Delay circuit arrangements.

This invention relates to delay circuit arrangements suitable for contour compensation processing of video signals.

Video. signals in video systems such as television receivers and television cameras pass through various electric circuits and signal transmission lines having finite operational frequency ranges. Therefore, attenuation of high frequency components occurs, resulting in reduction of resolution. By way of example, if the luminance signal contains a 3.58 MHz colour sub-carrier, a 35.8 MHz beat brilliance variation results in the reproduced image. To eliminate such beat interference, the video amplifier circuit in a colour television receiver has frequency characteristics such that the colour sub-carrier is attenuated by more than 15 to 16 dB. However, in such a video amplifier circuit, the high frequency components of the video signal are attenuated, resulting in reduction in the resolution of the reproduced image. In a shadow-mask type cathode ray tube, the brilliance modulation efficiency tends to be reduced when the frequency exceeds 2 MHz. Such reduction of the brilliance modulation efficiency reduces the contrast, so reducing the resolution.

To compensate for such loss of resolution, it has been the practice to effect contour compensation processing on portions of the luminance signal waveform corresponding to the contour of the image, to produce overshoot or undershoot of 20 to 30%. This processing has the effect of increasing the sharpness of the contour portions of the image, thus improving the resolution.

A vertical contour compensation circuit 10 as shown in Figure 1 of the accompanying drawings has been used for improving the resolution of the image in the vertical direction thereof.

In the vertical contour compensation circuit 10 shown in Figure 1, an input luminance signal Y_in is supplied to a signal input terminal 1 to be fed to a delay line 2 and a first adder 3. The input luminance signal Y_in has a waveform as shown, for example, in Figure 2A of the accompanying drawings. The delay line 2 produces a first delayed luminance signal Y_DL1 having a waveform as shown in Figure 2B of the accompanying drawings, and which is delayed relative to the input luminance signal Y_in by one horizontal scanning period 1 _H, and a second delayed luminance signal Y _DL2 having a waveform as shown in Figure 2C of the accompanying drawings, which is delayed relative to the input luminance signal Y_in by 2 H. The first delayed luminance signal Y_DL1 obtained from the delay line 2 is fed to the subtracter 5 and a second adder 7. The second delayed luminance signal Y_DL2' on the other hand, is fed to the first adder 3. The first adder 3 adds the input luminance signal Y_in and second delayed luminance signal Y_DL2, and feeds the resulting signal Y_A (having a waveform as shown in Figure 2D of the accompanying drawings) through an attenuator 4 to the subtracter 5. The subtracter 5 substracts the signal YA from the first delayed luminance signal Y_DL1 to obtain a contour compensation signal SAC having a waveform as shown in Figure 2E of the accompanying drawings. This contour compensation signal S_AC is fed through a level controller 6 to the second adder 7. The second adder 7 superimposes the contour compensation signal S_AC on the first delayed luminance signal Y _DL1 and produces an output luminance signal Y_out as shown in Figure 2F of the accompanying drawings. The signal Y_out appears at an output terminal 8. It has a vertical contour compensated waveform with an overshoot and an undershoot resulting from the superimposition of the contour compensation signal S_AC on the luminance change portions, that is, contour portions in the vertical direction of the image.

The delay line 2 in the vertical contour compensation circuit 10 usually uses two 1 H delay lines 22 and 25 each providing a delay time equal to 1 H. Referring to Figure 1, the input luminance signal Y_in supplied to the input terminal 1 is fed to an amplitude modulator 21 in the delay line 2 for amplitude modulation. The output of the amplitude modulator 21 is fed to the first delay line 22. The delayed output signal from the first delay line 22 is fed through a first gain controlled amplifier 23 to a first demodulator 24. The first gain controlled amplifier 23 is gain controlled by the output of the first demodulator 24. The delayed output signal from the first delay line 22 is fed through the first gain controlled amplifier 23 to the second delay line 25. The delayed output signal from the second delay line 25 is fed through a second gain controlled amplifier 26 to a second demodulator 27.

When the input luminance signal Y_in as shown in Figure 2A is fed to the amplitude modulator 21, the first demodulator 24 demodulates the 1 H delayed luminance signal from the first delay line 22 and produces the first delayed luminance signal Y _DL1 delayed by 1 H relative to the input luminance signal Y_in as shown in Figure 2B. The second demodulator 27 demodulates the luminance signal that has been delayed by 1 H in each of the first and second delay lines 22 and 25, and produces the second delayed luminance signal Y _DL2 delayed by 2 H relative to the input luminance signal Y DL2 as shown in Figure 2C.

As has been shown, the delay line 2 in the vertical contour compensation circuit 10 uses two 1 H delay lines 22 and 25 in order to obtain the first and second delayed luminance signals Y_DL1 and Y_DL2 delayed by 1 H and 2 H relative to the input luminance signal Y_in, respectively. However, delay lines are generally expensive, and the vertical contour compensation circuit 10, which used two high performance 1 H delay lines which are required to provide a comparatively long delay time and nevertheless have wide frequency band characteristics, is inevitably very expensive, the major part of the price being accounted for by the two delay lines. Moreover, the signal level attenuation and temperature characteristics vary with individual delay lines even of the same ratings and specifications. Therefore, where the two delay lines 22 and 25 are used as in the above case, the delayed output signals must be passed through the gain controlled amplifiers 23 and 26 for automatic level control.

According to the present invention there is provided a delay circuit arrangement comprising: <ul id="ul0001" list-style="none"><li>modulating means for effecting contour modulation of a signal using a signal from a carrier oscillator as a carrier;</li><li>delay means for delaying the modulation output of said modulating means; variable phase shifting means for phase shifting said carrier oscillator output signal;</li><li>demodulating means for effecting demodulation by synchronous detection using the output of said variable phase shifting means as a synchronizing signal;</li><li>adding means for superimposing a reference signal on a first demodulated signal from said demodulating means corresponding to a first input signal to said modulating means and supplying the resultant signal as a second input signal to said modulating means; and</li><li>control means for controlling the amount of phase shift by said variable phase shifting means according to the reference signal demodulated by said demodulating means;</li><li>said demodulating means producing a first demodulated signal delayed relative to said first input signal supplied to said modulating means by an amount determined by said delay means and a second demodulated signal delayed relative to said first input signal by double said amount.</li></ul>

The invention will now be described by way of example with reference to the accompanying drawings, in which: <ul id="ul0002" list-style="none"><li>Figure 1 is a block diagram of a prior art vertical contour compensation circuit;</li><li>Figure 2 shows waveforms for explaining the operation of the circuit of Figure 1;</li><li>Figure 3 is a block diagram of an embodiment of the invention;</li><li>Figure 4 is a vector diagram for explaining the operation of first and second amplitude modulators in the embodiment;</li><li>Figure 5 is a waveform diagram showing an input signal to the second amplitude modulator; and</li><li>Figures 6 and 7 are vector diagrams for explaining the operation of a voltage controlled variable phase shifter in the embodiment.</li><li>Figure 3 is a block diagram showing an embodiment of the invention applied to a vertical contour compensation circuit.</li></ul>

The illustrated vertical contour compensation circuit 100 incorporates a delay circuit 40, which employs a single 1 H delay line 43 which can provide first and second delayed luminance signals Y_DL1 and Y_DL2 respectively delayed 1 H and 2 H relative to an input luminance signal Y_in. A first adder 60 adds the input luminance signal Y. which is supplied to an input terminal 30 and the second delayed luminance signal Y_DL2. A subtracter 70 produces a contour compensation signal S_AC from the first delayed luminance signal Y_DL1 and the sum signal from the first adder 60. A second adder 80 superimposes the contour compensation signal S_AC on the first delayed luminance signal Y _DL1 to obtain a vertical contour compensated output luminance signal Y_out.

The delay circuit 40 also includes first and second amplitude modulators 41A and 41B for effecting so-called orthogonal modulation of a carrier from a carrier oscillator 50. The input luminance signal supplied to the input terminal 30 is fed to the first amplitude modulator 41A. The carrier output signal from the carrier oscillator 50 is supplied directly to the first amplitude modulator 41A, while it is supplied to the second amplitude modulator 41B through a phase shifter 51 for shifting the phase by 90°. The orthogonal modulation is thus done with carriers 90° out of phase with each other to produce first and second amplitude modulated components S₁ and S₂ which are 90° out of phase with each other as shown in the vector diagram of Figure 4, these modulated components S₁ and S₂ being fed to an adder 42 to be added together. The resultant sum signal S, from the adder 42 is fed through the 1 H delay line 43 to a voltage controlled variable gain amplifier 44. The 1 H delay line 43 delays the sum signal S_A by 1 H. The voltage controlled variable gain amplifier 44 effects insertion loss temperature compensation of the 1 H delay line, and it is gain controlled by the output of a reference signal detector 49 to be described later. The output of the voltage controlled variable gain amplifier 44 is fed to first and second demodulators 45A and 45B. The carrier output signal from the carrier oscillator 50 is supplied as a synchronizing signal through a voltage controlled variable phase shifter 52 to the first and second demodulators 45A and 45B for demodulating the sum signal output from the voltage controlled variable gain amplifier 44 by synchronous detection. A phase shifter 53 provides a phase difference of 90 between the synchronizing signals supplied to the demodulators 45A and 45B. The amount of phase shift by the voltage controlled variable phase shifter 52 is controlled by the output of a level comparator 55 to be described later.

The first demodulator 45A demodulates only a component of the sum signal output of the voltage controlled variable gain amplifier 44 corresponding to the first amplitude modulation S₁ by synchronous detection of the sum signal output. It recovers the first delayed luminance signal Y_DL1 delayed _{1 H} relative to the input luminance signal Y_in, because the sum signal output fed to it from the variable gain amplifier 44 has been delayed 1 H through the 1 H delay line 43 and the first amplitude modulated component S₁ in the sum signal S_A is the amplitude modulation of the input luminance signal Y_in on the carrier.

The first delayed luminance signal YDL1 from the first demodulator 45A is fed to the subtracter 70 and the second adder 80 as mentioned earlier. It is further fed through a clamp circuit 46 in the delay circuit 40 to a sample/hold circuit 54 and an adder 47. A reference signal S6 coupled to a reference signal input terminal 48 is fed to the adder 47 to be superimposed on the first delayed luminance signal Y _DL1 at a position corresponding to the blanking period as shown in Figure 5. The output of the adder 47, consisting of the reference signal S and the first delayed luminance signal Y_DL1 superimposed on each other, is fed to the second amplitude modulator 41B.

The second demodulator 45B, which corresponds to the second amplitude modulator 41B, demodulates only a component of the sum signal output of the voltage controlled variable gain amplifier 44 corresponding to the second amplitude modulated component S₂, by synchronous detection of the sum signal output. It recovers the second delayed luminance signal Y_DL1, which is delayed 1 H relative to the first delayed luminance signal Y_DL1, that is, delayed 2 H relative to the input luminance signal Y_in, under the control of the reference signal S, because the second amplitude modulated component S₂ is the amplitude modulation of the output consisting of the reference signal S and the first delayed luminance signal YDL1 superimposed on each other on the carrier, and has been delayed 1 H in the 1 H delay line 43 before being fed to it.

The second delayed luminance signal Y_DL1 is fed to the first adder ₆₀ for addition to the input luminance signal Y_in. The sum signal Y_A from the first adder 60 is fed through an attenuator 65 to the subtracter 70. The subtracter 70 subtracts the first delayed luminance signal Y_DL1 and the sum signal Y_A one from the other to obtain the contour compensation signal S_AC. The second adder 80 superimposes the contour compensation signal S_AC on the first delayed luminance signal Y_DL1, whereby the vertical contour compensated output luminance signal Y_out is produced at an output terminal 90.

In this embodiment, a reference signal detector 49 detects the reference signal S6 demodulated by the second demodulator 45B and controls the gain of the voltage controlled variable gain amplifier 44 to make the signal level of the reference signal S6 constant. By this automatic gain control function, the insertion loss temperature compensation of the 1 H delay line 43 is done in the voltage controlled variable gain amplifier 41 on the sum signal input thereto, that is the first and second amplitude modulation components S₁ and S₂, which have been delayed in the 1 H delay line 43. The first and second demodulators 45A and 45B, to which the sum signal S_A is fed through the voltage controlled variable gain amplifier 44, demodulate the first delayed luminance signal Y _DL1 completely free from the reference signal S, so long as the phase relation of the synchronous detection, that is, the phase relation between the synchronizing signals, is correct.

In this embodiment, the output signal of the carrier oscillator 50 is supplied as the synchronizing signal through the voltage controlled variable phase shifter 52 to the first and second demodulators 45A and 45B. The amount of phase shift by the voltage controlled variable phase shifter 52 is controlled according to the output of the level comparator 55. More specifically, the level comparator 55 compares a reference voltage VREF supplied to one input terminal of it with a hold voltage V _SH supplied from the sample/hold circuit 54. The output representing the result of the comparison is fed through a signal selection switch 56 to the voltage controlled variable phase shifter 52. The sample/hold circuit 54 samples and holds the output of the clamp circuit 46 at a position corresponding to the reference signal S6 superimposed on the first delayed luminance signal Y_DL1' The level comparator 55 compares the levels of the reference voltage V_REF' which is equal in level to the clamp voltage of the clamp circuit 46, that is, the first delayed luminance signal YDL1, and the hold voltage V_SH. The first delayed luminance signal Y_DL1, demodulated by the first demodulator does not contain any component corresponding to the second modulation component S₂ of the second amplitude modulator 41B, so long as the phase of synchronous detection by the first demodulator 45A is correct. In other words, with the right phase of synchronous detection by the first demodulator 45A the first delayed luminance signal Y_DL1 fed to the sample/hold circuit 54 does not contain the reference signal S. In this case, the clamp level is sampled and held by the sample/hold circuit 54.

It is to be understood that by controlling the amount of phase shift by the voltage controlled variable phase shifter 52 according to the output of the level comparator 55, which compares the hold voltage V_SH from the sample/hold circuit 54 with the reference voltage V _REF equal to the clamped voltage, the correct phase of the synchronizing signal supplied to the first demodulator 45A can be maintained. Also, by feeding the synchronizing signal noted above through the 90° phase shifter 53 to the second demodulator 45B, the correct phase of the synchronous detection by the second demodulator 45B is maintained. In other words, through automatic phase control of the synchronizing signals using the voltage controlled variable phase shifter 52, the correct phases of synchronous detection by the demodulators 45A and 45B can be maintained stably and reliably irrespective of variations of the delay characteristics of the 1 H delay line 43 due to temperature changes or aging.

The control state, in which the automatic phase control loop described above is established when power is first applied by closing a power switch is not known. If the phase of the synchronous detection is deviated by 180° or more at the time of the establishment of the loop, stable pull-in cannot be obtained. For example, if the phase of the synchronous detection of the first demodulator 45A is in a range indicated by Q_A in Figure 6, where the phase range of the voltage controlled variable phase shifter 52 is indicated at Q₀, the automatic phase control is stopped at one limit Q_LA of the range Q₀, so that the phase can no longer be locked at the correct phase.

In this embodiment, the amount of phase shift by the voltage controlled variable phase shifter 52 is tentatively fixed at the centre 8_c of the phase range as shown in Figure 7 at the time of the closure of the power switch. By so doing, reliable pull-in to the correct phase can be obtained. More specifically, at the time of the closure of the power switch, the selection switch 56 is tentatively switched to a fixed power supply 57 by a time constant circuit 58, which detects the rising of the power source voltage. The voltage of the fixed power supply 57, which is supplied as the control voltage to the voltage controlled variable phase shifter 52, is set to fix the phase amount to the centre Q_c. The selection switch 56 is switched to the level comparator 55 after the lapse of a predetermined period of time determined by the time constant circuit 58. With this switching, the voltage controlled variable phase shifter 52 in the phase control loop starts the pull-in of phase from the centre 6 . The synchronous detection phase thus can be automatically and reliably locked to the correct phase.

As has been shown, in the above embodiment the delayed luminance signals Y_DL1 and Y _DL2 respectively delayed 1 H and 2 H behind the input luminance signal Y_in for effecting the vertical contour compensation can be obtained with a single 1 H delay line 43, and the insertion loss temperature compensation of the 1 H delay line 43 is obtained through the automatic gain control function of the variable gain amplifier 44, so that the levels of the delayed luminance signals Y_DL1 and Y_DL2 can be automatically controlled to obtain stable regular vertical contour compensation processing.

As has been described in the foregoing, two delayed signals delayed by different amounts can be obtained with a simple construction utilizing a single delay line and orthogonal modulation/demodulation means. Also, the orthogonally modulated signal can be reliably demodulated for steady recovery of the delayed signals through synchronous detection using the phase controlled carrier from the variable phase shifter as the synchronizing signal.