JPH0785533A - Switching pulse supply circuit - Google Patents

Abstract

PURPOSE:To properly correct a switching noise in a HiFi signal processing circuit in a magnetic recording/reproducing device with a helical scan system. CONSTITUTION:Magnetic heads 1, 2 and head amplifiers 3, 4, and an FM de- modulator 16, a decoding circuit 17 and a switch 5 for switching the magnetic heads 1, 2 are loaded in a rotary cylinder LS. A switching signal transmitting a switching pulse modulated by an FM modulator 14 inputting the switching pulse for switching the magnetic heads 1, 2 and modulating it into the rotary cylinder LS through a rotary tramsmission, demodulating it by the FM demodulator 16 and controlling the switch 5 by the decoding circuit 17 is obtained outside the rotary cylinder LS. The switching pulse switching the magnetic heads 1, 2 is delayed, and an audio signal reproduced by the magnetic heads 1, 2 is outputted as a control signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching pulse supply circuit for supplying a switching pulse to a rotary cylinder equipped with a plurality of magnetic heads and head amplifiers, and a switch circuit for switching the magnetic heads to switch the switch circuits. Regarding

[0002]

2. Description of the Related Art In a magnetic recording / reproducing apparatus of a helical scan system such as a VTR, reproduced video signals read by a plurality of rotary heads during reproduction are respectively transmitted through a rotary transformer, passed through a preamplifier, and then head switching is performed. It is common to obtain the effective reproduction signals by connecting them.

In recent years, the number of rotary heads has increased due to the adoption of systems such as HiFi voice, narrow and flying erase. For this reason, the above method requires as many rotary transformers as the number of rotary heads, resulting in an increase in cost.

Therefore, there has been considered a system shown in FIG. 8 in which the number of rotary transformers can be reduced by mounting a recording amplifier and a reproducing amplifier in the rotary cylinder and switching signals in the rotary cylinder.

FIG. 8 shows a simplified reproduction audio FM signal path and its control signal path. In the rotary cylinder LS, the head signal output from the Ach head 1 and the Bch head 2 is received by the reproduction amplifiers 3 and 4, the switch 5 selects a channel and the effective signals are connected, and then the rotary transformer 7 is passed through the drive amplifier 6. To drive. The output of the rotary transformer 7 is
The reproduced audio FM signal is output to the audio signal processing circuit 9 via the current-voltage conversion amplifier 8. The audio signal processing circuit 9 performs processing such as demodulation of the reproduced audio FM signal and reproduces the audio signal from its output.

On the other hand, the audio switching pulse for the switch 5 is transmitted as follows. That is, the video switching pulse is input from the input terminal 10, the audio switching pulse is input from the input terminal 11, and the switching pulse is synthesized by the adder 12. The combined signal is subjected to wave difference conversion by the encoding circuit 13, modulated by the FM modulator 14, and the drive amplifier 15 drives the other channel of the rotary transformer 7. On the rotary cylinder LS side, the FM demodulator 16 receives the other channel output of the rotary transformer 7,
The decoding circuit 17 separates and reproduces the audio and video switching pulses.

In this system, the reproducing amplifiers 3 and 4 are provided in the rotary cylinder LS, and the heads are switched by transmitting a control signal. Therefore, if the video signal path and the like are also combined, the number of channels required for the rotary transformer 7 is reduced. There is a feature that you can.

FIG. 9 shows the signal waveform of each part of FIG. At the output of the adder 12, a combined switching pulse c obtained by adding the video and audio switching pulses a and b supplied to the input terminals 10 and 11 respectively is obtained. The encoding circuit 13 converts the combined switching pulse c into an edge pulse d corresponding to each edge. This edge pulse d is FM-modulated and transmitted to the rotary cylinder LS via the rotary transformer 7. And the decoding circuit 1
The audio switching pulse e is separated and reproduced by 7 to control the switch 5. The head signal output from the Ach head 1 and the Bch head 2 is the switching pulse b.
A and B channel head outputs f and g corresponding to
Becomes The reproduced signal whose channel is switched by the switch 5 is output to the audio signal processing circuit 9 as a reproduced audio FM signal h. The audio signal processing circuit 9 performs processing such as demodulation and outputs it as a reproduced audio signal.

By the way, when the reproduced audio FM signal h is connected by channel switching, noise is generated at that portion. If this is demodulated, it will be heard as switching noise. Therefore, in the HiFi signal processing circuit, so-called switching noise correction is performed to correct noise in this portion. Various proposals have been made for this switching noise correction, but noise cannot be completely corrected by any of the methods. For this reason, it is important to make the correction period as short as possible and correct the timing in a timely manner. The audio switching pulse b shown in FIG. 9 is used as the timing signal for correcting the noise portion.

In the above system, an audio switching pulse transmission circuit and the like are added to the general system. Therefore, the edge position of the audio switching pulse b used for head switching and the audio F
There is a delay between the positions where the M signal h actually switches.

This requires a long correction time to cover the switching noise correction in the HiFi signal processing circuit, which causes a significant deterioration of the correction accuracy. Furthermore, as in the above system, I
When C is premised, there is a problem that the relative variation due to the process variation and the like becomes large in addition to the absolute delay time, which is a very disadvantageous condition for the switching noise correction. It was

[0012]

Since the conventional switching pulse generation circuit is provided with an audio switching pulse transmission circuit and the like, it is located between the edge position of the audio switching pulse used for head switching and the position where the audio FM signal is switched. However, there is a problem that a delay occurs in the switching noise and it is necessary to lengthen the correction time in the switching noise correction to cover the switching noise, which significantly deteriorates the correction accuracy.

According to the present invention, in a helical scan type magnetic recording / reproducing apparatus in which heads are switched for reproducing signals from a plurality of heads in a rotary cylinder, a system capable of appropriately performing switching noise correction in a HiFi signal processing circuit is provided. provide.

[0014]

According to the present invention, an audio switching pulse is delayed by using a delay element for transmitting an audio switching pulse and the same delay element, and synchronized with both edges of the audio switching pulse. It is characterized in that it is converted into an edge trigger pulse and outputted.

[0015]

By the above means, the time difference between the edge position of the audio switching pulse and the channel switching of the audio FM signal can be canceled out, so that the switching noise in the HiFi signal processing circuit can be properly corrected. Further, by supplying the timing signal used for the switching noise correction as the edge trigger pulse, the variation factor due to the difference between the rising and falling slew rates of the output circuit is eliminated, so that the degree of freedom in design is improved.

[0016]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a circuit configuration diagram for explaining an embodiment of the present invention, and the same parts as those of the conventional FIG. In this embodiment, an audio switching pulse is reproduced by a pulse reproducing circuit 18 from an output signal of the encoding circuit 13, a pulse is delayed by a delay circuit 19, and then the pulse is used as a control signal from an output terminal 20 of the audio processing circuit 9. 8 is different from that shown in FIG.

The circuit operation of FIG. 1 will be described with reference to FIG. As described with reference to FIG. 8, the audio switching pulse b is supplied to the input terminal 11 outside the rotary cylinder LS, and the FM signal output h is output from the edge to the audio processing circuit 9 as the reproduced audio FM signal. There will be a delay. Therefore, from the output of the encoding circuit 13,
It can be compensated by reproducing the switching pulse b like the switching pulse j1 or j2 by the pulse reproducing circuit 18 and delaying it by the delay circuit 19.
Therefore, if the switching pulse j1 or j2 output from the output terminal 20 is used as the switching noise correction timing signal for the audio processing circuit 9, the accuracy of noise correction can be improved.

By the way, the FM modulation frequency of the control signal is
In particular, in order to avoid image quality deterioration due to crosstalk to the video signal, it is desirable to set it in a high band outside the video signal band. However, since it is necessary to select an appropriate frequency band due to the frequency characteristics of the rotary transformer, the FM
The modulation input requires band limitation of the modulated signal. An LPF is generally required at the output of the encoding circuit 13. This LPF increases the delay amount from the edge of the audio switching pulse to the switching of the audio FM signal.

However, if the signal after the LPF is input to the pulse reproduction circuit 18, the same delay element is equivalently added to the transmission path to the output terminal 20 and the transmission path to the input of the audio processing circuit 9. That is, no delay occurs between the edge position of the audio switching pulse and the position where the audio FM signal switches.

FIG. 3 shows a concrete example of the pulse reproduction circuit 18, and FIG. 4 shows signal waveforms of respective parts of FIG. In this circuit, the encoded output of the switching pulse input from the input terminal 31 is input to the comparators 32 and 33 and compared by the reference power sources 34 and 35, respectively. The output of the comparator 32 is input to the T input of the T-FF 36, the Q output of the T-FF 36 is inverted to the T input of the T-FF 37, the Q output of the T-FF 37 is connected to the output terminal 38, and the Q output of the comparator 33 is connected. Output is R of T-FF36,37
Connect to each input.

The switching pulse a is applied to the input terminal 31.
Input the encoded output of. Comparator 32, 33
, The pulses are separated into pulses b and c, respectively. T-FF
The audio switching of the pulse d is reproduced by 36 and 37, and output from the output terminal 38.

FIG. 5 shows another specific example of the pulse reproduction circuit 18, and FIG. 6 shows the signal waveforms of the respective parts of FIG. The part different from FIG. 3 is the output of the comparator 32,
The Q output of the T-FF 37 is input to the input of the AND gate 39, and the Q output of the T-FF 36 is input to the AND gate 39.
The input of the AND gate 39 and the output of the cooperator 33 are connected to the input of the OR gate 40 and the output of the OR gate 40 is connected to the output terminal 38, respectively.

The signals a to c are the same as in FIG. A
The output of the ND gate 39 becomes like a pulse e, and by the OR with the pulse c, a pulse like f is obtained at the output terminal 38. This is an edge pulse of the audio switching pulse d in FIG.

In the case of this circuit, the switching pulse d
Is supplied as an edge trigger pulse, it is not necessary to consider the delay variation due to the slew rate difference between the rising edge and the falling edge as compared with FIG.
This has the advantage that the degree of freedom in designing the output buffer is large.

Although various other examples are possible,
The point is that the encoded switching pulse may be reproduced, restored to the original audio switching pulse, or converted into an edge trigger pulse and output through a delay circuit. That is, the present invention is not limited to the above-described embodiment as long as it is a circuit that compensates for the delay that occurs between the edge of the audio switching pulse and the channel switching of the audio FM signal.

For example, in FIG. 1, the output of the FM modulator 14 may be input to the pulse reproduction circuit 1 via a new demodulator. Further, even if the audio switching pulse of the audio switching pulse input 11 is directly output from the output terminal 30 through the delay circuit 19, the variation factor of the delay amount increases, but there is an improvement effect as compared with the conventional example. Alternatively, there is no problem even if the signal processing order of the pulse reproduction circuit 18 and the delay circuit 19 is exchanged.

FIG. 7 is a circuit configuration diagram for explaining another embodiment of the present invention. In this embodiment, the number of required channels of the rotary transformer is reduced by frequency-multiplexing the FM modulation output of the switching pulse of FIG. 1 with the audio FM signal.

The circuit of FIG. 7 frequency-multiplexes the output of the drive amplifier 15 with the rotary transformer 7 for audio FM signal transmission, as compared with FIG. On the rotary transformer side, the HPF 21 separates the FM modulation signal of the switching pulse. Also, in the reproduction audio FM signal path, for FM modulation signal separation of the switching pulse,
LPF 22 is required. Other configurations are similar to those of the embodiment shown in FIG.

Also in the case of such a system, the LPF 22
As a result, the delay caused from the edge of the audio switching pulse to the channel switching of the reproduced audio FM signal is further increased, but the timing of the audio switching pulse can be adjusted by the compensation in the delay circuit 19. Particularly in the case of delay compensation by the LPF 22 or the like, if the delay circuit 19 and the delay circuit 19 are configured in the same IC and with the same circuit configuration, delay time variations due to process variations can be canceled.
There is an advantage.

In each of the above-described embodiments, the method of encoding the switching pulse has been described on the premise of the method shown in the conventional example, but the invention is not limited to this. Even if the encoding method is different, since the audio switching pulse can be reproduced by the decoding circuit 17 of FIG. 1, the reproduced audio switching pulse can be always obtained at the output of the pulse reproducing circuit 18 by using the same method.

[0031]

As described above, according to the present invention,
Since the delay from the edge of the audio switching pulse supplied to the switching pulse input to the output of the reproduced audio FM signal can be compensated, H
The accuracy of the switching noise correction in the iFi signal processing circuit can be kept good.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram for explaining an embodiment of the present invention.

FIG. 2 is a characteristic diagram for explaining the operation of FIG.

FIG. 3 is a specific circuit configuration diagram of the pulse reproduction circuit of FIG.

FIG. 4 is a signal waveform diagram of each part of FIG.

5 is another specific circuit configuration diagram of the pulse reproduction circuit of FIG.

6 is a signal waveform diagram of each part of FIG.

FIG. 7 is a circuit configuration diagram for explaining another embodiment of the present invention.

FIG. 8 is a conventional circuit configuration diagram.

9 is a signal waveform diagram of each part of FIG.

[Explanation of symbols]

 1, 2 ... Magnetic heads 3, 4 ... Playback amplifier 5 ......... Switch 7 ......... Rotary transformer 9 ...... Audio signal processing circuit 13 ......... Encoding circuit 14 ......... FM modulator 16 ......... FM demodulation Decoder 17 Decoding circuit 18 Pulse regeneration circuit 19 Delay circuit

Claims (4)

[Claims] 1. A helical scan type magnetic recording / reproducing apparatus, comprising: a rotary cylinder comprising at least a plurality of magnetic heads, an amplifier for amplifying the reproduction signals, and a switch means for switching the magnetic heads; and the magnetic head. Switching means for inputting a switching pulse for switching and modulating the pulse, transmitting means for transmitting the switching pulse modulated by the means into the rotary cylinder, demodulating the switching pulse and switching means A switching pulse supply circuit comprising: demodulation means for generating a control signal; and means for delaying the switching pulse and outputting as a control signal for correcting a signal reproduced from the magnetic head. 2. The switching pulse according to claim 1, further comprising conversion means for converting into an edge trigger pulse synchronized with a rising edge and a falling edge of the input switching pulse, and the control signal is an edge trigger signal. Supply circuit. 3. A synthesizing unit for synthesizing the switching pulse input with another control signal, an encoding unit for encoding the synthesized control signal into a waveform suitable for modulation in a stage preceding the modulating unit, and the modulating unit. The switching pulse supply circuit according to claim 1, further comprising a reproducing unit that reproduces the switching pulse immediately before. 4. The delay of the switching pulse is set to be substantially the same as that of a circuit which causes a time difference between the input of the head switching signal and the switching of the reproducing head output. 1. The switching pulse supply circuit according to 1.