JPH0336892A - Color process circuit - Google Patents

Abstract

PURPOSE:To facilitate the circuit integration by deviating a center frequency of a BPF from a frequency of a conversion carrier signal a little and setting the result so as to supply an inverted conversion carrier signal with excellent convergence to a frequency converter even when the band width of the BPF is made narrow. CONSTITUTION:The center frequency of a BPF 13A is set to 4.21MHz with respect to a frequency 4.27MHz of a conversion carrier signal fc. As a result, only the lower side band frequency among side band frequencies caused at the phase inversion when the frequency of the conversion carrier signal is switched passes through the BPF. Thus, the original signal waveform is reproduced by a narrow band BPF and an inverse conversion carrier signal with excellent convergence is supplied to a frequency conversion equipment. Thus, the BPF can be made of a ceramic material and the circuit integration is facilitated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for recording or reproducing video signals.
Involved in color process circuits that process conveyed color signals.
In particular, it relates to the characteristics of a bandpass filter used to invert the phase and convert the frequency of a carrier color signal in a predetermined order.

[Summary of the Invention J The color process circuit of the present invention is used in a frequency conversion circuit that converts a carrier color signal to be recorded in a VTR or the like to a low frequency, for example, by changing the phase of a converted carrier signal in a predetermined order for one horizontal period. a circuit that inverts the signal by 180 degrees for each rotation, and a bandpass filter that extracts a desired converted carrier signal from the output of the inversion circuit, and the center frequency of the bandpass filter is set to be slightly shifted from the frequency of the converted carrier signal. It is.

Therefore, even if the bandwidth of the bandpass filter is narrower than that of conventional ones, it is possible to pass the signal of one sideband frequency of the converted carrier signal caused by phase inversion, and it has good convergence for the frequency converter. It becomes possible to supply an inverted converted carrier signal.

[Conventional technology]

When recording television signals with a VTR, etc., generally the brightness signal and color signal are separated, the brightness signal is converted to a low carrier FM signal, and one color signal is converted to a low frequency carrier color signal (688KH,) by a frequency converter. has been converted.

When this low-frequency carrier color signal is supplied to the rotating head and recorded on tracks formed diagonally on the tape, it is easily reproduced as a crosstalk signal from adjacent tracks, so the phase of the low-frequency carrier color signal is are reversed 180 degrees in a predetermined order to eliminate crosstalk.

Figure 4 shows an example of a color processing circuit including a circuit for inverting a low-frequency carrier color signal, in which 1 is a bandpass filter that extracts a carrier color signal (fg) from a color composite signal, and 2 is a chroma level filter. automatic control circuit,
3 is a frequency converter that converts the extracted carrier color signal (3,58MH) into a low-frequency carrier color signal (688KH2), and as will be described later, the converted carrier signal (fc) is passed through the bandpass filter 13. Supplied.

The signal frequency-converted (fc-fs) by the frequency converter 3 is supplied to a rotary head 6 via a low-pass filter 4 and a recording amplifier 5.

7 indicates a synchronization separation circuit that separates the horizontal synchronization signal from the color composite signal, and 8 indicates the period of the horizontal synchronization signal of 35.
This is a frequency multiplier that multiplies the frequency by 0/8.

The output of this frequency multiplier 8 (43, 25 MH2) and the frequency (3, 58 MH2) of the reference oscillator 10 are supplied to the converter 9, and the converted carrier signal (4, 27 MH2) is supplied to the converter 9.
MH, ) components are generated.

Reference numeral 11 indicates a flip-flop circuit that is inverted by the horizontal synchronization signal, and the output of this flip-flop circuit 11 and the OR output of the switching pulse of the rotating drum are supplied to an inverting circuit 12, and the phase of the output waveform of the converter 9 is are reversed 180 degrees for each IH in a specific order.

(In this example, A is recorded by two rotating heads.)
, a PI method is illustrated in which only the field signal corresponding to the B track in the B track has its phase inverted every IH. ) The output of the inverting circuit 12 passes through a bandpass filter 13 to extract a converted carrier signal (f c =4.27MHz) to be subjected to frequency conversion. A carrier color signal that has been low-frequency converted is obtained.

[Problem to be Solved by the Invention 1] According to the frequency conversion method of the color processing circuit as described above, since the converted carrier signal is formed by a signal whose phase is locked with respect to the horizontal synchronization signal, The second harmonic that causes beat interference is located at a point shifted by 1/2f in the frequency spectrum, making it easy to separate it from the luminance signal.

Furthermore, it is known that crosstalk from adjacent tracks can be suppressed by inverting the carrier color signal that has been converted to a low frequency band in a similar process during playback, converting the frequency, and then demodulating the signal.

By the way, the inverting circuit that has the function of inverting the phase of the output signal of the converter 9 for each IH has a built-in nonlinear circuit that interrupts the signal, so the output of the inverting circuit 12 contains many harmonic signals. Contains sideband frequencies that occur.

Therefore, if the band of the bandpass filter 13 that selects the frequency of the desired converted carrier signal is narrow (if Q is high), for example, as shown in FIG. 5, the rise time (attack time) T, immediately after the phase is reversed, becomes long, and it takes time for this to converge.

Therefore, as a bandpass filter, at least 300KH! centered around the frequency of the converted carrier signal (4.27MH2)! However, a bandpass filter having wideband characteristics requires multi-stage LC circuit elements, making it difficult to integrate into an IC.

[Means for Solving the Problem] The present invention has been made to solve the problem, and the center frequency of the bandpass filter for selecting the converted carrier signal is set to a predetermined value with respect to the frequency of the converted carrier signal. By employing ceramic band-pass filters shifted by the frequency of , a color process circuit is constructed that is inexpensive and easy to integrate into an IC.

[Function] For example, if a bandpass filter whose center frequency is 4.21MH2 is used for a converted carrier signal (4.27MH2), one side band frequency of the converted carrier signal that occurs when the phase is inverted. This makes it possible for the signal waveform to converge sufficiently quickly on the output side of the bandpass filter.

[Example] FIG. 1 is a block diagram showing one embodiment of the present invention.

In this figure, the same parts as in FIG. 4 are given the same symbols, but the characteristics of the bandpass filter 13A are as shown in FIG. . It has the feature that it is set to 4.21MH2.

(The characteristic of the conventional BPF is shown by the dotted line) Therefore, in this embodiment, among the sideband frequencies that occur when switching the frequency of the converted carrier signal and performing phase inversion, the upper sideband frequency is filtered by the bandpass filter. 13A, resulting in a lack of frequencies in this band.

However, the lower sideband frequency including the carrier signal can be passed in a band of about 150 KH2.

Generally, when a signal that becomes a carrier signal remains, as seen in the residual sideband signal, the original signal waveform is reproduced by the signal in the lower sideband region.

Therefore, even with a bandpass filter having a band of ±75KH2 as used in the embodiment of the present invention, the original signal waveform can be recovered by extracting the lower sideband frequency generated by nonlinear signal processing of the converted carrier signal. This makes it possible to sufficiently reproduce the waveform, and even if the phase is reversed by 180 degrees at the time point shown in FIG. 3, for example, the subsequent convergence time of the envelope waveform can be sufficiently shortened.

Note that there will be some phase distortion at the time of inversion, but
By designing the group delay characteristic of the bandpass filter 13A to be flat, the adverse effects of phase modulation can be avoided.

A bandpass filter with a bandwidth of about ±75KH can be constructed from a ceramic material, which is a mechanical resonant element, so the bandpass filter 13A becomes inexpensive and can be integrated into an IC (automatic insertion). It can be used as a circuit.

Although the above embodiment has been described with respect to the recording system circuit of a β-type VTR, the present invention is not limited to the recording/reproducing system of a VTR, but can also be applied to a frequency conversion circuit of a color process circuit in a reproduction system circuit. It goes without saying that it can be done.

[Effects of the Invention] As explained above, the color process circuit of the present invention has the following effects:
In a color processing circuit that inverts the phase of a carrier color signal in a predetermined order and converts the frequency, a band pass filter that supplies the converted carrier signal to the frequency conversion circuit has a band that is at least 1/2 narrower than that of conventional filters. can be used, so instead of using electrical circuit elements,
For example, it becomes possible to use a ceramic band-pass filter, which facilitates integration into an IC, and at the same time has the advantage of simplifying the circuit configuration and reducing costs.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a characteristic diagram showing an example of a bandpass filter used in the color process circuit of the invention, and Fig. 3 is an inversion filter that has passed through the bandpass filter. Carrier signal waveform diagram, Figure 4 is V
FIG. 5 is a block diagram of a color process circuit applied to a TR recording system, and shows a signal waveform diagram of an inverted carrier signal passed through a narrow band pass filter. In the figure, 3 is a frequency converter, 7 is a synchronous separation circuit, 8 is a frequency multiplier, 9 is a converter, 10 is a reference oscillator, 13A
indicates a bandpass filter. "Line--=1"--n+1 line chart

Claims (1)

[Claims] A color processing circuit that inputs a converted carrier signal whose phase is periodically inverted in a predetermined order to a frequency converter via a bandpass filter, and performs frequency conversion and phase inversion of the carrier color signal in the frequency converter. 2. A color processing circuit, wherein said bandpass filter has a center frequency set so as to pass one sideband frequency of said converted carrier signal.