JPS6121621A - Digital-analog converter - Google Patents

Abstract

PURPOSE:To improve inconvenience such as noise on sense of listening by increasing the time constant of a low-pass filter when there is a dropout in a digital signal and bringing an analog signal at dropout not suddenly to 0 level but to a level decided when the time constant of the said low-pass filter is increased. CONSTITUTION:An output analog signal of a digital-analog converter 2 is transmitted normally to a capacitor 8 in synchronization with a clock signal and signal just before dropout is stored in the capacitor 8 at dropout, an analog signal holding the signal just before the dropout is obtained at an analog signal output terminal 9 at dropout and the signal level does not go to 0, then the noise on sense of listening is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a digital-to-analog conversion device suitable for use in digital audio equipment and the like.

BACKGROUND TECHNOLOGY AND PROBLEMS Generally, when reproducing a recorded signal recorded as a digital signal such as a compact disc and converting it into an analog signal, there are times when the digital signal cannot be reproduced due to a missing part of the recorded signal. When interpolation is also not possible, this portion of the reproduced digital signal is normally set to a low level signal "'0" so as not to output an erroneous signal. In this case, conventionally, for example, in a compact disc player, muting is performed simultaneously on the analog signal system as well. When this compact disc player plays a severely scratched compact disc, for example, muting occurs frequently during music performance, which is inconvenient and unpleasant. Furthermore, when muting is not performed in the analog signal system, there is an inconvenience that audible noise increases.

Purpose of the Invention In view of the above, the present invention solves the above-mentioned audible inconvenience when there is a dropout in a digital signal.
The purpose is to encourage people to do the same.

SUMMARY OF THE INVENTION The present invention is a digital-to-analog converter, in which the time constant of a low-pass filter provided on the output side of an analog converter is greatly changed, thereby solving the audible inconvenience when there is a dropout in a digital signal. It is designed to improve.

Embodiment Hereinafter, one embodiment of the digital-to-analog converter of the present invention will be described with reference to FIGS. 1 and 2.

In Fig. 1, (1) shows a digital signal input terminal to which a digital signal obtained from, for example, a compact disc through a digital processing circuit is supplied; The signal is supplied to a digital-to-analog converter (2) that converts the digital signal into an analog signal, and the output signal of the digital-to-analog converter (2) is passed through a switch circuit (3) to an amplifier circuit (with high input impedance). 4). Further, (5) indicates the clock 1g input terminal to which the clock signal for processing the digital 1g is supplied, and the clock signal supplied to the clock G+' input terminal (5) is connected to the digital analog converter. (2) and also to one input terminal of the AND circuit (6). In addition, (7) indicates a dropout signal input terminal to which a dropout detection signal of the digital signal detected by the digital processing circuit is supplied, and the dropout signal supplied to the dropout signal input terminal (output) is input to the AND circuit (6). ).In this case, in this example, as this dropout signal, only the part of the digital signal that cannot be interpolated is set as a low level signal "0" as shown in FIG. 2B, and The other parts are designed to obtain a high level signal "1".

The output signal of this AND circuit (6) is transferred to the switch circuit (3).
control signal. In other words, the dropout signal of this switch circuit (3) is normally a high level signal "1", so it is turned on when the clock signal reaches a high level signal "1n", and when this clock signal is a low level signal "0" When a dropout occurs in the digital signal, the dropout signal becomes a low level signal "'0'", so the switch circuit (3) is turned on at this time. The output side of this switch circuit (3) is grounded via a capacitor (8) which together with this switch circuit (3) constitutes a sampling and holding circuit. In this case, normally the switch circuit (3) is turned on and off by the clock signal.
Since the switch circuit (3) and the capacitor (8) are turned off, the sampling and hold circuit composed of the switch circuit (3) and the capacitor (8) corresponds to a low-pass filter with a relatively small time constant, and during the dropout, the switch circuit (3) continues to turn off. Therefore, it corresponds to a low-pass filter with a relatively large time constant.

The output side of this amplifier circuit (4) is connected to the analog signal output terminal (
9) Busy connection.

This example is configured as described above, so that, for example, when the dropout signal supplied to the dropout signal input terminal (power) is as shown in FIG. ) is transmitted to the capacitor (8) in synchronization with the clock signal, and at the time of dropout the analog signal of the output signal is transmitted to the capacitor (8). An analog signal is obtained, and according to this example, the signal level does not become 0 as shown by the broken line in Figure 2H2, as shown in the conventional example. When playing back a compact disc, tK muting is not performed frequently, and there is no audible discomfort.

Further, FIG. 3 shows another embodiment of the present invention. In FIG. 3, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and detailed line cuts are omitted.

In FIG. 3, (101 indicates a digital processing circuit that digitally processes a reproduced digital signal from, for example, a compact disc, and this digital processing circuit (10)
A reproduced digital signal subjected to predetermined processing is supplied to a digital signal input terminal (1). The digital signal obtained at this digital signal input terminal (1) is supplied to a digital-to-analog converter (2b), and the output INI+ of this digital-to-analog converter (2b) is
Obtain an analog signal as shown in Figure A, and use this analog ig-
qwo is supplied to the low-pass filter (13). This low-pass filter (131) has a cut-off frequency F2 of an extremely low value as shown in FIG. Its structure has a relatively large time constant.Since the cutoff frequency F2 of this low-pass filter u3 is extremely low, when an analog signal as shown in FIG. 4A is supplied, the output signal of this low-pass filter (13i) is For example, as shown in FIG. 4B, the signal will be a signal without sudden changes.
The fixative solution is supplied to the other point □ (14b). In addition, the digital signal obtained at the digital signal input terminal (1) is input to the predetermined value:l! ! This digital-to-analog converter (za) is supplied to the digital-analog converter (za) through a delay circuit 0D having a delay time τ. Figure 4 C on the output side of unit A (2a)
An analog signal as shown in FIG. 4A delayed by a time τ is obtained, and this analog signal is supplied to a low-pass filter 114. This low-pass filter 112 has a cut-off frequency F1 as shown in FIG. do.

In addition, a dropout signal as shown in FIG.
7) and this dropout signal input terminal (7)
The dropout signal obtained at
is supplied to the delay expansion circuit u9 which slightly expands (Tt+δ), and the output signal from this delay and expansion circuit switches the movable contact (14C) of the selector switch u4J. The movable contact (14G) is connected to the other fixed contact (14b) only during the dropout period (Tz+δ) of the output signal, and at other times this movable contact (14G) is connected to one fixed contact (14a). This changeover switch is for En-no-Machi-Duketen (14C).
) to the analog (H output terminal (9)).

Since the example in FIG. 3 is configured as described above, the cutoff frequency F! is, for example, a 20 kHz low-pass filter (for example, the audio signal as shown in the fourth diagram obtained at the output side 1 of 11 is rlp to the analog signal output terminal (9)).
When analog 4B drops out as shown in No. 411D, the changeover switch (+41 movable contact (1
4c) is connected to the other fixed contact (14b), and during this time, the signal obtained through a relatively large low-pass filter (13) with a cut-off frequency F2 and an extremely low time constant as shown in FIG. 4B is converted into an analog signal. It is supplied to the output terminal (9). In this case, to switch this movable contact (14C), the dropout period is slightly longer than TI (T1+δ).
Therefore, there is no effect at all due to dropout on the analog signal output terminal (1).

It is easy to understand that the example in FIG. 3 can also provide the same effects as the example in FIG. 1.

Further, FIG. 6 shows still another embodiment of the present invention.

In this Figure 6, the parts corresponding to the first row and Figure 3 have the direction number d-'4! : The stabbing and congratulations are omitted.

In this example, the digitally processed reproduced digital signal obtained by the digital processing circuit α0) is
A transversal filter a constituting a low-pass filter supplies the analog signal to the analog converter (2) and converts the analog signal obtained at the output side of the digital-to-analog converter (2).
The output terminal of this transversal filter αe is connected to the analog signal output terminal (9). In this example, this transversal filter (161 is 2N
delay lines each having a predetermined time τ2, and converts the tapping coefficient into a tapping coefficient as shown in FIG.
From a-1+ "0 + "1 """N-1+ aN, for example b-N + b-(N-1) "1b-1+
bQ +b1...bN-1, bN. In this case, the tapping coefficient is a-N r a-(N-
1) ””a-1+ aOr al ””aN-1+
Cutoff frequency f of the low-pass filter when aN
i”x is the maximum audio frequency, for example 20, as shown in Figure 5.
The cutoff frequency F1 is determined by F1=□2τ3. Here, τ3 is the tapping coefficient a-N, a-(N-1) from the origin as shown in Fig. 7. ”a
-1+ aO+a1...aN 1 + "This is the time until the point where the N curve crosses the zero response for the first time. Also, the tapping coefficient is as shown in Fig. 7 < b - N l
b(N-1) ""b-11') O+b1...
The cutoff frequency F2 of the low-pass filter of bN71 l bN is set as shown in FIG. As shown in the figure, the tapping coefficient b-N+ b-(N-1) "" b-
1+bO.

bl...This is the time until the point where the curve bN-1+bN crosses the zero response for the first time. In this case, the tapping coefficient is b-N + b-(N-1)...°b-1・
When bO2bl..°.bN-1.bN, the cutoff frequency of the low-pass filter becomes extremely low, which is essentially equivalent to the time constant of the low-pass filter becoming relatively large.

Also, the delay time of the signal obtained at the output terminal in this case is N×τ2 It is.

In such a transversal filter aω, the cutoff frequency of the low-pass filter in normal operation is set to FI in FIG. 5, and during dropout, this cutoff frequency can be made extremely low as F2 in FIG. .

Therefore, it can be easily understood that the embodiment shown in FIG. 6 can also provide the same effects as the embodiments shown in FIGS. 1 and 3.

It goes without saying that the present invention is not limited to the above-described embodiments, and that various other configurations can be adopted without departing from the gist of the present invention.

Effects of the Invention In the present invention, when there is a dropout in the digital signal, the time constant of the low-pass filter is increased, and the time constant of the low-pass filter is increased so that the analog signal at the time of dropout does not suddenly reach the θ level. Since the level determined when the signal is increased is t, there is an advantage in that inconveniences such as auditory noise can be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the digital-analog device of the present invention, FIG. 2 is a diagram for explaining FIG. 1, and FIGS. FIG. 4 and FIG. 5 are diagrams used to explain FIG. 3, and diagrams shown in FIG. Input terminal, (2) digital-to-analog converter, (3) switch circuit, (41t
1 circuit, (5) is clock signal input terminal, (6)
(AND circuit, (7) is a dropout signal input terminal, (decoy capacitor, (9) is an analog signal output terminal.

Claims (1)

[Claims] 1. A digital-to-analog converter, characterized in that a dropout of an input digital signal is detected, and the time constant of a low-pass filter provided on the output side of a digital-to-analog converter is greatly changed based on the dropout detection signal.