The present invention generally relates to a data reproducing circuit for a memory system having a reading head, such as a magnetic disk memory system, a magnetic tape memory system, an optical memory system, etc., and reproducing analog signals read out from the head as digital reproduction signals, with a high accuracy.
A conventional data reproducing circuit for a magnetic disc device is designed to detect the position of a peak of a reproduction signal from a magnetic disk through a data sensing head and an amplitude thereof exceeding a predetermined slice level and to generate, on the basis of the detected position of peak and the detected amplitude, a rectangular-wave read (reproduction) signal which represents the original or correct signal with high fidelity. As is well known, the peak position deviates from its original peak position due to a correlation between the peak position of interest and its adjacent peak positions (magnitude of the time interval). From this point of view, it is required to provide for an equalizing circuit which corrects a shift of the peak position (peak shift). Further, the amplitude of the reproduction signal varies due to a change of the reproduction frequency. Thus, it is required to provide for an equalizing circuit which corrects the amplitude variation. Moreover, the equalizing circuit directed to correcting a peak shift has an optimum value which is different from that for the equalizing circuit directed to correcting an the amplitude variation. For this reason, it is required to determine an optimum equalizing character, taking into consideration the difference between the optimum values of the two different equalizing circuits.
Referring to FIG. 1, there is illustrated a conventional data reproducing circuit. The illustrated data reproducing circuit includes a data sensing head 10, which reads a recording medium (not shown) and generates a reproduction signal. A preamplifier 24 amplifies the reproduction signal from the head 10, and outputs an amplified reproduction signal. The amplified reproduction signal is pulled up to a power source voltage Vcc through a resistor 26, and is then supplied to a delay circuit 16-1 and an attenuator 18-1. An output from the delay circuit 16-1 is input to a non-inverting input terminal of a subtracter amplifier 20. An output from the attenuator 18-1 is input to an inverting input terminal of the subtracter amplifier 20, which subtracts the output supplied from the attenuator 18-1 from the output supplied from the delay amplifier 16-1, and outputs the result of this subtraction. The output from the subtracter amplifier 20 is pulled up to the power source voltage Vcc through a resistor 28, and is then input to a delay circuit 16-2 and an attenuator 18-2. An adder amplifier 22 adds an output from the delay circuit 16-2 and an output from the subtracter amplifier 18-2.
The illustrated data reproducing circuit has a first function of correcting a peak shift of the reproduction signal which occurs during reproduction and a second function of correcting an amplitude variation due to a change of the reproduction frequency. An optimum correction characteristic of the data reproducing circuit can be provided by adjusting the amount of attenuation in each of the attenuators 18-1 and 18-2.
As shown in FIG. 2, the reproduction signal supplied from the head 10 has negative edges 32 having amplitude components which have a polarity opposite to that of a main signal waveform 30 of the reproduction signal and which are located on both sides thereof. From this viewpoint, the attenuator 18-1 is adjusted so as to have a characteristic suitable for correcting the peak shift and amplitude variation of the main signal waveform 30, and the attenuator 18-2 is adjusted so as to have a characteristic suitable for correcting the peak shift and amplitude variation arising from the negative edges 32.
It is noted that generally the optimum values to be provided for the attenuators 18-1 and 18-2 for correcting the peak shift of the main signal waveform 30 are not equal to those to be provided for the attenuators 18-1 and 18-2 for correcting the amplitude variation thereof. For this reason, it is impossible to provide each of the attenuators 18-1 and 18-2 with an optimum value suitable for correcting both the peak shift and amplitude variation. For this reason, the data reproducing circuit shown in FIG. 1 cannot correct both the peak shift and the amplitude variation effectively and cannot reproduce the original signal with a high accuracy.
The above discussion holds true for another conventional data reproducing circuit as shown in FIG. 3, in which those parts which are the same as those shown in FIG. 1 are given the same reference numerals. The output from the preamplifier 24 is input to the delay circuit 16-1 and the attenuator 18-2. The output from the delay circuit 16-1 is input to the delay circuit 16-2 and the attenuator 18-1. The output from the delay circuit 16-2 is applied to a first non-inverting input terminal of an adder/subtracter amplifier 20'. The outputs from the attenuators 18-1 and 18-2 are applied to an inverting input terminal and and a second non-inverting input terminal of the adder/subtracter amplifier 20', respectively. The adder/subtracter amplifier 20' subtracts the output supplied from the delay circuit 16-2 from the output supplied from the attenuator 18-1, and adds the output from the attenuator 18-2 to the result of subtraction.
The arrangement shown in FIG. 3 has the same problem as the arrangement shown in FIG. 1. That is, the optimum values to be provided for the attenuators 18-1 and 18-2 for correcting the peak shift of the main signal waveform 30 are not equal to those to be provided for the attenuators 18-1 and 18-2 for correcting the amplitude variation. Thus, it is impossible to provide each of the attenuators 18-1 and 18-2 with an optimum value suitable for correcting both the peak shift and amplitude variation. For this reason, the data reproducing circuit shown in FIG. 3 cannot correct both the peak shift and the amplitude variation effectively and cannot reproduce the original signal with a high accuracy.