JPH02268584A - Signal transmitting method - Google Patents

Abstract

PURPOSE:To perform transmission with good linearity by imposing pulse frequency modulation upon a luminance signal and frequency modulation on two color difference signals respectively, further imposing pulse width modulation upon the pulse-frequency-modulated signal with the two frequency-modulated color difference signals alternately, and transmitting the signals as one pulse train signal. CONSTITUTION:The pulse frequency modulation is imposed upon the luminance signal Y among component video signals which contain the luminance signal and two color difference signals Pr and Pb and the frequency modulation is imposed upon the two color difference signals Pr and Pb and the pulse width modulation is imposed on the pulse-frequency modulated signal with the two frequency-modulated color difference signals alternately and the signals are transmitted as one pulse train signal. Consequently, efficient multiplexing is performed and even if interference between waveforms is caused because of the band limitation, etc., of a transmission line, the transmission with good linearity is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a signal transmission method for transmitting component video signals, particularly through a -core optical fiber.

Conventional technology Conventionally, when transmitting component video signals through a single optical fiber, each signal is modulated with a different frequency and then frequency-multiplexed for transmission. Alternatively, each signal is PCM encoded and then multiplexed. PC to transmit
The M multiplexing method or the wavelength multiplexing method in which light emitting elements transmit data using three different wavelengths was used. Using these methods, broadband high-definition color television signals (hereinafter referred to as H
When transmitting DTV signals (called DTV signals), there were the following drawbacks.

In the frequency multiplexing method, a light emitting element with a wide band and good linearity is required for the electric-optical converter (hereinafter referred to as E10), and selection of this light emitting element is difficult.

With the PCM multiplexing method, the transmission speed of Elo is several hundred Mbps.
As a result, the scale of the equipment is large and the cost is high.
Moreover, the optical fiber for the transmission line is required to have a very wide band.

The wavelength multiplexing method requires many types of light emitting elements and optical components such as optical multiplexers and demultiplexers. Furthermore, the propagation speed of the optical signal in the optical fiber varies depending on the refractive index of the light emitting element depending on the wavelength. Therefore, the relative phase of the signal differs depending on the transmission distance, and this has the drawback of being difficult to correct.

As described above, the conventional methods have the above-mentioned drawbacks, especially when transmitting broadband component signals such as HDTV signals.

As a transmission method to solve these problems, the luminance signal is pulse frequency modulated (hereinafter referred to as PFM), and the PFM signal is alternately pulse width modulated (hereinafter referred to as PWM) with two color difference signals. There is a transmission method that transmits component video signals as two pulse trains (Patent application 1986-
No. 177428). This is a transmission method that greatly expands the transmission band and efficiently transmits the signal as one pulse train signal.

Problems to be Solved by the Invention In the above transmission method, a PF is applied to the rising component of the pulse train.
The luminance signal component subjected to M is included in the falling component, and the color difference signal component subjected to PWM is included in the falling component.

In other words, the color difference signal is the luminance signal PF? PWM is performed using a baseband color difference signal using the rising edge as a reference.

Here, if waveform distortion occurs due to band limitations such as transmission lines,
Compared to the ideal waveform, there are temporal fluctuations in the rising and falling edges. The amount of variation in the rising edge and the amount of variation in the falling edge are, when demodulated, P
This has a greater influence on the PWM color difference signal than on the FM luminance signal.

Therefore, the present invention has been made in view of these points,
It is an object of the present invention to provide a signal transmission method that can perform transmission with good linearity even when interference between waveforms occurs due to band limitations of a transmission path or the like.

Means for Solving the Problems The present invention provides a component video signal having a luminance signal and two color difference signals, in which the luminance signal is subjected to pulse frequency modulation (hereinafter referred to as PFM), and the two color difference signals are each subjected to frequency modulation, The PFM signal is sequentially pulse width modulated (hereinafter referred to as PW) with the two frequency modulated color difference signals.
This is a signal transmission method characterized by transmitting the signal as one pulse train signal.

Further, the present invention is a signal transmission method that performs signal processing of differentiating and amplifying one pulse train signal upon reception, and demodulating the component video signal.

Further, the present invention is a signal transmission method that performs signal processing to differentiate and amplify one pulse train signal at the time of reception, performs automatic gain control on the amplified signal, and demodulates the component video signal.

Further, the present invention is a signal transmission method that performs addition with a luminance signal during color difference signal demodulation.

As described above, the present invention performs frequency modulation on two color difference signals and then performs PWM on the PFM luminance signal and multiplexes the signals, thereby achieving efficient multiplexing and transmission with good linearity.

Further, according to the present invention, amplification in the subsequent stage can be facilitated by differentiating the signal in a minute signal state at the time of reception and removing the DC component.

Further, according to the present invention, gain control can be performed easily and accurately by differentiating the signal in a minute signal state at the time of reception to remove the DC component, and then amplifying and holding the peak.

Furthermore, in the present invention, since the color difference signal is subjected to PWM based on the PFM-processed brightness signal, the brightness signal component is superimposed upon demodulating the color difference signal, and by adding the brightness signals, only the color difference signal can be obtained. .

Embodiments Examples of the present invention will be described below with reference to FIGS. 1 to 7.

In FIG. 1, Y of the component video signal.

The Pr and Pb signals are input to low pass filters (hereinafter referred to as LPF) 4 and 5.8, respectively. These LPFs 4 to 6 remove extra high frequency components so that aliasing beat interference with the pulse frequency of the sample value to be converted into a pulse train does not occur.

The Y signal 200 that has passed through the LPF 4 is input to the PFM modulator 7, which has a constant pulse width and a pulse interval T that changes depending on the signal amplitude of the Y signal, and is converted into a PFM signal 201. The waveforms of the input and output signals of this PFM modulator 7 are shown at 200 and 201 in FIG.

This PFM signal 201 is applied to a flip-flop (hereinafter referred to as FF).
8). This FF8 is the PFM signal 2
01 is divided by half, and two Q signals 202 and 203 having a 180' phase difference are output. 2 in Figure 2
02.203 and 201 show the relationship between these two Q and Q signal waveforms and the signal waveform of the PFM signal. Q signal 202 and Q signal 203, which are the output signals of FF8, are respectively output from R8.
-Input to the set terminals of FF9 and FF10.

On the other hand, the Pr signal is input to the 2M modulator 11 via the LPF 5. The output of this 2M modulator 11 is input to a comparator 13. This comparator 13 compares the signal amplitude 204 that is the output signal of the 2M modulator 11 with the sawtooth wave voltage 205 that is the output signal of the sawtooth wave generation circuit 12, and the sawtooth wave voltage 205 is the output signal of the 2M modulator 11. If the signal amplitude is larger than the signal amplitude 204, a trigger pulse 206 of Hl level is output. The trigger pulse 206 which is the output of the comparator 13 is R5-FF
It is input to the reset terminal of 9.

R3-FF9 is set by the rising edge of the output signal Q202 of FF8 and outputs H+ level, and is reset by the rising edge of trigger pulse 208, which is the output of comparator 13, and outputs LO level. The output signal 207 of R3-FF9 is input to the sawtooth wave generation circuit 15. The sawtooth wave generation circuit 15 rises from the time when the input signal reaches the Hl level.
Also, the sawtooth wave voltage 205 returns to the initial value at the LO level.
occurs. Therefore, the output signal 20 of R8-FF9
During the set to reset period of 7, the frequency modulated Pr
It changes depending on the signal amplitude of the signal. Therefore, R8-FF9
The falling edge of is the output signal 20 of the PFM modulator 7.
Pulse width modulation is performed using a frequency modulated Pr signal with the rising edge of 1 as a reference.

Similarly, it is input to the FM modulator 12 via the pb multiplied signal LPF'6. The output of this FM modulator 12 is input to a comparator 14. This comparator 14 outputs a signal amplitude 208 that is the output signal of the FM modulator 12 and a sawtooth wave voltage 209 that is the output signal of the sawtooth wave generation circuit 16.
If the sawtooth voltage 209 is larger than the signal amplitude 208 which is the output signal of the FM modulator 12, a trigger pulse 210 of Hl level is output. Trigger pulse 210, which is the output of comparator 14, is R8-F
Input to the reset terminal of F10.

R8-FFl0 is set at the rising edge of the output signal Q203 of FF8, outputs HIl level, and
It is reset by the rising edge of the trigger pulse 210, which is the output of the comparator 14, and outputs a Lo level. The output signal 211 of this R3-FF 10 is input to the sawtooth wave generation circuit 1e. The sawtooth wave generation circuit 16 generates a sawtooth wave voltage 209 that rises from the time when the input signal reaches the Hl level and returns to its initial value at the LO level. Therefore, the set to reset period of the output signal 211 of R8-FF10 changes depending on the amplitude of the frequency-modulated pb times signal.

Therefore, the falling edge of the output signal 211 of R8-FF10 is pulse width modulated by the Pb signal which is frequency modulated with the rising edge of the output signal 201 of the PFM modulator 7 as a reference.

R8-FF9.10 output signals 2 with different phases
07 and 211 are added by the adder 17.

The output signal 212 of this adder 17 is one pulse train signal. This one pulse train includes information on the Y signal in the pulse interval T, and information on the frequency-modulated Pr and Pb signals in alternating pulse widths Dr and Db, respectively. The output signal 212 of this adder 15 is E101
8, it is converted into an optical signal and sent out.

A method of receiving this pulse train signal converted into an optical signal and demodulating a component video signal will be explained with reference to FIGS. 3 and 4.

The optical signal input to the light receiving element 300 is converted into a current. This current is converted into current and voltage by the preamplifier 301. This signal includes frequency components ranging from a DC component to a high frequency component corresponding to the minimum pulse width of the PFM. Further, this signal voltage is a minute signal and needs to be amplified. However, it is difficult to amplify signals ranging from DC components to high frequency components by several tens of dB in terms of circuit implementation. Furthermore, since the DC level of this signal changes depending on the signal amplitudes of the luminance signal and the two color difference signals, the accuracy of peak detection deteriorates and gain control is difficult. Therefore,
This signal is differentiated by a differentiating circuit 302 to remove a DC component, and then amplified by a variable gain AC amplifier 303.

The signal component at a level higher than the zero level of the differential signal is a rising component of the received pulse train signal, and therefore includes a luminance signal component. Further, since the signal component at a level lower than the zero level is a falling component of the received pulse train signal, it includes a color difference signal component.

Output 400 of variable gain AC amplifier 303 is input to peak detection circuit 304 and comparators 305 and 306.

The peak detection circuit 304 detects the signal amplitude of the output signal 400 of the variable gain AC amplifier 303, and controls the gain of the variable gain AC amplifier 303 to be varied so that the output signal 400 of the variable gain AC amplifier 303 is constant. . By amplifying and controlling the gain after differentiating in this way, since the DC component does not change due to the luminance signal and the color difference signal, peak detection can be performed with high precision, and gain control with high precision can be easily performed.

The comparator 305 identifies the output signal of the variable gain AC amplifier 303 using a DC level (+y) higher than the zero level of the output signal of the variable gain AC amplifier 303 as a threshold. Similarly, the comparator 306 outputs a DC level (-y
) is used as a threshold to identify the output signal of the variable gain AC amplifier 303.

The output signal 401 of the comparator 305 is the LPF 307
．． It is input to the set terminal of R8-FF 308 and the 1/2 cycle 309.

The output signal 401 of this comparator 305 is a luminance signal subjected to PFM. Therefore, the low frequency component of the output signal 401 of the comparator 305 is a luminance signal,
It can be reproduced from the output of the LPF 307. This L
The output of PF 307 is input to adders 313 and 318.

The output signal 402 of the comparator 306 includes a color difference signal component, and is input to the reset terminal of the R3-FF 308.

R8-FF308 is the output signal 4 of the comparator 305.
Set at the rising edge of 01, comparator 3
It is reset at the falling edge of the output signal 402 of 08. Therefore, the output signal 403 of R8-FF308
is the original pulse train signal that is the transmission signal. This signal 403 is input to separator 310.

A 1/2 frequency divider 309 divides the output signal 401 of the comparator 305 into 1/2. This 1/2 frequency divided signal 404 is input to a separator 310.

The separator 310 has a half divider 30 at the output terminal A.
When the output signal 404 of R9 is H rubel, R8-FF3
The output signal 403 of 08 is output, and the 1/2 divider 30
When the output signal 404 of No. 9 is at Lo level, the LO level is output. Also, a half divider 3 is connected to the output terminal B.
When the output signal 404 of 09 is Lo level, R8-FF
308, and when the output signal 404 of the 1/2 period divider 809 is H level, it outputs the LO level.

The output signal 405 at the output terminal A of the separator 310 is transmitted to a sawtooth wave generation circuit 311 and a sample hold circuit 312.
is input. The sawtooth wave generation circuit 311 generates a sawtooth wave voltage 406 that rises from the time when the input signal reaches the H level and returns to the initial value at the LO level.

This sawtooth wave voltage 406 is applied to the sample hold circuit 3
12 is input.

The sample and hold circuit 312 samples and holds the sawtooth voltage 406 at the falling edge of the output signal 405 at the output terminal A of the separator 310, and resets it at the rising edge. Since the frequency-modulated color difference signal is PWMed based on the PFM luminance signal, the interval from reset to reset is the PFM component of the luminance signal.

Therefore, the output signal 4 of the sample and hold circuit 312
In the low frequency component of 07, a luminance signal is superimposed on a color difference signal. Output signal 407 of this sample hold circuit 312
is input to the adder 313, and the adder 313 adds a certain amount of a negative polarity luminance signal, which is the same as the luminance signal component included in the output signal 407 of the sample and hold circuit 312, to the output signal of the sample and hold circuit 312. This adder 313
The output of is input to the LPF 314. This LPF31
The output of 4 is a frequency modulated color difference signal. This L
The output of the PF 314 is input to the FM demodulator 315.

A color difference signal can be reproduced from the output of this FM demodulator.

In addition, the output terminal B of the dividing period 310 also has a sawtooth wave generation circuit 316, a sample hold circuit 3, and
17, adder 318, LPF 319, FM demodulator 320
The color difference signal can be reproduced through the .

Now, assume that waveform distortion occurs due to band limitation or the like, and the position of the modulated pulse changes when received. As shown in FIG. 4, the luminance signal can be demodulated by reproducing only the PFM pulse from the rising edge of the modulation pulse and extracting the low frequency component. In FIG. 5, the demodulated signal S1 can be expressed as 51=A-d-f A: pulse potential d: pulse width f: PFM frequency. Moreover, the demodulated signal S2 when the pulse changes by Δt can be expressed as 52=A−d/(1/f±Δt). Therefore, the absolute value of the amount of signal fluctuation is (S 1
-82) /S 1 = Δt-f/(i±Δt-f) (1) Here, if f is in the MHz order, Δt is in the n5ec order, so O〈Δt-f((1 It is.

Next, the amount of variation in the color difference signal when the pulse position variation occurs by Δt will be shown. In FIG. 6, when Δt is sufficiently higher than the frequency at which the color difference signal is frequency modulated, the position of the zero cross of the frequency modulated wave is shifted by Δt with respect to the frequency modulated color difference signal.

When demodulating is performed by reproducing a pulse with a constant pulse width based on the zero crossing of this FM wave, the absolute value of the amount of signal fluctuation can be expressed as shown in the following equation.

Δt-fl/(i±Δt-f 1)...(2)f
l: Frequency modulated by the difference signal, now fl
Therefore, the maximum value of equation (2) is less than or equal to equation (1).

Here, when PWM modulation is performed using a baseband difference signal in the conventional method, the amount of signal fluctuation can be expressed as Δt/P P: maximum deviation amount of PWM. This maximum deviation amount P has the following relationship with the highest frequency f wax of the PFM frequency.

P≦1/(24max) Therefore, Δt/P≧2・Δt・f wax≧2・Δt −f
--- (3) When X = Δt-f, the minimum value of (3) = 2·X The maximum value of (2) = x/(i±X) This magnitude relationship is shown in FIG. Here, since 0<x<×1, the minimum value of (3)>the maximum value of (2) holds true.

Therefore, even if interference between waveforms occurs due to band limitations of the transmission path, etc., demodulated signal displacement is small and transmission with good linearity can be performed.

As explained above, the present invention frequency-modulates two color difference signals and then performs PWM on the PFM luminance signal and multiplexes the signal, thereby achieving efficient multiplexing and transmission with good linearity. can.

Further, by differentiating the signal in a minute signal state during reception, amplification in the subsequent stage can be facilitated, and furthermore, the luminance signal and the color difference signal can be easily separated. In addition, gain control can be performed easily and accurately by amplifying and peak-holding after differentiating and removing a DC component. Further, by performing addition with the luminance signal when demodulating the color difference signal, the color difference signal can be reproduced satisfactorily.

As described in detail, according to the invention described in claim (1), transmission with good linearity can be performed even when interference between waveforms occurs due to band limitation or the like.

Furthermore, according to the invention described in claim (2), by differentiating the signal in a minute signal state at the time of reception, amplification in the subsequent stage can be facilitated, and furthermore, the luminance signal and the color difference signal can be easily separated.

Further, according to the invention as set forth in claim (3), gain control can be performed easily and accurately by differentiating the signal at the time of reception to remove the DC component, and then amplifying and holding the peak.

Further, according to the invention described in claim (4), the color difference signal can be reproduced satisfactorily by performing addition with the luminance signal when demodulating the color difference signal.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a waveform diagram showing the operation of each part of the same embodiment, FIG. 3 is a block diagram showing another embodiment of the present invention, and FIG. 4 1 is a waveform chart showing the operation of each part of the same embodiment, and FIGS. 5, 6, and 7 are explanatory diagrams showing the operation of the present invention. 4-8,307,314,319...LPF', 7.
・・PFM modulator, 8...FF19, 10.308・
...R3-FF, 11.12...Frequency modulator, 13
．． 14... Comparator, 15, 18, 311, 3
16... Sawtooth wave generation circuit, 17... Adder, 1
6...Elo, 300...Photodetector, 3o1...
Preamplifier, 302... Differentiation circuit, 303... Variable gain AC amplifier, 304 =-=Peak detection circuit, 30
5.308-, comparator, 3o9...1/2
Frequency division JL310...Distributor, 312, 317...Sample bold circuit, 313,318...Adder, 3
15,320...FM demodulator. Name of agent: Patent attorney Shigetaka Awano

Claims (4)

[Claims] (1) Of the component video signals having a luminance signal and two color difference signals, the luminance signal is subjected to pulse frequency modulation, the two color difference signals are each subjected to frequency modulation, and the pulse frequency modulated signal is sequentially modulated by the frequency modulation. A signal transmission method characterized in that two color difference signals are alternately subjected to pulse width modulation and transmitted as one pulse train signal. (2) The signal transmission method according to claim 1, wherein signal processing is performed to differentiate and amplify one pulse train signal upon reception, and demodulate the component video signal. (3) The signal transmission method according to claim 1, wherein signal processing is performed to differentiate and amplify one pulse train signal upon reception, automatic gain control is performed on the amplified signal, and demodulation of the component video signal is performed. . (4) The signal transmission method according to claim 1, characterized in that addition with a luminance signal is performed during color difference signal demodulation.