JPH0834036B2 - Envelope detection circuit for magnetic recording / reproducing apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention records a video signal of a still image on a magnetic disk,
Or, it relates to an apparatus for reproducing, for example, an electronic still camera, an envelope detection circuit used in a television photo system.

<Prior Art> A magnetic recording / reproducing apparatus compliant with the standard of an electronic still camera system uses a magnetic disk called a video floppy, and has a track pitch of 100 μm and a track width of 60 μm.
Form 0 tracks in concentric circles. Video floppies are constant speed, for example 3 in a 525 line-60 field system.
Rotation is performed at 600 rpm, the rotation phase is maintained so that the PG pulse generated for each rotation has a predetermined phase relationship with the vertical synchronization signal of the video signal, and the video signal is recorded or reproduced at the field or frame speed. In field recording, one track is used for one still image, and one magnetic head records one of the first and second fields. In frame recording, two tracks are used for one still image, and the first field and the second field are recorded separately by two magnetic heads. The luminance signal Y of the video signal including the synchronization signal S uses a high frequency band of 2.5 MHz or more and is frequency-modulated (FM) over 6 MHz to 7.5 MHz.
The chroma signal is frequency-modulated by the color-difference line-sequential method using a lower band than that.

In this type of magnetic recording / reproducing apparatus, not only recording / reproducing machines, but also reproduction-only machines and recording-only machines perform envelope detection of the reproduction output signal of the magnetic head called reproduction RF signal, and record by the magnitude of the DC value of the detection output. It is designed to determine the presence or absence. At the time of creating a track map at the time of reproduction or recording, the magnetic head is moved to determine the presence / absence of recording on all tracks. Immediately after recording, the presence or absence of recording on the same track is determined, and if it is not recorded, an alarm is issued.

A conventional envelope detection circuit is shown in FIG. In the figure, the reproduced RF signal from the magnetic head 1 is input to the envelope detection circuit 10 via the preamplifier 2, the bandpass filter 3, the buffer amplifier 4, the coupling capacitor 5, and the diode clamp circuit 6. Reference numeral 7 is a detection diode, 8 is a smoothing capacitor, and 9 is a discharging resistor. The value of the resistor 9 is usually set to a sufficiently high resistance value so that the detection output (DC) 11 does not fluctuate even if the envelope of the reproduction RF signal fluctuates during one round of the track.

In the frame recording or reproducing device, one envelope detecting circuit 10 of FIG. 4 is used, and as shown in FIG. 5, reproducing RF of two magnetic heads 1A and 1B of A channel and B channel is reproduced.
Signals are respectively passed through the preamplifiers 2A and 2B, switched by the switch 12 and input to the envelope detection circuit 10. The detection output 11 is input to the evaluation circuit 13, where it is compared with a reference value in a digital or analog manner, and if it is greater than or equal to the reference value, it is determined to be "recorded", and if it is less than the reference value, "not recorded".

In this case, the magnetic head to be evaluated is forcedly selected by the switch 12 between 2V and 3V (V is a vertical scanning period). The reason is that the resistor 9 of the envelope detection circuit 10 has a high resistance, so that the discharge time of the capacitor 8 is long. The charging time is short regardless of the resistance 9. This will be described with reference to FIG. For example, there is a reproduction RF signal in the A channel magnetic head 1A, and the B channel magnetic head
It is assumed that when there is no reproduction RF signal in 1B, the A channel magnetic head 1A is selected first, and then the B channel magnetic head 1B is selected. In this case, since the discharge time is long, it takes 2V to 3V until the detection output 11 is attenuated to an evaluable level after the B-channel magnetic head 1B is selected. Therefore, the magnetic head 1B must be continuously 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 is shortened, but this causes the DC value of the detection output 11 to fluctuate due to the fluctuation of the reproduction RF signal within one round of the track. It becomes useless for determining the presence or absence.

In view of the above-mentioned conventional technique, the present invention provides an envelope detection circuit in which the detection output does not fluctuate even if the reproduction RF signal fluctuates within one track, and the detection output attenuates in a short time when there is no reproduction RF signal. The purpose is to do.

<Means for Solving the Problem> The envelope detection circuit of the magnetic recording / reproducing apparatus according to the present invention comprises a switch means that is turned on at the end of the synchronization period in parallel with the smoothing capacitor for the output of the rectifier every vertical scanning period. It is characterized by being connected.

<Operation> Since the capacitor is forcibly and rapidly discharged every one vertical scanning period (hereinafter, the vertical scanning period is referred to as V) when the switch means is turned on, the capacitor is detected immediately when the input of the reproduction RF signal from the magnetic head is stopped. Output decreases. Further, since the capacitor is forcibly discharged by the switch means, it is not necessary to reduce the value of the discharging resistance of the capacitor, and even if the resistance is high,
Alternatively, it may be omitted, and the detection output is stabilized even if the reproduced RF signal changes.

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

FIG. 1 shows a circuit configuration of an embodiment in which the present invention is applied to an envelope detection circuit of a frame regenerator. In this embodiment, the switch means is turned on every 1 V and synchronized with the vertical synchronizing signal.
PG pulse is used. In the figure, the diode (rectifier)
The anode of the diode 14 is connected to the positive terminal of the smoothing capacitor 8 for the output of 7, and the low active PG pulse 15 is supplied between the cathode of the diode 14 and the ground. The diode 14 functions as a switch for forced discharge, and is turned on when the PG pulse 15 is at low level. Reference numeral 16 is a PG sensor, and 17 is a PG pulse generation circuit. The PG pulse 15 is generated once per one rotation of the magnetic disk, and becomes low level at the end of 1V as shown in the figure. The value of the resistor 9 is set sufficiently high so that the detection output 11 does not fluctuate even if the envelope of the reproduced RF signal fluctuates during one round of the track. The magnetic heads 1A and 1B, the preamplifiers 2A and 2B, the bandpass filter 3, the buffer amplifier 4, the coupling capacitor 5, the diode clamp circuit 6, the detection diode 7, the channel switching switch 12, and the evaluation circuit 13 are shown in FIG. It has the same function as that of the same reference numeral, and duplicate description is omitted.

The operation will be described. As shown in FIG. 2, the two magnetic heads 1A and 1B are selected by the switch 12 for channel selection by 1V, and the PG pulse 15 turns on the diode 14 for forced discharge every 1V. When the diode 14 is turned on, the capacitor 8 is rapidly discharged and the charge is removed. As a result, even if the reproduction RF signal is input from the previously selected magnetic head, for example, 1A and the signal is not input from the subsequent magnetic head 1B, the detection output 11 immediately settles to a level that can be evaluated.
That is, regardless of which magnetic head is selected, 1A or 1B, the presence or absence of recording can be determined within 1V, and in the case of frame recording, it can be determined with 2V in total.

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 significantly reduced.

FIG. 3 shows another embodiment in which the collector and emitter of the transistor 18 are connected to both ends of the smoothing capacitor 8 and a high active PG pulse 19 is supplied to the base to turn on the transistor 18. The transistor 18 functions as a switch for forced discharge. The operation is the same as that of the embodiment shown in FIG.

The present invention can be applied not only to a frame regenerator but also to a frame recorder, a field recorder or a regenerator, and an envelope detection circuit of a device for recording or reproducing a voice signal or a data signal on a magnetic disk. .

<Effects of the Invention> According to the envelope detection circuit of the present invention, the smoothing capacitor is forcibly discharged at every 1 V, so that the detection output immediately decreases when the reproduction output signal of the magnetic head is not input, and moreover within one track circumference. The detection output does not change even if the reproduction output signal changes. Therefore, for example, it greatly contributes to the reduction of the time required for creating a track map with a frame player.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is an operation explanatory diagram thereof, FIG. 3 is a circuit diagram of another embodiment, and FIGS. 4 and 5 are circuit diagrams of a conventional example. FIG. 6 is an operation explanatory diagram relating to FIG. In the drawing, 1A and 1B are magnetic heads, 7 is a detection diode,
Reference numeral 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, and 18 is a transistor as a forced discharge switch.

Claims (1)

[Claims] 1. A rectifier for detecting an envelope of a reproduction output signal of a magnetic head of a magnetic recording / reproducing apparatus for recording or reproducing a still image signal on a magnetic disk, and a smoothing capacitor for an output of the rectifier. An envelope detection circuit for a magnetic recording / reproducing apparatus, characterized in that in the circuit having the smoothing capacitor, a switch means which is turned on at an end portion of a synchronization is connected in parallel to each of the vertical scanning periods.