JPS63231769A - Bit synchronizing circuit - Google Patents

Abstract

PURPOSE:To enable data reproduction in fast-forward mode by switching the characteristics of a phase-locked loop circuit which extracts reproduced data and performs bit synchronization to characteristics with a wide capture range when a fast-forward reproducing means is put in operation. CONSTITUTION:Signals reproduced by heads 2A and 2B are applied to a playback amplifier 13 through a switch 12 at the time of reproduction and then applied to a bit synchronizing circuit 15 through a waveform shaping circuit 14. The output data and clock of the circuit 15 are supplied to a reproduction processing circuit 16. The circuit 15 inputs data by an FF 100 and a clock is generated by a PLL circuit which compares the data of the circuit 14 with the clock of a voltage-controlled oscillator 10. In normal play mode, a transistor (TR) 108 is turned on with outputs 21F and 21R of a microcomputer 21. In fast search mode, the TR 108 is turned off and the characteristics of the PLL circuit are switched to the characteristics with the wide capture range. Thus, the circuit is put in operation with characteristics with a good error rate in normal play mode and data reproduction can be performed even in fast search mode.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a digital signal reproducing device, and more particularly to a bit synchronization circuit suitable for fast forwarding and rewinding reproduction in a rotary head type magnetic recording and reproducing device.

[Prior Art] A conventional bit synchronization circuit is designed as a phase-locked loop (PLL circuit) to improve the error rate during normal reproduction.
A circuit such as that listed in Publication No. 24013 is used.

[Problems to be Solved by the Invention] The above-mentioned conventional technology does not take into account the fact that the data transmission rate changes significantly during high-speed search, especially in a rotating head type magnetic recording/reproducing device. At this time, there was a drawback that the data could not be reproduced.

An object of the present invention is to reproduce data without deteriorating the performance during normal reproduction even when the transmission rate fluctuates significantly compared to normal reproduction, such as during high-speed search.

[Means for Solving the Problems] The above object is achieved by providing means for switching the constant of the loop filter of the PLL circuit to the high frequency side.

[Function] During normal playback, the loop filter is selected on the low frequency side, so it is possible to suppress the occurrence of jitter due to pulse-like internal disturbances such as in the phase comparator, and data errors can be minimized. During high-speed search, the loop filter is selected on the high frequency side. From choosing to the side,
The capture range is large, and data can be captured while following large fluctuations in the transmission rate.

[Example] Hereinafter, an example of the present invention will be described with reference to FIG. 1st
The figure shows a configuration diagram of a rotary head type magnetic recording/reproducing apparatus according to the present invention. 1 in Figure 1 is a cylinder,
Two heads 2A and 2B with different azimuth angles are attached, and by rotating the cylinder 1, data is recorded and reproduced on the tape 3. The tape 3 is fed by a capstan that does not have a capstan. Signals from heads 2A and 2B are coupled to switch 12 via a rotary transformer (not shown). During recording processing, the analog signals added to 6L and 6R are processed in an analog manner such as whether or not emphasis is applied in the audio circuit 7, and then sent to the S/H8.
Sampled at a constant sampling frequency at L, 8R, A/D
The data is converted into digital data by a converter 9. The recording signal processing circuit 10 inputs this PCM audio data and control signals such as the song number, time, and song start signal from the microcomputer 21, and processes it into a certain format such as adding an error correction code and a synchronization signal. The data is processed according to the following and is applied to the switch 12 via the recording amplifier 11. The switch 12 selects the recording amplifier 11 side during recording, applies signals to the heads 2A and 2B, and records the signals on the tape 3.

During reproduction, the signals reproduced by the heads 2A and 2B are applied to the reproduction amplifier 13 via the switch 12, where they are amplified and subjected to waveform equalization processing. After that, the waveform shaping circuit 14 outputs 1.0
The pulse waveform is shaped into a pulse waveform and applied to the bit synchronization circuit 15.

The output data and clock of the bit synchronization circuit are applied to a reproduction processing circuit 16, which performs data error detection and correction processing on PCM audio data and control signals.The audio data is sent to a D/A converter 17, and the control signal is Add to microcomputer-21. The output of the D/A converter 17 is
Analog signals are output to 2OL and 2OR via the S/H circuits 18L and 18R and the audio circuit 19.

In such a configuration, the bit synchronization circuit 15 performs the operation of taking in data with the flip-flop 100, and its clock is obtained by combining the data of the waveform shaping circuit 14 and the clock of the voltage controlled oscillator 101 with the phase comparison circuit 103. ,
Resistors 104, 106, 107 that constitute the loop filter
, is generated by a PLL circuit consisting of a capacitor 105 and an amplifier 102. Here, the loop filter is configured such that a transistor 108 is provided in series with the resistor 106, and the base of the transistor is ON10 FF controlled via an AND circuit 110 and a resistor 109. The servo circuit 22 is a circuit that controls tape feeding and cylinder rotation speed, and 21F is fast forward when O is set, 21R is rewind when O is set,
When both are 1, it is in the play state. Also, 21S is
These control signals are controlled by the microcomputer 21, which controls whether the player is in a play state or a stop state. With the above configuration, in the normal play state, 21. F, 2
Since both 1R are 1, the AND circuit 110 becomes a level, and the transistor 108 is turned on, forming a loop filter. A resistor 106 is inserted in parallel with resistor 107. Therefore, since the resistor 104 does not change, the gain in the high frequency range decreases and the capture range decreases.
No phase shift occurs due to high-frequency noise, and the bit synchronization circuit has a configuration with a good error rate. Further, during fast forwarding and rewinding, either 21F or 21R becomes O level, and as a result, the transistor 108 is turned FF.

Therefore, it becomes a lag-lead filter composed of resistors 104, 107 and capacitor 105. This means that the gain in a wide range is increased compared to normal playback, and the capture range is expanded. During a high-speed search, it is not necessary to reproduce the music signal faithfully, but to read the control signal reliably, and by widening the capture range, data can be captured without malfunction.

FIG. 2 is a diagram showing head trajectories during high-speed search according to the present invention. Tracks 30B and 30B recorded on tape 3,
31A, . . . , 33A, the head 2A traces them while crossing them as shown in the figure.

30B, 31B, . . . are not reproduced because their azimuth angles are different, and 30A, 31A, 32A, . . . can be read by the head 2A.

FIG. 3 is a diagram showing the timing of signals read out by the head 2A, and track signals 30A to 39A can be reproduced with respect to cylinder rotation.

The control signals recorded therein are read out, and the playback signal processing circuit 16 and microcomputer 21 determine whether the desired beginning signal of the song is detected.

FIG. 4 is a timing chart during the search operation of FIG. 1, in which the microcomputer 21 is 21S.

21R and 21F are all set as rubels and put into play mode. Here, in order to search for a song, 21F is set to O level and a high-speed fast forward operation is performed. The signal processing circuit 16 reads out the control signal, and at timing 16S when the desired song start signal is detected, the microcomputer 21 sets 21F to 1 and stops the fast forward operation. In order to correct the tape overrun, 21R is set to 0 and the tape is rewound until the beginning signal in the direction is detected again. Therefore, during the search operation, the AND circuit 110 can be set to O, and the capture range can be expanded during the search operation.

FIG. 5 is a diagram showing changes in the capture range with respect to the value of the resistor 107 in FIG. 1. By increasing the resistor 107, the capture range can be widened.

FIG. 6 is a graph of the data error rate with respect to the value of the resistor 107, and the smaller the resistance value 107, the better the error rate will be.

[Effects of the Invention] As described above, according to the present invention, during play and during high-speed search,
By installing a circuit to switch the loop filter,
During normal playback, the music signal can be reproduced with good error rate and faithfully, and during high-speed search, the capture range is expanded to follow fluctuations in data transmission speed, ensuring no errors.
Since the PLL circuit can be locked, the control signal can be detected without malfunction.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a rotary head type magnetic recording and reproducing apparatus according to the present invention, FIG. 2 is a diagram showing the head trajectory during high-speed search, FIG. 3 is a diagram showing the reproduced signal during high-speed search, and FIG. 4 is a diagram showing the head trajectory during high-speed search. is a timing diagram of FIG. 1, FIG. 5 is a diagram showing the capture range of FIG. 1, and FIG. 6 is a diagram of the error rate of FIG. 15...Bit synchronization circuit, 16...Reproduction signal processing circuit, 21...Microcomputer, 22...Servo circuit,

Claims (1)

[Claims] (1) A digital signal reproducing device that has means for recording and reproducing digital signals on a recording medium, and means for intermittently extracting data from the recording medium and performing fast-forward reproduction of the data during normal reproduction. When operating a phase-locked loop circuit having a first characteristic for extracting data and performing bit synchronization, a means for switching to a second characteristic having a wider capture range than the first characteristic, and a means for fast forward reproduction, A bit synchronization circuit characterized in that it synchronously switches to a phase-locked loop circuit having a second characteristic.