JPH061606B2 - RF signal detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an RF signal detecting device, and more particularly to an RF signal detecting device in a DAT (digital audio tape player).

<Prior Art> In DAT, audio data (P
A sub code, an ATF signal, etc. are recorded together with CM data). And, in the subcode area of each track, a second
As shown in the figure, the song number (program number), the start ID indicating the beginning of the song, the elapsed time from the beginning of the tape (absolute time), the elapsed time of the song (single time), and other not shown index , Sub-code information such as running time, year / month / day / hour / minute / second (calendar time) at the time of recording is recorded, and these sub-code information is properly displayed at the time of reproduction and used for a search which is a desired music number.

In the case of recording using a recorded tape in such a DAT, the state of the recording start position is (i) the RF signal is already recorded and the absolute time is also recorded, or (ii) the RF signal is also absolute. It is necessary to identify and display whether the time is not recorded or in the state (non-recorded state), or (iii) whether the RF signal is recorded but the absolute time is not recorded. The reason is that in the state of (i), the user can record at the latest recording position (REC
It can be recognized that absolute time can be continuously recorded from the end position), and it can be recognized that if recording is performed in the state of (ii), a blank part without RF signal and absolute time will be formed, and the state of (iii) If you record with, you can recognize that only absolute music is recorded and only music is recorded.Therefore, whether to record depending on the state of (i) to (iii), or search for another recording start position and record from there This is because it is possible to determine whether to perform.

From the above, the DAT has a function of detecting the presence or absence of the RF signal. FIG. 3 is a block diagram of a conventional RF signal detection device,
FIG. 4 is a waveform chart of each part. In FIG. 3, 11 is a recording / reproducing head, 12 is an amplifier, 13 is an amplifier output (playback signal), and a detection signal S _D having an envelope waveform of an RF signal S _RF (see FIG. 4 (a)) is detected. An output detection circuit, 14 is a smoothing filter that smoothes the detection signal S _D and outputs a DC level L _RF , and 15 is a threshold level L _S (see FIG. 4 (b)) and the level output from the smoothing filter. A comparator 16 for comparing the magnitude of L _RF is a system controller, which identifies the presence or absence of an RF signal according to the output from the comparator 15 and displays the status.
There is an RF signal when L _RF ≧ L _S , and R when L _RF <L _S
Judge that there is no F signal.

<Problems to be Solved by the Invention> However, in the above-mentioned conventional method for identifying the RF signal based on whether the output level from the smoothing filter is equal to or higher than a predetermined threshold level, malfunction easily occurs due to the noise level of the reproduced signal, and It was vulnerable to noise from the outside, and there were cases where it was determined that there was no RF signal.

From the above, it is an object of the present invention to provide an RF signal presence / absence detection device capable of accurately detecting the presence / absence of an RF signal.

<Means for Solving Problems> FIG. 1 is a block diagram of an RF signal detecting device of the present invention.

Reference numeral 1 is a level determination unit, 2 is a signal processing unit, 3 is a PLL lock state determination unit, 2a is a PLL circuit, 4 is a system controller, and 5 is a recording / reproducing head.

<Operation> The level discriminating unit 1 detects and smoothes the reproduction signal AS from the recording / reproducing head 5, discriminates whether or not the smoothing level L _RF is equal to or higher than a predetermined threshold level L _S , and the PLL lock state discriminating unit The lock state of the PLL circuit 2a is identified. The system controller 4 receives the signals from the level discriminating unit 1 and the PLL lock state discriminating unit 2, and determines that the RF signal is present when the PLL circuit 2a is in the locked state and the level L _RF is equal to or higher than the threshold level L _S. .

<Embodiment> FIG. 1 is a block diagram of an RF signal detecting apparatus according to the present invention, in which 1 is a reproduction signal AS from a recording / reproducing head, and a smoothed level L _RF is a predetermined threshold level L _S.
Level discriminating unit for discriminating whether or not the above is satisfied, 2 is a signal processing unit, and 3 is a signal reproducing unit for reproducing a clock signal included in the reproduced signal.
A PLL lock state determination unit 4 for identifying the lock state of the LL circuit 2a, a system controller 4 for performing various controls,
Reference numeral 5 is a recording / playback head, and 6 is an amplifier.

The level discriminating unit 1 has the same configuration as that of the conventional example shown in FIG. 3, and detects the output (reproduced signal) AS of the amplifier 6 to detect the envelope waveform of the RF signal S _RF (see FIG. 4 (a)). A detection circuit 1a that outputs the detection signal S _D that it has, and a smoothing filter 1b that smoothes the detection signal S _D and outputs a DC level L _RF.
And a comparator 1c for comparing the threshold level L _S (see FIG. 4 (b)) with the level L _RF output from the smoothing filter. When L _RF ≧ L _S , the comparator 1c is high. The level signal RFS is output.

The signal processing unit 2 includes a PLL circuit 2a for reproducing the clock signal CL included in the reproduction signal AS and a reproduction clock signal C.
The reproduction signal AS is read in synchronization with L, and 1 symbol 10
Converts bit audio data into a bit pattern of 1 symbol and 8 bits, and further adds 144 bits to the playback signal of 1 track.
Demodulation unit 2 that performs a parity check on the ID code (W ₁ , W ₂ ) recorded at the beginning of each block.
b, a RAM 2c that sequentially stores 8-bit data of 1 symbol demodulated by the demodulation unit, an error detection / correction processing unit 2d that performs error detection / correction processing for each predetermined number of symbols stored in the RAM, and a RAM 2c. The stored audio data after error correction processing is read out symbol by symbol in synchronization with a predetermined clock and is DA converted and output.
It has an A converter 2e.

The PLL lock state detection unit 3 counts the error pulse EP output from the demodulation unit 2b as a result of the parity check,
When the error count value N and the set value A are compared, the high level lock signal LKS is output when N <A, and the low level lock signal LKS is output when N ≧ A.

The overall operation of FIG. 1 will be described below.

Level judging unit 1 detects the reproduction signal AS from the recording and reproducing head 5, smoothed level L _RF is determined whether a predetermined threshold level L _S above, the high level if L _RF ≧ L _S A signal RFS is output, and if L _RF > L _S , a low level signal is output.

In parallel with the level determination, the demodulation unit 2 of the signal processing unit 2
The read signal b is stored in the RAM 2c while reading the reproduced signal AS in synchronization with the clock signal CL reproduced by the PLL circuit 2a and converting it from 10 to 8 symbols.
In d, error correction processing is performed on the data stored in the RAM.

The demodulator 2b also performs a parity check on the ID code. That is, for 2 bytes of ID codes W ₁ and W ₂ ,
Parity P is added and W detected from the reproduced signal
_It is checked whether W ₁ + W ₂ = P for ₁ and W ₂ .

An error pulse EP is generated every time an error is detected.
The error detection / correction processing unit 2b detects whether there is an error with a predetermined number of symbols to which an error correction code is added as one unit, and corrects it if any.

The PLL lock state detection unit 3 clears the count value for each scan, counts the error pulse EP output from the demodulation unit 2b, compares the error count value N with the set value A, and determines whether N <A. At times, a high level lock signal LKS indicating a locked state is output, and when N ≧ A, a low level signal lock LKS indicating an unlocked state is output. When the signal RFS and the lock signal LKS are both at high level, the system controller 4, in other words, the PLL circuit 2
When a is in the locked state and the level L _RF is equal to or higher than the threshold level L _S , it is determined that there is an RF signal, otherwise it is determined that there is no RF signal, and the determination result is displayed on a display device (not shown).

From the above, when there is no RF signal, if there is no RF signal even if the detection / smoothing level of the reproduction signal becomes higher than the threshold level due to noise or the like, the PLL circuit 2
Since "a" does not lock, it is not erroneously determined that there is an RF signal.

<Effects of the Invention> As described above, according to the present invention, detection of the reproduction signal, smoothing level and P
Since the presence or absence of the RF signal is detected in consideration of both the lock states of the LL circuit, the presence or absence of the RF signal can be accurately detected.

[Brief description of drawings]

 FIG. 1 is a block diagram of an RF signal detecting device of the present invention, FIG. 2 is an explanatory diagram of a sub-coat, FIG. 3 is a block diagram of a conventional RF signal detecting device, and FIG. 4 is a waveform diagram of each part in FIG. is there. 1 ... Level discriminating unit, 2 ... Signal processing unit, 2a ... PLL circuit, 3 ... PLL lock state discriminating unit, 4 ... System controller, 5 ... Recording / playback head

Claims (1)

[Claims] 1. An RF signal detecting device in a DAT, a level discriminating section for discriminating whether or not a level obtained by detecting and smoothing a reproduced signal from a head is equal to or higher than a predetermined level, and reproducing a clock signal included in the reproduced signal. PLL
And a RF signal presence / absence determining unit that determines that there is an RF signal when the detection and smoothing level of the reproduction signal is equal to or higher than the predetermined level. RF characterized by
Signal detection device.