JPH0337794B2 - - 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 color video cameras using solid-state image sensors, there are various means for obtaining 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 as many times as the number of pixels in the horizontal direction of the image sensor, as shown in Figure 2B. The spectral distribution of the column is as shown in FIG. Frequency f is the horizontal clock frequency,
R, G, and B color carriers occur near the frequency of 1/3f. 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・F), and 4 is a band pass filter (hereinafter abbreviated as B・P・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 driving pulse generator for the image sensor, and 10 indicates an NTSC composite 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 it through the AGC circuit, 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 components of the signal output from the image sensor using an LPF.
After separating the color carriers by BPF,
Two color difference signals {R-
(G+B)/2} and {√3/2(BG)}.

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 is 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 change due to changes in circuit operating conditions such as temperature fluctuations. becomes worse. 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. This results in a phase difference and 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 integrated circuit transistors are generally worse than those of individually manufactured transistors, and the difference in PNP transistors is significant, making it difficult to improve the phase characteristics of IC integrated circuits. It becomes very difficult to flatten the required frequency band. For this reason, the signal processing circuit implemented as an IC has the disadvantage that the relative phase relationship between the two signals fluctuates due to temperature changes. In a color video camera, such characteristics of the signal processing circuit cause a change in the hue of the output image and a significant deterioration in color reproducibility.

Purpose of the Invention The purpose of the present invention is to solve the problem of the synchronous detection circuit that occurs when the signal processing circuit of a color video camera including the synchronous detection circuit is integrated into an IC, as described above, because the phase characteristics of the circuit fluctuate depending on the temperature. The present invention provides a signal processing circuit that always performs stable color signal separation by correcting detection output errors.

Structure of the Invention The present invention provides a multiplexed synchronous detection circuit including a pilot signal addition circuit for phase detection, a pilot signal phase detection circuit, and a reference carrier signal phase control circuit to be input to the synchronous detection circuit. This is a signal processing circuit for a color video camera that separates color signals, and corrects errors in the output signal of the synchronous detection circuit that occur due to changes in the phase characteristics of the circuit.
It performs stable color separation.

DESCRIPTION OF EMBODIMENTS FIG. 4 shows a first embodiment of a signal processing circuit equipped with a phase characteristic compensation type synchronous detection circuit of the present invention.

In Fig. 4, 11 is a color image sensor, 12 is an addition circuit, 13 is a gate circuit for generating a pilot signal, 14 is a gamma correction and AGC circuit, 15 is an LPF, 16 is a BPF, and 17 and 18 are synchronizers. Detection circuit, 19 and 20 are phase control circuits, 21 is a phase detection circuit, 22 is a 90 degree phase shift circuit, 23 and 24
is an LPF, 25 is an encoder, 26 is a drive pulse generator for the image sensor, and 27 is a synchronization signal generator.

The operation of the embodiment of the above configuration will be explained as follows.

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 fp
has the same frequency as the carrier wave (1/3 of the horizontal clock frequency f) of the multiplexed color signal output from the image sensor, and the continuous wave as shown in A is gated by the gate pulse B to obtain 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 expressed by the horizontal rate. As shown in FIG. d, 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 added to the output signal 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. Input to the detection circuit. These two synchronous detection circuits can generate the NTSC carrier color signal by quadrature two-phase modulation of the two color difference signals, so the three color signals multiplexed in the image sensor are separated and the two color difference signals are generated. It is for making. The reference carrier wave used for synchronous detection is generated by a synchronous signal generator 27, and is synchronized with the horizontal clock pulse of the image sensor. The reference carrier wave output from the synchronous signal generator is generated by 22 90-degree phase shift circuits to create two signals with a 90-degree phase difference, and then passed through 19 and 20 phase control circuits, respectively, to the synchronous detection circuit 1.
7 and 18. For example, the phase of the reference carrier wave input to the detection circuit 17 is set to the same phase as the R of the multiplexed modulated color signal, and the phase of the reference carrier wave input to the detection circuit 17 is
Assuming that the input to 8 is detected with a delay of 90 degrees from the phase described above, the output of the detection circuit 17 is as follows.
R-(G+B)/2, the output of the detection circuit 18 is √3/2(
B - G) signals can be obtained. However, since the output of the detection circuit contains harmonic components, LPF2
3 and 24, only the low frequency components are extracted to obtain the two signals. On the other hand, the luminance signal is generated 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, the detection output of the synchronous detection circuit is as follows: When detected using the reference carrier wave shown as A, for signal B which has a phase difference of 90 degrees from the reference carrier wave, it is clearly shown in the figure. Similarly, even if there is a slight phase change, the detection output level has a characteristic that varies 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 you set it so that the phase of the pilot signal changes due to temperature fluctuation, the detection output level will change from the zero level.
The amount and direction of phase fluctuation can be detected accurately depending on whether it is positive or negative. FIG. 8 shows an example of the phase detection circuit shown in FIG. The sample and hold circuit 28 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 it by a hold circuit 29 and comparing and amplifying these two potentials by a comparator 30. Using this control voltage, the reference carrier phase is adjusted by reference carrier phase control circuits 19 and 20, and negative feedback is applied so that the difference in output voltage between the two sample and hold circuits becomes zero.

The sampling pulse for detecting the voltage during the pilot signal mentioned above is the same as the gate pulse input to the gate circuit 13.

An example of phase adjustment by the phase control circuits 19 and 20 is shown in FIG. Since the two reference carrier waves CW ₁ and CW ₂ have a phase difference of 90 degrees and are created by a 90 degree phase shift circuit, by controlling the addition ratio of these two CW ₁ and CW ₂ , It is possible to create CW ₁ ′ and CW ₂ ′ with a relative phase difference of 90 degrees, and the absolute phase adjustment range is 90 degrees, which is sufficient as a phase compensation range in the signal processing circuit configured according to the present invention. It is a variable range.

According to the signal processing circuit of the present invention configured as described above, by adding the pilot signal to the output signal of the image sensor and performing electric circuit processing, the modulated color signal multiplexed by synchronous detection is generated. Even if you separate
The phase fluctuation can be detected by the pilot signal level at the detection output, and the phase of the reference carrier signal input to the synchronous detection circuit can be controlled according to this detection signal, without being affected by the phase characteristics of the circuit. Color signals can be separated in a temperature-stable state.

FIG. 9 shows a second embodiment of the invention.

In the figure, 11 is an image sensor, 12 is an adder circuit, 13 is a pilot signal generation gate circuit, 1
4 is gamma correction, AGC circuit, 15 is LPF, 16
is BPF, 17 and 18 are synchronous detection circuits, 21 is phase detection circuit, 22 is 90 degree phase shift circuit, 23 and 24 are
25 is an encoder, 26 is a drive pulse generator, 27 is a synchronizing signal generator, and 32 is a phase control circuit.

The second embodiment configured in this manner differs from the first embodiment in that the number of phase control circuits for the reference carrier input to the synchronous detection circuit is reduced to one, and the phase is shifted by 90 degrees after phase control. The point is that two reference carrier waves are created by a circuit. The operation is no different from the first embodiment, so the explanation will be omitted, but by using only one phase control circuit as in this embodiment, element variations and DC offsets that occur in the design of the phase control circuit can be reduced. It is possible to further reduce variations in the control characteristics of the two reference carrier waves, that is, variations in the relative phase difference (90 degrees) due to the influence of factors such as the following.

FIG. 10 shows a third embodiment of the invention. In the figure, 11 is an image sensor, 12 is an addition circuit,
13 is a pilot signal generation gate circuit, 14 is a gamma correction and AGC circuit, 15 is an LPF, and 16 is a
BPF, 17 and 18 are synchronous detection circuits, 22 is a 90 degree phase shift circuit, 23 and 24 are LPFs, 25 is an encoder, 26 is a drive pulse generator, and 27 is a synchronization signal generator. The configuration is similar to the second embodiment, and the difference from the first and second embodiments is as follows.
A pilot signal gate circuit 33, a phase comparison circuit 34, and an oscillator 35 are provided so that the oscillator generates a reference carrier wave synchronized with the phase of the pilot signal, and a 90 degree phase shift circuit generates two reference carrier waves of different phases. The point is that the modulated color signal is configured to compensate for phase fluctuations of the modulated color signal by inputting it to two synchronous detection circuits and performing synchronous detection.

Regarding the third embodiment configured as above,
The operation of the phase compensation circuit portion of the reference carrier wave will be explained. Modulated color signal and pilot signal are BPF16
After being separated by , the signals are input to two synchronous detection circuits and a pilot signal gate circuit. The pilot signal gate circuit uses the same gate pulse as the gate circuit for generating the pilot signal, and gates the pilot signal added to the vertical blanking period of the modulated color signal.

The phase comparator circuit 34 compares the phase difference between the pilot signal output from the aforementioned gate circuit and the continuous wave (same frequency as the pilot signal) output from the oscillator 35, and feeds back this error signal to the oscillator. This controls the phase of the oscillator output. In this way, in this embodiment, in order to synchronize the phase of the oscillator output with the phase of the pilot signal and use this oscillator output as the reference carrier input of the synchronous detection circuit, the phase characteristics and phase fluctuations of the circuit are compensated for. Stable color separation can be performed.

Effects of the Invention The signal processing circuit of the color television camera according to the present invention adds a pilot signal to the output signal of the image sensor, detects the phase change of the pilot signal, and adjusts the detection phase ( By changing the phase characteristics of the signal processing circuit (reference carrier wave phase), even if the phase characteristics of the signal processing circuit fluctuate due to temperature, the fluctuation can be compensated for, making it possible to always perform stable color separation and achieve good color reproduction. The image quality and white balance can be stabilized. Note that if this signal processing circuit is implemented as an IC, its practical effects will be even greater.

[Brief explanation of the drawing]

Figure 1 is a front view of an example of a colored image sensor, Figure 2 is a diagram for explaining the signal waveform output from the image sensor in Figure 1, and Figure 3 is a diagram showing an example of a color image sensor using a synchronous detection circuit. FIG. 4 is a circuit diagram of a signal processing device for a conventional color video camera that separates color signals. FIG. A circuit diagram of the signal processing device, FIG. 5 is a waveform diagram of the pilot signal, FIG. 6 is a waveform diagram of the detection output of the synchronous detection circuit, and FIG. 7 is a vector diagram for explaining the phase control of the reference carrier wave of the device. FIG. 8 is a block diagram of a phase detection circuit of the same device, FIG. 9 is a block diagram of a signal processing device for a color video camera according to another embodiment of the present invention, and FIG. 10 is a block diagram of a signal processing device of a color video camera according to another embodiment of the present invention. FIG. 2 is a block diagram of a configuration in which phase compensation is performed by a phase synchronized oscillator. 11...Image sensor, 12...Addition circuit, 14...
...Gamma correction AGC circuit, 15, 23, 24...
LPF, 16...BPF, 17...synchronous detection circuit,
25... Encoder, 26... Drive pulse generator, 13... Gate circuit, 19... Phase control circuit, 18... Synchronous detection circuit, 22... 90° phase shift circuit, 20... Phase control circuit, 21 ...Phase detection circuit.

Claims (1)

[Scope of Claims] 1. Means for adding a pilot signal for phase detection to the output signal of an image sensor, means for detecting a phase change of the pilot signal synchronously detected by a synchronous detection circuit at the same time as the color signal, a signal processing device for a color video camera, comprising means for controlling the phase of a reference carrier wave input to the synchronous detection circuit in accordance with a detection signal detected by the means for controlling the synchronous detection circuit. 2. The pilot signal has the same frequency as the carrier wave of the modulated color signal output from the image sensor, and the clock pulse of the image sensor, the pilot signal, and the reference carrier wave input to the synchronous detection circuit are synchronized. A signal processing device for a color video camera according to claim 1. 3. The signal processing device for a color video camera according to claim 1, wherein the pilot signal is added within a vertical blanking period of the signal output from the image sensor.