JPH0570965B2 - - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to an amplifier that amplifies an input signal as desired, and particularly to an automatic amplification factor control circuit.

Prior Art In general, in amplification processing of an input signal consisting of a necessary signal component superimposed on a DC component such as a drift, the input signal is passed through a CR coupling circuit to remove the DC component and then input to an amplification circuit. Attempts have been made to amplify only desired signal components via an amplification factor control circuit or the like. Even in recent optical information recording and reproducing devices, the digital signal modulation method used is FM, which is capable of self-clocking.
(Frequency Modulation) Modulation method and MFM
(Modified Frequency Modulation) There is a modulation method, and in recent years, MFM modulation method, which can record at twice the density of FM modulation method, is often used. Amplification processing is a challenge, and various automatic amplification factor control circuits are being considered. The prior art will be described below with reference to FIGS. 3 to 8 of the accompanying drawings.

Figure 3 shows "11011000" as an example of the conventional technology.
FIG. 3 is a recording waveform diagram of the MFM modulation method for data. In the MFM method, recording waveforms are recorded depending on data with or without inversion as shown in the figure.

FIG. 4 is a circuit diagram of a reproducing/reading circuit of an optical information recording/reproducing apparatus, and FIG. 5 is a waveform diagram of each part of the circuit. Information recorded on the optical disk 1 is detected by an optical pickup 2, converted into an electrical signal a, and inputted to a CR coupling circuit 3. CR coupling circuit 3
inputs the signal component b from which the DC component has been removed to the preamplifier section 4, amplifies the signal to a desired level, and then outputs the signal component b to the comparator 5.
input to the terminal. A terminal of the comparator 5 is grounded and outputs a waveform-shaped output signal c. A, b, and c in FIG. 5 indicate signal waveforms corresponding to a, b, and c in FIG. 4 above. As shown in the figure, at point a, the signal information recorded on the optical disk 1 has a waveform in which a DC component is superimposed, but at point b, the DC component is removed, and at point c, the waveform is shaped with reference to the ground potential. I know that there is.

By the way, although FIGS. 4 and 5 are conventional examples in which the amplitude of the input signal is constant, the amplitude of the input signal often fluctuates, for example, due to variations in the optical characteristics of optical disks. If the intensity of the reproduction light fluctuates due to reasons such as the above, it becomes impossible to amplify the desired signal using only the CR coupling circuit. For this reason, conventional attempts have been made to perform waveform shaping while amplifying the signal via an automatic amplification factor control circuit 14 as shown in FIG. A signal a having fluctuations in amplitude is input to one end of a voltage control amplifier 15 made up of a differential amplifier _{, etc., and its output signal c is input to one end of a voltage control amplifier 15 made} up of a differential amplifier etc. Signal generation circuit 17
input to the terminal. The output b of the control signal generation circuit 17 is inputted to a terminal of the control signal generation circuit 17 via a voltage dividing circuit of R ₂ and R ₃ and also inputted to another input terminal of the voltage control amplifier 15 . Figure 7 is a waveform diagram showing the waveforms of each part of the circuit in Figure 6.
Points a, b, and c in FIG. 7 correspond to points a, b, and c in FIG. 6. As shown in the figure, at point a, the input signal waveform is a waveform whose amplitude fluctuates with respect to the amplitude reference level _V1 , but the input signal is superimposed on the constant level _V2 , which is the output signal of the control signal generation circuit 17. The amplification factor of the voltage control amplifier 15 is controlled by the positive envelope signal (control signal) b, and c
It can be seen that the waveform has been shaped into an output signal having a constant output level _V3 at the point.

By the way, the circuit diagram shown in FIG. 6 induces yet another problem when an input signal is inputted through a CR coupling circuit as shown by reference numeral 3 in FIG. For example, assuming that recorded information is read from an optical disk in an optical information recording/reproducing apparatus as in the above example, a,
The signals at points b and c become as shown in the waveform diagrams shown in FIG. 8 b, c, and d. In other words, the information signal (waveform a in Figure 8) superimposed on the DC component input to the CR coupling circuit at point a in Figure 4 is superimposed on the attenuating DC component unique to the CR coupling circuit at point a in Figure 6. The resulting waveform (Fig. 8b) is obtained. Such a phenomenon often occurs, for example, when an optical pickup intermittently reproduces and reads an area on an optical disk where data is recorded and an area where data is not recorded. As a result, the waveform at point b in FIG. 6, that is, the output waveform of the control signal generation circuit 17, becomes an envelope signal with the DC component biased as shown in FIG. 8c, and controls the amplification factor of the voltage control amplifier 15. Therefore, the waveform at point c in FIG. 6, that is, the output signal, has an inaccurate amplitude as shown in FIG. 8d, resulting in incorrect information processing. In addition, in the MFM modulation method, the positive and negative levels become unbalanced on the time axis, so if the CR coupling circuit is used as described above, the duty ratio of the reproduced signal will be disturbed and the recorded signal will be erroneously reproduced. There are drawbacks that arise.

OBJECTS OF THE INVENTION An object of the present invention is to provide an automatic amplification factor control circuit that eliminates the influence of direct current bias in an input signal to an amplifier and obtains an accurate output signal at a desired level.

SUMMARY OF THE INVENTION To achieve the above object, the present invention obtains positive and negative envelope signals of an input signal, and calculates the amplification factor of the input signal based on the sum signal of the positive and negative envelope signals. The present invention provides an automatic amplification factor control circuit for an amplifier that controls, amplifies an input signal as desired, and shapes the waveform to obtain an accurate output signal.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of an automatic amplification factor control circuit 14 showing an embodiment of the present invention. Note that the same elements as in FIG. 6 are given the same reference numerals. The voltage control amplifier 15, which is composed of a differential amplifier or the like, which inputs an input signal to one end of its input terminal, outputs its output to an output terminal via a buffer amplifier 31, and the inverted output of the buffer amplifier 31 generates a negative envelope signal. Input to circuit 32d, and further buffer amplifier 3
The non-inverted output of 1 is a positive envelope signal generation circuit 32c.
Enter. Positive and negative envelope signal generation circuit 32
The outputs of 32d and 32d are inputted via resistors R _c and R _d to the terminals of an operational amplifier 33 constituting an adder circuit, respectively, to obtain a sum signal of positive and negative envelope signals. Since the output of the operational amplifier 33 is inverted in polarity, its polarity is inverted via the inverting amplifier 34 and connected to the other input terminal of the voltage control amplifier 15 as a control signal for controlling the amplification factor. The positive and negative envelope signal generating circuits 32c and 32d are each constituted by an integrating circuit consisting of resistors R _1c and R _1d and capacitors C _1c and C _1d connected in series with diodes D _c and D _d , respectively. In this way, the voltage controlled amplifier 1
5 controls the amplification factor of the input signal by the sum signal of the positive and negative envelope signals to output a desired accurate output signal.

FIG. 2 shows signal waveforms at points b to f in FIG. 1 when optically recorded information is read from an optical disk in an optical information recording/reproducing apparatus as an embodiment of the present invention. Figure 2b-f
The waveform diagrams correspond to points b to f in FIG. 1, respectively. The waveforms in FIGS. 2a and 2b are the same as in the conventional example shown in FIG. Fig. 2c shows a positive envelope signal (point c in Fig. 1), and Fig. 2d shows a negative envelope signal (point d in Fig. 1). The waveform in FIG. 2e shows a sum signal (point e in FIG. 1) of positive and negative envelope signals that have been added and inverted and amplified. The sum signal e is inputted to the voltage control amplifier 15 as a control signal to automatically control the amplification factor of the input signal, and in the unlikely event that the amplification fluctuates with respect to the reference level V ₁ of the conventional example as shown in FIG. 7a. It is possible to output an output signal with a constant amplitude V ₃ even if an input signal of It is possible to output an information signal with a constant amplitude without outputting an output signal having an inaccurate amplitude. In the above example
Although we have explained the MFM modulation method, M ² FM,
Modulation methods such as EFM, NRZ, and NRZI have similar effects in that they eliminate the effects of amplitude fluctuations and do not output erroneous information due to the effects of superimposed DC attenuation components.

Effects of the Invention As described above, in the present invention, the amplification factor of the input signal is controlled based on the sum signal of the positive and negative envelope signals, and the input signal is amplified and waveform-shaped to obtain the output signal. It is possible to perform signal amplification processing without being affected by DC bias or amplitude fluctuations, thereby preventing errors in information processing and increasing the reliability of the signal amplification device. Furthermore, when the present invention is applied to an optical information recording/reproducing device, it facilitates accurate reading and detection of recorded information, and further improves the practicality of the device as a highly reliable storage device.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an automatic amplification factor control circuit according to an embodiment of the present invention, FIG. 2 is a signal waveform diagram of each part of the circuit shown in FIG. 1, and FIG. 3 is a recording waveform diagram of the MFM modulation method. Fig. 4 is a circuit diagram of a reproducing/reading circuit of a conventional optical information recording/reproducing device, Fig. 5 is a waveform diagram of each part of the circuit shown in Fig. 4, and Fig. 6 is a circuit diagram of a conventional automatic amplification factor control circuit. , FIG. 7 is a waveform diagram of each part of the circuit of FIG. 6, and FIG. 8 is a waveform diagram showing problems caused by the conventional automatic amplification factor control circuit. 14... Automatic amplification factor control circuit, 15... Voltage control amplifier, 31... Buffer amplifier, 32c...
Positive envelope signal generation circuit, 32d... Negative envelope signal generation circuit, 33... Operational amplifier, 34... Inverting amplifier.

Claims (1)

[Scope of Claims] 1. An automatic amplification factor control circuit for an amplifier that obtains an output signal by amplifying an input signal as desired, comprising: means for generating positive and negative envelope signals of the input signal; and means for generating positive and negative envelope signals of the input signal; An automatic amplification factor control circuit comprising: control means for controlling an amplification factor of the input signal based on a sum signal of the signals.