JPH04302597A - Carrier generator - Google Patents

Abstract

PURPOSE:To provide the carrier generator which generates a carrier signal capable of improving the S/N of a carrier to convert the frequency of the chrominance signal in a video tape recorder and transient reply. CONSTITUTION:A converter 2 inputs 160fH and 4fSC frequency signals and outputs 4(fSC+40fH) frequency signals. A filter 8 takes out a main component from the output of the converter 2. A frequency divider 4 divides signals passing through the filter 8 in a quarter and converts it into four signals with 90 deg.-deviated phase. A changeover circuit 5 switches four-phased signals from the frequency divider 4 with their phase shifted by 90 deg. during one horizontal synchronization period successively and outputs them as carrier.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to processing of color signals of a video tape recorder (VTR), and more particularly to a carrier generator for frequency conversion of color signals.

0002

[Prior Art] Figure 2 shows the configuration of a carrier generator for a main converter for color signal processing in a conventional color signal processing device.
Explain with reference to.

In FIG. 2, the oscillation frequency is 160 fH (
fH is the horizontal sync frequency, typically 15.75KHz
) is supplied to a 1/4 frequency divider 4. The 1/4 frequency divider 4 divides the input signal into 1/4
By dividing the frequency by 4, four signals with a frequency of 40 fH and a phase shift of 90 degrees are obtained, that is, the phases are 0 degrees, 90 degrees,
Outputs signals with a relationship of 180° and 270°.

The switching circuit 5 switches the four-phase output signal of the 1/4 frequency divider 4 every 1H (one horizontal synchronization period) and supplies it to the sub-converter 2. The subconverter 2 is also supplied with an output signal from a crystal oscillator 7 whose oscillation frequency is fsc (color signal subcarrier frequency, generally 3.58 MHz). The sub-converter 2 converts the frequency of the output signal of the switching circuit 5 using the output signal of the crystal oscillator 7. The output of the sub-converter 2 includes a signal whose frequency is fsc±40fH and whose phase is shifted by 90° every 1H and its sideband.

[0005] The output signal of the sub-converter 2 is supplied to a bandpass filter 3 . The bandpass filter 3 attenuates unnecessary components of the output signal of the sub-converter 2 whose frequency is fsc-40fH and whose frequency is fsc+
Take out the 40fH component. The signal component that has passed through the bandpass filter 3 is supplied to a main converter (not shown) as a carrier signal f0 for the main converter of color signals. The carrier f0 has a frequency of 40fH, which is supplied from the switching circuit 5 and has a phase shift of 90° every 1H.
Since the carrier f0 is obtained from the signal, the phase of the carrier f0 is naturally shifted by 90 degrees every 1H.

[0006]

In the carrier generator configured as described above, the output signal of the sub-converter 2 includes a component having a frequency of fsc±40fH and each sideband component. The bandpass filter 3 has a frequency of fs
It is necessary to suppress the component whose frequency is fsc-40fH by -40 dB or more than the component of c+40fH. For this reason,
The attenuation characteristics of the bandpass filter 3 are required to have characteristics as shown in FIG.

However, the bandpass filter 3 has a frequency f
It also drops the sc+40fH sideband component. Therefore, the transient response of the envelope of carrier f0 at the phase shift switching point deteriorates. Since the switching point is usually in the horizontal synchronization signal, the transient response of the carrier signal f0 may deteriorate up to the position corresponding to the burst signal period. When the waveform of the carrier f0 during the burst signal period is disturbed, the burst of the color signal whose frequency has been converted by the carrier f0 is also disturbed, and the APC of the color signal processing based on the burst signal is changed. As a result, the S/N of the color signal deteriorates. Furthermore, as shown in FIG. 4, the characteristics of the band-pass filter 3 are quite wide-band, and the noise component also affects the carrier f0 by the band of the band-pass filter 3, degrading the S/N of the color signal.

The present invention has been made in view of the above problems, and is a carrier generator capable of obtaining a carrier for a main converter for color signal processing that is not affected by a bandpass filter, and in particular a color carrier generator for a video tape recorder. It is an object of the present invention to provide a carrier generator that can generate a carrier signal that can improve the S/N and transient response of a carrier for performing frequency conversion of a signal.

[0009]

[Means for Solving the Problems] A carrier generator according to the present invention includes a converter that inputs signals with frequencies of 160fH and 4fSC and converts them into a signal with a frequency of 4·(fSC+40fH), and a main source from the output of the converter. a filter that extracts the components; a frequency divider that divides the output signal of the filter into four signals whose phases are shifted by 90 degrees; It is composed of a switching circuit that sequentially switches and outputs so that the phase is shifted by 90 degrees every horizontal synchronization period.

0010

[Operation] In the present invention, the converter has a frequency of 160
Input the fH and 4fSC signals, and the frequency is 4・(fSC
+40fH) signal is output. The filter extracts the principal components from the output of the converter. Since the input signal to the filter has no rotation, a relatively narrow filter passband width can be used. The frequency divider divides the frequency of the signal that has passed through the filter into 1/4 and converts it into four signals whose phases are shifted by 90 degrees. The switching circuit sequentially switches and outputs the four phase signals from the frequency divider so that the phase is shifted by 90 degrees every horizontal synchronization period.

[0011]

[Example] The present invention will be described below with reference to the accompanying drawings.
A carrier generator according to an embodiment applied to R color signal processing will be described with reference to FIGS. 1 and 3. In FIG. 1, the same parts as those in FIG. 2 are denoted by the same reference numerals, and detailed explanation thereof will be omitted.

In FIG. 1, the oscillation frequency is 160 fH (f
An output signal of a VCO (voltage controlled oscillator) 1 with an oscillation frequency of 4 fsc (fsc is a color signal subcarrier frequency) is supplied to a sub-converter 2. The output signal of the sub-converter 2 is supplied to a 1/4 frequency divider 4 via a bandpass filter 8 for removing unnecessary components. The 1/4 frequency divider 4 divides the input signal into 1/4 and divides the input signal into 4 signals with a phase shift of 90°.
Outputs two signals. The output signal of the switching circuit 5 becomes the output carrier f0 of this carrier generator.

Next, the operation of the carrier generator having the above configuration will be explained.

The sub-converter 2 receives a signal with a frequency of 160 fH from the VCO 1 and a signal with a frequency of 4 fs from the crystal oscillator 6.
It receives the signal of c and mixes both. Therefore, the frequency of the output signal of sub-converter 2 is 4fsc±160
fH=4·(fsc±40fH). The bandpass filter 8 is filtered at a frequency 4.(fsc-40f) which is an unnecessary component.
Attenuate and remove the signal of H). Bandpass filter 8
The signal having a frequency of 4·(fsc+40fH) that has passed is input to the 1/4 frequency divider 4.

The 1/4 frequency divider 4 divides the frequency of the input signal into 1/2, and further divides the frequency of the 1/2 frequency-divided signal into 1/2. As a result, four signals having a frequency of 1/4 of the input signal and whose phases are shifted by 90 degrees are obtained. That is, 1/4 frequency divider 4
The frequency is fsc+40fH and the phase is 0°90°18
Outputs four signals having a relationship of 0°270°. These four signals whose phases are shifted by 90 degrees can be easily generated by the 1/4 frequency divider 4, and the phases are accurate.

The switching circuit 5 converts the four-phase output of the 1/4 frequency divider circuit 4 into 1H (1H) for color signal processing in the VHS system.
(horizontal synchronization period) and selectively outputs. As a result, the carrier f0 is obtained as a signal whose frequency is fsc+40fH and whose phase changes by 90° every 1H (that is, with four-phase rotation).

In the configuration of FIG. 1, the frequency of the output signal of the sub-converter 2 is 4 times higher than that of the output signal of the conventional sub-converter 2.
The signal is multiplied by 4·(fsc+40fH), and since the input signal of the sub-converter 2 does not involve four-phase rotation, there is no sideband component. Therefore, the bandpass filter 8 uses the main component 4 of the output of the sub-converter 2.
It is sufficient to extract only (fsc+40fH). Therefore,
The characteristics of the bandpass filter, as shown in FIG. 3, can be narrower than the conventional characteristics shown in FIG. Therefore, the noise band is reduced and the S/N of carrier f0 is improved.

Furthermore, in the conventional configuration, the sub-converter 2
Since the frequency of the output signal is fsc±40fH, a 1/4 frequency divider cannot be used after frequency conversion to obtain a 4-phase signal. Therefore, it is difficult to obtain four-phase signals accurately and easily. However, in this embodiment, since the frequency after frequency conversion is 4.(fsc+40fH), which is four times that of the conventional frequency, after passing through the bandpass filter 8, the 1/4 frequency divider 4
Since the switching device 5 can be connected to the switching device 5, it is possible to easily and accurately generate a four-phase rotation signal without deterioration of the transient response.

Note that the present invention is not limited to the above embodiments, and various modifications are possible. For example, in the above embodiment, the bandpass filter 8 is used, but a lowpass filter, a highpass filter, etc. may be used. Further, a combination of a plurality of filters may be used.

[0020] Also, when obtaining a four-phase rotation signal from a signal with a frequency other than those shown in the embodiment,
The present invention can be applied.

[0021]

[Effects of the Invention] As explained above, according to the present invention,
Converter is 160fH and 4fs without rotation
Since the frequency conversion is performed using the signal of c, a narrowband bandpass filter can be used. Therefore, the S/N ratio of the carrier is improved. Further, since the frequency divider and the switching circuit are arranged after the filter, the four-phase rotation can be performed easily and accurately, and the transient response of the carrier at the phase switching point can be performed without deterioration. Therefore, by performing frequency conversion using the four-phase rotation signal generated in the configuration shown in FIG. 1, the S/N of the color signal can be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a circuit configuration of a carrier generator for frequency conversion according to an embodiment of the present invention.

FIG. 2 is a block diagram showing the circuit configuration of a conventional carrier generator.

FIG. 3 is a diagram showing attenuation characteristics of the bandpass filter shown in FIG. 1;

FIG. 4 is a diagram showing attenuation characteristics of the bandpass filter shown in FIG. 2;

[Explanation of symbols]

1; VCO 2; Sub converter 3, 8; Bandpass filter 4; 1/4 frequency divider 5; Switcher 6,7; Crystal oscillator

Claims (1)

[Claims] 1. A converter that inputs signals with frequencies of 160fH and 4fSC and converts them into signals with a frequency of 4·(fSC+40fH), a filter that extracts the main component from the output of the converter, and a converter that converts the output signal of this filter into 1.
A frequency divider that divides the frequency by /4 and converts it into four signals whose phases are shifted by 90 degrees, and a frequency divider that converts the frequency into four signals whose phases are shifted by 90 degrees, and a phase shift of the four phase signals from this frequency divider by 90 degrees every horizontal synchronous period 1. A carrier generator comprising a switching circuit that sequentially switches and outputs.