JPS63237248A - Pilot signal generation circuit - Google Patents

Abstract

PURPOSE:To generate four kinds of pilot signals and to simplify the constitution of a device so as to make it into an IC by selecting respective value which are stored in a table ROM in accordance with the output values of a programmable counter and D/A converting and outputting them and making the output level variable in accordance with the output value of the programmable counter. CONSTITUTION:Digital signals from a data bus are inputted to the programmable counter 12 and the table ROM13 through a latch 11, and the counter 12 counts digital values, which are given to the ROM13 as address values. Outputs from the ROM13 are inputted to a latch 14, and are written by the output signals of an NOR gate 144. The output levels of the ROM13 are selected in accordance with the values which the counter 12 counts and the D/A converter by a multiplier 15 and analogue switches 16-19 are controlled. The level of the D/A converter is varied in accordance with the outputs of the counter 12, and the pilot signals of staircase waves are outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a pilot signal generation circuit that can be used in a recording device, particularly a magnetic recording device that performs tracking control using a pilot signal.

' Conventional technology In recent years, magnetic recording and reproducing devices (hereinafter referred to as VTRs) have been promoted to higher density recording magnetization trajectories (hereinafter referred to as tracks).
The width of this trend is becoming narrower. Ideally, tracks should be recorded on a magnetic tape in a straight line, but in reality, tracks are recorded with a unique curvature for each VTR due to variations in mechanical precision. For this reason, when performing compatible playback in which a magnetic tape recorded on one VTR is played back on another VTR, control using conventional control signals does not allow both VTRs to
It is not possible to correct the inherent bending difference between TRs, and the reproduced image quality deteriorates accordingly. This problem is caused by a narrow track width (which is obviously a big problem).

In order to solve this problem, it is sufficient to obtain a tracking error signal corresponding to the track bending by some method, and to displace the rotary head in the direction of the rotation axis in accordance with the error signal.

A well-known method for displacing the rotary head in the direction of the rotation axis is a method using an electro-mechanical transducer composed of a piezoelectric element.

A method of obtaining a tracking error signal corresponding to track bending includes a method of using a pilot signal for tracking control (hereinafter simply referred to as a pilot signal). Since this method is well known as a control method for an 8 mm VTR, a brief outline thereof will be explained here.

Figure 4 shows the magnetization locus where the pilot signal was recorded.
A1. Bl, A2. B2. . . . is a magnetization locus recorded by the A head and the B head in which a video signal for one field is recorded as one track. f1 to f4 are four types of pilot signals, which are cyclically switched for each field and recorded while being superimposed on the video signal. The frequency of each pilot signal is 1 horizontal opening signal frequency f
When H, as shown in Table 1, approximately 6.5 fH to 10
．． The frequency is set to 5fH.

During playback, the pilot signals recorded on both adjacent tracks located before and after the main recording track scanned by the head are played back by a head wider than the recording track pitch, or as a crosstalk signal, and the pilot signals recorded on both adjacent tracks are The control system is configured so that it becomes stable at the point where the levels of the pilot signals reproduced from the tracks are equal. With this configuration, the head can perform reproduction scanning while on-tracking the main scanning track.

In order to obtain a single common control signal using four types of pilot signals f1 to f4, generally, as shown in FIG. A multiplexer 55 for selective output was required to form a single pilot signal 56.

FIG. 6 is a block diagram of a reproducing circuit for obtaining a tracking error signal using four types of pilot signals. In the figure, a reproduced RF signal, which is a combination of a video signal and a pilot signal, is input from a terminal 61. The circuit 62 is a low-pass filter, and separates and extracts only the pilot signal from the reproduced RF signal. The pilot signal obtained at this time is a composite signal of the pilot signals recorded on the main scanning track and both adjacent tracks.

The circuit 63 is a balanced modulation circuit, and the reference signal supplied from the terminal 64 is a pilot signal having the same frequency as the pilot signal recorded on the main scanning track. For example, in FIG. 4, when the head scans the track A2 for reproduction, the input signal to the balanced modulation circuit 63 is f2.
゜f3. f4, and the reference signal supplied from terminal 64 is f3. Therefore, the output signal of the balanced modulation circuit 63 is f
2. f3. The sum and difference signals of each signal of f4 and the signal of f3 are output. The circuit 65 and the circuit 66 are tuned amplifier circuits, the circuit 65 is tuned to the fH signal, and the circuit 66 is tuned to the fH signal.
f) Tunes into the signal of (. Circuits 67 and 68 are detection rectifier circuits, and circuit 69 is a level comparison circuit. Therefore,
Each pilot signal taken out as a crosstalk signal from both adjacent tracks is separated and taken out as a difference signal from the pilot signal recorded on the main scanning track, and then level comparison circuits 6 and 9 compare the pilot signals. A signal corresponding to the level difference is taken out to the terminal 60. The signal output to the terminal 60 includes information on the amount and direction of track deviation of the head, and therefore can be used as a tracking error signal.

The above is an overview of the method for obtaining a tracking error signal using four types of pilot signals.

Methods for accurately obtaining each of the pilot signals f1 to f4 shown in Table 1 include, firstly, a method using four types of crystal oscillation circuits, and secondly, a method using one reference oscillation circuit with a common multiple. A method of creating four types of pilot signals using a frequency dividing circuit and a method of creating four types of pilot signals, for example,
There is a method using a ternary staircase wave shown in the above publication.

The method of biasing the first four types of crystal oscillation circuits is disadvantageous in that it is expensive.

The method of providing one reference oscillation circuit with the second common multiple and creating four types of pilot signals with a frequency dividing circuit is to This signal is useful in that it can also be used as a reference signal. Then, the value should be selected as 378fH, and at this time, the same signal should be set to 1158.1150. l/
If the frequency is divided by 36°1/40, signals f1 to f4 shown in Table 1 can be obtained. The pilot signal obtained by frequency division is a rectangular wave and contains harmonic components, so if it is recorded and played back as it is along with the video signal, the harmonic components of the pilot signal will be lost to the video signal, especially if it has been low frequency converted. The color signal becomes a noise signal.

The influence of the harmonic components of the pilot signal on the color signal is such that the S/N ratio of the reproduced color signal is, for example, 40d.
Assuming that B or more is required, the recording current 1 pn of the n-th harmonic of the pilot signal is I p n /I c ≦-40d B ・- with respect to the recording current 1 c of the color signal.
...It is necessary to do (1).

On the other hand, the recording current tp+ of the fundamental wave of the pilot signal is 8
@! Ipl/Ic=-14dB according to AvTR standard
±2 dB ・−・・−(2). Therefore, the harmonic level with respect to the fundamental wave of the pilot signal is the value obtained by subtracting the stricter condition of equation (2) from equation (1): Ipn/ip+ ≦-28d B ......-
(3) must be satisfied.

One way to attenuate the harmonic components of the pilot signal is to perform D/A conversion. However, it has the disadvantage of requiring a highly accurate resistor to perform D/A conversion, and
When four types of pilot signals are handled by one D/A conversion circuit, a common number of bits that divides the half cycle of each pilot signal into an integer fraction cannot be found. This is 1. D/
The positive half period and negative half period of the A-converted pilot signal are different, and even harmonics are generated. Therefore, in order to sufficiently attenuate the level of even harmonics, it is necessary to select a large number of bits, which is not practical in terms of cost. Although there is a method of using a high-order low-pass filter to attenuate harmonic components, it cannot be said that sufficient attenuation can be achieved even if a third-order low-pass filter having a corner frequency of 200 KHz is used.

3 shown in the third Japanese Patent Application Laid-Open No. 1982-19224
The method using a value staircase wave has a circuit configuration shown in FIG. 7, and the waveforms of each part are shown in FIG.

In FIG. 7, a signal of 378 fH is supplied from the terminal 71. Circuit 72 is a programmable counter,
The output signal a generates a pulse by counting (11+12) 378fH.

This signal a generates pulses at a period of (11+12) as shown in FIG. On the other hand, the output signal S of the programmable counter 72 generates a pulse when 378fH is counted 11 times.

Therefore, as shown in FIG. 8, the period from signal a to b is 11. The circuit 73 is a reset set flip-flop (R3-F, F,), which is set by the signal a and reset by the signal a, and outputs the signal C. The circuit 74 is a toggle flip-flop (T-F,F,) and outputs a signal d. Circuits 75 and 76 are AND circuits, and R8
-F, F.

AND outputs e and f of the Q output of 73 and the Q and OK signals of T-F, F, -74 are output. 77 and 78 are analog switches, which are closed when the signals e and f are at high level, and open when the signals are at low level. One side of the switch is connected to the power supply voltage and ground side respectively, and switches 77 and 78 and resistor R1
, R2, and R3 are set so that when only switch 77 is on, the level is high, when only switch 78 is on, it is low level, and when both switches 77 and 78 are off, it is set to middle level. can make waves. In order to obtain four types of pilot signals, the frequency division ratio (11
and 11+12).

With the ternary staircase wave produced by this device, an attenuation amount that satisfies the conditions as shown in Table 2 can be obtained, but it cannot be said that there is sufficient margin, and a high-order low-pass filter is required.

Table 2 Problems to be Solved by the Invention The conventional method requires a high-order low-pass filter to sufficiently attenuate the harmonic components of the pilot signal, and also requires a D/A converter with a large number of bits. It had the drawback of trying to

The present invention provides a concrete and simple circuit configuration for creating a staircase wave signal.

Means for Solving the Problems In order to solve the above problems, the present invention includes a programmable counter, a table ROM, and a D/A converter,
Select each value stored in the table ROM according to the output value of the programmable counter and output it through the D/A converter, and set the output level of the D/A converter according to the output value of the programmable counter. variable so that a predetermined staircase wave signal is output.

Furthermore, in order to switch between the four types of pilot signals f1 to f4, two bits for switching the block in which each signal output data of f1 to f4 is stored in the table ROM and output data to the programmable counter are required. By giving a frequency division ratio corresponding to any one of f1 to f4, the output signal can be switched.

According to the present invention, it is possible to implement a staircase wave signal circuit with ±4 steps in an IC to obtain a pilot signal in which the values of the third, fifth, and seventh harmonic components are sufficiently attenuated.
A staircase wave signal of ±4 steps can now be used for R tracking control.

Example FIG. 1 is a block diagram showing an embodiment of the present invention.

There are two ways to store the data of the staircase wave signal of ±4 steps in the table ROM.
Store the level switching data of the staircase wave signal in the OM (
It is a device. In the figure, 11 is a latch, 12 is a programmable counter, and 13 is a table ROM.
, 14 is a latch, and 15 is a multiplexer (
MPX), and 16 to 19 are analog switches.

Taking fl as an example, this device applies the output of a programmable counter 12 that counts while dividing a reference signal (378fH) to the frequency division ratio of fl to a table ROM 13 as an address, and the output state is determined by the programmable counter 12. The count value “+1 at O-”
level (analog switch 19 is on, analog switch 16°17.18 is off),
The reference signal is counted, and when the count value reaches 4", data is output from the table ROM 13 to turn off the analog switches 16, 17, and 19 of the D/A converter, and turn on the analog switch 18. The count continues, and when the count value reaches 6", the analog switch 16°18.19 is turned off from the table ROM13, and the analog switch 1 is turned off.
It outputs the data that turns on 7 and switches to the +3 level. This device creates a staircase wave signal of fl by repeating such operations. In the figure, the latch 11 is f1
2 bits of selection data of any of f4 to 6 bits of frequency division ratio data are stored (prepared for this purpose), and f1 to f4 can be switched by rewriting this data. , table ROM13
A data signal 141 is prepared to store the switching data of the D/A converter output from the latch, and indicates whether or not the output data of the table ROM 13 for switching the D/A converter is stored in this latch. The falling edge of the output signal 143 of the N0R 144 between
When the signal 141 is at "L" level and the reference signal 142 falls), the output of the table ROM 13 becomes latch 1.
Written to 4. MPX15 has a positive half cycle (+1 to +4 to +1) with 1/2vdd as the center (level O)
It is used to change the setting of the potential corresponding to each switch in order to switch between the negative half cycle (-1 to -4 to -1), and when outputting the positive half cycle, the negative half cycle is output to the power supply side. When outputting, set it to the ground side (GND). This M
By using PX15, it is possible to reduce the number of resistors (and reduce the number of bits of output data of table ROM 13).By turning on one of the analog switches 16 to 19, It is possible to output the level corresponding to each.

This device has the problem that the potential corresponding to each analog switch changes between the positive half cycle and the negative half cycle, so it takes time for the potential to stabilize, and the waveform of the staircase wave signal becomes dull. However, harmonics are sufficiently attenuated.

With the above device, a staircase wave signal of ±4 steps can be created using the table ROM. Next, a second example will be described.

The second device is a device that stores, as data, a count value at which the level of the staircase wave signal should be switched next in a table ROM, and has a circuit configuration shown in FIG. In the figure, 21 is a latch, 22 is a programmable counter, 23 is a comparator, 24 is a table ROM, 25 is a counter, 27 is a decoder, and 280 to 287 are analog switches. 2
30 is the output data of the table ROM 24, 231
is the output data of the programmable counter 22, and 2
6 is a pulse output from the comparator 23 when the data 230 and the data 231 are equal.

This device will be explained by taking fl as an example. When a frequency division ratio is given, the programmable counter 22 counts while dividing the frequency of the reference signal 378fH according to the division ratio. Now, when the output of the programmable counter 22 is 0'', the output of the counter 25 is also 0'', and the staircase wave signal is -4
When outputting the level of (only analog switch 287 is on, other analog switches are off), table R
It is assumed that the OM 24 is outputting a count value "9" up to the next output level of -3. The programmable counter 22 counts the reference signal and when the count value reaches 9'', the comparator 23 determines that the data 230 and 231 match and outputs the pulse 26.
6 is counted by the counter 25, and the count value becomes "1". The decoder 27 switches the analog switches 280 to 287 based on the output of the counter 25 (only the analog switch 286 is turned on, and the other analog switches are turned off), thereby changing the staircase wave signal from the level of -4 to the level of -3. Further, due to the change in the count value of the counter 25, the address value given to the table ROM 24 changes, and the data output of the table ROM 24 is switched to the count value .degree. 13'' at the -2 level of the staircase wave signal to be output next. In this way, the table ROM 24 outputs the count value to be switched next, and when the programmable counter 22 reaches that value, the value of the counter 25 is increased, and the level of the staircase wave signal is switched according to the change in the value of the counter 25. The method is to output the count value of the next level in the table ROM 24.As in the case of the first device, the latch 21 receives 2 bits of selection data of fl to f4 and 6 bits of its division ratio data. Prepared for memorization.Analog switch 28
0 to 287 output a level of +4 when only the analog switch 280 is turned on, and a level of +3 when only the analog switch 281 is turned on. It can output levels compatible with analog switches.

FIG. 3 is a waveform diagram of a staircase wave signal of ±4 steps,
This waveform is obtained with the timing, level and count number in Table 3.

(Margin below) Table 3 In addition, by using a staircase wave signal of ±4 steps, f1 to f4
The harmonic components of each pilot signal have values as shown in Table 4, and the harmonic components can be further attenuated to a value with sufficient margin by using a first-order low-pass filter around the corner frequency of 300 KHz.

Table 4 Therefore, by creating a staircase wave signal of ±4 steps as shown in Figure 3, which increases and decreases at a constant equal level with the predetermined count value shown in Table 3, the 3rd, 5th, and 7th order It is possible to obtain a pilot signal in which the value of each harmonic component of The wave can be attenuated to a necessary and sufficient value, and since it is a staircase wave of ±4 steps that changes at the same level, the D/A converter does not require a large number of bits.

Therefore, this ±44 step wave signal can be used as a pilot signal for VTR tracking control.

This device has more resistors than the first device, but since there is no need to switch the potential, the problem of rounding of the staircase wave signal waveform when switching the level is largely solved. Furthermore, in the first embodiment, the ROM capacity of the table ROM is (
The second embodiment requires only a minimum of 16x4x6 bits, compared to a minimum of 58+50+36+40)x6 bits.

According to the devices shown in these first and second embodiments, when creating a staircase wave signal of ±4 steps, the switching data of the D/A converter or each level can be adjusted. Processing and management of count value data can now be performed using only the table ROM without relying on peripheral parts other than the staircase wave signal generator, and the peripheral parts only need to manage switching of f1 to f4. When configuring the control system with a microcomputer, the burden on the software is light (by using a table ROM, it is possible to create four types of staircase wave signals with one circuit, and this circuit configuration Then, there is no need for a highly accurate D/A converter,
A switchable D/A converter as shown in Figs. 1 and 2 is sufficient, and there is no need for a conventional high-order filter, and the corner frequency is 300 K Hr, which is about 1 There are three effects that the following rough filter is sufficient.

In addition, the circuit configuration is simple and does not include inductance or capacitance components, making it suitable for IC implementation.In addition, it is suitable for use not only with pilot signals for tracking control of VTRs, but also when different frequencies or a large number of steps are required. In case,
There is an advantage that a signal free of harmonics can be created by changing the original signal, changing the contents of the table ROM and the number of bits, and changing the D/A converter.

Effects of the Invention According to the present invention, when creating four types of pilot signals, it is possible to obtain a pilot signal that is suitable for IC implementation due to its simple circuit configuration, and in which harmonic components are attenuated to a sufficient value. There is an effect that it can be done.

[Brief explanation of the drawing]

1 and 2 are block diagrams showing an embodiment of a four-frequency staircase signal generation circuit according to the present invention, FIG. 3 is a waveform diagram of the staircase signal used in the present invention, and FIG. 4 is a tracking pilot. FIG. 5 is a block diagram showing a conventional example; FIG. 6 is a block diagram showing a reproducing circuit of a four-frequency tracking control system; FIG. FIG. 8 is a circuit diagram for generating a conventional ternary staircase wave signal, and is a diagram showing waveforms at various parts in FIG. 7. 11.14...Latch, 12...Programmable counter, 13...Table ROM
, 15...Multiplexer, 16-19...
...Analog switch. Name of agent: Patent attorney Toshio Nakao and one other person Figure 2 Figure 3 Figure 4 \-ノ \-/ \1ノ \, ノ+H3Fh 4
H3rs Figure 5 Figure 6 Figure 8

Claims (1)

[Claims] Programmable counter, table ROM and D/A
a converter, selects each value stored in the table ROM according to the output value of the programmable counter and outputs it through the D/A converter, and converts the output level of the D/A converter into the output level of the programmable counter. A pilot signal generating device that outputs a staircase wave signal that varies according to an output value.