JPH03273764A - Waveform equalizer for band compressing video signal - Google Patents

Abstract

PURPOSE:To reduce the amount of fluctuating a signal level by waveform equalization while keeping the output signal level of a transversal filter constant by sensing the output signal level of the filter and controlling the gain of the transversal filter. CONSTITUTION:A gain calculation part 34 calculates the gain of the transversal filter 22 by comparing the peak value of a read VIT signal with the peak value of an ideal VIT signal stored in advance. A multiplier part 36 multiplies the output signal of the gain calculation part 34 to a tap coefficient from a tap coefficient calculation part 26' for waveform equalization and outputs a multiplied result. In such the case, the peak value of the VIT signal read into a microcomputer 32 is compared with the prescribed level and based on this output, the gain of the transversal filter 22 is decided. Then, the gain of the transversal filter 22 is multiplied to all corrected tap gains. Thus, the output signal level of the transversal filter 22 is kept constant and prevented from being fluctuated by the quantization processing.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a waveform equalizer for band-compressed video signals. In particular, it relates to a waveform equalizer for MUSE signals.

(b) Conventional technology A waveform equalizer is well known as a circuit for correcting distortion occurring in a signal transmission path (for example, JP-A-59-2
No. 19033, HO4B3106).

Incidentally, a multiplex sub-Nyquist sampling encoding method (MUSE method) is used as a method for band-compressing a high-quality video signal and transmitting it using a broadcasting satellite. This method uses a single channel of satellite broadcasting (bandwidth 2
7MHz) to transmit high-definition video signals at band 8
, into a 1 MHz band compressed video signal (MUSE signal).

For this MUSE signal, in order to equalize the characteristics of the transmission path,
V I T (Ve
A signal (interval Te5t) is added in advance to the first and second lines of the MUSE signal on the transmitting side together with the frame pulse shown in FIG. In the band compression decoder (MUSE decoder), after A/D converting the MUSE signal that has been transmitted as an analog sample value, it takes in the response of the VIT signal and compares the response with an ideal impulse response (ideal waveform, ideal response). It has a built-in waveform equalizer to equalize the waveform so that the shape error of the waveform is reduced.

Incidentally, this kind of thing is mentioned in the proceedings of the 1988 Television Society National Conference "18-5 MUSE Decoder Built-in Waveform Equalizer"
3) etc.

FIG. 6 shows the MUSE decoder.

(10) is the MUSE signal input terminal, (11) is the analog AGC circuit, (12) is the A/D conversion circuit, (14) is the waveform equalizer, (16) is the MUSE decode circuit, (18R
) (8G) (18B) is a D/A conversion circuit, (20R) (
20G) (20B) are output terminals for R, 'G, and B signals, respectively.

(22) is a variable tap gain transversal filter,
(24) is a VIT signal acquisition circuit, (26) is a microcomputer for tap gain correction calculation, (28) is a tap gain memory, and (30) is a timing signal generation circuit.

The MUSE signal input from the input terminal (10) is AGC
After the signal level is set to a predetermined value in the circuit (11), it is converted into a digital signal in the A/D conversion circuit (12).

The digital signal is passed through a transversal filter (22)
After being filtered in the MUSE decoding circuit (16), it is reproduced into a high-quality video signal. The reproduced high-definition video signal is processed by a D/A conversion circuit (18R) (18G) (18
B), it is converted to an analog signal and sent to the output terminal (20
R) (20G) (20B).

The timing signal generation circuit (30) receives a frame synchronization signal, horizontal synchronization signal, etc. from the MUSE decoding circuit (16), and generates various timing signals in the waveform equalizer (14) such as a VIT signal capture timing signal. The VIT signal acquisition circuit (24) extracts the received IT signal from the output of the transversal filter (22) based on the VIT signal acquisition timing signal. The microcomputer (26) corrects the tap gain. One tap gain correction uses the error between the VIT signal captured by the VIT signal capture circuit (24) and the ideal response (Fig. 3b), and adjusts the tap gain at that point so that the error is small. to correct. The modified tap gain is written to the tap gain memory (28).

This changes the tap gain of the transversal filter (22) and performs waveform equalization.

Waveform equalization is performed by repeating the above operations until the error between the VIT signal and the ideal response falls within a certain range.

FIG. 7 shows the ideal waveform (b) and the transversal filter outputs (a) and (c). However, the waveforms are displayed in analog form for easy understanding. The waveform shapes of (a) and (c) are waveform equalized so as to substantially match the waveform shape of the ideal waveform (b), and the waveform equalization process is completed. However, the ideal waveform (
Compared to b), output (c) has a lower peak value, and output (a) has a higher peak value. Therefore, at output (C), the output signal level is lower than the specified level, and output (a)
It becomes large when . As a result, when the output signal level becomes smaller than the specified level, the contrast decreases, and when it becomes larger, effects such as blackout appear on the reproduced video.

For vases such as waveforms, transversal filters (2
The gain of 2) is controlled to be constant. However, fluctuations occur in the output signal level of the waveform equalizer, which affects the reproduced video signal.

(c) Problem to be solved by the invention The amplitude of the MUSE signal input to the input terminal (10) is
The gain is adjusted in advance by an analog AGC circuit (11) or the like according to the input amplitude range of the A/D conversion circuit (12).

However, the waveform equalization process of the transversal filter (22) causes the output signal level of the transversal filter (22) to fluctuate.

An object of the present invention is to maintain the level of the output signal of the transversal filter (22) at a predetermined constant level with high precision even when waveform equalization processing is performed.

In other words, the present invention conventionally uses transversal filters (
22) is also used as a variable amplifier to prevent the output of the transversal filter (22) from varying due to equalization processing and to keep it constant.

B.) Means for Solving the Problems The present invention provides variable tap gain transversal filter means (22) to which a band compressed video signal in which a reference waveform (VIT) periodically exists is input, and the variable tap gain transversal A band compression video comprising tap gain modification means (32) for reading the reference waveform (VIT) from the output signal of the filter means (22) and modifying the tap gain of the variable tap gain transversal filter means (22). In the signal waveform equalizer, the tap gain modification means (32) modifies the tap gain so that the level of the output waveform of the transversal filter (22) becomes a predetermined value.

(E) Function In the present invention, the VIT signal output from the transversal filter (22) is read, and the tap coefficient (tap gain) is set so that waveform distortion is removed as in the conventional manner, and the output level is adjusted. The tap coefficient is also corrected so that it becomes a predetermined level.

(f) Example An embodiment of the present invention will be described with reference to FIG.

(32) is a microcomputer. (26°) shows a hardware part of the software that operates in the same way as a conventional microcomputer, and is a waveform equalization tap coefficient calculation unit that calculates tap coefficients from the read VIT signal.

(34) is a gain calculation unit that calculates the gain of the transversal filter (22) by comparing the peak value of the read VIT signal with the peak value of the ideal VIT signal stored in advance. (36) is a multiplication unit which multiplies the tap coefficient from the waveform equalization tap coefficient calculation unit (26°) by a gain (output signal from the multiplication unit (34)) and outputs the result.

In this embodiment, the operation is the same as the conventional one, and the peak value of the VIT signal read into the microcomputer (32) is compared with a predetermined level, and based on this output,
The gain of the transversal filter (22) is determined, all corrected tap gains (tap coefficients) are multiplied by the gain, and the process ends.

Due to this operation, the transversal filter (2
The output signal level of 2) is kept constant.

In the above embodiment, waveform equalization and gain adjustment were performed at the same time, but after the waveform equalization process, the output signal level is sensed from the output VIT signal of the variable tap gain transversal filter, and the output signal level of the transversal filter is adjusted. The gain of the transversal filter may be modified to keep the level constant.

Referring to FIG. 2, a second embodiment of the present invention will be described.

In the example shown in FIG. 1, the gain calculation unit (34) detects the peak level of the VIT signal and controls the tap coefficient. but,
Peak level detection using the VIT signal is less reliable.

Therefore, in the example shown in FIG. 2, level detection is performed using frame pulses.

In FIG. 2, (40) is a frame pulse acquisition circuit. (34) is a gain calculation unit that calculates a gain from the captured frame pulse. The frame pulse capture circuit (40) captures a signal during the frame pulse period using a signal from the timing signal generation circuit (30).

In this circuit, the VIT signal acquisition circuit (24)
Based on the IT signal acquisition timing signal, the frame pulse acquisition circuit (40) extracts the received VIT signal and the received frame pulse from the output of the transversal filter (22).

The microcomputer (32) compares the received frame pulse with the specified level of the ideal frame pulse with the waveform equalization tap coefficient calculating section (26') which has the same function as conventional waveform equalization, and then converts the transversal filter. (22) a gain calculation unit (34) that determines the gain of the tap coefficient calculation unit (26);
') by an output signal from a gain calculation unit (34) and outputs the result.

The waveform equalization vase in this embodiment operates in the same manner as in FIG. 1, determines the gain of the transversal filter (22) so that the captured frame pulse is at a specified level, and uses tap coefficients modified for waveform equalization. is multiplied by the gain and the process ends.

In the above embodiment, the VIT signal capture circuit (24)
Although the frame pulse capture circuit (40) and the frame pulse capture circuit (40) are shown separately, they are actually formed by one memory circuit. and,
The microcomputer (32) takes in the data of the VIT signal and the data of the frame pulse signal, respectively, and performs gain calculation and tap coefficient calculation.

By the way, if the tap coefficient correction and the gain correction are performed at the same time using data taken in at the same time, you may get used to malfunctions because both corrections are performed at the same time. In addition, in order to perform both corrections at the same time, the processing load on the microcomputer (32) becomes large, so the microcomputer (32)
32) for other control purposes.

For this reason, it is conceivable to perform gain correction and tap coefficient correction in a time-sharing manner.

Figure 3 shows a third example in which gain correction and tap coefficient correction are performed alternately.
An example is shown.

In FIG. 3, (42) is a tap coefficient switching output circuit. (28) is a tap gain memory circuit, and this circuit (28) is a tap coefficient switching output circuit (42).
The tap coefficients from the multiplier (36) and the tap coefficient correction calculation unit (26'')
Output to.

(30) is a timing signal generation circuit, and the tap coefficient switching output circuit (42) is controlled by this timing signal generation circuit (30).

(26'') is a tap coefficient correction calculating section that calculates a corrected tap coefficient using the current tap coefficient from the tap gain memory circuit (28) and the read VIT signal.The multiplication section (36) is a tap gain memory circuit. Automatic level control is performed by multiplying the current tap coefficient from (28) by the gain correction value calculated using the read frame pulse signal.

In this circuit, in order to operate waveform equalization stably, the tap coefficient switching output circuit (42) is switched for each frame, and waveform equalization and correction of tap coefficients by automatic level control are performed alternately.

Incidentally, when this is performed by software of the microcomputer (32), the operation is performed in a time-division manner, and this is shown in hardware as shown in FIG. (44) is an inverting circuit, (42
a) (42b) is an operation stop signal input terminal.

In other words, in this circuit, while the gain calculation section (34) is operating,
The tap coefficient correction calculation unit (26”) is in a stopped state, and 1
This state is reversed every frame.

(G) Effects of the Invention In the present invention, the level of the output signal of the transversal filter (22) is sensed and the gain of the transversal filter is adjusted to keep the level of the output signal of the transversal filter constant. The amount of signal level fluctuation due to equalization can be reduced.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention. FIG. 2 is a diagram showing a second embodiment of the present invention. FIG. 3 is a diagram showing a third embodiment of the present invention. FIG. 4 is a diagram showing a fourth embodiment of the present invention. 5 6 FIG. 5, FIG. 6, and FIG. 7 are diagrams showing conventional examples. (22)...Variable tap gain transversal filter means (transversal filter), (32)...
Tap gain correction means (microcomputer) (waveform equalization means) (automatic level control means), (42)...Tap coefficient switching output circuit, (42a
) (42b)...Operation stop signal input terminal, (34).
...Gain calculation section, (26')...Tap coefficient calculation section, (26")...Tap coefficient correction calculation section, (36)...
- Multiplication section.

Claims (6)

[Claims] (1) Variable tap gain transversal filter means (22) to which a band compressed video signal in which a reference waveform (VIT) periodically exists is input; and the variable tap gain transversal filter means (22).
The reference waveform (VIT) of the output signal of step 2) is read and the tap gain variable transversal filter means (
22) tap gain modifying means (3) for modifying the tap gain of
2), wherein the tap gain modifying means (32) modifies the tap gain so that the level of the reference waveform becomes a predetermined value. Equalizer. (2) variable tap gain transversal filter means (22) to which a band compressed video signal in which a reference waveform (VIT) periodically exists is input; and the variable tap gain transversal filter means (22);
The reference waveform (VIT) of the output signal of step 2) is read and the tap gain variable transversal filter means (
22) tap gain modifying means (3) for modifying the tap gain of
2), wherein the tap gain modification means (32) corrects the tap gain so that the level of the read reference waveform becomes a predetermined value. Signal waveform equalizer. (3) variable tap gain transversal filter means (22) to which a band compressed video signal in which a reference waveform (VIT) periodically exists is input; and the variable tap gain transversal filter means (22);
The reference waveform (VIT) of the output signal of step 2) is read and the tap gain variable transversal filter means (
22) tap gain modifying means (3) for modifying the tap gain of
2), wherein the tap gain modifying means (32) corrects the tap gain so that the signal level of the output signal for a predetermined period becomes a predetermined value. Video signal waveform equalizer. (4) variable tap gain transversal filter means (22) to which a band compressed video signal in which a reference waveform (VIT) periodically exists is input; and the variable tap gain transversal filter means (22).
The reference waveform (VIT) of the output signal of step 2) is read and the tap gain variable transversal filter means (
22) tap gain modifying means (3) for modifying the tap gain of
2), wherein the tap gain modifying means (32) modifies the tap gain so that the level of the frame pulse period of the output signal becomes a predetermined value. Video signal waveform equalizer. (5) A variable tap coefficient transversal filter (
22), and the transversal filter (22) based on the predetermined waveform of the output signal of the transversal filter (22).
Waveform equalization means (32) for sequentially correcting the tap coefficients of 2)
and an automatic level that controls the output signal level of the transversal filter (22) to be kept constant by modifying the tap coefficient of the transversal filter (22) based on the output signal of the transversal filter (22). a control means (32); correction of the tap coefficient by the waveform equalization means (32);
A waveform equalizer for a band-compressed video signal, comprising means (42) for temporally dividing correction of tap coefficients by the automatic level control means (32). (6) The waveform equalizer for a band-compressed video signal according to claim 5, wherein the correction of the tap coefficients by the waveform equalization means (32) and the correction of the tap coefficients by the automatic level control means (32) are performed alternately.