JPH02270413A - Signal reproducing circuit - Google Patents

Abstract

PURPOSE:To detect a non signal without being affected by noise by providing a non-signal detection circuit detecting the presence or absence of a pulse signal being an output of a data detection circuit and using a signal of digital system via a differentiation circuit so as to detect the non-signal. CONSTITUTION:High frequency noise is eliminated from a signal S1 reproduced from an optical disk by a low pass filter 1 and the result is inputted to a 1st stage amplifier 2. The signal is amplified therein and inputted to an attenuator circuit 3, where the signal is attenuated and the result is inputted to an automatic gain control(AGC) amplifier circuit 4. A signal S2 amplified by the AGC amplifier circuit 4 is inputted to a differentiation circuit 5. The differentiated output S3 is inputted to a recording data detection circuit 7. Its output S4 is given to a non-signal detection circuit 22. The high frequency noise is eliminated in the low pass filter 1, and the low frequency noise is eliminated by the differentiation circuit 5 and non-signal is detected, then mis-detection hardly takes place.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a signal reproducing circuit for reproducing signals recorded on a recording medium such as a magneto-optical disk.

[Prior art] Figure 5 is a patent application filed in 1982-2202 filed by the applicant of the present application.
The structure of this type of signal reproducing circuit described in No. 97 is shown,
FIG. 6 shows signal waveforms at each part. A signal SI detected from a recording medium by an optical head (not shown) has high-band noise removed by a low-pass filter l, is amplified by a first-stage amplifier 2, is further attenuated by an attenuator circuit 3, and is further attenuated by an AGC (automatic gain control) amplifier circuit. 4
is amplified by

The output S2 of the AGC amplifier circuit 4 is differentiated by a differentiating circuit 5, and the differentiated output S is input to a header detection circuit 6 and a recorded data detection circuit 7. The rain detection circuits 6 and 7 detect information points from the input signal, the header detection circuit 6 detects data in the header section recording addresses for specifying tracks and sectors, and the recorded data detection circuit 7 detects information points from the input signal. The data in the recorded data section in which target data and the like are recorded is detected. The output S of the recording data detection circuit 7 is applied to a pulse generation circuit 8 which removes spurious pulses due to noise contained in the output and widens the pulse width to produce an output S.

The automatic gain control amplifier circuit 4 includes an amplifier section 20 related to signal amplification.
, a control circuit 23 for controlling the gain, and a VFO signal for detecting the VFO signal recorded on the optical disc.
It consists of an FO signal detection circuit 21 and a no-signal detection circuit 22 that detects the absence of a recording signal. Amplifier section 20
Output is VFO signal detection circuit 2I and no signal detection circuit 22
The former outputs a binary signal "l+82" depending on the presence or absence of the VFO signal, and the latter outputs a binary signal "l+82" depending on the presence or absence of some signal, which is manually input to the control circuit 23. AGC reset signal furnace 3
2-bit signals C, , C, determined according to the combination of these three binary signals, are supplied to the amplifier section 2o. These signals C1 and Cz sample the mode of the amplifier section 2o,
It switches between three modes: hold and reset.

In this signal reproducing circuit, the AGC amplifier circuit 4 is used to control the level of the reproduced signal S obtained from the header section.
This is because the level of the reproduced signal S+ obtained from the data section is different, and the signal level of the subsequent stage is made constant.

In addition, the hold mode is used because, for example, if the gain increases significantly during playback of an unrecorded part of the data section, the amplification output will become excessive when the next playback signal is input. This causes the gain to be held.

Further, an unrecorded gap section is provided between the header section and the data section.

If this is detected, the gain is initialized to a predetermined value as a reset mode.

[Problem to be solved by the invention]

However, in such a conventional configuration, the AG is affected by noise.
The mode of the C amplifier circuit 4 sometimes fluctuated. That is, in the no-signal detection circuit 22, the output S2 of the amplifier section 20 is set to the threshold T,
(shown by the broken line at S), and from the time when this becomes above to tdO, the signal a! which becomes "H level" is output,
When this goes to "L" level, it is assumed that there is no signal, and the control circuit 23 should set the hold mode to the signal C+.
, Ct are output. Although this delay time td is provided to provide noise resistance, it is not possible to prevent a2 from changing from a low level to a high level due to noise.

The present invention has been made in order to solve such problems, and it is a signal regeneration method that enables detection of no signal without being affected by noise by detecting no signal using a digital signal that has passed through a differentiating circuit. The purpose is to provide circuits.

[Means to solve the problem]

In the present invention, no signal is detected by a signal that has passed through a low-pass filter, an automatic gain control circuit, a differentiation circuit, and a data detection circuit.

[Effect]

High-frequency noise has been removed from the signal that has passed through the low-pass filter, and low-frequency noise has been removed from the signal that has passed through the differential circuit. Therefore, no signal is detected for components other than the signal to be originally detected, that is, noise is removed, so that false detection is less likely to occur.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on drawings showing embodiments thereof. FIG. 1 is a block diagram showing the circuit of the present invention. A signal S reproduced from an optical disk has high-frequency noise removed by a low-pass filter 1 and is input to a first-stage amplifier 2, where it is amplified and sent to an attenuator circuit 3. The signal is input, attenuated here, and input to the AGC amplifier circuit 4. The signal S2 amplified by the AGC amplifier circuit 4 is input to the differentiating circuit 5, and the output S differentiated here is input to the header detection circuit 6 and the recorded data detection circuit 7. The data detection circuit 7 output S4 is output to the pulse generation circuit 8, from which a reproduction pulse signal S is output.

Therefore, in the embodiment, the output S of the recorded data detection circuit 7
4 is given to the no-signal detection circuit 22. The GC amplifier circuit 4 includes an amplifier section 20 that inputs and amplifies the output of the attenuator circuit 3 and inputs it to the differentiating circuit 5, a no-signal detection circuit 22, a VFO signal detection circuit 21, and the gain of the amplifier section 20. The control circuit 23 includes a VFO signal detection circuit 21 output a2.
, the output a2 of the no-signal detection circuit 22, and the AGC reset signal signal generator 3, and based on these, 2-bit signals C, , C are sent from the control circuit 23 to the amplifier section 20 to control the mode.

is giving.

Table 1 shows al t at l a, + CI +
It shows the relationship between c2 and control mode.

Table 1 *mark may indicate either H or L level.

As shown in this table, when the no-signal detection circuit 22 detects no signal, it outputs a! becomes "L" level, and both CI and Ct are outputted from the control circuit 23 at "H" level, setting the control mode of the amplifier section 20 to the hold mode.

FIG. 2 shows signal waveforms at various parts of the circuit shown in FIG.

An input signal S to this circuit is amplified by an AGC amplifier circuit 4 to become an output S2, and differentiated by a differentiator circuit 5 to output a signal S. The recorded data detection circuit 7 binarizes the input signal using a threshold value T shown by a broken line superimposed on S3 and outputs a pulse signal S4. The pulse generating circuit 8 expands the pulse width to S,
Output. Also, the output S4 of the recorded data detection section 7 is input to the no-signal detection circuit 5. This no-signal detection circuit 5 is composed of, for example, a retriggerable multivibrator, and maintains the "H" level when pulses are continuously input, and when there is no pulse that continues for a time tdO after the pulse rises. It outputs a signal a2 which changes to "L" level.

FIG. 3 is a graph showing the frequency components of the output S of the differentiating circuit 5. Since the low-pass filter 1 removes high frequency components, its output has the characteristics shown by the dashed line. On the other hand, since the differentiating circuit 5 greatly attenuates signals in the low frequency range, its single output has the characteristics shown by the broken line. Therefore, the composite characteristic of the output S3 of the differentiating circuit 5 becomes a mountain shape shown by a solid line, in which frequencies outside the frequency band of the signal to be detected (circuit constants are determined so as to be at the top of the mountain) are attenuated.

In other words, the possibility of erroneously detecting no signal due to noise on the low frequency side is significantly lower than in the conventional case.

FIG. 4 shows another embodiment of the present invention, in which no-signal detection is performed by the output of a pulse generating circuit 8.

That is, the output Ss of the pulse generation circuit 8 is input to the no-signal detection circuit 22, and the output a2 thereof is applied to the control circuit 23. Since the other parts are the same as those in the embodiment shown in FIG. 1, the same reference numerals are given and the explanation will be omitted. Recorded data detection circuit 7 output S, pulse generation circuit 8 output S,
Since the presence or absence of is substantially the same, the embodiment shown in FIG.
It has the same effect as the embodiment shown in the figure.

〔Effect of the invention〕

According to the device of the present invention as described above, it is possible to detect no signals with strong noise resistance, and it is possible to realize a signal reproducing circuit equipped with an automatic gain control amplifier circuit that can set an appropriate gain. The device of the present invention also has the advantage that it does not require any special circuitry other than the circuitry conventionally required for signal reproduction.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of the signal reproducing circuit of the present invention, FIG. 2 is a signal waveform diagram for explaining its operation, FIG. 3 is a signal frequency characteristic diagram, and FIG. FIG. 5 is a block diagram showing the embodiment, FIG. 5 is a block diagram of a conventional circuit, and FIG. 6 is a signal waveform diagram for explaining its operation. 1...Low pass filter 4...Automatic gain control amplifier circuit 5...Differentiating circuit 7...Recorded data detection circuit 22...No signal detection circuit Note that the same symbols in the figures indicate the same or equivalent parts. shows. Agent Masuo Oiwa Sl Yan 2 Condolences 3 Diagram No. 6 Procedural amendment (voluntary) Signal regeneration circuit 3, relationship to the case of the person making the amendment Patent applicant address 2-2-3 Marunouchi, Chiyoda-ku, Tokyo Name (601) Mitsubishi Electric Corporation Representative Moriya Shiki 4, Agent Address 2-2-3-5 Marunouchi, Chiyoda-ku, Tokyo
, Column 6 of "Detailed Description of the Invention" of the specification to be amended, contents of the amendment (1) In the 19th line of page 2 of the specification, the phrase "increase the width" was changed to "increase the width to a predetermined value.""I did it," he corrected. (2) In the 4th line of page 8 of the specification, "Ss J with expanded pulse width" has been replaced with "Output Ss with pulse width set to a predetermined value."
Correct it with J. that's all

Claims (1)

[Claims] (1) Data that inputs the signal reproduced from the recording medium to an automatic gain control amplifier circuit via a low-pass filter, inputs its output to a differentiator circuit, binarizes the output of the differentiator circuit with a predetermined threshold value, and outputs a pulse signal. The signal reproducing circuit including a detection circuit includes a no-signal detection circuit that detects the presence or absence of a pulse signal output from the data detection circuit, and when the no-signal detection circuit detects that the pulse signal does not exist, the automatic gain A signal reproducing circuit characterized in that the gain of a control amplifier circuit is fixed.