JPH06303140A - Waveform synthesis circuit and reproduction device - Google Patents

Abstract

PURPOSE:To make the circuit small and to reduce the cost by applying time division multiplex to plural input data strings and converting them into analog signals and then limiting the band. CONSTITUTION:A digital data string is inputted respectively to input terminals 30, 31, and a selection circuit 34 selects the data string from the input terminals 30, 32 under the control of a control circuit 36 and multiplexes the string on a time axis. A D/A converter 38 converts. output data from the circuit 34 into an analog signal according to a clock from a clock generating circuit 40. An LPF 42 applies band limit to an analog output of the D/A converter 38 to provide an output to an output terminal 44. The cut-off frequency of the LPF 42 depends on a transfer rate of the digital data string received by the input terminals 30, 32. Through the constitution above, waveform synthesis by digital arithmetic operation is attained with a small scale circuit and small size and low cost are attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveform synthesizing circuit and a reproducing apparatus using the same, and more specifically, a digital waveform synthesizing circuit and a reproducing apparatus using the same for a head trace during special reproduction. Regarding

[0002]

2. Description of the Related Art With the spread of microcomputers and small computers, various signals have been digitally processed. For example, audio signals are widely subjected to digital processing in the fields of recording / playback, editing, special effects and the like. In addition, various control signals, for example, feedback control signals have also been digitally processed, and it has become convenient to perform waveform synthesis, that is, addition and subtraction with digital signals in the middle.

FIG. 2 shows a schematic block diagram of a conventional circuit for waveform-synthesizing two digital data strings (for example, PCM audio signal). Digital data strings are input to the input terminals 10 and 12, respectively. The two input data are weighted with predetermined coefficients by the coefficient multipliers 14 and 16, and then input to the addition / subtraction circuit 18 to be added or subtracted. As a result, a signal obtained by digitally combining the waveforms of the two inputs can be obtained. The output of the adder / subtractor circuit 18 is D / A
Converted to an analog signal by the converter 20,
The band is limited by the filter (LPF) 22 and output to the output terminal 24.

In addition, the outputs of the coefficient multipliers 14 and 16 are individually D
There is also known a circuit in which an analog signal is converted by an / A converter and then analog addition / subtraction is performed by an analog adder / subtractor.

Such a waveform synthesis circuit is also used for video
It is used for head trace control of a helical scanning type magnetic recording / reproducing apparatus such as a tape recorder (VTR), particularly for head trace control during special reproduction. Figure 3
The schematic block diagram of the conventional example is shown.

In FIG. 3, the magnetic head 110 is displaceable in the direction of the rotation axis of a rotating drum (not shown) by a head displacement mechanism (for example, bimorph) 112. With the traveling speed of the magnetic tape 114 and the rotating speed of the rotating drum kept constant or with little fluctuation, the head displacement mechanism 11
The head drive can be precisely controlled within a predetermined range by the drive signal of 2.

A signal indicating the position of the magnetic head 110 with respect to the rotary drum is applied to the position information calculation circuit 116. The position information calculation circuit 116 generates a reset signal 118 when the magnetic head 110 reaches a predetermined position (for example, the end of the movable range) on the rotating drum.

The sawtooth wave generation circuit 120 has a reset signal 11
The digital data which is a sawtooth wave having a constant slope reset by 8 is generated, and the signed coefficient unit 122 multiplies the output of the sawtooth wave generation circuit 120 by a coefficient with a positive or negative sign. Further, the fixed level generation circuit 124 generates a fixed level of digital data, and a signed coefficient unit 126
Multiplies the output of the fixed level generation circuit 124 by a coefficient with a positive or negative sign.

The running speed information of the magnetic tape 114 is input to the input terminal 128, and the control circuit 130 generates the coefficients of the coefficient units 122 and 126 according to the tape running speed information from the input terminal 128. Controls the number and its sign (positive or negative). The control circuit 130 is, for example,
Predetermined signed coefficients are set in the signed coefficient units 122 and 126 according to the running reproduction speed and the reproduction direction.

The adder 132 is a signed coefficient unit 122, 1
The output of 26 is digitally added, and the D / A converter 134 converts the digital output of the adder 132 into an analog signal. The LPF 136 limits the band of the output of the D / A converter 134, and the drive circuit 138 drives the head displacement mechanism 112 according to the output of the LPF 136.

With this control loop, the position of the magnetic head 110 on the rotating drum is set so that the magnetic head 110 traces a recording track correctly even when the magnetic tape 114 is run at a tape running speed different from that during recording. Can be controlled.

[0012]

However, the waveform synthesizing circuit shown in FIG. 2 has a drawback in that the digital adding / subtracting circuit 18 is a considerably large circuit having many circuit components.
In the conventional example shown in FIG. 3, in addition to this, since the signed coefficient units 122 and 124 are large circuits, there is a drawback that downsizing and cost reduction are difficult.

An object of the present invention is to provide a waveform synthesizing circuit and a reproducing device that overcome these problems.

[0014]

A waveform synthesizing circuit according to the present invention comprises a multiplexing means for time-division multiplexing a plurality of input data sequences at a designated time ratio, and a digital output of the multiplexing means into an analog signal. D / A conversion means for converting and the D
It is characterized by comprising band limiting means for band limiting the output of the / A converting means.

A reproducing apparatus according to the present invention is a reproducing apparatus having a head displacement mechanism for displacing a magnetic head in a predetermined direction on a rotating drum, and is calculated from a relative position of the magnetic head with respect to a recording pattern on a recording medium. A sawtooth wave generating means for generating sawtooth wave data with reference to a reset signal
First inverting means for inverting the output of the sawtooth wave generating means,
Fixed data generating means for generating fixed data, second inverting means for inverting the output of the fixed data generating means, zero level generating means for generating zero level data, the sawtooth wave generating means, Multiplexing means for time-division multiplexing the outputs of the first inverting means, the fixed data generating means, the second inverting means, and the zero level generating means, and the multiplexing means according to the traveling speed information of the recording medium. And a control means for controlling.

[0016]

By the above means, a plurality of inputs can be combined in waveform at a desired ratio. Since the above-mentioned multiplexing means can be basically constituted by the switch means, it can be realized by a small circuit, and therefore,
The entire circuit can be made smaller.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic block diagram of a position embodiment of the present invention relating to a waveform synthesizer circuit.

In FIG. 1, digital data strings are input to the input terminals 30 and 32, respectively, and the selection circuit 34 is selected.
Under the control of the control circuit 36, selects the data strings from the input terminals 30 and 32 and multiplexes them on the time axis. That is, if you want to give more weight, select a long time,
On the contrary, when it is desired to give a smaller weight, a shorter time is selected.

The D / A converter 38 is used in the clock generation circuit 4
According to the clock from 0, the output data of the selection circuit 34 is converted into an analog signal. Low-pass filter (LP
F) 42 band-limits the analog output of the D / A converter 38 and outputs it to the output terminal 44. The cutoff frequency of the LPF 42 is determined according to the transfer rate of the digital data string input to the input terminals 30 and 32.

Referring to FIGS. 3 and 4, the input terminals 30, 3
The operation in the case of uniformly synthesizing the waveform of the data string input to 2 will be described. FIG. 3 is a timing chart shown as a digital data string. FIG. 3 (a) is a data string input to the input terminal 30, FIG. 3 (b) is a data string input to the input terminal 32, and FIG. The output data string of the circuit 34 is shown. FIG. 3D shows a selection control signal of the selection circuit 34,
The selection circuit 34 selects the data string from the input terminal 30 when it is "L" (or "0"), and selects the data string from the input terminal 32 when it is "H" (or "1").

FIG. 4 is a timing chart for displaying each data at a level according to its size. FIG. 4A shows a data string input to the input terminal 30, and FIG. 4B shows an input terminal 32.
The data string input to the same, and (c) shows the output data string of the selection circuit 34. FIG. 4D shows an output signal waveform of the output terminal 44 for the data string shown in FIG. Figure 4
(E) shows a clock signal for the D / A converter 38.

As can be seen from FIGS. 4 (a), 4 (b) and 4 (d), according to this embodiment, an analog signal obtained by averaging the digital inputs of the input terminals 30 and 32 can be obtained.

Here, the two digital inputs are 1: 1.
Although the case where the addition is performed has been described, the same applies when the addition is performed at an arbitrary ratio. To be able to select subtraction,
As described below, an inverting circuit for inverting the sign of the input data of the input terminals 30 and 32 may be provided, and the selecting circuit 34 may be a 4-input selecting means.

FIG. 6 shows a schematic block diagram of an embodiment of the present invention corresponding to the conventional example shown in FIG.

In FIG. 6, like the magnetic head 110, the magnetic head 150 is displaceable in the direction of the rotation axis of the rotating drum (not shown) by the head displacement mechanism 152.
The head trace can be precisely controlled within a predetermined range by the drive signal of the head displacement mechanism 152 while keeping the running speed of the magnetic tape 154 and the rotating speed of the rotating drum constant or with little fluctuation.

A signal indicating the position of the magnetic head 150 with respect to the rotary drum is applied to the position information calculation circuit 156. The position information calculation circuit 156 generates a reset signal 158 when the magnetic head 150 reaches a predetermined position (for example, the end of the movable range) on the rotating drum.

The sawtooth wave generation circuit 160 has a reset signal 15
8 generates digital data that is a sawtooth wave having a constant slope and is inverted by the inverting circuit 162.
The output data of 60 is sign-inverted (from positive to negative). The fixed level generation circuit 164 generates a fixed level of digital data, and the inverting circuit 166 generates the fixed level generation circuit 1.
The output data of 64 is sign-reversed (from positive to negative). The zero level generation circuit 168 generates a zero level data string.

The traveling speed information of the magnetic tape 154 is input to the input terminal 170, and the control circuit 172 controls the selection circuit 174 according to the tape traveling speed information from the input terminal 170. The selection circuit 174 is a control circuit 172.
Output of the sawtooth wave generation circuit 160 and the inverting circuit 16
2 output, output of fixed level generation circuit 164, output of inverting circuit 166 or output of zero level generation circuit 168 is selected. That is, the selection circuit 174 is the selection circuit 3 of FIG.
Similar to 4, four inputs are time-multiplexed. The control circuit 172 determines the multiplexing rate on the time axis according to the tape running speed information from the input terminal 170.

The D / A converter 176 converts the digital output of the selection circuit 174 into an analog signal, the LPF 178 band-limits the output of the D / A converter 176, and the drive circuit 18
0 drives the head displacement mechanism 152 according to the output of the LPF 178.

With this control loop, the position of the magnetic head 150 on the rotating drum is set so that the magnetic head 150 traces the recording track correctly even when the magnetic tape 154 is run at a tape running speed different from that during recording. Can be controlled.

Referring to FIG. 7, FIG. 8, FIG. 9 and FIG.
The characteristic operation of the embodiment shown in FIG. 6 will be described in detail. Figure 7
Shows the relationship between the output of each circuit 160 to 168 and the output waveform of the LPF 178 by the time division multiplexing,
An example of time division multiplexing in which the period from t0 to t1 is enlarged is shown in FIGS. 8, 9 and 10.

FIG. 7A shows the reset signal 158,
The same (2) shows the output (level display) of each circuit 160-168. In FIG. 7B, a is a fixed level generation circuit 1
64 is an output value, b is an output value of the sawtooth wave generating circuit 160, c is an output value of the zero level generating circuit 168, and d is an inverting circuit 1.
The output value of 62 and e indicate the output value of the inverting circuit 166. The same (3) schematically shows the timings of the output data strings of the circuits 160 to 168 in an enlarged manner.

(4) shows three output examples of the LPF 178 depending on the time division multiplexing ratio of each circuit 160 to 168.
In FIG. 7 (4), f is the LPF1 when the selection circuit 174 selects only the output c of the zero level generation circuit 168.
The output value of 78, g is mainly the output b of the sawtooth wave generation circuit 160.
Is the output value of the LPF 178 when h is selected, and h is mainly the LPF 17 when the output d of the inverting circuit 162 is selected.
8 output values are illustrated.

FIG. 8 shows an output example f of the LPF 178 (see FIG. 7).
It is an enlarged view between t0 and t1 corresponding to (4)). The same (1) is the input data string of the selection circuit 174, the same (2) is the output data string of the selection circuit 174, and the same (3) is , D / A converter 176 output. In this example, the selection circuit 174
Selects only the output of the zero level generation circuit 168, the output of the D / A converter 176 becomes zero level.

FIG. 9 shows an output example g (FIG. 7) of the LPF 178.
It is an enlarged view between t0 and t1 corresponding to (4)). The same (1) is the input data string of the selection circuit 174, the same (2) is the output data string of the selection circuit 174, and the same (3) is , D / A converter 176 output. In this example, the selection circuit 174
Has a fixed level a, a sawtooth b and a zero level c of 2:
Time division multiplexing is performed at a ratio of 1: 1.

FIG. 10 shows an output example h of the LPF 178 (see FIG. 7).
It is an enlarged view between t0 and t1 corresponding to (4)). The same (1) is the input data string of the selection circuit 174, the same (2) is the output data string of the selection circuit 174, and the same (3) is , D / A converter 176 output. In this example, the selection circuit 174
Is a negative sawtooth wave d, a negative fixed level e and a zero level c
Are time-division multiplexed at a ratio of 1: 2.5: 0.5.

The output of the D / A converter 176 is shown in FIG. 9 (3).
Also, as shown in FIG. 10C, it varies depending on the time division multiplexing ratio in the selection circuit 174. The bias and time change (slope) of the output waveform of the LPF 178 are determined by the selection circuit 17
It is determined by the multiplexing ratio at 4.

The relationship with the running speed of the magnetic tape will be briefly described. When the tape running speed information input to the input terminal 170 indicates the same tape running speed as the tape speed at the time of recording, the control circuit 172 causes the selection circuit 174 to select only the output of the zero level generation circuit 168. This is Figure 8
The output of the LPF 178 is as shown in FIG.
As indicated by f in (4), the level becomes zero, and the head displacement mechanism 112 holds the magnetic head 110 at a fixed position.

When the tape running speed information input to the input terminal 170 indicates a tape running speed faster than the tape speed at the time of recording, the control circuit 172 causes the selection circuit 174 to cause the circuits 160, 164, and 1604, as shown in FIG. The output of 168 is switched and selected on the time axis. This allows the LPF
The output of 178 changes as indicated by g in FIG. 7 (4), and the head displacement mechanism 112 cyclically displaces the magnetic head 110 accordingly.

On the contrary, when the tape running speed information input to the input terminal 170 indicates a tape running speed slower than the tape speed at the time of recording, the control circuit 172 causes the selection circuit 17 to operate.
4, the circuits 162, 166, 168 are provided as shown in FIG.
The output of is switched on the time axis and selected. As a result, the output of the LPF 178 changes as indicated by h in FIG. 7D, and the head displacement mechanism 112 accordingly responds to the magnetic head 1.
10 is displaced cyclically.

As described above, in the embodiment shown in FIG. 6, an accurate head trace at the time of special reproduction can be realized with a small circuit.

[0043]

As can be easily understood from the above description, according to the present invention, waveform synthesis by digital operation can be realized by a small circuit, and downsizing and cost reduction can be realized.

Further, in the magnetic recording / reproducing apparatus, accurate head trace during special reproduction can be realized with a small circuit.

[Brief description of drawings]

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

FIG. 2 is a schematic block diagram of a conventional waveform synthesis circuit.

FIG. 3 is a schematic block diagram of a conventional head trace control circuit of a magnetic recording / reproducing apparatus having a head displacement mechanism.

FIG. 4 is a timing diagram of FIG. 1.

5 is a timing diagram based on the level display of FIG.

FIG. 6 is a schematic configuration block diagram of an embodiment of the present invention applied to a magnetic recording / reproducing apparatus having a head displacement mechanism.

7 is a timing diagram of FIG.

FIG. 8 is a first time division multiplexing example of the selection circuit 174.

FIG. 9 is a second time division multiplexing example of the selection circuit 174.

FIG. 10 is a third time division multiplexing example of the selection circuit 174.

[Explanation of symbols]

10, 12: Input terminal 14, 16: Coefficient device 18: Addition / subtraction circuit 20: D / A converter 22: Low-pass filter (LPF) 24: Output terminal 30, 32: Input terminal 34: Selection circuit 36: Control circuit 38 : D / A converter 40: Clock generation circuit 42: Low-pass filter 44: Output terminal 110: Magnetic head 112:
Head displacement mechanism 114: Magnetic tape 116: Position information calculation circuit 118: Reset signal 120: Sawtooth wave generation circuit 12
2: Signed coefficient unit 124: Fixed level generation circuit 1
26: Signed coefficient unit 128: Input terminal 130: Control circuit 132: Adder 134: D / A converter 13
6: LPF 138: Drive circuit 150: Magnetic head
152: Head Displacement Mechanism 154: Magnetic Tape 15
6: Position information calculation circuit 158: Reset signal 16
0: sawtooth wave generation circuit 162: inversion circuit 164: fixed level generation circuit 166: inversion circuit 168: zero level generation circuit 170: input terminal 172: control circuit 1
74: Selection circuit 176: D / A converter 178: LP
F 180: Drive circuit a: Fixed level generation circuit 164
Output value of b: output value of sawtooth wave generation circuit 160 c: output value of zero level generation circuit 168 d: inversion circuit 162
Output value of e: output value of inverting circuit 166

Claims (2)

[Claims] 1. A multiplexing means for time-division multiplexing a plurality of input data sequences at a designated time ratio, a D / A converting means for converting a digital output of the multiplexing means into an analog signal, and the D / A. A waveform synthesizing circuit comprising: band limiting means for band limiting the output of the converting means. 2. A reproducing apparatus having a head displacement mechanism for displacing a magnetic head in a predetermined direction on a rotating drum, wherein a reset signal calculated from a relative position of the magnetic head with respect to a recording pattern on a recording medium is used as a reference. Saw wave generating means for generating sawtooth wave data, first inverting means for inverting the output of the sawtooth wave generating means, fixed data generating means for generating fixed data, and inverting the output of the fixed data generating means. Second inverting means for generating, zero level generating means for generating zero level data, the sawtooth wave generating means,
Multiplexing means for time-division multiplexing the outputs of the first inverting means, the fixed data generating means, the second inverting means, and the zero level generating means, and the multiplexing according to the traveling speed information of the recording medium. And a control means for controlling the means.