JP3170695B2 - Burst signal generation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a burst signal generation circuit, and more particularly, to a circuit used in a video signal processing circuit such as a so-called color video device such as a television, a VTR and a video camera, and a color video signal processing device. A burst which is a signal constituting a composite video signal (so-called a composite color video signal, hereinafter abbreviated as a composite signal) defined by the NTSC standard, the PAL standard, or the like, which is a standard in color television broadcasting. The present invention relates to a burst signal generation circuit that generates a signal.

[0002]

2. Description of the Related Art FIG. 3 shows a waveform example of a composite signal defined by the NTSC system, the PAL system or the like. The composite signal A in this example is a signal corresponding to one scanning line on the television screen (see FIG. 3A). This is a combination of three signals of a horizontal synchronization signal HSYNC, a burst signal C, and a video signal D. Horizontal synchronization signal HSYN
C is a basic synchronization signal serving as a reference for determining timing such as the start of horizontal scanning (see FIG. 3B).

[0003] The burst signal C is a signal that is inserted so that the receiving side or the demodulating side can synchronize with the chrominance carrier (see FIG. 3C). The chrominance signal is modulated by a so-called chrominance subcarrier for the chrominance signal different from the carrier of the luminance signal. This is because demodulation of this color signal requires that the demodulation side also know the phase of the color carrier. The video signal D is a video signal for one scanning line (see FIG. 3).
(D)). These include a luminance signal, a color signal, and the like.

[0004] Usually, the above-mentioned burst signal must be included in a certain section after a predetermined period from the horizontal synchronizing signal in the composite signal. This section is a burst section, and a signal indicating this timing is a burst flag pulse BFP (see FIG. 3E). Then, the burst signal generation circuit generates the above-mentioned chrominance carrier or an oscillation signal F (FIG. 3
(F)) and the burst flag pulse BFP,
This is a circuit for generating a burst signal C.

FIG. 4 shows an example of a conventional burst signal generation circuit conforming to the NTSC system. Here, 1 is a mixing circuit, 2 is a bandpass filter, and 3 is a constant current circuit.
The mixing circuit 1 includes an oscillation signal Fa having the same cycle as the chrominance carrier (see FIG. 5A) and an oscillation signal F having the opposite phase to the oscillation signal Fa.
b (see FIG. 5B). Then, by mixing these oscillation signals Fa and Fb, the phase and the like are set to NT.
A composite signal F ′ (see FIG. 5C) conforming to the SC system is generated.

However, the mixing circuit 1, the constant current circuit 3, and the switch circuit SW1 are connected to the power supply Vcc and the ground GND in this order.
The switch circuit SW1 opens and closes in response to the burst flag pulse BFP. For this reason, only when the switch circuit SW1 conducts and the operating current (I1) flowing through the constant current circuit 3 flows, the mixing circuit 1
Works. Therefore, the composite signal F 'is output only during that time. That is, the composite signal F ′ is not a simple oscillation signal but a signal that oscillates in response to a burst section of the composite signal. The band-pass filter 2 removes excess harmonics and low-frequency components from the synthesized signal F ′ and performs NTSC
A burst signal C conforming to the method is output.

FIG. 6 shows an example of a conventional burst signal generating circuit conforming to the PAL system. Its configuration is shown in FIG.
Is substantially the same as the configuration of the burst signal generation circuit of FIG. However, there are two differences. The first difference is that the input signal
Oscillation signal Fc (FIG. 7)
(See FIG. 7A), the phase of the oscillation signal Fb differs by 90 ° with respect to the oscillation signal Fb (see FIG.
Leading or lagging by 0 °). This allows
The composite signal F ″ has a phase of 135 ° with respect to the oscillation signal Fa.
Alternatively, the signal changes by 225 °, and the value changes into two stages (see FIG. 7C).

The second difference is that, first, the same characteristic
Assuming that a filter is used, it is necessary to supply an operating current larger than the current value I1 to the constant current circuit 4 instead of the constant current circuit 3. As a result, the amplitude of the composite signal F ″ becomes larger than the amplitude of the composite signal F ′.
In the figure, the current value of the constant current circuit 4 is changed from the current value I1.
In the sense that it is large, and in relation to the present invention, I1 +
Although shown as I2, in reality there is one current source
The current value of this current source is considered as I3 (= I1 + I2).
Has been obtained. Otherwise, due to the fact that the waveform of the composite signal F ″ is different from the waveform of the composite signal F ′, the ratio of these when passing through the same band-pass filter 2 is different,
As a result, the level of the burst signal C, which is the output signal, does not match. When the synthesized signal F ″ passes through the band-pass filter 2, a burst signal C conforming to the PAL system is generated (see FIG. 7D).

[0009]

In such a conventional burst signal generation circuit, the PAL is also used for the NTSC system.
The circuit configuration for the system is almost the same.
However, the operating current flowing through the mixing circuit is different. For this reason,
When a burst signal generation circuit is integrated into an IC, if a constant current circuit for determining an operation current value is also built in, it is necessary to use two different types of ICs. Requires an external constant current circuit, and it is difficult to incorporate all the circuits into one IC.

[0010] If the IC cannot be shared, the productivity of the IC will be poor, and if all the circuits cannot be integrated, the downsizing of devices and apparatuses cannot be achieved. SUMMARY OF THE INVENTION An object of the present invention is to solve such problems of the prior art.
An object of the present invention is to realize a burst signal generation circuit which can be applied to both the TSC system and the PAL system and in which all circuits can be integrated into an IC.

[0011]

The burst signal generating circuit according to the present invention which achieves the above object has the structure of NTSC.
Receiving a first oscillation signal having a cycle equal to the cycle of the color carrier of the system and a second oscillation signal having a phase inverted with respect to the first oscillation signal, and a first operating current is passed. When the first and second oscillation signals are mixed, a first mixed signal having an amplitude corresponding to the current value of the first operating current and adapted to the chrominance carrier of the NTSC system is formed. Receiving a first mixing circuit, a third oscillating signal having a cycle equal to the cycle of the chrominance carrier of the PAL system, and a fourth oscillating signal having a phase different from that of the third oscillating signal by 90 °. By mixing the third and fourth oscillation signals when the second operating current is flowing, the PA
A second mixing circuit that outputs a second mixed signal that is compatible with the L-type chrominance carrier and has an amplitude corresponding to the current value of the second operating current; the NTSC method and the PAL;
Receiving a selection signal for selecting one of the systems and a burst pulse indicating a burst section in the composite video signal of the selected system, and receiving the burst pulse when the selection signal indicates the NTSC system. An operation current selection unit that receives the burst pulse and supplies a second operation current having a current value larger than the first operation current in response to the burst pulse when the selection signal indicates the PAL method; A circuit and a frequency within a predetermined band from the first mixed signal.
A predetermined band from the second mixed signal.
And a band-pass filter that allows a frequency component within a predetermined band to pass from the synthesized signal, and a burst signal suitable for the composite video signal is output from the band-pass filter. It is.

[0012]

In the burst signal generating circuit of the present invention having such a configuration, the field of the NTSC system which has been conventionally considered individually is used.
PA and the operating current of the PAL system
Focusing on the large operating current value of the L system, the NTSC method
When the operating current value of the equation is I1, the operating current of the PAL system is
The current value is taken as I1 + I2, and I
Providing two constant current circuits, 1 and I2, for the switch circuit
I have more choices. At this time,
The large operation current value is not different from the current value of the PAL method.
Therefore, integration as one IC is possible. But
Therefore, when the NTSC system is selected, the current value I is adjusted so that a first mixed signal conforming to the NTSC system is generated.
One first operating current is passed, and when the PAL method is selected, a second operating current having a current value of I1 + I2 is passed so that a second mixed signal conforming to the PAL method is generated. Therefore, the amplitude of the input signal of the bandpass filter is determined according to these operating currents. In other words, the second mixed signal having a low pass ratio of the band-pass filter has a larger amplitude than the first mixed signal at this stage in response to the large attenuation. As a result, the band pass
Set the proper output level after passing through the filter
Can be switched from NTSC to PAL.
No need for a correction circuit to adjust the color carrier level
Become. To that extent, the circuit configuration is simplified, and the
Sticking can also be reduced.

Thus, a burst signal of an appropriate level is output regardless of whether the NTSC system or the PAL system is selected. In addition, both types can be dealt with by selecting with a selection signal. In addition, since the constant current circuit, which had to be externally connected in the past, is taken into the operating current selection circuit, and the first and second operating currents are selected by the selection signal, the constant current circuit is provided. Almost all circuits including circuits can be made into ICs.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a burst signal generating circuit having the configuration of the present invention will be described below. FIG. 1 is a block diagram showing a state in which an oscillation circuit is added to the circuit. Where 1,1
a is a mixing circuit, 2 is a bandpass filter, 3 and 3a are constant current circuits, 5 is an oscillation circuit, 10 is a selection synthesis circuit, and 11 is an operation current selection circuit. The configuration and operation will be described below in detail. The burst signal generation circuit is roughly divided into a preceding stage selection / synthesis circuit 10 and a subsequent stage bandpass filter 2.

The selecting / synthesizing circuit 10 includes mixing circuits 1 and 1a to be described later and an operating current selecting circuit 11. And
An oscillating signal or the like which is almost always oscillating is received, and then a synthesized signal F 'which is oscillating at a predetermined timing is generated. The band-pass filter 2 removes excess harmonics and low-frequency components from the composite signal F ′,
A burst signal C having a waveform conforming to the AL method is generated and output. The oscillation circuit 5 provided before the burst signal generation circuit includes three oscillation signals Fa (corresponding to a first oscillation signal) and an oscillation signal Fb (second and third oscillation signals) required as inputs to the burst signal generation circuit. Oscillation signal F)
c (corresponding to a fourth oscillation signal).

The oscillation signals Fa, Fb, and Fc have a period equal to the period of the chrominance carrier, and the phase is synchronized with the horizontal synchronization signal HSYNC. Then, the oscillation signal Fa
Is the reference phase, that is, the phase angle is 0 °, the phase angle of the oscillation signal Fb is 180 °. Further, the oscillation signal F
The phase angle of c differs from that of the oscillation signal Fa by 90 °,
In each of the scanning lines, the scanning is advanced by 90 ° or delayed by 90 °. That is, the phase angle is 90 ° or 270 °.

The mixing circuit 1 has the same configuration as the conventional one,
Receiving an oscillation signal Fa and an oscillation signal Fb, an operating current (I1)
Are flowing, these oscillation signals Fa, Fb
To generate a mixed signal Fn having an amplitude corresponding to the operating current (I1). The mixed signal Fn is converted to a composite signal F 'after being wired-ORed. It is known that the phase of the composite signal F' when only the mixed signal Fn is output conforms to the NTSC system in the conventional example. As described above.

The mixing circuit 1a has the same configuration as the mixing circuit 1, receives the oscillation signal Fb and the oscillation signal Fc, and mixes the oscillation signals Fb and Fc when the operating current (I1 + I2) is flowing. Thus, the mixed signal Fp having a phase angle of 135 ° or 225 ° alternately for each scanning line.
Generate The amplitude of the mixed signal Fp depends on the operating current (I1 +
The size is in accordance with I2). This mixed signal Fp is wired-ORed with the mixed signal Fn to become a composite signal F ′.
As described above in the conventional example, the phase of the composite signal F ′ when only the mixed signal Fp is output conforms to the PAL method.

The operating current selection circuit 11 includes a constant current circuit 3 for flowing a current value I1 and a constant current circuit 3a for flowing a current value I2.
And switch circuits SW1, SW2 and SW3. The switch circuit SW1 is based on the NTSC system and the PA
A selection signal NT which is a signal for selecting one of the L systems
In response to the PAL, one of the operating current lines of the mixing circuit 1 and the mixing circuit 1a is selectively connected to the constant current circuit side. The switch circuit SW2 is also provided with the selection signal NTPAL.
In response, the current line of the constant current circuit 3a is opened and closed. The switch circuit SW3 opens and closes according to a timing at which the burst signal C is to be inserted into the composite signal, that is, a burst flag pulse BFP indicating a burst section.

Then, the selection signal NTPAL is used to select NTS.
When the C method is selected, the switch circuit SW2
Is cut off, the constant current I2 is cut off, and the switch circuit SW3
Is conducted to the mixing circuit 1 side, and the connection between the constant current circuit 3 and the mixing circuit 1 is established. When the burst flag pulse BFP is received in this state, the switch circuit SW1 conducts only during the pulse period, and the constant current I1 from the constant current circuit 3 flows as the operating current of the mixing circuit 1. As described above, the mixed signal Fn is correspondingly generated.

When the PAL system is selected by the selection signal NTPAL, the switch circuit SW2 conducts, the constant current I2 is added to the constant current I1, and further, the switch circuit SW3 conducts to the mixing circuit 1a side and the constant. The connection between the current circuits 3, 3a and the mixing circuit 1a is established. When the burst flag pulse BFP is received in this state, the switch circuit SW1 conducts only during the pulse period, and the constant current I1 + I2 from the constant current circuit 3 and the constant current circuit 3a flows as the operating current of the mixing circuit 1a. As described above, the mixed signal Fp is correspondingly generated.

With such a configuration, when the NTSC system is selected, the operating current (I1) is passed to generate a composite signal F 'having an amplitude corresponding to the operating current (I1). When the PAL method is selected, the operating current (I1 + I2) is supplied to generate a composite signal F ′ having an amplitude corresponding to the operating current (see FIG. 7C for the waveform). Therefore, even if the pass ratio in the band-pass filter 2 is different due to the waveform or the like, the amplitude of the input signal of the band-pass filter 2 is adjusted in advance by the operating current. It is possible to deal with both the NTSC system and the PAL system without changing the pass filter 2 at all.

Further, a constant current circuit conventionally provided externally is included in the operating current selection circuit together with the switch circuit. Therefore, it is sufficient to receive the selection signal NTPAL and the burst flag pulse BFP from the outside, and the selection and synthesis circuit 10 can be all integrated into one chip. As a result, sharing of circuits and ICs can be achieved between the NTSC system and the PAL system. FIG. 2 shows two specific circuit configuration examples of the above-described selective synthesis circuit. In these circuits, since the mixing circuit 1 and the mixing circuit 1a do not operate at the same time, the resistors on the power supply side are shared between the mixing circuit 1 and the mixing circuit 1a, thereby further simplifying.

[0024]

As can be understood from the above description, in the burst signal generation circuit having the configuration of the present invention, the mixing circuit and its operating current can be selected. As a result, N
The present invention is applicable to both the TSC system and the PAL system, and has the effect that almost all circuits can be integrated into an IC.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a burst signal generating circuit having a configuration of the present invention.

FIG. 2 is a specific circuit example of a selection / synthesis circuit in the burst signal generation circuit having the configuration of the present invention;

FIG. 3 is a waveform diagram for explaining the positioning of a burst signal in a composite color video signal.

FIG. 4 is a conventional burst signal generation circuit for the NTSC system.

FIG. 5 is an example of a signal waveform in the circuit.

FIG. 6 is a conventional burst signal generation circuit for the PAL system.

FIG. 7 is an example of a signal waveform in the circuit.

[Explanation of symbols]

 1, 1a mixing circuit 2 bandpass filter 3, 3a, 4 constant current circuit 5 oscillation circuit 10 selection synthesis circuit 11 operating current selection circuit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 9/44-9/78

Claims (1)

(57) [Claims] A first oscillation signal having a cycle equal to the cycle of an NTSC chrominance carrier; and a second oscillation signal having a phase inverted with respect to the first oscillation signal. By mixing the first and second oscillating signals when the operating current is flowing, it has an amplitude corresponding to the current value of the first operating current, adapted to the color carrier of the NTSC system. A first mixing circuit for outputting the first mixed signal; a third oscillating signal having a period equal to the period of the PAL color carrier; and a fourth oscillating signal having a phase different from the third oscillating signal by 90 °. And the third and fourth oscillation signals are mixed when the second operating current is flowing, so as to be compatible with the color carrier of the PAL system and perform the second operation. Outputting a second mixed signal having an amplitude corresponding to the current value of the current; A second mixing circuit, a selection signal for selecting one of the NTSC system and the PAL system, and a burst pulse indicating a burst section in a composite video signal of the selected system. When the burst signal is received, the first operating current is supplied when the burst signal is received, and when the selection signal indicates the PAL system, the first operating current is received. Second with large current value
An operating current selection circuit for passing an operating current of a predetermined frequency; and a frequency component within a predetermined band from the first mixed signal.
And a frequency within a predetermined band from the second mixed signal.
A band-pass filter that passes several components or passes a frequency component within a predetermined band from a synthesized signal thereof, and a burst signal that matches the composite video signal is output from the band-pass filter. And a burst signal generating circuit.