JPS6354260B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a receiving circuit system for time-division bidirectional transmission. INDUSTRIAL APPLICATION This invention can be utilized for the bidirectional time division transmission apparatus in a telephone subscriber line.

FIG. 1 shows a conventional transmitting/receiving circuit system for time-division bidirectional transmission. In Figure 1, 1 is a transmission signal input terminal, 2 is a transmission clock signal input terminal, 3 is a transmission circuit, 4 is a matching termination resistor, 5 is a transmission circuit output section, 6 is a transformer, 7 is a transmission line, and 8 is a switch. , 9 is a reception circuit, 10 is a variable attenuator, 11 is an equalization amplifier, 12 is an automatic gain control section, 13 is a time constant circuit, 14 is a reception equalization signal output terminal, and 15 is a transmission/reception control signal. At the time of transmission, the transmission signal is sent from the transmission signal input terminal 1 to the transmission line 7 from the transmission circuit 3 according to the transmission instruction command of the transmission/reception control signal 15. is open, so the transmission signal is not input to the receiving circuit 9. At the time of reception, the transmission signal at the transmission signal input terminal 1 is no signal due to the reception instruction command of the transmission and reception control signal 15, the output of the transmission circuit 3 is at zero level, and the switch 8 is closed, so that the reception signal from the transmission line 7 is not transmitted. is inputted from the transmitting circuit output section 5 to the receiving circuit 9, equalized and amplified, and outputted to the received equalized signal output terminal 14.

However, in the circuit shown in Fig. 1, switch 8 is in the signal path of the received signal, so if switch 8 is configured with a mechanical switch such as a relay, high-speed operation is difficult, and analog
When configured with an IC switch, there are drawbacks such as the reception equalization characteristics of the received signal being degraded due to fluctuations in the level of the received signal due to fluctuations in conduction resistance and signal distortion caused by low power supply voltage operation.

An object of the present invention is to improve the reception equalization characteristics of a reception circuit by overcoming the above-mentioned drawbacks of the conventional technology. The transmitting circuit and the receiving circuit are connected to a variable attenuator connected to the input terminal, and the receiving circuit is connected to a variable attenuator connected to the input terminal, and the receiving circuit is connected to the variable attenuator connected to the input terminal, and the receiving circuit is connected to the variable attenuator connected to the input terminal, and the receiving circuit is connected to the variable attenuator connected to the input end, and the receiving circuit is connected to the variable attenuator connected to the input end, and the receiving circuit is connected to a variable attenuator connected to the input end, and the receiving circuit is connected to the variable attenuator and the receiving circuit is connected to the variable attenuator connected to the input end, and the receiving circuit is connected to the variable attenuator and the receiving circuit is connected to the variable attenuator connected to the input end. time-division bidirectional transmission, including an equalizing amplifier that provides an output signal to an equalized signal output terminal; and an automatic gain control section that controls the amount of attenuation of the variable attenuator according to the level at the received equalized signal output terminal. In the receiving circuit system, the input selector has a first input and a second input between the output of the equalizing amplifier and the received equalized signal output terminal, and the input is switched according to the transmitting/receiving control signal. is provided, the first input is connected to the output of the equalization amplifier, the second input is connected to a predetermined potential, and the first input is selected during the reception instruction period of the transmission/reception control signal. During the transmission instruction period, the receiving circuit system employs time-division bidirectional transmission in which the second input is selected. Examples will be described below with reference to the drawings.

FIG. 2 shows an embodiment of the present invention, in which 21 is a transmission signal input terminal, 22 is a transmission clock signal input terminal, 23 is a transmission circuit, 24 is a matching termination resistor, 25
is a transmitting circuit output section, 26 is a transformer, 27 is a transmission line, 28 is a receiving circuit, 29 is a variable attenuator, 30
31 is an equalization amplifier, 31 is an input selection amplifier, 32 is a first positive phase input, 33 is a second positive phase input, 34 is an automatic gain control section, 35 is a time constant circuit, 36 is a received equalization signal output terminal, 37 is a transmission/reception control signal.

In time-division bidirectional transmission, one set of transmission lines is repeatedly used for transmission and reception in a time-division manner. To explain the signal flow in Figure 2, the transmission signal input terminal 2
The transmission signal inputted to 1 is shaped by the transmission clock signal of the transmission clock signal input terminal 22,
The signal is sent from the low-impedance output transmission circuit 23 to the transformer 26 via the matching termination resistor 24, and then to the transmission line 27. On the other hand, the reception signal sent from the transmission line 27 passes through the transformer 26, is branched at the transmission circuit output section 25, and is input to the reception circuit 28. The receiving circuit 28 includes an automatic gain control system to compensate for signal attenuation caused by the transmission line 27. When the amplitude of the received signal is detected and the amplitude becomes large, the time constant circuit 35 of the automatic gain control section 34 is configured. is charged to increase the attenuation of the variable attenuator 29 and send it to the equalizing amplifier 30 to lower the gain of the receiving circuit 28. When the amplitude is small, the time constant circuit 35 is discharged to increase the attenuation of the variable attenuator 29. By reducing the amount of attenuation and increasing the gain of the receiving circuit 28,
The signal level of the received equalized signal output terminal 36 is always kept constant.

Considering the time of transmission, as described above, the transmission signal is sent from the transmission circuit 23 to the transmission line 27 via the matching termination resistor 24 and the transformer 26 in accordance with the transmission clock signal. At the same time, a transmission signal is also input to the reception circuit 28 from the transmission circuit output section 25. Generally, during reception, the received signal is at a very low level due to transmission line loss, and the receiving circuit 28 is maintained at a high gain by the automatic gain control section 34. When a high-level transmission signal is input in such a state, the receiving circuit 28 selects the input selection amplifier 31.
Without this, the time constant circuit 35 of the automatic gain control section 34 generally has a small charging time constant, so it responds quickly and lowers the gain of the receiving circuit 28. However, on the contrary, since the discharge time constant of the time constant circuit 35 is generally large, when switching from transmission to reception, the reception circuit 28
The gain cannot suddenly increase and the received signal will not be equalized correctly. Therefore, it is a type of operational amplifier that has many input parts and each input is selectively controlled by a control signal, for example, it has one negative phase input, two positive phase inputs, and two positive phase inputs. Introducing the input selection amplifier 31, which is an input selector that selects one of the two positive-phase inputs by controlling each constant current source section to conduct or non-conduct. The input selection amplifier 3
1 is controlled by a transmission/reception control signal 37, and when a transmission instruction command is received, the second positive phase input which is the receiving circuit control signal input of the input selection amplifier 31 is selectively outputted, and for example, a relative signal is output as a receiving circuit control signal. If a zero level is set, the output of the input selection amplifier 31 becomes zero level, and when a reception instruction command is received, the first positive phase input, which is the reception signal input, is selected and output. Therefore, during transmission, the transmission signal input from the transmission circuit output section 25 to the reception circuit 28 is transmitted to the automatic gain control section 34.
cannot be reached, and the input to the automatic gain control section 34 is always a zero level signal regardless of the input level to the receiving circuit 28, and the gain of the receiving circuit 28 is maintained at approximately the value set at the time of reception in preparation for the next reception. be able to.

On the other hand, during reception, the transmission signal input to the transmission signal input terminal 21 is controlled to be non-signal by the transmission/reception control signal 37, so the output of the transmission circuit 23 is at zero level, and the output of the transmission circuit is low. Since the impedance is impedance, the received signal from the transmission line 27 passes through the transformer 26, is impedance matched by the matching termination resistor 24, and is received, and is input from the transmitting circuit output section 25 to the receiving circuit 28. During reception, the input selection amplifier 31 selects the first input which is the received signal input.
In order to selectively output the positive phase input, the receiving circuit 28 forms a normal loop including the automatic gain control section 34 to perform the receiving operation, correctly equalizes the received signal, and outputs it to the received equalized signal output terminal 36. .

As explained above, in the embodiment, in the transmitting/receiving circuit for time-division bidirectional transmission, by introducing an input selection amplifier into the receiving circuit, the receiving circuit is configured with the transmitting circuit output section and the receiving circuit input section directly connected. It is possible to prevent sudden changes in the control gain of the receiving circuit during transmission even when the signal is transmitted, and since there is no switch in the signal path of the received signal, signal degradation can be suppressed.Furthermore, the input selection amplifier can be used in the receiving circuit. Since it can be achieved using the same technology as other amplifiers such as equalizing amplifiers, it has the advantage that the entire receiving circuit including the selection circuit can be implemented as an LSI.

By introducing an input selection amplifier into the receiving circuit for time-division bidirectional transmission, the present invention can easily configure a transmitting/receiving circuit for time-division bidirectional transmission that suppresses signal deterioration. It can be used for split bidirectional transmission equipment.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a conventional time-division bidirectional transmission transmission/reception circuit, and FIG. 2 is a configuration diagram of a time-division bidirectional transmission transmission/reception circuit according to the present invention. In each figure, 1 is a transmission signal input terminal, 2 is a transmission clock signal input terminal, 3 is a transmission circuit, 4 is a matching termination resistor,
5 is a transmitting circuit output section, 6 is a transformer, 7 is a transmission line, 8 is a switch, 9 is a receiving circuit, 10 is a variable attenuator, 11 is an equalization amplifier, 12 is an automatic gain control section, 13 is a time constant circuit, 14 is a reception equalization signal output terminal, 15 is a transmission/reception control signal, 21 is a transmission signal input terminal, 22 is a transmission clock signal input terminal, 2
3 is a transmission circuit, 24 is a matching termination resistor, 25 is a transmission circuit output section, 26 is a transformer, 27 is a transmission line,
28 is a receiving circuit, 29 is a variable attenuator, 30 is an equalization amplifier, 31 is an input selection amplifier, 32 is a first positive phase input, 33 is a second positive phase input, 34 is an automatic gain control section, and 35 is a time constant. 36 is a reception equalization signal output terminal, and 37 is a transmission/reception control signal.

Claims (1)

[Claims] 1. The output end of the transmitting circuit and the input end of the receiving circuit are connected to a common transmission path, and the transmitting circuit and the receiving circuit are switched in a time-sharing manner according to a transmitting/receiving control signal, The receiving circuit includes a variable attenuator connected to the input terminal, an equalizing amplifier connected to the output thereof and providing an output signal to the received equalized signal output terminal, and a variable attenuator connected to the input terminal, an equalizing amplifier connected to the output thereof and providing an output signal to the received equalized signal output terminal, and the receiving circuit according to the level at the received equalized signal output terminal. In a receiving circuit system for time-division bidirectional transmission, which includes an automatic gain control section that controls the amount of attenuation of a variable attenuator, a first input signal is connected between the output of the equalizing amplifier and the received equalized signal output terminal. and a second input, the input selector being switched in accordance with the transmit/receive control signal, the first input being connected to the output of the equalizing amplifier, and the second input being previously selected. connected to a predetermined potential, the first input is selected during the reception instruction period of the transmission/reception control signal, and the second input is selected during the transmission instruction period;
Receiving circuit system for time-division bidirectional transmission. 2. The input selector is an operational amplifier having at least two positive phase inputs, each positive phase input being
A receiving circuit system for time-division bidirectional transmission according to claim 1, characterized in that the receiving circuit system is an input and a second input.