JPH11195942A - Automatic gain controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automatic gain controller from which an output signal controlled to an optimum level is obtained even when an offset is produced in an input signal. SOLUTION: The automatic gain controller 10 is provided with a gain control amplifier 1 and a feedback circuit consisting of a full wave rectifier 2 applying full wave rectification to an output signal of the gain control amplifier 1, an amplitude error detector 3 that compares the output signal of the full wave rectifier 2 with a prescribed amplitude reference and that outputs the comparison result as an amplitude error signal, and of a control diagonal generating circuit 4 that generates a control signal to the gain control amplifier 1 based on the output signal from the amplitude error detector 3 and that provides an output of it to the gain control amplifier 1. The gain controller 10 is also provided with an offset detection circuit 5 that an absolute value of the offset from the output signal of the gain control amplifier 1, and with an arithmetic circuit 8 that subtracts the output signal of the offset detection circuit from any output signal of the feedback circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an automatic gain control device, and more particularly to an automatic gain control device capable of obtaining an output that is not affected by an offset of an input signal.

[0002]

2. Description of the Related Art In recent years, PRML (Partial Response Maxim) has been developed as an effective technique to cope with the progress of higher density recording devices and higher transfer rates of communication means.
Techniques such as um likelyhood detection and multi-level detection are widely used. These techniques are premised on detecting a signal based on a certain amplitude level. Therefore, the amplitude value of the signal to be detected is specified, and if the amplitude value fluctuates, the signal is erroneously detected. It causes detection. In addition, these techniques use a sampled signal to detect a signal.
Clock recovery by a cked Loop (phase locked loop) is required.

[0003]

Incidentally, when a signal has a non-signal portion or a defect, or a signal having a different modulation factor is mixed, an offset due to a change in the DC level of the signal may occur. Further, an offset may also be caused by a sag generated at the beginning of a signal due to an intermittent signal, at a boundary between signals having different modulation degrees and amplitudes, and the like. A signal with such an offset is applied to an automatic gain control (AGC).
Causes an error in the output amplitude of the PRM.
There is a concern that erroneous detection in L detection, multi-level detection, etc., and adverse effects on the clock reproduction due to the PLL may occur.

FIG. 8 shows a configuration of a general automatic gain control circuit (hereinafter, referred to as an AGC circuit) used in an optical disk reproducing apparatus or the like. The AGC circuit 100 has a gain control amplifier (hereinafter referred to as GCA) 1.
01 and a full-wave rectifier 1 that performs full-wave rectification on an input signal
02, and an amplitude error detector 103 that compares the input signal with a predetermined amplitude reference value and outputs the comparison result as an amplitude error signal; and a control signal for the GCA 101 based on the output signal from the amplitude error detector 103. And a loop filter 104 that generates AGC circuit 1
At 00, the full-wave rectifier 102 and the amplitude error detector 1
03 and the loop filter 104, the GCA 101
Is formed. Hereafter, this AGC
The case where the circuit 100 controls the gain of the reproduction signal of the optical disk will be described.

For example, when a normal reproduction signal without offset shown in FIG. 9A is input to the GCA 101,
This reproduced signal is subjected to full-wave rectification by the full-wave rectifier 102, and has a waveform in which the peak values of the positive and negative amplitudes are equal to each other as shown in FIG. 9B. Then, the full-wave rectified reproduction signal is compared with an amplitude reference value in an amplitude error detector 103, and based on the comparison result, FIG.
An amplitude error signal as shown in FIG. Further, the amplitude error signal is subjected to a predetermined filtering process in the loop filter 104, so that a GCA control signal as shown in FIG. 9D is fed back to the GCA 101. As a result, the AGC circuit 100
By controlling the output of the GCA by the A control signal, a signal having an optimum amplitude level set by the amplitude reference value is output as shown in FIG.

On the other hand, in the AGC circuit 100, FIG.
A reproduced signal having an offset as shown in FIG.
When the reproduced signal is input to A101, the reproduced signal is full-wave rectified by the full-wave rectifier 102 to have a waveform as shown in FIG. Here, it can be seen that in the output waveform from the full-wave rectifier 102, the peak values of the positive and negative amplitudes are not equal. The full-wave rectified reproduction signal is compared with an amplitude reference value in an amplitude error detector 103, and based on the comparison result, becomes an amplitude error signal as shown in FIG. This amplitude error signal is a signal determined to be larger than the original amplitude by comparison with the amplitude reference value.

Further, the amplitude error signal is subjected to a predetermined filtering process in a loop filter 104, so that a GCA signal as shown in FIG.
The control signal is fed back to the GCA 101. As a result, in the AGC circuit 100, the output of the GCA is controlled by such a GCA control signal, so that the output signal from the GCA 101 is lower than the optimum level having no offset as shown in FIG. There was a problem that the amplitude was reduced.

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above circumstances, and is intended to obtain an output signal whose amplitude value is controlled to an optimum level even when a reproduced signal with an offset is input. It is an object of the present invention to provide an automatic gain control device capable of performing the following.

[0009]

In order to solve the above-mentioned problems, an automatic gain control apparatus according to the present invention has a gain control amplifier, a full-wave rectifier for full-wave rectifying an output signal of the gain control amplifier, and a full-wave rectifier. An amplitude error detector that compares the output signal with a predetermined amplitude reference value and outputs the comparison result as an amplitude error signal, and a control signal for a gain control amplifier is generated based on the output signal from the amplitude error detector. A feedback signal comprising a control signal generation circuit for outputting to the gain control amplifier, an offset detection circuit for detecting the absolute value of the offset from the output signal of the gain control amplifier, and the offset detection circuit from any output signal of the feedback circuit. And an arithmetic circuit for subtracting the output signal of

In the automatic gain control device, an output signal from a gain control amplifier is supplied to a feedback circuit and an offset detection circuit, and an output signal of the offset detection circuit is subtracted from any output signal of the feedback circuit by an arithmetic circuit. Is done.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an apparatus to which the present invention is applied will be described in detail with reference to the drawings. The automatic gain control device 10 shown in FIG. 1 is suitably used for controlling the gain of a reproduction signal of an optical disk in, for example, an optical disk reproduction device, and includes a gain control amplifier (Gain Control A).
mp, hereinafter referred to as GCA. 1) a full-wave rectifier 2 for performing full-wave rectification of an input signal, an amplitude error detector 3 for comparing an input signal with a predetermined amplitude reference value, and outputting a comparison result as an amplitude error signal; Filter that generates a control signal for the GCA1 and outputs it to the GCA1
Filter, hereinafter referred to as LF. 4), an offset detector 6 for detecting a DC component at the time of offset from the output signal of the GCA 1, an absolute value circuit 7 for converting the amplitude of the output signal from the offset detector 6 into an absolute value, and an arithmetic circuit 8. Have. The output side of the automatic gain control device 10 has a PRML (Partial Response Maximum Likely
ood) and a detector (not shown) for multi-level detection or the like are connected.

In the automatic gain controller 10, the GCA is controlled by the full-wave rectifier 2, the amplitude error detector 3, and the LF4.
1 is configured as a feedback circuit. As shown in FIG. 1, in the automatic gain control device 10, the offset detector 6 and the absolute value circuit 7 constitute the offset detection circuit 5.

Here, for example, as shown in FIG. 2, the offset detector 6 has a maximum value (peak value) of the voltage of the input signal.
, A bottom value detector 12 for detecting the minimum value (bottom value) of the voltage of the input signal, and a detection of the input signal from the output signals of the peak value detector 11 and the bottom value detector 12. And a calculator 13 for calculating the center value of the voltage.

The peak value detector 11 comprises, for example, a peak hold circuit, and detects the peak value of the envelope of the input signal. The bottom value detector 12 includes, for example, a bottom hold circuit, and detects the bottom value of the envelope of the input signal.

The arithmetic unit 13 calculates the center value of the voltage of the input signal by adding the output signals of the peak value detector 11 and the bottom value detector 12, and uses the added signal as an offset signal as an absolute value circuit. 7 is output.

Thus, in the offset detector 6, when the reproduced signal of the optical disk in which the offset has occurred is input, for example, with a waveform as shown in FIG. As shown in FIG. 3B, the peak value of the envelope of the reproduction signal is detected, while the bottom value detector 12 detects the bottom value of the envelope of the reproduction signal as shown in FIG. 3C. And
These signals detected by the peak value detector 11 and the bottom value detector 12 are further input to an arithmetic unit 13 and added, as shown in FIG. The waveform indicating the center value between them is output from the computing unit 13 as an offset signal.

The offset detector 6 may be constituted by a low-pass filter, and the input signal may be passed through the low-pass filter to extract a low-frequency component, thereby detecting a DC component at the time of offset as an offset signal.

In the automatic gain control device 10, the output signal from the GCA 1 is input to both the full-wave rectifier 2 and the offset detection circuit 5. Further, in the automatic gain control device 10, the operation circuit 8 performs an operation based on the output signal of the amplitude error detector 3 and the output signal of the offset detection circuit 5 in the feedback circuit, and outputs an output signal based on the operation. It is configured to output to LF4. Specifically, the operation circuit 8 performs an operation of subtracting the output signal of the absolute value circuit 7 from the output signal of the amplitude error detector 3.

Hereinafter, a case where the automatic gain control device 10 performs gain control on a reproduction signal of an optical disk will be described.

For example, when a normal reproduced signal having no offset shown in FIG. 4A is input to the GCA 1, the reproduced signal is full-wave rectified by the full-wave rectifier 2 and FIG.
As shown in the figure, the waveforms have the same peak values of the amplitude on the plus side and the minus side. The full-wave rectified reproduction signal is compared with an amplitude reference value by the amplitude error detector 3, and based on the comparison result, becomes a pulse-like amplitude error signal as shown in FIG. .

On the other hand, the offset value (in this case, zero) of the reproduced signal is detected by the offset detector 6 (see FIG. 4D), and the absolute value circuit 7 converts the offset value into an absolute value. (See FIG. 4E). And
In the automatic gain control device 10, the arithmetic circuit 8 performs an arithmetic operation of subtracting the output signal of the absolute value circuit 7 from the amplitude error signal which is the output signal of the amplitude error detector 3, thereby obtaining the signal from the arithmetic circuit 8 as shown in FIG. An output signal as shown in f) is generated. In this case, since the offset is zero,
The output signal of the arithmetic circuit 8 is equal to the amplitude error signal from the amplitude error detector 3.

In the automatic gain control device 10, the output signal of the arithmetic circuit 8 is supplied to the loop filter 4, and a predetermined filter process is performed by the loop filter 4, whereby the GCA as shown in FIG. The control signal is fed back to GCA1. As a result, the output of GCA1 is controlled by the GCA control signal, and
As shown in (h), the signal of the optimum amplitude level set by the amplitude reference value is output from GCA1.

On the other hand, in the automatic gain control device 10A, a reproduced signal having an offset as shown in FIG.
When input to CA1, this reproduced signal is full-wave rectified by full-wave rectifier 2 to be a signal having a waveform as shown in FIG. Here, the output waveform from the full-wave rectifier 2 is
It can be seen that the peak values of the plus and minus amplitudes are not equal. And the full-wave rectified reproduction signal is
The amplitude error detector 3 makes a comparison with the amplitude reference value, and based on the comparison result, a pulse-shaped amplitude error signal as shown in FIG. This amplitude error signal is a signal determined to be larger than the original amplitude by comparison with the amplitude reference value.

On the other hand, the reproduction signal input to GCA1 is
The offset value is detected by the offset detector 6, and an offset signal as shown in FIG. This offset signal is further converted by the absolute value circuit 7 into a waveform indicating the absolute value of the offset value as shown in FIG. Then, in the automatic gain control device 10, the arithmetic circuit 8 performs an arithmetic operation of subtracting the output signal of the absolute value circuit 7 from the amplitude error signal that is the output signal of the amplitude error detector 3, thereby obtaining a signal from the arithmetic circuit 8. An output signal as shown in FIG. 5 (f) is generated. In this case, the output signal of the arithmetic circuit 8 is a signal obtained by correcting the offset from the amplitude error signal.

In the automatic gain control device 10, the output signal of the arithmetic circuit 8 is supplied to the loop filter 4, and a predetermined filtering process is performed by the loop filter 4, so that the GCA as shown in FIG. The control signal is fed back to GCA1. As a result, the output of GCA1 is controlled by the GCA control signal, and
As shown in (h), the GCA1 outputs a signal having an optimum amplitude level set by the amplitude reference value while including an offset.

Therefore, according to the automatic gain control device 10, since a signal having an optimum amplitude level is output even for a reproduced signal having an offset, a PRML (Partial Response Maximum Likelyhoo) connected to the output side is output.
d) S by detectors such as detection and multi-level detection
/ N can be detected with high accuracy.

FIGS. 6 and 7 show other examples of the configuration of the automatic gain control device. An automatic gain control device 10A shown in FIG. 6 includes a GCA 1, a full-wave rectifier 2, an amplitude error detector 3, an LF 4, an offset detector 6, an absolute value circuit 7, and an arithmetic circuit, similarly to the automatic gain control device 10 described above. 8
The difference from the automatic gain control device 10 is that one input side of the arithmetic circuit 8 is connected to the output side of the GCA 1 and the output side of the arithmetic circuit 8 is connected to the input side of the full-wave rectifier 2. That is, in the automatic gain control device 10A, the arithmetic circuit 8 outputs the absolute value
The operation of subtracting the output signal is performed.

The automatic gain control device 10B shown in FIG.
Also includes a circuit similar to the automatic gain control device 10 described above, except that one input side of the arithmetic circuit 8 is connected to the output side of the LF4, and the output side of the arithmetic circuit 8 is connected to the GCA1. It is different from the control device 10.
That is, in the automatic gain control device 10B, the arithmetic circuit 8 performs an operation of subtracting the output signal of the absolute value circuit 7 from the output signal of the LF4.

The automatic gain control devices 10A, 10A
Also in B, the same effects as those of the automatic gain control device 10 described above can be obtained.

[0030]

As described above in detail, according to the automatic gain control device of the present invention, the output signal from the gain control amplifier is supplied to the feedback circuit and the offset detection circuit,
The output signal of the offset detection circuit is subtracted from one of the output signals of the feedback circuit by the arithmetic circuit. Therefore, when the input signal has a DC offset, the first part of the intermittent signal, the modulation degree, and the amplitude Automatic gain control can be performed correctly even when there is an offset due to sag or the like that occurs at the boundary between different signals. As a result, even for an input signal having such an offset, highly accurate signal detection with good S / N can be performed. Also, P
Phase information required for LL can be accurately detected.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an automatic gain control device to which the present invention has been applied.

FIG. 2 is a block diagram illustrating a configuration example of an offset detector.

FIG. 3 is a waveform chart for explaining the operation of the offset detector.

FIG. 4 is a waveform chart for explaining the operation of the automatic gain control device.

FIG. 5 is a waveform diagram for explaining an operation when a reproduction signal with an offset is input in the automatic gain control device.

FIG. 6 is a block diagram showing another configuration example of the automatic gain control device.

FIG. 7 is a block diagram showing another configuration example of the automatic gain control device.

FIG. 8 is a block diagram showing a configuration of a conventional automatic gain control circuit.

FIG. 9 is a waveform chart for explaining the operation of the conventional automatic gain control circuit.

FIG. 10 is a waveform diagram for explaining an operation when a reproduction signal with an offset is input in a conventional automatic gain control circuit.

[Explanation of symbols]

10, 10A, 10B Automatic gain control device, 1 GC
A, 2 full-wave rectifier, 3 amplitude error detector, 4 LF, 6
Offset detector, 7 absolute value circuit, 8 operation circuit

Claims (2)

[Claims] 1. A gain control amplifier, a full-wave rectifier for full-wave rectifying an output signal of the gain control amplifier, and comparing the output signal of the full-wave rectifier with a predetermined amplitude reference value. A feedback circuit comprising: an amplitude error detector that outputs an error signal; and a control signal generation circuit that generates a control signal for the gain control amplifier based on an output signal from the amplitude error detector and outputs the control signal to the gain control amplifier. An offset detection circuit that detects an absolute value of an offset from an output signal of the gain control amplifier; and an arithmetic circuit that subtracts an output signal of the offset detection circuit from any output signal of the feedback circuit. Automatic gain control device. 2. The automatic gain control device according to claim 1, wherein the arithmetic circuit subtracts an output signal of the offset detection circuit from an output signal of the amplitude error detector in the feedback circuit.