JPH0150994B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a data signal detection circuit, and particularly to a data signal detection circuit for reliably detecting "1" and "0" of a data signal supplied as a serial digital value such as in a digital audio disc player. The present invention relates to a data signal detection circuit.

A digital audio disk is a device in which audio signals and synchronization signals are digitized and optically recorded at high density on the surface of the disk at a constant linear velocity.The signal format recorded on the disk is, for example, as shown in Figure 1. It is stipulated in That is, in this method, one frame is made up of a fixed number of bits (for example, 588 bits), and these frames are consecutively recorded on the same disk at a constant linear velocity. The signal format of each frame is divided into a synchronization section A and an information section B, and the synchronization section A is positioned at the beginning of each frame. As shown in Fig. 1, the synchronization part A is composed of 22 bits, and the first 11 bits are "0" continuously.
In this case, the following 11 bits are set as "1" continuously, and when the first 11 bits are continuously "1", the following 11 bits are set as "0" continuously. In this case, the first 11 bits are set to be the opposite of the last bit of the previous frame, and in this way, a predetermined unit bit (11 bits) is set to be "0" or "1". The format with a series of "" is limited to only this synchronization part A in one frame. That is, the information section B is configured so that a format in which 11 bits of "0" or "1" are consecutive does not occur under any circumstances. In addition, the information part B is a signal in which "1" or "0" signals are always continuous over 3 bits or more in order to prevent conversion to direct current when there is no signal. In other words, the information part B is represented as a continuous signal only over the range of 2<B<11 bits.

With a digital audio disk constructed in this manner, a high-fidelity audio signal can be easily obtained by optically reading and demodulating digital information on the disk at a constant linear velocity.

The most important thing in performing fidelity reproduction is to accurately distinguish between "1" and "0" of the data signal reproduced from the information recorded on the surface of the disk.

In this case, conventional data signal detection circuits detect "1" and "0" by comparing the data signal supplied from the optical pickup that reproduces the recorded information on the disc with the reference value _VR . It is configured to send out the discrimination signal as detection data.

However, when the reference value is fixed to a constant value in this way, there is a problem that errors occur in the detected data because the reference level of the disk fluctuates due to variations in the manufacturing process of the disk. There is. In other words, digital audio disks use the narrowband PCM method, and the output level of the pickup changes greatly depending on the width of the recorded pulse. The oscilloscope waveforms are as shown in waveforms a to h in FIG. 2, for example.
The information bit in this waveform is a diamond-shaped portion shown by diagonal lines centered at the reference level Vr, and the cross point of the reference value Vr in this diamond-shaped portion is the boundary of the bit. From the manufacturing point of view, the disc has a reference level Vr of ±20% above and below.
The standard allows for variations over a period of time. Therefore, information that exists only in a range of about 1/5 of the total around the reference level Vr is ±20
% range, and the reference value
If an attempt is made to perform detection with V _R fixed, there is a problem in that signal detection may not be possible due to variations in disk manufacturing.

Therefore, an object of the present invention is to provide a data signal detection circuit that can accurately detect data signals of "1" and "0" from a reproduced signal supplied from a pickup.

In order to achieve such an object, the data signal detection circuit according to the present invention has a reference value V _R of a comparator that compares the reproduced signal and extracts the data signal in response to fluctuations in the reference level Vr of the disc reproduced signal.
It changes the Hereinafter, a data signal detection circuit according to the present invention will be explained in detail using the drawings.

FIG. 3 is a circuit diagram showing one embodiment of a data signal detection circuit according to the present invention. In the figure, 1 is a comparator that compares the disc playback signal HF supplied to input terminal 2 with a reference value V _R and outputs a data signal DS, and 3 is a positive detection circuit that receives the output of comparator 1 as input. , a coupling capacitor 4, a diode 5 for positive detection, a resistor 6,
7 and a capacitor 8. Reference numeral 9 denotes a negative detection circuit which receives the output of the comparator 1 as an input, and, like the positive detection circuit 3, includes a coupling capacitor 4' and a negative detection diode 5' connected in the opposite direction to the detection diode 5. It is composed of resistors 6, 7 and a capacitor 8'. Reference numeral 10 denotes an adding circuit that adds the output of the positive polarity detection circuit 3 and the output of the negative polarity detection circuit 9 to each other and outputs the result, and is constituted by resistors 11 and 12 for addition and a resistor 13 for bias. 1
A loop filter 4 extracts only the DC component included in the addition output supplied from the addition circuit 10, and is composed of capacitors 15 and 16 and a resistor 17, and has a sufficiently large time constant. 18 is an operational amplifier as a servo amplifier that compares the output of the loop filter 14 with the zero level and outputs the difference; 19 is a voltage limiter circuit that connects the output terminal of the operational amplifier 18 and the comparator 1;
By limiting the reference voltage V _R supplied to the comparator 1 to a certain range, the reference voltage at the initial operation can be adjusted between the reference voltage input terminal of the
This is provided to prevent excessive fluctuations in _VR and ensure reliable judgment. This voltage limiter circuit 19 is constituted by a generally known circuit including resistors 20 and 21 and a capacitor 22.

In the data signal discriminating circuit configured as described above, when the reproduced signal HF of the digital audio disk is supplied to the input terminal 2 from the optical pickup (not shown), the comparator 1 detects the reproduced signal based on the reference voltage _VR . HF is determined and a data signal DS of "H" and "L" is generated. The data signal DS generated from this comparator 1 is transmitted to a positive polarity detection circuit 3 and a negative polarity detection circuit 9.
By being detected by the diodes 5 and 5' provided in the diodes 5 and 5', the positive polarity and the negative polarity are respectively extracted. The outputs of the positive detection circuit 3 and the negative detection circuit 9 are connected to the resistor 1.
1 and 12, they are added to each other in an adder circuit 10, and are biased to a predetermined level by a resistor 13 and output.

In this case, the format of the recording signal for the digital audio disk is such that one symbol consists of 17 bits as described in FIG. 1, 14 bits of the 17 bits are information bits, and the remaining 3 bits are redundant bits. This redundant portion satisfies the condition that the same signal continues only within the range of 3 bits or more and 11 bits or less, and furthermore, the ratio of "H" and "L" signals from several symbols before becomes the smallest. It is set so that the DC component is reduced. Therefore, when the reference value V _R of the comparator 1 matches the reference value Vr of the reproduced signal HF shown in FIG. The bias level is fixed at a bias level of 13. And comparator 1
If the reference value V _R of the playback signal HF deviates in the positive direction from the reference value Vr of the reproduced signal HF, the data signal DS
The pulse width for the "L" portion is widened, and the output of the loop filter 14 is lowered from the bias level by a level corresponding to the amount of deviation. Also,
If the reference value V _R of comparator 1 deviates in the negative direction with respect to the reference value Vr of the reproduced signal HF,
The pulse width for the "H" portion of the data signal DS output from the comparator 1 is widened, and the output of the loop filter 14 rises from the bias level by a level corresponding to the amount of deviation.

The output signal of the loop filter 14 corresponding to the difference between the reference value Vr of the reproduced input signal HF detected in this way and the reference value V _R of the comparator 1 is detected by the operational amplifier 18 as the difference from the zero level. output. The output signal of the operational amplifier 18 is fed back to the comparator 1 as a reference value V _R via the voltage limiter circuit 19. Therefore, the reference value V _R of the comparator 1 is changed in response to fluctuations in the input reproduced signal, and accordingly, accurate data signals can always be extracted.

Note that the voltage limiter circuit 19 is provided to prevent malfunctions caused by large fluctuations in the output of the operational amplifier 18 during initial operation, and this problem can be solved with other configurations. If so, it's not necessarily necessary.

As explained above, the data signal detection circuit according to the present invention focuses on the fact that the DC component of the input reproduced signal is set to be small, and adds the positive and negative detection signals of the detected data signal. By extracting the output through a loop filter with a large time constant, the difference between the reference value of the reproduced signal and the reference value of the comparator which extracts the data signal from the reproduced signal is detected, and the reference value of the comparator is adjusted according to this difference. It changes the Therefore, since the reference level of the comparator is varied in response to variations in the reference level of the input reproduced signal, there is an excellent effect that the data signal can always be detected reliably.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the signal format of digital information recorded on a digital audio disk, FIG. 2 is a waveform diagram of a reproduced signal of the digital audio disk, and FIG. 3 is an example of a data signal detection circuit according to the present invention. FIG. 2 is a circuit diagram showing an example. DESCRIPTION OF SYMBOLS 1... Comparator, 3... Positive polarity detection circuit, 9... Negative polarity detection circuit, 10... Addition circuit, 14... Loop filter, 18... Operational amplifier, 19... Voltage limiter circuit.

Claims (1)

[Claims] 1 Compare the reproduction signal supplied from the pickup that reproduces information recorded in time division in a signal format determined to reduce the DC component with a reference value, and determine the "H" and "L" data signals. a comparator to extract, a positive and negative polarity detection circuit that inputs the output signal of this comparator, an addition circuit that adds the outputs of the positive and negative polarity detection circuits to each other, and a loop filter that averages the output signal of this addition circuit; An operation that changes the reference value of the comparator in conjunction with fluctuations in the reference level of the reproduced signal by performing negative feedback control on the reference value of the comparator in accordance with the difference between the output of the loop filter and the reference value. A data signal detection circuit comprising an amplifier.