JPS58196605A - Automatic gain control system for read-out voltage - Google Patents

Abstract

PURPOSE:To obtain always the stable read-out data block amplitude voltage, by detecting the envelope waveform voltage of a read-out data signal and controlling the gain of a gain control circuit in response to the fluctuation of said envelope waveform voltage. CONSTITUTION:While a data block detecting circuit 7 is detecting a data block, the envelope waveform voltage is amplified by an amplifying circuit 12 and supplied as the gain control voltage signal of a gain control circuit 4. In other words, the gain of the circuit 4 is lowered at a part where the read-out data amplitude voltage is high and raised up at a part where said amplitude voltage is low respectively. Thus no envelope wavefrom voltage is supplied to the circuit 4 in the periods other than the data block. As a result, an envelope waveform is fed back to the circuit 4 to compensate the fluctuation of the envelope waveform voltage when a waveform which varies in terms of time is read out to the data block waveform voltage. In such a way, the stable read-out data block amplitude voltage can be always obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention The present invention relates to an automatic gain control system for continuous data output in a magnetic tape recording/reproducing device (IK).

BACKGROUND OF THE INVENTION A data output system in a conventional magnetic tape recording/reproducing apparatus using a magnetic tape is constructed as shown in FIG. Further, FIG. 82 is a diagram schematically showing signal waveforms at various parts in FIG. 1. in general.

The gain settings for the data succession system are read after loading is completed when loading the magnetic tape (Fig. 1).

Burst (all 1 pattern) written at the beginning of the magnetic tape in Figure 1 by performing an afterwrite operation.
The waveform α shown in FIG. 2 is successively outputted by the magnetic head shown in FIG. 1, and is amplified by the preamplifier circuit shown in FIG. Ru. The gain of this gain control circuit (FIG. 1) is calculated from the count circuit (FIG. 1) by the second clock pulse for gain setting of the gain control circuit (FIG. 1).
According to the gain control circuit shown in FIG. 1,
During the readout burst α in FIG. 2, the start-up gain is gradually increased by the gain control circuit shown in FIG. 1, as shown in FIG. 2C. This signal C in FIG. 2 is input to the differentiator circuit in FIG. 1, in which the high frequency range is emphasized, passes through the full-wave rectifier circuit in FIG. 1, and is subsequently applied to the data block width detection circuit in FIG. This successive data block, the silkworm width detection circuit in FIG. 1, is created by slicing the successive full-wave rectified burst waveform in FIG. If it is below the threshold voltage, a low level signal is generated, and a high level signal is generated during the period in which the full-wave rectified burst waveform (FIG. 2E) exceeds the second threshold voltage. More.

The output signal (FIG. 5, FIG. 2, F) of the successive data block amplitude detection circuit a11 in FIG. At this time, the gain control circuit $1 stops the gain up operation shown in FIG. 4, and sets the gain for the continuous data output system. This set gain remains unchanged while the magnetic tape (FIG. 1) is loaded into the magnetic tape recording/reproducing apparatus. In the gain control method described above, the setting of the continuous output level is determined by the continuous output voltage level of the burst (all 1 pattern) written in the rhyme part of the magnetic tape, so as shown in Fig. 5. For example, if there is a fluctuation in the amplitude of the indulgence waveform.

Figure 5 shows a dropout of the read amplitude due to scratches and dust on the magnetic tape. The disadvantage is that it is rarely possible to correct for amplitude level reversal due to repeated changes in direction.

OBJECT OF THE INVENTION The object of the present invention is to solve the above-mentioned problems by providing a data portion recorded on a magnetic tape.

The envelope waveform voltage of the read data signal is detected, and the gain of the gain control circuit is controlled according to the fluctuation of the envelope waveform voltage, thereby improving the system so that the R output data 1 amplitude voltage is kept at a fairly constant level. The purpose of this invention is to provide a magnetic tape device with the purpose of improving data reliability.

Embodiment of the Invention An embodiment of the present invention will be described below with reference to FIGS. 4, 5, and 6.

FIG. 4 is a block diagram of the main parts of a magnetic tape recording/reproducing apparatus embodying the present invention. Further, FIG. 5 is a diagram schematically showing the signal waveform of the reporting unit shown in FIG. 4.

In FIG. 4, reference numeral 1 denotes a magnetic tape, and the tape 1 is moved in the direction of an arrow 15 by a feeding means (not shown). Reference numeral 2 denotes a fixed magnetic head, which reproduces data from data tracks recorded on the magnetic tape 1. When the magnetic head 2 traces the data track 1, for example, as shown in FIG. Voltage Figure 5 α
14 is the amplitude voltage in the middle part of the data block in Fig. 5 g15
The data block waveform increased with respect to the magnetic head 2
When the data block waveform is read out by the user, the data block waveform whose amplitude fluctuates is amplified by the preamplifier circuit 5 and then inputted to the gain control circuit 4.
! ! 6 for control voltage 16 as shown in FIG.

This is an amplifier circuit with gain characteristics as shown in 17.

Therefore, the read data block waveform $5 (alpha) that has passed through the gain control circuit 4 is input to the differentiating circuit 5, where the high frequency range is emphasized. One output signal of the differentiating circuit 5 is converted into a digital signal by an analog/daisymel conversion circuit 11, and then transmitted to trc@. The other output of the differentiating circuit 5 passes through a full-wave rectifier circuit 6 to be outputted from the υ data block full-wave rectifier circuit shown in FIG. From this low-pass filter circuit 9, an envelope waveform voltage (FIG. 5E) corresponding to the amplitude voltage fluctuation of the successive data block full-wave rectified waveform (FIG. 5) is obtained and inputted to the analog switch circuit 10.

The other output signal of the full-wave rectifier circuit 6, FIG. 5C, is a data block! @The data block amplitude detection circuit 7 compares the data block full-wave rectified waveform (C) with the reference level (FIG. 5), as shown in FIG. 5 (hc). As shown, if the voltage amplitude is higher than the reference level in FIG. 5, a high level signal is output, and if the voltage amplitude is lower than the reference level in FIG. 5, a low level signal is output. This fifth output signal is supplied as a control signal to the analog switch circuit 10, and opens and closes the analog switch circuit 10 to switch the gain of the gain control circuit. While detecting figure C, i.e. the fifth
During the period when the signal is at a high level, the analog switch 10 is closed (ON. The same applies hereinafter). The four-waveform voltage E in FIG. It is supplied as a gain control voltage signal to the control circuit 4. That is, as shown in FIG. 5 α, when a waveform in which the successive data block swing IIK voltage fluctuates is input, Kll! as shown in FIG. 5 α14 is input. In areas where the output data amplitude voltage is large, the gain of the gain control circuit 4 is lowered.

In a portion where the read data amplitude voltage is small like α15 in FIG. 5, the fIi116 is
4. In periods other than data blocks, the analog switch is 10V! Since the envelope waveform voltage E in FIG. 5 is not supplied to the gain control circuit 4, the gain of the gain control circuit 5 is OFF.

The gain is set by the resistance of the fixed resistor R1R2 inside the amplifier circuit 12 and the variable resistor VR1. I wanted to,
When the preamplifier circuit 5 outputs a waveform in which the continuous data block waveform voltage fluctuates over an hour as shown in FIG. 5E is obtained and fed back to the gain control circuit 4. Therefore, the gain of the gain control circuit 4 is controlled, and as shown in FIG.

Effects of the Invention As described above, according to the present invention, the fluctuation of the starting data block due to fluctuations in the voltage level of successive data waveforms, for example, fluctuations in the spacing between the magnetic tape and the magnetic head that occur due to worn heads, etc. Due to width voltage fluctuations, scratches on the magnetic tape, dust, etc. Successive data block vehicle width voltage dropout magnetic tape FORFARI)/BA
It is possible to constantly correct the fluctuation in the width level in the CKN direction in the heave direction.
A consistently stable continuous data block amplitude voltage can be obtained.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of the main parts of the magnetic tape recording/reproducing device, Figure 2 is a signal waveform diagram of the reporting section in Figure 1, Figure 5 is a fluctuating waveform diagram of successive data blocks, and Figure 4 is an application of the present invention. FIG. 5 is a diagram showing the signal waveform of the reporting unit in FIG. 4, and FIG. 6 is a diagram showing the gain characteristics of the gain control circuit with respect to the control voltage. 1...Magnetic tape, 2...Magnetic head. S... Preamplifier circuit, 4... Gain control circuit, 5
...Differentiating circuit, 6...Full wave rectifier circuit, 7...
- Data block amplitude detection circuit, 8...count circuit. 9...Low pass filter circuit, 10... Analog switch circuit. 11...Analog/digital conversion circuit. 12...Amplification circuit. 15...Magnetic tape running direction. 14...Large portion of readout waveform. 15...Small portion of continuous waveform. 16... Control voltage of gain control circuit. 17... Gain of gain control circuit. Representative Patent Attorney Susuki 1) Li, 7. 'Saichi 1 Kidney [No - Shizuku -

Claims (1)

[Claims] In a magnetic tape recording and reproducing device that reads data by tracing data blocks on a magnetic tape with a magnetic head,
means for creating an envelope waveform voltage of a starting data signal successively output from the magnetic head during a period of tracing a data signal portion recorded on the magnetic tape by the magnetic head; and a data block read from the magnetic tape. and supplying the envelope waveform voltage of the successive data signal as a control voltage of the gain control circuit during the detection period, and adjusting the gain of the gain control circuit according to the envelope waveform voltage level. . A successive voltage automatic gain control system, characterized in that the successive data amplitude voltage of the successive data system of a magnetic tape recording/reproducing apparatus is controlled so as to always be at one constant level.