JPH06253324A - Acc amplifying circuit - Google Patents

Abstract

PURPOSE:To provide the ACC amplifying circuit which is small in the ratio of a change from an amplifier to an attenuator. CONSTITUTION:This circuit is provided with a 1st ACC amplifying circuit which has a large gain and a narrow dynamic range and a 2nd ACC amplifying circuit 202 which has a small gain and a wide input dynamic range. Further, the circuit is provided with an ACC amplification switching circuit 203 which selects the output of the 1st ACC amplifying circuit 201 in a small input color burst level state and the output of the 2nd ACC amplifying circuit 202 in a large color burst level state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an AC of a color signal reproducing circuit.
It relates to a C amplifier circuit.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram of a conventional general color signal reproducing circuit. The carrier color signal from which the luminance component has been removed from the composite signal by a band pass filter (not shown) is amplified by the carrier color signal amplifier circuit 1. Next, after being amplified by the ACC amplifier circuit 2 in the next stage, the carrier color signal is input to the burst amplifier circuit 3 and the chroma amplifier circuit 4, respectively. The chroma amplifier circuit 4 separates and amplifies only the chroma signal of the carrier color signals, and the RY, B- of the next stage is amplified.
It is input to the Y demodulation and G-Y matrix circuit 9.
The burst amplification circuit 3 extracts and amplifies only the color burst of the carrier color signal. The amplified color burst is input to the ACC detection circuit 5, and this ACC detection circuit 5
Generates an ACC control voltage inversely proportional to the amplitude of the color burst and inputs this to the ACC amplifier circuit 2. This AC
The gain of the ACC amplifier circuit 2 is controlled by the C control voltage,
The outputs of the ACC amplifier circuit 2 and the burst amplifier circuit 3 become constant. The color burst output of the burst amplifier circuit 3 is input to one input terminal of the APC detection circuit 10 and the killer detection circuit 11. Reference subcarrier generation circuit (VC
XO) 6 generates a 3.58 MHz reference subcarrier signal, which is made into a reference subcarrier signal having a proper phase relationship by 90 ° phase amplification and hue control 7.
This reference subcarrier signal is further amplified by 90 ° phase amplification and matrix 8 and input to the other input ends of the APC detection circuit 10 and the killer detection circuit 11, respectively. In the APC detection circuit 10, color burst and 9
0 ° phase amplification and phase detection of the reference subcarrier signal from the matrix 8. By this phase detection output, VCX
The O6 reference subcarrier signal is pulled to the frequency of the color burst of the carrier color signal. The killer detection circuit 11 determines whether to receive a color broadcast or a monochrome broadcast depending on the presence or absence of a color burst. When receiving a monochrome broadcast, the operation of the chroma amplification circuit 4 is stopped. The 90 ° phase amplification and the reference subcarrier signal from the matrix 8 are input to the R-Y, B-Y demodulation and G-Y matrix 8 and phase-detected with the chroma signal from the chroma amplification circuit 4 to obtain the color difference signal R-. Y,
G-Y and B-Y are output.

Considering the ACC control state of the color signal reproducing circuit, the ACC amplifying circuit 2 operates so as to attenuate the signal when the input level is high in order to keep its output constant, and the input level is When low, it operates to amplify the signal. In this way, the amplifier is switched to the attenuator, or vice versa, depending on the magnitude of the color burst level. Therefore, when the input level is high, the function as an attenuator becomes stronger, and the original signal itself is greatly attenuated, which may deteriorate the S / N. In addition, when the weak electric field is input, the carrier color signal contains noise, and this noise is also amplified.

Next, FIG. 5 shows a circuit configuration of a general conventional ACC amplifier circuit 2. The carrier color signals a and -a amplified by the carrier color signal amplifier circuit 1 are input to the bases of the transistors Q ₁₁ and Q ₁₂ of the differential amplifier, respectively. And
Upper double-balanced differential amplifier (transistor Q ₇
To Q ₁₀ ) and amplified and output from the collectors of the transistors Q _{7 and} Q ₁₀ with resistors R _L1 and R _L2 as loads. The emitters of the transistors Q ₁₁ and Q ₁₂ are connected to the collector of the current source transistor Q ₁₃ via resistors R _E1 and R _E2 , and the bases of the transistors Q ₇ and Q _{10 and} the bases of Q ₈ and Q ₉ are connected to each other. , A predetermined bias is applied to each. The bias source transistors Q ₁ through Q ₆
And resistors R _{1 to} R ₈ . From the emitter of the transistor Q ₅ to the bases of the transistors Q ₈ and Q ₉ , and from the emitter of the transistor Q ₆ to the transistors Q ₇ and Q ₁₀₀
A predetermined bias is applied to each of the bases. The maximum gains of the ACC amplifier circuit 2 thus configured are about R _L1 / (R _E1 + R _E2 ) and R _L2 / (R _E1 + R _E2 ), respectively.

The carrier color signals a, -a extracted from the collectors of the transistors Q _{7 and} Q ₁₀ are the capacitors C ₁
DC cut by a circuit including C ₂ , resistors R _{10 and} R ₁₁ , and input to the burst amplifier circuit 3 and the chroma amplifier circuit 4 of the next stage through the transistors Q ₁₆ and Q ₁₇ . The color burst extracted and amplified from the carrier color signal by the burst amplification circuit 3 is transferred to the ACC detection circuit 5
Is detected and smoothed by and converted to direct current. This direct current ACC
The control voltage is supplied to the base of the transistor Q ₂₀ and further applied to the base of the transistor Q ₆ via the resistor R ₆ .

Now, when the carrier color signal level is low, the ACC control voltage, which is the ACC detection output, also rises and the transistor Q
The base potential of ₂₀ becomes high. This allows the transistor Q
The emitter potential of ₆ becomes higher than the emitter potential of the transistor Q ₅ , the base potentials of the transistors Q ₇ and Q ₁₀ of the upper stage double-balanced differential amplifier of the ACC amplifier circuit 2 increase, and the maximum gain (about R _L1 / (R _E1 + R _E2 ), R _L2 / (R
The carrier color signals a and −a of _E1 + R _E2 )) are output from the ACC amplifier circuit 2.

Next, assuming that the level of the carrier color signal has increased, the ACC detection voltage, which is the ACC detection output, decreases and is transmitted to the base of the transistor Q ₂₀ . As a result, the emitter potential of the transistor Q ₆ drops, and when it falls below the emitter potential of the transistor Q ₅ , the base potentials of the transistors Q ₇ and Q ₁₀ of the double-balanced differential amplifier drop. As a result, the ACC amplifier circuit 2 outputs carrier color signals a, -a having a constant amplitude and a small gain.

Further, assuming that the level of the input carrier color signal has increased, the ACC control voltage detected and smoothed by the ACC detection circuit 5 decreases, which causes the transistor Q ₆
The emitter potential of is also lowered. Then, the base potentials of the transistors Q ₇ and Q ₁₀ of the double-balanced differential amplifier are further lowered, and the signal currents of the collectors of the transistors Q ₇ and Q ₁₀ are narrowed down. Thus, the ACC amplifier circuit 2
The output of is changed in gain in inverse proportion to the input color burst level and outputs carrier color signals a and -a having a constant amplitude.

When the input level becomes higher than the normal input color burst level (for example, assuming 100 mvp-p), the ACC amplifier circuit 2 switches from the amplifier to the attenuator, so that the ACC amplitude circuit operates. It becomes less efficient. That is, in order to reduce the size of the original signal itself, ACC
The drive current of the transistors Q ₇ and Q ₁₀ forming the amplifier circuit 2 becomes a minute current, and there is a possibility that noise will increase.

Further, since the input dynamic range of the ACC amplifier circuit 2 is constant, in a weak electric field input state (equivalent to noise and equivalent to a large input carrier color signal state), noise is amplified and the input dynamic range is increased. It is easy for the range to be exceeded, and noise may occur in the chroma signal part, which may change the appearance.

[0011]

As described above, in the conventional ACC amplifier circuit, when the input level is large, the ratio of conversion from the amplifier to the attenuator is large, the level of the signal itself is narrowed, and the S / N ratio of the transistor is reduced. May get worse. Further, in a weak electric field input state, noise may be amplified, input dynamic range collapse of the ACC amplifier circuit may occur, the appearance may be changed, and the flatness of the ACC amplifier circuit characteristic may be deteriorated.

Therefore, according to the present invention, the ratio of the change from the amplifier to the attenuator in accordance with the color burst level of the carrier color signal is reduced, and the S / N ratio of the constituent transistors is made efficient. ACC with improved flatness by suppressing collapse of input dynamic range
An object is to provide an amplifier circuit.

[0013]

An input terminal to which a color information signal including a color burst and a chroma signal is supplied as an input signal, and a gain control terminal to which a control voltage that changes according to the amplitude of the color burst is supplied. An ACC amplifier circuit having an output terminal for obtaining an output signal, having a first gain and a first input dynamic range, and controlling an input signal supplied to the input terminal to a gain control terminal. A first ACC amplifier circuit that performs an amplification process according to a voltage, a second gain that is smaller than the first gain, and a second input dynamic range that is wider than the first input dynamic range. A second ACC amplifier circuit for amplifying an input signal supplied to the terminal according to the control voltage supplied to the gain control terminal; When the level of the color burst is below a predetermined value, the signal amplified by the first ACC amplifier circuit is selectively output, and when the level of the color burst exceeds a predetermined value, the signal is sent to the second ACC amplifier circuit. Switching means for selectively outputting the amplified and amplified signal and supplying it to the output terminal.

[0014]

In the small input color burst level state, the first ACC amplifier circuit operates, and in the large input color burst level state, the second ACC amplifier circuit operates so that the amplifier of the entire ACC amplifier circuit can operate. Since the ratio to the attenuator can be reduced unlike the conventional one, the S / N of the entire ACC amplifier circuit is less likely to deteriorate. Since the signal current of the transistor forming the ACC amplifier circuit does not need to be narrowed as compared with the conventional case, the S / N of the transistor is improved. Further, in the weak electric field large input color burst state, since the amplification is controlled by the second amplifier circuit having a small gain, the flatness is improved and the collapse of the input dynamic range can be reduced. Further, the grain of screen noise is unlikely to be large.

[0015]

1 is a block diagram of a color signal reproduction circuit using an ACC amplifier circuit of the present invention. The carrier color signal from which the luminance component has been removed from the composite signal is amplified by the carrier color signal amplifier circuit 101 by a band pass filter (not shown). Next, it is supplied to the ACC amplifier circuit 200 of the next stage, and the first ACC amplifier circuit 201 or the second ACC is supplied.
One of the carrier color signals amplified by the amplifier circuit 202 is a burst amplifier circuit 103 and a chroma amplifier circuit 104.
Be transmitted to. Here, the first ACC amplifier circuit 201
Has a large gain and a narrow input dynamic range, and the second ACC amplifier circuit 202 has a small gain and a wide input dynamic range. Then, in the state of the small input color burst level, the ACC amplification switching circuit 203 of the next stage causes the first ACC amplification circuit 2 to operate.
When the output of 01 is selected and the input color burst level is large, the output of the second ACC amplifier circuit 202 having a small gain is selected.

The chroma amplifying circuit 104 separates and amplifies only the chroma signal of the carrier color signals, and the RY, B in the next stage.
-Y demodulation and input to the G-Y matrix 109. The burst amplification circuit 103 extracts and amplifies only the color burst of the carrier color signal, and the ACC detection circuit 10
Tell 5. This ACC detection circuit 105 generates an ACC control voltage inversely proportional to the amplitude of the color burst,
The CC amplifier circuit 200 is controlled. This ACC control voltage is applied to the first and second ACC amplifier circuits 201 and 20 respectively.
2 and the ACC amplification switching circuit 203,
Controlling the gain of the second ACC amplifier circuits 201 and 202,
The output of either the first ACC amplifier circuit 201 or the second amplifier circuit 202 is switched and output depending on the magnitude of the ACC control voltage.

The ACC-controlled color burst output is the ACC detection circuit 110 and the killer detection circuit 111.
Entered in. Reference subcarrier generation circuit (VCXO) 10
6 generates a 3.58 MHz reference subcarrier signal, which is converted into a reference subcarrier signal having a proper phase relationship by 90 ° phase amplification and hue control 107. This reference subcarrier signal is further amplified by 90 ° phase amplification and matrix 108 and input to the other ends of the APC detection circuit 110 and the killer detection circuit 111, respectively. AP
The C detection circuit 110 phase-detects the color burst, 90 ° phase amplification, and the reference subcarrier signal from the matrix 108. By this phase detection output, the VCXO10
The 6 reference subcarrier signal is pulled to the frequency of the color burst of the carrier chrominance signal. The killer detection circuit 111 determines whether to receive a color broadcast or to receive a monochrome broadcast depending on the presence or absence of a color burst. When receiving a monochrome broadcast, the operation of the chroma amplification circuit 104 is stopped. The 90 ° phase amplification as well as the reference subcarrier signals from the matrix 108 are RY, B-
It is input to the Y demodulation and G-Y matrix 108, and phase detection is performed with the chroma signal from the chroma amplification circuit 104,
Color difference signals R-Y, G-Y, and B-Y are output.

Considering the ACC control state of the color signal reproducing circuit described above, for example, when the color burst level of the carrier color signal is low, the first ACC amplifier circuit 201 corresponds and when the color burst level becomes high. Is the second AC
The ACC increase switching circuit 203 performs switching so that the C amplifier circuit 202 responds. Compared with the conventional ACC amplifier circuit,
In the first ACC amplifier circuit 201, the rate of change from the amplifier to the attenuator becomes small, and the S of the ACC amplifier circuit 200 as a whole is reduced.
/ N is less likely to deteriorate. Further, since the signal current of the transistor forming the ACC amplifier circuit 200 is shallow, the S / N ratio of the transistor is improved. Further, in the weak electric field large input state, the carrier color signal becomes S + N and the amplitude becomes large, but since the second ACC amplifying circuit 202 is switched so as to correspond, the input dynamic range of the ACC amplifying circuit 200 as a whole is widened and the screen The feeling of painting is difficult to change.

Next, FIGS. 2 and 3 show the circuit configuration of the ACC amplifier circuit 200 of the present invention. Although divided into FIGS. 2 and 3 due to the restriction of the drawing size, the terminals (A) to (I) of FIG. 2 are connected corresponding to the terminals (A) to (I) of FIG. 3, respectively. Has been done.

The carrier color signals a and -a amplified by the carrier color signal amplifier circuit 101 are applied to the bases of the transistors Q ₁₉ and Q ₂₀ of the differential amplifier in the first ACC amplifier circuit 201 and the second ACC amplifier. The signals are input to the bases of the transistors Q ₃₁ and Q ₃₂ of the differential amplifier in the circuit 202, respectively. Furthermore, the first and second ACC amplifier circuits 20
Reference numerals 1 and 202 have upper double-balanced differential amplifiers (transistors Q _{11 to} Q ₁₄ and transistors Q _{23 to} Q ₂₆ ), respectively, and the amplified signals are output with the resistors R _L1 and R _L2 as loads. Further, the difference between the upper double-balanced differential amplifier (transistors Q _{11 to} Q ₁₄ ) and the differential amplifier transistor (Q ₁₉ , Q ₂₀ ) and the upper double-balanced differential amplifier (Q _{23 to} Q ₂₆ ). The intermediate stage double-balanced differential amplifiers (transistors Q _{15 to} Q ₁₈ and Q ₂₇ ) are respectively connected to the dynamic amplifier transistors (Q ₃₁ , Q ₃₂ ).
To Q ₃₀ ) are arranged. Transistors Q ₁₉ , Q ₂₀
Each emitter of is connected to the collector of current source transistor Q ₂₁ via the resistor R _E1, R _E2, transistors Q _31,
Each emitter of Q ₃₂ is connected to the collector of the current source transistor Q ₃₃ via resistors R _E3 and R _E4 . A predetermined bias is applied to the bases of the transistors Q ₂₇ and Q _{30 and} the bases of Q ₂₈ and Q ₂₉ , respectively. Similarly predetermined bias to the base of the base and Q _16, Q ₁₇ of the transistor Q _15, Q ₁₈ are added. These bias source is composed of transistors Q ₁ to Q ₁₀ and resistors R ₁ to R _14, the base of the transistor Q _28, Q ₂₉ from the emitter of the transistor Q _5, also the transistor Q _27, Q ₃₀ from the emitter of the transistor Q ₆ A predetermined bias is applied to the base of. A predetermined bias is applied from the emitter of the transistor Q ₉ to the bases of the transistors Q ₁₆ and Q ₁₇ , and from the emitter of the transistor Q ₁₀ to the bases of the transistors Q ₁₅ and Q ₁₈ . The maximum gain of the first ACC amplifier circuit 201 configured in this way is about R _L1 /
(R _E1 + R _E2 ), R _L2 / (R _E1 + R _E2 ). The maximum gain of the second ACC amplifier circuit 202 is about R _L1 / (R _E3 +
R _E4 ), R _L2 / (R _E3 + R _E4 ).

The carrier chrominance signals a, -a taken from the collectors of the transistors Q ₁₁ and Q _{23 and} the collectors of the transistors Q ₁₄ and Q ₂₆ are supplied by a circuit including capacitors C _{1 and} C ₂ , resistors R _{17 and} R _18. The direct current is cut, and is input to the burst amplification circuit 103 and the chroma amplification circuit 104 at the next stage via the transistors Q ₃₆ and Q ₃₇ . The color burst extracted and amplified by the burst amplification circuit 103 is detected and smoothed by the ACC detection circuit 105 and converted into a direct current to become an ACC control voltage. This ACC control voltage is a voltage that is inversely proportional to the amplitude of the color burst.
The ACC control voltage is applied to the base of the transistor Q ₆ via the transistor Q ₅₀ and the resistor R ₆ . Further, this ACC control voltage is applied to the base of the transistor Q ₁₀ via the transistor Q ₄₉ and the resistor R ₁₂ .

On the other hand, the ACC amplification switching circuit 203 is composed of transistors Q _{40 to} Q ₄₈ , has differential amplifier transistors Q ₄₅ and Q ₄₆ , a constant current source transistor Q ₄₇ , and further has a collector / base of the transistor Q _45. It has current mirror transistors Q ₄₀ and Q ₄₁ coupled between them, and current mirror transistors Q ₄₂ and Q ₄₃ coupled between the collector and base of the transistor Q ₄₆ . Further, it has a transistor Q ₄₄ that forms a current mirror together with the transistor Q ₄₂ and an output transistor Q ₄₈ , and the collector of this Q ₄₈ is the first and second ACC amplifier circuits 201 and 202.
Are connected to the bases of the transistors Q ₁₂ and Q _{13 and} the bases of the transistors Q ₂₃ and Q ₂₆ . Further, the bases of transistors Q ₄₅ and Q ₄₆ are coupled to the emitters of transistors Q ₅ and Q ₆ , respectively.

Next, the operation of the circuit shown in FIGS. 2 and 3 will be described. First, when the carrier color signal level is low,
The ACC control voltage detected and smoothed by the ACC detection circuit 105 becomes high, which increases the base potentials of the transistors Q ₅₀ and Q ₄₉ . Then, the emitter potentials of the transistors Q _{6 and} Q ₁₀ become higher than the emitter potentials of the transistors Q _{5 and} Q ₉ . Therefore, the first and second A
Middle double balance type differential amplifier of the transistors Q ₁₅ and Q ₁₈ of CC amplifying circuit 201 and 202, and the base potential of the transistor Q ₂₇ and Q ₃₀ is increased ACC maximum sensitivity direction. Further, the potential of the transistor Q ₄₆ of the ACC amplification switching circuit 203 rises due to the rise of the emitter potential of the transistor Q ₆ . Then, the collector current of the current mirror transistor Q ₄₃ increases, and the base voltage of the transistor Q ₄₆ rises. Further, the collector current of the transistor Q ₄₄ also increases and flows through the resistor R ₂₉ , so that the transistor Q ₄₈ is saturated. Due to the saturation of the transistor Q ₄₈ , the first and second ACC amplifier circuits 201 and 202
Upper double-balanced differential amplifier transistor Q ₁₂
And Q ₁₃ and the base potentials of the transistors Q ₂₃ and Q ₂₆ are lowered, and the carrier color signals a and −a having the maximum gain are output from the collectors of the transistors Q _{11 and} Q ₁₄ of the first ACC amplifier circuit 201. This maximum gain is approximately R _L1 / (R _E1 + R _E2 ) and R _L2 / (R _E1 + R _E2 ) as described above. On the other hand, no output is obtained at the collectors of the transistors Q ₂₃ and Q ₂₆ of the second ACC amplifier circuit 202, and the first
The signal amplified by the ACC amplifier circuit 201 is output.

In the next state, for example, when the level of the input carrier color signal becomes high, the ACC control voltage detected and smoothed by the ACC detection circuit 105 is lowered and the transistor Q ₅₀
And the base potential of Q ₄₉ drops. Then, the emitter potentials of the transistors Q _{6 and} Q ₁₀ fall below the emitter potentials of the transistors Q _{5 and} Q ₉ . Thus, the transistors Q ₁₅ and Q ₁₈ of the middle double balance type differential amplifier of the first and second ACC amplifier circuit 201 and 202, and the base potential of the transistor Q ₂₇ and Q ₃₀ are slide into lowered. Further, the emitter potential of the transistor Q ₆ is ACC.
Although it is transmitted to the base of the transistor Q ₄₆ of the amplification switching circuit 203, the base potential of the transistor Q ₄₆ is unlikely to drop due to the potential difference (hysteresis) of the resistor R ₂₇ due to the collector current of the transistor Q ₄₃ of the current mirror. If the difference in the emitter potentials of the transistors Q ₅ and Q ₆ is small, the base of the transistor Q ₄₆ of the ACC amplification switching circuit is higher than the base of the transistor Q ₄₅ , so that the current mirror (transistors Q _{42 to} Q ₄₄ ) still operates. . Then, due to the collector current of the transistor Q ₄₄ and the resistance R ₂₉ , the transistor Q ₄₈ continues the saturated operation, and the first A still remains.
From the CC amplifier circuit 201, the carrier color signals a,-
a is output.

Next, when the level of the input carrier color signal further increases, the ACC control voltage detected and smoothed by the ACC detection circuit 105 further decreases, which further decreases the base potentials of the transistors Q ₅₀ and Q ₄₉ . Then, the emitter potential of the transistor Q ₆ and Q _{1 0} further falls below the emitter potential of the transistor Q ₅ and Q _9. Further, the first and second ACC amplifier circuits 201 and 2
The base potentials of the transistors Q ₁₅ and Q ₁₈ , and the transistors Q ₂₇ and Q ₃₀ of the middle-stage double-balanced differential amplifier 02 are further lowered. Also, the transistor Q ₆
Is lowered to the emitter potential of the transistor Q ₅ , and is transmitted to the base of the transistor Q ₄₆ of the ACC amplification switching circuit 203 of the next stage. As a result, when the base potential of the transistor Q ₄₆ becomes lower than the base potential of Q ₄₅ , the transistor Q ₄₅ is turned on, the collector current of the current mirror transistor Q ₄₀ flows, the base potential of the transistor Q ₄₅ further rises, and the current mirror transistor (Q _{42 to} Q ₄₄ ) do not work. Thus transistors Q ₁₂ and Q ₁₃ of the upper double-balanced differential amplifier of the first and second ACC amplifier circuit 201, and the base potential of the transistor Q ₂₃ and Q ₂₆ is increased.
As a result, the transistors Q ₁₁ and Q ₁₄ are turned off and Q ₂₃ and Q ₁₄ are turned off.
₂₆ signal amplified by the second ACC amplifier circuit 202 becomes turned on, the carrier chrominance signal a constant from the collector of the transistor Q ₂₃ and Q ₂₆ amplitude is output as -a. Further, since the second ACC amplifier circuit 202 is operated at this time, the ACC control voltage detected and smoothed by the ACC detector circuit 105 is slightly lower than that of the first ACC amplifier circuit, but the ACC amplifier switching circuit 203 Since it has hysteresis, it is fixed by the operation of the second ACC amplifier circuit 202.

As described above, depending on the magnitude of the input level of the carrier color signal, the first or second ACC amplifier circuit 20.
Since any one of 1 and 202 is selected, the ratio of changing from the amplifier of the first ACC amplifier circuit 201 to the attenuator can be made small when the input level is small, unlike the conventional case, and S / of the first ACC amplifier circuit 201 can be reduced. N is less likely to deteriorate. Further, since the signal current of the transistor forming the first ACC amplifier circuit 201 does not need to be narrowed as compared with the conventional case, the S / N of the transistor is improved. Further, in the input color burst state with a large weak electric field, since the amplification is controlled by the second ACC amplifier circuit 202 having a small gain, the flatness is improved and the collapse of the input dynamic range can be reduced. Further, the grain of screen noise is unlikely to be large.

[0027]

As described above, in the ACC amplifier circuit of the present invention, the ratio of change from the amplifier to the attenuator is small. Then, the S / N ratio of the transistors forming the ACC amplifier circuit is improved. Further, even in a weak electric field large input color burst state, the flatness is improved, the width of the screen noise due to the large input dynamic range expansion is narrowed, and the change in the image quality is less noticeable.

[Brief description of drawings]

FIG. 1 is a block diagram of a color signal reproducing circuit using an ACC amplifier circuit of the present invention.

FIG. 2 is a circuit configuration diagram of the left half of the ACC amplifier circuit of the present invention.

FIG. 3 is a circuit configuration diagram of the right half of the ACC amplifier circuit of the present invention.

FIG. 4 is a block diagram of a conventional general color signal reproducing circuit.

FIG. 5 is a circuit configuration diagram of a conventional ACC amplifier circuit.

[Explanation of symbols]

101 ... Carrier signal amplification circuit, 103 ... Burst amplification circuit, 104 ... Chroma amplification circuit, 105 ... ACC detection circuit, 106 ... VCXO (reference subcarrier generation circuit), 1
07 ... 90 ° phase and hue control, 108 ... 90 ° phase amplification and matrix, 109 ... RY, BY demodulation and GY matrix, 200 ... ACC amplification circuit,
201 ... First ACC amplifier circuit, 202 ... Second ACC
Amplifier circuit 203 ... ACC amplifier switching circuit.

Claims (1)

[Claims] 1. An input terminal to which a color information signal including a color burst and a chroma signal is supplied as an input signal, a gain control terminal to which a control voltage that changes according to the amplitude of the color burst is supplied, and an output signal are obtained. An ACC amplifier circuit having an output terminal, which has a first gain and a first input dynamic range and outputs an input signal supplied to the input terminal according to a control voltage supplied to the gain control terminal. First amplification processing
Of the ACC amplifier circuit, a second gain smaller than the first gain, and a second input dynamic range wider than the first input dynamic range, the input signal supplied to the input terminal, A second ACC amplifier circuit that performs an amplification process according to the control voltage supplied to the gain control terminal; and a first ACC circuit that responds to the magnitude of the control voltage and the level of the color burst is equal to or less than a predetermined value. The signal amplified by the amplifier circuit is selectively output, and when the level of the color burst exceeds a predetermined value, the second AC
An ACC amplifier circuit comprising: switching means for selectively outputting a signal amplified by a C amplifier circuit and supplying the signal to the output terminal.