JPS6322501B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to amplitude multilevel transmission, and particularly to a multilevel signal discriminator.

A multilevel signal discriminator receives an analog signal and determines its level.As will be explained in detail later, it has a number of thresholds equal to the majority value minus 1, and these thresholds and the received signal The level is determined by comparing the magnitude of the . The most typical examples are analog-to-digital converters (hereinafter referred to as AD converters) consisting of sample-and-hold circuits, voltage comparators, and local decoders, and external digital-to-analog converters (hereinafter referred to as AD converters).
It consists of a DA converter (abbreviated as a DA converter), a low-pass waveformer, and an input adder, and is combined with a quantization feedback circuit that feeds back part of the output to the input. However, the DA converter used in the latter quantization feedback circuit is required to have a high degree of stability regarding the voltage and current of the power supply, and is also required to perform high-speed switching operation. This has the disadvantage of increasing the cost of the circuit.

Accordingly, an object of the present invention is to provide a multilevel signal discriminator that uses an AD converter as its main component and does not require the use of an external AD converter for quantization feedback.

In order to achieve the above object, in the present invention, instead of using an external AD converter, a sample and hold circuit is added to the local analog signal output section of the local decoder of the AD converter to have the same function. This is what I did.

According to the present invention, analog-to-digital conversion converts an input analog signal into a digital signal by arranging in series a sample hold circuit, an amplitude comparator, and a local decoder having a function of feeding back a local analog signal to the amplitude comparator. a second sample-and-hold circuit that samples and holds the local analog signal of the local decoder; a low-pass filter that passes the low frequency of the sample-and-held signal; A multi-level signal discriminator is obtained which includes a quantization feedback means for feeding back and compensating for distortion of low frequency components.

Next, refer to the drawings for details. Although amplitude multilevel transmission is an established and well-known technique, the principle necessary to explain the present invention will be explained first.

FIG. 1 shows a pulse waveform in the so-called baseband when a single-value input pulse is output through a transmission medium. Since the frequency band of the input pulse, which is a rectangular wave, is usually limited by the transmission medium 11, an output pulse waveform as shown in the figure is received.

Figure 2 shows input and output waveforms in amplitude multilevel transmission. In 8-level transmission, the left input pulse eye pattern (also called eye diagram) passes through the transmission medium 12 and becomes the right output pulse eye pattern. This shows the state in which the data is received. A multilevel signal discriminator is used to receive such a multilevel signal and determine which level has been transmitted. This discriminator has a threshold value that is equal to the number subtracted by 1 from the multilevel number (7 in this case), and performs level determination by comparing the magnitude of the received signal with these threshold values. The most typical example of such a multi-level signal discriminator is a circuit mainly based on an AD converter.

FIG. 3 is a block diagram showing the circuit configuration of the above-mentioned conventional multilevel signal discriminator. In FIG. 3, 21 is the most well-known successive approximation type AD converter. In this AD converter, 22 represents a sample and hold circuit, 23 represents a voltage comparator, and 24 represents a local decoder. and
Outside the AD converter 21, 25 is an external AD
The converter, 26 represents a low-pass wave generator, and 27 represents an input adder. Next, the operation of this discriminator will be explained.

FIG. 4 shows the output waveform of the local decoder in the AD converter which is the main body of the discriminator. That is, the broken line in the figure shows the sample-and-hold value of the input analog signal a, and the solid line shows the actual local analog output b of the local decoder 24, which has a waveform that successively approximates the input sample-and-hold value according to the output bits. The remaining dotted lines indicate possible amplitudes of the local decoder output when the sample-and-hold value of the input signal takes on other values. As is well known, it has a branched structure. Although FIG. 4 depicts up to eight branches, in reality, the branches are more finely divided depending on the number of bits of the digital output signal. When such an AD converter is used to identify the 8-value signal described above, at the third branch, the local decoder converts into 8-value signals.
reach the branch corresponding to the identified level of the two levels. Therefore, the amplitude of the output of the local decoder at this point corresponds to the amplitude of the identified multilevel transmission signal.

Although multi-value identification is possible to some extent in the above manner, problems remain. In actual multi-value transmission, the transmission medium 12 in the multi-value transmission described above not only suffers from band limitations but also usually experiences low-frequency cutoff, which causes extremely large waveform distortion and causes the received signal to may not be correctly identified. A quantization feedback system consisting of an AD converter 25, a low-pass wave generator 26, and an input adder 27 shown in FIG. 3 is provided to correct such low-frequency cutoff distortion. This quantization feedback technique is known, for example, by Bennett and Davey.
Co-authored “Data Transmission”
(published by MoGraw-Hill, 1965), Chapter 15. In other words, according to the multi-value discriminator shown in FIG. 3, the output digital signal c (3 bits in 8-value transmission) is digital-to-analog converted by the AD converter 25 to create a quantized amplitude, which is The configuration is such that the signal is fed back to the input adder 27 of this multi-value discriminator through the low-pass wave filter 26. The principle of conventional quantization feedback is the method shown in FIG. 3, and in this case, an external AD converter was required in addition to the AD converter. The problem here is that AD converters, as mentioned earlier, have to be expensive.

FIG. 5 is a block diagram showing the circuit configuration of an embodiment of the present invention. The components of this circuit that are the same as those in Figure 3 are added to the reference number in Figure 3 by 10.
Reference numbers are added. And 38 is a sample and hold circuit for sampling and holding the local decoder output 34. d is a sample hold pulse, and the temporal position of this pulse is as clear from the explanation regarding FIG.
In the case of 8-level transmission, the position of the third branch or the branch having eight amplitudes is selected. Note that a,
b and c both indicate the same as in the case of FIG. With this configuration, the output b of the local decoder 34 at this point corresponds to the identified amplitude of the input multilevel signal, that is, the quantized amplitude, so the output e of the sample and hold circuit 38 is as shown in FIG. It is the same as that obtained by converting the digital signal output c into a multi-level amplitude by the AD converter 25. Incidentally, this sample-and-hold circuit 38 has far less demanding characteristics than those for a DA converter, and is therefore inexpensive.

As explained above, according to the present invention, a quantization feedback type multilevel signal discriminator can be obtained at a low cost and having the same characteristics as the conventional one.

[Brief explanation of the drawing]

Figure 1 is a diagram showing input/output waveforms in pulse transmission of a single-value input pulse, Figure 2 is a diagram showing input/output waveforms in pulse transmission of a multi-value input pulse, and Figure 3 is a diagram showing input/output waveforms in pulse transmission of a multi-value input pulse.
The figure shows a block diagram of the circuit configuration of a conventional multilevel signal discriminator. Figure 4 shows the analog-to-digital converter (AD converter) that is the main component of the multilevel signal discriminator.
FIG. 5 is a block diagram showing the circuit configuration of an embodiment of the present invention. Explanation of symbols, 21 is AD converter, 25 is external digital/analog converter (DA converter), 31
is an AD converter, 32 is a sample hold circuit, 3
3 represents a voltage comparator, 34 a local decoder, 36 a low-pass wave generator, 37 an input adder, and 38 a sample-and-hold circuit, respectively.

Claims (1)

[Claims] 1 first sample and hold circuit, amplitude comparator,
A local decoder with a function of feeding back the local analog signal to this amplitude comparator is arranged in series to convert the input analog signal into a digital signal.
a digital conversion means; a second sample-and-hold circuit that samples and holds the local analog signal of the local decoder; a low-pass filter that passes the low frequency of the sample-and-held signal; A multilevel signal discriminator comprising: quantization feedback means for feeding back to the signal to compensate for distortion of low frequency components.