GB2094092A - Signal processing circuit - Google Patents

Abstract

A video signal recorder/reproducer comprises a multi-functioning circuit, selected elements of which are used commonly in both recording and reproducing modes. Color signals are obtained from the output terminal of a color signal amplifier (41) in both modes. In the recording mode, color signals appearing at the output terminal of the color signal amplifier are by-passed by a low-pass filter (42), and only ACC detector voltages which are used as color killer signals are supplied to a mixer circuit (16) which mixes brightness (Y) and color (C) signals for recording. Circuit (16), when necessary, prevents color signals from being supplied to a recording head (H1) in response to color killer signals. In the reproducing mode, color signals appearing at the output terminal of the color signal amplifier are supplied to a mixer (60) which provides composite color signals from brightness and color signals. Comb filter (35) serves in the recording mode to separate brightness and colour signals and in the reproducing mode to remove crosstalk components. <IMAGE>

Description

SPECIFICATION Signal processing circuit The video tape recorder (VTR) is served to record video signals onto a magnetic tape or reproduce the signals recorded on the magnetic tape according to recording or reproducing mode, respectively. It is necessary these days that the VTR has a circuit for treating signals in recording mode and another circuit for treating signals in reproducing mode because the video signals are different in their characters, e.g. frequencies and levels, in recording and reproducing modes. Having the different circuits for every modes becomes a problem for making the circuits in single integrated circuit (IC) chip. It is therefore desirable that one circuit can commonly operate in both modes so that the circuit may be integrated and the number of connection pins may be reduced.

The present invention relates to a circuit suitable for use in the color signal processing system of the color VTR and aims to provide a signal processing circuit suitable for making the color VTR circuit system in IC form by reducing the number of connection pins and circuit parts and simplifying circuits and, more particularly, by the multifunctioning of the circuit.

Another object of the present invention is to provide a signal processing circuit including circuit capable of performing two functions of a color signal amplifier in reproducing mode and a color killer signal amplifier in recording mode.

Further object of the present invention is to provide a signal processing circuit capable of causing the color killer amplifier to be commonly used in recording and reproducing modes in the colorVTR.

Further object of the present invention is to provide a signal processing circuit including a circuit capable of performing two functions of comb filter, which serves to remove crosstalk components from color signals of adjacent tracks in reproducing mode and a means for separating brightness and color signals, which makes an automatic gain control (AGC) of the separated brightness signals effect and supplies the separated color signals to the circuit functioning as the color signal amplifier in recording mode.

This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Figure lisa block diagram showing a color VTR in which the signal processing circuit according to the present invention is used; and Figure 2 is a circuit diagram of the signal processing circuit according to the present invention.

The reason why the signal processing circuit according to the present invention is useful for the VTR circuit, which operates in two modes such as recording and reproducing modes, is that the signal processing circuit is used commonly in these two modes, and thatthe number of connection pins is reduced at the time of being integrated, and that the VTR circuit system is stably operated. It will become apparent from the following detailed description.

Figure 1 is a block diagram of the VTR circuit in which the signal processing circuit is employed. The incorporation of the signal processing circuit into the VTR circuit is important in that a color killer amplifier is used commonly in recording and reproducing modes, that a comb filter operates in two modes, that color killer operation is achieved through a mixer circuit of brightness and color signals, and that color killer signals are applied to a color signal amplifier at the time of recording mode.

The VTR circuit will be now described referring to the recording mode.

When a mode changeover switch SW0 is turned on to recording mode, all of mode changeover circuits SW1 - SW4 are connected to terminals R. Color signals to be recorded and whose subcarrierfre- quency is fO (3.58 MHz) are supplied to the terminal R of the mode changeover circuit Sow1, thus allowing the color signals to be supplied to an automatic color control (ACC) amplifier 10. The color signals are amplified to a predetermined level by the ACC amplifier 10. Signals fO appear therefore on the output terminal of the ACC amplifier.It is necessary to record color signals on a magnetic tape that their frequency f0 (3.58 MHz) is transformed to low frequency f, (688 kHz), and this is achieved by a frequency transformer circuit 11. Signals (f0) to be recorded are supplied to one terminal T10 of the frequency transformer circuit 11, while signals whose frequency is 4.27 MHz (= f0 + f1) are supplied from a frequency transformer circuit 12 to the other terminal T11 thereof.The frequency (f0 + fi) impressed to the terminal T11 is obtained by adding signals, which are generated due to horizontal synchronizing signals in an AFC circuit 13 and whose frequency is 44 fH, with outputs of an oscillator 14 in the frequency transformer circuit 12, the oscillator 14 oscillating in a fixed frequency of 3.58 MHz - 1/4 fH.

Signals whose frequency is fO are thus impressed to one terminal To of the frequency transformer circuit 11 while frequency of fO + fa to the other terminal T11 thereof, and therefore, signals fa (688 kHz) which have been low-pass transformed are obtained from the output of the frequency transformer circuit 11.

Color signals to be recorded and which have been low-pass transformed by the frequency transformer circuit 11 are supplied via a filter 15 to a mixer 16, which serves to compose color signals (C) to be recorded and brightness signals (Y). The level of color signals supplied to the mixer 16 is held constant by ACC operation due to an ACC loop formed when the SW2 is connected to the terminal R.

The ACC loop at the time of recording mode comprises the ACC amplifier 10, mode changeover circuit SW2, an ACC detector circuit 17 of synchronizing detector type, a sampling and holding circuit 18 for sampling and holding detected outputs, a filter 19, and a DC amplifier 20.

As described above, color signals f0 to be recorded are low-pass transformed to f, and supplied to the mixer 16 with their level held constant due to ACC operation.

Brightness signals (Y) at the time of recording mode will be now described. Composite color signals containing color signals to be recorded and brightness signals are impressed to the terminal T30 of an AGC amplifier 30. The output terminal of the AGC amplifier 30 is connected to a low-pass filter LPF 31 and the terminal R of the mode changeover circuit SW3. The LPF 31 is connected via a switch circuit 32 to an FM modulator 33, which serves to FM-modulate Y signals in a range of 3.5 - 4.8 MHz and supply them to the mixer 16. The input terminal of the FM modulator circuit 33 is selectively connected to the low-pass filter 31 and a comb filter 35 by means of a switch circuit 32 which is controlled by color killer signals as will be described later.Selective connection of this switch circuit 32 serves to change over the first ACC loop through which composite color signals flow from a second AGC loop comprising the AGC amplifier 30, low-pass filter 31, switch circuit 32 and an AGC detector circuit 34 to another AGC loop comprising the AGC amplifier 30, comb filter 35 and AGC detector circuit 34 and vice versa. Changeover of these two AGC loops at the time of recording mode means that the comb filter 35 is used as a means for separating brightness signals from color signals when color killer operation is not needed but is removed from the AGC loop when color killer operation is needed. Operation of the comb filter 35 will be further described.The comb filter 35 comprises the mode changeover circuit SW4 which changes over mode instantly responsive to the switching of the mode changeover switch circuit SW0, an 1 H delay line 36, an inverter 37 and adders 38,39. The comb filter 35 at the time of recording mode supplies to a terminal T32 the sum of composite color signals impressed to a terminal T31 and signals obtained by 1 H-delaying composite color signals, while to a terminal T33 the sum of composite color signals and signals obtained by inverting composite color signals. Brightness signals and color signals contained in composite color signals are in frequency interleaving relation and therefore, brightness signals are obtained from the terminal T32 while color signals from the terminal T33 at the time of recording mode.Namely, the comb filter 35 functions at the time of recording mode to separate brightness and color signals from composite color signals.

Attention should be paid to the matter that when the switch circuit 32 is switched to B/W mode by the color killer signal generated in a color killer amplifier 40, the first AGC loop is formed by the AGC amplifier 30, low-pass filter 31 and AGC detector circuit 34 leaving the comb filter 35 off from separation of brightness and color signals. Brightness signals are separated from composite color signals in this case by extracting through the low-pass filter 31 only brightness signal components whose frequency is lower than that of color signals.

Attention should be further paid to the matter that those two AGC loops are changed over responsive to the level of color signals through the color killer signal generated in the color killer amplifier 40 is a control signal for preventing color signals in the mixer 16 from being supplied to a recording head H1 when the level of color signals is lower than the predetermined one. In other words, the matter that the color killer signal is used as a control signal for determining whether or not the comb filter is employed to separate brightness signals from composite color signals can be achieved by incorporating the signal processing circuit of the present invention into the VTR circuit.

It will be now described that color killer signals obtained by the color killer amplifier 40 are effectively used by the present invention.

The color killer amplifier 40 is a DC amplifier to which control signals obtained through the filter 19 to control the ACC amplifier 10 are applied as inputs.

As already described above, it is necessary at the time of recording mode to supply outputs of this color killer amplifier 40 to the mixer 16 and the switch circuit 32. Output signals of the color killer amplifier 40 are not impressed direct to the mixer circuit 16 and the switch circuit 32, but through a color amplifier 41 and a low-pass filter 42 in this case. It is aimed to commonly use the color killer amplifier 40 in reproducing mode. It is further aimed to reduce the number of pins at the time of being integrated by usefully using even in reproducing mode the color amplifier which is not essentially needed in recording mode. It is still further aimed to achieve color killer operation in the mixer stage.It is still further aimed to use outputs of the color killer amplifier 40 to control whether or not the comb filter is employed as a means for separating brightness and color signals. It is still further aimed to enable the comb filter 35 to be used as a means for separating brightness and color signals at the time of recording mode and for removing crosstalk components in signals recorded by crosstalk on adjacent tracks at the time of reproducing mode.

These matters will become apparent from the following description.

The color amplifier 41 is needed only in reproducing mode to make color signals obtained from the tape through the reproducing head to a high level of signals, but not essentially in recording mode.

However, the operation of the color amplifier 40 shown in Figure 1 will be described in recording mode. As described above at the time of recording mode, color signals separated from composite color signals by the comb filter 35 are impressed to the input terminal of the color amplifier 41. Impressed to the color amplifier 41 are color killer signals of DC type obtained from the output of the color killer amplifier 40. As the result, a signal obtained from superposing the color killer signal of DC type on the color signal appears at the output of the color amplifier 41 in recording mode. This superposed signal is impressed to the low-pass filter 42. Of superposed signals, color signals low-pass tranformed and having frequency of f1 are by-passed by the low-pass filter 42. Therefore, impressed to the mixer 16 having the switch circuit 32 and another switch circuit (not shown) are only color killer signals.

As described above, the color amplifier has color killer signal transmission function in recording mode, said function being essentially different from its reproducing mode operation to amplify color signals. Therefore, the color amplifier 41 which is not essentially needed in recording mode is usefully used as the color killer signal transmission circuit to thereby provide multi-function of the same circuit.

This means that the color killer amplifier 40 itself, which is essentially needed in recording and reproducing modes, can be commonly used in both modes. As described above, the control signal of the color killer amplifier 40 controls the switch circuit 32 as well as color killer operation in the mixer circuit 16 in recording mode. When the switch circuit 32 is switched to BIW mode in this case, brightness signals are extracted by by-passing color signals through the low-pass filter 31. Brightness signals extracted this time are BiW signals for high resolution because the comb filter 35 which causes deterioration of resolution is not used.

Description has been made about the color VTR circuit shown in Figure 1 and switched to recording mode, and will be now made about the usefulness of the color VTR circuit shown in Figure 1 but switched to reproducing mode, said color VTR circuit including the signal processing circuit according to the present invention.

All of the mode changeover circuits SW1 - SW4 are connected to terminals PB by switching the mode changeover switch circuit SW0 to reproducing mode.

Color signals f, to be reproduced are impressed from a head H2, which operates in reproducing mode, through the mode changeover circuit SW1, which has been switched to reproducing mode, to the ACC amplifier 10 at the time of reproducing mode. Frequency of color signals obtained from the magnetic tape through the head is f, which is low-pass transformed at the time of recording mode.

Reproducing color signals f, appearing to the output of the ACC amplifier 10 through the head are impressed to the terminal Tao of the frequency transformer circuit 11. Signals (f0 + f, = 4.27 MHz) are applied to the terminal T of the frequency transformer circuit 11 in both recording and reproducing modes. Therefore, reproducing color signals applied to the terminal T10 of the frequency transformer circuit 11 and having frequency f are transformed to have frequency off0 = 3.58 MHz.Reproducing color signals whose frequency has been thus transformed to f0 are applied via a 3.58 MHz band-pass filter BPF 50 and the mode changeover switch circuit SW2, which has been switched to reproducing mode, to the terminal T31 of the comb filter 35. The mode changeover switch circuit SW4 arranged in the comb filter 35 is now switched to reproducing mode. Therefore, the comb filter 35 serves to add signals applied to the terminals T31 with signals, which are obtained by delaying only by 1 H signals applied to the terminal T3r, and supply them to the terminal T33 in reproducing mode.Color signals are recorded on the tape at the time of recording mode in such a way that they are inverted in phase every 1 H relative to a track A of adjacent tracks A and B. The phase of crosstalk components mingled from the track B to the track A is equal this time to that of color signals in the track B. The phase of crosstalk components mingled from the track A to the track B is also equal to that of color signals in the track A. Therefore, the comb filter 35 which functions to delay signals by 1 H at the time of reproducing mode serves to remove crosstalk components at the time of reproducing mode.

Reproducing color signals whose crosstalk components have been removed and which are obtained from the terminal T33 of the comb filter 35 are supplied to the color amplifier 41 so as to be amplified to a predetermined level. Color signals amplified by the color amplifier 41 are supplied via a capacitor 51 to a mixer 60, which serves to mix reproducing color and brightness signals. Signals of the color killer amplifier 40 are also applied to the color amplifier 41, but signals which have been applied to the color amplifier 41 are amplified regardless of the level of output signals of the color killer amplifier 40, as will be described later referring to Figure 2, and then supplied via the capacitor 51 to the mixer circuit 60. Outputs of the color killer amplifier 40 are applied to the color amplifier 41 and also supplied to the mixer circuit 60.

Color killer operation at the time of reproducing mode is achieved by the switch circuit (not shown) in the mixer circuit 60 responsive to the color killer signal supplied to the mixer 60 from the color killer amplifier 40.

ACC operation at the time of reproducing mode is achieved by a loop comprising the ACC amplifier 10, frequency transformer circuit 11, band-pass filter BPF 50, mode changeover switch circuit 5W3, comb filter 35, mode changover switch circuit 5W2, ACC detector 17, sampling and holding circuit 18, filter 19 and DC amplifier 20.

As described above, ACC control signals are used as color killer signals, the color killer amplifier 40 is commonly used in both recording and reproducing modes, and the color amplifier 40 is used at the time of recording mode as a means for transmitting color killer signals, thus enabling the number of pins to be reduced on the output side of the color amplifier 41.

This is an effect attained by employing the signal processing circuit of the present invention as the color amplifier of the color VTR. If the signal processing circuit of the present invention is not employed as the color amplifier, color killer amplifiers must be separately arranged in recording and reproducing modes. Two pins will be therefore needed to introduce color killer signals to a circuit having a switch for use in recording mode and another circuit having another switch for use in reproducing mode. A pin will also be needed to introduce outputs of the color amplifier to the mixer circuit for use in reproducing mode. These pins can be simplified to the output terminal pin P1 of the color amplifier 41 in the circuit shown in Figure 1.

According to the present invention color killer signals are supplied via the pin P1 to the mixer circuit 16 and also skillfully supplied to the switch circuit 32 at the time of recording mode, so that selection to determine whether or not the comb filter is employed to separate brightness signals from composite color signals in recording mode can be achieved in addition to color killer operation.

Figure 2 shows a circuit diagram showing the signal processing circuit of the present invention employed as the color amplifier41 shown in Figure 1. Terminals T70, T71 and T72 shown in Figure 2 correspond to those shown in Figure 1. Same parts as those shown in Figure 1 are represented by same numerals.

The input terminal T70 of the color amplifier 41 is connected to the base of a transistor Q1 in a differential amplifier, which comprises a differential pair of transistors 01, as, resistors R1 - R5 and a resistor R5. A power source Erg is connected via resistors R1 and R2to the bases of transistors Q1 and C2, respectively.A transistor Q3 whose emitter is connected to resistors R7 and R8 is connected to the resistor R6 which is connected to the transistor Q2 The base of a transistor 04 iS connected to the emitter of the transistor C3, and the base and emitter of the transistor Q4 are connected each other via a resistor Rg. A resistor R10 is connected to the collector of the transistor Q4 and a resistor R11 to the low potential emitter of the transistor 04. The collector and emitter of a transistor Q5 are connected to the connection point of resistors R7 and R8 and between reference potentials.The base of the transistor at is connected via a resistor R12 to the terminal T71 to which output signals of the color killer amplifier 40 are applied. The collector and emitter of a transistor Q6 are connected to the base of the transistor Q5 and between reference potentials, respectively. The base of the transistor Q6S connected via a resistor R13 to the output terminal T72 of the mode changeover switch circuit SWO.

Connected to the output terminal P1 of the color amplifier 41 are the low-pass filter 42 and capacitor 51, as described in Figure 1.

The circuit shown in Figure 2will be described in recording mode. Outputs of the mode changeover switch SW0 or voltages of the terminal T72 are in low level and the transistor Or is under OFF-condition in recording mode. Therefore, the transistor QS achieves switching operation responsive to the voltage level of outputs of the color killer amplifier 40 (Figure 1). When color signals are treated without color killer operation in recording mode, the voltage level of the output terminal T71 of the color killer amplifier 40 is high. On the contrary, when color killer operation is carried out, the voltage level of the terminal T71 is low.Attention should be paid here to the matter that voltages of the terminal T71 (or output voltages of the color killer amplifier 40) are in low level and the transistor C is under OFFcondition when color killer operation is carried out at the time of recording mode. When this transistor Q5 is under OFF-condition, color signals applied from the terminal T70 and separated from composite color signals by means of the comb filter 35 (Figure 1) are supplied from the output terminal of the differential amplifier through the transistor Q3 of emitterfollow- ertype and then through the transistor Q4 to the terminal P1.Color signal components (f0 = 3.58MHz) of signals supplied to the terminal P1 this time are by-passed by the low-pass filter 42, and a V killer of DC type is obtained from the output of the low-pass filter. The switch (not shown) arranged in the mixer circuit 16 is rendered operative and the switch circuit 32 is switched to BIW mode by this V killer of DC type.

When color signals are recorded without color killer operation in recording mode, the transistor QS is under ON-condition. Namely, when no color killer operation is carried out, voltages of the terminal T71 is in high level keeping the transistor Q5 ON and transistors Q3,Q4 OFF. The potential of the terminal P1 becomes substantially grounded this time. Therefore, when no color killer operation is carried out and the switch circuit 32 is switched to color mode in recording mode, the voltage level of the terminal P1 becomes low.

As described above, color signals to be recorded on the tape are not obtained from the color amplifier 41 but from the filter 15 (Figure 1) off1 = 688 kHz in recording mode.

Description will be made about the operation attained in reproducing mode by the circuit shown in Figure 2.

The voltage level of the terminal T72 is made high in reproducing mode by switching the mode changeover switch circuit SWO to reproducing mode.

The transistor Os is thus turned ON. As the result, the transistor Q5 is kept OFF no matter how voltages of the output terminal T71 of the color killer amplifier 40 may take any values. Therefore, color signals to be reproduced and obtained from the comb filter 35 (Figure 1) at the time of reproducing mode are applied to the terminal T70, amplified by the color amplifier 41, and supplied via the terminal P1 and capacitor 51 to the mixer circuit 60, which serves to mix brightness and color signals to be reproduced.

And the switch circuit (not shown) included in this mixer circuit 60 is rendered operative responsive to voltages of the output terminal T71 of the color killer amplifier 40 to effect color killer operation on reproducing color signals at the time of reproducing mode.

Claims (14)

1. Asignal changeover and processing circuit comprising: a signal gate circuit for receiving a predetermined input AC signal and selectively transmitting a signal corresponding to said input AC signal to an output terminal thereof according to a control signal impressed upon a control signal input terminal; AC signal by-passing means connected to the output terminal of said signal gate circuit for bypassing the AC signal component of the output thereof; a first signal transmission path connected to an output terminal of said AC signal by-passing circuit; a second signal transmission path connected to the output terminal of said signal gate circuit and having a function of blocking the DC signal component;; a control signal generating circuit for supplying a first or second control signal to the control signal input terminal of said signal gate circuit for controlling said signal gate circuit; and mode switching means for switching a mode in which said first or second control signal is impressed upon said control signal input terminal and a mode in which said control signal input terminal is held at a predetermined potential and the voltage at the output terminal of said signal gate circuit is made constant irrespective of the output of said control signal generating circuit.

2. A signal changeover and processing circuit according to claim 1, wherein said mode switching means is constituted by a switching circuit which functions in one of the modes to prevent the first or second control signal generated in said control signal generating circuit from being supplied to the control signal input terminal of said signal gate circuit.

3. A signal changeover and processing circuit according to claim 1, wherein the transmission of said AC signal to the output terminal of said signal gate circuit is prevented when the control signal delivered from said control signal generating circuit to said control signal input terminal of said signal gate circuit is a first control signal.

4. A signal changeover and processing circuit according to claim 1, wherein a color signal is coupled to said input terminal either in the recording or playback mode so as to let said signal gate circuit function as a color amplifier and let said control signal generating circuit function as a color killer circuit, and said mode switching means has a function of a mode selector switch for switching the recording and playback modes, said signal changeover and processing circuit being thereby suited for a color signal processing circuit of a color VTR circuit.

5. A signal changeover and processing circuit according to claim 1,wherein a color signal is coupled to said input terminal either in the recording or playback mode, a color killer control signal is transmitted in said first signal transmission path in the recording mode, and the color signal is transmitted in said second signal transmission path in the playback mode, said signal changeover and processing circuit being thereby suited for a color signal processing circuit of a color VTR circuit.

6. A signal changeover and processing circuit in a composite color signal recording and reproducing system, comprising an input to which a color signal is coupled in either recording or playback mode and an output terminal from which a color killer control signal is provided at the time of the recording mode and a color signal is provided at the time of the playback mode.

7. A signal changeover and processing circuit in a composite color signal recording and reproducing system, wherein a color signal with the level thereof controlled to a constant level by an ACC action is coupled to an input terminal either in the recording or reproducing mode, a color killer control signal is derived at an output terminal in the recording mode, and a color signal is derived at the output terminal in the reproducing mode.

8. A signal changeover and processing circuit in a composite color signal recording and reproducing system according to claim 7, wherein a color signal for which ACC action is provided by the same ACC amplifier and ACC detector circuit is coupled to said input terminal either in the recording or playback mode.

9. A signal changeover and processing circuit in a composite color signal recording and reproducing system, wherein a color signal with the level thereof controlled to a constant level by the ACC action is coupled to an input terminal either in the recording or playback mode, and the control for deriving a color killer control signal at an output terminal in the recording mode and deriving a color signal at the output terminal in the playback mode is effected according to a control signal provided according to the output of the ACC detector circuit impressed upon a control signal input terminal.

10. A signal changeover and processing circuit according to claim 9, wherein said ACC action is provided by the same ACC amplifier and ACC detector circuit either in the recording or playback mode, and an output of the ACC detector circuit is supplied to said control signal input terminal.

11. A signal changeover and processing circuit in a composite color signal recording and reproducing system, wherein a high frequency original color signal to be recorded, after having been subjected to ACC action, is coupled to an input terminal in the recording mode, a high frequency color signal obtained as a result of conversion of a low frequency color signal for recording to the original high frequency signal is coupled to the input terminal in the playback mode, a color killer signal is provided at an output terminal in the recording mode, and a color signal is provided at the output terminal in the playback mode.

12. A signal changeover and processing circuit according to claim 11, wherein a high frequency color signal obtained as a result of the separation of a color signal from a composite color signal for recording through a comb filter is coupled to said input terminal in the recording mode, a signal obtained by converting a low frequency converted color signal to said high frequency signal and then removing color signal crosstalk portion from the resultant signal through said comb filter is coupled to said input terminal in the playback mode, and a color signal is derived at the output terminal in the playback mode.

13. Asignal changeover and processing circuit in a composite color signal recording and reproducing system, comprising an input terminal to which a color signal is coupled either in the recording or playback mode, a first signal transmission path for transmitting a DC signal component and a second signal transmission path for transmitting an AC signal component to the output terminal, in the recording mode a color killer control signal is transmitted through said first signal transmission path according to a signal impressed upon said control signal input terminal to prevent said color signal from being derived as the output of a first mixer circuit for mixing recording color signal and luminance signal, and in the playback mode a color signal to be reproduced is transmitted through said second transmission path.

14. A signal processing circuit, substantially as hereinbefore described with reference to the accompanying drawings.