JPH04356890A - Chrominance signal processor - Google Patents

Abstract

PURPOSE:To prevent beat or waveform distortion from being generated in the case of converting a low frequency converting chrominance signal to a carrier chrominance signal. CONSTITUTION:A first carrier (a) and a third carrier (d) are multiplied by a first balanced modulator 4, and a fourth carrier (f) is extracted from the output of the first balanced modulator 4 by a first BPF 5 as a frequency adding the frequency of the first carrier (a) and the frequency of the third carrier (d) and afterwards frequency divided into 4 by a second frequency divider circuit 6. Since the phase is shifted by a selecting circuit 7, even when the band of the first BPF 5 is narrowed down, transient fluctuation is not enlarged at the phase discontinuing point of an output from the selecting circuit 7. Therefore, by narrowing the band of the first BPF 5, unwanted components contained in an output (k) of the selecting circuit 7 can be sufficiently suppressed and the beat or the waveform distortion can be prevented from being generated in the case of converting the low frequency converting chrominance signal to the carrier chrominance signal at a second balanced modulator 8 and a second BPF 9.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a video tape recorder (
The present invention relates to a color signal processing device used in a VTR (hereinafter referred to as a VTR).

0002

[Prior Art] In recent years, color signal processing devices of consumer VTRs such as VHS system and 8 mm system convert carrier color signals into low-range converted color signals for recording, and inversely convert them during playback to produce low-range converted color signals. A color under system is used in which the signal is returned to a carrier color signal.

[0003] Hereinafter, with reference to the drawings, the conventional VTR
The color signal processing device will be explained.

As shown in FIG. 2, a crystal oscillator (hereinafter referred to as X
(abbreviated as OSC) Color subcarrier frequency fsc created in 18
is applied to the phase comparator 10 and the first balanced modulator 21. In the phase comparator 10. The burst signal included in the carrier color signal output from the output terminal 17 is sent to the burst gate 12.
The output is extracted and phase-compared, and the output is applied to a voltage-controlled oscillator (hereinafter referred to as VCO) 11 to control it, and then applied to a divide-by-2 circuit 3. The output from the divide-by-2 circuit 3 passes through the divide-by-4 circuit 19 and then is applied to a selection circuit 20 controlled by the output signal of the control signal generation circuit 13. The signal from the selection circuit 20 passes through a first balanced modulator 21 and a first band pass filter (hereinafter referred to as BPF) 22, and then passes through a second balanced modulator 8 and a second BPF 9 and is output. is configured to do so.

The operation of the color signal processing device configured as described above will be explained below. In Figure 2, XOS
C18 creates a carrier s of color subcarrier frequency fsc and supplies it to the phase comparator 10 and the first balanced modulator 21. The VCO 11 creates a carrier c with a frequency of 8fs (fs is the low-pass conversion color subcarrier frequency), and the frequency divider 3 divides the carrier c into 2
The frequency-divided carrier d having a frequency of 4 fs is supplied to a frequency divider circuit 19 .

A divide-by-4 circuit 19 divides the output d of the divide-by-2 circuit 3 by four to create four carriers t1, t2, t3, and t4 having a frequency fs and a phase difference of 90 degrees. t2, t3
, t4 are +90 degrees and +180 degrees with respect to t1, respectively.
The phase is +270 degrees. The control signal generation circuit 13 generates a control signal j for controlling the selection circuit 20 from the horizontal synchronization signal h input from the input terminal 15 and the rotating drum pulse i input from the input terminal 16. The selection circuit 20 selects carriers t1, t2, t for every horizontal scan according to the control signal j.
3, t4 is selected and output. here,
The operation of the selection circuit 20 differs depending on each format (
As shown in Table 1).

[0007]

[Table 1]

The first balanced modulator 21 multiplies the carrier s of the frequency fsc supplied from the XOSC 18 by the carrier u of the frequency fs supplied from the selection circuit 20. 1st
The output v of the balanced modulator 21 has a frequency (fsc+fs)
, (fsc-fs) are included. Further, unnecessary components such as frequencies fsc and fs are generated due to circuit imbalance, distortion, and the like. The first BPF 22 extracts a frequency (fsc+fs) component w from the output v of the first balanced modulator 21 and supplies it to the second balanced modulator 8 .

In the second balanced modulator 8, the first BP
The low frequency converted color signal m supplied from the input terminal 14 using the output w of the F22 as a conversion carrier is subjected to frequency conversion, and the carrier color signal y is extracted by the second BPF 9, and the output terminal 17
It is outputted from the burst gate 12 and supplied to the burst gate 12.

A burst signal z included in a carrier color signal y is extracted by a burst gate 12 and compared in phase with a carrier s of a frequency fsc supplied from an XOSC 18 in a phase comparator 10 . By controlling the oscillation frequency of the VCO 11 using this phase error r, the burst signal z included in the carrier color signal y is synchronized with the carrier s of frequency fsc supplied from the XOSC 18.

[0011]

[Problems to be Solved by the Invention] However, in the above-mentioned conventional configuration, the carrier is
After being phase shifted by 80 degrees, the first balanced modulator 21
Since the signal passes through the first BPF 22, if the first BPF 22 has a narrow band, the transient fluctuation at the phase discontinuity point of the conversion carrier w becomes large. For this reason, the first BPF 22 cannot be made into a narrow band, so the frequency in the conversion carrier (fsc-
fs), fsc, fs, etc. cannot be sufficiently suppressed, and beats and waveform distortions occur when converting the low frequency conversion color signal m to the carrier color signal y using the second balanced modulator 8 and the second BPF 9. This had the problem of causing

[0012] The present invention solves the above problems.
It is an object of the present invention to provide a color signal processing device that does not generate beats or waveform distortion when converting a low frequency conversion color signal into a carrier color signal.

[0013]

[Means for Solving the Problems] In order to achieve the above object, the color signal processing device of the present invention converts a carrier color signal into a low-range converted color signal for recording, and inversely converts it during playback to produce a low-range converted color signal. A color under type video tape recorder that returns a signal to a carrier color signal includes a crystal controlled oscillator that creates and outputs a first carrier having a frequency four times the color subcarrier frequency, and a crystal controlled oscillator that divides the frequency of the first carrier. a first divide-by-four circuit that creates and outputs a second carrier of a color subcarrier frequency;
The third one has a frequency four times the low-pass conversion color subcarrier frequency.
a divide-by-2 circuit that creates and outputs a carrier; a first balanced modulator that multiplies the first carrier and the third carrier and outputs the result; A first B extracting a fourth carrier having a frequency that is the sum of the frequency of the carrier and the frequency of the third carrier.
PF, and a second carrier that divides the fourth carrier to create and output four carriers having a phase difference of 90 degrees at a frequency that is the sum of the color subcarrier frequency and the low-pass conversion color subcarrier frequency.
a frequency dividing circuit; a selection circuit that selects and outputs one of the four carriers output from the second 4-frequency divider circuit for each horizontal scan; and a selection circuit that converts the output from the selection circuit into a low frequency conversion color signal. a second balanced modulator for multiplication and output; and a second B for extracting and outputting a carrier color signal from the output of the second balanced modulator.
PF, and a phase comparator that compares the phases of the burst signal included in the carrier color signal outputted from the second BPF and the second carrier and outputs a phase error, and the output of the phase comparator is By controlling the frequency of the third carrier created by the frequency divider circuit, the burst signal included in the carrier color signal output from the second BPF is
It has a configuration that allows it to be synchronized with the carrier.

[0014]

[Operation] With the above-described configuration, the present invention multiplies the first carrier and the third carrier by the first balanced modulator, and the first BPF multiplies the output of the first carrier from the output of the first balanced modulator. After extracting the fourth carrier having a frequency that is the sum of the frequency and the frequency of the third carrier, the second frequency divider circuit divides the fourth carrier into 4
Since the frequency is divided and the phase is shifted by the selection circuit, the first B
The first BPF is
By making the band narrow, unnecessary components included in the output of the selection circuit can be sufficiently suppressed, and the second balanced modulator and second BP
This can solve the problem that beats and waveform distortion occur when converting a low frequency conversion color signal into a carrier color signal in F.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, a crystal oscillator (XOSC)
The output from 1 is applied to a first divide-by-four circuit 2 and a first balanced modulator 4. The point that the output of the first balanced modulator 4 is applied to the second balanced modulator 8 through the first BPF 5, the second 4-frequency dividing circuit 6, and the selection circuit 7 is that as shown in FIG. Although the circuit configuration is different from that of , the other circuits are the same, so the explanation will be omitted.

The operation of the color signal processing device configured as described above will be explained below. In Figure 1, XOS
C1 creates a first carrier a having a frequency four times the color subcarrier frequency fsc and supplies it to the first frequency divider circuit 2 and the first balanced modulator 4. The first frequency divider circuit 2 divides the frequency of the first carrier a by four, and supplies the second carrier b having the color subcarrier frequency fsc to the phase comparator 10.

In the VCO 11, a carrier c with a frequency of 8 fs (fs is the low-pass conversion color subcarrier frequency) is created, and the frequency is divided by 2 in the divide-by-2 circuit 3 to form a third carrier d with a frequency of 4 fs.
is supplied to the first balanced modulator 4.

The first balanced modulator 4 multiplies the first carrier a supplied from the XOSC 1 and the third carrier d supplied from the divide-by-2 circuit 3. The output e of the first balanced modulator 4 has frequencies 4(fsc+fs) and 4(fsc-fs).
) contains ingredients. Also, circuit imbalance,
Unnecessary components such as frequencies 4fsc and 4fs are generated due to distortion and the like. The first BPF 5 converts the output e of the first balanced modulator 4 into a fourth carrier f having a frequency of 4 (fsc+fs).
is extracted and supplied to the second 4-frequency divider circuit 6.

The second 4-frequency divider circuit 6 divides the fourth carrier f by 4 to create four carriers g1, g2, g3, and g4 having a frequency (fsc+fs) and a phase difference of 90 degrees. g2, g3, g4 are respectively +90 degrees and +
The phase is 180 degrees and +270 degrees. The control signal generation circuit 13 generates a control signal j for controlling the selection circuit 7 from the horizontal synchronization signal h input from the input terminal 15 and the rotating drum pulse i input from the input terminal 16. The selection circuit 7 selects carriers g1 and g for each horizontal scan according to the control signal j.
2, g3, and g4 and outputs it. Here, the operation of the selection circuit 7 differs depending on each format (Table 2).

[0021]

[Table 2]

In the second balanced modulator 8, the output k of the selection circuit 7 and the low frequency converted color signal m supplied from the input terminal 14 are
The carrier color signal p is extracted by the second BPF 9, outputted from the output terminal 17, and supplied to the burst gate 12.

The burst signal q included in the carrier color signal p is extracted by the burst gate 12, and compared in phase with the second carrier b in the phase comparator 10, and a phase error r is output. By controlling the oscillation frequency of the VCO 11 using this phase error r, the burst signal q included in the carrier color signal p is synchronized with the second carrier b.

Here, the first carrier a and the third carrier d are multiplied by the first balanced modulator 4, and the output of the first balanced modulator 4 is multiplied by the first BPF 5. a fourth carrier having a frequency that is the sum of the frequency and the frequency of the third carrier d.
After extracting the carrier f of
Since the frequency is divided and the phase is shifted by the selection circuit 7, the transient fluctuation at the phase discontinuity point of the output of the selection circuit 7 does not become large even if the first BPF 5 is set to a narrow band. By making the BPF 5 narrow-band, unnecessary components included in the output k of the selection circuit 7 can be sufficiently suppressed, and the second balanced modulator 8 and the second BPF 9 convert the low-frequency conversion color signal into a carrier color signal. It is possible to prevent the occurrence of beats and waveform distortion at the time of recording.

As described above, according to this embodiment, the XOSC
1 creates a first carrier a with a frequency four times the color subcarrier frequency, and divides the first carrier a with a first 4 frequency divider circuit 2 to create a second carrier b with a color subcarrier frequency. A third carrier d having a frequency four times as high as the low frequency conversion color subcarrier frequency is generated by the VCO 11 and the frequency divider circuit 3.
is created, and the first carrier a is created by the first balanced modulator 4.
is multiplied by the third carrier d, and the first BPF 5 converts the output e of the first balanced modulator 4 into a fourth signal having the sum of the frequencies of the first carrier a and the frequency of the third carrier d. The carrier f is extracted, and the fourth carrier f is frequency-divided by the second 4-divider circuit 6 to produce four carriers whose phases differ by 90 degrees at a frequency equal to the sum of the color subcarrier frequency and the low-pass conversion color subcarrier frequency. g1, g2, g3, and g4 are created, and the selection circuit 7 selects and outputs one of the four carriers g1, g2, g3, and g4 output from the 4-frequency divider circuit 6 every horizontal scan, The second balanced modulator 8 multiplies the output k of the selection circuit 7 by the low frequency conversion color signal m, and the second BPF 9 extracts the carrier color signal p from the output n of the second balanced modulator 8 and outputs it. Then, the burst gate 12 and the phase comparator 10 compare the phase of the burst signal q included in the carrier color signal p output from the second BPF 9 with the second carrier b, and output the phase error. VCO11 with output r
, by controlling the frequency of the third carrier d created by the frequency divider circuit 3 to synchronize the burst signal q included in the carrier signal p output from the second BPF 9 with the second carrier b. Even if the first BPF 5 is made narrow-band, the transient fluctuation at the phase discontinuity point of the output of the selection circuit 7 does not become large, so by making the first BPF 5 narrow-band, the output k of the selection circuit 7 The included unnecessary components can be sufficiently suppressed, and the occurrence of beats and waveform distortion when converting the low frequency conversion color signal m to the carrier color signal p using the second balanced modulator 8 and the second BPF 9 can be prevented. .

[0026]

Effects of the Invention As described above, the present invention provides a color-under system video recording system in which a carrier color signal is converted into a low-frequency converted color signal for recording, and upon playback, the low-frequency converted color signal is converted back to the carrier color signal. In a tape recorder, an XO that creates and outputs a first carrier having a frequency four times the color subcarrier frequency.
a first frequency divider circuit that divides the first carrier to create and output a second carrier having a color subcarrier frequency; a divide-by-2 circuit that creates and outputs a carrier of 3;
A first multiplier that multiplies the carrier by the third carrier and outputs the product.
a balanced modulator, and a first BPF that extracts a fourth carrier having a frequency that is the sum of the frequency of the first carrier and the frequency of the third carrier from the output of the first balanced modulator; a second 4-frequency divider circuit that divides the fourth carrier to create and output four carriers having a phase difference of 90 degrees at a frequency that is the sum of a color subcarrier frequency and a low-pass conversion color subcarrier frequency; a selection circuit that selects and outputs one of the four carriers output from the second 4-frequency divider circuit for each horizontal scan; and a second selection circuit that multiplies the output from the selection circuit by a low frequency conversion color signal and outputs the result. a balanced modulator, a second BPF that extracts and outputs a carrier color signal from the output of the second balanced modulator, and a burst signal included in the carrier color signal output from the second BPF and the second a phase comparator that compares the phase of the third carrier with the carrier and outputs a phase error; By synchronizing the burst signal included in the carrier color signal output from the BPF with the second carrier, it is possible to prevent beats and waveform distortion from occurring when converting the low frequency conversion signal to the carrier color signal. This makes it possible to realize an excellent color signal processing device.

[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.

[Figure 2] Block diagram of a conventional color signal processing device

[Explanation of symbols] 1 XOSC 2 First divide-by-4 circuit 3 divide-by-2 circuit 4 First balanced modulator 5 First BPF 6 Second divide-by-4 circuit 7 Selection circuit 8 Second balanced modulator 9 Second BPF

Claims (1)

[Claims] 1. Regarding a color-under type video tape recorder that converts a carrier color signal into a low-band converted color signal for recording, and inversely converts the low-band converted color signal to the carrier color signal during playback, the color subcarrier frequency is The first with a frequency four times that of
a crystal controlled oscillator that creates and outputs a carrier of a color subcarrier, a first frequency divider circuit that divides the first carrier to create and output a second carrier of a color subcarrier frequency, and a low frequency conversion color subcarrier. a divide-by-2 circuit that creates and outputs a third carrier having a frequency four times that of the frequency; a first balanced modulator that multiplies the first carrier and the third carrier and outputs the result; a first band-pass filter (hereinafter referred to as BPF) that extracts a fourth carrier having a frequency that is the sum of the frequency of the first carrier and the frequency of the third carrier from the output of the balanced modulator; a second 4-frequency divider circuit that divides the fourth carrier to create and output four carriers having a phase difference of 90 degrees at a frequency that is the sum of a color subcarrier frequency and a low-pass conversion color subcarrier frequency; a selection circuit that selects and outputs one of the four carriers output from the second 4-frequency divider circuit for each horizontal scan; and a second selection circuit that multiplies the output from the selection circuit by a low frequency conversion color signal and outputs the result. a balanced modulator, a second BPF that extracts and outputs a carrier color signal from the output of the second balanced modulator, and a burst signal included in the carrier color signal output from the second BPF and the second a phase comparator that compares the phase of the third carrier with the carrier and outputs a phase error; A color signal processing device that synchronizes a burst signal included in a carrier color signal output from a BPF with the second carrier.