JPH0869605A - Quantization feedback circuit - Google Patents

Abstract

PURPOSE: To obtain a quantization feedback circuit capable of well reproducing the low frequency range components of ternary analog signals in which the low frequency range components are lost. CONSTITUTION: The RR-I equalization signal from an equalizer 12 is supplied as a ternary equalization signal to comparators 19, 20 constituting a ternary level identifying means via an analog adder 18. The output of this comparator 19 attains a '1' when the ternary equalization signal is higher than the threshold voltage + Eth. The output attains a '0' in other cases. On the other hand, the output of the comparator 20 attains a '1' when the ternary equalization signal is lower than the threshold voltage - Eth and the output attains a '0' in other cases. The output signal of these comparators 19, 20 are ORed and are led out as reproducing data to an output terminal 24. The outputs of the compartors 19, 20 are supplied to a differential amplifier 2 as a ternary analog signal restoring means. The low frequency components are extracted by a low-pass filter 23 by the restored ternary analog signals and the ternary equalization signal is formed by adding these components to the output of the equalizer 12 by an adder 18.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a low frequency component (including a DC component) such as a class 1 partial response.
The present invention relates to a quantized feedback circuit suitable for use in reproducing a low frequency component in a reproducing system of a magnetic recording / reproducing apparatus using a multi-valued level detection method that requires

[0002]

2. Description of the Related Art In a digital magnetic recording / reproducing apparatus, since a reproduction frequency characteristic is a differential characteristic, a low frequency region of a reproduction signal is insufficient and a DC component is not reproduced. Therefore, a DC reproducing circuit is required in a magnetic recording / reproducing apparatus using a channel code that requires a low frequency component such as an NRZ code.
Conventionally, a quantization feedback circuit (QFB
Circuit) is used.

FIG. 5 shows a structural example of a reproducing system of a digital magnetic recording / reproducing apparatus using a quantized feedback circuit. In the figure, the signal reproduced by the reproducing magnetic head 2 from the magnetic tape 1 is amplified by the reproducing amplifier 3 and then supplied to the AGC circuit 5 via the rotary transformer 4. This AGC
The reproduction signal from which the level fluctuation has been removed by the circuit 5 is equalized by the reproduction equalizer 6 according to the Nyquist first standard (zero ISI standard).

The signal equalized by the reproduction equalizer 6 is supplied to the positive terminal of the comparator 8 via the analog adder 7, and the negative terminal of the comparator 8 is grounded. In the comparator 8, the signal supplied to its positive terminal is discriminated into two values of "1" and "-1". Comparator 8
The binary identification data identified in (3) is derived as reproduction data at the output terminal 9 and is supplied to the low-pass filter 10. The low-pass filter 10 extracts low-frequency components from the binary identification data, and the low-frequency components are supplied to the analog adder 7 and added to the signal equalized by the reproduction equalizer 6.

Here, the analog adder 7, the comparator 8 and the low-pass filter 10 constitute a quantized feedback circuit 11, which operates as described above to reproduce a low frequency component. According to the one using the quantized feedback circuit 11 as the direct current reproducing circuit, the low frequency noise is not emphasized as compared with the case where the low frequency is emphasized by an amplifier or the like. Therefore, the magnetic recording / reproducing apparatus adopting so-called azimuth guard bandless recording. It is suitable as a DC regeneration circuit of

[0006]

By the way, recently, as the recording density has been increased, it has become difficult to obtain a sufficient S / N at the shortest recording wavelength. Therefore, a partial response equalization method that does not require the component of the shortest recording wavelength is drawing attention.

Partial response equalization is performed, for example, when the recorded data is "..010 ..."
・ "And" ・ ・ 010-10 ・ ・ "are equalization methods. Since the shortest recording wavelength component, and hence the Nyquist frequency component, becomes zero, it is discriminated compared to the conventional Nyquist first reference equalization. The S / N at points can be improved.
The method of equalizing “·· 0110 ··” when “·· 010 ··” is Class 1 partial response (P
R-I), and when "... 010 ..."
A method of equalization such as 010-10 ... "is called Class 4 partial response (PR-IV).

6 and 7 show a frequency spectrum and an eye pattern in Nyquist's first reference equalization, respectively. On the other hand, FIGS. 8 and 9 show the frequency spectrum and eye pattern in PR-I, and FIGS.
-Shows the frequency spectrum and eye pattern at IV. The horizontal axes of FIGS. 6, 8 and 10 are normalized frequencies (f / fb), where f is frequency and fb is bit frequency.

As described above, in the Nyquist's first standard equalization method, the identification data is binary of "1" and "-1", but in the PR-I and PR-IV partial response equalization methods, the identification data is identified. The data has three values of "1", "0", and "-1". Therefore, in the partial response equalization method that requires a low frequency component such as PR-1, there is a problem that the quantized feedback circuit 11 in the example of FIG. 5 cannot be used as it is as a DC reproducing circuit.

Therefore, the present invention provides a quantized feedback circuit capable of favorably reproducing the low-frequency component of a multilevel analog signal in which the low-frequency component is lost.

[0011]

According to another aspect of the present invention, there is provided a quantized feedback circuit which includes an analog adding means for adding a low frequency component to a multilevel analog signal in which the low frequency component is lost, and an analog adding means for the analog adding means. A multilevel level identifying means for identifying a multilevel level from the output signal, a multilevel analog signal restoring means for restoring a multilevel analog signal from the identification data of the multilevel level identifying means, and a restore by the multilevel analog signal restoring means And a filter means for extracting a low frequency component from the generated multilevel analog signal.

According to a second aspect of the present invention, in the quantizer circuit of the first aspect, the multivalued analog signal is a ternary analog signal, and the multivalued level identification means is composed of two comparators. The analog signal restoring means is composed of a differential amplifier to which the outputs of two comparators are supplied.

The quantization feedback circuit according to the invention of claim 3 is
In the invention of claim 2, the ternary analog signal is class 1
This is a signal after high-frequency equalization in the partial response ternary level detection method.

[0014]

According to the invention of claim 1, a multi-valued analog signal is restored from the multi-valued level identification data, a low frequency component is extracted from the restored multi-valued analog signal, and the extracted low frequency component is extracted. The low-frequency component is added to the lost multi-valued analog signal to reproduce the low-frequency component, and the quantization feedback circuit makes it possible to reproduce the low-frequency component of the multi-valued analog signal.

According to the invention of claim 2, the multi-valued analog signal is a ternary analog signal, and it is possible to discriminate a ternary level from the ternary analog signal with two comparators, and two It becomes possible to restore the ternary analog signal by the differential amplifier supplied with the output of the comparator.

In the invention of claim 3, the ternary analog signal is a signal after high-frequency equalization in the ternary level detection system of class 1 partial response, and the ternary level can be identified by two comparators. Further, it becomes possible to restore the ternary analog signal by the differential amplifier supplied with the outputs of the two comparators.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. In this example, the PR-I partial response equalization method is adopted. In FIG. 1, parts corresponding to those in FIG. 5 are designated by the same reference numerals, and detailed description thereof will be omitted.

In the figure, the reproduction signal from which the level fluctuation has been removed by the AGC circuit 5 is supplied to the class 1 partial response equalizer 12 and equalized. This equalizer 12 is
A Nyquist first similar to the reproduction equalizer 6 in the example of FIG.
The reference equalizer 13 includes a 1-bit cycle delay circuit 14, an analog adder 15, and a scaling circuit 16.

That is, the reproduced signal from which the level fluctuation has been removed by the AGC circuit 5 is supplied to the equalizer 13 and equalized according to the Nyquist first standard. Further, the output signal of the equalizer 13 is directly supplied to the analog adder 15, and the output signal thereof is delayed by one bit period in the delay circuit 14 and supplied to the analog adder 15. The signals are added and equalized to the PR-I standard. Further, the output signal of the analog adder 15 is supplied to the scaling circuit 16 to reduce its level to 1/2, and the output signal of the scaling circuit 16 is used as the output signal of the equalizer 12.

The reproduced signal (PR-
The I equalized signal) is supplied to the quantization feedback circuit 17. The quantization feedback circuit 17 is composed of an analog adder 18, comparators 19 and 20, an OR gate 21, a differential amplifier 22 and a low pass filter 23. That is, the output signal of the equalizer 12 is supplied to the positive terminal of the comparator 19 and the negative terminal of the comparator 20 via the analog adder 18 as a three-value equalized signal (three-value analog signal). The negative voltage terminal of the comparator 19 has a threshold voltage +
Eth is supplied, and the threshold voltage −Eth is supplied to the positive terminal of the comparator 20. Comparators 19, 20
Constitutes a ternary level identification means. Threshold voltage +
Eth and -Eth have the same absolute value and opposite polarities.

The output signal of the comparator 19 becomes "1" when the ternary equalization signal supplied to the positive terminal is higher than the threshold voltage + Eth, and otherwise becomes "0". On the other hand, the output signal of the comparator 20 is “1” when the ternary equalization signal supplied to the negative terminal is lower than the threshold voltage −Eth, and is “0” otherwise. In the partial response method, "0" of the ternary equalization signal is changed to "0".
Then, "1" and "-1" are determined as "1". for that reason,
The output signals of the comparators 19 and 20 are supplied to the OR gate 21 to be ORed, and the output signal of the OR gate 21 is derived to the output terminal 24 as reproduction data.

Further, the output signals of the comparators 19 and 20 are supplied to the positive side terminal and the negative side terminal of the differential amplifier 22 as the ternary analog signal restoring means, respectively.
As shown in FIG. 2, the differential amplifier 22 outputs "1" when the output signal of the comparator 19 is "1" and "-" when the output signal of the comparator 20 is "1".
1 "and the output signals of the comparators 19 and 20 are both" 0 ", a three-valued signal" 0 "is output.

The ternary analog signal restored by the differential amplifier 22 is supplied to the low pass filter 23 to extract the low frequency component. The low-pass component extracted by the low-pass filter 23 is supplied to the analog adder 18 and added to the output signal of the equalizer 12 to generate a three-value equalized signal (three-value analog signal).
Is formed.

As described above, in this example, the differential amplifier 22 restores the ternary analog signal from the ternary identification data output from the comparators 19 and 20, and the low-pass filter 23 is restored from the restored ternary analog signal. The low-frequency component is extracted by and the extracted low-frequency component is added to the output signal of the equalizer 12 in which the low-frequency component is lost, so that the low-frequency component is reproduced well. Therefore, according to this example, the quantization feedback circuit 17 can favorably reproduce the low-frequency component of the ternary analog signal.

Next, with reference to FIG. 3, a quantization feedback circuit for handling a four-valued analog signal will be described. The four-valued analog signal SAL4 in which the low frequency component is lost is supplied to the quantization feedback circuit 30. This quantization feedback circuit 30
Is composed of an analog adder 31, comparators 32 to 34, decoders 35 and 36, and a low pass filter 37. That is, the four-level analog signal SAL4 is supplied to the positive terminals of the comparators 32 to 34 via the analog adder 31. Threshold voltages Eth1, Eth2 and Eth3 (Eth1 <Eth2 <Eth3) are supplied to the negative terminals of the comparators 32, 33 and 34, respectively. The comparators 32 to 34 compose four-value level identification means.

The output signals of the comparators 32, 33 and 34 are "1" when the four-valued analog signals supplied to the positive terminals are higher than the threshold voltages Eth1, Eth2 and Eth3, and "0" otherwise. It will be. The output signals of the comparators 32 to 34 are respectively supplied to the decoder 35 and converted into 2-bit identification data, and this identification data is output to the output terminal 38 as reproduction data.

The 2-bit identification data output from the decoder 35 is supplied to the decoder 36 as a 4-level analog signal restoring means. The decoder 36 restores the four-valued analog signal according to the 2-bit identification data, and the restored four-valued analog signal is supplied to the low pass filter 37 to extract the low frequency component. The low frequency component extracted by the low pass filter 37 is supplied to the analog adder 31 and added to the four-valued analog signal SAL4.

Thus, in this example, the decoder 35
The decoder 36 restores a 4-valued analog signal from the 2-bit 4-valued identification data that is the output signal of the low-pass filter 37, and the low-pass filter 37 extracts a low-frequency component from the restored 4-valued analog signal. Since the component is added to the 4-value analog signal SAL4 in which the low frequency component is lost, the low frequency component is reproduced well. Therefore, according to this example, the quantization feedback circuit 30 can favorably reproduce the low-frequency component of the four-level analog signal.

Next, referring to FIG. 4, a quantization feedback circuit for handling a multi-valued analog signal will be described. The multilevel analog signal SALM in which the low frequency component is lost is supplied to the quantization feedback circuit 40. This quantization feedback circuit 40
Is an analog adder 41, an AD converter 42, a decoder 43, a DA converter 44, and a low-pass filter 4.
It is composed of 5. That is, the multilevel analog signal SALM
Is supplied to the AD converter 42 as the multi-level level identifying means via the analog adder 41.

The output signal of the AD converter 42 is supplied to the decoder 43, the reproduced data is synthesized, and the output terminal 46.
Be derived to. The decoder 43 includes, for example, a Viterbi decoder or the like. Further, the output signal of the AD converter 42 is supplied to the DA converter 44 which constitutes the multilevel analog signal restoring means. The DA converter 44 restores the multi-valued analog signal according to the output signal of the AD converter 42, and the restored multi-valued analog signal is supplied to the low-pass filter 45 to extract low-frequency components. The low-pass component extracted by the low-pass filter 45 is supplied to the analog adder 41 and added to the multilevel analog signal SALM.

As described above, in this example, the multi-level analog signal is restored by the DA converter 44 from the multi-level identification data which is the output signal of the AD converter 42, and the low-pass filter 45 lowers the restored multi-level analog signal. The low-frequency components are extracted, and the extracted low-frequency components are added to the multilevel analog signal SALM in which the low-frequency components are lost, so that the low-frequency components are reproduced well. Therefore, according to this example, the quantization feedback circuit 40 can favorably reproduce the low-frequency component of the multilevel analog signal.

[0032]

According to the first aspect of the present invention, a multi-valued analog signal is restored from the multi-valued level identification data, a low frequency component is extracted from the restored multi-valued analog signal, and the extracted low-frequency component is extracted. The low-frequency component is reproduced by adding the low-frequency component to the multivalued analog signal in which the low-frequency component is lost, and the low-frequency component of the multi-valued analog signal can be reproduced by the quantization feedback circuit.

According to the invention of claim 2, the multi-valued analog signal is a ternary analog signal, and it is possible to discriminate the ternary level from the ternary analog signal by two comparators. The ternary analog signal can be restored by the differential amplifier supplied with the output of the comparator.

According to the third aspect of the invention, the ternary analog signal is a signal after high-frequency equalization in the ternary level detection method of class 1 partial response, and the ternary level can be identified by two comparators. Also, a ternary analog signal can be restored by a differential amplifier supplied with the outputs of two comparators.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a quantization feedback circuit according to the present invention.

FIG. 2 is a diagram showing an operation of a differential amplifier.

FIG. 3 is a diagram showing another example of a quantization feedback circuit.

FIG. 4 is a diagram showing another example of a quantization feedback circuit.

FIG. 5 is a diagram showing a configuration of a reproducing system of the digital magnetic recording / reproducing apparatus.

FIG. 6 is a diagram showing a frequency spectrum of Nyquist's first reference equalization.

FIG. 7 is a diagram showing an Nyquist first reference equalization eye pattern.

FIG. 8 is a diagram showing a frequency spectrum of PR-I.

FIG. 9 is a diagram showing an eye pattern of PR-I.

FIG. 10 is a diagram showing a frequency spectrum of PR-IV.

FIG. 11 is a diagram showing an eye pattern of PR-IV.

[Explanation of symbols]

 1 Magnetic Tape 2 Magnetic Playback Head 4 Rotary Transformer 5 AGC Circuit 12 Class 1 Partial Response Equalizer 13 Nyquist First Reference Equalizer 14 Delay Circuit 15, 18, 31, 41 Analog Adder 16 Scaling Circuit 17, 30, 40 Quantization feedback circuit 19, 20, 32 to 34 Comparator 21 Or gate 22 Differential amplifier 23, 37, 45 Low pass filter 24, 38, 46 Output terminal 35, 36, 43 Decoder 42 AD converter 44 DA converter

Claims (3)

[Claims] 1. An analog adding means for adding a low-frequency component to a multi-valued analog signal in which a low-frequency component is lost, and a multi-value level identifying means for identifying a multi-valued level from an output signal of the analog adding means, Multi-valued analog signal restoration means for restoring the multi-valued analog signal from the identification data of the multi-valued level identification means, and filter means for extracting the low frequency component from the multi-valued analog signal restored by the multi-valued analog signal restoration means A quantized feedback circuit comprising: 2. The multi-valued analog signal is a three-valued analog signal, the multi-valued level identification means is composed of two comparators, and the multi-valued analog signal restoration means is the two-valued analog signal.
The quantized feedback circuit according to claim 1, wherein the quantized feedback circuit comprises a differential amplifier to which the outputs of the individual comparators are supplied. 3. The quantized feedback circuit according to claim 2, wherein the ternary analog signal is a signal after high-frequency equalization in a ternary level detection method of class 1 partial response.