JPS59152743A - Pcm signal reproducing device - Google Patents

Abstract

PURPOSE:To simplify the characteristic of a filter means by applying digital smoothing to attenuate harmonics. CONSTITUTION:When a data A at an input terminal 11 is advanced by one by a sampling clock C, a preceding data and an average data are outputted at a period of a preceding multi-clock D, and the present data A at the input terminal 11 is outputted at a period of the succeeding multi-clock D. Thus, an analog signal itself applied with D/A-conversion does not include much harmonics by smoothing a digital signal, then a filter inserted to an output circuit is simplified more than that of a conventional system.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is directed to PCM communication and digital audio.
The present invention relates to a GM signal reproducing device.

Conventional configuration and its problems Conventionally, POM signal reproducing devices convert the reproduced digital signal into an analog signal, and then insert a filter means having a high cutoff frequency of approximately one-half of the sampling frequency to convert the reproduced digital signal into an analog signal. It was used as a playback signal. The purpose of this filter means is to remove the extra spectrum added by sampling and reproduce the spectrum of the recorded original signal. As is clear from the sampling theorem, it is necessary to sample at twice or more the highest frequency of the original signal, and an aliasing distortion spectrum is generated on both sides of the sampling frequency. Therefore, the boundary between the original signal and the aliasing spectrum is one-half of the sampling frequency, and the above-mentioned filter means uses this frequency as the boundary between the passband and cutoff band. Since the sampling frequency is proportional to the digital recording density, it is necessary to keep it as low as possible, so in reality, the highest frequency of the original signal and the frequency that is half the sampling frequency should be close values. many. Therefore, the filter means is required to have a steep cutoff characteristic, and at the same time, in order to faithfully reproduce the original signal, the amplitude characteristic in the passband must be flat and free from phase distortion.1 These conditions must be met. It was very difficult to create a filter means completely equipped with the following.

OBJECTS OF THE INVENTION The present invention improves the drawbacks of the conventional examples as described above, and provides an excellent jPcM signal reproducing device that can significantly reduce the required performance of the filter means and at the same time improve the fidelity of the reproduced signal. The purpose is to

Structure of the Invention The present invention comprises a means for demodulating and reproducing a digital signal from a recording medium or a communication channel, a means for converting the digital signal into an analog signal, and a filter means. By time-divisionally smoothing the original signal in frequency, the extra spectral components derived from both bands of the sampling frequency are reduced, thereby significantly reducing the required performance of the filter means, and at the same time reducing the filter cut-off frequency was approximately one-half of the sampling frequency, but by changing the range from this sampling frequency to approximately one-half of the time-division clock frequency, the amplitude flatness of the spectral region of the original signal and This improves phase characteristics and enables high-fidelity reproduction.

DESCRIPTION OF EMBODIMENTS An actual case of the present invention will be described below with reference to the drawings.

FIG. 1 shows a block diagram of a PCM signal reproducing apparatus in a first embodiment of the present invention. In Figure 1,
1 is a circuit that demodulates by digital signal processing, a digital signal smoothing circuit that calculates and interpolates the average value of the preceding and following data between the original digital data at a frequency period twice the 2-digit sampling frequency, and a 3-digit signal smoothing circuit. A digital-to-analog conversion circuit (hereinafter referred to as a DA conversion circuit), 4 is a low-pass filter.

The operation of the PCM signal reproducing apparatus of this actual case constructed as described above will be explained below. A digital signal from a recording medium applied to an input terminal 9 is reproduced by a digital signal demodulation circuit 1. This signal jJ;'j[,' is one word assigned to each sampling period during recording. This signal is time-divided by a wave number twice as high as the sampling frequency, and the digital 1 is converted into a signal smoothing circuit 2 ((interpolated between the original words by calculating the average value of the words before and after the original word). A specific example of this digital signal smoothing circuit 2 is shown in FIG. 2. In FIG. The data A is latched by the D-type flip-flop 5 using the sampling clock C and stored.

That is, the previous data and input data A are given to the adders, and full addition is performed. The addition result is transferred to the bit shift circuit 7 (r), so it is shifted by 1 bit and divided by 2.

That is, the average value of the previous data and the currently input data A is obtained. Next, this average value data and the current scale data A are switched by a multiplexer 8 and output as an output B to an output terminal 12. This timing is controlled by multi-clock D. The multi-clock D has twice the frequency of the sampling clock C.

That is, when the data A at the input terminal 11 is advanced by one by the numbering clock C, the average value data with the previous data is output in synchronization with the preceding multi-clock D, and the subsequent multi-clock D/7) lq period. In this case, the current data of input tm11 is output. In this way, the digital signal is smoothed. Let me explain about Figure 1 again.

The smoothed digital data obtained in the above manner is input to the DA converter circuit 3 to become an analog signal, which is passed through a simple low-pass filter 4 and taken out from the output terminal 10 as an analog output.

FIG. 3 shows temporal changes in data smoothed by the next VC digital signal smoothing circuit. In Figure 3,
The horizontal axis represents time, and the vertical axis represents the size of digital data. The dotted line in the graph indicates smoothed retinal data, and the solid line indicates smoothed data. As is clear from Figure 3, it can be seen that the changes in the data size become smaller due to smoothing. FIG. 4 is a graph showing the frequency spectrum of a signal obtained by converting these smoothed data and data that is not converted into 4's into analog signals.

In FIG. 4, the solid line represents the spectrum of smoothed data, and the dotted line represents the spectrum of unsmoothed data. As can be seen from FIG. 4, the spectrum of the smoothed data is small at higher frequencies, and there is a noticeable difference especially above one half of the sampling frequency.

With the above configuration, the DA-converted analog signal itself does not contain many high-order components due to smoothing, so the filter inserted in the output circuit can be configured more easily than before, and the high cutoff frequency There is no problem even if the range is from 1/2 of the sampling frequency to approximately 1/2 of the multi-clock, that is, the sampling frequency fs.

Therefore, overall the maximum flatness performance of the filter.

It becomes possible to optimize phase characteristics and the like.

Effects of the Invention As described above, the present invention comprises a means for reproducing a digital signal from a recording medium or a communication channel, a means for converting the digital signal into an analog signal, and a filter means, and the sampling frequency for signal encoding is The original signal is time-divided and smoothed at a clock frequency that is twice or an integral multiple of , and the high cutoff frequency of the filter is changed from approximately half of the sampling frequency to approximately the above zero frequency. It is within the range of 1/2, and has the advantage that digital smoothing can attenuate high-order components and simplify the characteristics of the filter means. Furthermore, since it can be combined with other digital circuits using integrated circuit technology, it is highly economical and provides remarkable effects such as easy adjustment.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a PCM signal reproducing device showing an embodiment of the present invention, FIG. 2 is a specific circuit diagram of a digital signal smoothing circuit of the same device, and FIG. 3 is a block diagram of a digital signal smoothing circuit of the same device. FIG. 4 is a diagram showing the spectrum of the smoothed signal in the same device. 1 dyntal (i demodulation circuit, 2 ・Discicle signal smoothing (tJl path, 3 ・Discicle amplification converter circuit, 4 ・Low pass filter.

Claims (1)

[Claims] It is equipped with a means for reproducing a digital signal from a recording medium or a communication channel, a means for converting this digital signal into an analog signal, and a filter means, and at a clock frequency that is twice or an integral multiple of the sampling frequency for signal encoding. The original signal is time-divided and smoothed, and the high-frequency cutoff frequency of the filter means is set within the range from one-half of the sampling frequency to approximately one-half of the above-mentioned a-track frequency. PGM signal reproducing device.