JPH02288581A - Color signal processing device - Google Patents

Abstract

PURPOSE:To attain high speed processing for the time till phase lock by providing a switch circuit switching an output signal for a phase comparator and a reference voltage source and a leading circuit outputting a control signal for a prescribed time from the leading of the power supply to control the switch circuit. CONSTITUTION:A reference voltage source 10, a switch circuit 11 and a leading circuit 14 are provided and the leading circuit 14 outputs a control signal for about 0.2sec from the leading of the power supply to control the switch circuit 11 to connect an LPF 12 to the reference voltage source 10. Thus, an output voltage of an LPF 12 is approached to the control voltage at which a VXO (voltage controlled crystal oscillator) 13 is oscillated at a center frequency by 0.2sec and the output signal of the VXO 13 and the color burst signal from a BG(burst gate circuit) 8 is phase-locked. Thus, the time from the leading of the power supply till the phase lock is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a color signal processing device useful for use in video tape recorders.

BACKGROUND OF THE INVENTION In recent years, video tape recorders have become widespread. In particular, camera-integrated video tape recorders are showing signs of becoming rapidly popular, and their various performances are attracting attention.

An example of color signal processing in a conventional video tape recorder will be described below with reference to the drawings.

FIG. 4 is a block diagram of a recording system for color signal processing in a conventional video tape recorder. In the figure, a carrier color signal is extracted from a decoded video signal input through an input terminal 1 through a band pass filter (hereinafter referred to as BPF) 2. This carrier color signal is transmitted to an automatic gain control circuit (hereinafter referred to as ACC) 3.
The amplitude of the color burst signal is controlled so as to be constant, and the color burst signal is supplied to a frequency converter (hereinafter referred to as FC) 4. A low-pass filter (hereinafter referred to as LPF) 5 removes unnecessary components generated during frequency conversion and extracts a reduced converted color signal. This reduced conversion color signal is the killer switch 6
The signal passes through and is output from the output terminal 7. On the other hand, the output signal of ACC3 is a burst gate circuit (hereinafter referred to as BG) 8
Only the color burst signal is extracted. B.G.
A phase comparator (hereinafter referred to as APC, PC) 9 compares the phases of the color burst signal from 8 and the output signal of a voltage controlled crystal oscillator (hereinafter referred to as VXO) 13, and the error signal passes through LPF 12 and is output to VXO13. control the VX
The output signal of Ol3 and the color burst signal from BG8 are phase locked. The phase of the output signal of VXOl3 is shifted by 90° in the 90' shifter 15. A phase comparator (hereinafter referred to as killer PC) 16 compares the phases of the color burst signal from the BG 8 and the signal from the 90° shifter 15. The output signal is smoothed by LPF 17, and depending on the level, a killer discriminator (hereinafter referred to as killer D) determines whether the input signal from input terminal 1 is a color signal or a monochrome signal.
(denoted as ET) 18 to control the killer switch 6.

Here, an example of the circuit of Arc, PC9 and LPF12 is shown in FIG. Below, FIG. 5 will be explained. In the figure, Vl, V2. V4. V5゜v6 is the input terminal, V
7. V8 is a voltage source, v9 is a voltage, R1, R3, R4, R
5 is a resistor, C1 and C2 are capacitors, Ql, Q2. Q3
．． Q4. Q5゜Q6. Q7. Q8. Q9. QIO, Ql
l, Ql2゜Ql3. Ql4. Ql5. Ql7. Ql8
．． Ql9 indicates a transistor. vl indicates the power supply voltage. A pulse (hereinafter referred to as BFP) indicating a color burst period is input to v2. V4. From V, signals from VXOl 3 in FIG. 4 are input with their respective polarities inverted, and from v6, a signal from BG8 in FIG. 4 is input. R5, C1 and C2 constitute the LPF 12 in FIG. 4, and the others constitute the Arc and PC9 in FIG. 4 (17).

V4. The V5 (7) input signal and the color burst signal from v6 send an error signal to LPF9 only during the BFP period,
Other periods are on hold. This work is done by BFP from v2. The LPF9 has a voltage of v9 and controls the VXO13 in FIG. 4.

Problems to be Solved by the Invention However, in the above configuration, after the color burst signal from BG8 in FIG. It takes some time for the phase to lock when increasing. Therefore, when the power is turned on, even if the input signal is a color signal, it is determined to be a black and white signal, and there is a period in which no signal is output from the output terminal 7. The reason why it takes time to phase lock when the power is turned on will be explained using the circuit shown in FIG. The LPF voltage v9 creates a control voltage centered around the voltage of v8, but when the power is turned on, v
The voltage at 9 is initially Ov. The main operation for bringing v9 closer to v8 is to connect to v8 via the RFP period R4.

The LPF has capacitors C1 and C2, and since the period for charging these is only during the BFP period, it takes time.

For the above reasons, when recording starts almost at the same time as the power is turned on (which is often the case with camera-integrated videotape recorders), color signals are not recorded during the visually detected period, causing discomfort to the user. I had an issue.

In view of the above-mentioned problems, the present invention provides a color signal processing device for a video tape recorder that can make the period during which color signals are not recorded within the period during which they are not visually detected even when recording is started almost simultaneously with power-on. It is something to do.

Means for Solving the Problems In order to solve the above problems, the color signal processing device of the present invention comprises:
vXO whose center frequency is approximately the subcarrier frequency, and the v
APC, PC that performs a phase comparison between the output signal of the XO and the color burst signal, and the APC.

an LPF that smooths the output error signal of the PC to create a control voltage of the vXO; a reference voltage source having a control voltage that causes the vXO to oscillate at approximately the center frequency; output signals of the APC and PC; and the reference voltage source. Select one of the above LP, F
This device includes a switch circuit that outputs an output to the power supply, and a rise circuit that outputs a control signal for a predetermined time from the rise of the power supply to control the switch circuit.

Effect of the present invention With the above-described configuration, the power supply start-up circuit outputs a control signal for a predetermined time after the power supply rises, and the switch circuit selects the reference voltage source side based on the control signal, so that vXO becomes close to the center frequency. Control voltage to LPF
As a result, the phase of the VXO output signal and the color burst signal can be quickly locked, and KeIlerDET can also be distinguished as a color signal within a time that cannot be visually detected. Therefore, it is possible to solve the problem that color signals are not recorded when the power is turned on.

Embodiment Hereinafter, a color signal processing device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a recording system of a color signal processing device of a video tape recorder in an embodiment of the present invention. The difference between FIG. 1 and the conventional example shown in FIG. 4 is that the reference voltage source 10, the switch circuit 11,
4 was established. Other operations are similar to those in FIG. 4. The rise circuit 14 outputs a control signal for about 0.2 seconds after the power supply rises, controls the switch circuit 11, and controls the LPF 1.
2 to the reference voltage source side. As a result, LPF12 becomes 0 to the control voltage for VXOl3 to oscillate at the center frequency.
．． The output signal from the VXO 13 and the color burst signal from the BG 8 can be brought close to each other for 2 seconds, and then the output signal of the VXO 13 and the color burst signal from the BG 8 are phase-locked, so that the time from power-up to phase lock can be shortened.

FIG. 2 shows a circuit example of the APC, PC 9, reference voltage source 10, and switch circuit 11. The difference between FIG. 2 and the conventional example shown in FIG. 5 is that a terminal V3 for inputting a control signal from a power supply start-up circuit, a transistor Q16, and a resistor R2 are provided. Q16. R2 constitutes a switch circuit. Other operations are the same as in FIG. 5. Here v8 is VXOl 3
is the voltage that oscillates at the center frequency, but v8 and v9 are R
The connection state is established via V4 during the BFP period and the control signal period from v3. At the time of voltage rise, the voltage of v9 is OV, but since a control signal is input from V3, it rapidly approaches the voltage of v8.

Next, a circuit example of the power supply start-up circuit 14 is shown in FIG. Third
In the figure, Vlo is a power supply, Vll is a control signal output terminal, 11.12 is a current source, C3 is a capacitor, V12 is the voltage of C3, R6, R7° R8, R9, RIO are resistors,
Q20 is a diode, Q21. Q22. Q23. Q24
．． Q25゜Q26. Q27 indicates a transistor. When the power is turned off, V12 shows OV, and the voltage remains lower than V13 for a predetermined time after the power is turned on. V
If 12 is set to 0.2 seconds from power on to the voltage of V13, Q2 will be 0.2 seconds from power on.
1 is off and Q22 is on. Q23. Q
24 constitutes a current mirror, and when Q21 is off, Q25 is off. Therefore, a control signal is output from Vll.

The voltage of V12 is thicker than V13 (then Q21 turns on,
Q25 turns on and vll becomes OV. As a result, a control signal will be output for 0.2 seconds from power up.

As described above, according to this embodiment, the VXOl3 whose center frequency is approximately the subcarrier frequency, and the APC and PC9 that perform phase comparison between the output signal of the VXOl3 and the color burst signal.
, smooth the output error signals of APC and PC9 and output VXOl3.
PF12 and a reference voltage source 10 having a control voltage that causes VXO13 to oscillate at approximately the center frequency.
and a switch circuit 11 that selects one of the output signals of the APC and PC 9 and the reference voltage source 10 and outputs it to the LPF, and outputs a control signal for 0.2 seconds from the rise of the power supply to control the switch circuit 11. By providing the riser circuit 14, the LPF 12 can have a control voltage that causes the VXOl3 to rapidly oscillate at the center frequency when the power is turned on, thereby reducing the time required for the output signal of the VXOl3 and the color burst signal to phase lock. be able to. This also shortens the time it takes for the rekiller DET 18 to determine whether it is in a color state.

Effects of the Invention As described above, the present invention can speed up the time it takes to phase lock the vXO and color burst signals when the power is turned on, and thereby speed up the time it takes to identify them as color signals. becomes. Therefore, an excellent effect can be obtained in that a color signal can be recorded to the extent that it is not visually perceptible when the power is turned on.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a color signal processing device according to an embodiment of the present invention, FIGS. 2 and 3 are circuit diagrams of the blocks shown in FIG. 1, and FIG. 4 is a block diagram of a conventional color signal processing device. ,
FIG. 5 is a circuit diagram of the block shown in FIG. 4. 1...Input terminal, 2...BPF, 3.
...ACC14=Freq, Con
v, 5-LP F, 6... Killer switch,
7...Output terminal, 8...BG, 9...
...APC, PC, 10...Reference, quasi-voltage source, 11...Switch circuit, 12...L
PF, 13...VXo, 14...Rising circuit, 15...90° shifter, 16...
...Killer PC, 17...LPF, 18...
...Killer DET. Name of agent: Patent attorney Shigetaka Awano and one other person

Claims (1)

[Claims] In a videotape recorder, the carrier color signal is frequency-converted to a low frequency band and recorded, and then converted back to the carrier color signal during playback.
a voltage-controlled crystal oscillator whose center frequency is approximately the subcarrier frequency; a phase comparator that compares the phases of the output signal of the voltage-controlled crystal oscillator and the color burst signal; and a phase comparator that smoothes the output error signal of the phase comparator and calculates the voltage a low-pass filter that creates a control voltage for a controlled crystal oscillator; a reference voltage source having a control voltage that causes the voltage-controlled crystal oscillator to oscillate at approximately a center frequency; and an output signal of the phase comparator and one of the reference voltage sources. A color signal processing device comprising: a switch circuit that selects and outputs the selected signal to the low-pass filter; and a rise circuit that outputs a control signal for a predetermined time from the rise of power to control the switch circuit.