JPS6245722B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a signal processing circuit for a simple color television camera.
A detector with a simple circuit configuration and better linearity than the low-level part is used to detect the modulated signal of a color television camera that obtains the color signal from the modulated signal obtained from the image pickup tube. With a simple circuit configuration, the linearity of the color signal obtained by detecting the modulated signal and the non-modulated signal match from the low level portion.

Conventional configurations and their problems Conventionally, general AM detectors include square-law detectors that use square-law characteristics of nonlinear elements such as diodes, and linear detectors that use straight-line parts. With either detector, there is no problem in normal cases where the modulation depth is not very deep, but when the signal is modulated nearly 100%, the drawback is that the low level part (when modulated positively) is suppressed. be. In order to improve this problem, conventionally known means is to provide negative feedback to the detected signal, the basic configuration of which is shown in FIG. To explain this circuit, input terminal 1
After adding an AM modulated wave to and amplifying it with amplifier 3,
A half-wave rectified wave is obtained using a diode or transistor, and a carrier wave component is removed using a low-pass filter (LPF) 6 to obtain a detected output signal. Then, the half-wave rectified wave output from the clip circuit 4 is transferred to the feedback circuit 5.
The signal is fed back to the amplifier 3 as a negative feedback to correct the non-linear distortion of the detector.
However, since a half-wave rectified wave is fed back, in order to prevent the DC level of the signal input to the cropping circuit 4 from varying depending on the input signal level and to maintain a constant clip level, this closed loop must be directly connected to the DC circuit. so that the loop gain has no frequency characteristics, or add a bandpass filter (B.
PF) or a high-pass filter (HPF) to prevent the DC component from being fed back from the output section to the input section, thereby eliminating the loop gain of the low-frequency component. However, if the closed loop is directly connected in a DC manner, there are problems with the dynamic range and the stability of the DC operating point (particularly due to temperature) when the loop gain is increased. In addition, when the loop gain is increased in a circuit that inserts a filter to improve linearity, harmonic components that cause positive feedback appear due to delay elements in the loop in the method that inserts a high-pass filter. In the method of causing oscillation at frequency and inserting BPF, BP
Phase deviation within the passband of F. is already up to ±90
°, and since it is difficult to obtain an ideal BPF, the amount of attenuation in the cutoff frequency band is not infinite, so there are frequencies near the passband of the BPF that result in positive feedback. However, if the loop gain is increased, oscillation will occur at this frequency.

Furthermore, since filters with ideal characteristics are difficult to obtain, fluctuations in the DC level due to the input signal level are not completely zero, so the loop gain is limited to a small value and low-level distortion is prevented. The improvement effect was not satisfactory.

For this reason, a striped color filter is placed in front of the image pickup tube to spatially modulate the color signal, and the color signal is obtained from the modulated signal obtained from the image pickup tube, such as in a color television modulation signal detector. In places where good linearity is required, the above-mentioned simple detection circuit cannot be used, resulting in a complicated circuit and high cost. An example of this will be explained next.

FIG. 5 is a basic configuration diagram of a simple color television camera. 9 shows an image pickup tube with a striped color filter 8 attached to the front. From now on, the striped color filter 8 repeats white (W), cyan (Cy), W, Cy, etc. for the frequency separation method. And (W)・Yellow (Ye)・W・Ye...
It will be explained as a combination of repeating...
The output of the image pickup tube 9 is amplified by 10. Reference numeral 11 denotes a low-pass filter for luminance signals, which removes the color signal component spatially modulated by the striped color filter 8 to obtain a luminance signal _YH . On the other hand, 12 is a low pass filter (LPF) that passes the same bandwidth as the color signal, and obtains a luminance signal Y _L for obtaining a color difference signal. 13 and 14 are an R (red) signal separation circuit and a B (blue) signal separation circuit, respectively; in the case of single frequency separation, a comb filter using a delay line of one horizontal period is used;
As the output, an AM signal is obtained which is 100% modulated using a frequency corresponding to the pitch of the striped color filter as a carrier wave, as shown in FIG. 3a.
Detection circuits 15 and 16 each detect the R/B modulated signal to obtain a low frequency signal. 17, 18,
19 is a gamma correction circuit, which leads to Y
_L. In addition to adjusting the RB signal to an appropriate gamma characteristic,
The linearity of each signal is matched. Each gamma-corrected signal is then led to a matrix circuit 20, where color difference signals RY and BY are obtained. Among the basic configuration circuits of the simple color television camera briefly described above, the circuit that detects the separated modulated signal and performs gamma correction (the part surrounded by the dotted line in the block diagram in Figure 5) is conventional. used a circuit as shown in Figure 6. To explain the operation of this circuit, a modulated color signal input to an input terminal 21 is amplified by an amplifier 22 and guided to a detector 23. (The detector here refers to a general detector circuit excluding the smoothing circuit.) This detector is used because it is necessary to match the black level to the white balance for a color television camera. It was common to use a synchronous detection circuit that could detect low levels with good linearity. Detection circuit 2
The carrier wave component is removed from the output of 3 by a low pass filter (LPF) 24, and then the output is passed to a clamp circuit 2 to obtain a reference level for gamma correction.
5, the DC level during the horizontal blanking period is fixed, and based on this level, the gamma circuit 26 performs gamma correction to obtain a color signal with gamma characteristics matching the gamma characteristics of the _YL signal. In this way, conventionally, since a synchronous detection circuit is used as a detection circuit, the circuit is complicated and the cost is high.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a signal processing circuit for color television, which has a simple circuit configuration and is low in cost.

Structure of the Invention The present invention provides a clamping means for fixing the DC level of a reference portion of a modulated signal modulated by a striped color filter of a color television camera, and a clamping means for fixing the DC level of a reference portion of a modulated signal modulated by a striped color filter of a color television camera, and a clamping means for fixing the DC level of a reference portion of a modulated signal modulated by a striped color filter of a color television camera. clipping means for clipping an arbitrary level of the output signal; means for feeding back the clipped output signal so as to be superimposed on the modulation signal; The present invention provides a signal processing circuit for a television camera, which is provided with means for making nonlinear characteristics based on the level.

DESCRIPTION OF EXAMPLE First, it is used in the present invention. An improved AM detector will be explained.

FIG. 2 is a basic configuration diagram of the AM detector, and
The same parts as in FIG. 1 are designated by the same reference numerals.

To explain the operation, a 100% modulated AM signal with intermittent parts, such as a television signal, as shown in FIG. 3a, is input to the input terminal 1. Hereinafter, for the sake of simplicity, the signal will be explained as a television signal. In the signal shown in FIG. 3a, th is one horizontal scanning period, _t1 is a horizontal blanking period, and _t2 is an effective horizontal scanning period. After this signal is input to the input terminal 1, it is passed through the adder circuit 2 to the half-wave rectified wave (shown in Figure 3d) of the output of the clip circuit 4 which passes through the feedback circuit 5.
As shown in Figure 4 in detail, only the half wave obtained by the clip circuit 4 receives feedback, resulting in a vertically asymmetrical wave as shown in Figure 3b.
This signal is inverted and amplified by the amplifier 3, resulting in the waveform shown in FIG. 3c. Next, in the clamp circuit 7, keyed clamping is performed during the blanking period, and the DC level during the blanking period _t1 is fixed and guided to the clip circuit 4, where the DC level is clipped with this fixed DC level as a reference. A half-wave rectified wave shown in FIG. 3d is obtained. This half-wave rectified wave is fed back to the input signal via a feedback circuit 5, and the suppression of the low level portion by the clip circuit 4 is improved. Note that Fig. 4 a, b, and c are enlarged views of Fig. 3 a, b, and c, respectively, and the clip output (Fig. 4 b) is fed back to the input signal (Fig. 4 a), and one half of the input signal (Fig. 4 a) is fed back. This shows how only the waves undergo negative feedback and become vertically asymmetrical waves as shown in Figure 4c.

With this circuit, the DC level of the reference part is regenerated by the clamp just before the clip circuit, so the DC level of the reference part is completely fixed.
Therefore, there is no variation in the clip level due to the input signal level. Furthermore, since there is no element in the loop that causes a large phase shift, such as a filter, oscillation is less likely to occur. Therefore, it is possible to increase the feedback loop gain, and the nonlinear distortion in the low level portion can be greatly improved. In the above explanation, the amplifier in the basic configuration diagram of the present invention (Fig. 2) was explained as a class A amplifier, but in this method, the linearity of the half wave of the input signal that is not necessary as the output of the clip circuit is Since there is no need to amplify the input signal well, if this amplifier is a class AB amplifier that amplifies only the required half wave of the input signal with good linearity, the dynamic range will be large and the input signal to the clip circuit 4 will be increased. The signal level can be increased, and the influence of non-linear distortion in the low level portion generated by the clip circuit 4 is reduced.

Next, by applying the above-mentioned improved AM detector to the conventional simple color television camera shown in Figure 5, we created a signal processing circuit for a color television camera with a simple circuit configuration and good characteristics. An example of the basic configuration of the present invention that has been realized will be described.

Figure 7 shows the improved AM detector described above in the fifth
This is an example of the basic configuration of the present invention applied to the conventional simple color television camera shown in the figure.

To explain the operation of FIG. 7, the part surrounded by the dotted line in FIG.
It is added to the output of the feedback circuit 32, and amplified by the amplifier 29. The DC level during the horizontal blanking period is fixed by the clamp circuit 30, and the DC level is set to a predetermined level by a simple clip circuit 31 composed of a diode or transistor. Clip the signal below or above the level to obtain a half-wave rectified wave. This half-wave rectified wave is fed back to the input via the feedback circuit 32 to improve the non-linear distortion in the low level portion generated by the clip circuit 31. Since the DC level of the reference part of the output signal of the clip circuit 31 is reproduced by the clamp circuit 30, there is no need to insert a separate clamp circuit, and the output signal of the clip circuit 31 is converted to the next gamma signal as a half-wave rectified wave based on this level. The correction circuit 33 can perform gamma correction, and the gamma-corrected half-wave rectified wave is passed through the LPF 34 to obtain a low-frequency signal, and the gamma is adjusted so that the gamma characteristics of this low-frequency signal match those of other signals. By adjusting the correction circuit, it is possible to obtain a signal with the same characteristics as the conventional example using a synchronous detection circuit.

Comparing the circuit of the present invention shown in FIG. 7 with the conventional circuit shown in FIG. 6, a simple clip circuit 31 and a feedback circuit 32 are added instead of the synchronous detection circuit 23 shown in FIG. The feedback circuit can most easily be configured with just one resistor, with only a few changes, making the circuit extremely compact and low-cost, while still achieving the same performance. .

Effects of the Invention As described above, according to the present invention, a simple color television circuit that obtains color signals using striped color filters can be applied with a simple circuit and good linearity.
By using an AM detection circuit, it is possible to reduce the size and cost of the circuit without degrading performance.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional AM detection device, Fig. 2 is a block diagram of an improved AM detection device used in the present invention, and Fig. 3 a, b, c, and d are operations of the device in Fig. 2. Waveform diagrams for explanation, Figure 4 a, b,
c is an enlarged view of the waveform in Fig. 3, Fig. 5 is a block diagram of a conventional example of a simple color television camera using a striped color filter, and Fig. 6 is a conventional diagram of the part surrounded by the broken line in Fig. 5. FIG. 7 is a circuit diagram showing the basic configuration of the present invention, which is the part surrounded by the broken line in FIG. 5. 1...Input terminal, 2...Addition circuit, 3...Amplifier, 4...Clip circuit, 5...Feedback circuit, 6...
...Low pass filter, 7...Clamp circuit, 8...
...filter, 9...imaging tube, 16...detection circuit,
19... Gamma correction circuit, 29... Amplifier, 30
... Clamp circuit, 31 ... Clip circuit, 32
...Feedback circuit.

Claims (1)

[Claims] 1. Clamping means for fixing the DC level of a reference part of a modulated signal modulated by a striped color filter of a color television camera, and a clamping means for fixing a DC level of a reference part of a modulated signal modulated by a striped color filter of a color television camera; clipping means for clipping the level; means for feeding back the clipped output signal so as to be superimposed on the modulation signal; and the output signal of the clamping means is referenced to the DC level of the reference portion fixed by the clamping means. 1. A signal processing circuit for a color television camera, characterized in that a signal processing circuit for a color television camera is provided with means for making a nonlinear characteristic.