JPH05183923A - Phase comparator circuit, pll circuit and burst signal replace circuit - Google Patents

Abstract

PURPOSE:To obtain the PLL circuit and the burst signal replace circuit which does not require any accurate phase shifter. CONSTITUTION:The burst signal replace circuit to replace a burst signal related to an input chrominance signal aa with a burst signal improving the S/N is composed of a subtraction circuit 23 to calculate difference between both outputs from first and second phase difference detection circuits 21 and 22, voltage controlled crystal oscillator circuit 15 to be supplied this output through an LPF 24, voltage controlled amplifier circuit 16, automatic amplitude control circuit 18, and switch circuit 3 to be supplied with a burst gate signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a phase comparison circuit and a PLL.
The present invention relates to a circuit and a burst signal replacement circuit.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram of a conventional burst signal replacement circuit. To explain a conventional technique with reference to the drawings, a video signal reproduced from a video device such as a VTR (not shown) is used. The input color signal aa concerned is the PLL circuit 1
(PLL) and one input of a switch circuit 3 (SW) described later.

The PLL circuit 1 is supplied with a burst gate signal BGP which is at a high level only during the burst period of the input color signal aa and is at a low level during the other periods,
By using this, the burst signal is separated from the input color signal aa. Then, PLL is applied to this burst signal,
A signal having a phase shifted by 90 degrees from the phase of the burst signal is output to the phase shifter 2. Thus the phase is 9
The shift of 0 degrees is because the circuit configuration of the PLL circuit 1 employs an exclusive OR circuit (EX-OR).

Then, in order to restore the phase shifted by the PLL circuit 1 in the phase shifter 2, the signal obtained by shifting the phase in the opposite direction by the same amount is supplied to the other input of the switch circuit 3. Then, the switch circuit 3 outputs the output of the phase shifter 2 while the burst gate signal BGP is at a high level.
On the other hand, during the low level period, the output color signal 3a obtained by selecting the input color signal aa is supplied to the reproducing circuit (not shown) or the like.

In this way, the conventional burst signal replacement circuit obtains the output color signal 3a with the burst signal replaced.

[0006]

However, in the above-mentioned conventional burst signal replacement circuit, the phase shifter 2 is used for P
Since it is necessary to correct the shifted phase in the LL circuit 1, the accuracy of the correction amount is required, and it is difficult to satisfy this accuracy.

Therefore, according to the present invention, a highly accurate phase shifter 2 is provided.
It is an object of the present invention to provide a phase comparison circuit that does not use the above, and a PLL circuit and a burst signal replacement circuit using the same.

[0008]

The present invention provides the following constitution in order to solve the problems.

In a phase comparison circuit for comparing the phases of the first signal and the second signal, the phase of the first signal and the phase of the comparison signal having a first phase difference from the second signal. Is detected as the second phase difference, the phase difference between the phase of the second signal and the phase of the comparison signal is detected as the third phase difference, and the second phase difference and the third phase difference are detected. And a phase difference between the phase of the first signal that cancels the first phase difference and the phase of the second signal are detected and output.

The phase difference between the phase of the input signal and the phase of the comparison signal having the first phase difference with the output signal is detected as a second phase difference, and the phase of the output signal and the phase of the comparison signal are detected. A phase difference is detected as a third phase difference, and the phase of the input signal and the phase of the output signal are canceled by canceling the first phase difference using the second phase difference and the third phase difference. Phase difference of 4th
A PLL circuit which detects the phase difference between the output signal and the comparison signal by the fourth phase difference, and outputs the output signal.

In a burst signal replacement circuit for replacing the first burst signal related to the input color signal with the second burst signal, the phase of the first burst signal and the first phase difference between the second burst signal and the second burst signal are calculated. A phase difference between the phase of the comparison signal and the phase of the comparison signal is detected as a second phase difference, a phase difference between the phase of the second burst signal and the phase of the comparison signal is detected as a third phase difference, and the second phase difference is detected. The phase difference between the phase of the first burst signal and the phase of the second burst signal, in which the phase difference of the first burst is canceled by using the phase difference of the second burst signal and the phase difference of the third burst. And adjust the amplitude of the reference signal generated by the fourth phase difference so that the amplitude difference between the first burst signal and the second burst signal is eliminated, and then the second signal is adjusted based on this signal. Of the input color signal and the burst signal of Burst signal substitution circuit and outputs a to output color signals replace the burst signal of the first to the burst signal of the second.

[0012]

1 is a block diagram for explaining one embodiment of the present invention, FIG. 2 is a block diagram for explaining another embodiment of the present invention, and FIG. 3 is another block diagram of the present invention. FIG. 4 is a timing chart for explaining the embodiment, and FIG. 4 is a diagram for explaining input / output characteristics of the phase comparison circuit. The same components as those in FIG. Embodiments according to the present invention will be described below with reference to the drawings.

The structure described in the claims corresponds to, for example, the following structure in this embodiment. That is, the “phase of the input signal” described in the claims is, for example, “θ”, and the “phase of the output signal” is, for example, “θ + Δ”.
The “first phase difference” is, for example, “α”, and the “comparison signal” is, for example, the “first phase shift circuit output signal 17”.
In “a”, the “phase of the comparison signal” is, for example, “θ + α + Δ”.
The “second phase difference” is, for example, “α + Δ”, the “third phase difference” is, for example, “α”, the fourth phase difference is, for example, “Δ”, and the “reference signal” is, for example, Each corresponds to the “voltage control crystal oscillation circuit output signal 15a”.

(First Embodiment) FIG. 1A is a block diagram of a PLL circuit according to the first embodiment, and FIG. 1B is a block diagram of a burst replacement circuit using the same.

First, the PLL circuit will be described first.
The PLL circuit according to the embodiment is essentially different from the related art in that the output of the phase comparison circuit AA is the phase of the burst signal related to the input color signal aa and the phase of the final output that is the same phase as this. It is a point that is a phase difference. The input color signal a
The phase of the burst signal of a is “θ” and the second output which is the final output
The phase difference between the phase shift circuit output signal 17b and the burst signal is defined as “Δ”, and the phase difference between the first and second phase shift circuit output signals 17a and 17b is defined as “α”.

In FIG. 1A, an input color signal aa relating to a video signal reproduced from a video device such as a VTR (not shown) is a first phase difference detection circuit (PD1) in the phase comparison circuit AA.
And the phase θ of the burst signal of the input color signal aa and the phase θ of the first phase shift circuit output signal 17a supplied from the phase shift circuit 17 (PS) described later.
The phase difference with + α + Δ is detected and the first phase difference detection circuit output signal 21a having the phase difference information α + Δ is supplied to one input of the subtraction circuit 23.

Further, the first and second phase shift circuit output signals 17a and 17b are supplied to the second phase difference detection circuit (PD2), where the first phase shift circuit output signal 17 is supplied.
a phase θ + α + Δ and the second phase shift circuit output signal 1
The second phase difference detection circuit output signal 22a having the phase difference information α is detected by detecting the phase difference between the phase 7b and the phase θ + Δ, and is supplied to the other input of the subtraction circuit 23. The burst gate signal BGP is applied to the first and second phase difference detection circuits 21 and 22.
Are supplied, and phase difference detection is performed during the burst signal period.

Then, the subtraction circuit 23 subtracts the second phase difference detection circuit output signal 22a (α) from the first phase difference detection circuit output signal 21a (α + Δ) to obtain a phase comparison having phase error information Δ. The circuit output signal 23a is passed through the low pass filter 24 (LPF) to the voltage controlled crystal oscillation circuit 15
(VXO). Since the subtraction circuit 23 obtains the phase error information Δ, it may be an addition circuit depending on the sign of the output signals 21a and 22a of the first and second phase difference detection circuits. Of course, it is okay.

Then, in the voltage controlled crystal oscillation circuit 15, Δ
The voltage-controlled crystal oscillation circuit output signal 15a obtained by oscillating so as to correct the phase error based on the phase error information is supplied to the phase shift circuit 17. The phase of the voltage control crystal oscillation circuit output signal 15a is the same as that of the phase shift circuit 1 in the subsequent stage.
The phase delay of β caused by the delay time of 7 is also taken into consideration and becomes θ + β + Δ. It should be noted that “θ” is included in “θ + β + Δ” because “Δ” is the residual phase error.

Then, the first and second phase shift circuit output signals 17a and 17b (θ + α + Δ, θ +) having a phase difference of α in the phase shift circuit 17 having a phase delay of β.
Δ) has been obtained. Here, considering the phase difference α between the output signals 17a and 17b of the first and second phase shift circuits, since this phase difference is canceled by the subtraction circuit 23,
The accuracy does not matter, and further, even if α changes due to the secular change of the phase shift circuit 17 and the temperature characteristic, it does not matter because it does not affect the phase comparison circuit output signal 23a. It should be noted that the phase difference of α is the first and second when the circuit configuration of the first and second phase difference detection circuits 21 and 22 in the phase comparison circuit AA is configured using an exclusive OR circuit or the like. Considering the dynamic range of the phase difference detection circuits 21 and 22, it is desirable to set it to about 90 degrees.

In this way, the phase of the burst signal relating to the input color signal aa and the second phase shift circuit output signal 17
The phase difference from b becomes approximately 0 degrees when the PLL loop is closed, thus achieving the purpose.

Next, a burst replacement circuit using the above-described PLL circuit will be described with reference to FIG. 1B. The same components as those in FIG. 1A are designated by the same reference numerals and their description is omitted. To do.

The difference between FIG. 1B and FIG. 2A is that the voltage controlled crystal oscillation circuit 15 and the phase shifter circuit 1 are different.
7, a voltage control amplifier circuit 16 (VCA) is inserted between
An automatic amplitude detection circuit 18 (AGC DET) for supplying an amplitude control signal to the control input is provided, and the burst gate signal BGP is used to convert the burst signal of the input color signal aa into the second phase shift circuit output signal 17b. The point is that a switch circuit 3 is provided for the replacement.

Then, the automatic amplitude detection circuit 18 detects the amplitude difference between the second phase shift circuit output signal 17b and the burst signal related to the input color signal aa, and outputs the amplitude control signal to the voltage control amplifier circuit 16. The output signal of the voltage control amplifier circuit 16 having a predetermined output amplitude obtained by controlling the second phase shift circuit output signal 17b and the input color signal aa to have the same amplitude. Is supplied to.

The switch circuit 3 uses the burst gate signal BGP to select the second phase shift circuit output signal 17b during the burst gate signal period and the input color signal aa during the other period to obtain the output color signal 3a. ing.

(Second Embodiment) In the above-described first embodiment, since the phase difference α is canceled by the subtraction circuit 23, the input color signal aa is not affected by the characteristics of the phase shift circuit 17. It was possible to obtain the output color signal 3a having a burst signal in which the phase and amplitude of the burst signal match and the S / N was improved.

However, the first, which is the preceding stage of the subtraction circuit 23,
If there is a difference in the detection characteristics of the second phase difference detection circuits 21 and 22, the phase difference α is not completely canceled, and the error is the burst related to the second phase shift circuit output signal 17b and the input color signal aa, which are the final output. The signal phase difference Δ may be affected.

Therefore, in the second embodiment, the phase comparison circuit AA for detecting the phase difference by using the same phase difference detection circuit by detecting the phase difference at timings different in time is used.

2 and 3, the same components as those in FIG. 1 are designated by the same reference numerals. Comparing FIG. 1 and FIG. 2, the above-mentioned first and second phase difference detection circuits 21 and 22 correspond to the phase difference detection circuit PD, and the subtraction circuit 23 corresponds to the differential amplifier circuit 12. Then, the first switch circuit 7
(SW1) and the sample hold circuit 11 (SH) are configured to detect two types of phase differences at timings that are different in terms of time, and include a phase difference detection circuit PD, a first switch circuit 7, and a differential amplifier. Phase comparison circuit AA with circuit 12
Is configured.

2 and 3, the input color signal aa shown in FIG. 3A relating to the video signal reproduced from a video device such as a VTR (not shown) is the first limiter 4 (LIM1).
Is supplied to the input of the second switch circuit 19 (SW2) described later. The first limiter 4 receives the input color signal a
A is amplified to obtain the first limiter output signal 4a shown in FIG. 3B, and this is supplied to one input of the first switch circuit 7.

On the other hand, the other input of the first switch circuit 7 is one output of a phase shifter 17 described later,
The second phase shifter output signal 17b having the same phase as the average phase of the burst signal in the input color signal aa is obtained via the second limiter 5 (LIM2) having an amplifying action, as shown in FIG. 3C. The second limiter output signal 5a shown in FIG. In addition, the first switch circuit 7 receives the first control signal 20a shown in FIG. 3D which is at the high level during the burst signal period and is at the low level during the other period from the control circuit (not shown). Supplied, this first control signal 2
Both inputs are selectively output using 0a. That is, the first limiter output signal 4a is selected during the high level period of the first control signal 20a, and the second limiter output signal 5a is selected during the low level period, which is shown in FIG. The switch circuit output signal 7a of 1 is supplied to one input of the exclusive OR circuit 8 (EX OR) in the phase difference detection circuit PD.

The phase difference detection circuit PD includes an exclusive OR circuit 8 as well as an amplifier circuit 9 (AMP) and a first low-pass filter 10 (LPF1), and is input to the other input of the exclusive OR circuit 8. Is the other output of the phase shifter 17, which will be described later, and is approximately 90 with the second phase shifter output signal 17b.
A third phase limiter output signal 6a shown in FIG. 3 (F), which is obtained through the third limiter 6 (LIM3) having an amplifying effect, from the first phase shifter output signal 17a whose phase is shifted.
Is supplied to detect the phase difference between both inputs to obtain the exclusive OR output signal 8a.

Here, the operation of the phase difference detection / comparison circuit PD will be described with reference to FIG. 4, in which the first switch circuit output signal 7a and the third limiter output signal 6a which are both inputs of the phase difference detection circuit PD. Has a phase difference of about 90 degrees, the phase difference detection output is about X / 2, and the dynamic range (0 to X)
Can take the approximate median value of.

Then, the exclusive OR output signal 8a obtained by detecting the phase difference between the two inputs is supplied to the first low-pass filter 10 via the amplifier circuit 9, and the high frequency component is removed here. The obtained phase difference detection circuit output signal 10a shown in FIG. 3 (G) is supplied to the sample-hold circuit 11 and the positive input of the differential amplifier circuit 12.

The sample-hold circuit 11 samples and holds the first low-pass filter output signal 10a by using the second control signal 20b shown in FIG. 3 (H) supplied from a control circuit (not shown) as a sample pulse. ..
That is, the sample pulse has a high level at one location in one horizontal period, and the period exists except the burst signal period, and the sample-hold circuit output signal 11a obtained by sample-holding at that timing is input to the negative input of the differential amplifier circuit 12. To supply. Since the sample-and-hold circuit output signal 11a serves as a reference for obtaining the phase error signal in the differential amplifier circuit 12 described below, it is necessary to consider the discharge of the electric charge of the hold capacitor (not shown) when the hold period is long. Therefore, it is desirable that the sample pulse becomes high level immediately before the start of the burst signal period.

Then, the differential amplifier circuit 12 finds the difference between the first low-pass filter output signal 10a and the sample hold circuit output signal 11a. The output signal of the differential amplifier circuit 12 is the output signal of the phase comparison circuit AA, and the output signal is supplied to the second low-pass filter 14 (LPF) via the gate circuit 13 (gate) to which the first control signal 20a is supplied.
Supply to 2). The gate circuit 13 supplies the signal to the second low pass filter 14 while the first control signal 20a is at the high level, and cuts off the signal during the low level. Since the cutoff frequency of the second low-pass filter 14 is set to a frequency sufficiently lower than the horizontal scanning frequency, even if the output signal of the differential amplifier circuit 12 is cut off by the gate circuit 13, there is no problem. .

The output signal of the second low-pass filter 14 thus obtained is supplied to the voltage-controlled crystal oscillating circuit 15, where it is obtained by oscillating based on the output signal of the second low-pass filter 14. The voltage controlled crystal oscillator circuit output signal 15a is supplied to the voltage controlled amplifier circuit 16. The voltage control amplifier circuit 16 is supplied with the output of an automatic amplitude detection circuit 18 (AGC DET) that detects the difference in amplitude between the second phase shift circuit output signal 17b and the input color signal aa.
Based on this output, the second phase shift circuit output signal 17
The output signal of the voltage control amplifier circuit 16 having a predetermined output amplitude obtained by controlling the amplitudes of b and the input color signal aa to be equal is supplied to the phase shift circuit 17 (PS).

The phase shift circuit 17 is synchronized with the phase of the voltage control crystal oscillation circuit output signal 15a based on the voltage control crystal oscillation circuit output signal 15a and has a phase difference of about 90 degrees. 17a and 17b are obtained by using a well-known delay circuit or the like. Then, the first phase shift circuit output signal 17a is supplied to the third limiter circuit 6, and the second phase shift circuit output signal 17b is supplied to one input of the second limiter circuit 5 and the automatic amplitude detection circuit 18 and the second input. It supplies to the switch circuit 19 and respectively.

Then, the second switch circuit 19 inputs the input color signal aa, the second phase shift circuit output signal 17b and the DC voltage signal 19b supplied from a voltage source (not shown).
The signals are selectively output using the first, third, and fourth control signals 20a, 20c, and 20d supplied from a control circuit (not shown). That is, the first control signal 20a (shown in FIG. 3D) which is the burst signal period is in the second level during the high level period.
Phase shift circuit output signal 17b, the input color signal aa when the third control signal 20c (shown in FIG. 3I), which is a color signal period, is at a high level, and the burst signal period or color. During a period when the fourth control signal 20d (shown in FIG. 3 (J)) is at a high level, which is a period other than the signal period, the output color signal 19a obtained by selecting the DC voltage signals 19b is transmitted to a transmission line (not shown). Supply.

The burst signal related to the output color signal 19a thus obtained is the voltage control crystal oscillation circuit output signal 15a.
S / N is improved because it is a signal based on the above, and the phase matches the burst signal related to the input color signal aa. Further, during the period other than the burst signal period or the color signal period of the output color signal 19a, the voltage DC voltage signal 19b having the same potential as the average potential of the input color signal aa is replaced. N has been improved.

In the first embodiment described above, instead of the switch circuit 3, the first switch circuit 19 used in the second embodiment is used, and a DC voltage is applied during periods other than the burst signal period and the color signal period. Of course, you may choose.

In the second embodiment described above, the PLL circuit may be constructed by appropriately removing the voltage control amplifier circuit 16, the automatic amplitude detection circuit 18, the second switch circuit 19 and the like from the burst replacement circuit. Of course.

In the PLL circuits of the above first and second embodiments, when the input signal is a continuous signal, the burst gate signal BGP, the first control signal 20a, etc. may be omitted. Of course.

In the burst signal replacement circuits of the above-described first and second embodiments, the voltage control amplifier circuit 16 is interposed between the voltage control crystal oscillation circuit 15 and the switch circuit 3 / first switch circuit 19. For example, the voltage control amplifier circuit 16 may include the phase shift circuit 17 and the switch circuit 3.
The output of the voltage controlled crystal oscillator circuit 15 is directly connected to the input of the phase shift circuit 17 while being interposed between the first switch circuit 19 and the second phase shift which is one input of the automatic amplitude detection circuit 18. Of course, the circuit output signal 17b may be changed to the voltage control amplifier circuit 16 to control the amplitude.

[0045]

As described above, according to the present invention, the first
The phase difference (Δ) between the phase of the signal of and the phase of the second signal is
The second phase difference (α + Δ) and the third phase difference (α) are used to cancel the first phase difference (α) which is the phase difference between the phase of the second signal and the phase of the comparison signal. Since it is possible to provide a phase comparison circuit that can be obtained as a result, the phase difference (Δ) between the phase of the first signal and the phase of the second signal can be directly obtained with high accuracy.

As described above, according to the present invention, the fourth phase difference (Δ), which is the phase difference between the phase of the input signal and the phase of the output signal, is compared with the second phase difference (α + Δ). 3 is used to cancel the first phase difference (α), which is the phase difference between the phase of the output signal and the phase of the comparison signal, to obtain the fourth phase difference (Δ). ), It is possible to provide a PLL circuit that generates the output signal and the comparison signal and outputs the output signal. Therefore, when generating the comparison signal, absolute accuracy of α is not required, and further, secular change, temperature characteristic And so on
There is an effect that it is possible to provide a PLL circuit in which the phase of the input signal and the phase of the output signal coincide with each other even if is changed.

Further, as described above, according to the present invention, it is possible to provide a burst signal replacement circuit using the PLL circuit, and in particular, the reference signal is generated due to the amplitude difference between the first burst signal and the second burst signal. Is adjusted so that the amplitude difference is eliminated, so that not only the phase of the first burst signal of the input color signal and the phase of the second burst signal of the output color signal match but also the amplitude of the burst There is an effect that a signal replacement circuit can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining an embodiment according to the present invention.

FIG. 2 is a block diagram for explaining another embodiment according to the present invention.

FIG. 3 is a timing chart for explaining another embodiment according to the present invention.

FIG. 4 is a diagram for explaining input / output characteristics of a phase difference detection circuit.

FIG. 5 is a block diagram of a conventional burst signal replacement circuit.

[Explanation of symbols]

3a, 19a Output color signal 15a Voltage control crystal oscillation circuit output signal (reference signal) 17a First phase shift circuit output signal (comparison signal) aa Input color signal θ Burst signal phase related to input color signal (phase of input signal ) Α Phase difference between first and second phase shift circuit output signals (first phase difference, third phase difference) Δ Phase of burst signal relating to input color signal and second phase shift circuit output signal Phase difference (fourth phase difference) θ + Δ Phase of second phase shift circuit output signal (phase of output signal) α + Δ Phase difference between burst signal phase related to input color signal and first phase shift circuit output signal (Second phase difference) θ + α + Δ Phase of first phase shift circuit output signal (phase of comparison signal)

Claims (2)

[Claims] 1. A phase comparison circuit for comparing the phases of a first signal and a second signal, wherein a phase of the first signal and a comparison signal having a first phase difference from the second signal The phase difference from the phase is detected as the second phase difference, the phase difference between the phase of the second signal and the phase of the comparison signal is detected as the third phase difference, and the second phase difference and the phase difference are detected. A phase comparison circuit, which detects and outputs a phase difference between the phase of the first signal and the phase of the second signal that cancels the first phase difference by using the third phase difference. 1. A phase difference between a phase of an input signal and a phase of a comparison signal having a first phase difference with an output signal is detected as a second phase difference, and a phase of the output signal and a phase of the comparison signal. Phase difference with
Is detected as the phase difference between the input signal and the output signal, and the second phase difference is used to cancel the first phase difference. A PLL circuit which detects the phase difference of 4 and generates the output signal and the comparison signal by the fourth phase difference to output the output signal. 2. A burst signal replacement circuit for replacing a first burst signal relating to an input color signal with a second burst signal, the phase of the first burst signal, the second burst signal and the first position. The second phase difference from the phase of the comparison signal having the phase difference
Of the second burst signal and the phase of the comparison signal are detected as a third phase difference, and the second phase difference and the third phase difference are detected. Using the phase of the first burst signal that cancels the first phase difference and the second
Of the burst signal is detected as a fourth phase difference, and the amplitude of the reference signal generated by the fourth phase difference is calculated as the amplitude of the first burst signal and the second burst signal. After adjusting so that there is no difference, the second burst signal and the comparison signal are generated based on this signal, and the first burst signal in the input color signal is replaced with the second burst signal. A burst signal replacement circuit, which outputs an output color signal.