JPH01189058A - Tracking adjusting signal generating circuit for helical scanning system tape reproducing device - Google Patents

Abstract

PURPOSE:To make an arithmetic output into a tracking adjusting signal, and to obtain the title tracking adjusting signal generating circuit with excellent characteristics by adding the characteristics, which sharply raise an output level, even in an SP mode, in which the range of the amplitude level of a tape regenerative signal for the relative position between a head and a track is narrow. CONSTITUTION:A regenerative FM signal is inputted to an input terminal 11 of the tracking adjusting signal generating circuit, the level of the FM signal is controlled by a variable gain circuit 12 by using the signal of an AGC circuit 18, and outputted to an output terminal. The output level of the circuit 12 is detected by an amplitude detecting circuit 14, and the output level is inputted to a comparing circuit 15. A detection level from the circuit 14 and the terminal voltage of a capacitor 17 is impressed through respective connecting terminals 21 and 22 to an arithmetic circuit 23, and the tracking adjusting signal obtained by an operation in the arithmetic circuit 23 is outputted from an output terminal 24 together with the output signal compared with a reference potential 16 by the circuit 15.

Description

[Detailed Description of the Invention] [Purpose of the Invention (Industrial Application Field) The present invention relates to a helical scan type tape reproducing device capable of reproducing tapes recorded in standard recording mode and long-time recording mode. In particular, the present invention relates to improvements in the tracking adjustment signal generation circuit.

(Prior Art) As is well known, recent home video tape recorders (V
With the aim of achieving high sound quality (high-fidelity), the FM modulation/demodulation recording/playback system, which is equipped with a rotary head exclusively for audio, has become the main audio recording/playback system used in TR). Such home VTRs are equipped with a tracking adjustment function in order to correct the positional deviation between the head and the recording track on the tape.

This tracking adjustment function allows you to manually adjust the relative position of the head and tape while looking at indicators such as a pointer or light emitting diode (LED) so that the output level of the head is maximized. be. In this case, the tracking adjustment signal for driving the indicator is generally generated by detecting the amplitude level of the audio reproduction FM signal.

FIG. 5 shows a conventional circuit for generating such a tracking adjustment signal.

That is, the reproduced FM signal obtained from the audio head is supplied to the input terminal 11 after being amplified by a head amplifier (not shown). The reproduced FM signal supplied to this input terminal 11 is amplified by a variable gain circuit (OCA) 1.2, then derived from an output terminal 13, and is then subjected to FM demodulation processing through a limiter (not shown) and drop The signal is supplied to an out detection circuit or the like and subjected to predetermined processing.

Further, the amplitude level of the output of the variable gain circuit 12 is detected by an amplitude detection circuit 14. The detected amplitude level is compared with the reference level of the constant voltage source 16 by the comparator circuit 15, and the capacitor is adjusted according to the comparison result.
7 is charged and discharged. Based on the terminal voltage level of the capacitor 17, the gain of the variable gain circuit 12 is automatically controlled so as to maintain the output amplitude of the variable gain circuit 12 at a constant level.

That is, variable gain circuit 12. Amplitude detection circuit 14° comparison circuit 15. The constant voltage source 1B and the capacitor 17 constitute an automatic gain control circuit (hereinafter referred to as AGC circuit) 18 for keeping the signal level derived from the output terminal 13 constant. This AGC circuit 18 corrects the deviation between two audio heads that are generally provided, removes the A Fv1 component of the head switching cycle, and detects dropouts under the same conditions even if the output of the audio head varies from model to model. This is essential for this type of tape playback device.

Here, the simplest means for obtaining the tracking adjustment signal is to use the output of the amplitude detection circuit 14 as it is. However, since this means uses the amplitude detection output after passing through the variable gain circuit 12, the output level of the amplitude detection circuit 14 remains constant in the region where the AGC circuit 18 performs gain control operation. , it can no longer be used as a tracking 1 adjustment signal.

Therefore, conventionally, as shown in FIG.
An amplitude detection circuit 19 is installed in parallel with the input terminal 8, and the reproduced FM signal supplied to the input terminal 11 is amplitude-detected as it is, so that a tracking adjustment signal is obtained from the output terminal 20.

However, the following problems occur in the conventional tracking adjustment signal generation means as described above. That is, the amplitude detection circuit 19 has a linear input/output characteristic as shown in FIG. 6(a). On the other hand, most home VTRs have a standard recording mode (SP
It is equipped with a function that allows the user to selectively switch between a long-term recording mode (hereinafter referred to as an EP mode) and a long-term recording mode (hereinafter referred to as an EP mode).

In EP mode, the head output level decreases due to the narrowing of the recording track width on the tape.
Because it is easier to receive crosstalk from adjacent tracks, the range of the amplitude level of the reproduced FM signal with respect to the relative position between the head and the track is different from that in the SP mode, as shown in Figure 6(a). It's narrow.

Therefore, when the tracking adjustment knob (not shown) is rotated, the level change of the tracking adjustment signal with respect to the rotation angle of the knob is as shown in FIG. 6(b).
Compared to the SP mode, the EP mode has a lower peak value and is also less sensitive to the rotation angle of the knob.

(Problems to be Solved by the Invention) As described above, in the conventional tracking adjustment signal generation circuit, in the EP mode, the peak value of the tracking adjustment signal level is significantly lower than in the SP mode, and There is also a problem in that the sensitivity to the amount of operation of the tracking adjustment operator is degraded.

Therefore, the present invention has been made in consideration of the above circumstances, and is an extremely good method that achieves approximately the same peak value in both SP mode and EP mode, and also provides the same level of sensitivity to the operation amount of the tracking adjustment operator. The object of the present invention is to provide a tracking adjustment signal generation circuit for a helical scan type tape playback device.

[Structure of the Invention] (Means for Solving the Problems) That is, the tracking adjustment signal generation circuit of the helical scan tape playback device according to the present invention is capable of playing back tapes recorded in SP mode and EP mode. The target is and a variable gain jt1 circuit that amplifies the tape playback signal, an amplitude detection circuit that detects the output amplitude level of the variable gain circuit, a comparison circuit that compares the amplitude level detected by the amplitude detection circuit with a reference level, and Automatic gain 1 control, which consists of a capacitor that is charged and discharged according to the output of the comparison circuit, controls the gain of the variable gain circuit based on the terminal voltage level of the capacitor, and maintains the output amplitude of the variable gain circuit at a constant level. Using a circuit, a calculation is performed to give a characteristic that the output level rises sharply within the range of the tape playback signal level recorded in EP mode, based on the output voltage level of the amplitude detection circuit and the terminal voltage level of the capacitor. The calculated output is used as a tracking adjustment signal.

(Function) According to the above-mentioned IS configuration, even in the EP mode where the range of the amplitude level of the tape playback signal with respect to the relative position of the head and the track is narrow, the tracking 5! I adjustment signal is SP
In addition to being able to have approximately the same peak value as in mode! - Sensitivity to the amount of operation of the racking adjustment operator can also be obtained to the same level.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. In FIG. 1, the same parts as in FIG. 5 are shown with the same symbols, and only the different parts will be described here. That is, the amplitude level detected by the amplitude detection circuit and the terminal voltage of the capacitor 17 are applied to the arithmetic circuit 23 via the connection terminals 21 and 22, respectively, and the arithmetic circuit 23 generates a tracking adjustment signal and sends it to the output terminal. 2
I try to take it out from 4.

Here, FIG. 2 shows a specific configuration of the arithmetic circuit 23. As shown in FIG. That is, the connection terminal 21 is connected to the base of the NPN type transistor Q1. The emitter of this transistor Q1 is connected to another N via a resistor R1.
It is connected to the emitter of a PN type transistor Q2.

The connection point between the emitter of transistor Q2 and resistor R1 is
It is grounded via a constant current source 25. Further, the base of the transistor Q2 is grounded via a constant voltage source 26 with the illustrated polarity.

On the other hand, the collector of the transistor Ql is connected to the collector of a PNP type transistor Q3. The emitter of this transistor Q3 is connected to a DC voltage V through a resistor R2.
It is connected to the power supply terminal 27 to which CC is applied. Further, the collector of the transistor Q2 is also connected to the power supply terminal 27.

Here, the collector and base of the transistor Q3 are commonly connected, and the connection point is connected to the base of a PNP type transistor Q4.

The emitter of this transistor Q4 is connected to the power supply terminal 27 via a resistor R3, and the collector is connected to the output terminal 24 and grounded via a resistor R4.

Further, the connection terminal 22 is connected to an NPN type transistor Q.
It is connected to the base of 5. The emitter of this transistor Q5 is grounded via a resistor R5. Further, the collector of the transistor Q5 is connected to the collector of a PNP type transistor Q6.

The emitter of this transistor QB is connected to the base and collector of a PNP transistor Q7, respectively, and is also connected to the power supply terminal 27 via a resistor R6. The emitter of transistor Q7 is connected to power supply terminal 27.

The collector and base of the transistor Q6 are connected through J (C), and the connection point is connected to the base of a PNP type transistor Q8.
The emitter of is connected to the power supply terminal 27 via the resistor R7, and the collector is connected to the output terminal 24.

According to the arithmetic circuit 23 having such a configuration, first, the amplitude level applied to the connection terminal 21 is converted into a current by the resistor R1, and then the transistor Q3. The current is reflected by the current mirror circuit formed by Q4 and converted into a voltage by the resistor R4, so that a voltage proportional to the input amplitude level can be obtained from the output terminal 24.

Also, the end of the capacitor 17 applied to the connection terminal 22]
'-The voltage is converted into a current by the transistor Q5 and the resistor R5, and the circuit consisting of the transistors Q6 to Q8 and the resistors RG and R7 amplifies the current for minute currents and suppresses the t-d current for large currents. After the control aII is applied, it is converted to a voltage by the resistor R4 and added to the voltage previously added to H+7, so that the output terminal 24 becomes empty 1↓1. be done.

Here, the operation of the arithmetic circuit 23 described above will be specifically considered. Now, when the level Vi of the reproduced FM signal lj supplied to the input terminal 11 is "0", the output voltage of the constant voltage source 26 is set to be equal to the amplitude level applied to the connection terminal 21. Then, automatic gain control does not work and variable gain circuit 1
2 operates at the maximum gain, the level component Vl obtained from the output terminal 24 due to the human amplitude level applied to the connection terminal 21 increases the maximum gain of the variable gain circuit 12 to gmR.
I, then Vl-(R2R4/RI R3)gn+
RL-Vi-(1). In addition, in the region where automatic gain control works, the level component V1 has a flat level of the automatic gain control circuit 18 as V AGC.
Then, Vl - (R2R4/RI R3) VAGC... (
2). Therefore, the characteristics of the level component V1 with respect to the level of the reproduced FM signal applied to the input terminal 11 are as shown in (2) in FIG.

Next, in a region where the variable gain circuit 12 operates at maximum gain under automatic gain control, the level component V2 obtained from the output terminal 24 depending on the input level to the connection terminal 22 is: (2-0) (3) V
Yes, in the region where automatic +1 gastric control works, the above-mentioned Bell component V:) is: V2- (R4/R7) Vx = 14
). Here, Vx is the thermal voltage of the transistor v1', and Is is the reverse saturation current of the transistor.

If RE is the resistance value that determines the minimum gain of the i-+J variable gain j11 circuit 12, it is a voltage that satisfies the following two equations.

(Vx/Re)+ I s exp (VX/VT)-
1AGC-=(5)+VT,/(R1SIIAGC+V
T )l Grn RL -Vl -VAGC- (6)
Note that for the sake of simplicity, the control current of the variable gain circuit 12 and the collector current of the transistor Q5 are both equal, and <! If it's AGO, it's 12.

As mentioned above, although the level component V2 cannot be matched by the equation of q1, the characteristic of the level component V2 with respect to the level of the reproduction 1 signal applied to the input terminal 11 is
It becomes as shown in ■ in the figure. Note that the symbol (■) in FIG. 3 represents the change in IAGC at this time.

Therefore, in the end, the level of the reproduced FM signal supplied to the ζ inner terminal 11 is 1. Therefore, the characteristic of the output voltage obtained from the output terminal 24 is the sum of ■ and ■ in FIG.
It will be as shown in Table 1. In other words, until the automatic gain control starts working, the output level increases in proportion to the input amplitude, and the automatic column i'? In the region where the control starts to work, the output level increases sharply relative to the human input amplitude, and the automatic train i
After the control is fully activated, the output level will gradually increase with respect to the input amplitude.

Here, as shown in Fig. 4(a), the portion where the output level sharply increases with respect to the input amplitude is determined by the playback F M with respect to the relative position between the head and the track in the EP mode.
By setting the position within the amplitude level range of the signal, when the tracking and adjustment knobs (not shown) are rotated, the tracking and adjustment knobs relative to the rotation angle of the knobs are adjusted.
As shown in the same figure (l), the level change of the Tsuki leg adjustment signal can make the peak value approximately equal in SP mode and EP mode, and the sensitivity to the rotation angle of the knob is also approximately the same. It can be done to a certain extent.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and can be implemented with various modifications without departing from the gist thereof.

[Effects of the Invention] As detailed above, according to the present invention, the SP mode and the EP mode have approximately the same peak value, and the sensitivity to the operation amount of the tracking adjustment operator can also be obtained to the same degree, which is extremely good. According to the present invention, it is possible to provide a tracking adjustment signal generation circuit for a helical scan type tape playback device.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a circuit diagram showing the main parts of the embodiment, and Figs. 3 and 4 are characteristic curves showing the operation of the embodiment. Figure, 5th
The figure is a block diagram showing a conventional circuit, and FIG. 6 is a characteristic curve diagram showing the operation of the conventional circuit. 11... Input terminal r112... Variable gain circuit, 13.
... Output terminal, 14... Amplitude detection circuit, 15... Comparison circuit, 16... Constant voltage source, 17... Capacitor,
18...AGC circuit, 19...amplitude detection circuit, 20
...output terminal, 21.22...connection terminal, 23...
- Arithmetic circuit, 24... Output terminal, 25... Constant current source, 26... Constant voltage source, 27... Power supply terminal. Applicant's agent Patent attorney Takehiko Suzue (Ma) Q- (2) (b) Figure 5 (Kyu) (b)

Claims (1)

[Claims] In a helical scan type tape playback device capable of playing back tapes recorded in standard recording mode and long-time recording mode, a variable gain circuit that amplifies the playback signal of the tape and an amplitude that detects the output amplitude level of the variable gain circuit. It consists of a detection circuit, a comparison circuit that compares the amplitude level detected by the amplitude detection circuit with a reference level, and a capacitor that is charged and discharged according to the output of the comparison circuit, and the variable gain is adjusted based on the terminal voltage level of the capacitor. an automatic gain control circuit that controls the gain of the circuit to maintain the output amplitude of the variable gain circuit at a constant level; and the long-time recording mode based on the output voltage level of the amplitude detection circuit and the terminal voltage level of the capacitor. and a calculation means for performing calculation to give a characteristic that the output level increases sharply within the range of the playback signal level of the tape recorded on the tape, and the output of the calculation means is used as a tracking adjustment signal. Signal generation circuit for tracking adjustment of a helical scan tape playback device.