JPH0243824A - Transmitter-receiver - Google Patents

Abstract

PURPOSE:To allow a reception section to receive a signal from a transmission line at all times, and to prevent leakage of the signal from a transmission section to the transmission line by providing 1st and 2nd changeover circuits having a specific circuit constitution respectively. CONSTITUTION:In the case of sending a signal from a transmission section 2 to a transmission line 8, both the 1st changeover circuit 5 for constituting an attenuation circuit, and the 2nd changeover circuit 7 for constitution a filter circuit are energized and a reception signal from the transmission line 8 reaches the reception section 3 through the 2nd changeover circuit 7 and a branch circuit 4. When no signal is sent from the transmission line 2 to the transmission line 8, both the changeover circuits 5, 7 are not energized, and the transmission signal at a 1st frequency from the transmission section 2 is attenuated by the 1st changeover circuit 5 and the signal component leaked to the branch circuit 4 is reflected in the 2nd changeover circuit 7 and is not supplied to the transmission line 8. Moreover, the reception signal from the transmission line 8 has a 2nd frequency, then the signal passes through the 2nd changeover circuit 7 and reaches the reception section 3. Thus, the leaked transmission signal to the transmission line is prevented and the signal from the transmission is always made receptible.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a transmitting/receiving device used in CATV, data transmitting/receiving systems, and the like.

(Prior art) Conventionally, this type of transmitter/receiver has connected a branching circuit to a transmission line, and the signal from the transmitter is sent to the transmission line via the branching circuit, and the signal from the transmission line is branched. The signal is guided to the receiving section via a circuit.

A switching circuit is interposed between the transmitter and the branching circuit, and the switching circuit is made conductive only when necessary to send signals such as data signals to the transmission line.

(Problems to be Solved by the Invention) The conventional transmitting/receiving device described above uses an attenuator in which PIN diodes are arranged in a T-type or a π-type as a switching circuit for transmitting or cutting off signals to a transmission line. When sending a signal to the transmission line, the attenuation amount of the attenuator is made as small as possible, and when sending the signal to the transmission line is cut off, the attenuation amount of the attenuator is made as large as possible. However, when a switching circuit such as the one described above is used, the amount of attenuation cannot be increased even when it is desired to cut off the signal, so the signal leaks to the transmission line. On the other hand, if you connect attenuators in multiple stages, you can cut off the signal, but when sending the signal to the transmission line, the signal will be weakened by the amount of multiple stages and sent to the transmission line. It is a cine economy.

An object of the present invention is to provide a transmitting/receiving device that can send signals from a transmitting section to a transmission line when necessary, and can always receive signals from the transmission line at a receiving section. To provide a transmitting/receiving device capable of significantly attenuating a signal from a transmitting section when there is no need to send a signal to a transmission line, thereby preventing leakage of signals from the transmitting section to the transmission line.

(Means for Solving the Problems) The present invention takes the measures as described in the claims above, and its effects are as follows.

(Function) When sending a signal from the transmitter to the transmission line, both the first switching circuit and the second switching circuit are rendered conductive. The transmission signal having the first frequency from the transmitter is transmitted to a first switching circuit,
The signal passes through the branching circuit and the second switching circuit in order and is sent out to the transmission line. Since the second switching circuit has a filter circuit configuration, unnecessary loss of the transmitted signal can be prevented. The received signal from the transmission line still passes through the second switching circuit and the branching circuit and reaches the receiving section.

When no signal is sent from the transmitter to the transmission line, both the first switching circuit and the second switching circuit are rendered non-conductive. The transmission signal of the first frequency output from the transmitter is attenuated by the first switching circuit, and the signal component leaking to the branching circuit is also reflected by the second switching circuit and does not go out to the transmission line. The first one on the transmitter side
Since the switching circuit has the configuration of an attenuation circuit, it is possible to prevent adverse effects caused by reflection of the transmitted signal to the transmitter. Furthermore, since the received signal from the transmission line has the second frequency, it passes through the second switching circuit without being blocked, passes through the branching circuit, and reaches the receiving section.

(Example) The drawings showing the embodiments of the present application will be described below.

FIG. 1 shows a block circuit diagram of a transmitter/receiver connected to a transmission line. la and Ib each indicate a transmitting/receiving device, which has the same configuration as shown in the figure. Reference numeral 2 denotes a transmitting section, from which a data signal obtained by supporting a carrier wave whose frequency is a first frequency f1 is transmitted. 3 indicates the receiving section,
It receives a data signal obtained by modulating a carrier wave whose frequency is a second frequency f2 when it is sent from a transmission line, which will be described later. 4 indicates a branching circuit. Reference numeral 5 denotes a first switching circuit, which has a well-known variable attenuator type configuration in which variable impedance elements such as PIN diodes are arranged in a π type or π type. When the control DC voltage is applied to the control end 5c, the amount of attenuation becomes maximum, and the input end 5a and the output end 5b become substantially non-conductive. Further, when no control DC voltage is applied to the control terminal 5C, the amount of attenuation is minimum, and the signal applied to the input terminal 5a is sent to the output terminal 5b with only small attenuation. Reference numeral 6 denotes a control circuit, which is provided to control the sending of data signals from the transmitter 2 to a transmission line 8, which will be described later, or to stop sending data signals. The control circuit 6 can be composed of, for example, a microcomputer. 7 is a second switching circuit, which has a first end 7a, a second end 7b, and a control end 7C.
The specific circuit configuration will be described later.

8 indicates a transmission line such as CATV, and 9 indicates a tap-off.

Next, FIG. 2 is a circuit diagram showing a specific configuration of the second switching circuit 7. As shown in FIG. Components corresponding to those in FIG. 1 are designated by the same reference numerals. Reference numeral 10 indicates a capacitor for coupling with the next stage, which is provided as necessary. 11 is a coil.
12 is a capacitor, and both constitute a parallel resonant circuit. 13 is a capacitor, coil 11 and capacitor 12
and is used to couple a resonant circuit consisting of the signal line 14 with the signal line 14. A diode 15 is used to connect or disconnect the resonance circuit consisting of the coil 11 and the capacitor 12 and the capacitor 13. As the diode 15, for example, a PIN diode is used. Further, two diodes 15 may be connected in series. Reference numeral 16 indicates a choke coil that passes direct current and blocks high frequencies. 17 indicates a high frequency bypass capacitor.

To explain the operation of the second switching circuit 7, the diode 15 exhibits high impedance when no control DC voltage is applied to the control terminal 7C.

Therefore, the high frequency signal applied to the first end 7a is transmitted to the second end 7b with less loss. Further, the high frequency signal applied to the second end 7b is also transmitted to the first end 7a with little loss.

Next, a case where a control DC voltage is applied to the control end 7c will be described. A direct current flows through the diode 15, and the resonant circuit consisting of the coil 11 and the capacitor 12 and the capacitor 13 are directly connected at high frequency. The coil 11, capacitor 12, and capacitor 13 collectively constitute a resonant circuit, and the resonant frequency is set to the frequency of the data signal from the transmitter 2 (for example, 40 MHz at the first frequency f1). Therefore, the signal of the first frequency f1 applied to the first end 7a does not appear at the second end 7b. For the same reason, the signal of the first frequency f1 applied to the second end 7b also does not appear at the first end 7a. On the other hand, the second frequency f2 (for example, 70 MHz) directed toward the aforementioned receiving section 3
The signal 0 is applied to the second end 7b and transmitted to the first end 7a.Next, the operation of the transmitting/receiving system shown in FIG. 1 will be explained in detail. Although not shown, it is assumed that a center device is connected to the transmission line 8. It is also assumed that a call signal requesting data transmission from a specific transmitting/receiving device 1a is being sent from the center device.

(I) Signal flow in the transmitting/receiving device 1a The calling signal of the second frequency f2 is applied to the second end 7b of the second switching circuit 7, and reaches the receiving section 3 via the first end 7a1 branching circuit 4. As is well known, the receiving section 3 determines whether the calling signal is calling its own device. In this case, it is determined that it is a calling signal for the own machine, a determination signal is transmitted to the control circuit 6, and the control DC voltage from the control circuit 6 is stopped for a predetermined period of time. Then, the input terminal 5a and the output terminal 5 of the first switching circuit 5
b is still the first end 7a and second end 7 of the second switching circuit 7.
b are in a conductive state for the predetermined time period. As a result, the data signal of the first frequency fl from the transmitter 2 passes through the first switching circuit 5, the branching circuit 4, and the second switching circuit 7, is superimposed on the transmission line 8 from the tap-off 9, and is sent to the center device. It will be done.

(I[) Signal flow in the transmitting/receiving device 1b The calling signal of the second frequency f2 reaches the receiving section 3 through the same route as in the case (I) above. The receiving section 3 determines that the calling signal is not the own device, and the determination signal is transmitted to the control circuit 6, which continues to output the control DC voltage in the previous state. The data signal having the first frequency f1 from the transmitter 2 is sufficiently blocked by the first switching circuit and the second switching circuit, and does not go out to the transmission line 8. On the other hand, the data signal from the transmitting/receiving device 1a that has come around from the transmission line 8 is blocked by the second switching circuit 7 in the transmitting/receiving device 1b, so that it is prevented from having an adverse effect on the receiving section 3.

The above example shows that the transmitting/receiving devices 1a and 1b are directly connected to the tap-off 9 interposed in the transmission line 8, but it is also possible to incorporate the transmitting/receiving devices 1a and 1b into one main line amplifier. Needless to say.

(Effects of the Invention) As described above, in the present application, the signal from the transmitter is sent to the transmission line only when necessary, and when it is not necessary, the leakage of the transmitted signal to the transmission line can be kept to an extremely low level. It has the advantage of being possible.

Moreover, since the received signal can always be transmitted from the transmission line to the receiving section, even in the event of an emergency, the signal from the transmission line can be immediately received and a response can be taken.

[Brief explanation of the drawing]

The drawings relate to embodiments of the present application, and FIG. 1 is a block circuit diagram of a transmitter/receiver connected to a transmission line, and FIG. 2 is a circuit diagram showing a specific configuration of a second switching circuit. la, lb... fist transmitting/receiving device, 2... transmitting section, 3...
- Receiving section, 4... Branching circuit, 5... First switching circuit, 7... Second switching circuit, 8... Transmission line. Patent applicant Maspro Electric Works Co., Ltd. Representative Yama Hata
Takashi 1st figure 2nd figure

Claims (1)

[Claims] a transmitter that transmits a signal having a first frequency;
a receiving section that receives a signal having a frequency of , and the transmitting section and the receiving section are connected by a branching circuit,
Moreover, a first switching circuit having an attenuator circuit configuration is interposed between the transmitting section and the branching circuit, and furthermore, a first switching circuit having an attenuator circuit configuration is provided at a later stage of the branching circuit to be connected to the transmission line. 1. A transmitting/receiving device comprising a second switching circuit having a filter circuit configuration that allows a signal of the second frequency to always pass through and makes the signal of the first frequency conductive or non-conductive.