JPH0816962B2 - Reproduction equalizer circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a reproducing equalizer circuit for a magnetic tape direct recording / reproducing apparatus or the like.

[Prior Art] The frequency characteristic of the output voltage of the reproducing head of the magnetic tape recording / reproducing apparatus is not flat, and as shown in Fig. 4, it shows a decrease of 6 dB / octave in the low range and a decrease due to loss in the high range. Show. Also, the frequency characteristic is B due to the change in tape running speed.
It changes like 1, B2, B3. Therefore, the frequency characteristic of the reproducing equalizer circuit of the magnetic tape recording / reproducing apparatus is set as shown by characteristic lines A1, A2, A3 in FIG. 2 to compensate the frequency characteristic of the head output voltage in FIG. The total frequency characteristics must be flat as shown in FIG.

FIG. 7 shows a typical reproduction equalizer circuit of a conventional multi-speed data recorder. This reproduction equalizer circuit is composed of a combination of an integrating circuit 1 and a high frequency compensating circuit 2. The integrator circuit 1 obtains an integral characteristic in a low frequency range, and includes an operational amplifier 3, a resistor 6 connected between the inverting input terminal and the reproduction signal input terminal via a coupling capacitor 5, and
A resistor 7 and capacitors 8 and 9 connected between the output terminal and the inverting input terminal of the operational amplifier 3, and a variable resistor connected in series to the capacitor 9 via an analog switch 10 that is switch-controlled according to the tape speed. It consists of 11a and 11b. The non-inverting input terminal of the operational amplifier 3 is connected to the ground.

The high frequency compensating circuit 2 includes an operational amplifier 12, a resistor 14 connected between the inverting input terminal and the output terminal of the operational amplifier 3 in the preceding stage through a coupling capacitor 13, and an output terminal of the operational amplifier 12 and an inverting terminal. Capacitor 15 connected between input terminal
And resistors 16 and 17, and inductances 19a and 19b, capacitors 20a and 20b, and a variable resistor 21 that are selectively connected between the ground of the resistors 16 and 17 and the ground via an analog switch 18.
It consists of a and 21b. The non-inverting input terminal of the operational amplifier 12 is connected to the ground.

The switches 10 and 18 are interlocked with the switching operation of the tape speed and set the reproduction equalizer characteristic corresponding to the speed. For convenience of illustration, only two switching contacts are shown in FIG. 7, but the switches 10 and 18 are actually configured to switch the reproduction equalizer characteristics in eight stages. , Six more variable resistors 11a and 11b are provided, and inductances 19a and 19b and capacitors 20a and 20 are provided.
Further, six pieces corresponding to the b and variable resistors 21a and 21b are provided. The resistors 11a, 11b, 21a and 21b are variable resistors for finely adjusting the characteristics.

The integrating circuit 1 has the frequency characteristic shown in FIG.
It has the effect of increasing at a ratio of 6 dB / octave. The high frequency compensating circuit 2 has the function of increasing the gain in the high frequency band as shown in FIG.

The combined frequency characteristic of the integrating circuit 1 and the high frequency compensating circuit 2 is
As shown in FIG. 10, the frequency characteristic of the head shown in FIG. 3 can be compensated. The characteristic lines shown by the dotted lines in FIGS. 8, 9 and 10 show the characteristics when the switches 10 and 18 are switched.

[Problems to be Solved by the Invention] However, the conventional reproduction equalizer circuit has the following problems.

(1) The high-frequency compensating inductances 19a and 19b are required, and the two operational amplifiers 3 and 12 are required, resulting in high cost.

(2) The values of the inductances 19a and 19b must be increased as the tape speed decreases. Therefore, it is difficult to miniaturize the inductances 19a and 19b, and it is also difficult to miniaturize the reproduction equalizer circuit.

(3) Since the inductances 19a and 19b are composed of coils, they are generally inferior in vibration resistance, temperature characteristics, failure rate, and change over time in characteristics as compared with resistors and capacitors.

(4) Since the integrating circuit 1 and the high frequency compensating circuit 2 are combined and configured, it is difficult to obtain a target frequency characteristic.

(5) Two variable resistors for one tape speed 11
Since a, 21a or 11b, 21b, etc. are provided, not only the configuration becomes complicated, but also the number of adjustment points increases.

Although the multi-speed data recorder has been described above, other magnetic recording / reproducing apparatuses having the same structure also have the same problem.

Therefore, it is an object of the present invention to provide a reproduction equalizer circuit having a relatively simple structure.

[Means for Solving the Problems] The present invention for achieving the above object will be described with reference to the reference numerals of the drawings showing the embodiments, and is obtained by relative scanning motion between a magnetic recording medium and a reproducing head. A reproduction equalizer circuit configured to perform a mirror integration operation in a low frequency band and a differentiation operation in a high frequency band in order to frequency-compensate the reproduced signal, and input a signal obtained from the reproduction head. A reproduction signal input terminal 55, an operational amplifier 58, an input capacitor 56 having one end connected to the reproduction signal input terminal 55, the other end of the input capacitor 56 and one input terminal of the operational amplifier 58. A first input resistor 57 connected between them; an equalizer characteristic changing capacitor 60a-60c connected in parallel to the first input resistor 57 via a second input resistor 59; The other Means for connecting the power terminal to ground, the operational amplifier 58
Feedback resistor 64 connected between the output terminal of the operational amplifier 58 and the one input terminal, and a first feedback capacitor 62 connected between the output terminal of the operational amplifier 58 and the one input terminal. The present invention relates to a reproduction equalizer circuit including a series circuit with the feedback capacitor 63 and the equalizer characteristic changing resistors 65a to 65c connected in parallel to the second feedback capacitor 63.

[Operation] According to the above invention, a desired equalizer characteristic is obtained by combining one operational amplifier and a plurality of resistors and capacitors without using an inductance element, so that the circuit can be simplified, downsized, and cost reduced. become.

[Embodiment] Next, a multi-speed data recorder according to an embodiment of the present invention will be described with reference to FIGS.

As shown in FIG. 3, this multi-speed data recorder has a capstan 34, a pinch roller 35, a capstan motor 36, and a pair of reel motors 37, 38 for running a tape 33 mounted on a pair of reels 31, 32. And a travel control circuit 39. Under the control of the control circuit 39, the tape 33 is
cm / s, 38cm / s, 19cm / s, 9.5cm / s, 4.8cm / s, 2.4cm / s,
It can run in 8 steps of 1.2 cm / s and 0.6 cm / s.

Between the analog recording signal input terminal 40 and the recording head 41, an input level adjuster 42, an input amplifier 43, and a high frequency compensating circuit.
44, a recording amplifier 45 having a constant current characteristic (characteristic that keeps the current constant regardless of changes in the head impedance) and supplying a head current, and a bias trap circuit 46 are sequentially connected. Further, a bias oscillator 48 is connected to the recording head 41 via a capacitor 47.

A head amplifier 50, a reproduction equalizer circuit 51, a reproduction level adjuster 52, an output amplifier 53, and an output terminal 54 are sequentially connected to the output stage of the reproduction head 49.

FIG. 1 shows the reproduction equalizer circuit 51 of FIG. 2 in detail. A reproduction signal input terminal 55 connected to the head amplifier 50 in FIG. 3 is connected to an inverting input terminal of an operational amplifier (op amp) 58 via a 1 μF input capacitor 56 and a 10 kΩ first input resistor 57. . The non-inverting input terminal of the operational amplifier 58 is connected to the ground. Any one of the equalizer characteristic changing capacitors 60a, 60b, 60c is connected in parallel to the first input resistor 57 via the second input resistor 59 of 2 kΩ via the first switch 61. Operational amplifier 58
A series circuit of a first feedback capacitor 62 of 1200 pF and a second feedback capacitor 63 of 220 pF is connected between the output terminal and the inverting input terminal, and a feedback resistor of 3.3 MΩ is further connected. Any one of the equalizer characteristic changing resistors 65a, 65b, and 65c is connected in parallel to the second feedback capacitor 63 via the second switch 66. The output terminal 67 of the reproduction equalizer circuit 51 is connected to the operational amplifier 58.

The first and second switches 61 and 66 are analog switches which interlock with each other and interlock with the speed control circuit 39 shown in FIG. That is, the switch is switched according to the switching of the running speed of the tape 33.

The first, second and third characteristic changing capacitors 60a, 60b,
60c shows the values of 100pF, 180pF, and 360pF, and the first, second, and third characteristic changing resistors 65a, 65b, and 65c are 2.4kΩ, 5.1kΩ, 1
It has a value of 0 kΩ.

In FIG. 1, only three capacitors 60a-60c and three resistors 65a-65c are shown corresponding to three tape speeds, but in actuality, five tape speeds are additionally provided. Five capacitors and five resistors are provided. The contact point a of the first and second switches 61, 66 has a tape speed of 76 cm.
The contact point b is turned on when the tape speed is 38 cm / s, and the contact point c is turned on when the tape speed is 19 cm / s. The relationship between other tape speeds and the characteristic changing capacitors and resistors is as follows.

Tape speed capacitors Resistance 9.5cm / s 750pF 20kΩ 4.8cm / s 1500pF 39kΩ 2.4cm / s 3300pF 75kΩ 1.2cm / s 6800pF 150kΩ 0.6cm / s 12000pF 300kΩ Capacitors corresponding to the above tape speeds of 9.5 to 0.6cm / s And each resistor is a characteristic changing capacitor 60a-6 of FIG.
0c and resistors 65a to 65c are arranged in parallel, and switches 61 and 66 are arranged.
To selectively connect.

The characteristic changing resistors 65a to 65c are variable resistors in order to adjust variations in the characteristics of the reproducing head 49.

When the contact a of the first and second switches 61 and 66 of the reproduction equalizer circuit 51 of FIG. 1 is turned on, the frequency characteristic of A1 in FIG. 2 is obtained, and when the contact b is turned on, the frequency of A2 is obtained. A characteristic is obtained, and when the contact c is turned on, the frequency characteristic of A3 is obtained.

The second input resistor 59 of 2 kΩ and the second feedback capacitor 63 of 220 pF have the function of limiting the high frequency gain in order to determine the band of the reproduced signal.

The 1 μF input capacitor 56 and the 3.3 MΩ feedback resistor 64 are for zeroing the direct current and the gain in the vicinity thereof.

10 kΩ input resistance 57 and 1200 pF first feedback capacitor 6
2 is for determining the low-frequency integration characteristics.

In the circuit of FIG. 1, when the second switch 66 is fixed to an arbitrary contact and the first switch 61 is switched in the order of a, b, and c, the peak of high frequency compensation in FIG. 2 is −6 dB / Move up along the octave line. Further, the first switch 61 is fixed to an arbitrary contact and the second switch 66 is connected to the contacts a, b,
Even when switching is performed in the order of c, the peak of high frequency compensation in FIG.
Move up along the 6 dB / octave line.

In order to set the frequency characteristic suitable for the tape speed, for example, each constant is set so that the ideal frequency characteristic can be obtained at the tape speed of 76 cm / s. The constants of each part of the circuit shown in FIG. 1 are values when the bias current is set to −3 dB over bias and the Maxell video cassette HG X GOLD 120 is used as the tape 33.

Next, the frequency characteristic of each tape speed is set as follows. Now, the capacitor 60a selected by the first switch 61
Let C be a capacitance value such as ~ 60c, R be a resistance value of the resistors 65a to 65c selected by the second switch 66, and n be a tape speed multiplication factor. Product of (C
R) is set to (1 / n) ² times. At this time, C is 1 / n times and R is 1 / n
Of course, it does not matter if it is n times, or if the ratio of C and R is changed.

A1, A2 and A3 in Fig. 2 are tape speeds of 76 cm / s, 38 cm / s and 19
The frequency characteristic of cm / s is shown, and by this, B1 and B of Fig. 4
2. The frequency characteristics of the B3 head can be compensated.

 This embodiment has the following advantages.

(1) Since high frequency compensation characteristics can be obtained without using an inductance element, miniaturization, cost reduction, and improvement in reliability are achieved.

(2) When C and R of a certain tape speed are determined, the values of C and R of another tape speed can be calculated. Therefore, it is possible to easily set desired frequency characteristics of a large number of tape speeds. Note that the resistors 65a to 65c are variable resistors in order to correct the variation in the characteristics of the head 49, but since the frequency characteristics shift along the −6 dB / octave line according to the CR product, only one of CR is You can change it. In the conventional example shown in FIG. 7, it is necessary to change both the resistors 11a and 11b on the one hand and the resistors 21a and 21b on the other hand, so that the adjustment is troublesome. It will be easier.

(3) Since a single operational amplifier 58 is used to obtain a low-frequency integration characteristic and a high-frequency compensation characteristic, the circuit is simplified and the mid-frequency characteristic is improved.

[Modification] The present invention is not limited to the above-described embodiments, and the following modifications are possible, for example.

(1) The capacitor C and the resistor R in FIG.
As shown in the figure, a variable capacitor 60 and a variable resistor 65 may be used, and the values of C and R may be changed according to the tape speed. Further, in the case of a single tape speed, the variable capacitor 60 and the variable resistor 65 may be fixed capacitors and fixed resistors.

(2) The connection locations of the resistor 59 and the capacitors 60a to 60c may be exchanged, and the connection locations of the capacitors 62 and 63 may be exchanged.

(3) It can also be applied to an audio tape recorder.

(4) Replace the first and second switches 61 and 66 with capacitors.
An analog switch such as a transistor having a number corresponding to 60a to 60c and resistors 65a to 65c may be used.

[Effects of the Invention] As is apparent from the above, according to the present invention, desired frequency characteristics can be easily obtained.

[Brief description of drawings]

1 is a circuit diagram showing a reproduction equalizer circuit according to an embodiment of the present invention, FIG. 2 is a frequency characteristic diagram of the reproduction equalizer circuit of FIG. 1, and FIG. 3 is a data recorder according to the embodiment of the present invention. Block diagram, FIG. 4 is a frequency characteristic diagram of the reproducing head of FIG. 3, FIG. 5 is a diagram showing a general frequency characteristic of the data record of FIG. 3, and FIG. 6 is a circuit showing a modified example of the reproducing equalizer circuit. FIG. 7 is a circuit diagram showing a conventional reproduction equalizer circuit, FIG. 8 is a diagram showing frequency characteristics of the integrating circuit of FIG. 7, and FIG. 9 is a frequency characteristic of the high frequency compensating circuit of FIG. FIG. 10 and FIG. 10 are diagrams showing frequency characteristics of the reproduction equalizer circuit of FIG. 49 …… Playback head, 51 …… Playback equalizer circuit, 56 ……
Input capacitor, 57 ... First input resistance, 58 ... Operational amplifier, 59 ... Second input resistance, 60a, 60b, 60c ... Characteristic changing capacitor, 61 ... First switch, 62 ... First
Feedback capacitor, 63 ... Second feedback capacitor, 64 ...
… Feedback resistors, 65a, 65b, 65c… Characteristic changing resistors.

Claims (1)

[Claims] 1. In order to frequency-compensate a signal obtained by relative scanning motion between a magnetic recording medium and a reproducing head, a mirror integration operation is performed in a low frequency band and a differential operation is performed in a high frequency band. A reproduction signal equalizer circuit, one end of which is connected to a reproduction signal input terminal (55) for inputting a signal obtained from the reproduction head, an operational amplifier (58), and a reproduction signal input terminal (55). Input capacitor (56), the other end of the input capacitor (56) and the operational amplifier (5
8) A first input resistor (57) connected to one of the input terminals, and a first input resistor (57) connected in parallel to the first input resistor (57) via a second input resistor (59). Between the equalizer characteristic changing capacitors (60a to 60c), the means for connecting the other input terminal of the operational amplifier (58) to the ground, and the output terminal of the operational amplifier (58) and the one input terminal. A connected feedback resistor (64), a first feedback capacitor (62) connected between the output terminal of the operational amplifier (58) and the one input terminal, and a second feedback capacitor (62)
And a feedback circuit (63) in series, and equalizer characteristic changing resistors (65a to 65c) connected in parallel to the second feedback capacitor (63). .