JPS62120127A - Digital-analog converter - Google Patents

Abstract

PURPOSE:To eliminate higher harmonics by one kind of low pass filter by applying sampling frequency conversion to make the center frequency K.Fs in the distribution of the higher harmonics of signals different in sampling frequencies equal to each other. CONSTITUTION:A digital signal decoding means 1 outputs a signal suitable for DA conversion but does not apply direct DA conversion but applies DA conversion after the sampling frequency is converted. Signals having sampling frequencies fs2, fs3 (3fs2=2f2) are subject to thrice and double conversion respectively by the sampling frequency conversion means 2 to make the sampling frequency equal to each other. In converting the sampling frequency, the higher harmonics of the fundamental waves A, B are distributed at K(K=1, 2, 3...) multiple of the same sampling frequency Fs(=3fs2=2fs3) to restore the original signal while using one low pass filter to eliminate the higher harmonic components.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a digital-to-analog conversion device for converting digital signals into analog signals.

BACKGROUND OF THE INVENTION In recent years, as devices have become increasingly digitalized, technology for converting digital signals into analog signals has become important. Moreover, the sampling frequency may differ depending on the device, or even within the same device, signals with different sampling frequencies may be processed. For example, a satellite broadcast receiver uses 32K.
Signals with sampling frequencies of Hz and 48 KHz must be processed.

A conventional digital-to-analog conversion device will be described below.

FIG. 2 shows a block diagram of the main parts of a conventional digital-to-analog converter. 1 is a digital signal decoding means, which converts the transmitted signal into a digital analog (hereinafter referred to as DA)
) Outputs all signals suitable for conversion. 3 is a DA conversion means which converts a digital signal into an analog signal. 4
is a sample hold means which holds the level of the analog signal obtained by the DA conversion means 3 during the sampling period to obtain a stepped waveform signal. Reference numerals 5 and 8 denote signal switching means, which switch between the input pass filters 6 and 7 in response to a signal switching control signal from the digital signal decoding means 1. 6,7
are low-pass filters, which are used corresponding to signals of sampling frequencies fS3 and fS2, respectively, to remove harmonic components and obtain source analog signals.

The operation of the digital-to-analog converter configured as above will be explained. The digital signal decoding means 1 decodes signals with different sampling frequencies and outputs all signals suitable for DA conversion.This decoded digital signal is subjected to DA conversion (-by sampling and holding, a stepped waveform signal can be obtained. By the way, if the sampling frequency of the transmitted signal is fs5, the low-pass filter 6 is selected by the signal switching control signal output of the signal switching means 5, 8 and the all-digital signal decoding means 1, and if the sampling frequency is fs2, the same applies. A low-pass filter 7? is selected, and the source analog signal is completely restored by removing all harmonic components from the stepped waveform signal using the low-pass filter I7 most suitable for each sampling frequency.

Problems to be Solved by the Invention However, in the conventional configuration, a single band pass filter is required for each type of sampling frequency, and many signal switching means are all required, making the circuit in the analog signal domain complicated. There was always a problem with analog signal deterioration.

The present invention solves the above-mentioned conventional problems. Signals with different sampling frequencies are processed by the same low-pass filter, thereby eliminating the need for a signal switching means and converting analog signals into analog signals. The overall purpose of the present invention is to provide a complete digital-to-analog conversion device without signal deterioration by simplifying the circuitry in the area.

Means for Solving the Problems In order to solve the above problems, the digital-to-analog converter of the present invention geometrically changes the sampling frequency to n (n=
2.3.4...) sampling frequency conversion means for doubling the sampling frequency, D-person conversion means for converting a digital signal into an analog signal, sample hold means for holding the analog signal level for a certain period of time, and harmonic It is equipped with a paper passing film that removes components.

Operation The present invention uses the above-described configuration to generate signals J' gm(, J'Sm"fS2'fSs'-
's4...'' to the same sampling frequency, the entire circuit in the analog signal domain can be simplified by using one type of low-pass filter, and signal deterioration can be eliminated.

Embodiment FIG. 1 is a block diagram of essential parts of a digital-to-analog converter according to an embodiment of the present invention. 1 is a digital signal decoding means which converts the transmitted signal into a signal suitable for DA conversion. 2 is a sampling frequency conversion means;
The signals with sampling frequencies f32 and 183 are converted by 3 times and 2 times respectively to obtain 3-'52''2'S 3
, and the sampling frequency after conversion is made equal.

It is a 3UDA conversion means and converts a digital signal into an analog signal. Reference numeral 4 denotes a sample and hold means, which holds the amplitude of the analog signal for a certain period of time to obtain a stepped waveform signal. Reference numeral 9 denotes a low-pass filter that removes harmonic components from the stepped waveform signal to obtain a source signal.

The operation of the digital-to-analog converter of this embodiment configured as described above will be explained.

The digital signal decoding means 1 outputs a signal suitable for DA conversion, but does not perform direct conversion but performs zero conversion after converting the sampling frequency. sampling frequency fS
The signals of 2 and fs3 (here, 3fs2-213) are subjected to triple and double conversion by the sampling frequency conversion means 2, respectively, to equalize the sampling frequencies. By the way, FIG. 3 and FIG. 4 respectively show the distribution of frequency spectra when sampling frequency conversion is not performed and when it is not performed. As is clear from Figure 3, the harmonics of the fundamental friend overlap within the band of the fundamental wave B, so
It is necessary to completely remove harmonics using low-pass filters suitable for each of the fundamental waves A and B. However, by converting the sampling frequency, the harmonic components of fundamental waves A and B each have the same sampling frequency Fs (=3fB2=2
1. ．． ) can be distributed at k (k-1, 2, 2...) times the position, and the same low-pass filter can be used to remove harmonic components and restore the source signal. .

In this way, when converting a digital signal into an analog signal, this embodiment performs all signal processing in the sampling frequency conversion means 2, and converts two types of signals with different sampling frequencies.
Since the sampling frequencies of ``82 'j'S 5 are made equal, unnecessary harmonic components also move to high frequencies as shown in Figure 4, and the basic
Harmonics can be effectively removed using one type of low-pass filter common to both.

Effects of the Invention The present invention performs sampling frequency conversion to make the center frequency of the distribution of harmonics of signals with different sampling frequencies equal to -Fsi, thereby making it possible to remove harmonics with one type of low-pass filter. It is possible to simplify the circuitry in the signal domain and realize a complete digital-to-analog conversion device without signal deterioration.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the main parts of a digital-to-analog converter according to an embodiment of the present invention, Fig. 2 is a block diagram of main parts of a conventional digital-to-analog converter, and Fig. 3 is a frequency spectrum when sampling frequency conversion is not performed. The distribution diagram in Figure 4 shows the signal of J'2Brf53 multiplied by 3 times,
FIG. 4 is a distribution diagram of a frequency spectrum when double sampling frequency conversion is performed. 1...Digital signal decoding means, 2...
- Sampling frequency conversion means, 3...Digital-to-analog conversion means, 4...Sample bold means, 9...Low pass filter. Name of agent: Patent attorney Toshio Nakao
Figure 3 (flL)

Claims (1)

[Claims] A sampling frequency conversion means for equivalently converting a signal transmitted at a sampling frequency f_S into a signal having a sampling frequency n (n=2, 3, 4...) times higher, and a digital signal to an analog signal. It has digital-to-analog conversion means for converting, sample-hold means for holding the level of an analog signal for a certain period of time, and a low-pass filter for removing harmonic components generated during digital-to-analog conversion, and has a different sampling frequency f_S.
m = 2, 3, 4...) types of signals f_S_m(
f_S_m=f_S_2, f_S_3, f_S_4...
...) to the same sampling frequency.