JPS6149742B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic amplitude control circuit, and more particularly to an automatic amplitude control method for absorbing signal amplitude fluctuations due to variations in head efficiency, non-uniformity of media, etc. in magnetic disk drives. .

In magnetic disk drives, there are amplitude fluctuations in the read signal even on the same track of the magnetic disk due to variations in head efficiency, non-uniformity of the medium, instability of the flying characteristics of the head, or changes in the element over time. - There is also a level difference between the track and outer track signals.

Fig. 1 is a block diagram showing the automatic amplitude control method of a conventional magnetic disk device, and Fig. 2 is the same as Fig. 1.
AGC characteristic curve diagram, Figure 3 is a connection diagram of a part of the amplitude discriminator and low-pass filter in Figure 1, Figure 4 a,
b is an input and output waveform diagram of FIG. 1;

Now, the input signal V _si as shown in Fig. 4a is amplified by the variable gain amplifier GCA,
When the wave is detected, the detection output V _d as shown in the solid line
is obtained, so this can be converted into a low pass filter LF
By passing it through, a DC control signal V _AGC as shown by the dotted line is obtained. Amplifier with this control signal V _AGC
When the gain G of GCA is controlled, as shown in FIG. 2, the gain G decreases when the DC level of the control signal V _AGC is high, and increases when the DC level is low.

Therefore, an appropriate point P on the curve is selected so that gains G _U to G _D within a certain range can be obtained.

Typically, the input signal V _si is limited by the head, air gap, medium, etc., and has different amplitudes depending on the data pattern. Therefore, since the detection output V _d and the control signal V _AGC also change according to the difference in the amplitude of the input signal V _si , when the output signal V _SO is controlled by this control signal V _AGC , the result as shown in Fig. 4b is obtained. In the output signal V _sp , a portion A where the amplitude increases and a portion B where the amplitude decreases occur. The peak point is generally detected by slicing the original waveform at a certain level using a comparator, and then using the output that exceeds that level and the output that corresponds to the point of zero slope in the signal obtained by differentiating that output, that is, the differential zero crossing output. Created by the AND condition. In this case, if the level fluctuation of the original waveform is large, the control amount becomes large, so the level fluctuation until it reaches a steady state becomes large, and the setting margin of the slice level of the comparator described above decreases.
The range in which peak detection can be performed correctly becomes narrower, making it difficult to detect peak points reliably. Note that in the figure, CLVL indicates the control target level, and converges to this level in a steady state.

Conventional countermeasures have been to assume randomness of the data and make the time constant of the filter LF sufficiently large, and to sample the input level by turning on a loop at a specific part of the track (for example, all 1's). , fixes the control signal V _AGC while retaining its level when the loop is turned off.
There are AGC loop control methods, etc. By increasing the time constant, it is possible to reduce the drop in level at data "0", but it is not possible to follow a high-speed modulation signal where data "1" continues.
Furthermore, the method of fixing the control signal V _AGC also has the disadvantage that it can only absorb the difference in output level between the inner and outer parts of the truck.

The object of the invention is to eliminate the above-mentioned drawbacks:
The purpose is to reduce the dependence of the detection output V _d on the data pattern, thereby reducing the time constant of the low-pass filter and absorbing amplitude fluctuations of the high-speed modulation signal.

The automatic amplitude control circuit of the present invention includes a variable gain amplifier that amplifies a read signal read from a medium of a magnetic recording device, an amplitude discriminator that discriminates the amplitude of an output signal of the variable gain amplifier, and the amplitude discriminator and a low-pass filter into which the output signal of is input,
An automatic amplitude control circuit configured to control the gain of the variable gain amplifier by the output of the low-pass filter, the circuit including (1-
The above objective was achieved by providing an amplitude equalizer with a transfer characteristic expressed as Kcosωτ)e ^-j 〓〓 (where τ is the amount of delay, ω is the angular frequency, and K is the control coefficient). do.

Embodiments of the present invention will be described below with reference to the drawings.

Figure 5 is a block diagram of the automatic amplitude control circuit, and Figure 6 is a block diagram of the automatic amplitude control circuit.
The figure shows the specific circuit of Fig. 5, Fig. 6A shows the readout signal waveform, Fig. 7 a and b show the input and output waveforms in Fig. 5, and Fig. 8 shows the amplitude equalizer of Fig. 6. Amplitude and phase characteristic curve diagrams, Figures 9 a to c
6 is an explanatory diagram of the operation of the amplitude equalizer of FIG. 6. FIG.

In the present invention, as shown in FIG. 5, an amplitude equalizer EQL is inserted immediately before the amplitude discriminator DET in the AGC loop, thereby aligning the levels of the input signals V _{si and} Emphasizes the harmonic content of , narrowing the pulse and reducing peak shift.

The present invention also provides an amplitude equalizer in the AGC loop.
In addition to providing the EQL, an amplitude equalizer EQL' may also be provided in the output signal path, as shown by the dotted line in FIG.

This amplitude equalizer EQL' is provided to equalize the amplitude change, that is, the amplitude, of the automatically gain-controlled magnetic disk device output signal V _sp , and to prevent the peak point from shifting.

In FIG. 6, when the input signal V _si is amplified by the variable gain amplifier GCA, the characteristic impedance Z ₀
input to the amplitude equalizer EQL via the delay time τ
The signal with a delay time of 2τ that is applied to one input of the differential amplifier DIFAMP through the delay line DL having K to the other input of the differential amplifier DIF AMP. FIGS. 9a and 9b are the waveforms of both input signals of the differential amplifier DIF AMP, respectively, and when these differences are taken, a signal with a small pulse width as shown in FIG. 9c is obtained.

The amplitude equalizer EQL is a cosine equalizer having transfer characteristics as described below, and has frequency versus amplitude and phase characteristics as shown in FIG. That is, the gain for low frequencies is small and the gain for high frequencies is large. As shown by the solid line in FIG. 6A, the "1111" pattern has only a fundamental wave component and almost no harmonics. Therefore, even if the signal passes through the amplitude changer EQL, the waveform remains unchanged and only the amplitude decreases. On the other hand, “1010”
In the case of the pattern, as shown in FIG. 6A, the fundamental wave component with half the frequency of the "1111" pattern and its third harmonic are included. Therefore, when passing through the amplitude equalizer EQL, the fundamental wave is attenuated and the third harmonic is amplified. Since the third harmonic component is originally small, the signal level and pulse width at the output of the amplitude equalizer EQL decrease. For this reason, the level of the output signal V _seq of the amplitude equalizer EQL is equalized. amplitude equalizer
The delay time τ and control coefficient K in EQL are given constant values as described later.

As shown in FIG. 7a, the amplitude of the signal V _si input to the variable gain amplifier GCA in FIG. 5 changes as shown in FIG.
Causes large level fluctuations. FIG. 6A explains this, and the readout signal is generally a combination of solitary waves indicated by broken lines. Therefore, as shown in FIG. 6A, when moving from a region without magnetization reversal to a region with magnetization reversal, waveform interference with adjacent solitary waves decreases and the level increases. However, as shown in Figure 7b, the signal V _seq that has passed through the amplitude equalizer EQL has an equalized signal level and a sharp pulse waveform, and as the fundamental wave component decreases, waveform interference with adjacent waves occurs. decreases, and the deviation of the peak position also becomes smaller. In FIG. 6A, a and b indicate peak shifts caused by the synthesis of solitary waves.

This equal amplitude output signal V _seq is the discriminator
Through DET, the DC control signal V _AGC is generated by the low-pass filter LF, and this signal V _AGC is used to control the amplifier GCA.
control the gain of. However, because of this, the inner
The difference in output level between the track and the outer track is absorbed.

The amplitude equalizer EQL was developed by the inventors of the present invention on August 30, 1976, entitled "Reproduced Waveform Modification Using a Cosine Equalizer" (IEICE Technical Research Report [IEICE Tech. It consists of a cosine-shaped equalizer as described in [Report Vol. 76, No. 102]), and its characteristics are generally expressed as (1-Kcosωτ)e ^j 〓〓. Here, τ is the delay amount of the delay line DL,
A rough guideline is approximately 1/2 the half-width of a solitary wave. Further, ω indicates the angular frequency, and K is a control coefficient, which is approximately 0.5 and is determined experimentally.

Furthermore, the amplitude characteristics and phase characteristics of the amplitude equalizer EQL are as shown in FIG.
If ≦K≦1) is set to 0, the amplitude becomes constant for all frequency components, but as the control coefficient K increases, the amplitude for each frequency component increases. However, the delay is a constant delay (τ).

FIG. 10 is a block diagram of an automatic amplitude control circuit showing another embodiment.

As shown in Figure 10, variable gain amplifier GCA
It is also possible to install an amplitude equalizer EQL at the front stage.

In this case, the amplitude of the input signal V _si is equalized and the phase shift is eliminated before inputting it to the amplifier GCA, so the operation of the variable gain amplifier GCA becomes insensitive, but the time constant of the low-pass filter LF can be reduced. can absorb high-speed modulation.

As described above, according to the present invention, the output amplitude can be strictly controlled regardless of the data pattern, so the time constant of the low-pass filter can be made small, high-speed modulation can be absorbed, and the pull-in time can be shortened. .

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the AGC system of a conventional magnetic disk device, Figure 2 is a diagram of the AGC characteristic curve of Figure 1, and Figure 3 is a partial connection diagram of the amplitude discriminator and low-pass filter in Figure 1. , FIGS. 4a and 4b are input and output waveform diagrams of FIG. 1, FIG. 5 is a block diagram of an automatic amplitude control circuit showing an embodiment of the present invention, and FIG.
The figure is a specific circuit diagram of Figure 5, Figure 6A is a diagram showing the readout signal waveform, Figures 7a and b are input and output waveform diagrams in Figure 5, and Figure 8 is the amplitude equalization of Figure 6. Amplitude and phase characteristic curve diagrams of the device, Figure 9 a~
c is an operating waveform diagram of the amplitude equalizer shown in FIG. 6, and FIG. 10 is a block diagram of an automatic amplitude control circuit showing another embodiment of the present invention. GCA...variable gain amplifier, LF...low pass filter, EQL, EQL'...amplitude equalizer, DET...
Amplitude discriminator, V _AGC ... Control signal, CLVL... Control target level, V _d ... Discriminator output signal, G...
Gain, K...control coefficient.

Claims (1)

[Scope of Claims] 1. A variable gain amplifier that amplifies a read signal read from a medium of a magnetic recording device, an amplitude discriminator that discriminates the amplitude of an output signal of the variable gain amplifier, and an output of the amplitude discriminator. an automatic amplitude control circuit comprising a low-pass filter to which a signal is input, and configured to control the gain of the variable gain amplifier by the output of the low-pass filter,
Automatic amplitude control characterized by being provided with an amplitude equalizer having a transfer characteristic expressed as Kcosωτ)e ^-j 〓〓 (where τ is the amount of delay, ω is the angular frequency, and K is the control coefficient) circuit.