JPH03261239A - Reception circuit for time division bi-directional transmitter - Google Patents

Abstract

PURPOSE:To prevent noise caused at switching from transmission to reception state from being amplified by starting the operation of an automatic gain control section of a reception circuit of a time division bi-directional transmitter with a signal retarding a transmission reception control signal. CONSTITUTION:The reception circuit is provided with an automatic gain control section 6 generating a gain control signal in response to a level of an output signal of an input selection amplifier 5 and controlling the gain of a variable gain amplifier 4, and a delay element delaying a transmission reception control signal to control the operation start of the automatic gain control section 6 with an output of the delay element 8. That is, the transmission reception control signal is inputted to the delay element 8 and its output starts the operation of the automatic gain control section 6, then a fact of amplifying a switching noise as a reception signal is avoided. Then the level is adjusted by a gain control signal with respect to a substantial reception signal. Thus, the noise caused from the transmission to the reception is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a receiving circuit for a time-division bidirectional transmission device.

[Prior Art] FIG. 3 is a block diagram showing a receiving circuit of a conventional time-division bidirectional transmission device disclosed in, for example, Japanese Patent Publication No. 63-54260. In the figure, (1) is a circuit for transmitting signals. Transmission circuit, (2) is a transformer that receives the signal from transmission circuit (1), (3) is a transmission line connected to transformer (2), (4)
is a variable gain amplifier receiving the signal from the transformer (2);
(5) is an input selection amplifier which receives the output and zero level of the variable gain amplifier (4) as input and selects and outputs the input according to the transmission/reception control signal; (6) observes the output of the input selection amplifier (5); Variable gain amplifier (4) by gain control signal
The automatic gain control section ()) that controls the gain of the variable gain amplifier (4), the input selection amplifier (5), and the automatic gain control section (
6) is the receiving circuit.

Next, the operation will be explained. In time-division bidirectional transmission, one set of transmission paths is repeatedly used for time-division transmission and reception.

During transmission, a transmission signal is sent from the transmission circuit (1) to the transmission line (3) via the transformer (2). At this time, the transmitted signal is also received in the receiving circuit (7) and sent to the input selection amplifier (5) through the variable gain amplifier (4). However, since the input selection amplifier (5) selects and outputs the zero level input of the +2 input terminal according to the transmission/reception control signal, the output of the receiving circuit (A) becomes zero level, and the transmitted signal does not affect the receiving side. Never.

On the other hand, during reception, the output of the transmitting circuit (1) is at zero level, and the received signal from the transmission line (3) is passed through the variable gain amplifier (
4) and is further sent to the input selection amplifier (5). The input selection amplifier (5) is set to +1 by the transmit/receive control signal.
The output of the input variable gain amplifier (4) is selected and output. The output of the input selection amplifier (6) is controlled by the automatic gain control section (
6), the variable gain amplifier (gain of 0) is controlled by the gain control signal so as to approach the desired level.

(Problem to be solved by the invention).

The receiving circuit of a conventional time-division bidirectional transmission device is configured as described above, so that it treats the noise of the input selection amplifier (5) that occurs when switching from transmitting to receiving as a received signal and amplifies it. There was a problem that it could get lost.

This invention was made to solve the above-mentioned problems, and provides a time-division bidirectional transmission device that can treat noise generated when switching from transmission to reception as a received signal and prevent it from being amplified. The purpose is to obtain a receiving circuit for

[Means to solve the problem]

A receiving circuit of a time-division bidirectional transmission device according to the present invention includes a transmitting circuit that sends a signal to a transmission path via a transformer, and a variable gain amplifier that receives a signal from the transformer and changes the gain using a gain control signal. and a first input terminal and a second input terminal, the output of the variable gain amplifier is connected to the first input terminal, a zero level potential is connected to the second input terminal, and the output signal is inputted by the transmitting/receiving control signal. An input selection amplifier that selects one input and a second input, and an automatic gain control section that monitors the output signal of the input selection amplifier and generates a gain control signal according to its level to control the gain of the variable gain amplifier. The receiving circuit of the time-division bidirectional transmission apparatus is provided with a delay element for delaying the transmission/reception fee al signal, and the start of operation of the automatic gain control section is controlled by the output of the delay element.

[Effect]

In this invention, the operation of the automatic gain control section is controlled by a signal obtained by delaying a transmission/reception control signal by a delay element, thereby preventing noise that occurs when switching from transmission to reception.

(Embodiment) Hereinafter, an embodiment of the present invention will be described with reference to FIG. 1, in which the same parts as the conventional example shown in FIG. 3 are denoted by the same reference numerals.

In FIG. 1, (8) indicates a delay element that delays the transmission/reception control signal, and the automatic gain control section (6) starts its operation based on the output signal of this delay element and controls the input selection amplifier (5). The gain of the variable gain amplifier (4) is controlled by a gain control signal according to the output.

Next, the operation will be explained. In time-division bidirectional transmission, 1
A set of transmission paths is used repeatedly for transmission and reception in a time-division manner.

During transmission, a transmission signal is sent from the transmission circuit (1) to the transmission line (3) via the transformer (2). At this time, the transmission signal is also received by the receiving circuit (7) and sent to the input selection amplifier (5) through the variable gain amplifier (4).

However, since the input selection amplifier (5) selects and outputs the zero level input of the +2 input terminal according to the transmission/reception control signal, the output of the receiving circuit (7) becomes zero level.

On the other hand, during reception, the output of the transmitting circuit (1) is at zero level, and the received signal from the transmission path is input to the variable gain amplifier (4) and further sent to the input selection amplifier (5). The input selection amplifier (5) selects and outputs the output of the variable gain amplifier (4) which is the +1 input when the transmission/reception control signal is switched from the transmission mode to the reception mode.

At this time, the input selection amplifier (5) generates switching noise. In the conventional circuit configuration shown in FIG. 3, the automatic gain control section (6) recognizes this switching noise as a received signal and adjusts the gain of the variable gain amplifier (4) as shown in the waveform diagram of FIG. It will be raised and amplified. However, in this embodiment, as shown in the waveform diagram of FIG. 2, the transmission/reception control signal is input to the delay element (8), and the output thereof starts the operation of the automatic gain control section (6). Therefore, switching noise will not be mistaken for a received signal and amplified. and,
The level of the original received signal is adjusted by the gain control signal.

In the above embodiment, an analog element is used as the input selection amplifier (5), but a digital element may be used via an A/D converter.

〔Effect of the invention〕

As described above, according to the present invention, the automatic gain control unit of the receiving circuit of the time-division bidirectional transmission device is configured to start operation by a signal obtained by delaying the transmission/reception control signal. This has the effect of preventing noise that occurs when switching to a received signal from being regarded as a received signal and amplified.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a receiving circuit of a time-division bidirectional transmission device according to an embodiment of the present invention, and FIGS. 2(a) to (d)
is a signal waveform diagram in a receiving circuit of a time-division bidirectional transmission device according to an embodiment of the present invention, FIG. 3 is a block diagram showing a receiving circuit of a conventional time-division bidirectional transmission device, and FIG. 4(a)
-(c) are signal waveform diagrams in a receiving circuit of a conventional time-division bidirectional transmission device. (1) is a transmission circuit, (2) is a transformer, (3) is a transmission line, (4) is a variable gain amplifier, (5) is an input selection amplifier,
(6) is an automatic gain control section, (A) is a receiving circuit, and (8) is a delay element. m:1-“

Claims (1)

[Claims] A transmission circuit that sends a signal to a transmission path via a transformer, a variable gain amplifier that receives a signal from the transformer and changes the gain according to a gain control signal, and has a first input terminal and a second input terminal, The output of the variable gain amplifier is
an input selection amplifier connected to the input terminal and having a zero level potential connected to the second input terminal to select the first input and the second input according to the transmission/reception control signal; and observing the output signal of the input selection amplifier. In a receiving circuit of a time-division bidirectional transmission device including an automatic gain control unit that generates a gain control signal according to the level and controls the gain of a variable gain amplifier, the receiving circuit includes a delay element that delays the transmission and reception control signal, A receiving circuit for a time-division bidirectional transmission device, characterized in that the output of the delay element controls the start of operation of the automatic gain control section.