KR100293696B1 - Ntsc digital color modulating apparatus and method - Google Patents

Abstract

PURPOSE: An NTSC digital color modulating apparatus and method are provided to demodulate a modulated in-phase signal having the bandwidth of 1.5MHz and to improve resolution of the in-phase signal so as to output vivid colors. CONSTITUTION: An NTSC digital color modulator includes the first latch(21) for receiving a demodulated chrominance signal to latch a quadrature-phase signal according to the first clock, and the second latch(31) for receiving a demodulated chrominance signal to latch a demodulated in-phase signal according to the second clock. The modulator further includes the first low pass filter(22) for receiving the signal of the first latch to output a quadrature-phase signal in a predetermined frequency band, and a low pass filter(10) for accepting the signal of the second latch to output an in-phase signal in a predetermined frequency band. The low pass filter has the second low pass filter(11) for receiving the signal of the second latch, the first delay matching unit(12) for matching the output signals of the second latch and the second low pass filter with each other, a subtractor(13) for subtracting the output signal of the second low pass filter from the output signal of the first delay matching unit, an amplifier(14) for amplifying the output signal of the subtractor, and an adder(15) for adding up the output signals of the amplifier and the second low pass filter. The amplitude of the radio-frequency portion of the in-phase signal output from the low pass filter becomes identical to the amplitude of the low-frequency portion.

Description

NTSC Digital Color Demodulation Apparatus and Method

1 is a characteristic diagram of the frequency spectrum of an NTSC color television signal,

2 is a two-dimensional array diagram when a quadrature modulated color signal of NTSC color television signal is sampled at 4f _sc ,

3A is a clock diagram used in the NTSC color demodulation apparatus according to the prior art.

(b) is a block diagram of a conventional NTSC color demodulation device,

(c) is a characteristic diagram of the frequency spectrum output from the NTSC color demodulation device according to the prior art,

4 (a) is a block diagram of an NTSC digital color demodulation device according to the present invention;

(b) is a characteristic diagram of the frequency spectrum output from the NTSC digital color demodulation device according to the present invention,

5 (a) is a clock diagram used in another embodiment of the NTSC digital color demodulation device according to the present invention.

(b) is a block diagram of another embodiment of an NTSC digital color demodulation device according to the present invention;

6 is a block diagram of another embodiment of an NTSC digital color demodulation device according to the present invention.

* Explanation of symbols for the main parts of the drawings

10 low pass filter 21 first latch portion

22: first low pass filter 23: first absolute value generator

24: first D-flip flop 25: second delay matching part

26: first inverter 27: first multiplexer

31: second latch portion 32: first absolute value generating portion

33: second D-flip flop 34: third delay matching unit

35: second inverter 36: second multiplexer

40: third low pass filter

The present invention relates to a digital color demodulation device and method for an ID (Improved Density) television receiver for receiving NTSC color television signals.

In general, the modulation of NTSC color television signals is performed by inserting color signals into luminance signals in order to efficiently use a limited bandwidth. Among them, color signals that affect the quality of skin color where human eyes respond most sensitively ( Orthogonal modulation of the in-phase signal and the quadrature-phase signal to the color subcarrier (f _sc = 455f _H / 2 ≒ 3.57MHz) signal is used. Here, the color orthogonal (Q) signal has a bandwidth of about 0.5 MHz, and the color image (I) signal has a bandwidth of about 1.5 MHz to improve the quality of the color signal.

Since the bandwidth of NTSC video signal is generally about 4.2MHz, signals in band other than 4.2MHz among modulated waves are cut off and transmitted. When the color orthogonal (Q) signal and the color image (I) signal are modulated by a DSB-amplitude modulation method with a color subcarrier of f _sc = 3.57 MHz, the modulation wave of the color orthogonal (Q) signal The band of is (f _sc -0.5) MHz to (f _sc +0.5) MHz, and the band of the modulated wave of the color image (I) signal is (f _sc -1.5) MHz to (f _sc +1.5) MHz. Since the band of the color orthogonal (Q) signal modulation wave is within 4.2 MHz of the bandwidth of the NTSC video signal, the color orthogonal (Q) signal can be modulated and transmitted by the DSB-amplitude modulation method, but the color image (I) signal is The modulated wave is truncated by one side band signal other than 4.2MHz. That is, it is modulated in VSB-Vestigial Side Band-AM.

The frequency spectrum of the NTSC color television signal described above is shown in FIG. (a) shows the frequency spectrum of an NTSC color television signal subjected to a frequency insertion process by orthogonally modulating the color signal with the luminance signal, and (b) shows only the spectrum of the color signal in the frequency spectrum of the NTSC color television signal of (a). . (c) shows the components of the color image (I) signal shown in (b) again. The color image (I) signal modulated by the VSB-amplitude modulation method is divided into a high frequency I _H signal and a low frequency I _L signal. The I _H signal is considered to be modulated by SSB-Amplitude Modulation (Single Side Band-AM), and the I _L signal is modulated by DSB-Amplitude Modulation.

That is, the band of the I _L signal is (f _sc -0.5) MHz I _L (f _sc +0.5) MHz, and the band of the I _H signal is (f _sc -1.5) MHz I _H <(f _sc -0.5) MHz.

2 is a two-dimensional data array that appears when the color signal c (t) orthogonally modulated by the following equation is separated from the luminance signal in the NTSC color television signal by 4f _sc (or 910f _H ). It can be seen that it is inverted every two samples in the horizontal direction.

Quadrature Modulated Color Signal: c (t) = I (t) cos2πf _sc t + Q (t) sin2πf _sc t --- (1)

3 shows a conventional NTSC color television color demodulation device, in which (I) of (a) is a clock having a frequency of sampling frequency 4f _sc , and (II) is a color of color signals separated from the luminance signal. A clock (I clock) generated for the in phase (I) signal, and (III) is a clock (Q clock) generated for the color orthogonal (Q) signal among the color signals separated from the luminance signal.

(b) shows a configuration of a conventional color demodulation device, in which a first latch portion 1 and a second latch portion 2 to which a demodulated color signal Cin is input, and a demodulation latched by the first latch portion 1; A first low pass filter 3 that receives the received color orthogonal Cq signal and outputs a color orthogonal Q signal, and a demodulated color image Ci signal latched by the second latch unit 2. And a second low pass filter 4 which outputs the color image (I) signal.

The first latch unit 1 of the color demodulation device receives a demodulated color signal Cin and outputs a demodulated color orthogonal Cq signal present at the moment when the Q clock of (a) rises and cuts off the frequency. Is passed through the first low pass filter 3 of 0.5MHz color orthogonal (Q) signal is output. The second latch unit 2 receives the demodulated color signal Cin and outputs a demodulated color image (Ci) signal present at the moment when the I clock in (a) rises, and has a cutoff frequency of 0.5 MHz or 1.5 MHz. The color image (I) signal is outputted through the second low pass filter 4.

FIG. 3 (c) shows frequency spectrums of the demodulated color orthogonal (Cq) signal and the demodulated color image (Ci) signal outputted from the color demodulation device. As shown in (c) of FIG. 1, the color image (I) signal modulated by the VSB-amplitude modulation method is an I _H signal modulated by the SSB-amplitude modulation method and an I _L signal modulated by the DSB-amplitude modulation method. Are distinguished. From this fact, Equation (1) can be expressed by the following equation, and the same result can be obtained by Fourier transforming the two equations.

c (t) = {I _L (t) + I _H1 (t) / 2} cos2πf _sc t + {Q (t) + I _H2 (t) / 2} sin2πf _sc t --- (2)

Where I _H1 = I _H and I _H2 are orthogonal to I _H.

The output signal Ci of the second latch portion 2 operating in accordance with the I-clock has the frequency spectrum of (I) of FIG. If the cutoff frequency of the second low pass filter 4 is 0.5 MHz, only the frequency component corresponding to the I _L signal is output as the color image (I) signal, and if it is 1.5 MHz, the color image corresponding to (I) of (c) (I) A signal can be obtained. On the other hand, the output signal Cq of the first latch portion 1 operating in accordance with the Q clock has the same frequency spectrum as (II) in FIG. When the signal passes through the first low pass filter 3 having a cutoff frequency of 0.5 MHz, the I _H2 / 2 signal component is removed and only the color orthogonal (Q) signal is output.

When the color demodulation device demodulates a color image (I) signal modulated by the VSB-amplitude modulation method, and uses a low pass filter having a cutoff frequency of 0.5 MHz, the high frequency portion is removed to improve the resolution of the color image (I) signal. When the low pass filter having a cutoff frequency of 1.5 MHz is used and the low frequency part and the high frequency part have different amplitudes, distortion occurs and the resolution of the color image signal is degraded. there was.

Accordingly, the present invention has been made to solve the above-mentioned problems of the prior art, and when demodulating a color image (I) signal modulated by a VSB-amplitude modulation method, it is possible to modulate without using an expensive VSB-amplitude demodulator. The 1.5MHz bandwidth of the full color image (I) signal is secured, and the amplitude of the high frequency portion of the color image (I) signal is equal to the amplitude of the low frequency portion, thereby improving the resolution of the color image signal (I). Accordingly, an object of the present invention is to provide an NTSC digital color demodulation device that outputs clearer colors.

The NTSC digital color demodulation device of the present invention for achieving the above object is a first latch unit for receiving a demodulated color signal and latching a demodulated color orthogonal signal according to a first clock, and a second clock for receiving a demodulated color signal. A second latch unit for latching the demodulated color image signal according to the first embodiment, a first low pass filter for receiving a signal of the first latch unit and outputting a color orthogonal Q signal, and a signal for the second latch unit; And a low pass filter for outputting a color image (I) signal, wherein the low pass filter comprises a second low pass filter which receives a signal of a second latch, and the second clock unit as a synchronization signal. A first delay matching unit configured to match an output signal to an output signal of the second low pass filter, and an output signal of the second low pass filter and an output signal of the first delay matching unit to receive the first delay matching unit; Print A subtractor for subtracting the output signal of the second lowpass filter in the call, an amplifier for amplifying the output signal of the subtractor, and an adder for adding the amplified signal and the output signal of the second lowpass filter, It is characterized by outputting a more vivid color by making the amplitude of the high frequency portion of the color image (I) signal output from the low pass filter portion equal to the amplitude of the low frequency portion.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The NTSC digital color demodulation device according to the present invention receives a demodulated color signal (Cin) as shown in the block diagram of FIG. 4 (a) and latches a demodulated color orthogonal (Cq) signal according to a Q clock. Receiving a latch unit 21 and a demodulated color signal and latching a demodulated color image (Ci) signal according to the I-clock; and receiving an output signal Cq of the first latch unit 21. A first low pass filter 22 having a cutoff frequency of 0.5 MHz that outputs a color orthogonal Q signal, and an output signal Ci of the second latch unit 31 are input to output a color image signal I. It is composed of a low pass filter unit (10).

In addition, the low pass filter unit 10 has a second low pass filter 11 having a cutoff frequency of 0.5 MHz to receive the output signal of the second latch unit 31 and the second clock using the I clock as a synchronization signal. A first delay matching unit 12 which matches the two output signals by inputting the output signal of the latch unit 31 and the output signal of the second low pass filter 11, and the second low pass filter ( A subtractor for receiving the output signal of the first delay matching unit 12 and the output signal of the second low pass filter 11 from the output signal of the first delay matching unit 12. (13), an amplifier (14) for amplifying the output signal of the subtractor (13), and the amplified signal and the output signal of the second low pass filter (11) are combined to output a color image signal (I). The adder 15 is comprised.

The frequency spectrum of the demodulated color orthogonal (Cq) signal, the color orthogonal (Q) signal, the demodulated color image (Ci) signal, and the color image (I) signal outputted from the NTSC digital color demodulation apparatus is shown in FIG. ) Is shown.

The first latch unit 21 of the NTSC digital color demodulation device according to the present invention having the above-described configuration is present at the moment when the Q clock of FIG. The demodulated color orthogonal (Cq) signal having the frequency spectrum as shown in (III) of FIG. The demodulated color orthogonal (Cq) signal passes through the first low pass filter 22 having a cutoff frequency of 0.5 MHz, and the I _H2 / 2 signal is cut off, as shown in (IV) of FIG. 4 (b), 0.5 MHz. A color orthogonal (Q) signal having a bandwidth of is output.

The second latch unit 31 exists at the instant of the rising of the I clock of FIG. 3 (a) of the input demodulated color signal Ci and has the same frequency spectrum as (I) of FIG. 4 (b). The demodulated color image (Ci) signal is output and input to the second low pass filter 11 and the first delay matching unit 12. The demodulated color image (Ci) signal that has passed through the second low pass filter 11 has a signal of a band other than 0.5 MHz is blocked, and only the I _L signal passes, and the I delay is matched to the first delay matching signal. Matched with the demodulated color image (Ci) signal input to the unit 12. The subtractor 13 subtracts the I _L signal from the Ci signal and outputs only the I _H1 / 2 signal. The output I _H1 / 2 signal is amplified twice in the amplifier 14 and then merged in the adder 15 with the I _L signal passing through the second low pass filter 11 to obtain a final color image (I) signal. As shown in (II) of FIG. (B), a color image (I) signal in which the I _L signal and the I _H signal have the same amplitude is output.

Another embodiment of the NTSC digital color demodulation device according to the present invention is shown in FIG. (I) of (a) is a clock having a frequency of 4f _sc , (II) is an I 'clock having a frequency twice as high as the I clock by rising from the + I and -I signals, and (III) is + Q, Q 'clock rises in Q signal and has twice the frequency of Q clock.

The NTSC digital color demodulation device shown in FIG. 5 (b) has a first latch portion 21 which receives a demodulated color signal Cin and operates according to the Q 'clock, and the first latch portion 21 and the first latch portion 21. A first absolute value generator 23 connected between the first low pass filter 22 and a first D-flip flop operated by a Q clock and receiving a sign bit among the output signals of the first latch portion 21; (24), a second delay matching section (25) which receives the output signal of the first D-flip flop (24) and matches the Q 'clock as a synchronization signal, and the first low pass filter (22). The first inverter 26 for inverting the output signal of the signal, the output signal of the first low pass filter 22 and the output signal of the first inverter 26 in accordance with the output signal of the second delay matching section 25 A first multiplexer 27 for outputting one of the output signals, a second latch portion 31 for inputting a demodulated color signal Cin and operating according to the I 'clock, and the second latch portion 31; Wow A second absolute value generator 32 connected between the reverse pass filter unit 10 and a second D-flop flop operated by the I-clock and receiving a sign bit among the output signals of the second latch unit 31; 33) and a third delay matching unit 34 which receives the output signal of the second D-flip flop 33 and matches the I 'clock as a synchronization signal, and the low pass filter unit 10. Among the output signal of the low pass filter unit 10 and the output signal of the second inverter 35 in accordance with the output signal of the second inverter 35 and the third delay matching unit 34 to invert the output signal The second multiplexer 36 outputs one signal.

In the NTSC digital color demodulation device, when the demodulated color signal Cin is input to the first latch unit 21, the demodulated color orthogonal signal Cq, which is present at the moment when the Q 'clock rises, is latched and thus the first absolute value. The sign bit of the output signal of the first latch unit 21 is converted into an absolute value in the generator 23 and input to the first D-flip flop 24 operated by the Q clock, and then the second delay matching unit ( In step 25), the Q 'clock is input to the first multiplexer 27. Meanwhile, the output signal of the first absolute value generator 23 passes through the first low pass filter 22 and outputs only a signal of 0.5 MHz band, and other signals are cut off and input to the first multiplexer 27. The first inverter 26 is input and inverted, and then input to the first multiplexer 27.

If the color orthogonal (Q) signal corresponding to the Q 'clock of FIG. 5 (a) is negative, the first absolute value generator 23 outputs the inverted signal and inputs the first D-flip flop 24. The sign bit to be made high. The sign bit is input to the first multiplexer 27 via a second delay matching unit 25. The first multiplexer 27 outputs the output signal of the first low pass filter 22 when the sign bit is input as a high signal. Outputs the inverted signal as a final color orthogonal (Q) signal.

In addition, if the color orthogonal (Q) signal corresponding to the Q 'clock of FIG. 5 (a) is positive, the first absolute value generator 23 outputs the original signal and inputs it to the first D-flop flop 24. The sign bit to be turned low. The sign bit is input to the first multiplexer 27 through a second delay matching unit 25. When the sign bit is input as a low signal, the first multiplexer 27 outputs an output signal of the first low pass filter 22. Is output as the final color orthogonal (Q) signal.

When the demodulated color signal Cin is input to the second latch unit 31, the demodulated color image Ci signal present at the moment when the 'I' clock is raised is latched to the absolute value in the second absolute value generator 32. The sign bit of the converted signal of the second latch unit 31 is input to the second D-flip flop 33 operated by the I clock and then matches the I 'clock in the third delay matching unit 34. And input to the second multiplexer 36. On the other hand, the output signal of the second absolute value generator 32 is passed through the low pass filter unit 10 is also input to the second multiplexer 36 or is input to the second inverter 35 is inverted after the second Input to the multiplexer 36.

Like the color orthogonal signal, if the color image (I) signal corresponding to the I clock is negative like the color orthogonal signal, the sign bit is high and the second multiplexer 36 outputs the output signal of the low pass filter unit 10. The inverted signal is output as a final color image (I) signal, and when the color image (I) signal is positive, the sign bit is low and the second multiplexer 36 outputs the output signal of the low pass filter unit 10. Is output as the final color image signal (I).

FIG. 6 is a circuit for suppressing noise added to the color image (I) signal which may appear in FIG. 4 or FIG. A third low pass filter having a separate cutoff frequency of 1.5 MHz is formed between the second latch portion 31 and the low pass filter portion 10 of FIG. 4, and the second absolute value generator 32 and the low pass of FIG. A third low pass filter 40 having a separate cutoff frequency of 1.5 MHz is configured between the pass filter units 10.

In this way, before the demodulated color image signal is input to the low pass filter unit 10, frequencies other than 1.5 MHz are cut off to suppress noise added to the color image signal (I).

The present invention demodulates a color image (I) signal modulated by a VSB-amplitude modulation scheme to secure a bandwidth of 1.5 MHz of a color image (I) signal before modulation without using an expensive VSB-amplitude demodulator. The amplitude of the high frequency portion of the color image (I) signal is made equal to the amplitude of the low frequency portion to improve the resolution of the color image (I) signal, thereby producing a more vivid color.

Claims (5)

A first latch unit for receiving a demodulated color signal and latching a demodulated color orthogonal signal according to a first clock, a second latch unit for receiving a demodulated color signal and latching a demodulated color image signal according to a second clock; A first low pass filter that receives the signal of the first latch unit and outputs a color orthogonal (Q) signal of a predetermined frequency band, and outputs a color image (I) signal of a predetermined frequency band by receiving the signal of the second latch unit; And a low pass filter unit configured to receive a signal from a second latch unit, the output signal of the second latch unit and the second low pass unit using the second clock as a synchronization signal. A first delay matching unit configured to mutually match an output signal of a filter, an output signal of the second low pass filter and an output signal of the first delay matching unit, and the second low pass from the output signal of the first delay matching unit; A subtractor for subtracting the output signal of the filter, an amplifier for amplifying the output signal of the subtractor, and an adder for summing the signal amplified by the amplifier and the output signal of the second lowpass filter. NTSC digital color demodulation device, characterized in that the amplitude of the high frequency portion of the output color image (I) signal is equal to the amplitude of the low frequency portion. The method of claim 1, The first clock is a clock that is generated for a color orthogonal (Q) signal when a color signal obtained by quadrature modulation of a color orthogonal (Q) signal and a color image (I) signal is sampled at a frequency four times the color subcarrier. 2 is a clock generated for a color image (I) signal when a color orthogonal modulated color signal of a color orthogonal (Q) signal and a color image (I) signal is sampled at a frequency four times the color subcarrier. Digital color demodulation device. The method of claim 1, Operate the first latch portion in accordance with a third clock having a frequency twice the first clock; A first absolute value generator connected between the first latch portion and the first low pass filter, a first D-flip flop operated by the first clock and receiving a sign bit of an output signal of the first latch portion; A second delay matching unit for matching an output signal of the first D-flip flop with the third clock as a synchronization signal, a first inverter for inverting an output signal of the first bandpass filter, and the second And a first multiplexer configured to output one of the output signal of the first low pass filter and the output signal of the first inverter according to the output signal of the delay matching unit. The method according to claim 1 or 3, Operate the second latch unit in accordance with a fourth clock having a frequency twice the second clock; A second absolute value generator connected between the second latch unit and the low pass filter unit, a second D-flip flop operated by the second clock and receiving a sign bit of an output signal of the second latch unit; A third delay matching unit for matching the output signal of the second D-flip flop with the fourth clock as a synchronization signal, a second inverter for inverting the output signal of the band pass filter unit, and the third delay matching unit And a second multiplexer configured to output one of an output signal of the low pass filter unit and an output signal of the second inverter according to an output signal. Dividing an input color signal into a demodulated color orthogonal signal and a demodulated color orthogonal signal, filtering the demodulated color orthogonal signal to output a color orthogonal signal of a predetermined frequency band, and Filtering a low frequency signal to match the demodulated color image signal, subtracting the low frequency signal from the demodulated color image signal, and detecting only a high frequency signal of a demodulated color image signal; amplifying the high frequency signal and amplifying the low frequency signal; NTS digital color demodulation method comprising the step of outputting a color image signal of a predetermined frequency band.