequency band in which an optical input signal is photoelectrically converted.
A high- frequency relay switch that selectively switches between a high-frequency signal and a second high-frequency signal, and a first switching control signal for switching control of the high-frequency relay switch according to the presence or absence of the plurality of high-frequency signals. A high frequency signal switching circuit comprising: first control signal generating means; and second control signal generating means for outputting a second switching control signal for switching the high frequency relay switch to a predetermined terminal. The switching control means is connected to the anodes of the first and second differential amplifiers, which detect the presence or absence of the first and second high-frequency signals, and the outputs of the first and second differential amplifiers, respectively. , First and second with their cathodes commonly connected
And a switching transistor whose base is connected to the cathode common connection end of the diode and is energized by the output of the diode, wherein the second control signal generating means includes a common cathode connection of the diodes. A high-frequency signal switching circuit including switch means connected between an end and a ground end.