KR0166741B1 - Automatic gain control device for trick play - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a trick-playing apparatus of a digital video cassette recorder, and in particular, an automatic gain compensating device for trick-playing that compensates for the repetitive reduction in the output level of a playback signal during trick-playing. It is about. In the present invention, the waveform of a signal that has been reproduced and amplified during trick reproduction is corrected by an impedance value obtained from the envelope waveform of the reproduced amplification signal. Therefore, the automatic gain compensation device for trick play according to the present invention makes the level of the output signal even during trick play as in normal play. In addition, it has the effect of improving the bit error rate of the system during trick play.

Description

Automatic gain compensation device for trick play

1 is a block diagram showing a regeneration system of a general digital V-CR.

(A) of FIG. 2 shows the trajectory of the head on the tape when the tape is played back at 9 times speed in FIG. 1, and (b) (c) is an output waveform diagram of the head.

3 is a block diagram showing a digital system of a digital VD (D-VCR) including an automatic gain compensation device for trick reproduction according to the present invention.

4 is an input and output waveform diagram of each part of the automatic gain compensation apparatus of FIG.

5 is a view for explaining the operation of the switched capacitor in FIG.

* Explanation of symbols for main parts of the drawings

10: play head 12: regeneration amplifier

14: reproduction equalizer 16: data detector

18: playback clock recovery section 20: data / clock synchronization section

30: delay 40: automatic potential detection unit

50: voltage controlled oscillator 60: automatic gain control unit

62: variable resistor section 64: gain adjustment section

100: automatic gain compensation device SW1 to SW3: first to third switches

AMP: Amplifier C: Condenser

R: resistance

The present invention relates to a trick-playing apparatus of a digital video cassette (D-VCR), in particular, to compensate for the repetitive reduction in the output level of a playback signal during trick-playing. An automatic gain compensation device for trick play.

FIG. 1 is a block diagram showing a reproduction system of a general D-VCR. In FIG. 1, the reproduction head 10 reads out a signal recorded on a predetermined recording medium and applies it to the reproduction amplifier 12. The reproduction amplifier unit 12 receives the read signal, amplifies the signal to a predetermined size, and applies the read signal to the reproduction equalizing unit 14. The reproduction equalization unit 14 corrects the waveform of the amplified signal to be applied to the data detection unit 16 and the reproduction clock recovery unit 18. The data detector 16 detects the original digital data recorded on the recording medium from the received reproduction equalization waveform and outputs the original digital data to the data / clock synchronizer 20. The reproduction clock recovery unit 18 detects and recovers the reproduction clock from the received reproduction equalization waveform and outputs the reproduction clock to the data / clock synchronization unit 20 and the reproduction clock output terminal. The data / clock synchronizer 20 outputs the detected digital data in synchronization with the reproduction clock.

In a reproducing system as shown in FIG. 1, high-speed reproduction is generally performed when a desired signal is quickly found among signals recorded on a predetermined recording medium. Fast Play is also called 'Quick Finder' or 'Trick Play' (hereafter referred to as the term 'Trick Play'). It's called a REVIEW. The trick play is 3 times, 5 times, 7 times and 9 times speed. (A) of FIG. 2 shows the trajectory of the head on the tape when playing back at 9x speed. Normal play is when the head travels on track number 1. However, playback of tracks up to track number 9 becomes cue, and playback of tracks up to track number -9 in reverse direction results in review. At this time, the tape speed is about nine times that of normal playback. (B) and (c) of FIG. 2 show the output waveforms of the head at the time of review and cue, respectively. It can be seen that the envelope waveform of the signal output during the trick play is different from the normal play. In other words, the envelope waveform at the time of trick play is a continuous rhombus form, and the level drops to 'zero' at the point where the waveforms intersect (in the dotted line circle). The part where the output level becomes 'zero' becomes noise, which causes the system's bit error rate (BER) to decrease.

SUMMARY OF THE INVENTION An object of the present invention for solving the above problems is to provide an automatic gain compensation device for trick play that can maintain the same output level as normal play even during trick play by correcting that the level of the output signal is unbalanced during trick play. Is in.

The automatic gain compensation device for trick reproduction according to the present invention for achieving the above object is a gain compensation device of a reproduction amplification signal for trick reproduction of a magnetic recording / playback device, wherein the user selects a normal playback or trick playback mode. A first switch switched by inputting a signal; When the first switch is connected to the trick play mode, a signal read out from the play head and amplified by the play amplified signal is detected and full-wave rectified by detecting the envelope waveform. Detection unit; A voltage controlled oscillator which receives the output signal of the potential detector and generates and outputs an oscillation frequency proportional to the voltage; A delayer for receiving the regeneratively amplified signal and delaying and outputting the regeneratively amplified signal received while the oscillation frequency is generated and output from the voltage controlled oscillator; And a gain control unit which receives the oscillation frequency from the voltage controlled oscillator and adjusts the gain of the reproduction amplification signal applied from the delay unit by using a resistor which is inversely proportional to the input oscillation frequency and outputs the signal to the reproduction equalizer. do.

Hereinafter, the present invention will be described in detail with reference to FIGS. 3 to 5.

3 is a block diagram showing a regeneration system of a digital-VCR according to the present invention. In FIG. 3, the output terminal of the reproducing amplifier 12 of FIG. 1 includes a first switch SW1 switched according to the mode selection signal CTL _{N / T.} The first contact a of the first switch SW1 is connected to the contactor c when in the normal play mode and the second contact b is in the trick play mode. An automatic gain compensation device 100, which is a main part of the present invention, is connected between the regeneration amplifier 12 and the second contact b of the first switch SW1. The automatic gain compensator 100 firstly, a delay unit 30 for delaying the reproduction amplifier signal received from the reproduction amplifier unit 12 for a predetermined time and an automatic potential detection unit 40 for outputting a voltage corresponding to the reproduction amplifier signal. ). The automatic potential detection unit 40 includes a full-wave rectifier 42 and an inverting integrator 44. A voltage controlled oscillator (VCO) 50 for generating an oscillation frequency proportional to the output voltage is connected to the output terminal of the automatic potential detection unit 40.

On the other hand, the automatic gain control unit 60 for controlling the gain of the reproduction amplifier signal is connected to the output terminal of the delay unit 30. The automatic gain control unit 60 is composed of a variable resistor unit 62 and a gain adjustment unit 64. The variable resistor unit 62 receives the output signal of the voltage controlled oscillator 50 and outputs in phase with the in-phase buffer unit 61 for outputting in phase with the reverse phase buffer unit 63 for outputting in reverse phase, and the in-phase buffer unit 61 and reverse phase buffer. It is composed of a switched capacitor circuit that receives the output signal of the unit 63 as a switching control signal. The switched capacitor circuit is composed of second and third switches SW2 and SW3 connected in series and a capacitor C connected in parallel with the switches SW2 and SW3. An amplifier AMP of the gain adjusting unit 64 is connected to the output terminal of the variable resistor unit 62. The resistor R is connected between the input and output terminals of the amplifier AMP, and the output terminal of the amplifier AMP is connected to the second contact b of the first switch. In this way, the contactor c of the first switch SW1 is configured to be connected to the first or second contact points a and b, and one side of the contactor c is connected to the regenerative equalizer 14. Since the following structure is the same as that of FIG. 1, it abbreviate | omits.

The operation of the present invention configured as described above will be described in more detail with reference to FIGS. 4 and 5 as follows.

First, when the user inputs the mode selection signal CTL _{N / T} for normal reproduction, the contactor c of the first switch SW1 is connected to the first contact a. The reproduction amplifier unit 12 receives the digital data read out from the recording medium through the reproduction head 10 and amplifies it to a predetermined size. The signal amplified by the reproduction amplifier 12 is directly applied to the reproduction equalizer 14 by connecting the first contact a connected to the output terminal of the reproduction amplifier 12 and the contactor c. Since the operation of the regeneration system is the same as that of the regeneration system of FIG. 1, the description thereof is omitted.

On the other hand, when the user inputs the mode selection signal CTL _{N / T} for trick reproduction, the contactor c of the first switch SW1 is connected to the second contact b. The signal amplified by the reproduction amplifier unit 12 is applied to the delay unit 30 and the automatic potential detection unit 40 of the automatic gain compensation device 100. In the trick regeneration mode, the regenerated amplified signal decreases at a predetermined period as shown in FIG. Therefore, the automatic potential detection unit 40 detects the level of the reproduction amplification signal and increases the gain at the small level and decreases the gain at the large level, and has a reverse phase with respect to the waveform of the reproduction amplification signal. Generates. To this end, the full-wave rectifier 42 of the automatic potential detection unit 40 first, full-wave rectified the applied regenerative amplification signal. The inverting integrator 44 receives the full-wave rectified signal, integrates it to an appropriate level, and then inverts and outputs a phase. Ⓑ in FIG. 4 represents the output signal of the inverting integrator 44, and it can be seen that the phase of the upper envelope waveform of the regenerated amplified signal ⓐ is reversed. The voltage controlled oscillator 50 generates an oscillation frequency proportional to the voltage of the signal applied from the inverting integrator 44. That is, since the output voltage of the inverting integrator 44 increases in the portion where the level of the regenerative amplification signal decreases, the voltage controlled oscillator 50 generates and outputs a large oscillation frequency, and inverts in the portion where the level of the regenerative amplification signal increases. Since the output voltage of the integrator 44 decreases, the voltage controlled oscillator 50 generates and outputs a small oscillation frequency. The oscillation frequency output from the voltage controlled oscillator 50 is input to the automatic gain control unit 60. Thus, the in-phase buffer portion 61 and the reverse phase buffer portion 63 of the variable resistor portion 62 in the automatic gain control portion 60 receive the oscillation frequency signal. The in-phase buffer unit 61 applies the input oscillation frequency signal to the third switch SW3 as a switching control signal, and the reverse phase buffer unit 63 transfers the reverse phase of the input oscillation frequency signal to the second switch SW2. It is applied as a switching control signal. Then, the second and third switches are turned 'on' at the high level of the input switching control signal, and are turned 'off' at the low level so that the second and third switches are alternately turned on and off. Repeat the state. If the oscillation frequency generated from the voltage controlled oscillator 50 is large, the switching cycle of the on / off operation of the second and third switches is faster, and if the oscillation frequency generated from the voltage controlled oscillator 50 is smaller, the second and third switches are used. The switching cycle of the on / off operation is delayed. Therefore, when the switching cycle of the on / off operation of the second and third switches becomes faster, the charge amount of the capacitor C increases, resulting in a decrease in the resistance value of the variable resistor unit 62, and the on and off of the second and third switches. When the switching cycle of the on / off operation is delayed, the charge amount of the capacitor becomes small, and as a result, the resistance value of the variable resistor portion 62 is increased.

On the other hand, the retarder 30 from the regenerative amplifier 12 while the voltage controlled oscillator 50 generates an oscillation frequency corresponding to the regenerative amplification signal and outputs the oscillation frequency to the in-phase buffer unit 61 and the inverted buffer unit 63. The inputted reproduction amplification signal is delayed and then output to the second switch SW2 of the automatic gain control unit 60. When the variable resistance value variable in the variable resistor unit 62 is referred to as R _V , the gain adjusting unit 64 at the rear end of the automatic gain control unit 60 converts the regenerative amplification signal input from the delay unit 30 to the gain ratio of R / R _V. Adjust the level.

Herein, the operation of the switched capacitor circuit will be described with reference to FIG. 5 to help understand the operation of the variable resistor unit 62.

As shown in (d) of FIG. 5, the second switch SW2 receives an oscillation frequency signal output from the voltage controlled oscillator 50 from the reverse phase buffer unit 63 in reverse phase and turns on `` off ''. off'… The operation is repeated, and the third switch SW3 receives the oscillation frequency signal output from the voltage controlled oscillator 50 in phase from the in-phase buffer unit 61 in phase 'on' 'off' 'on'. Repeat the operation.

First, as shown in (a) of FIG. 5, when the second switch SW2 is in the on state and the third switch SW3 is in the off state, the capacitor C is supplied with the power supply voltage E by the charging current I _IN . ) Is charged. If the capacity of the capacitor C is selected to be small, the capacitor C is charged in a short time and the charging current I _IN becomes 'zero' (see Fig. 5 (e)). On the other hand, when the second switch SW2 is in the off state and the third switch SW3 is in the on state, as shown in (b) of FIG. 5, the capacitor C is discharged and the discharge current I _OUT immediately becomes. It becomes '0 (zero)' (see (e) in FIG. 5). At this time, the amount of charges charged in the capacitor C and the amount of charges discharged are the same. Therefore, if the on / off states of the second and third switches SW2 and SW3 are repeatedly repeated, the capacitor C repeats the charging / discharging, and the average value of the charging current I _IN and the discharge current I _OUT. ) Have the same magnitude (I _AVE ) (see (e) in FIG. 5). Considering this from the power supply voltage E side, the circuits (a) and (b) of FIG. 5 can be reconfigured into an equivalent circuit composed of a resistor R _V through which the average current I _AVE flows. Here, since the amount of charges charged and discharged at one time is constant unless the capacitance of the capacitor C is changed, the average current I _AVE is doubled when the on / off switching speed of the second and third switches is doubled. Then, the resistance R _V of the virtual is reduced to 1/2. Accordingly, the resistance value Rv can be changed at the switching control speed (on / off switching speed) of the second and third switches, and the oscillation frequency signal from the voltage controlled oscillator 50 is switched to the second and third switches. When applied as a signal, the resistance value Rv changes in inverse proportion to the oscillation frequency.

The operation of the switched capacitor circuit in the variable resistance section 62 of the present invention will now be described.

In FIG. 3, when the second switch is in the on state and the third switch is in the off state, the regenerative amplification signal from the delay unit 30 is applied to the second switch, thereby charging the capacitor C. Alternately, when the second switch is turned off and the third switch is turned on, the capacitor C that has been charged is discharged. The charging / discharging of the capacitor is repeated according to the on / off state of the second and third switches. Therefore, when the oscillation frequency of the voltage controlled oscillator 50 is large (in this case, the level of the regenerative amplification signal is small), the switching cycle of the on / off operation of the second and third switches becomes faster, and thus the amount of charge charged in the capacitor (Current) becomes large. Then, the variable resistor Rv input from the variable resistor section 62 to the gain adjusting section 64 becomes small, so that the gain ratio of R / Rv becomes large. Therefore, a small level reproduction amplification signal from the delay unit 30 is inputted to the automatic gain control unit 60 and output after the level is increased.

In addition, when the oscillation frequency of the voltage controlled oscillator 50 is small (in this case, the level of the regenerative amplification signal is large), the switching cycle of the on / off operation of the second and third switches is delayed, thereby eventually charging the capacitor. The amount of electric charge (current) becomes small. Then, since the variable resistor Rv input from the variable resistor section 62 to the gain adjusting section 64 becomes large, the gain ratio of the R / Rv becomes small. Therefore, a large level reproduction amplification signal from the delay unit 30 is inputted to the automatic gain control unit 60 and output after the level is reduced.

Thus, the signal output from the gain adjusting section 64 has a flat level characteristic as shown in? Of FIG. That is, in the trick regeneration mode, the gain of the reproducing amplification signal is compensated in this way and then applied to the reproducing equalizer 14. The operation of the regeneration system is the same as that of the regeneration system of FIG. 1, and thus description thereof is omitted.

As described above, the automatic gain compensation device for trick reproduction according to the present invention makes the level of the reproduction amplification signal constant during the trick reproduction as in the normal reproduction. Therefore, the effect of improving the bit error rate (BER) of the system during the trick playback.

Claims (5)

A gain compensation device for a reproduction amplification signal for trick reproduction of a magnetic recording / reproducing apparatus, comprising: a first switch switched by input of a selection signal for normal reproduction or trick reproduction mode from a user; When the first switch is connected to the trick play mode, a signal read out from the play head and amplified by the play amplified signal is detected and full-wave rectified by detecting the envelope waveform. Detection unit; A voltage controlled oscillator which receives the output signal of the potential detector and generates and outputs an oscillation frequency proportional to the voltage; A delayer for receiving the regeneratively amplified signal and delaying and outputting the regeneratively amplified signal received while the oscillation frequency is generated and output from the voltage controlled oscillator; And a gain control unit which receives the oscillation frequency from the voltage controlled oscillator and adjusts the gain of the reproduction amplification signal applied from the delay unit by using a resistor which is inversely proportional to the input oscillation frequency and outputs the reproduction amplifier signal to the reproduction equalizer. Automatic gain compensation device for trick play. The electronic device of claim 1, wherein the potential detection unit comprises: a rectifier for full-wave rectifying the regenerative amplification signal; And an inverting integrator for integrating the rectified signal and outputting an inverted phase of the rectified signal. The resistor of claim 1, wherein the gain control unit receives a reproducing amplification signal from the delay unit at an input terminal of one side and receives an oscillation frequency of the voltage controlled oscillator at an input terminal of the other side thereof and varies in inverse proportion to the oscillation frequency. A variable resistor unit having a value; And a gain adjusting unit which receives a variable resistor value from the variable resistor unit and adjusts and outputs a gain of the regenerative amplification signal according to the variable resistor value. 4. The apparatus of claim 3, wherein the variable resistor unit comprises: an in-phase buffer unit and an in-phase buffer unit for receiving an oscillation frequency from the voltage controlled oscillator and outputting in-phase and inverse-phase signals with respect to the oscillation frequency; The regeneration amplifier signal from the delay unit is input to the first contact point, and the output signal of the inverse buffer unit is applied as a control signal, and the on state operation is performed when the output signal is a high level, and the off state is the low level output signal. A second switch alternately repeating an operation of the second switch; When the output signal of the in-phase buffer unit is applied as a control signal, the operation in the on state is repeatedly performed in the case of the high level output signal, and the operation in the off state is alternately repeated in the case of the low level output signal. A third switch connected to a second contact and a fourth contact connected to the gain adjusting unit; And connected in parallel between a second contact of the second switch and a third contact of the third switch, charged when the second switch is on, the third switch is off, and the second switch is off. And a condenser that alternately repeats the discharge operation when the third switch is in an on state, and performs a role of a variable resistor. 4. The apparatus of claim 3, wherein the gain adjusting unit comprises: a resistor connected between input and output terminals of the amplifier; And an amplifier for adjusting and outputting a gain of a reproducing amplification signal from the delayer by adjusting a gain ratio with a variable resistor value received from the variable resistor unit and a value of the resistor. Compensator.