JPS5920214B2 - Crosstalk suppression method for PAM multiplexing circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for suppressing crosstalk signals to other channels in a circuit that multiplexes multi-channel signals using a PAM multiplexing method.

The PAM multiplex modulation method can multiplex a large number of channels by time-division multiplexing, and is therefore used in various multiplex modulation methods.

Particularly, in PCM terminal equipment that multiplexes and transmits a plurality of baseband signals, a method of sharing one encoding unit among a large number of channels is often used as an encoding method. In other words, the encoder operates at high speed and encodes each channel in a time-sharing manner.By sharing the encoder, it is possible to create a PCM terminal that is effective from the viewpoint of device circuit size and cost. This is what realizes the device. Said PCM
Since terminal equipment performs time-division encoding, it is necessary to multiplex baseband signals in a time-division manner, and a multiplexing method using PAM multiplexing is generally used as a method for achieving this. As described above, the PAM multiplexing system plays an important role in configuring multiplexed transmission using PCM modulation. However, in the configuration of a PAM multiplexing circuit, a major problem in terms of characteristics is the crosstalk characteristic, which is
This is due to imperfections in the pulse response of M. The main reason for this is the high-frequency cut-off characteristics of the circuit, and when the number of multiplexed channels is increased to take advantage of the advantages of the encoder, the crosstalk characteristics also deteriorate accordingly, which is a serious disadvantage. An object of the present invention is to eliminate the above-mentioned drawbacks and provide a PAM multiplexing circuit having good crosstalk characteristics.

Hereinafter, the present invention will be explained in detail using Examples.

FIG. 1 shows an embodiment of the present invention, in which a three-chuck channel multiplexing case is described, and the circuit configuration is such that only the crosstalk from the first channel to the second channel is compensated for. FIG. 2 shows operating waveforms of various parts in the embodiment shown in FIG.

In Figure 1, 1 is the input terminal for the first channel, 2 is the input terminal for the second channel, 3 is the input terminal for the third channel, 4 is the input terminal for the sampling pulse for the first channel, and 5 is the sampling pulse for the second channel. Pulse input terminal, 6 is a sampling pulse input terminal for the third channel, 7 is a PAM multiple output terminal, 11 is a gate circuit for the first channel, 12 is a gate circuit for the second channel, 13
14 represents a gate circuit for the third channel, 14 represents a gate circuit for suppressing crosstalk from the first channel to the second channel, and 15 represents a polarity inversion circuit having an amplitude attenuation function.
In FIG. 2, a is a first channel input signal, b is a second channel input signal, c is a third channel input signal,
d is the sampling pulse for the first channel, e is the sampling pulse for the second channel, f is the sampling pulse for the third channel, g is the PAM multiplex output when crosstalk suppression is not performed, h is the crosstalk suppression compensation signal, and i is the crosstalk FIG. 6 is a waveform diagram of PAM multiplexed output when suppression is performed.

In FIG. 1, a gate circuit 14 and an inversion circuit 15 are circuits for suppressing crosstalk.

Next, the operation of this embodiment will be explained.

The first channel input signal is sampled at an arbitrary interval by a sampling pulse 4 in a gate circuit 11,
The second channel input signal is sampled at an arbitrary interval by the sampling pulse 5 in the gate circuit 12,
The third channel input signal is sampled at an arbitrary interval by the sampling pulse 6 in the gate circuit 13 and is supplied to the output terminal 7. Now, from the first channel to the second
If channel crosstalk is not suppressed and the operations of the gate circuit 14 and inverting circuit 15 are not considered, the PAM multiplexed signal at the output terminal 7 will have the waveform shown by the solid line in FIG. 2g. The dashed line in the figure shows the operation of an ideal PAM waveform, and shows a state where there is no crosstalk to other channels. However, in actual circuits, the PAM waveform becomes sluggish due to the high-frequency cutoff characteristics of the PAM multiplexing circuit.
As shown in the figure, it can be seen that the signal amount in the shaded area becomes a crosstalk signal to other channels. Crosstalk to other channels
If it is due to high-frequency cutoff characteristics, the PAM waveform is considered to be exponential, and it can be understood that the most significant amount of crosstalk is in the adjacent channel located later in time.

In other words, it is sufficient to mainly consider crosstalk to adjacent channels located later in time; if the first channel is the second channel, then the second channel is the third channel, and if the third channel is the third channel, the crosstalk to the first channel is considered. You just have to pay attention. In this embodiment, as a crosstalk suppression method, a signal having the same amount of crosstalk and the opposite polarity is inserted into a channel located later in time to compensate for the crosstalk characteristics.

Now, if we pay attention to the crosstalk from the first channel to other channels, we only need to consider the crosstalk to the adjacent channels located later in time, so in the case of the first channel, the second
Just think about crosstalk to the channel. In other words, it is sufficient to add a signal to the time slot of the second channel at the same level as the amount of crosstalk from the first channel and with the opposite polarity. Next, considering a specific example of a circuit, as shown in FIG. A crosstalk compensation signal as shown in Fig. 2h is created by sampling with a sampling pulse of A PAM multiplexed waveform with suppressed crosstalk signals can be obtained.

As described above, according to the present invention, it is possible to improve the crosstalk characteristics of a PAM multiplexing circuit by adding a gate circuit and an inverting circuit in addition to the original sampling circuit.

In this embodiment, we focused only on crosstalk to adjacent channels located later in time, but it is also possible to take measures against crosstalk to channels other than adjacent channels, and the present invention can be effectively utilized as a crosstalk suppression method for PAM multiplexing circuits. can.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 a-
1 is a waveform diagram showing the operation of FIG. 1...First channel input terminal, 2...
- 2nd channel input terminal, 3...3rd channel input terminal. 4... Input terminal for sampling pulse for the first channel, 5... Input terminal for the sampling pulse for the second channel, 6... Input terminal for the sampling pulse for the third channel. ,7...PAM
Multiple output terminal, 11... Gate circuit for first channel, 12... Gate circuit for second channel, 13... Gate circuit for third channel, 14
. . . Gate circuit for suppressing crosstalk from the first channel to the second channel, 15 . . . Polarity inversion circuit with amplitude attenuation function.

Claims (1)

[Claims] In a crosstalk suppression method for preventing crosstalk from one channel to another channel in a PAM multiplexing circuit having a first sampling gate provided corresponding to one channel, one of the channels is provided with the time of a subsequent channel of the channel. A second sampling gate that opens and closes the output of the second sampling gate circuit and a polarity inversion circuit that attenuates the output of the second sampling gate circuit and inverts its polarity are provided. 1. A crosstalk suppression method for a PAM multiplexing circuit, characterized in that a signal amount and an opposite phase signal amount is added to a PAM multiplexed output.