JPH0846987A - Acc circuit - Google Patents

Abstract

PURPOSE:To reduce S/N and distortion rate and to attain highly-accurate level control by using an analog control loop and a digital control loop jointly. CONSTITUTION:When a decoder 20 signal-processes a carrier chrominance signal (e), based on a level detected by a level detection circuit 14, the analog control loop supplies control data obtained by an ACC module 11 to VCA 12v through D/A converter 15 and the digital control loop supplies the output of a multiplication coefficient circuit 17 to a multiplying circuit 16. Then, the analog and digital control circuits are connected in series through an A/D converter 13. In the circuit constitution like this, The rough control of a color level is executed by the analog control loop and accurate ACC is executed by the digital control loop so that the burden on both control loops are reduced to reduce S/N and the deterioration of the distortion rate and highly-accurate level control is attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ACC circuit suitable for use in a color signal system of a VTR recording / reproducing system.

[0002]

2. Description of the Related Art In a VTR such as an 8 mm VTR,
On the recording side, the luminance signal Y is converted to FM and, for example, a carrier color signal C having a color subcarrier frequency of 3.58 MHz.
Is converted into a carrier color signal CLo having a color subcarrier frequency of 743 kHz, for example, and both are added and recorded on a magnetic tape via a magnetic recording head.

On the reproducing side, the FM luminance signal YFM and the low-frequency conversion carrier color signal CLo are separated from the output signal of the head by a filter and subjected to demodulation processing and frequency conversion processing, respectively. Luminance signal Y and carrier color signal C
Is obtained.

In the VTR, an ACC circuit is provided in front of the frequency conversion circuit on the recording side and the reproducing side in order to make the color density (saturation) of the reproduced image constant.

In this ACC circuit, the amplitude (level) of the color burst signal is detected, the gain of the amplifier is controlled by the detected output, and the level of the carrier color signal C or CLo is made constant.

As a conventional ACC circuit, for a carrier color signal in the state of an analog signal, control by an analog loop for controlling the level of the color burst signal in the carrier color signal to be constant, or carrier color signal In the state where the signal is converted into a digital signal, one of the control by a digital loop is used for controlling the digital carrier color signal so that the level of the color burst signal in the digital signal is constant.

[0007]

However, in the ACC control by the analog loop, there is a problem that the S / N and the distortion rate are easily deteriorated and the variation is large when the gain control range is widened.

Further, in the ACC control by a digital loop, there is a problem that quantization noise increases when a sufficient dynamic range cannot be secured before A / D conversion.

In view of the above point, an object of the present invention is to provide an ACC circuit which solves the above-mentioned problems and has a good S / N and a good distortion factor and which enables highly accurate level control. is there.

[0010]

In order to solve the above-mentioned problems, the ACC circuit according to the present invention has an analog level control means for controlling the level of an analog color signal when the reference numerals of the embodiments to be described later are made to correspond to the analog level control means. An A / D converter for converting the color signal output from the level control means into a digital signal, a digital level control means for controlling the level of the output signal of the A / D converter, and a burst signal in the color signal. Level detection means for detecting a level, a first level control signal supplied to the analog level control means in accordance with the detection output of the level detection means, and a second level control signal supplied to the digital level control means. And a control signal generating means for generating.

[0011]

According to this structure, the analog level control means can first perform a rough ACC and the digital level control means can perform a high-precision ACC, thereby reducing the load on both level control means. , S / N and distortion are prevented from being deteriorated, and highly accurate level control is possible.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a VTR to which an embodiment of a color synchronizing circuit according to the present invention is applied will be described with reference to FIGS.

In FIG. 2, reference numeral 100 denotes a VTR recording system of this example, in which the analog luminance signal Y passes through an A / D converter 111 through a low pass filter (not shown) for band limitation.
Is converted into a digital signal, and the digital luminance signal from the A / D converter 111 is supplied to the signal processing circuit 113.
Is supplied to. The signal processing circuit 113 includes a pre-emphasis processing circuit 114 and an FM modulation processing circuit 115, and an output from the signal processing circuit 113 is converted by a D / A converter 116 into an analog FM luminance signal YFM. The signal is supplied to the adder 117 through a bandpass low-pass filter (not shown).

Further, the carrier color signal C is passed through an A / D converter 121 through a band limiting band pass filter (not shown).
And is converted into a digital signal, and the digital carrier color signal from the A / D converter 121 is supplied to the decoding circuit 1.
22 is supplied. Then, in the decoding circuit 122, a pair of baseband color difference signals R-Y and B-Y.
Are formed and supplied to the signal processing circuit 125.

The output of the signal processing circuit 125 is supplied to the encoding circuit 126, and the output of the low frequency conversion signal generating circuit (not shown) is supplied to the encoding circuit 126.
In the encoding circuit 126, data corresponding to the low frequency conversion carrier color signal CLo is generated. This data is D
In the A / A converter 128, it is converted into an analog low-frequency conversion color signal CLo, is supplied to an adder 117 through a bandpass band-pass filter (not shown), and is supplied to the magnetic head 1 through the recording amplifier 101 together with the FM luminance signal YFM.
02 and recorded on the tape MT.

FIG. 3 is a block diagram of the reproducing system 200 of the VTR of this example. Tape M by magnetic head 201
The signal reproduced from T passes through the reproduction amplifier 202,
High pass filter 211 and band pass filter 22
1, the FM luminance signal YFM is obtained from the high pass filter 211, and the low-pass conversion carrier color signal CLo is obtained from the band pass filter 221.

The FM luminance signal YFM from the high pass filter 211 is supplied to an A / D converter 212 through a band limiting low pass filter (not shown) and converted into a digital signal. The digital FM signal from the A / D converter 212 is supplied.
The luminance signal is supplied to the signal processing circuit 213. The signal processing circuit 213 includes an FM demodulation processing circuit 214 and a de-emphasis processing circuit 215. An output from the signal processing circuit 213 is converted into an analog luminance signal Y by a D / A converter 216. It is supplied to the adder 217 through a bandpass low-pass filter (not shown).

The low-pass conversion carrier color signal CLo from the bandpass filter 221 is supplied to an A / D converter 222 through a bandpass bandpass filter (not shown) and converted into a digital signal. The digital low-frequency conversion carrier color signal from 222 is supplied to the decoding circuit 223, and a pair of baseband color difference signals RY and BY.
Are formed and supplied to the signal processing circuit 224. The output of the signal processing circuit 224 is supplied to the encoding circuit 225, and the encoding circuit 225 generates data corresponding to the carrier color signal C. This data is D /
In the A converter 227, it is converted into an analog carrier color signal C, supplied to an adder 217 through a bandpass band-pass filter (not shown), superposed on the luminance signal Y, and derived.

Note that, as shown in FIG. 3, the luminance signal Y and the carrier color signal C can be independently derived.

[Description of Embodiment of ACC Circuit] Next, referring to FIG.
An embodiment of the ACC circuit according to the present invention will be described with reference to FIG. In the following embodiments, for simplicity of explanation, the band-limiting pre-filter and post-filter provided before and after the A / D converter are omitted.

FIG. 1 shows the configuration of an embodiment of the ACC circuit according to the present invention. In FIG. 1, reference numeral 10 is a microcomputer in which an ACC module 11 is mounted.
The carrier color signal C is supplied to a decoding circuit 20 through a variable gain amplifier (hereinafter referred to as VCA) 12v, an A / D converter 13 and a multiplication circuit 16, and data processing such as frequency band conversion and color demodulation is performed. .

The output signal of the multiplication circuit 16 is also supplied to the level detection circuit 14. Then, the level detection circuit 14 is supplied with a burst gate signal Sbg for gating the period of the color burst signal, and the level detection circuit 14 outputs the level value of the color burst signal being output from the multiplication circuit 16. To be detected. The detection data from the level detection circuit 14 is supplied to the ACC module 11.

The control data obtained by the ACC module 11 is supplied to the VCA 12v through the D / A converter 15 to form an analog control loop and the AC
The control data from the C module 11 is supplied to the variable multiplication coefficient generation circuit 17, and the output of the variable multiplication coefficient generation circuit 17 is supplied to the multiplication circuit 16 to form a digital control loop.

Regarding the level control of the input color signal, the analog control VCA 12v, the digital control multiplication circuit 16 and the variable coefficient circuit 17 are connected in series via the A / D converter 13.

In this embodiment, rough color level control is performed by the analog control loop as described above.
Thus, a dynamic range suitable for A / D conversion can be obtained before A / D conversion. Further, in the VCA 12v, the carrier color signal is amplified within a range where the S / N and the distortion rate can be properly secured.

In the digital control loop, accurate color level control is performed up to a level at which adjustment is unnecessary. Further, the amplification factor lacking in the analog control loop is further increased to obtain the required amplification factor.

In this embodiment, the analog control loop and the digital control loop are used together as described above, and a dynamic range necessary and sufficient for A / D conversion can be secured before A / D conversion. Quantization noise in A / D conversion is reduced. Moreover, even if the total coverage is large, for example, -10 to +20 dB, since the amplification is performed in two stages, the load per stage is reduced, and the S / N and distortion ratio do not deteriorate and the color level is reduced. You can make adjustments.

Further, since the digital control loop controls the level with high precision and absorbs the variation which occurs in the case of only the analog control loop, the adjustment becomes unnecessary.

[Description of Other Embodiments] Although not shown,
By taking the input of the level detection circuit 14 between the A / D converter 13 and the multiplication circuit 16, the digital control can be performed in the feedforward format.

Further, in the above embodiment, the case of the carrier color signal of the color subcarrier frequency has been described.
Similarly, the present invention can be applied.

[0031]

As described above, according to the present invention, since the analog control loop and the digital control loop are used together, highly accurate color level adjustment can be performed. Moreover, since the analog control loop can secure a necessary and sufficient dynamic range for A / D conversion before A / D conversion, quantization noise in A / D conversion is reduced.

The total coverage is, for example,
Even if it is as large as 10 to +20 dB, since the amplification is performed in two stages, the load per stage is reduced, and the color level can be adjusted without deteriorating the S / N and the distortion rate.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of an ACC circuit according to the present invention.

FIG. 2 is a block diagram for explaining an example of a VTR recording system to which the present invention is applied.

FIG. 3 is a block diagram for explaining an example of a VTR reproduction system to which the present invention is applied.

[Explanation of symbols]

 11 ACC module 12v variable gain amplifier 13 A / D converter 14 level detection circuit 15 D / A converter 16 multiplication circuit 17 variable coefficient circuit 100 recording system 200 reproduction system Sbg burst gate signal

Claims (3)

[Claims] 1. An analog level control means for controlling a level of an analog color signal, an A / D converter for converting a color signal output from the level control means into a digital signal, and an output of the A / D converter. A digital level control means for controlling the level of the signal, a level detection means for detecting the level of the burst signal in the color signal, and a first level supplied to the analog level control means according to the detection output of the level detection means. An ACC circuit comprising: a level control signal; and a control signal generation means for generating a second level control signal to be supplied to the digital level control means. 2. An input signal of the level detecting means is an output signal of the digital level controlling means.
The ACC circuit described in 1. 3. The input signal of the level detecting means is the A signal.
The A as claimed in claim 1, which is an output signal of a / D converter.
CC circuit.