JPH02238792A - phase control circuit - Google Patents

Abstract

PURPOSE:To improve response characteristic and deterioration in a color signal due to time base fluctuation by varying the characteristic of a loop filter in response to the quantity of a phase error so as to switch the response characteristic of the loop. CONSTITUTION:A control signal generator 5 generating a signal switching the characteristic of a loop filter 4 and the loop filter 4 whose filter constant is varied with an output signal of the control signal generator 5 are provided to the phase control circuit. Thus, the circuit follows sufficiently the phase fluctuation being discontinuous at head changeover or the like and does not follow noise in other cases. Thus, the matching of the response characteristic is improved and the deterioration in a color signal due to time base fluctuation is improved.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention converts the color signal of a video signal such as a consumer VTR into a low frequency band, and modulates the frequency of a brightness signal into a high frequency band and records it on a magnetic recording medium. , and relates to a phase control circuit (APC circuit) used in a reproduction device (color under one-way type VTR).

2. Description of the Related Art Generally, in a consumer VTR, the color signal of a video signal is frequency-converted to a low frequency band, and the luminance signal is frequency-modulated to a high frequency band, and then recorded on a magnetic recording medium. During playback, in the process of frequency converting the low frequency converted color signal back to the original high frequency range, a phase control circuit is used to remove time axis fluctuations (phase fluctuations) contained in the color signal, and the signal obtained by FM demodulation is The output signal is added to the reproduced luminance signal and output to a monitor television receiver. This is because a certain amount of time axis fluctuation occurs in the magnetic recording and reproducing system of consumer VTRs, and this time axis fluctuation causes the phase of the color signal to fluctuate significantly, so it is necessary to remove this phase fluctuation. . Moreover, since the frequency of the time axis fluctuation included in the luminance signal is low, it is almost eliminated by the AFC circuit included in the monitor television receiver.

(For example, "Time axis fluctuation and its correction method" Konishi et al. Journal of the Television Society, pp. 495-503, Vol. 3, No. 6, 198
1 year).

An example of a conventional phase control circuit will be described below with reference to the drawings.

FIG. 7 is a block diagram showing the configuration of main parts of a conventional phase control circuit. In FIG. 7, a low frequency converted color signal reproduced from a magnetic tape is inputted from an input terminal 1 and then inputted to a balanced modulator 2. As shown in FIG. The low frequency color signal input to the balanced modulator 2 and having a carrier wave of 629 kHz is multiplied by the 4.2 MHz signal output from the balanced modulator 8, frequency-converted to 3.58 MHz, and output from the output terminal 10. It is output as a signal returned to the frequency of .

On the other hand, the color signal output from the balanced modulator 2 is input to the phase comparator 3, and the 3.58M signal output from the reference signal generator 9 is input to the phase comparator 3.
The phase is compared with the Hz signal. The phase error signal output from the phase comparator 3 passes through a loop filter 60 and is input as a phase error voltage to a voltage controlled oscillator 6 (hereinafter referred to as vCO). This VCO 6 oscillates a frequency commensurate with the phase error of the output of the phase comparator 3. vcoe
The output is inputted to the 90 degree rotation circuit 7, and after correcting the 90 degree rotation applied during recording,
It is input to a balanced modulator 8. The output of the 90-degree rotation a circuit 7 input to the balanced modulator 8 is multiplied by the output of the reference signal oscillator 9 at 3.58 MHz, frequency-converted to 4.2 MHz, and input to the balanced modulator 2.

In this way, the phase control circuit has a loop configuration and performs frequency conversion while following phase fluctuations that occur during recording and reproduction.

Problems to be Solved by the Invention However, in the above-mentioned conventional configuration, the low-frequency conversion color signal component input from the input terminal 1 has phase discontinuity at the head switching point, etc. Therefore, as a phase control circuit, It is designed to be pulled within several horizontal synchronization periods. For this reason, even though there is no large phase discontinuity in areas such as the center of the screen, the fast response characteristics may cause incorrect phase control to follow noise components, which often causes image quality deterioration. becomes.

The present invention solves the above conventional problems, and provides a phase control circuit that can adaptively change response characteristics and noise bands, and improve image quality such as color reproducibility, compared to conventional phase control circuits. The purpose is to

Means for Solving the Problems To achieve this object, the phase control circuit of the present invention includes a control signal generator that generates a filter characteristic switching signal from a reproduced color signal after frequency conversion, and an output of this control signal generator. It has a configuration with a loop filter in which the constant of the filter is changed by changing the filter characteristic.

Effect of the Invention With the above-described configuration, the present invention changes the characteristics of the loop filter according to the size of the phase error and switches the response characteristics of the loop, thereby speeding up the phase pull-in time when the phase error is large, such as after switching heads. In other areas, the response characteristics are slowed down to reduce the influence of noise.

Embodiment Hereinafter, a phase control circuit according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the main part configuration of a phase control circuit in a first embodiment of the present invention. In FIG. 1, a low-frequency converted color signal is inputted from an input terminal 1 and inputted to a balanced modulator 2. As shown in FIG. The low frequency conversion color signal input to the balanced modulator 2 and having a carrier wave of 629 kHz is multiplied by the 4.2 MHz signal output from the balanced modulator 8, frequency-converted to 3.58 MHz, and output to the output terminal 10.
The signal is then output as a signal restored to its original frequency.

On the other hand, the output of the balanced modulator 2 is input to the phase comparator 3,
The phase is compared with the 3.58 MHz output from the reference signal generator 9. The phase error signal output from the phase comparator 3 is input to a loop filter 4.

Further, the output of the balanced modulator 2 is input to the control signal generator 5. An example of the configuration of the control signal generator is shown in FIG. The signal input from the terminal 24 (output of the balanced modulator 2) is input to the phase comparator 25.28. The 3.58 MHz signal outputted from the reference signal generator 9 is inputted from the terminal 21, and inputted to the phase comparator 25 as a signal whose phase is shifted by 45 degrees by the 45 degree shifter 22. The output of this 45 degree shifter 22 becomes the A axis in the color signal vector diagram shown in FIG. In the phase comparator 25, the output of the 45 degree shifter 22 and the input signal from the terminal 24 are compared in phase. The output of the phase comparator 25 passes through a low-pass filter (hereinafter referred to as LPF) 26 and is input to a threshold circuit 27 as a phase error voltage. In the example shown in FIG. 4, a voltage of level X is input. In the threshold hold circuit 27, depending on the level of the phase error signal, it is either high (hereinafter referred to as "H") or low (hereinafter referred to as "H").
The NAND circuit 32
is input. In the example shown in FIG. 4, one point m line LA
is the threshold level, and the NAND circuit 32 has rH
J is input.

On the other hand, the output of the 45 degree shifter 22 is the same as that of the 90 degree shifter 2.
3, the phase is further delayed by 90 degrees, and the signal is input to the phase comparator 28. The output of this 90 degree shifter 23 becomes the B axis in the color signal vector diagram shown in FIG. In the phase comparator 28, the output of the 90 degree shifter 23 and the input signal from the terminal 24 are compared in phase. The output of the phase comparator 28 passes through the LPF 29 and is input to the threshold hold circuit 30 as a phase error voltage. In the example shown in FIG. 4, a level voltage of y is input.

Depending on the level of the phase error signal, the threshold circuit 30 generates an "H" or rLJ signal, which is input to the NOT circuit 31 and then to the NAND circuit 32. In the example shown in FIG. 4, the dashed line LI1 is the threshold level, and "H" is input to the NAND circuit 32.

In the NAND circuit 32, when the output of the threshold circuit 27 and the output of the NOT circuit 31 are both rHJ, r
The output of LJ is changed, and this signal is input to the loop filter 4 from the terminal 33.

The output of this control signal generator 5 is input to the terminal 13 of the loop filter 4 shown in FIG. 2, and the constant of the filter is switched by this signal. The switching period can be adjusted by the level at which the phase is drawn. For example, in the vector diagram of the color signal shown in FIG. 4, it is assumed that the phase of the burst wave enters the shaded area. The constant of the filter makes the response characteristic faster if the phase error of the burst wave is outside the shaded area, and slows it down if it is within the shaded area.

That is, in the color signal vector diagram shown in FIG. 4, it is determined whether or not a burst wave exists in the shaded area, and
A control signal generator 5 generates a signal of '' or rLJ, and the characteristics of the loop filter 4 are changed by the output of this control signal generator 5.

The output of the loop filter 4 is vC as a phase error voltage.
Enter 06. In this vcoe, a frequency commensurate with the phase error of the output of the phase comparator 3 is oscillated.

The output of the vcoe is input to the 90 degree rotation frequency circuit 7, and after correcting the 90 degree rotation applied during recording, it is input to the balanced modulator 8, and the 3.58 MHz output of the reference signal oscillator 9 is input. The frequency is converted to 4.2 MHz, and the signal is input to the balanced modulator 2.

As a result, the phase control circuit forms a loop configuration, and can perform frequency conversion while following phase fluctuations that occur during recording and reproduction.

As described above, according to this embodiment, the characteristics of the loop filter change only during large phase fluctuations such as at head switching points, so that discontinuous phase fluctuations can be sufficiently tracked.
Since there is no noise tracking in other areas, response characteristics are improved, and deterioration of color signals due to time axis fluctuations can be improved.

FIG. 5 is a block diagram showing the main structure of a control signal generator constituting a phase control circuit in a second embodiment of the present invention. That is, while the first embodiment is comprised of the control signal generator shown in FIG. 3, the second embodiment is comprised of the control signal generator shown in FIG. .

The operation of the phase control circuit composed of the control signal generator shown in FIG. 5 will be explained below. In FIG. 1, a low-frequency converted color signal is input from input terminal 1, and balanced modulator 2
is input. 829k input to this balanced modulator 2
The low frequency conversion color signal with Hz as a carrier wave is multiplied by the 4.2 MHz signal output from the balanced modulator 8, and is converted to 3.58 MHz.
The frequency is converted to Hz and output from the output terminal 10 as a signal returned to the original frequency.

On the other hand, the output of the balanced modulator 2 is input to the phase comparator 3,
The phase is compared with the 3.58 MHz output from the reference signal generator 9. The phase error signal output from the phase comparator 3 is input to a loop filter 4.

Further, the output of the balanced modulator 2 is input to the control signal generator 6. An example of the configuration of the control signal generator is shown in FIG. The signal input from the terminal 43 (output of the balanced modulator 2) is input to the phase comparator 44.48. A 3.58 MHz signal output from the reference signal generator 9 is input from the terminal 41 and then input to the phase comparator 44 . This reference signal 3.5
8MHz is B in the color signal vector diagram shown in Figure 6.
−Y axis (however, the phase is reversed). Phase comparator 44
, the phases of the input reference signal from terminal 41 and the input signal from terminal 43 are compared. The output of the phase comparator 44 passes through the LPF 45 and is input as a phase error voltage to the threshold->shhold circuit 47.

Depending on the level of the phase error signal, the threshold circuit 47 generates an "H" or rLJ signal and inputs it to the NOR circuit 51. In the example shown in FIG. 6, the output of the threshold circuit 47 indicates rHJ.

On the other hand, the input signal of the input terminal 41 is transmitted to the 90 degree shifter 42.
is input to the phase comparator 48 and is delayed in phase by 90 degrees.
is input. This becomes the RY axis in the color signal vector diagram shown in FIG. 8 (however, the phase is reversed). Phase comparator 4
8, the output of the 90 degree shifter 42 and the input signal from the terminal 43 are compared in phase. The output of the phase comparator 48 passes through the LPF 49 and is input to the rectifier 4e as a phase error voltage. The output rectified by the rectifier 46 is input to the threshold circuit 50. In the threshold circuit 50, depending on the level of the phase error signal, "
A signal of "H" or "L" is generated and input to the NOR circuit 51 through the NOT circuit 53. In the example of FIG. 6, the output of LPF 49 is between -A and →・A, so
The output of the threshold circuit 50 indicates rLJ.

In the NOR circuit 51, the threshold circuit 47 and N
When one of the outputs of the OT circuit 53 is rHJ, the output of rLJ is changed, and this signal is input to the reloop filter 4 through the terminal 52.

The output of this control signal generator 5 is input to the terminal 13 of the loop filter 4 shown in FIG. 2, and the constant of the filter is switched by this signal. The switching period can be adjusted by the level at which the phase is drawn. For example, in the vector diagram of the color signal shown in FIG. 6, it is assumed that the phase of the burst wave enters the shaded area. The constant of the filter makes the response characteristic faster if the phase error of the burst wave is outside the shaded area, and slows it down if it is within the shaded area.

That is, in the color signal vector diagram shown in FIG. 6, it is determined whether or not a burst wave exists in the shaded area, and
A control signal generator 5 generates a signal of '' or rLJ, and the characteristics of the loop filter 4 are changed by the output of this control signal generator 5.

The output of the loop filter 4 is vC as a phase error voltage.
Input to O6. In this vcoe, a frequency commensurate with the phase error of the output of the phase comparator 3 is oscillated. The output of the VCO 6 is input to a 90 degree rotation circuit 7, and after correcting the 90 degree rotation applied during recording, is input to a balanced modulator 8, where it is multiplied by the 3.58 MHz output of the reference signal oscillator 9. , 4.2 MHz, and input to the balanced modulator 2.

As a result, the phase control circuit forms a loop configuration, and can perform frequency conversion while following phase fluctuations that occur during recording and reproduction.

As described above, according to this embodiment, the characteristics of the loop filter change only during large phase fluctuations such as at head switching points, so that discontinuous phase fluctuations can be sufficiently tracked.
In other places, it does not follow the noise, so
Response characteristics are improved, and deterioration of color signals due to time axis fluctuations can be improved.

In the first and second embodiments, the loop filter is of the RC lag lead type, but other types of filters may be used.

Effects of the Invention As described above, the present invention includes a control signal generator that generates a signal for switching the characteristics of a loop filter, and a loop filter whose filter constant changes depending on the output signal of the control signal generator. As a result, it is possible to sufficiently track discontinuous phase fluctuations such as when switching heads, and it does not follow noise at other times, improving matching of response characteristics and improving color signal deterioration due to time axis fluctuations. The practical effects are great.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a phase control circuit in a first embodiment of the present invention, FIG. 2 is a circuit diagram of a loop filter in the same embodiment, and FIG. 3 is a circuit diagram of a control signal generator in the same embodiment. FIG. 4 is a vector diagram showing the operation of the control signal generator in the same embodiment, FIG. 5 is a block diagram of the control signal generator in another embodiment of the present invention, and FIG. 6 is a control signal generation in the same embodiment. FIG. 7 is a block diagram of a conventional phase control circuit. 4...Loop filter, S...Control signal generator, 22...45 degree shifter 23...90 degree shifter 25...Phase comparator, 26...LPF1
27...Threshold circuit, 32...
NAND circuit, 42...90 degree shifter 44...
- Phase comparator, 46... Rectifier, 47... Threshold circuit, 51... NOR circuit. Agent's name: Patent attorney Shigetaka Awano (Idiot 1)

Claims (3)

[Claims] (1) A control signal generator that uses a reproduced color signal after frequency conversion as an input signal, compares the phase of this input signal with a reference signal, and generates a filter characteristic switching signal according to the resulting phase error. 1. A phase control circuit comprising: a loop filter whose filter constants are changed by the output signal of the control signal generator, and whose filter characteristics change. (2) The control signal generator includes a 45 degree shifter that delays the phase of the reference signal by 45 degrees, a first phase comparator that compares the phase of the input reproduced color signal and the output signal of the 45 degree shifter, and a first threshold circuit that generates a rectangular wave depending on the level of the phase comparator output; a 90 degree shifter that delays the phase of the output signal of the 45 degree shifter by 90 degrees; a second phase comparator that compares the phase with the output signal; a second threshold circuit that generates a rectangular wave based on the level of the output of the phase comparator; and a NOT circuit that inverts the output of the threshold circuit; 2. The phase control circuit according to claim 1, further comprising a NAND circuit that performs a NAND operation on the output of the first threshold circuit and the output of the NOT circuit. (3) The control signal generator includes a first phase comparator that compares the phase of the input reproduced color signal and a reference signal, and a first phase comparator that generates a rectangular wave according to the level of the output of this phase comparator. The threshold circuit and the phase of the reference signal are set to 9
a 90 degree shifter that delays by 0 degrees; a second phase comparator that compares the phase of the input reproduced color signal and the output signal of the 90 degree shifter; a rectifier that rectifies the level of the output of the phase comparator; The second wave generates a rectangular wave according to the output level.
2. The phase control circuit according to claim 1, further comprising: a threshold circuit; and a NOR circuit that NORs an output of the first threshold circuit and an output of the second threshold circuit.