JP2512021B2 - Digital signal recording / reproducing device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a digital video tape recorder (DVT).
R) and other digital signal recording / reproducing devices.

2. Description of the Related Art Since the digital signal recording / reproducing apparatus of the present invention uses multilevel quadrature amplitude modulation (QAM) in which the carrier wave is suppressed, the carrier wave required for synchronous detection must be reproduced. As a method of reproducing the carrier wave, there are a multiplication method, an inverse modulation method, a Costas method and the like.

(For example, "Digital Radio Communication", Masayoshi Murotani Sangyo Tosho (Showa 60), pages 40-48).

Also, a clock signal is required when converting a multi-valued signal into a digital signal, and there is a method for extracting edge information with a bandpass filter or the like and applying a phase locked loop (PLL) to the reproduction of the clock signal.

However, in the configuration using the carrier recovery circuit and the clock recovery circuit as described above, the hardware is complicated, and the recovered carrier wave and the clock have a plurality of phase shift stable points. , The phase information must be obtained by a method such as differential encoding in reproducing the carrier wave, which causes deterioration of S / N.

In view of the above problems, the present invention provides a digital signal recording / reproducing apparatus capable of reproducing a carrier wave and a clock signal having a phase reference with a simple structure.

Means for Solving the Problems In order to solve the above problems, a digital signal recording / reproducing apparatus of the present invention comprises a first frequency conversion circuit for generating a carrier wave and a pilot signal with reference to an input clock signal frequency. , Provided with an adder for adding a pilot signal to a modulation signal output from a multi-valued quadrature amplitude modulation (QAM) circuit, and a second frequency conversion circuit for reproducing a clock signal and a carrier wave from the pilot signal on the demodulation side Is.

Operation The present invention can simplify the carrier recovery circuit and the clock recovery circuit by the above-mentioned configuration. Moreover, since the phase reference is stored in the pilot signal, there is no need for means for newly providing the phase reference, and there is no deterioration in S / N or reduction in band utilization efficiency.

Embodiment A digital signal recording / reproducing apparatus according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a main configuration of a digital signal recording / reproducing apparatus according to an embodiment of the present invention. The n-bit digital signal is input to the input terminal 1. The digital signal input to the input terminal 1 is input to the multivalued circuits 2 and 4, respectively. In the multivalued circuits 2 and 4,
The input bit number n is converted into a 2 ^n- valued multilevel signal. The outputs of the multivalued circuits 2 and 4 are input to the low pass filters 3 and 5. Low pass filters 3 and 5
Has a cosine roll-off characteristic.

On the other hand, the clock signal input from the clock signal input terminal 7 is input to the frequency conversion circuit 8 which is the first frequency conversion circuit. A configuration example of the frequency conversion circuit 8 is shown in FIG. The clock signal input to input terminal 23 is
It is divided into 1 / N by 101 and is output from the output terminal 25 as a pilot signal through the bandpass filter 104. The output from the frequency divider 101 is input to the frequency multiplier 102 and is multiplied by M. The output from the multiplier 102 is output from the output terminal 24 as a carrier wave through the bandpass filter 103.

_{f P = f CLK / N f} C = M · f p = M / N · f CLK However, M, N is an arbitrary constant, f _P is the pilot signal frequency, f _CLK is the clock signal frequency, f _C is the carrier frequency And Further, in order to prevent the pilot signal from entering the band of the modulation signal, the relationship between the carrier frequency f _C , the base band W of the multilevel signal and the pilot signal frequency f _P needs to be f _C −W> f _P. There is.

The outputs of the low-pass filters 3 and 5 are input to a quadrature two-phase modulator 6 and are quadrature two-phase modulated by the carrier wave output from the frequency conversion circuit 8. The output from the quadrature two-phase modulator 6 is input to the adder 9 and added to the pilot signal from the frequency conversion circuit 8. The output signal from the adder 9 passes through the recording head 10 and is recorded on the magnetic recording medium 11.

The signal recorded on the magnetic recording medium 11 is taken out by the reproducing head 12 and inputted to the equalizer circuit 13 having no group delay. The equalizer circuit 13 improves frequency characteristics deteriorated by magnetic recording and reproduction.

On the other hand, the output from the reproducing head 12 is the bandpass filter 19
Is input to the frequency conversion circuit 20 which is the second frequency conversion circuit. An example of the structure of the frequency conversion circuit 20 is shown in FIG. Input terminal
The pilot signal input to 26 is input to the comparator 105 and shaped into a pulse waveform. The output of the comparator 105 is input to the multiplier 108, multiplied by N, and output from the output terminal 28 as a clock signal. The output of the comparator 105 is input to the multiplier 106, multiplied by M, passed through the bandpass filter 107, and output from the output terminal 27 as a carrier wave.

f _CLK = N · f _P f _C = M · f _P However, M and N are arbitrary constants, f _CLK is a clock signal frequency, f _P is a pilot signal frequency, and f _C is a carrier wave frequency. At this time, it is necessary to adjust the phase relationship with the pilot signal to be the same as the input / output relationship in the frequency conversion circuit 8 on the modulation side.

The output of the equalizer circuit 13 is input to the synchronous detection circuit 14 and is synchronously detected by the carrier wave output from the frequency conversion circuit 20. The output signal from the synchronous detection circuit 14 is input to the low pass filters 15 and 17, and only the original baseband component is extracted. The output signals of the low-pass filters 15 and 17 are input to the analog-digital converters 16 and 18, and become a n-bit digital signal by the clock signal output from the frequency conversion circuit 20 and output from the output terminal 21. At the same time, a clock signal is output from the output terminal 22.

As described above, according to the present embodiment, the frequency conversion circuit 8 for generating the carrier wave and the pilot signal by the clock signal, and the adder 9 for adding the pilot signal to the modulation signal.
By providing the frequency conversion circuit 20 which reproduces the carrier wave and the clock signal by the pilot signal, it is possible to reproduce the carrier wave and the clock signal having the phase reference with a simple circuit configuration.

In the present embodiment, the carrier wave regenerating circuit such as the Costas method and the clock regenerating circuit according to another method are not used, but the reproducibility can be improved by using them together.

Further, in the configuration example of the frequency conversion circuit 8, f _C = M ·
Although f _P is used, f _C = M / N · f _CLK may be directly multiplied by M / N from the clock signal to form a carrier.

In addition, in this embodiment. I mentioned QAM, but P
Similar effects can be obtained in other modulation methods such as SK and FSK.

As described above, according to the present invention, the first frequency conversion circuit for generating the carrier wave and the pilot signal, the adder for adding the pilot signal to the modulation signal, and the carrier wave and the clock signal are reproduced. By providing the second frequency conversion circuit, it is possible to easily reproduce the carrier wave having the phase reference and the clock signal, and to perform the synchronous detection without degrading the S / N. Extremely useful.

[Brief description of drawings]

FIG. 1 is a block diagram showing a digital signal recording / reproducing apparatus according to an embodiment of the present invention, FIG. 2 is a block diagram showing a configuration of a first frequency conversion circuit in the embodiment of the present invention, and FIG. 3 is a block diagram showing a configuration of a second frequency conversion circuit in the embodiment of FIG. 2 ... Multivalued circuit, 6 ... Quadrature two-phase modulator, 8 ... Frequency conversion circuit, 9 ... Adder, 13 ... Equalizer circuit, 14
...... Synchronous detection circuit, 16 …… Analog-digital converter, 20 …… Frequency conversion circuit, 101 …… divider, 102 …… multiplier, 105 …… comparator, 106 …… multiplier, 108 ……
Multiplier.

Claims (3)

(57) [Claims] 1. A multi-valued quadrature amplitude modulation circuit for recording and reproducing a digital signal, which multi-values an input digital signal in the amplitude direction and performs quadrature two-phase modulation.
A first frequency conversion circuit for generating a carrier wave and a pilot signal from an input clock signal, an adder for adding the modulated signal and the pilot signal, and an output signal from the adder for a magnetic recording medium. A magnetic recording / reproducing section for recording and reproducing, a synchronous detection circuit for converting the reproduced signal from the magnetic recording / reproducing section undergoing the above-mentioned modulation into an original digital signal, a pilot signal extracted from the reproduced signal, and a carrier wave and a clock. A digital signal recording / reproducing apparatus comprising a second frequency conversion circuit for reproducing a signal. 2. A first frequency conversion circuit for generating a carrier wave and a pilot signal from an input clock signal,
A frequency divider in which the frequency f _{CLK of the} clock signal and the frequency f _{P of the} pilot signal are f _P = f _CLK / N (where N is an arbitrary constant), and band pass that allows only the fundamental frequency component of the pilot signal to pass. Only a filter, a multiplier that makes the frequency f _P and carrier frequency f _{C of the} pilot signal output from the frequency divider f _C = M · f _P (where M is an arbitrary constant), and only the carrier frequency component A digital signal recording / reproducing apparatus according to claim 1, further comprising a band pass filter for passing the signal. 3. A second frequency conversion circuit for recovering a carrier wave and a clock signal from a pilot signal, and a comparator for shaping the input pilot signal into a pulse waveform,
The frequency f _{P of the} pilot signal output from the comparator and the carrier frequency f _C are such that f _C = M · f _P (where M is an arbitrary constant), and a carrier frequency component from the output of the multiplier. a band pass filter which passes only frequency f _CLK of the frequency f _P and the clock signal of the pilot signal output from the _{comparator, f CLK = N · f P} ( However, N is the arbitrary constant) multiplier a A digital signal recording / reproducing apparatus as set forth in claim 1, wherein: