JPH01282776A - Enveloping detecting circuit for magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To immediately lower a detecting output, when a reproducing output signal of a magnetic head is not inputted, and also, to prevent the detecting output from being fluctuated even if the reproducing output signal is fluctuated in one round of a track by bringing a smoothing capacitor to forced discharge at every 1 V (V: vertical scanning period). CONSTITUTION:A switch means 14 which becomes ON at every 1 V is connected in parallel to a smoothing capacitor 8, so that the capacitor 8 is brought to quick discharge forcibly by ON of the switch means 14. That is, by connecting the anode of a diode 14 to a plus terminal of the smoothing capacitor 8 and supplying a low active PG pulse 15 between the cathode of the diode 14 and a ground, the diode 14 works as a forced discharge use switch. In such a way, even if a reproducing RF signal is fluctuated in one round of a track, a detecting output is not fluctuated, and also, when there is no reproducing RF signal, the detecting output is attenuated in a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application> The present invention relates to an envelope detection circuit used in devices that record or reproduce still image video signals on magnetic disks, such as electronic still cameras and television photo systems.

<Prior art> A magnetic recording and reproducing device that complies with the standards for electronic still camera systems uses a magnetic disk called a video floppy, with a track pitch of 100 μm and a rack width of 60 μm.
50 tracks are formed in concentric circles. The video floppy rotates at a constant speed, for example, 3600 rpm in a 525 line-60 field system, and maintains the rotational phase so that the PG pulse generated every rotation has a predetermined phase relationship with the vertical synchronization signal of the video signal, and the rotational phase is maintained so that the field or frame Record or playback video signals at high speeds. In field recording, one track is used for one still image, and one magnetic head records one of the first or second fields. In frame recording, two tracks are used for one still image, and a first field and a second field are recorded separately using two magnetic heads.

In addition, among the video signals, the leg strength signal Y uses a high frequency band of 2.5 MHz or more including the synchronization signal S, and 6 MHz
Frequency modulated (FM) over ~7.5 MHz.

The chroma signal is frequency modulated in a color difference line sequential manner using a lower band.

This type of magnetic recording/reproducing device is not only a recording/reproducing device, but also a recording/reproducing device.
In both playback-only and recording-only machines, the playback output signal of the magnetic head, called the playback RF signal, is envelope-detected and the detected output signal is detected. [The presence or absence of recording is determined based on the magnitude of the flow value. When creating a track map during playback or recording, the magnetic head is moved to determine whether or not there is any recording over all tracks. Immediately after recording, it is determined whether or not there is any recording on the same track, and if there is no recording, a warning is issued.

4th TI of conventional envelope detection circuit! Shown in J. In the figure, the reproduced RF signal from the magnetic head 1 is transmitted to the preamplifier 2.
, a bandpass filter 3, a buffer amplifier 4, a coupling capacitor 5, and a diode clamp circuit 6 before being inputted to an envelope detection circuit 0. 7 is a detection diode, 8 is a smoothing capacitor, and 9 is a discharge resistor. The value of the resistor 9 is normally set to a sufficiently high resistance value so that the detection output (DC) 11 does not vary even if the envelope of the reproduced RF signal varies between tracks.

In the frame recording or reproducing machine, one envelope detection circuit $10 shown in FIG. 4 is used, and as shown in FIG. 2B, is switched by a switch 12, and is input to an envelope detection circuit 10. The detection output 11 is input to an evaluation circuit 13, where it is digitally or analogously compared with a reference value.
If it is greater than or equal to the reference value, it is determined that there is a record, and if it is less than the reference value, it is determined that there is no record.

In this case, the magnetic head to be evaluated is forced to 2V to 3V.
During this period (V is the vertical scanning period), the switch 12 continues to select. The reason for this is that since the resistor 9 of the envelope detection circuit 10 has a high resistance, the discharge time of the capacitor 8 is long. The charging time is short regardless of the resistance 9. This will be explained with reference to FIG.

For example, if the A channel magnetic head IA has a reproduction RF signal and the B channel magnetic head IB does not have a reproduction RF signal, the A channel magnetic head IA is selected first, then the B channel magnetic head IB is selected. Suppose you choose. In this case, since the discharge time is long, it takes 2 to 3 V after the B channel magnetic head IB is selected until the detection output 11 attenuates to an evaluable level, so the magnetic head IB must continue to be selected during that time. , it takes a long time to create a track map.

<Problems to be Solved by the Invention> If the value of the resistor 9 is lowered, the discharge time will be shortened, but in this case, the DC value of the detection output 11 will also fluctuate due to fluctuations within the track-period of the reproduced RF signal. It will no longer be useful for determining whether or not there is a record.

In view of the above-mentioned prior art, the present invention provides an envelope detection circuit in which the detection output does not fluctuate even if the reproduced RF signal fluctuates between tracks and stations, and the detection output attenuates in a short time when there is no reproduced RF signal. The purpose is to

Means for Solving the Problems The envelope detection circuit of the magnetic recording and reproducing apparatus according to the present invention is characterized in that a switch means that is turned on every 1 V is connected in parallel to the smoothing capacitor.

Function> Since the capacitor is forcibly discharged rapidly every 1 inch when the switch means is turned on, the detection output immediately decreases as soon as the input of the reproduced RF signal from the magnetic head stops. In addition, since the capacitor is forcibly discharged by the switch means, there is no need to lower the value of the capacitor's discharging resistor, and it is possible to use a high resistor or omit it, and the detection output is stable even if there are fluctuations in the reproduced RF signal. become

Embodiment An embodiment of the present invention will be described with reference to FIGS. 1 and 2.

FIG. 1 shows the circuit configuration of an embodiment in which the present invention is applied to an envelope detection circuit of a frame regenerator. In this embodiment, a PG pulse synchronized with a vertical synchronization signal is used to turn on the switch means every 1V. In the same figure, smoothing capacitor 8
The anode of the diode 14 is connected to the positive terminal of the diode 14, and a low active PG pulse 15 is supplied between the cathode of the diode 14 and the ground. Diode 14 acts as a forced discharge switch. 16 is a PG sensor, and 17 is a PG pulse generation circuit. One PG pulse 15 is generated per rotation of the magnetic disk. resistance 9
The value of is set sufficiently high so that even if the envelope of the reproduced RF signal varies between tracks, the detection output 11 does not vary. Magnetic head IA, IB.

The preamplifiers 2A, 2B, bandpass filter 3, buffer amplifier 4, coupling capacitor 5, diode clamp circuit 6, detection diode 7, channel switching switch 12, and evaluation circuit 13 are the same as those with the same symbols in FIG. This is a function to avoid duplication of explanation.

To explain the operation, as shown in FIG. 2, the channel changeover switch 12 selects two magnetic heads IA and IB by IV, and the PG pulse 15 turns on the forced discharge diode 14 every 1V. diode 1
4 turns on, the capacitor 8 rapidly discharges and eliminates the charge. As a result, the previously selected magnetic head, for example, IA
A reproduced RF signal is input from the magnetic head IB, and no signal is input from the later magnetic head IB (however, the detection output 11 settles to a level that can be evaluated immediately. In other words, no matter which magnetic head IA or IB is selected, The presence or absence of a record can be determined between 1■,
If frame recording is being performed, a total of 2v can be determined.

Therefore, the time required to create a track map such as which track is unrecorded and which two tracks are used for frame recording is greatly reduced.

FIG. 3 shows another embodiment in which the collector and emitter of a transistor 18 are connected to both ends of a smoothing capacitor 8, and an active PG pulse 19 is supplied to the base to turn on the transistor 18. Transistor 18 acts as a forced discharge switch.

The operation is the same as the embodiment of FIG.

Note that the present invention can be applied not only to frame playback machines, but also to frame recorders, field recording or playback machines, and envelope detection circuits of devices that record or play back audio signals or data signals on magnetic disks. .

<Effects of the Invention> According to the envelope detection circuit of the present invention, since the smoothing capacitor is forcibly discharged every 1V, the detection output immediately decreases when the reproduction output signal of the magnetic head is not input. Even if the reproduced output signal fluctuates, the detection output does not fluctuate. Therefore, it greatly contributes to reducing the time required to create a track map using a frame reproducing machine, for example.

[Brief Description of the Drawings] Figure 1 is a circuit diagram of one embodiment of the present invention, Figure 2 is an explanatory diagram of its operation, Figure 3 is a circuit diagram of another embodiment, and Figures 4 and 5 are FIG. 6, a circuit diagram of a conventional example, is an operation explanatory diagram related to FIG. 5. In the drawing, IA and IB are magnetic heads, 7 is a detection diode, 8 is a smoothing capacitor, 11 is a detection output, 12 is a channel switching switch, 14 is a diode as a forced discharge switch, 15 and 19 are PG pulses , 18 are transistors serving as forced discharge switches.

Claims (1)

[Scope of Claims] In a circuit for detecting the envelope of a playback output signal of a magnetic head of a magnetic recording and playback device that records or plays back still image video signals on a magnetic disk, An envelope detection circuit for a magnetic recording/reproducing device, characterized in that a switch means for turning on is connected.