JP2715349B2 - DA converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of digital audio reproduction waveform of a compact disk player or the like.

[0002]

2. Description of the Related Art In a DA converter for digital audio, a digital filter is provided to improve the phase characteristics of an analog filter, and the sampling frequency fs is set to n.
The frequency is doubled and D / A conversion is performed to increase the cutoff frequency of the analog filter, thereby improving the overall phase characteristics. In the case of an analog signal such as a general music signal, an aliasing filter is provided at the time of A / D conversion, so that fs /
The configuration includes only two or less frequency components, and there is no problem as long as the audio signal is reproduced by the DA conversion method at the time of the reproduction.

[0003]

However, there is another object that a pulse such as various test signals is put in a compact disc in addition to a general audio signal, and a reproduced signal is used as a test signal for an audio device or the like. is there. in this case,
There is a case where data is input digitally without using an aliasing filter at the time of A / D conversion and output as an output signal for the purpose of pulse wave reproduction.

In these pulse waves, during reproduction,
When output through a digital filter, because of the sharp filter characteristics, ringing always occurs before and after the pulse, reducing the effect of the test signal or narrowing the band used as the test signal for band limitation. Was.

[0005]

SUMMARY OF THE INVENTION The present invention provides a first circuit system for guiding input digital data to a D / A converter through a digital filter which outputs an input digital data at an n-times sampling frequency, and an output of the digital filter. A second circuit system for guiding digital data having a sampling frequency of n times to the DA converter through a thinning circuit for thinning the digital data at the sampling frequency of the input digital data; a first circuit system and a second circuit system A selector circuit for switching between the digital signal and the input digital data, a detection circuit for detecting a difference between each sample of the input digital data, and a discrimination circuit for discriminating between an audio signal and a pulse signal from an output of the detection circuit. When the input digital data is determined to be an audio signal, the input digital data is supplied to the first circuit system. When pulse signal is determined is obtained by, characterized in that switching to the second circuit system.

By comparing the data between the sample frequencies fs and detecting a point where the difference is 0, if the data pattern is such that the data changes continuously in the section of 0, it is detected that it is a pulse signal. Then, data is selected at an interval equal to the sample frequency fs, and the pulse waveform is reproduced to obtain a wide band pulse reproduction characteristic in which ringing by a digital filter is removed.

[0007]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 is a block diagram of one embodiment of the present invention. First, the sample frequency f
detection circuit 3 for detecting a difference between digital data of s
Is obtained as shown in FIG. That is, for example, if the sample data is 16 bits, it is latched for each sample by the 16-bit D flip-flop 6, and the output D1 and the input data IN are collated between all bits by the collator 8 and when all the bits match, the sample You can see that there is no change.

The collator 8 can be realized by an exclusive OR. If the signal is compared with the signal subjected to the one-sample delay as described above, the output E is output as a match signal.
Take out 1. Next, a target pulse wave is extracted from the coincidence signal. That is, the fact that the data does not change is basically almost the probability that the signal is a pulse wave, but it can also be stochastic in an audio signal.

For this reason, the target detection pulse is regarded as a pulse in which the data does not change for several samples, for example, two or more samples as shown by P1 in FIG. 3, and data which is different only by one sample is detected as shown in P2. Be able to do it. Such data cannot be digital data obtained by AD-converting an original audio signal.

In FIG. 2, the data collation between two samples may be further delayed by a D flip-flop D27 to collate with the input data IN in FIG. The output E2 is taken out as a coincidence signal by the collating unit 9. These outputs E1, E2
Is taken out from both ORs (E1 + E2) to obtain E1 + in FIG.
Only the sample that changes like E2 is output as L.

Next, the determination circuit 4 will be described. FIG. 4 is a block diagram, and FIG. 5 is a waveform diagram thereof. Assuming that signal data as indicated by IN in FIG. 5 is input to the data IN in FIG. 1, the input data includes pulse waveform data P or audio data A. The comparison output E1 between the samples obtained by the detection circuit 3 for detecting the difference between them is shown in FIG.
, E2, when the OR gate 10 is taken, a waveform in which only the edge portion is L in the case of the pulse P is obtained as described above. On the other hand, in the case of analog data, there is a possibility that a point where the data does not change as shown by 0 although the probability is low is generated. Therefore, E1 + E2 is also O
D appears.

The data of E1 + E2 is sequentially shifted by the flip-flops 11 and 12 by the sample clock. That is, a delay of up to two samples is performed. This E
1 + E2 input signal and flip-flop 11 output Q11
, Q11 and the output Q12 of the flip-flop 12, and E1
+ E2 input signal and Q12 output are each AND gate 1
ANDs are taken at 3, 14, and 15, all of these outputs are taken out by the OR gate 16, and an output SeL for selecting digital data at the fs interval of the thinning circuit 2 is output.

As shown in FIG. 5, when the SeL output is L, the output of the digital filter 1 is always
Is selected and output. Therefore, P1, P
For the pulse signal corresponding to 2, the output of the digital filter 1 is selected. Now, in the case of audio data such as IN in FIG. 5, the output of the discrimination circuit 4 is L for the audio section a and the output of the digital filter 1 is output at nfs, as in b.

The output waveforms of the input and SeL output gates 16 are shifted by two samples. For this reason, the input data is delayed by two samples by, for example, the buffer 18 shown in FIG.
What is necessary is just to perform DA conversion with an A conversion circuit. In this case, data obtained by delaying two samples should be selected and output to the DA conversion circuit. On the other hand, in the case of L with no SeL output, it is on the digital filter output side. At this time, digital filter 1
Must be equal to two samples. Generally, a digital filter is delayed by several to ten to several samples. In this case, when the amplitude and the DC level are different between the input and output of the digital filter, it is necessary to match them.

Therefore, in order to obtain data that has not been digitally filtered, the digital filter 1 is decimated by the thinning circuit 2 to extract data that is close to the original unfiltered data. FIG. 6 shows this embodiment, and FIG. 7 shows a waveform explanatory diagram thereof. As shown in the figure, a clock fs ′ having an output timing corresponding to an input / output input sample fs of the input digital filter 1 (generally fs
All the data of the bits are latched in the flip-flop 17. Thereby, as shown in FIG. 7, the digital filter OUT of the digital filter 1 becomes nfs
Is changed to the original fs as shown by the x mark.
It is realized by latching. This is realized by outputting the sample data of fs in the case of SeL output and performing DA conversion.

FIG. 8 shows the output waveform A of the present invention and the conventional waveform B in FIG. Again, the timing of the SeL output includes the delay of the digital filter 1 and performs the delay.
In this way, a conventional pulse wave without a high frequency band with much ringing can be reproduced as a pulse wave having an amplitude indicated by a substantially complete data waveform. Here, all the changing points of the waveform are output without a filter, but a signal from which only ringing has been removed can be reproduced. FIG. 9 shows an embodiment of the discrimination circuit 4 in this case.

In this case, the input of the discrimination circuit 4 is E1
Only the gate 1 shown in FIG.
When the outputs of the gates 13 and 14 excluding 5 are taken out by the OR gate 16, a waveform diagram shown in FIG. 10 is obtained. As a result, the output of G16 is a sample in which data has changed, for example, one sample at the rising and falling edges of P1, and P2 is SeL2 of two samples of the upper and lower samples, which is also the output timing of the digital filter 1 and the selection. By adjusting the output SeL, only the changing portion of the ringing waveform data of the digital filter 1 is extracted as shown in the waveform diagram of FIG. 10, and a pulse wave without ringing can be reproduced as indicated by OUT '. As described above, a pulse wave is reproduced in a disk or the like on which a pulse wave is recorded, and a general audio signal is always filtered by a filter as in the related art, so that out-of-band noise is cut. In this way, data can be converted to analog data according to the purpose. Various changes can be made in pattern detection, such as increasing the number of gates in the above embodiment and extracting only pulses of a low cycle.

[0018]

As described above, according to the present invention, a general audio signal is subjected to smooth DA conversion reproduction by a digital filter, and a pulse wave without ringing can be obtained without a digital filter.

[Brief description of the drawings]

FIGS. 1A and 1B are block diagrams showing an embodiment of the present invention, wherein FIG. 1A shows an example using a thinning circuit, and FIG. 1B shows a circuit example for selecting from a stage preceding a digital filter circuit.

FIG. 2 is a block diagram illustrating a detection circuit illustrated in FIG.

FIG. 3 is a waveform chart of each part in FIG. 2;

FIG. 4 is a block diagram illustrating a determination circuit shown in FIG. 1;

5 is a waveform chart of each part in FIG.

FIG. 6 is a block diagram illustrating a thinning circuit 2 shown in FIG.

FIG. 7 is a diagram showing the timing in FIG. 6;

FIG. 8 is a diagram showing a waveform of a pulse wave.

FIG. 9 is a view showing another embodiment of FIG. 4;

FIG. 10 is a diagram showing waveforms at various points in FIG. 9;

[Explanation of symbols]

 Reference Signs List 1 digital filter 2 thinning circuit 3 detection circuit 4 discriminating circuit 5 selector 6,7 D flip-flop 8,9 collator 10,16 OR circuit 11,12,17 D flip-flop 13,14,15 AND circuit 18 buffer

Claims (1)

(57) [Claims] 1. A first circuit system which leads an input digital data to a DA converter via a digital filter which outputs an input digital data at an n-times sampling frequency, and a n-times sampling frequency of an n-times sampling frequency obtained from an output of the digital filter. The digital data is passed through a thinning circuit for thinning digital data at the sampling frequency of the input digital data.
A second circuit system leading to the conversion unit, a selector circuit for switching between the first circuit system and the second circuit system, a detection circuit for detecting a difference between each sample of the input digital data, A discriminating circuit for discriminating between an audio signal and a pulse signal from an output of the circuit, wherein the selector circuit is provided in the first circuit system when the input digital data is discriminated as an audio signal by the discriminating circuit; When the input digital data is determined to be a pulse signal, switching to the second circuit system is performed.