JPS6399641A - Bidirectional communication equipment - Google Patents

Abstract

PURPOSE:To suppress the occurrence of signals caused by the differentiation of an offset voltage by canceling the offset voltage which occurs at the time of transmission to input in an equalizing amplifier at the time of reception. CONSTITUTION:A titled equipment is provided with a transmitting means which is connected to a two-wire type transmission line and transmits signal in the transmission period and a receiving means which receives the signals which arrives via the equalizing amplifier 7 connected to the transmission line in the reception period. A canceling means which cancels the offset voltage concerning the signals transmitted from the transmitting means is provided for the input of the equalizing amplifier 7. The canceling means may be switches 5, 6 and 8 which short the input of the equalizing amplifier 7. Thus, since offset canceling actions are executed from the end of the transmission period to the beginning of the reception period, the occurrence of the differential waveform concerning the offset voltage which can not be discriminated from the input signal can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an offset cancellation circuit in a two-wire time-division bidirectional communication device.

〔overview〕

The present invention provides a two-way communication device having a transmitting means and a receiving means for transmitting and receiving signals by time-divisionally transmitting and receiving signals on a transmission path. By inputting the offset voltage to the offset voltage, it is possible to suppress the generation of a signal caused by the differentiation of the offset voltage.

[Conventional technology]

A two-wire time-division two-way communication device is a device that performs two-way communication by temporally dividing two wires into two periods, a transmission period and a reception period.

FIG. 3 shows the configuration of a conventional example of this communication device.

This conventional device includes an input/output terminal 1, a transmitting driver 2, a transmitting transformer 3, a receiving transformer 4, a switch 5 for shorting the equalizing amplifier input, a switch 6 for disconnecting the equalizing amplifier, and an equalizing amplifier. Amplifier 7 and transmission driver input terminal 1z
and an output terminal 11□ of an equalizing amplifier.

FIG. 4 shows signal waveforms at various parts of this conventional device. During the transmission period Tt, the switch 5 is short-circuited and the switch 6 is opened so that a large-amplitude signal input is not applied to the input of the equalization amplifier 7. Here, transmission output S1. If there is an imbalance between the positive amplitude and the negative amplitude, a DC offset voltage will occur in the equalizing amplifier 70. Next, in the reception period T1, the switch 5 is opened and the switch 6 is short-circuited. Since the high-frequency gain of the equalizing amplifier 7 is increased to compensate for the high-frequency transmission loss of the transmission line 9, the output signal S3 of the equalizing amplifier 7 has a waveform obtained by differentiating the waveform of the input signal S2 of the equalizing amplifier 7. become.

[Problem that the invention seeks to solve]

In such conventional devices, when the DC offset voltage at the input and the input signal have the same amplitude, the output of the equalizing amplifier cannot distinguish between the differential waveform due to the DC offset voltage and the input signal, resulting in data errors. There is a drawback that this occurs.

The present invention aims to eliminate such drawbacks and provides a two-way communication device that is not affected by DC offset voltage from the output side.

[Means for solving problems]

The present invention includes a sending means connected to a two-wire transmission line and sending out a signal during a transmission period, and a receiving means connected to the transmission line during a reception period receiving a signal arriving via an equalizing amplifier. The two-way communication device is characterized in that the equalizing amplifier is equipped with canceling means for canceling an offset voltage related to the signal sent from the transmitting means.

The canceling means may be a switch that shorts the input of the equalizing amplifier.

[Effect]

During the period from the end of the transmission period to the arrival of the received signal,
The offset voltage caused by the unbalanced amplitude of the transmitted output is canceled and discharged. After this period, reception is performed.

As a result, the staircase waveform caused by the offset voltage is erased, and it is possible to prevent a signal obtained by differentiating the staircase waveform from appearing in the output of the equalizing amplifier.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a block diagram showing the configuration of this embodiment. FIG. 2 is a waveform diagram showing the operation of this embodiment. Note that the same reference numerals indicate the same objects throughout FIG. 1 and FIG. 2.

First, the configuration of this embodiment will be explained based on FIG.

This embodiment is characterized in that an off-cent discharge switch 8 is added to the conventional example shown in FIG.

Next, the operation of this switch 8 will be explained. Transmission period T,
An off-cent discharge period T is provided between the end of the process and the arrival of the human power signal S2.

Offset in this offset death period T4
The discharge switch 8 is short-circuited to discharge the input off-cent voltage. Activation of the switch 8 is performed simultaneously and in conjunction with switching from the transmitting state to the receiving state. When the offset discharge period Td ends, the switch 8 is released. In this case, it is the receiving period T, and the switch 6 is short-circuited and the switch 5 is open, so that the input signal S2 of the equalizing amplifier 7 does not have the staircase waveform shown in the fourth tooth, and the equalizing amplifier The output signal S3 of No. 7 does not include a differential waveform due to this.

〔Effect of the invention〕

As explained above, the present invention performs the offset cancellation operation from the end of the transmission period to the beginning of the reception period, so that it is possible to suppress the generation of a differential waveform related to the offset voltage that is indistinguishable from the input signal. be.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit connection diagram showing the configuration of an apparatus according to an embodiment of the present invention. FIG. 2 is an imaging chart for explaining the operation of the apparatus according to the embodiment of the present invention. FIG. 3 is a circuit connection diagram showing the configuration of a conventional device. FIG. 4 is a timing chart explaining the operation of the conventional device. 1... Human output terminal completed, 2... Transmission driver, 3...
Transmission 1-', >7 steps, 4...Reception transformer, 5.6.
8...Switch, 7...Equalizing amplifier. Structure of the embodiment Fig. 1 Operation of the embodiment Fig. 2 Structure of the conventional example Fig. 3

Claims (2)

[Claims] (1) A sending means connected to a two-wire transmission line and transmitting a signal during a transmission period, and a receiving means connected to the transmission line during a reception period and receiving a signal arriving via an equalizing amplifier. A two-way communication device comprising: a canceling means for canceling an offset voltage related to a signal sent from the transmitting means at an input of the equalizing amplifier. (2) The two-way communication device according to claim (1), wherein the canceling means is a switch that short-circuits the input of the equalizing amplifier.