SU953659A1 - Device for digital magnetic recording apparatus clocking - Google Patents

Description

The circuit of the invention is to improve the synchronization accuracy of a digital magnetic recording apparatus.

The circuit is achieved in that a synchronization device for a digital recording channel of the channel, containing a linear voltage generator connected in series, a sampling and storage circuit, a low-pass filter, a voltage controlled oscillator, is inserted into a compensation unit connected to the input and output of the device, a delay circuit for one cycle, connected to the output of the sampling and storage circuit and an adder, connected by inputs to the output of the delay section and output of the computing unit, and the output to the low-pass filter. FIG. 1 shows a block diagram of the proposed device; in fig. 2 is a timing diagram of its operation for a three-frequency recording method; in fig. 3 - block diagram of the compensation block. The device comprises a linear voltage generator 1, a sampling and storage circuit 2, a delay 3 circuit for one cycle of a compensation unit 4, an adder 5, a low-pass filter 6 and a voltage-controlled generator 7. With a high recording density, intersymbol distortions begin to play a significant role, leading to the mixing of the signals from the reproduced signal before the need of carrier magnetization. Due to the fact that the responses of the magnetic recording channel to each carrier magnetization dip attenuate, only two adjacent responses to the left and right of this peak have a fundamental effect on the displacement. The effect of more distant cells is practically unaffected. Therefore, the offset is determined by a combination of two adjacent characters of the recorded signal. The magnitude and direction of the bias for each combination of symbols at a given level and distortion is determined experimentally or by simulating on an electronic computer the influence of these distortions in the magnetic recording channel. Suppose that a three-frequency recording method is used to record information on magnetic media. At the same time (Fig. 2C |) Sigal records; b - reproducible signal; 6- pulses generated by the peaks of the reproduced signal; 1 signal taken from the output of the linear voltage generator 1; e is the voltage at the output of the sampling and storage circuit 2; tightly at the output of the 3 delay circuit;

3 - compensating voltage taken from the output of compensation block 4.

Compensation block 4 for — the case of a three-frequency recording method may be selected, for example, as shown in FIG. 3, de marked: 8 - the first input of the compensation unit; 9 - the second input of the compensation block; 1O is a two-digit counter with a throw; 11-14- t) - tritter; 15 0 - logic circuits AND 21-26 electronic keys; 27 - adder; 28 output block compensation. The device works as follows. Short pulses (Fig. 2b), generated from the peaks of the reproduced signal, are fed to the input of the entire device. As a result of the imposition of individual pulsed hops, the pulses 6 are shifted relative to the recording signal drops. FIG. 2, this offset for one of the pulses is denoted by d-t. The signal taken from the output of the generator controlled by voltage 7 triggers the linear voltage generator 1, which forms the sawtooth voltage b. At the moment of arrival of each pulse to the input of the sampling circuit AND storage 2, a voltage coming from the output of the linear voltage generator 1 is recorded at its output. The voltage from the output of circuit 2 is proportional to the magnitude of the phase error at the time of sampling. The signal delayed by one clock from the output of circuit 2 for sampling and storage is fed to the input of adder 5. In block 4, by comparing the duration of the time interval T with the clock interval, the value of the recorded symbol is decrypted and stored. Block 4 also stores the value of the previous T-character. Thus, in block 4, codes are stored corresponding to two adjacent characters. The magnitude and sign of the phase error occurring in a digital magnetic recording channel for each combination of two adjacent pulses is known a priori. At the output of block 4, a voltage is generated that is the opposite of the phase error voltage for a given combination of symbols. After the summation of the signals (Fig. 2 and c) in the adder 5, the effect of intersymbol distortion is practically neutralized. The signal from the output of the adder 5 through the low-pass filter 6 acts on the generator 7 controlled voltage such as to reduce the timing error.

The compensation unit (Fig. 3) works as follows.

The short pulses generated by the peaks of the reproduced signal, arriving at input 8, overwrite the states of the trigger 11-14 and set the counter 10 to the initial state. The second input 9 of block 4 is supplied with sync pulses. In the counter 10 forms with a code, Yu corresponding to the next played symbol. With each pulse of 8, the code is sequentially rewritten by D triggers 11, 13, and 12, 14. Thus, 15 codes of two adjacent characters are stored in N triggers. The states of D-triggers are deciphered by logic circuits AND 15-20. For each combination of symbols, excluding combinations of identical symbols, the output of one of the circuits AND appears a logical signal, opening the corresponding key. The compensating voltage through this key and the adder 27 passes to the output of the compensation unit 28. The magnitude and sign of the compensating voltages J - (J connected to the keys 21 26 are determined experimentally or inserted by simulating the effect of intersymbol distortions in the digital magnetic recording channel. The matching of the compensating voltages to the combinations of symbols is shown in the table. For the first three, combinations of the same characters do not shift peaks, so there is no need for compensation.

Claims (2)

When testing the device, the densities of the probability of a phase error were obtained. Comparison of the experimental results with similar characteristics of the known showed that the phase error dispersion is halved. This allows for improved timing accuracy. The invention of a clock synchronization device of a digital magnetic recording apparatus, comprising a linear-voltage generator, a sampling and storage circuit, a lower filter often and a voltage-controlled oscillator, characterized in that, in order to improve synchronization accuracy, a compensation unit connected to the input and output of the device, a delay circuit for one cycle connected to the output of the sampling and storage circuit, and an adder connected to the output of the delay circuit and the output of the block mpensatsii, and output - with a low pass filter Istochtpsh information rin Tide into account during examination 1. Problems magnetic recording.. Under the unit Korolkova V.G., M., 1975, p. 929. 2. US patent M 3689903, cl: cl. Q 11 B 5/44, 1972 (prototype). FIG. I