JPH07212782A - Color demodulation signal generating circuit - Google Patents

Abstract

PURPOSE:To obtain a color demodulation signal generating circuit generating a color demodulation use chrominance subcarrier with a phase with respect to an external control voltage to set a hue of a color demodulation output independently of the dispersion in the circuit characteristic between products. CONSTITUTION:In the signal generating circuit generating a color demodulation chrominance subcarrier by adjusting a phase of the chrominance subcarrier synchronously with a color burst signal with an external control voltage, a phase comparator 2 is used to detect a phase difference between the chrominance subcarrier and the color demodulation chrominance subcarrier. Then a voltage comparator 4 is used to obtain a voltage difference between an error voltage corresponding to the phase difference and the external control voltage and a phase correction device 5 corrects a phase of the color demodulation chrominance subcarrier based on the voltage difference.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color demodulation signal generation circuit, and more particularly to a circuit for correcting the phase of a color demodulation color subcarrier for demodulating a color signal.

[0002]

2. Description of the Related Art Normally, in the hue control of an NTSC color television receiver, when the input modulated color subcarrier (carrier color signal) is demodulated, the phase of the color subcarrier used for demodulation is supplied from the outside. It is performed by changing the control voltage.

FIG. 3 shows a block configuration of a conventional circuit for performing such hue control. In the figure, reference numeral 1 is a color for generating and outputting a plurality of color subcarriers having different phases synchronized with a color burst signal. The sub-carrier generator 3 outputs the phase of a predetermined color sub-carrier of the plurality of outputs of the color sub-carrier generator 1 from about -45 ° to about + 45 ° with respect to the input phase thereof by the external control voltage V _cont . Is a phase shifter that outputs a color subcarrier for color demodulation for demodulating a desired color signal by performing signal processing such as changing in a range of about 90 °.

FIG. 4 shows a concrete circuit configuration of the phase shifter 3. In FIG. 4, reference numeral 31 indicates a color subcarrier generated by the color subcarrier generator 1 and +4 with respect to its input phase.
A first phase shifter for generating a first color subcarrier having a phase of 5 ° and a second color subcarrier having a phase of −45 ° with respect to the input phase, each collector being a power supply. V _CC
Transistors Q ₁ and Q ₂ connected to each other, constant current sources I ₁ and I ₂ connected between the emitters of the respective transistors and ground, and resistors connected in series connected between the emitters of the respective transistors. R ₁ and a capacitor C ₁ , a series-connected capacitor C ₂ and a resistor R ₂ connected in parallel with these, and a resistor R ₃₁ having one end connected to the emitter of the transistor Q ₂ the output of the color subcarrier generator 1 to the base of Q ₁ is also adapted to a predetermined signal to the base of the transistor Q ₂ is is inputted.

Reference numeral 32 denotes a first differential amplifier which receives the above-mentioned first and second color subcarriers, amplifies them, and generates in-phase and antiphase color subcarriers, respectively, for a power supply and ground. Between the transistor Q ₇ and the resistor R
₇ , a transistor Q ₅ , a resistor R _5, and a constant current source I ₅ are sequentially connected in series, and a transistor Q ₈ , a resistor R ₈ , and a transistor are provided between the first output terminal O ₁ and the constant current source I _5. A first differential amplifier circuit in which Q ₆ and a resistor R ₆ are sequentially connected in series, and a transistor Q ₁₂ , a resistor R ₁₂ , a transistor Q ₁₀ , a resistor R _10, and a constant current source I between a power source and ground. ₆ are sequentially connected in series, and a transistor Q ₁₁ , a resistor R ₁₁ , a transistor Q ₉ and a resistor R ₉ are sequentially connected in series between the second output terminal O ₂ and the constant current source I _6. It is composed of a second differential amplifier circuit. Here, the transistors Q ₇ , Q ₈ , Q ₁₁ , Q
The bases of ₁₂ are all connected to the bias terminal T ₁ , the bases of the transistors Q ₆ and Q ₉ are connected to the other end of the resistor R ₃₁ of the first phase shifter 31, and the bases of the transistors Q ₅ and Q ₁₀ are The connection point between the resistor R ₁ and the capacitor C ₁ of the _first phase shifter 31, and the capacitor C ₂ and the resistor R _{2 respectively.}
Is connected to the connection point of.

Further, the reference numeral 33 receives two signals necessary for demodulation of the color signal among the outputs of the differential amplifier 32 and combines them, and at the same time, adjusts the combining ratio by the external control voltage V _cont to obtain a desired signal. Is a voltage-controlled phase shifter that outputs a color subcarrier having a phase of, and transistors Q ₁₃ and Q ₁₄ whose emitters are both connected to the _first output terminal O ₁ of the first differential amplifier 32 and whose emitters are Transistors Q ₁₅ and Q ₁₆ both connected to the _second output terminal O ₂ of the first differential amplifier 32, and resistors R ₁₃ and R connected between the collectors of the transistors Q ₁₃ and Q ₁₆ and the power supply. It is composed of ₁₄ and. Here, the collectors of the transistors Q ₁₃ and Q ₁₅ and the transistors Q ₁₄ and Q ₁₆ are commonly connected, and the bases of the transistors Q ₁₃ and Q ₁₆ and the transistors Q ₁₄ and Q ₁₅ are commonly connected. Therefore, an external control voltage is applied to each common connection point.

A second phase shifter 34 receives the phase-adjusted color subcarrier and outputs it as two color demodulated color subcarriers having a demodulation angle, that is, having a predetermined phase difference. Then, transistors Q ₃ and Q ₄ , resistors R ₃ and R ₄ ,
The circuit configuration is the same as that of the first phase shifter 31 and is composed of R ₃₄ , capacitors C ₃ and C _4, and constant current sources I ₃ and I ₄ . Here the output amplifier 36 and is connected via a capacitor C _5, also each said base of each transistor Q ₃ and Q ₄ are the resistance R _5a of the voltage-controlled phase shifter 33 to the base of the transistor Q ₃ are , R _5b to the bias terminal T ₂ .

Reference numeral 35 is a second differential amplifier which differentially amplifies these color demodulation color subcarriers and outputs them to the color demodulator. The collector is connected to the power supply and the base is common to the bias terminal T ₃ . Connected transistors Q ₂₁ and Q ₂₂ ,
Resistance R ₁₇ of the connected serially connected between ground and the transistor Q _21, the transistor Q _17, a resistor R ₁₅ and the constant current source I _7, the emitter and the constant current source I ₇ of the transistor Q ₂₁ A series-connected resistor R ₁₈ , a transistor Q ₁₈ , and a resistor R _16, which are connected in series, and a series-connected resistor R ₂₂ , a transistor Q ₂₀ , a resistor R _20, and a resistor R ₂₂ , which are connected between the transistor Q ₂₂ and the ground. a constant current source I _8, and a resistor R _21, the transistor Q _19, and a resistor R ₁₉ Metropolitan of connected serially connected between the emitter and the constant current source I ₈ of the transistor Q _22. The bases of the transistors Q ₁₇ and Q ₂₀ are the connection point between the resistor R ₃ and the capacitor C _{3 of} the second phase shifter 34, and the capacitor C _{4 respectively.}
Is connected to the connection point of the resistor R ₄ and the bases of the transistors Q ₁₈ and Q ₁₉ are the resistor R _{34 of} the second phase shifter _34.
Are commonly connected to the other end of each of the transistors Q _{17 to} Q
₂₀ collectors are output terminals for outputting the color subcarrier for color demodulation.

Next, the operation will be described. The color subcarrier generated by the color subcarrier generator 1 based on the color burst signal is processed by the first phase shifter 31, and the phase shifter 3
From 1, the first color subcarrier having a phase shift of + 45 ° with respect to the phase of the input signal and the second color subcarrier having a phase shift of −45 ° are output. The first differential amplifier 32 receives the first and second color subcarriers, amplifies them, and simultaneously outputs the in-phase and antiphase color subcarriers. Of these four differential amplification outputs, two signals whose phases correspond to color demodulation are input to the voltage control phase shifter 33, and color subcarriers of these two types of phases are combined to form one color. The subcarrier is output. At this time, the synthesis ratio is adjusted by the control voltage, and a color subcarrier of a desired phase is obtained at the output. The color subcarrier whose phase has been adjusted in this way is further input to the second phase shifter 34 and converted into two color subcarriers for color demodulation having a demodulation angle, that is, having two predetermined phase differences. And this 2
One color subcarrier for color demodulation is input to the second differential amplifier 35, and amplified color subcarriers for color demodulation in-phase and anti-phase with each are output, and these four outputs are output to the color demodulator. To be done.

[0010]

However, in the conventional color demodulation signal generating circuit, the color subcarrier generated by the color subcarrier generator 1 and having a phase corresponding to the color burst signal is the first shift signal. The offset voltage existing in these circuits is inputted to the color demodulator through the phase shifter 31, the differential amplifier 32, the voltage control phase shifter 33, the second phase shifter 34 and the second differential amplifier 35. The phase shift of the color subcarriers occurs due to the phase shift due to and the phase shift due to the fluctuation of the constants of the constituent elements (resistance and capacitance).

That is, a constant bias voltage is supplied to the transistors forming each circuit so that the transistors have predetermined characteristics. However, if the resistance values such as the bias resistances vary among products, the operating points of the transistors will increase. As a result, the DC level of the input / output signal of each circuit deviates from a predetermined level, and a phase deviation due to the offset voltage occurs. In addition, when the characteristics of the resistance and the capacity of the circuit vary among products, a phase shift is caused due to the constant fluctuation of the constituent elements.

Therefore, even if the external control voltage applied to the voltage control phase shifter 33 is set to a constant value, it is difficult to obtain color demodulation color carrier waves of the same phase among products, that is, There is a problem that the color demodulation output (color signal) of the correct hue cannot be obtained due to the phase shift of the color subcarrier in each part of the circuit configuration.

The present invention has been made in order to solve the above problems, and is compatible with an external control voltage for always setting the hue of the color demodulation output regardless of the variation in the circuit characteristics between products. It is an object of the present invention to obtain a color demodulation signal generation circuit capable of producing a color subcarrier for color demodulation.

[0014]

A color demodulation signal generation circuit according to the present invention adjusts a color subcarrier created based on a color burst signal and the phase of the color subcarrier based on an external control voltage. Phase comparison is performed with the obtained color demodulation signal, and phase difference detection means for outputting an error voltage corresponding to the phase difference is provided, and the error voltage is compared with the external control voltage to determine the difference voltage. A voltage comparison means for outputting is provided, and the phase of the color demodulation signal is corrected based on the difference voltage.

[0015]

According to the present invention, the phase comparison is performed between the color subcarrier created based on the color burst signal and the color demodulation signal obtained by adjusting the phase of the color subcarrier based on the external control voltage. , The phase of the color demodulation signal is corrected based on the difference voltage between the error voltage corresponding to the phase difference and the external control voltage. When the phase is deviated from the correct phase corresponding to the control voltage, the phase of the color demodulation signal will be corrected based on the phase error, so that the external control will always be performed regardless of the variation in circuit characteristics between products. A color demodulation signal having a phase corresponding to the voltage can be created.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block configuration diagram for explaining a color demodulation signal generation circuit according to an embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 3 denote the same elements, and 2 is input to a color demodulator. A phase comparator that compares the phase of a specific color subcarrier for color demodulation with a specific one of the color subcarriers generated by the color subcarrier generator 1 and outputs an error voltage corresponding to the phase difference. Reference numeral 4 is a voltage comparator that compares the error voltage with an external control voltage V _cont given to the phase shifter 3 and outputs a difference voltage. Reference numeral 5 is an output signal of the phase shifter 3 according to the difference voltage. The phase shift corrector corrects the phase of a predetermined color demodulation color subcarrier and outputs the phase-corrected color demodulation color subcarrier.

Next, specific circuit configurations of the phase comparator 2, the voltage comparator 4, and the phase shift corrector 5 will be described in detail with reference to FIG.

The phase comparator 2 includes transistors Q _{51 and} Q ₅₂ whose emitters are commonly connected _, a constant current source I _{51 which} is connected between the common emitter and ground, and an emitter connected to the collector of the transistor Q _51. Has a double balance circuit 21 including transistors Q ₅₃ and Q ₅₄ commonly connected to each other, and transistors Q ₅₅ and Q ₅₆ having emitters commonly connected to the collector of the transistor Q ₅₂ . Here, the collectors of the transistors Q ₅₄ and Q ₅₆ are commonly connected,
The common collector is connected to the base and collector of a transistor Q ₅₈ whose emitter is connected to the power supply V _CC through a resistor R ₅₁ , and the transistor Q _53.
And the collectors of Q ₅₅ are also connected in common, and at this connection point,
The base and collector of a transistor Q ₅₇ whose emitter is connected to the power supply V _CC through the resistor R ₅₂ are connected.

[0019] The common base of the transistors Q _53, Q _56, and the common base of the transistors Q _53, Q ₅₆ are turned respectively to the first input terminal of the phase comparator 2, the shift to the input terminal Among the outputs of the phase corrector 5, color demodulation color subcarriers having a phase shift of 180 ° with respect to the phase of the color burst signal are input.
The bases of the transistors Q ₅₁ and Q ₅₂ serve as a second input terminal, and the input terminal has 90 ° with respect to the phase of the color burst signal in the output signal of the color subcarrier generator 1. Alternatively, a color subcarrier locked in a phase shifted by 270 ° is input.

Further, the phase comparator 2 is connected between the power supply and the ground, and the series-connected resistance R ₅₃ , the transistors Q ₅₉ , Q ₆₀ , and the resistance R _56, and the power supply and the ground. Series connected resistors R ₅₄ , transistors Q ₆₁ , Q ₆₄ ,
And a resistor R _57, and the bases of the transistors Q ₅₉ and Q ₆₁ are the transistors Q ₅₇ and Q ₆₁ , respectively.
₅₈ is connected to the base of the base of the transistor Q ₆₀ and Q ₆₄ are commonly connected to the collector of the transistor Q _60. The connection point O of the transistors Q ₆₁ and Q ₆₄ is connected to the bias terminal A via the resistor R ₅₅ ,
Further, transistors Q ₆₃ and Q ₆₂ whose bases are connected to bias terminals T ₅₂ and T ₅₁ , respectively, are connected between the connection point O and the power supply and the ground, and the output voltage of the connection point O The maximum and minimum values can be set. A capacitor C ₅₁ is connected between the connection point O and the ground. The capacitor C ₅₁ is a smoothing capacitor and has a frequency twice that of the chroma signal, for example, about 7.
It is easy to incorporate in an integrated circuit to the extent that the frequency of MHz can be smoothed.

The voltage comparator 4 includes transistors Q ₆₅ and Q ₆₆ having emitters commonly connected, a constant current source I ₅₂ connected between the emitters and the ground, the transistors Q ₆₅ , and The resistors R ₅₉ and R ₅₈ , one end of which is connected to the collector of Q ₆₆ , and the collector is connected to the power supply,
The emitter is composed of a transistor Q ₆₇ connected to the other ends of the resistors R ₅₉ and R ₅₈ . Here, the base of the transistor Q ₆₇ is connected to the bias terminal T _53, and the base of the transistor Q ₆₆ is the phase comparator 2
Is connected to a connection point O which is an output terminal of the. The base of the transistor Q ₆₅ is input external control voltage V _cont, collectors of the respective transistors Q ₆₅ and Q ₆₆ is in the differential output D, C of the circuit.

Further, the phase shift corrector 5 has a pair of transistors Q ₆₈ and Q ₆₉ , Q ₇₀ and Q ₇₁ , Q ₇₂ and Q ₇₃ whose emitters are commonly connected, and a power source V _{CC at} one end. The other end of each of the transistors Q ₆₈ ,
It is composed of a resistor R ₆₀ connected to the collectors of Q ₇₁ and Q ₇₃ . Here, each of the transistors Q ₆₉ , Q ₇₀ , Q
The collector of ₇₂ is connected to the above-mentioned power supply V _CC , and transistors Q _{69 to} Q
The base of ₇₂ is commonly connected to the bias terminal B, and the bases of the transistors Q ₆₈ and Q ₇₃ are connected to the outputs C and D of the voltage comparator 4, respectively. A predetermined one of the four output signals of the phase shifter 3 is appropriately input to the common emitter of the transistors Q ₇₀ and Q ₇₁ ,
The signal of the predetermined phase to the emitter of the transistor Q ₆₈ and Q ₆₉ are the emitter of the transistor Q ₇₂ and Q ₇₃ are signals delayed 90 ° phase with respect to the signal is inputted, the transistors Q _68, Q _A phase-corrected color subcarrier for color demodulation is output from the commonly connected collector (output point O ₅₀ ) of ₇₁ and Q ₇₃ .

Next, the operation will be described. The phase shifter 3
Then, the color subcarriers are received, color subcarriers that are 180 ° and 270 ° out of phase with the color burst phase are created, and these are combined to obtain a color subcarrier with a desired phase. At that time, the phase control is performed by the external control voltage V _cont so that the phase of the obtained color subcarrier becomes a desired one. In the phase comparator 2, the specific color demodulation color subcarrier output to the color demodulator and the color subcarrier obtained from the color subcarrier generator 1 and having a phase shift of 270 ° with respect to the color burst phase are obtained. And are compared in phase, and the phase difference is detected as an error voltage. Further, in the voltage comparator 4, the error voltage corresponding to the phase difference and the external control voltage V applied to the phase shifter 3
Compare with _CONT and output the voltage difference. Then, the phase shift corrector 5 corrects the phase of a predetermined color demodulation color subcarrier of the output signal of the phase shifter 3 based on the difference voltage, and thereby the external control given to the phase shifter 3 is performed. A color subcarrier for color demodulation having a predetermined phase corresponding to the voltage is created and output to the color demodulator.

The above operation will be described below in correspondence with the circuit operations of the phase comparator 2, the voltage comparator 4, and the phase shift corrector 5.

In the phase comparator 2, the double balance circuit 2
1 upper input, that is, the second input terminal, receives the color subcarrier locked at 90 ° or 270 ° with respect to the color burst signal, and the lower input, that is, the first input terminal to the color demodulator. Among the color subcarriers used, those having a phase shift of 180 ° with respect to the color burst signal are received.

When the phase difference between the two input signals is 90 °, no current flows in or out of the resistor R ₅₅ , so that the output point O of the comparator 2 has a bias voltage of the bias terminal A. Appears. Further, when the two input signals approach the same phase, a current flows into the resistor R ₅₅ and the voltage at the output point O rises, and when these input signals approach the opposite phase, the opposite of the above. Then, the voltage at the output point O drops.

The voltage at the output point O is compared with the external control voltage V _CONT given to the phase shifter 3 by the voltage comparator 4, and at the same time, the difference voltage is amplified, and the differential phase shift corrector is provided. Added to 5. The phase shift corrector 5 corrects the phase of a predetermined color demodulation color subcarrier of the output from the phase shifter 3 according to the difference voltage and outputs the corrected color subcarrier to the color demodulator.

For example, the phase difference of the upper input with respect to the lower input of the phase comparator 2 should be 90.degree.
_{When CONT} is applied to the phase shifter 3, a phase shift of the color demodulation color subcarrier of the output of the phase shifter 3 occurs, and the voltage at the output point O of the phase comparator 2 becomes a high value. In this case, the voltage at the output point C of the voltage comparator 4 decreases and the voltage at the output point D increases, whereby the output signal of the phase shift corrector 5 is corrected in the direction in which its phase is delayed.

As described above, in this embodiment, the color subcarrier for color demodulation input to the color demodulator and the color subcarrier generated by the color subcarrier generator 1 are compared in phase, and the phase difference between the two signals is calculated. Is provided with a phase comparator 2 for outputting an error voltage corresponding to, and a voltage comparator 4 for outputting a difference voltage by comparing the error voltage with an external control voltage V _CONT given to the phase shifter 3 is provided. A phase shift corrector 5 for correcting the phase of a predetermined color demodulation color subcarrier of the output signal of the phase shifter 3 by the difference voltage.
Therefore, when the phase of the color subcarrier for color demodulation deviates from the phase corresponding to the external control voltage, the phase shift compensator 5 corrects this, and as a result, the difference between the products can be improved. Irrespective of the variation in the characteristics of
It is possible to always obtain a color demodulation color subcarrier having a phase substantially corresponding to the external control voltage, that is, it is possible to greatly reduce the variation in hue due to the phase shift of the color demodulation color subcarrier between products. is there.

Since the phase comparator 2, the voltage comparator 4 and the phase shift corrector 5 can be realized with a simple circuit configuration, the color demodulation signal generating circuit of this embodiment can be easily integrated into an IC. There is also the effect.

[0031]

As described above, according to the color demodulation signal generating circuit of the present invention, the color subcarrier generated based on the color burst signal and the phase of the color subcarrier are controlled based on the external control voltage. Phase comparison is performed with the color demodulation signal obtained by adjustment, and phase difference detection means for outputting an error voltage corresponding to the phase difference is provided, and the error voltage and the external control voltage are compared. Since the voltage comparison means for outputting the difference voltage is provided and the phase of the color demodulation signal is corrected based on the difference voltage, the phase of the color demodulation signal is external due to the variation in the circuit characteristics between products. If it deviates from the phase corresponding to the control voltage, the phase of the color demodulation signal will be corrected based on the phase error, which allows the external control voltage to be adjusted regardless of variations in circuit characteristics between products. There is an effect capable of creating a response to the phase color demodulation signal.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a color demodulation signal generation circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing a specific circuit configuration of a phase comparator 2, a voltage comparator 4, and a phase shift corrector 5 mounted on the color demodulation signal generation circuit.

FIG. 3 is a block configuration diagram for explaining a conventional color demodulation signal generation circuit.

FIG. 4 is a diagram showing a specific circuit configuration of a phase shifter mounted in the color demodulation signal generation circuit.

[Explanation of symbols]

 1 color subcarrier generator 2 phase comparator 3 phase shifter 4 voltage comparator 5 phase shift corrector 31 first phase shifter 32 first differential amplifier 33 voltage control phase shifter 34 second phase shifter 35 Second Differential Amplifier 36 Amplifier

Claims (1)

[Claims] 1. A color subcarrier generator that receives a color burst and outputs a plurality of color subcarriers synchronized with the color burst, and a predetermined signal of the output is adjusted in phase by an external control voltage. In a color demodulation signal generating circuit including a phase shifter for converting into a plurality of color demodulation signals, a specific color subcarrier other than the predetermined signal among the output signals of the color subcarrier generator, and A phase difference is detected by comparing the phase of a specific signal of the plurality of color demodulation signals with a specific signal and outputting the phase difference as an error voltage, and comparing the error voltage with the external control voltage to determine the difference voltage. A color demodulation signal generation circuit comprising: a voltage comparison unit for generating the voltage; and a phase correction unit provided after the phase shifter for correcting the phase of each of the color demodulation signals based on the difference voltage. .