JPH0518496B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an interface circuit suitable for digital audio equipment and digital video equipment. A further object of the present invention is to provide an interface circuit that can block uncorrelated components (unnecessary components) superimposed on a transmitted digital signal at the entrance of an analog signal processing section.

[Conventional technology]

FIG. 6 shows a block diagram of a compact disc (hereinafter referred to as CD) player equipped with a conventional interface circuit.

The digital signal processing section 61 includes a servo circuit 63 that controls the rotational drive system of the CD 62, and a digital signal processing circuit 6 that processes signals read from the CD 62.
4, and a crystal oscillator 65 serving as a synchronization reference. The interface circuit 66 includes a transmission side interface circuit 66a in the digital signal processing section 61 and a reception side interface circuit 66b in the analog signal processing section 67. The transmission side interface circuit 66a and the reception side interface circuit 66b are connected by an optical transmission element.

The analog signal processing section 67 includes a digital filter 68 and a digital/analog converter (DAC).
69 are provided.

As shown in FIG. 6, the digital signal processing section 61 and the analog signal processing section 67 have a separate structure (D/A separated structure). This is to prevent electrical noise generated in the servo circuit 63 and digital signal processing circuit 64 from affecting the analog signal processing section 67 (causing deterioration of sound quality). When implementing a D/A separation structure within the same housing, careful attention is paid to unnecessary radiation.

Further, in general, measures are taken to separate the power supplies for the digital signal processing section 61 and the analog signal processing section 67 to prevent the influence of the power supply ground line from changing sound quality.

Based on this, the digital signal is transmitted from the digital signal processing section 61 to the analog signal processing section 67. Recently, optical transmission has been used, which has excellent advantages such as complete electrical isolation and no unnecessary radiation. , both separate and single-casing types are being adopted.

However, this does not eliminate the influence of sound quality change factors from the digital signal processing section 61 to the analog signal processing section 67, and optical transmission also has drawbacks. Next, I will discuss the problems.

(B) In the process of transmitting the digital signal from the digital signal processing section to the analog signal processing section, jitter components and waveform distortion components are added to the digital signal waveform, deteriorating the quality of the digital signal waveform.

(b) Jitter components and waveform distortion components that are causes of sound quality changes generated in the digital signal processing section are transmitted to the analog signal processing section through digital signal transmission.

As a measure to improve the above problems (a) and (b), a method has been attempted in which the digital signal processing unit resamples the digital signal using a clock based on crystal precision and sends it out immediately before optical transmission. The analog signal processing section also compensates for variations in pulse width due to optical transmission, and uses two stages of PLL to improve timing clock accuracy.

Furthermore, conventionally, the digital signal processing section
The crystal oscillator, which serves as a synchronization reference or timing reference, is moved to the analog signal processing section, and the synchronization signal from this is used to more reliably synchronize the digital signal processing section, and the read data is resampled in the analog signal processing section using a clock based on crystal precision. However, various attempts have been made to improve the accuracy of digital signals. Although these effects vary in magnitude, they do improve distortion in the mid-high range and are effective to some extent.

[Problem that the invention seeks to solve]

However, even with each of the above improvement measures, it was not possible to fundamentally eliminate the factors that change sound quality (jitter components, waveform distortion components) that are added during the digital signal transmission process from the disk to the analog signal processing section. .

This "jitter component" and "waveform distortion component"
is an "uncorrelated part" that has no correlation with the original analog signal (the sound before being recorded as a digital signal on a CD). On the other hand, harmonic distortion in an analog signal can be called a "correlation component." Since humans have a very high detection level for uncorrelated signals, the sense of discomfort that the "uncorrelated part" gives to the auditory sound quality is much greater than that of the "correlated component."

In digital signal transmission systems, even if the 1 and 0 codes themselves do not change, this "uncorrelated part" changes the sound quality.

FIG. 7 shows the transmitted digital signal. The figure A is
The transmitted digital signal is transmitted from the digital signal processing unit to the analog signal processing unit via the interface circuit.B in the figure is the original code information read from the disk, and C in the figure is the jitter generated in the digital signal processing unit. component and waveform distortion component.

A transmission digital signal (A in the figure) in which the jitter component and the waveform distortion component (uncorrelated component) shown in the figure C are superimposed on the original code information shown in the figure B is transmitted to the analog signal processing section.

In this way, the "uncorrelated component" once added to a digital signal cannot be removed even by optical transmission used for the purpose of separating digital and analog blocks. Although optical fibers can prevent superimposition of external noise, they do not have the function to remove "uncorrelated components" from digital signals that already contain them, so "uncorrelated components" are not transmitted together. Therefore, there is almost no improvement effect on uncorrelated distortion.

In addition, the "uncorrelated component" that is transmitted once is
Since it also enters the ground and power lines in the analog signal processing section in the form of current, the apparent digital waveform will be clean even if you perform waveform shaping etc. afterwards, but the "uncorrelated component" will be lost in the digital/analog converter. There were problems such as passing through the analog signal and changing the quality of the analog signal (see Figure 8).

[Means for solving problems]

The present invention provides a transmission-side interface circuit provided in a digital signal processing section and a reception-side interface circuit provided in an analog signal processing section, which is electrically, electrostatically, and electromagnetically separated from the digital signal processing section. an interface circuit for transmitting a transmitted digital signal from the transmitting interface circuit to the receiving interface circuit via one of optical, sonic and magnetic coupling means; Ace circuit, in order to remove jitter components and waveform distortion components superimposed on the transmission digital signal, a driver control signal is supplied to the receiving side interface circuit, and the transmission digital signal removes the jitter components. a control driver that is in either an ON or OFF operating state at a timing that does not include the transmission signal and only for a very short time than the duration of one bit of the transmission digital signal; and the transmission side interface circuit of the coupling means. During the period when current is flowing through the transmission section located in the transmission section, there is a superinput section that performs code detection for a very short period of time at the same operation timing as the control driver, and the output signal of this reception section is supplied as data, and A read clock having the same timing as the control signal is supplied, and an output circuit that outputs the received digital signal, and an original signal is supplied from an oscillator that also serves as a synchronization reference for the digital signal processing section, and the driver control signal and the driver control signal without jitter components are supplied. a timing signal generator for generating the read clock.

[Effect]

According to the above configuration, it is possible to detect the logic of the transmitted digital signal at a timing that does not include jitter components in the transmitted digital signal in the reception side interface circuit, and furthermore, it is possible to detect the logic of the transmitted digital signal at a timing that does not include the jitter component in the transmitted digital signal. The transmitted digital signal can be removed and the transmitted digital signal can be regenerated based on the logic of the detected transmitted digital signal.

Therefore, the reception side interface circuit can obtain a digital signal in which no jitter components are mixed, and as a result, the circuits after the reception side interface circuit of the analog signal processing section are not adversely affected by uncorrelated components.

〔Example〕

The interface circuit of the present invention operates the receiving element of the receiving side interface circuit, which is the first entrance of the transmitted digital signal containing uncorrelated components to the analog signal processing section, for only a very short time. This is to block uncorrelated components at the entrance of the analog signal processing section. In other words, only the code information of 1 and 0 from a digital signal containing uncorrelated components is instantaneously read (sign detection by the receiving element) using another clock signal as a reference, and completely separated from the previous stage (digital signal processing section). This is an interface circuit that generates a completely new digital signal on a separate block (analog signal processing section).

Fig. 1 shows the block configuration diagram of the first embodiment, and Fig. 1 shows the block configuration diagram of the first embodiment.
The figure shows a signal waveform diagram.

The interface circuit is composed of a transmission side interface circuit 20 and a reception side interface circuit 21. Transmission side interface circuit 20
a digital signal processing section 1 having a receiver interface circuit 21; and an analog signal processing section 2 having a receiving side interface circuit 21.
means electrical (electrostatic,
Completely separated (including electromagnetic) (D/A separation structure)
has been done. Of course, the transmission side interface circuit 2
0 and the receiving side interface circuit 21 are similarly separated since they are only optically connected by photocouplers 3 and 11, which are one transmission element. This D/A separation structure can prevent electrical noise generated in the digital signal processing section 1 from entering the analog signal processing section 2.

Transmission of digital signals from the transmitting side interface circuit 20 to the receiving side interface circuit 21 is performed by the photocoupler 3. The receiving side interface circuit 21 includes a timing control signal generator 9 and a control driver 12 in order to read code information from the transmitted digital signal in an extremely short time.
(code detection switch) is provided.

Further, a photocoupler 11 is provided for transmitting timing information from the timing control signal generator 9 to the digital signal processing section 1.

Next, the operation of this interface circuit will be explained.

Original signal generator (crystal oscillator) 8 that serves as a synchronization reference
is arranged in the analog signal processing section 2, and is generated by the original signal generator 8 and the timing control signal generator 9.
All synchronization signals and timing control signals for this machine are generated. Among these, the synchronization signal is the driver 10
The signal is transmitted to the digital signal processing unit 1 through the photocoupler 11 and synchronized. The digital signal (code information) read from the CD becomes a transmission digital signal a in the digital signal synchronization control circuit 6 according to this synchronization timing, and is transmitted to the analog signal processing unit 2 via the driver 7 and the photocoupler 3. . This transmitted digital signal a has jitter components and waveform distortion components superimposed thereon, as shown in FIG. 2A.

Here, the logical code of the transmitted digital signal a is "0"
It is assumed that a current flows through the light emitting diode 3a of the photocoupler 3 at this time, and that the control driver (sign detection switch) 12 is turned on only when the driver control signal c is at a low level.

Therefore, current flows through the phototransistor 3b of the photocoupler 3 only when the control driver 12 is turned on at the logic code "0" of the transmission digital signal a, and when the control driver 12 is turned off, No current flows regardless of the logical sign of the transmitted digital signal a.

If the transmitted digital signal a is a signal read from a CD, it is sent under the control of a synchronizing signal of 44.1 kHz, so the logical code of the transmitted digital signal a is
Timing that is stable as “1” or “0” and does not include jitter components (“0” → “1”, “1” → “0”)
The control driver 12 is turned on by the driver control signal c (see FIG. 2c) at a timing that is not at the turn of , see FIG. 2A). Then, the transmitted digital signal a is not affected at all by the jitter component, which is a factor that changes the sound quality, superimposed on the transmitted digital signal a, and is only affected by the waveform distortion component only when the control driver 12 is on. Only code information in signal a can be detected.

Here, the ON period of this control driver 12 is set as short as possible (1 of the transmission digital signal a).
If the duration of the phototransistor 3 is made extremely shorter than the duration of the bit, the phototransistor 3 can be
The code can be detected with b. Phototransistor 3b
The code detection output b, which is the output of , is shown in FIG. 2B.

Output terminal 14 of receiving side interface circuit 21
The received digital signal e (see FIG. 2 E) output from the D flip-flop circuit (hereinafter referred to as D flip-flop) 13 reproduces the original digital signal waveform based on the sign detection output b. It has gained. This received digital signal e
is a signal obtained by removing uncorrelated components from the transmitted digital signal a, that is, a signal containing only code information read from a CD. D flip-flop 13
is supplied with a read clock d (see FIG. 2) having the same timing as the driver control signal c. Since the driver control signal c and the read clock d are generated from the output signal of the original signal generator 8, they do not contain jitter components.

FIG. 3 again shows the relationship between the transmitted digital signal and code detection.

In this way, the above interface circuit is
At the entrance of the analog signal processing section 2, uncorrelated components (jitter components and waveform distortion components) superimposed on the transmitted digital signal a can be blocked. Therefore, the analog signal processing section 2 is not adversely affected by uncorrelated components, and moreover, the analog signal processing section 2
In this case, it is possible to generate a digital signal e containing only the original code information and no uncorrelated components.

By converting this digital signal e into an analog signal using a digital/analog converter (not shown), the signals recorded on the CD can be faithfully reproduced.

Here, in the case of this embodiment, the synchronization signal necessary for the circuit operation of the digital signal processing section 1 is transmitted from the analog signal processing section 2. Therefore, unnecessary components affected by load fluctuations of the analog signal processing section are superimposed on the synchronization signal. However, even if that unnecessary part invades the digital signal processing section 1,
The digital signal processing section 1 is not adversely affected in any way.
This is because within the digital signal processing unit 1, there is a level difference of about 5V between the logical codes "0" and "1" of the digital signal to be processed, and the level of the unnecessary part included in the synchronization signal is the same as that of the digital signal. This is because it is so small that it can be ignored compared to the signal level.

Next, FIG. 4 shows a second embodiment. In the figure, the same components as those in FIG. 1 are given the same reference numerals, and the explanation thereof will be omitted. In the second embodiment, the phototransistor 3b of the reception side interface circuit 21' is
It is not controlled directly as shown, but indirectly. In other words, in the photocoupler 3, when the control driver 15 is off with current flowing to the light emitting diode 3a, current flows to the phototransistor 3b, and the received digital signal b is logically "0".
becomes. On the other hand, when the control driver 15 is on, no current flows to the phototransistor 3b regardless of the current of the light emitting diode 3a.

Therefore, the second embodiment is different from the one shown in FIG. 1 by controlling the off-period of the control driver 15 to be extremely short by the timing control signal generator 9 as in the one shown in FIG. Get a similar effect.

In addition, as shown in FIG. 5, the original signal generator 8 and
A synchronization signal generator 16 that generates synchronization signals, read clocks, and driver control signals is connected to the digital signal processing section 1.
It may also be configured to be provided outside the analog signal processing section 2. However, for example, the synchronization signal is not supplied to the digital signal processing section 1 through the synchronization signal generator 16 so that the digital signal processing section 1 and the analog signal processing section 2 are not electrically, electrostatically, or electromagnetically linked. is performed via a photocoupler.

In this third embodiment, even if the combination of digital signal processing section 1 and analog signal processing section 2 is multi-channel (for example, a 24ch multi-recorder),
There is no need to provide a synchronization signal generator 16 for each channel, and all channels can be synchronized with one synchronization signal generator.

Also, with this method, multiple devices can be synchronized with one synchronization signal generator.

The transmission side circuit 20 and the reception side circuits 21, 21'
In addition to photocouplers, there are other means of coupling
A photointerrupter, optical fiber, transformer, etc. may also be used.

〔Effect of the invention〕

In this way, the above interface circuit is
Since uncorrelated components (jitter components and waveform distortion parts) can be blocked at the entrance of the analog signal processing section,
The analog signal processing section is not adversely affected by uncorrelated components, and the analog signal processing section has features such as being able to generate a digital signal containing only original code information without uncorrelated components.

[Brief explanation of the drawing]

1 and 2 are block diagrams and signal waveform diagrams of the first embodiment of the circuit of the present invention, respectively. FIG. 3 is a diagram showing the relationship between the transmitted digital signal and code detection, and FIGS. 4 and 5. 6 is a block system diagram of the second and third embodiments of the circuit of the present invention, FIG. 6 is a diagram showing an example of a conventional circuit, FIG. 7 is a waveform diagram of each signal, and FIG. 8 explains problems with the conventional circuit. This is a diagram for 1... Digital signal processing section, 2... Analog signal processing section, 3, 11... Photocoupler, 3a...
Light emitting diode, 3b...phototransistor,
6...Digital signal synchronization control circuit, 7, 10...
... Driver, 8 ... Original signal generator, 9 ... Timing control signal generator, 12, 15 ... Control driver, 13 ... D flip-flop, 14 ... Output terminal, 20 ... Transmission side interface circuit, 2
1, 21'...Reception side interface circuit.

Claims (1)

[Claims] 1 Analog signal processing in which the transmission side interface circuit 20 provided in the digital signal processing section 1 and this digital signal processing section 1 are electrically, electrostatically, and electromagnetically separated. a receiving side interface circuit 21 provided in the transmitting side interface circuit 2, and transmitting the transmitted digital signal from the transmitting side interface circuit 20 through one coupling means 3 selected from optical, sonic and magnetic coupling means. an interface circuit that transmits data to the receiving interface circuit 21 via the receiving interface circuit 21, the receiving interface circuit 21 includes a driver control circuit for removing jitter components and waveform distortion components superimposed on the transmitted digital signal; control that turns on or off at a timing when a signal is supplied and the transmission digital signal does not include the jitter component, and only for a very short time than the duration of one bit of the transmission digital signal; driver 12
and a receiving section 3 that performs code detection only for a very short period of time at the same operating timing as the control driver 12 while current is flowing through the transmitting section 3a in the transmitting side interface circuit 20 of the coupling means 3.
b, an output circuit 13 to which the output signal of the receiving section 3b is supplied as data and a read clock having the same timing as the driver control signal, and outputs a received digital signal; The present invention is characterized in that an original signal is supplied from an oscillator 8 which also serves as a synchronization reference, and a timing signal generator 9 is provided for generating the driver control signal and the read clock without jitter components. 2. In the interface circuit according to claim 1, the timing signal generator is provided outside the digital signal processing section and the analog signal processing section, and the timing signal generator is disposed outside the digital signal processing section and the analog signal processing section. , an interface circuit characterized in that it is electrically, electrostatically and electromagnetically separated.