JPS60260223A - Automatic slice circuit - Google Patents

Abstract

PURPOSE:To follow sufficiently the quick fluctuation of a DC level by passing the output of a slicer inputting a high frequency signal through an LPF capable of switching a cut-off frequency, amplifying the DC fluctuation and feeding back it to the input of the slicer. CONSTITUTION:A high frequency input signal I having a DC level fluctuation is converted into a rectangular wave output O by the slicer 1 comprising a limiter amplifier or the like and its DC level fluctuation component is extracted by the LPF2. In this case, the cut-off frequency of the LPF2 is switched to a higher cut- off frequency by a switching signal S. The extracted DC level fluctuation component is compared with a reference voltage E, the voltage difference is fed to an amplifier 3, fed back negatively, a DC bias is added (4) to the signal I so as to cancel the DC level fluctuation of the signal I. When no DC level fluctuation exists in the signal I, the cut-off frequency of the LPF2 is switched to a lower cut-off frequency and since a voltage difference between its output and the voltage E is fed back negatively in terms of DC, a correct rectangular wave output without jitter is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an automatic slicing circuit that can be used for transmitting, recording, and reproducing digital signals.

Conventional configurations and their problems In recent years, digital audio equipment has become widespread, and slice circuits that convert distorted playback signals into rectangular waves are playing an important role.

A conventional automatic slicing circuit will be described below with reference to the drawings. Figure 1 is a block diagram of a conventional automatic slicing circuit, where 1 is a slicer, 2 is a low-pass filter, 3 is an amplifier, 4 is a summing point, 5 is a reference voltage, and the high frequency input signal processing is +7 mitter. It is converted into a rectangular wave output O by a slicer 1 consisting of an intensifier, etc., and a low-pass filter? Otherwise, the DC level fluctuation component is extracted, and the level difference from the reference voltage E is fed back and added to the high frequency input signal by the amplifier 3.

The operation of the automatic slice circuit configured as described above will be described below. The high frequency input signal was originally a digital signal, but now it is being transmitted.

It is distorted by being recorded and reproduced, and on the reproduction side, this is converted back to the original rectangular wave and subsequent digital processing such as error correction and D/A conversion is performed. For that purpose,
The wave is converted to the original rectangular wave by passing it through the slicer 1 using the center of amplitude of the input signal (this is called the DC level) as a reference.

If the input signal is a signal that does not have a low frequency component, such as an FM or EFM (8-14 modulation method) signal, the low frequency component of the signal converted to a square wave can be extracted using low-pass filter 2. , this extracted signal level should be a direct current half the level of the rectangular wave amplitude.

However, if a dropout or waveform distortion occurs in the input signal, the DC level of the input signal will fluctuate, and if this is converted into a rectangular wave by slicer 1 with a constant threshold voltage, the time width of the rectangular wave will change. If it is different from the original, it will not be played correctly.

Therefore, as shown in Fig. 1, the low frequency component of the rectangular wave output 0 is extracted by the low pass filter 2, and a DC bias is fed back to the input signal so that this becomes equal to a predetermined reference or quasi voltage. An automatic slice circuit was used that automatically followed level fluctuations.

However, in the above configuration, the selection of the cutoff frequency of the low-pass filter is very delicate; if it is too high, the DC bias will fluctuate due to the frequency components of the input signal I itself, and as a result, the rectangular wave There is a problem that jitter occurs in the output 0, and if it is too low, it cannot follow fast DC level fluctuations caused by dropouts, etc., and correct slicing cannot be performed, making it difficult to satisfy both conditions at the same time. was.

OBJECTS OF THE INVENTION An object of the present invention is to provide an automatic slicing circuit that can suppress jitter caused by frequency components of an input signal to a sufficiently low level and can sufficiently quickly follow fast DC level fluctuations caused by dropouts and the like.

Structure of the Invention The automatic slicing circuit of the present invention includes a slicer that converts a high-frequency input signal into a rectangular wave and outputs it, a low-pass filter that extracts a DC level fluctuation component of the rectangular wave, and negative feedback of the output of the low-pass filter. The low-pass filter is configured to include an amplifier for adding it to the high-frequency input signal, and to switch the cutoff frequency of the low-pass filter using a switching signal. The cut-off frequency is raised to enable fast tracking, and when the normal DC level does not fluctuate, the cut-off frequency is lowered to suppress the sick caused by the input signal itself. .

Furthermore, by providing a dropout detection circuit,
This automatically switches the cutoff frequency.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 shows a block diagram of an automatic slicing circuit according to a seventh embodiment of the present invention. In FIG. 2, 1 is a slicer, 2 is a low-pass filter, 3 is an amplifier, 4 is a summing point, and 6 is a reference voltage source (power), and the cutoff frequency of the low-pass filter is switched by a switching signal S.

The operation of the automatic slicing circuit of this embodiment configured as described above will be described below. First, a high frequency input signal signal having a DC level fluctuation is converted into a rectangular wave output O by a slicer 1 comprising a limiter/amplifier, etc., and a low pass filter 2 extracts its DC level fluctuation component. At this time, low pass filter 2
The cutoff frequency of is switched to the higher side. The extracted DC level fluctuation component is compared with the reference voltage E, and the difference voltage is negatively fed back by the amplifier 3, and a DC bias is added to the input signal. works to cancel out DC level fluctuations,
Correct square wave output 0 is obtained.

Next, when a high-frequency input signal signal having no DC level fluctuation is converted into a rectangular wave output O by the slicer 1, the DC level component extracted by the low-pass filter whose cut-off frequency is switched to a lower one is the reference voltage E. compared to
The differential voltage is negatively fed back DC by the amplifier 3 and added to the input signal as a DC bias, so the bias voltage does not fluctuate due to the frequency components of the input signal itself, resulting in a correct jitter-free signal. A square wave output of 0 is obtained. The switching signal S may be generated artificially depending on the state of the input signal, or may be generated automatically as described later.

As described above, according to this embodiment, by switching the cutoff frequency of the low-pass filter, if there is a DC level fluctuation in the input signal, slicing is performed correctly by sufficiently fast tracking, and if there is no DC level fluctuation in the input signal, slicing is performed correctly. achieves a jitter-free square wave output by slowing down the response sufficiently.

The cutoff frequency of the low-pass filter is shown in Figure 3 (,
FIG. 4 shows an example of the configuration of a low-pass filter for switching between fl and fz. 21 is a filter, 1.22 is a filter, 23 and 24 are changeover switches, and the changeover signal S
Accordingly, either filter 1 or 2 is selected.

By setting the cutoff frequencies of filters 1 and 2 to f1 (f2), it is possible to realize a low-pass filter 2 that satisfies the above characteristics.

Note that the number of filters is not limited to two,
In general, it is possible to achieve zero cutoff characteristics in 4t''·° in 26 configurations by switching n filters using a changeover switch, and it is possible to select the optimum cutoff frequency for each filter.

Next, another example of the configuration of the low-pass filter is shown in FIG. R1 and R2 are resistors, C1 and C2 are capacitors, 23.
24 is a changeover switch, which changes resistance by a changeover signal S;
This configuration changes the cutoff frequency by switching the capacitor.

Four types of cutoff frequencies can be selected by combining the changeover switches 23 and 24.

Note that the number of resistors and capacitors is not limited to two each; generally, if n resistors and m capacitors are provided, nxm types of cutoff frequencies can be selected.

Furthermore, in the above embodiment, the configuration of the low-pass filter is a first-order low-pass filter with a resistor and a capacitor, but it is also possible to use a second-order low-pass filter in which several of these are connected in series. Needless to say, any circuit is suitable as long as it can be implemented.

Next, it is important in what cases the cutoff characteristics of the low-pass filter are switched, and other embodiments of the present invention including a switching signal generator will be described with reference to the drawings.

FIG. 6 shows a block diagram of an automatic slicing circuit according to another embodiment of the present invention. In FIG. 6, 6 is a dropout detector, 61 is an envelope detector, 62 is a second reference voltage source (VT), 63 is a voltage comparator,
The envelope level of the high frequency input signal is detected by an envelope detector 61, and the level difference with the second reference voltage is compared by a voltage comparator 63 to output a switching signal S.

The operation of the automatic slicing circuit of this embodiment configured as described above will be explained below. As shown in FIG. 7, when the amplitude of the high frequency input signal is sufficiently large, the output level of the envelope detector 61 will be It is higher than the second reference voltage 7, the switching signal S is not output from the comparator 63, the cutoff frequency of the low-pass filter 2 remains low, and the jitter of the rectangular wave output 0 is sufficiently suppressed.

Next, when the amplitude of the input signal I fluctuates due to dropout or the like, the output level of the envelope detector drops by p below the second reference voltage vT, the switching signal S is output from the comparator 63, and the low-pass filter The cutoff frequency of is switched to the higher side, and slicing is performed so as to follow the DC level fluctuation of the input signal generator, so that a correct rectangular wave output of 0 is obtained.

As described above, according to this embodiment, by detecting fluctuations in the amplitude level of the input signal using the dropout detector, it is possible to automatically switch the cutoff frequency of the low-pass filter and always perform optimal slicing. are doing.

Next, a third embodiment of the present invention will be described with reference to the drawings.

FIG. 8 shows a block diagram of an automatic slice circuit according to a third embodiment of the present invention. In Figure 8 1, 7
is a low-frequency component detector, 71 is a second low-pass filter, and 72 is an amplitude detector; \ The low-frequency fluctuation component of the input signal is detected by the second low-pass filter 64 and amplitude detector 66. This configuration outputs a switching signal S.

The operation of the automatic slice circuit of this embodiment configured as described above will be described below. When the DC level of the high-frequency input signal varies, the amplitude of the low frequency component that is the output of the second low-pass filter 71 increases, so this is detected by the amplitude detector 72, and the switching signal Sf is generated. Then, the cutoff frequency of the low-pass filter 2 is switched to a higher side, and slicing is performed so as to follow the DC level fluctuation of the input signal i, so that a correct rectangular wave output of 0 is obtained.

If there is no low frequency component in the input signal, that is, if there is no DC level fluctuation, the switching signal S will not be output, and the cutoff frequency of the low-pass filter 2 will be low! ,”!.

The zero-width detector 72 which can obtain a jitter-free rectangular wave output can be realized using an envelope detector, a reference voltage source, and a voltage comparator as shown in FIG.

As described above, according to this embodiment, by detecting the low frequency components of the input signal, the cutoff frequency of the low-pass filter is automatically switched, thereby realizing optimal slicing at all times. .

Note that in the above embodiment, a limiter amplifier was used as a slicer that converts the input signal into a rectangular wave, but the slicer is not limited to a limiter amplifier, and has the function of returning a distorted input waveform to a rectangular wave. Anything is fine. For example, a voltage comparator can also be used. In this case, the output of the amplifier 3 may be applied not to the adder 4 but to one input terminal of the voltage comparator.

Effects of the Invention As is clear from the above description, the present invention provides a slicer that converts a high frequency input signal into a rectangular wave and outputs it, and a DC level of the rectangular wave. a low-pass filter for extracting a fluctuation component; As a result, an excellent effect can be obtained in that the optimum response characteristic can be selected according to the DC level fluctuation of the input signal.As a result, if the present invention is used in digital audio equipment, it will always be stable. This has the effect of enabling high-quality music playback.

Furthermore, by configuring the low-pass filter switching signal to be output by a dropout detector that detects a decrease in the amplitude of the input signal, even if the DC level of the input signal fluctuates due to dropouts, etc., the switching signal is automatically output. The effect is that optimal response characteristics can be obtained.

Furthermore, by configuring the low-pass filter switching signal to be output by a low-frequency component detector that detects DC level fluctuations in the input signal, optimal response characteristics can be automatically obtained for input signal DC level fluctuations. This effect can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional automatic slicing circuit, FIG. 2 is a block diagram of an automatic slicing circuit according to an embodiment of the present invention, FIG. 3 is an explanatory diagram of the operation of the automatic slicing circuit, and FIGS. The figure is a block diagram showing an example of a low-pass filter.
FIG. 6 is a block diagram of an automatic slice circuit according to another embodiment of the present invention, FIG. 7 is an explanatory diagram of the operation of the embodiment of FIG. 6, and FIG. 8 is an automatic slice circuit according to still another embodiment of the present invention. FIG. 2 is a block diagram of a slice circuit. 1... Slicer, 2... Low pass filter, 3... Amplifier, 21.22...
Filter, 6...Dropout detector, 7.
...Low frequency component detector 0 Name of agent: Patent attorney Toshio Nakao and 1 other person m1
Figure 2 Figure 3 Figure 4 Figure 7

Claims (4)

[Claims] (1) A slicer that converts a high-frequency input signal into a rectangular wave and outputs it, a low-pass filter that extracts the DC level fluctuation component of the rectangular wave, and a negative feedback of the output of the low-pass filter that is added to the high-frequency input signal. An automatic slice circuit comprising an amplifier and configured to switch the cutoff frequency of the low-pass filter using a switching signal. (2) The low-pass filter is composed of first to nth filter groups, and one filter is selected and used from the n filter groups by a switching signal. The automatic slicing circuit described in (1). (3) The automatic slicing circuit according to claim (1), wherein the switching signal is output by a dropout detector that detects a decrease in the amplitude of the high-frequency input signal. (4) The automatic slicing circuit according to claim 1, wherein the switching signal is outputted by a low frequency component detector that detects a first level fluctuation component of the high frequency input signal.