JPH07115347A - Equalizer filter - Google Patents

Abstract

PURPOSE:To improve S/N, and to prevent generation of a peak shift by providing an n-th order active band cut-off filter thereby optionally setting an attenuation characteristic in a high frequency band when a necessary equalizer characteristic is obtained. CONSTITUTION:A secondary differentiation circuit 1 functions as an equalizer for executing pulse slimming. An n-th order LPF 2 functions in order to eliminate a noise of a high frequency band. A primary HPF 3 is a primary differentiation circuit. A primary LPF 4 functions in order to fit a group delay characteristic to the primary HPF 3. The n-th order band eliminating filters(BEF) 5, 6 are constituted of two variable conductance circuits gm1-14, gm2-15, and two capacities C1-16, C2-17. By varying a value of a characteristic angular frequency of the BEFs 5, 6, an attenuation characteristic of the high frequency band can be varied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an equalizer filter which obtains an arbitrary equalizer filter characteristic, and particularly, in a read channel of a magnetic disk device or the like, an optimum waveform shaping process is performed for an arbitrary transfer speed to improve a reproduction margin. The present invention relates to an equalizer filter for achieving the purpose.

[0002]

2. Description of the Related Art Generally, a magnetic disk device detects a peak position of an analog waveform read from a magnetic head, converts it into digital data, and outputs it. However, the read waveform differs depending on the inner and outer circumferences of the disk, the recording / reproducing speed, the properties of the magnetic head and the disk medium, and so on.
Various waveform shaping processes are performed in order to detect an accurate peak position. FIG. 7 shows a block configuration of a conventional waveform shaping process, which includes an AGC amplifier 201, an equalizer filter 202, an AGC control 203, and a peak detection 204. The AGC amplifier 201
Is an amplifier circuit for keeping the amplitude of the read waveform, which mainly changes in the inner and outer peripheries of the disk, constant, and constitutes a feedback loop via the AGC control circuit 203. The equalizer filter 202 performs pulse slimming for reducing the half-value width of the read waveform and removal of noise in a high frequency band so that the peak detection 204 can detect an accurate peak position, and is suitable for a system. Various characteristics are required.

In recent years, along with the demand for downsizing and speeding up of devices and diversification of signals to be handled, high performance and high performance one-chip signal processing LSIs have been required. Particularly in magnetic disks, a method of changing the recording and reproducing speeds on the inner and outer circumferences of the disk has begun to be adopted in order to improve the recording density. In this recording method, since the frequency components of the reproduced signal are different on the inner and outer circumferences of the disc, the signal processing circuit of the reproducing system is required to have circuit characteristics optimized for each frequency component. Therefore, the equalizer filter 2
In 02, a characteristic variable filter having a configuration using a gm (variable conductance) amplifier for current output and a capacitor C is realized as being advantageous for an on-chip filter.

The structure of a conventional equalizer filter will be described with reference to FIG. FIG. 8 shows a configuration diagram of a conventional equalizer filter, which includes a second-order differentiating circuit 207, an n-th order low-pass filter, hereinafter LPF 208, first-order high-pass filter, HPF 209 and first-order LPF 210. The second-order differentiating circuit 207 functions as an equalizer for performing pulse slimming, and the transfer characteristic H1 (s) of this circuit in the case of being configured by bicut is the characteristic angle frequency ω.
It is expressed by the following equation using o, the quality factor Q, the constant K, and the complex angular frequency s.

[0005]

[Equation 1]

The nth-order LPF 208 functions to remove noise in a high frequency band, and the second-order transfer characteristic H2 (s) of this circuit in the case of a bicut is expressed by the following equation.

[0007]

[Equation 2]

At this time, a plurality of secondary LPF circuits and the primary LPF
The LPF at the time of n is constructed by combining. Further, the primary HPF 209 is connected to the peak detection circuit 20.
The transfer characteristic H3 (s) is expressed by the following equation in the first-order differentiating circuit for performing the zero-crossing detection in step 4.

[0009]

[Equation 3]

The primary LPF 210 is connected to the primary HPF.
209 and the group delay characteristic, and is used by the peak detection circuit 204 to generate a gate signal indicating a peak existence range. This transfer characteristic H4 (s) is expressed by the following equation.

[0011]

[Equation 4]

Since the data signal input to the equalizer filter 202 has various frequency components, the group delay characteristic of the equalizer filter must be constant in order to accurately detect the peak position. So these number 1
~ By setting the value of the characteristic angular frequency ωo of Expression 4 to the position of the pole of the Bessel characteristic or the equiripple characteristic, for example, an equalizer filter having a constant group delay characteristic is configured.

[0013]

In the above-mentioned prior art, the gain in the high frequency band is increased by the secondary differentiating circuit 207, but the value of the characteristic angular frequency ωo of each order of the equalizer filter has a constant group delay characteristic. From the band, the type of filter called Bessel filter and the order of the entire equalizer filter are determined. Therefore, when the required equalizer characteristic is obtained, the attenuation characteristic in the high frequency band cannot be arbitrarily set, so that the gain in the unnecessary high frequency band is amplified, the noise component increases, and the S / N deteriorates. There was a problem of doing. Further, for the same reason as described above, there is a problem in that the gain in the high frequency band in which the group delay characteristic changes also increases and a peak shift occurs.

A first object of the present invention is to arbitrarily set the attenuation characteristic in the high frequency band when the required equalizer characteristic is obtained, attenuate the unnecessary high frequency band gain, and reduce the noise component. To improve the S / N.

A second object of the present invention is to arbitrarily set the attenuation characteristic in the high frequency band when the required equalizer characteristic is obtained, and attenuate the gain in the high frequency band where the group delay characteristic changes. , To prevent the occurrence of peak shift.

[0016]

The first and second objects are to provide an equalizer filter, a plurality of variable conductance circuits, an nth-order active equalizer filter composed of a plurality of capacitors, and a plurality of variable conductance circuits. , An nth-order active band stop filter composed of a plurality of capacitors.

[0017]

In an nth-order active equalizer filter including a plurality of variable conductance circuits and a plurality of capacitors, an nth-order active band stop filter including a plurality of variable conductance circuits and a plurality of capacitors is provided, and each nth-order characteristic The value of the angular frequency ωo is set arbitrarily.

Thus, when the required equalizer characteristic is obtained, the attenuation characteristic in the high frequency band is arbitrarily set, the gain in the unnecessary high frequency band is attenuated, the noise component is reduced, and the S / N ratio is reduced. Can be improved. Further, when the required equalizer characteristic is obtained, the attenuation characteristic in the high frequency band can be arbitrarily set, the gain in the high frequency band where the group delay characteristic changes can be attenuated, and the occurrence of peak shift can be prevented. .

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 6 and 9.

FIG. 1 is a diagram showing the configuration of the equalizer filter of the present invention, which is a second-order differentiating circuit 1, an n-th order LPF 2,
It is composed of a first-order HPF 3, a first-order LPF 4, two nth-order band elimination filters, and hereinafter BEFs 5 and 6. 2 above
The secondary differentiating circuit 1 functions as an equalizer for performing pulse slimming, and the transfer characteristic H1 (s) of this circuit in the case of a bicut is expressed by the equation 1 as described above. The nth-order LPF2 functions to remove noise in a high frequency band, and the nth-order LPF2 of the circuit in the case of a bicut is used.
The next transfer characteristic H2 (s) is expressed by Equation 2 as described above. The first-order HPF3 is a first-order differentiation circuit for performing zero-cross detection in the peak detection circuit 204, and the transfer characteristic H3 (s) is represented by the equation 3 as described above. 1
The next-order LPF 4 functions to match the group delay characteristic with the first-order HPF 3, and is used in the peak detection circuit 204 to generate a gate signal indicating a position where a peak exists.
This transfer characteristic H4 (s) is expressed by the equation 4 as described above. Further, the nth-order BEFs 5 and 6 set attenuation characteristics in a high frequency band, and when this circuit is configured by the secondary bicut, the transfer characteristic H5 (s) is expressed by the following equation.

[0021]

[Equation 5]

FIG. 2 shows frequency characteristics of the equalizer filter of FIG. FIG. 2-a shows the input L7 from the primary L
In the graph showing the frequency characteristic up to the output of PF4, the high-frequency band amplification in the secondary differentiating circuit 1 and the n-th order L
The output is a combination of the attenuation characteristics in the high frequency band of the PF2 and the primary LPF4. FIG. 2B is a graph showing the frequency characteristics of the BEFs 5 and 6, and shows a band cutoff characteristic for cutting off a signal in the vicinity of the characteristic angular frequency ωo13. FIG. 2-c shows that the input in7 changes to the output out2-
9 is a graph showing the overall frequency characteristics up to 9 and is shown in FIG.
2 shows a frequency characteristic obtained by synthesizing the frequency characteristic graph 10 shown in FIG. 2 and the frequency characteristic graph 11 shown in FIG. From this graph 12, the characteristic frequencies ωo of the BEFs 5 and 6 are
It can be seen that the attenuation characteristic in the high frequency band can be changed by changing the value of.

FIG. 3 is a diagram showing an example of a circuit block in the case where the BEFs 5 and 6 are constructed by the secondary bicut, and two variable conductance circuits gm1-14 and gm2-1.
5 and two capacitors C1-16 and C2-17. The transfer characteristic H5 (s) at this time is expressed by the equation 5 as described above, and the characteristic angular frequency ωo and the quality factor Q therein are gm1-14, gm2-15, and C1-16. , C2-17, and is expressed by the following equation.

[0024]

[Equation 6]

Therefore, gm1-14, gm2-15,
By changing the value of
o and the quality factor Q can be set. Further, in this circuit block example, the variable conductance circuit of differential input and one side output is shown, but of course, a variable input differential output variable conductance circuit can also be used.

FIG. 4 is a graph showing the relationship between the quality factor Q and the frequency characteristic when the BEFs 5 and 6 are constructed by the secondary bicut. In the bi-cut second-order band stop filter, the bandwidth BW at -3 dB is expressed by the following equation.

[0027]

[Equation 7]

Therefore, as shown in the figure, when the value of Q is changed from Q0 to Q1, BW changes from BW0 to BW1, and the attenuation characteristic can be changed without changing the characteristic angular frequency ωo. , Any damping characteristic can be obtained.

FIG. 5 is a diagram showing an example of a circuit block in the case where the secondary differentiating circuit 1 is constructed by a secondary bicut.
Variable conductance circuits gm1-26 and gm2-2
7, two capacitors C1-28 and C2-29, and an amplification circuit-K30 having an amplification factor of -K times. The transfer characteristic H1 (s) at this time is expressed by the equation 1 as described above, and the characteristic angular frequency ωo and the quality factor Q therein are gm1-26, gm2-27, and C1-28. , C2
When -29 is used, it can be expressed by the equation 6 like BEFs 5 and 6. Therefore, by changing the values of the gm1-26 and gm2-27, it is possible to set the arbitrary characteristic angular frequency ωo and the quality factor Q. Further, the amplification factor in the high frequency band can be arbitrarily set by changing the value of the amplification circuit-K30 having the amplification factor-K times. Further, in this circuit block example, the variable conductance circuit of differential input and one side output is shown, but of course, a variable input differential output variable conductance circuit can also be used.

FIG. 6 is a diagram showing an example of a circuit block in the case where the nth-order LPF2 is constructed by a second-order bicut. Two variable conductance circuits gm1-31, gm2-32,
And two capacitors C1-33 and C2-34.
The transfer characteristic H2 (s) at this time is expressed by the equation 2 as described above, and the characteristic angular frequency ωo and the quality factor Q therein are gm1-31, gm2-32, and C, respectively.
When 1-33 and C2-34 are used, they are represented by the equation 6 like BEFs 5 and 6. Therefore, the gm1-31 and gm2-
By changing the value of 32, an arbitrary characteristic angular frequency ωo and quality factor Q can be set. Also, as described above, a plurality of secondary LPF circuits and one
By combining the next LPFs, an LPF for n hours can be constructed. Further, in this circuit block example, the variable conductance circuit of differential input and one side output is shown, but of course, a variable input differential output variable conductance circuit can also be used.

FIG. 9 is a system configuration diagram when the present invention is applied to a magnetic disk. The head 301, an R / W amplifier 302 for amplifying a signal, an AGC amplifier 303 for amplifying to a constant amplitude, and an amplitude. AGC control 304 for control, equalizer filter 305 of the present invention, peak detection 30 for detecting signal peak position and pulsing
6, a data separator 307 that generates a clock synchronized with a pulsed signal, an encoder / decoder 308 that performs encoding and decoding to a recording code, a controller 309 that controls data, an I / F that exchanges data ( Interface) 310, controller 30
9, a processor 311 that controls the I / F 310, a RAM / ROM 312 that stores data, and a host 313 that processes data.

[0032]

According to the present invention, when the required equalizer characteristic is obtained, the attenuation characteristic in the high frequency band is arbitrarily set, the gain in the unnecessary high frequency band is attenuated, and the noise component is reduced. , S / N can be improved. Further, when the required equalizer characteristic is obtained, the attenuation characteristic in the high frequency band can be arbitrarily set, the gain in the high frequency band where the group delay characteristic changes can be attenuated, and the occurrence of peak shift can be prevented. .

[Brief description of drawings]

FIG. 1 is a block diagram of an equalizer filter block of the present invention.

FIG. 2 is a frequency characteristic diagram of the equalizer filter of the present invention.

FIG. 3 is a block configuration diagram of the BEF circuit in FIG.

FIG. 4 is a frequency characteristic diagram of the BEF circuit of FIG.

5 is a configuration diagram of a secondary differentiating circuit in FIG.

FIG. 6 is a configuration diagram of the LPF circuit in FIG.

FIG. 7 is a configuration diagram of a conventional waveform shaping processing block.

FIG. 8 is a block diagram of a conventional equalizer filter.

FIG. 9 is a system configuration diagram of the present invention.

[Explanation of symbols]

First-order differential circuit, second-order LPF circuit, third-order HP
F circuit, 4 ... Primary LPF circuit, 5, 6 ... Nth order BEF circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsuguyoshi Hirooka, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa, Ltd. System Development Laboratory, Hitachi, Ltd. (72) Inventor Hiroshi Kimura 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Shares Hitachi Systems Development Laboratory (72) Inventor Koichi Awano 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Inside Hitachi Systems Development Laboratory (72) Inventor Takashi Nara 111 Nishiyote-cho, Takasaki-shi Gunma Address: Hiritsu Factory Semiconductor Division

Claims (4)

[Claims] 1. An nth-order active equalizer filter including a plurality of variable conductance circuits and a plurality of capacitors, wherein an nth-order active band stop filter including a plurality of variable conductance circuits and a plurality of capacitors is provided, and each of them is made variable. An equalizer filter characterized by changing the characteristics of a conductance circuit. 2. The equalizer filter according to claim 1, wherein a characteristic of the active band cutoff filter is changed to change a gain characteristic in a frequency band where a group delay characteristic is greatly changed. 3. A one-chip LS including the equalizer filter according to claim 1 and integrated on one chip.
I. 4. An equalizer filter built-in system, characterized in that a required equalizer filter characteristic is obtained by using the equalizer filter according to claim 1 or 2, or the one-chip LSI equalizer filter according to claim 3.