JP3345200B2 - Phase circuit and color signal processing circuit using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase circuit and a color signal processing circuit using the phase circuit,
This is a circuit used for a color signal processing circuit such as a color video equipment such as a TR and a video camera and a color video signal processing apparatus.
A burst signal generating circuit for generating a burst signal which is a signal constituting a part of a composite video signal (a so-called composite color video signal, hereinafter abbreviated as a composite signal) defined by an SC system, a PAL system, and the like; A phase circuit used to generate a burst signal of a predetermined phase serving as a reference for demodulation of a demodulation circuit, and a phase suitable for use in an IC that can easily generate a phase signal of ± 90 ° from an input signal. Circuit.

[0002]

2. Description of the Related Art A composite signal defined by the NTSC system, the PAL system or the like is a signal corresponding to one scanning line on a television screen. This is because the horizontal synchronizing signal HSYN
C, a color burst signal (color synchronization signal, hereinafter referred to as a burst signal), and a video signal.
A burst signal is a signal inserted so that synchronization with a chrominance carrier can be taken on the receiving side or the demodulation side. A chrominance signal is a subcarrier for a chrominance signal different from a carrier of a luminance signal, a so-called chrominance carrier. Modulated by In order to demodulate this color signal, it is necessary for the demodulation side to know the phase of the color carrier.

The above-mentioned burst signal must usually be included in a composite signal in a certain section after a predetermined period from the horizontal synchronizing signal. This section is a burst section, and a burst flag pulse B indicating this timing
The FP usually extracts the burst signal and generates a color subcarrier for color demodulation in synchronization with the burst signal.
In the NTSC system, the PAL system, and the like, the chrominance signal is generated by mixing signals having phases shifted by 90 ° or 180 ° from the phase of the subcarrier. A signal whose phase is shifted by a phase difference is often generated by a phase circuit.

As this kind of phase circuit, for example, a CR delay circuit composed of a variable resistor and a capacitor is used, which comprises a variable Gm amplifier for simulating a resistance component and a comparator for comparing and detecting the output of the variable Gm amplifier. A signal having a phase difference of ± 90 ° with respect to the subcarrier is generated, or in a digital VTR or the like, a plurality of gate circuits are cascaded to secure a phase difference of ± 90 ° with the delay amount. Apart from this, in digital VTRs, etc.,
Some phase circuits generate a pulse having a high period, divide the frequency, and generate pulses having various phases with respect to the input pulse.

[0005]

In the former phase circuit using a CR delay circuit, a large number of stages of delay circuits must be cascaded in order to obtain a phase signal of ± 90 °. In this case, there is a disadvantage that the circuit scale becomes large.
Similarly, in the case of a gate circuit, the number of stages for obtaining a phase signal of ± 90 ° increases, and the same problem as described above occurs. On the other hand, a phase circuit based on frequency division requires a high-frequency clock pulse generating circuit and a frequency dividing circuit, which increases the circuit scale.

SUMMARY OF THE INVENTION An object of the present invention is to solve such a problem of the prior art, and to provide a simple circuit of ± 90 °.
A phase circuit capable of generating a phase signal is provided. Another object of the present invention is to provide a color signal processing circuit using the phase circuit.

[0007]

SUMMARY OF THE INVENTION In order to achieve such an object, a phase circuit according to the present invention is characterized in that two pulses of substantially 50% duty and mutually opposite phases are inverted from each other from an input signal. A pulse generation circuit to generate these two
First and second switch circuits that are turned on / off alternately in response to one pulse, first and second constant current circuits provided downstream of the first and second switch circuits, respectively, And a capacitor provided between the second switch circuit and a comparator receiving both terminal voltages of the capacitor at a reference input terminal and a signal input terminal. And a signal having a phase difference of + 90 ° or −90 °.

[0008]

As described above, by charging and discharging both terminal voltages of the capacitor using the constant current circuit through the switch circuit which turns on / off with almost 50% duty, the linearity of the original input signal is improved. Thus, a waveform having a 180 ° phase difference over a phase width of approximately 180 ° can be generated. Then, when these signals are received by the comparator at the reference input terminal and the signal input terminal, the input signal becomes a triangular wave having a threshold value at the center, thereby producing an output signal having a phase difference of substantially ± 90 °. It can be obtained from a comparator. As a result, the number of elements is small, I
+ 90 ° with respect to the original input signal with a simple circuit suitable for C conversion
Alternatively, a signal of -90 ° phase is obtained.

[0009]

FIG. 1 is a block diagram mainly showing a phase circuit of the present invention, and FIG. 2 is a waveform diagram for explaining an operation of generating a ± 90 ° phase signal. In FIG. 1, reference numeral 1 denotes a phase circuit, and a differential comparator (COM) 2 receives a subcarrier signal from a subcarrier generation circuit 3. The comparator 2 receives the input signal of the subcarrier signal (see FIG. 2A).
A pair of pulses 180 ° out of phase from each other (FIG. 2
(see (b) and (c)) and sends them to the charge / discharge circuit 5 of the capacitor 4. The charge / discharge circuit 5 sends to the comparator 6 a ramp waveform of each phase generated at both terminals A and B by charging / discharging of the capacitor 4. The respective gradient waveforms at this time differ from each other by 180 ° according to the phase of the input pulse.

The comparator 6 is also a differential comparator similar to the comparator 2, and has two terminals A,
The voltage of B is received by the reference side terminal (−phase input) and the signal input terminal (+ phase input), respectively. Then, outputs having a phase difference of 180 ° are sent to the output circuit 7. Then, output signals having a phase difference of ± 90 ° with respect to the original input signal are output from the output terminals 8a and 8b of the output circuit 7.

Here, the charge / discharge circuit 5 is connected to a power supply line Vcc
A first series circuit 5a of a transistor Q1 and a constant current source I1 connected between the power supply line Vcc and the ground GND.
2 and a second series circuit 5b of a constant current source I2,
A capacitor 4 is connected between the connection points of these transistors and the constant current source. The transistor Q1 has its base receiving the non-inverting pulse from the comparator 2, its collector-emitter side is connected to the power supply line Vcc and the terminal of the capacitor 4, and the transistor Q2 has its base 180 ° out of phase with the comparator 2 at the base. A pulse on the different inversion side is received, and its collector-emitter side is connected to the power supply line V.
cc and the remaining terminals of the capacitor 4.

The output circuit 7 includes a first series circuit 7a of a transistor Q3 and a current source I3 connected between the power supply line Vcc and the ground GND, and a transistor Q4 similarly connected between the power supply line Vcc and the ground GND. Current source I
4 and a second series circuit 7b. Outputs from the connection points of these transistors and the current source are connected to output terminals 8a and 8b, respectively, and ± 9% with respect to the original input signal.
An output signal having a phase difference of 0 ° is generated. The transistor Q3 receives a pulse on the non-inverting side from the comparator 6 at its base, and its collector-emitter side has a power supply line Vcc.
The transistor Q4 has its base receiving a pulse on the inversion side having a phase difference of 180.degree. From the comparator 6 at its base, and its collector-emitter side connected to the power supply line Vcc and the current source I4. I have.

Here, the charge / discharge operation of the capacitor 4 and ± 9
The operation of generating the 0 ° phase output signal will be described with reference to FIG. 2. The input subcarrier signal is (a), and the phase of (b) and (c) is 180
° Two different pulse signals are obtained. These pulse signals cause the transistors Q1 and Q2 of the series circuits 5a and 5b to be turned on.
By N / OFF, the voltage at the terminal A of the capacitor 4 is charged and discharged by the constant current source in accordance with the ON / OFF, so that the voltage at the terminal B changes as shown in FIG.
Similarly, it changes as shown in (e). This voltage signal is sent to one input of the changeover switches 6a and 6b, respectively.

Regarding the change of the terminal voltage of the capacitor 4,
When the transistor Q1 is ON and the transistor Q2 is
Starting from the FF state, first, the transistor Q
When 1 is turned on and the transistor Q2 is turned off, the terminal A of the capacitor 4 is set to a predetermined level lower than the power supply line Vcc by a certain voltage, and the value is maintained. As a result, the terminal B rises by a fixed voltage. Next, the terminal B of the capacitor 4 is connected to the terminal A,
Since the current flows to the ground GND and the terminal B via the constant current source I2, the current gradually decreases. When the discharge is completed, the voltage returns to the original voltage before the rise. During this time, since the discharge is performed via the constant current source I2, the slope of the discharge characteristic is constant. Next, since the transistor Q1 is turned on, charging is started from the power supply line Vcc via the terminal A via the transistor Q1. As a result, the voltage at the terminal B gradually decreases. Since the charging at this time is also performed via the constant current source I2, the charging has a linear slope. When charging is completed, the transistor Q1 turns off and the transistor Q2 turns on. As a result, the voltage at the terminal B returns to the original constant value, and the voltage at the terminal A follows the same course as described above. As a result, the voltage at the terminal A changes as shown in (d), and the voltage at the terminal B changes as shown in (e).

As a result, the signals of (d) and (e) are input to the input of the comparator 6, respectively, resulting in a triangular waveform as shown in (f). At this time, the reference level of the comparator 6 is at the median value TH. As a result, as shown by (g) and (h), a pulse signal having a phase difference of ± 90 ° with respect to the input signal (a) is output to the output terminal 8.
a and 8b as output signals. In a digital VTR or the like, this can be used as it is, but in order to make an analog sine wave, it is only necessary to pass through a tank circuit. Also, the input signal (a) is
It is often given as a pulse waveform.

As described above, the comparators 2 and 6 in the embodiment use the differential comparator to simultaneously generate two pulses whose phases are different from each other by 180 °. A configuration in which a pulse is generated and the other pulse is generated by an inverter may be used. Further, in the embodiment, the bipolar transistor is used as the switch circuit. However, this is for high-speed switching. For example, an analog switch such as a transmission gate may be used. There is no. Further, although a signal having a phase difference of ± 90 ° is simultaneously obtained as an output, the phase circuit according to the present invention may obtain a signal having any one of the phase differences. By the way, in the embodiment, the color subcarrier is used as an input signal, but it goes without saying that, for example, a clock signal read from a video tape or the like or an output signal of a VCO may be used as an input signal.

[0017]

According to the present invention, the voltage at both terminals of the capacitor is reduced by approximately 50% duty by using a constant current circuit.
By charging / discharging through a switch circuit for N / OFF, almost 180 degrees with a good linearity gradient to the original input signal.
It is possible to generate waveforms having a phase difference of 180 ° over a phase width of °, and these signals are received by a comparator at a reference input terminal and a signal input terminal, so that the threshold value is set at the center as the input signal. An output signal having a certain triangular wave and substantially having a phase difference of ± 90 ° can be obtained from the comparator.

As a result, with a simple circuit having a small number of elements and suitable for IC, + 90 ° or −
A 90 ° phase signal is obtained. Therefore, it is not necessary to use a frequency dividing circuit using a high-frequency pulse, and a simple circuit that can be integrated into an IC for a digital circuit, particularly a clock generating circuit of a digital VTR, including a color signal processing circuit is realized. Can be.

[Brief description of the drawings]

FIG. 1 is a block diagram mainly showing a phase circuit according to the present invention;

FIG. 2 is a waveform diagram for explaining an operation of generating the ± 90 ° phase signal.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Clock control circuit, 2, 6 ... Comparator, 3 ... Subcarrier generation circuit, 4 ... Capacitor, 5 ... Charge / discharge circuit, 7
... Output circuit.

Claims (2)

(57) [Claims] 1. A pulse generating circuit for generating two pulses of substantially 50% duty and mutually opposite phases from an input signal, and a first pulse generator which is turned on / off alternately in response to these two pulses. And a second switch circuit, first and second constant current circuits provided downstream of the first and second switch circuits, respectively, and provided between the first and second switch circuits. A capacitor,
A phase circuit comprising a comparator receiving both terminal voltages of the capacitor at a reference input terminal and a signal input terminal, and obtaining a signal having a phase difference of substantially + 90 ° or −90 ° with respect to an input signal at an output of the comparator. . 2. A pulse generating circuit for generating two pulses of substantially 50% duty and mutually in opposite phases from an input signal, and a first pulse generator for turning on / off alternately in response to the two pulses. And a second switch circuit, first and second constant current circuits provided downstream of the first and second switch circuits, respectively, and provided between the first and second switch circuits. A capacitor,
A phase circuit comprising a comparator receiving both terminal voltages of the capacitor at a reference input terminal and a signal input terminal, and obtaining a signal having a phase difference of substantially + 90 ° or −90 ° with respect to an input signal at an output of the comparator. A color signal processing circuit having: