JPH0668548A - Envelope detection circuit - Google Patents

Abstract

PURPOSE:To provide the envelope detection circuit following up a tape running speed and a level fluctuation at time of reproduction and able to eliminate dropout. CONSTITUTION:An output signal of a reproduction head 1 is amplified by a reproduction amplifier 2, an A/D converter 3 converts the signal into a digital signal. An LPF 4 eliminates a high frequency component and a rectifier means 5 converts the output signal into a DC signal. A peak hold means 6 holds a peak level of the rectifier means 5, its output is divided by resistors R1, R2 and compared with an output of the rectifier means 5 at the comparator 7. A low level detection means 8 detects it that an output of the comparator 7 becomes a low level for a prescribed period to reset the peak hold means 6 via a reset means 12 to use the level for an output of the rectifier means 5. A high level detection means 10 measures a time when the comparator 7 reaches a high level and its output is given to a dropout protection means 9. A period measurement means 11 connects to a sample rate decision means 13 and its output decides the operating frequency of each circuit above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an envelope detecting circuit for detecting an envelope waveform of a signal intermittently recorded on an auxiliary track of a recording / reproducing apparatus.

[0002]

2. Description of the Related Art In recent years, a PCM recording / reproducing apparatus using a mechanism of a compact cassette tape recorder has been developed, and a signal recorded intermittently on an auxiliary track of the PCM is used to measure the running time of the tape or intermittently record the tape. By changing the signal cycle, it is possible to select songs at high speed.

Conventionally, in order to detect the envelope signal of the signal intermittently recorded on the auxiliary track, the intermittently recorded signal is rectified and input to two data holding means having different time constants, and the output thereof is obtained. I was comparing.

A conventional embodiment will be described below with reference to the drawings. FIG. 2 is a block diagram of a conventional envelope detection circuit. In FIG. 2, the reproduction amplifier 22 amplifies the output signal of the reproduction head 21. A low pass filter (hereinafter referred to as LPF) 23 removes high frequency components from the output signal of the reproduction amplifier 22. The rectifying means 24 is an LPF
The output signal of 23 is converted into DC. The output of the rectifying means 24 is connected to the data holding means 25 and 26 having different time constants. The output of the data hold means 26 is a resistor R2.
1, the voltage is divided by R22, the comparator 27 compares it with the output of the data hold circuit 25, and the envelope waveform is output terminal 28.
Is output to.

The operation of the envelope detection circuit configured as described above will be described below.

The signal read from the tape by the reproducing head 21 is amplified by the reproducing amplifier 22 and input to the LPF 23. The LPF 23 removes high frequency components from the output signal of the reproduction amplifier 21, and the rectifying means 24 converts the output signal of the LPF 23 into a direct current. The output of the rectifying means 24 is input to the data holding means 25 having a short time constant and the data holding means 26 having a long time constant. Further, the data hold means 26
Is divided by resistors R21 and R22, is compared with the output of the data hold means 25 by the comparator 27, and is output to the output terminal 28 as an envelope waveform.

[0007]

However, in the above-mentioned conventional configuration, there is no problem when the tape running speed is substantially constant, but when the tape running speed changes, all the circuit constants are changed in order to change the time constant. It is necessary to change it in tandem, which is difficult to achieve. Furthermore, if the level fluctuation during reproduction is large, tracking may be delayed and the envelope may be detected incorrectly. Further, there is a problem that even if dropout occurs, it cannot be removed.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide an envelope detecting circuit capable of removing the dropout by following the tape running speed and the level fluctuation at the time of reproduction. And

[0009]

To achieve this object, the envelope detection circuit of the present invention is an AD converter for converting a signal intermittently recorded on a tape into a digital signal, and a high frequency component from its output. , An rectifying means for rectifying the output of the LPF, a peak holding means for holding the peak of the output, a comparator for comparing the output of the rectifying means with the output of the peak holding means, and a low of the comparator. A reset means for measuring the level section and resetting the value of the peak hold means to the output value of the rectifying means if the low level continues for a certain period, a cycle measuring means for measuring the cycle from the signal of the comparator, and a cycle measuring means. Sample rate determining means for determining the operating frequency of each circuit from the values, high level detecting means for measuring a high level section of the output of the comparator, and high level The value of Le detecting means when the predetermined value or less has a structure of drop-out protection means for holding the output of the comparator signal to the high level.

[0010]

According to the present invention, with the above-mentioned structure, the cycle of the envelope waveform is measured even if the running speed of the tape is changed, and the sampling frequency of each circuit is changed by using the sample rate determining means. Envelope detection is possible by following the speed. Further, even when the level fluctuation at the time of reproduction is large, the detection level of the peak hold means follows the level fluctuation of the reproduction signal, the detection level of the comparator changes, and the envelope can be detected correctly.

Further, the high level time is measured by the high level detecting means, and the output of the dropout protection means 9 is held at the high level until the value exceeds a certain value, so that the dropout during that time can be eliminated. .

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an envelope detecting circuit according to an embodiment of the present invention. In FIG. 1, the reproducing amplifier 2 amplifies the output signal of the reproducing head 1. An AD converter (hereinafter referred to as ADC) 3 converts the analog signal of the reproduction amplifier 2 into a digital signal. LPF
Reference numeral 4 is connected to the output of the ADC 3 to remove high frequency components.
The rectifying means 5 converts the output signal of the LPF 4 into DC. The output of the rectifying means 5 is the peak hold means 6 and the comparator 7.
Connected to one input. Peak hold means 6
Detects the peak value of the rectifying means 5, and outputs the R1 and R
It is divided by 2 and is connected to the other input of the comparator 7. The output of the comparator 7 is connected to the low level detection means 8, the dropout protection means 9, the high level detection means 10, and the cycle measurement means 11. The output of the low level detection means 8 is connected to the reset means 12, and the output of the low level detection means 8 resets the signal of the peak hold means 6. The high level detection means 10 measures the high level time of the comparator 7, the output of which is connected to the dropout protection means 9 and the envelope waveform is output to the output terminal 28. Cycle measuring means 11
Is connected to the sample rate determining means 13 and its output is connected to each of the above circuits to determine its operating frequency.

The operation of the envelope detecting circuit configured as described above will be described below.

The signal read from the tape by the reproducing head 1 is amplified by the reproducing amplifier 2 and converted into a digital signal by the ADC 3. The LPF 4 removes a high frequency component from the output of the ADC 3, and the rectifying means 5 converts the high frequency component into a direct current. The output of the rectification means 5 is peak-held by the peak hold circuit 6, further divided by R1 and R2, and compared with the output of the rectification means 5 by the comparator 7, and the output of the rectification means 5 is divided by the peak hold means 6. If it is larger than the output value after compression, the output of the comparator 7 becomes high level, and if it is smaller, it becomes low level. The low level detecting means 8 keeps counting while the output of the comparator 7 is at a low level, and if the value exceeds a certain value, the reset means 12 takes timing as if the level of the reproduction signal has decreased, and the peak is reached. The value of the holding means 6 is reset to the current output level of the rectifying means 5. The high level detecting means 10 measures the time of the high level of the comparator 7, holds the output of the dropout protection means 9 at the high level until the value exceeds a certain value, and thereafter outputs the output of the comparator 7. Is output to the output terminal 14. Cycle measuring means 1
Reference numeral 1 measures the cycle of the output of the comparator 7, and the sample rate determining means 13 determines the current cycle, and each of the circuits described above, that is, ADC 3, LPF 4, rectifying means 5, peak holding means 6, low level detecting means. 8. The operating frequencies of the high level detecting means 10, the cycle measuring means 11 and the resetting means 12 are determined.

As described above, according to this embodiment, the cycle of the envelope waveform is measured even if the tape running speed changes, and the operating frequency of each circuit is determined by the sample rate determining means 13.
Since it is changed by using, the envelope detection is possible by following the tape running speed.

Further, when the level fluctuation during reproduction is large and the level sharply increases, the peak hold means 6 increases the detection level of the comparator 7, and when the level sharply decreases, the low level detection means 8 also. Since the fact that the level has been lowered is detected and the hold value of the peak hold means 6 is reset to the current level, the detection level of the comparator 7 decreases following the level fluctuation of the reproduction signal, and the envelope can be detected correctly.

Further, the high level detecting means 10 measures the time of the high level, and until the value exceeds a certain value,
Since the output of the dropout protection means 9 is held at the high level, the dropout during that time can be eliminated.

[0019]

As described above, according to the present invention, the signal recorded on the tape is converted into a digital signal by the AD converter, rectified by the rectifying means, and then the output is peak-held by the comparator. The envelope is detected by comparing with the value, the period is measured, and the operating frequency of each circuit is changed by using the sample rate determining means. It is possible. Further, since the peak value of the input signal is always held by the peak hold means, even if the level during reproduction sharply increases, the peak hold means increases the detection level of the comparator, and conversely the level sharply decreases. In this case, the low level detection means detects that the level has been lowered and the hold value of the peak hold means is reset to the current level. It can be detected.

Further, the high level section of the output of the comparator is measured by the high level detecting means, and when the value of the high level detecting means is equal to or less than a certain value, the output of the signal of the comparator is held at the high level. Since it is provided with an out protection means, the dropout between them can be eliminated.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an envelope detection circuit according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an envelope detection circuit in a conventional example.

[Explanation of symbols]

 3 AD Converter 4 Low Pass Filter 5 Rectifying Means 6 Peak Hold Means 7 Comparator 8 Low Level Detecting Means 9 Dropout Protecting Means 10 High Level Detecting Means 11 Cycle Measuring Means 12 Reset Means 13 Sample Rate Determining Means

Claims (2)

[Claims] 1. An AD converter for converting a signal recorded on a tape into a digital signal, a low-pass filter for removing high-frequency components from the output of the AD converter, and a rectifying unit for rectifying the output of the low-pass filter. A peak holding means for holding the peak of the output of the rectifying means, a comparator for comparing the output of the rectifying means with the output of the peak holding means, and a low level section of the comparator for measuring for a certain period of time. Low level detecting means for outputting if the level continues, reset means for resetting the value of the peak hold means to the output value of the rectifying means by the output of the low level detecting means, and measuring the period from the signal of the comparator. An envelope provided with cycle measuring means and sample rate determining means for determining an operating frequency from the value of the cycle measuring means. Out circuit. 2. A high level detecting means for measuring a high level section of the output of the comparator, and when the value of the high level detecting means is below a certain value, the output of the signal of the comparator is held at the high level. The envelope detection circuit according to claim 1, further comprising dropout protection means.