JPS63179407A - Envelope detection circuit - Google Patents

Abstract

PURPOSE:To make a comparator independent of the fluctuation of a reproduced envelope amplitude fluctuation with simple constitution by preparing a digital signal going to an H level only at a head touch period in addition to a digital signal being the result of a reproduced envelope given to the comparator and ANDing the both. CONSTITUTION:A counter circuit 5 outputting a digital signal synchronously with a number of revolutions of the rotary head drum and being at H only the head touch period, the comparator 4 outputting an H level corresponding to a reproduced signal envelope, and an AND circuit 6 outputting AND of two outputs, are provided. Thus, the comparator 4 outputs H level corresponding to the reproduced envelope with a sufficient time constant independently of the temporary missing of the reproduced envelope or amplitude fluctuation and its output and a signal being at an H level at the head touch period are ANDed and the result is outputted. Thus, the duty is accurate with respect to the reproduced envelope and the accuracy and the reliability are high.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an envelope detection circuit for a rotary head digital tape recorder.

2. Description of the Related Art An example of a conventional envelope detection circuit is shown in FIGS. 2 and 3.
This will be explained with reference to the figures. With a very simple configuration, when a reproduced signal envelope as shown in FIG. A digital signal that is "H" appears at the output 10 at a portion with an envelope as shown in (b).

Problems to be Solved by the Invention However, the reproduction envelope does not always maintain a constant amplitude. For example, during a high-speed search, the head crosses the trunk, so the amplitude of the reproduction envelope decreases in the reverse azimuth track portion. The problems that the above configuration has under such conditions will be explained below with reference to the drawings.

FIG. 4 shows the response of the envelope detection circuit during high-speed search. FIG. 4(a) is an example of a reproduced envelope waveform during a high-speed search, and the depression at the center of the envelope corresponds to the reverse azimuth section. If the time constant of the envelope detection circuit is set small for this input, the output will be "L" in the reverse azimuth track part as shown in Figure 4(b).
” and the envelope detection circuit makes an incorrect judgment.

Conversely, if the time constant is set larger, the output will be the fourth
As shown in the figure (C1), it is always in the “H” state and the light is off.
Specification 1, Name of the invention Envelope detection circuit 2, Claims A counting circuit that outputs a digital signal that is "H" only in a head touch section synchronized with the rotation speed of a rotating head drum;
An envelope detection circuit comprising: a comparator that outputs "H" in response to a reproduced signal envelope; and an AND circuit that outputs an AND of the two outputs.

3. Detailed Description of the Invention Field of Industrial Application The present invention relates to an envelope detection circuit for a rotary head type digital tape recorder.

2. Description of the Related Art An example of a conventional envelope detection circuit is shown in FIGS. 2 and 3.
This will be explained with reference to the figures. With a very simple configuration, when a reproduced signal envelope as shown in FIG. A digital signal that is "H" appears at the output 10 at a portion with an envelope as shown in (b).

Problems to be Solved by the Invention However, the reproduction envelope does not always maintain a constant amplitude. For example, during a high-speed search, the head crosses the trunk, so the amplitude of the reproduction envelope decreases in the reverse azimuth track portion. The problems that the above configuration has under such conditions will be explained below with reference to the drawings.

FIG. 4 shows the response of the envelope detection circuit during high-speed search. FIG. 4(a) is an example of a reproduced envelope waveform during a high-speed search, and the depression at the center of the envelope corresponds to the reverse azimuth section. If the time constant of the envelope detection circuit is set small for this input, the output will be "L" in the reverse azimuth track part as shown in Figure 4(b).
” and the envelope detection circuit makes an incorrect judgment.

Conversely, if the time constant is set larger, the output will be the fourth
As shown in the diagram (C1), there is a counting circuit that outputs a digital signal that is always in the "H" state and is synchronized with the number of revolutions and is "H" only in the head touch section, and a counter circuit that outputs "H" in response to the playback signal envelope. By providing a comparator and an AND circuit that outputs the AND of the above two outputs, it is possible to set the time constant of the comparator with some margin, maintain an accurate duty with respect to the playback envelope, and be sensitive to fluctuations in the amplitude of the playback envelope. It always operates accurately and stably without being affected.
It is extremely useful in practical terms.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing envelope detection in an embodiment of the present invention, FIG. 2 is a block diagram of a conventional envelope detection circuit, and FIG. 3 is a waveform diagram of main parts of the conventional envelope detection circuit during normal playback. FIG. 4 is a waveform diagram of a main part of a conventional envelope detection circuit during a high-speed search, and FIG. 5 is a waveform diagram of a main part of an embodiment of the present invention during a high-speed search. 4... Comparator, 5... Counting circuit, 6... AND circuit, 9... Comparator. Figure 1 Figure 2 Figure 3 - WIF Figure 4 (C) □ Time Figure 5 - Kamomaki

Claims (1)

[Claims] a counting circuit that outputs a digital signal that is "H" only in the head touch section synchronized with the rotation speed of the rotating head drum;
An envelope detection circuit comprising: a comparator that outputs "H" in response to a reproduced signal envelope; and an AND circuit that outputs an AND of the two outputs.