JPS63308766A - Automatic gain controller - Google Patents

Abstract

PURPOSE:To demodulate a data with less error by detecting the amplitude of a received digital signal so as to control a variable gain control amplifier. CONSTITUTION:A signal reproduced from a rotary head 1 is amplified and shaped by a preamplifier 2 and an equalizer 3 and the result is inputted to a variable gain amplifier 4. The output of the amplifier 4 is sent to a data demodulation circuit and supplied to an envelope detector 5. On the other hand, head position information and a tack pulse are given to a timing generation circuit 7, where a preamble position pulse (c) of the reproduced data is generated. The pulse (c) is used to allow a holding circuit 6 to hold the output of the detector 5 till the next preamble detection output is generated. The output of the circuit 6 controls the gain of the amplifier 4 to supply a reproducing signal of a proper level to the data demodulation circuit.

Description

[Detailed Description of the Invention] [Object of the Invention] (Field of Industrial Application) The present invention relates to communication devices or recording/reproducing devices, and is suitable for application to gain control devices normally installed in these devices. be.

(Prior Art) The principle of a conventional automatic gain device will be explained with reference to FIG. In conventional devices, the signal that determines the gain of the amplifier is
It is obtained by detecting and smoothing the envelope of the received signal.

That is, when the envelope level is large, the gain of the amplifier is reduced.

(Problem to be Solved by the Invention) However, in the conventional device as described above, the magnitude of the signal that determines the gain changes greatly depending on the content of the signal to be transmitted, even though the signal at the specified level is being received. There is. The above case will be explained below with reference to FIG. In the case of FIG. 3, a signal such as A is transmitted for data a, and is called a dicode. The signal of b is 1 when the data of a changes.
In this example, when the change is from O to 1, a positive pulse is transmitted, and when the change is from 1 to O, a negative pulse is transmitted. This signal is similar to the signal reproduced by a wound head in a normal magnetic recording/reproducing device. When receiving a signal such as 0, 0, 0, etc.
．． ...or a series of xi 1 n 1,1゜1, ...
, the number of pulses received per time will be very small.

On the other hand, the data often changes, for example, 1,0°1.0
．． When receiving a signal such as ..., the number of pulses is maximum. When trying to obtain a gain control signal from such a signal by envelope detection and smoothing using a conventional device, the value becomes small in the former case and becomes large in the latter case, regardless of whether the received signal is at a specified level. In either case, a correct control signal cannot be obtained.

[Structure of the invention]

(Means for solving the problem) The solution adopted by the present invention will be explained with reference to FIG.
In normal data transmission, a certain length of data is combined with some additional information (such as a synchronization signal indicating the start of data and a parity signal for detecting and correcting data errors) as one information unit (packet). Send. At this time, a preamble or run-up signal is used for data identification on the receiving side and to synchronize the regenerated clock generator.
Adds fixed data called ``up'' to the packet. This fixed data is usually selected in a pattern that maximizes the number of received pulses, in other words, maximizes the synchronization information of the clock generator.The present invention provides means for identifying the position of this fixed data. and means for detecting and smoothing the envelope of this fixed data to obtain a signal for controlling the variable gain control amplifier.

(for production) The operation of the present invention will be explained with reference to FIG.

In FIG. 5, the received signal is demodulated by a demodulator 2. In FIG. A synchronization signal in the demodulated data is detected by a synchronization signal detector 3, and its timing pulse a triggers a preamble position pulse generator 5. The preamble position generator 5 generates a pulse b corresponding to the preamble timing of the received signal, and this pulse gates the input of the envelope detector 6. The output of the detector 6 is held until the next input. , the gain of the amplifier 1 is controlled by this output. Since the preamble data pattern is fixed, the output of the detector 6 corresponds to the input signal level.
The data is always input to the data demodulator 2 at an appropriate level.

(Example) The present invention will be explained in detail below with reference to FIG.

FIG. 1 shows an example in which the present invention is applied to a reproducing amplifier of a rotary head type magnetic recording device. In a six rotary head type recording device, data is not continuous but is formed in a fixed length obliquely with respect to the tape, called a track. ) are recorded discontinuously.

Therefore, during reproduction, when the head moves from track 1 to track 2, for example, the timing information of the reproduction signal becomes discontinuous.

The beginning of the track cannot be played back correctly until resynchronization is performed. To avoid this, the preamble described above is usually recorded in this part instead of information. This preamble position information is the timing at which contact between the head and tape begins, and information on the rotational position of the head (tack pulse).
You can get more. This will be further explained with reference to FIG.

In FIG. 1, a signal reproduced by a rotary head 1 is amplified and shaped by a preamplifier 2 and an isograph 3, and is input to a variable gain amplifier 4. The output of the variable gain amplifier 4 is sent to a data demodulation circuit and is also supplied to an envelope detector 5. On the other hand, the head position information and tack pulse b are input to a timing generation circuit 7, which generates a preamble position pulse C of reproduction data. This preamble position pulse causes the holding circuit 6 to hold the output of the envelope detector 5, that is, the preamble envelope detection signal, until the next preamble detection output is generated.

The output of the holding circuit 6 controls the gain of the variable gain amplifier 4,
In this embodiment, the input of the envelope detector is not gated, but the output is gated to the holding circuit 6 so that the reproduced signal is supplied to the data demodulation circuit at an appropriate level. Although this is different from the above (prior art), there is no fundamental difference.

〔Effect of the invention〕

As explained above, according to the present invention, a signal of an appropriate level can be supplied to the data demodulation circuit regardless of the contents of received or reproduced data, and data can be demodulated with few errors.

[Brief explanation of the drawing]

Fig. 1 shows an embodiment of the present invention, and Fig. 2 shows the operation of a conventional device.
FIG. 3 is a diagram for explaining each of the problems of the conventional device, FIG. 4 is a diagram illustrating a transmission type in data transmission, etc., and FIG. 5 is a diagram for explaining the present invention in detail. 1...Rotating head 2...Preamplifier 3...Equivalent device 4...Variable amplifier 5...Envelope line detector 6...Holding circuit 7...Timing generation circuit Agent Patent attorney rules Ken Ken Double amount Mitsunoichi Matsuyama? -1 training lesson 1p si 1bo Ori t redoku! Second
Figure 00/l//10101010

Claims (1)

[Claims] An automatic gain control device comprising means for extracting fixed pattern information at a specific position of a received digital signal and configured to determine the amplification degree of the circuit by detecting the amplitude thereof.