JPH0378835B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a semiconductor integration (hereinafter abbreviated as IC) technology for a video signal processing circuit in a color video camera.

Conventional configurations and their problems In a color video camera using a solid-state image sensor, there are various ways to obtain color signals, depending on the colorization method determined by the combination of color filters and the signal processing method. However, here we will explain a circuit that uses synchronous detection to separate a color signal from a signal obtained by a combination of a color filter and an image sensor as shown in FIG.

Figure 1 shows a configuration in which a red transmission filter R, a green transmission filter G, and a blue transmission filter B are sequentially arranged in the horizontal direction on an image sensor to obtain continuous R, G, and B signals from the image sensor. . The output signal from this image sensor can be obtained as a signal in which the R, G, and B signals are repeated only for the pixels in the horizontal direction of the image sensor, as shown in Figure 2B, and the signal sequence at that time is The spectral distribution is as shown in FIG. frequency is the horizontal clock frequency,
R, G, and B color carriers occur near 1/3 of the frequency. Further, the phases of the color carriers at this time have a phase difference of 2/3π for each of R, G, and B, as shown in FIG. FIG. 3 shows an example of a signal processing circuit for a color video camera using the image sensor shown in FIG.

In Fig. 3, 1 is an image sensor, 2 is a gamma correction and AGC circuit, 3 is a low-pass filter (hereinafter abbreviated as L, P, and F), and 4 is a band-pass filter (hereinafter abbreviated as B, P, and F). , 5 is a synchronous detection circuit, 6 is a phase shift circuit, 7 is an encoder, 8 is a synchronous signal generator, 9
Reference numeral 10 indicates a drive pulse generator for the image sensor, and 10 indicates an NTSC multiple signal output terminal. A brief explanation of the operation is as follows. The signal output from the image sensor is first subjected to gamma correction, and then
By passing the signal through the AGC circuit 2, the amplitude of the input signal to the next stage circuit is stabilized. The luminance signal is
The color signal is created by separating the low frequency component of the signal output from the image sensor using LPF3.
After separating the color carriers by BPF4,
The synchronous detection circuit 5 generates two color difference signals R-(G+B)2 and {3/2(B-G)}.

A luminance signal and two color difference signals are processed by an encoder, a color burst signal and a synchronization signal are added, and an NTSC composite signal is output. In a signal processing circuit with such a configuration, it is most convenient for operation to generate a signal synchronized with the horizontal clock pulse of the image sensor by a drive pulse generator and use it as the reference carrier signal of the synchronous detection circuit. Yes, it becomes stable. However, as is clear from Figure 3, the reference carrier wave is directly input from the pulse generator to the synchronous detection circuit, while the modulated color signal is input to the detection circuit after passing through the gamma correction circuit and AGC circuit. Become. Therefore, if the phase characteristics of the circuit are flat, there will be no problem, but if the phase characteristics are not flat near the carrier frequency of the color signal, the detection characteristics of the synchronous detection circuit will deteriorate due to changes in circuit operating conditions such as temperature fluctuations. Become. In other words, in the example shown in Figure 3, the absolute phase of the modulated color signal input to the synchronous detection circuit fluctuates, but the phase of the reference carrier wave does not fluctuate, or the amount of fluctuation is extremely small, so the relative phase between the two signals varies. A phase difference will occur, resulting in a detection output error.
Fluctuations in phase characteristics in such a circuit system are generally caused by the phase characteristics of the circuit determined by the cut-off frequency of the transistor. When converting the block shown in Figure 3 into an IC to make the circuit smaller and more dense, the problem is the detection error in the synchronous detection circuit caused by the above-mentioned fluctuation in the phase characteristics of the circuit. . In other words, the characteristics of IC-converted transistors are generally worse than those of separately manufactured transistors, and for PNP transistors, the difference is significant, making it necessary to improve the phase characteristics of IC-converted circuits. It becomes very difficult to flatten the frequency band. For this reason, a signal processing circuit implemented as an IC has the disadvantage that the relative phase relationship between two signals changes due to temperature changes.
Such characteristics of the signal processing circuit, when used as a color video camera, cause the hue of the output image to change, resulting in a significant deterioration in color reproducibility.

Purpose of the Invention The present invention solves the above-mentioned conventional problems.
The present invention aims to provide a signal processing circuit for a color video camera that has good temperature characteristics even when integrated into an IC by detecting phase fluctuations in the processing circuit using a pilot signal.

Structure of the Invention The present invention provides a gate circuit that generates a pilot signal synchronized with the clock frequency of an image sensor within a vertical blanking period of an image sensor output signal and within a period corresponding to a horizontal effective scanning period. , an addition circuit that adds the pilot signal output from the gate circuit to the image sensor output signal; a bandpass filter that separates the modulated color signal including the pilot signal; and a bandpass filter that detects the output signal of the bandpass filter to determine the color. a synchronous detection circuit that demodulates the signal and a pilot signal; a phase detection circuit that detects phase fluctuations in the pilot signal included in the output signal of the synchronous detection circuit as a phase error output signal; and a phase error output signal of the phase detection circuit. A phase adjustment circuit that controls the phase of the color subcarrier applied to the modulation circuit accordingly, or a burst phase control circuit that controls the phase of the color burst signal according to the phase error output signal of the phase detection circuit. , it is possible to prevent deterioration of color reproducibility caused by phase characteristic fluctuations in the signal processing circuit.

DESCRIPTION OF EMBODIMENTS FIG. 4 shows a first embodiment of a signal processing device according to the present invention. In FIG. 4, 11 is an image sensor;
12 is an adder circuit, 13 is a gate circuit, 14 is a gamma correction and AGC circuit, 15 is an LPF, 16 is a BPF,
17 and 18 are synchronous detection circuits, 19 is a phase control circuit, 20 is a 90 degree phase shift circuit, 21 is a phase detection circuit,
22 and 23 are LPF, 24 is a horizontal aperture compensation circuit, 25 is an addition circuit, 26 is a pedestal adjustment circuit, 27 and 28 are modulation circuits, 29 is a 90 degree phase shift circuit, 30 is a drive pulse generator, and 31 is a synchronization signal The generator 32 is an NTSC output terminal.

The operation of this embodiment configured as above will be described below.

The color image sensor has the same configuration as the conventional example shown in FIG. 1, and its output signal is as shown in FIG. 2.

A pilot signal generated by a gate circuit 13 is added to the output signal of this image sensor by an adder circuit 12. This pilot signal is as shown in FIG. Pilot signal frequency p
has the same frequency as the carrier wave (1/3 of the horizontal clock frequency) of the multiplexed color signal output from the image sensor, and the continuous wave as shown in A is gated by gate pulse B and converted to C. Create a pilot signal as shown. Gate pulse B uses a pulse width corresponding to the vertical blanking period or a pulse shorter than that so as not to affect the video signal.The period of the pilot signal is represented by a horizontal sheet as shown in the figure. d, and no pilot signal is generated in the portion corresponding to the horizontal blanking period. The reason for this, which will be explained later, is that the phase detection circuit uses the horizontal blanking period to detect the phase reference signal.

The pilot signal obtained by adding the output signals of the image sensor is subjected to predetermined processing by 14 gamma correction and AGC circuits, and then separated along with the modulated color signal multiplexed by 16 BPFs, and is divided into two synchronized signals. Input to the detection circuit. These two synchronous detection circuits convert the NTS carrier color signal into two color difference signals at right angles.
Since it can be created by phase modulation, it is used to separate three color signals multiplexed in an image sensor to create two color difference signals. A reference carrier wave used for synchronous detection is generated by a synchronous signal generator 31, and is synchronized with the horizontal clock pulse of the image sensor. The reference carrier wave outputted from the synchronous signal generator is used by a 90 degree phase shift circuit 20 to generate two signals having a phase difference of 90 degrees, and these signals are input to synchronous detection circuits 17 and 18, respectively. For example, suppose that the phase of the reference carrier wave is detected such that the phase input to the detection circuit 17 is the same as that of the multiplexed modulated color signal R, and the phase input to the detection circuit 18 is delayed by 90 degrees from the phase. For example, the output of the detection circuit 17 is R-(G+B)/2, and the output of the detection circuit 18 is √3/2(B-G). However, since the output of the detection circuit contains high frequency components, only the low frequency components are extracted by the LPFs 22 and 23 to obtain the two signals. On the other hand, the luminance signal is
It is created by extracting the DC component of the image sensor output using the LPF 15.

The output signal of the synchronous detection circuit 18 is also input to the phase detection circuit 21. As shown in Figure 6, when the detection output of the synchronous detection circuit is detected using the reference carrier wave A, the detection output of the synchronous detection circuit is as shown in the figure. To,
The detection output level has a characteristic that even if there is a slight phase change, the detection output level fluctuates greatly. The phase of the pilot signal is determined by using the above-mentioned characteristics of the synchronous detection circuit, such that at a certain temperature the output level of the synchronous detection circuit 18 becomes zero (that is, it has a phase difference of 90 degrees from the reference carrier wave). If the phase of the pilot signal changes due to temperature fluctuation, the detection output level will accurately detect the amount and direction of the phase change depending on whether it is positive or negative relative to the zero level. I can do things. The example of the phase detection circuit shown in 21 is shown in
As shown in the figure. The sample and hold circuit 37 detects the potential during the pilot signal period (vertical blanking period) in the output color difference signal from the synchronous detection circuit, and samples the horizontal blanking period potential in which neither the color signal nor the pilot signal exists as the reference potential. A control voltage corresponding to the phase error is obtained by detecting the voltage by the hold 36 and comparing and amplifying these two potentials by the comparator 34. Using this control voltage, the subcarrier phase control circuit 19 controls the phase of the subcarrier input to the modulation circuits 27 and 28, thereby compensating the detection phase fluctuation in the synchronous detection circuit in the modulation circuit. . In other words, when a color signal having the same phase and amplitude a as the reference carrier wave CW1 input to the synchronous detection circuit 17 as shown in FIG. 9A changes its phase by θ as shown in FIG. 9C due to temperature fluctuations. The explanation is as follows. The output level b of the synchronous detection circuit 17 detected by the reference carrier wave CW1 is b=a′・cosθ, and CW1 and 90
The output level c of the synchronous detection circuit 18 detected by the reference carrier wave CW2 having a phase difference of 1° is c=a′cos
(90−θ). In this way, the two color difference signals output from the two synchronous detection circuits are transmitted to the modulation circuit 27,
28, the subcarrier is modulated by the subcarrier and converted into a carrier color signal.The phase of the subcarrier input to these two modulation circuits is determined by the phase of the subcarrier in the synchronous detection circuit, as shown in Figure d. By changing the phase variation amount θ of the signal, the vector of the carrier color signal modulated by the subcarriers SC1 and SC2 can be corrected to be the same as the vector before the phase variation shown in FIG. In d of the same figure, a can be expressed as a=b/cosθ or a=c/cos(90-θ), and by substituting the aforementioned detection outputs for b and c, a=a'・cosθ/cosθ or a=a′・cos(90−θ)
/cos(90-θ), and since a=a' holds true, the phase fluctuation θ in the detection circuit is corrected by the phase of the color subcarrier in the modulation circuit.

The color subcarrier phase adjustment circuit 19 adds the two subcarriers output from the synchronization signal generator 31 and have a phase difference of 90 degrees as shown in FIG. 7, and adjusts the addition level and polarity. The phase is changed by adjusting the control voltage from the phase detection circuit. By inputting the subcarrier whose phase has been adjusted in this way and the subcarrier whose phase difference has been made 90 degrees again by the 90 degree phase shift circuit 26 to the modulation circuits 27 and 28, the two color difference signals are quadrature two-phase modulated and the carrier wave is It is converted into a color signal. Horizontal aperture compensation circuit 2
The luminance signal and the carrier color signal that have been aperture corrected in step 4 are added by an adder circuit 25, and then the synchronization signal and the burst signal are added by an adder circuit 26 to adjust the pedestal level and output from the output terminal 32.
Sending out NTSC composite signal.

As described above, according to this embodiment, the pilot signal for phase detection is added to the output signal of the image sensor,
By using the phase change of this pilot signal, the detection error caused by the phase fluctuation in the synchronous detection circuit is equivalently detected, and this detection signal is used to control the phase of the color subcarrier, so that the signal processing circuit It is possible to easily correct fluctuations in the phase characteristics of the image and obtain a stable color reproduction image.

FIG. 10 shows an example in which 33 burst signal phase control circuits are provided in place of the color subcarrier phase control circuit in the first embodiment of the signal processing circuit of the present invention. The operation is explained as follows. The amount of phase fluctuation of the pilot signal is converted into a control voltage by the phase detection circuit 21, and this control voltage controls the burst phase control circuit to change the burst phase by the amount of phase fluctuation θ in the synchronous detection circuit. I'm letting you do it.

Effects of the Invention The signal processing device for a color video camera of the present invention adds a pilot signal to the output signal of an image sensor, detects the amount of phase change of this pilot signal,
The phase of the color subcarrier or color burst signal is controlled according to this detection signal, and when a synchronous detection circuit is used for color separation, it is possible to correct the deterioration in color reproduction caused by fluctuations in the phase characteristics of the circuit. , its practical effects are great.

[Brief explanation of drawings]

Figure 1 is an example of a colorized image sensor, Figure 2 is a diagram for explaining the output signal of the image sensor, and Figure 3 is a diagram for explaining the output signal of the image sensor.
Figure 4 is a block diagram of a conventional signal processing device, Figure 4 is a block diagram of a signal processing device for a color video camera according to an embodiment of the present invention, Figure 5 is a pilot signal waveform diagram, and Figure 6 is a diagram of a synchronous detection circuit. Output characteristic diagram, Figure 7 is a vector diagram showing an example of phase change in the phase control circuit, Figure 8 is a block diagram of the phase detection circuit, and Figure 9 is a vector diagram of an example of correction in the phase compensated signal processing circuit according to the present invention. 10 are block diagrams of other embodiments of the signal processing circuit according to the present invention. 11...Image sensor, 12...Addition circuit, 14...
...Gamma correction AGC circuit, 15, 22, 23...
LPF, 16... BPF, 17, 18... Synchronous detection circuit, 27, 28... Modulation circuit, 24... Horizontal aperture compensation circuit, 25... Addition circuit, 26...
Addition, pedestal adjustment circuit, 30... Drive pulse generator, 31... Synchronization signal generator, 13... Gate circuit, 19... Phase detection circuit, 19... Phase adjustment circuit, 20, 26... 90° shift phase circuit.

Claims (1)

[Scope of Claims] 1. A gate circuit that generates a pilot signal synchronized with the clock frequency of an image sensor within a vertical blanking period of an image sensor output signal and within a period corresponding to a horizontal effective scanning period; an addition circuit that adds a pilot signal output from the gate circuit to the image sensor output signal; a bandpass filter that separates a modulated color signal including the pilot signal; and a color signal that detects the output signal of the bandpass filter. and a synchronous detection circuit that demodulates the pilot signal; a phase detection circuit that detects phase fluctuations in the pilot signal included in the output signal of the synchronous detection circuit as a phase error output signal; A color video camera equipped with either a phase adjustment circuit that controls the phase of a color subcarrier applied to a modulation circuit by a color subcarrier, or a burst phase control circuit that controls a phase of a color burst signal according to a phase error output signal of the phase detection circuit. signal processing device.