KR0152935B1 - Variable band pass digital filter - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable band digital filter (VBPF). In the related art, the video device using one of video signal systems such as NTSC, PAL, SECAM, etc., has fixed frequency band characteristics so as to fit each system. If this is changed, there was a problem that the image quality may be degraded. In order to improve this point, the present invention variably adjusts the position of the frequency band for the high frequency compensation according to each video signal system having a different frequency band, and changes the amplification factor for the high frequency correction at each selected frequency band so as to change the low frequency. The present invention is designed to increase the sharpness of the image by compensating the luminance modulation efficiency in the high frequency region with respect to the region. The present invention provides the luminance in the NTSC, PAL, SECAM video signal system and S-VHS signal having different frequency bands It is possible to improve the resolution by amplifying the high range of the signal, and to adjust the correction level of the high range in each frequency band by adjusting the gain parameter (α), so that it is possible to adjust each signal type in a video device such as a digital TV (TV) or a computer. You can make it compatible.

Description

Variable Band Digital Filter (VBPF)

1 is a block diagram of a conventional fixed band digital filter.

2 is a waveform diagram showing a frequency band in FIG.

3 is a waveform diagram showing a frequency characteristic in the conventional high-frequency amplification of the luminance signal.

4 is a block diagram of a variable band digital filter of the present invention.

FIG. 5 is a waveform diagram showing characteristics of synthesized frequencies in FIG. 4. FIG.

6 is a high-pass correction circuit in FIG.

7 is a table showing the impulse response in FIG.

8 is a center frequency conversion circuit diagram in FIG.

9 is a waveform diagram showing the frequency characteristics in FIG.

(A) and (b) of FIG. 10 show an impulse response in FIG.

* Explanation of symbols for main parts of the drawings

210: high pass correction circuit 211: amplifier

212 ~ 215,221,222: Delay 216,217,223,227: Adder

218,225,226: multiplexer 220: center frequency conversion circuit

224: Inverter

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable band digital filter, and more particularly, to a variable band digital filter (VBPF) for outputting a signal in which the amplification factor of each frequency component is varied with respect to a frequency band of an input signal.

In general, the brightness modulation efficiency for each frequency in shadow mask type CRT varies slightly depending on the diameter and pitch of the shadow mask aperture. Is lowered.

Therefore, amplifying and compensating the high range of 2 MHz or more so that the luminance modulation efficiency of the signal frequency band is constant, which is referred to as aperture correction.

FIG. 1 is a block diagram of a conventional fixed band digital filter, and as shown therein, a frequency selection for outputting a fixed frequency band signal by selecting a specific frequency band component among input frequencies f _RF according to a reference frequency f _LO . The center 110 and the center frequency converter 120 adjusts the position of the center frequency according to the reference frequency f _LO based on the output frequency of the frequency selector 110 and varies the bandwidth according to the reference frequency f _OFF . And an oscillator 130 for outputting a reference frequency f _LO (f _OFF ) to the frequency selector 110 and the center frequency converter 120.

The frequency selector 110 and the center frequency converter 120 are each a band pass filter (BPF), and each includes a mixer and a fixed frequency band filter.

Referring to the operation of the prior art as follows.

The prior art has a characteristic of varying the center frequency and the bandwidth by forming a cascade connection between the band filter 112 having a fixed center frequency of the same structure and the band filter 122 capable of varying the center frequency. A single frequency band characteristic, such as the frequency characteristic shown in FIG. 3, is used to adjust the high pass correction level.

In the aperture correction method, when the high frequency f _RF is input to the frequency selector 110, the oscillator 130 oscillates the reference frequency f _LO , and the mixer 111 generates the two signals f _RF . obtaining the sum and the difference of (f _LO), a predetermined frequency band component to generate the band pass filter frequency band components of the specific frequencies of the mixer 111 to adjust the position of the center frequency by the frequency (f _LO) in 112 The band component is output to the center frequency converter 120.

In this case, the center frequency converter 120 adjusts the position of the center frequency at the reference frequency f _LO in the mixer 121 by inputting a specific frequency band signal having a fixed center frequency of the frequency selector 110. The band pass filter 122 adjusts the frequency bandwidth to the reference frequency f _OFF .

Accordingly, the center frequency converter 120 outputs a signal having a high frequency level corrected by varying the overlapping bandwidth by converting the center frequency with respect to a component of a specific frequency band.

If the bandwidth of the band pass filter 112 is equal to that of FIG. 2A and the bandwidth of the band pass filter 122 is equal to the area of FIG. 2B, the final output bandwidth of the center frequency converter 120 Is the overlapping portion as in the region of FIG.

Therefore, by varying the degree of overlap between the center frequency of the bandpass filter 122 and the bandwidth of the bandpass filter 112 by the frequency f _OFF of the oscillator 130, the overall bandwidth can be changed.

On the other hand, if the band widths of the band filters 112 and 122 coupled by the cascade connection are the same, that is, the frequency f _OFF is 0, the frequency band of the band filter 112 and the band filter 112 As the frequency bands coincide, the input frequency is output as it is, meaningless.

Therefore, the reference frequency f _OFF should be adjusted so as not to be zero.

However, conventionally, since the position of the frequency band characteristic is fixed to each video device using one of the video signal methods such as NTSC, PAL, SECAM, etc., there is a problem that image quality may be degraded when the signal method is changed. there was.

Accordingly, the present invention variably adjusts the position of the frequency band for the high frequency compensation according to each video signal method having different frequency bands and improves the amplification factor for the high frequency correction in each selected frequency band in order to improve the conventional problem. The present invention relates to a variable band digital filter (VBPF) designed to increase image sharpness by compensating luminance modulation efficiency in a high frequency region with respect to a low frequency region.

In the variable band digital filter of the present invention, as shown in FIG. 4, a high pass correction circuit 210 for changing the amplification level for the same band characteristics by adjusting the gain parameter α of the band characteristic centered on an arbitrary frequency. And a center frequency conversion circuit 220 for adjusting the frequency band for high frequency amplification by varying the amplitude characteristics at a predetermined position by using the output Y _H of the high frequency correction circuit 210 as an input. cascade) to connect.

As shown in FIG. 6, the high pass correction circuit 210 sequentially delays the output of the amplifier 211 and the amplifier 211 which amplifies the luminance input signal Y according to the gain α. A delayer 212 to 215, an adder 216 that sums the output of the delayer 215 and the output of the amplifier 211, an output of the adder 216, and an output of the delayer 213. An adder 217 for obtaining a difference and a multiplexer 218 for selecting one of the outputs of the adder 217 and the delayer 213 according to a control signal C _O and outputting the result to the center frequency conversion circuit 220. It consists of.

As shown in FIG. 8, the center frequency conversion circuit 220 includes delayers 221 and 222 which sequentially delay the output Y _H of the high pass correction circuit 210, and the delay unit 222. As shown in FIG. An adder 223 for summing the output of the high pass correction circuit 210 and the output of the high pass correction circuit 210, an inverter 224 for inverting the sign of the output signal of the adder 223, for controlling high and low pass conversion. The output gain of the multiplexer 225 according to the signal BPFS2 for selecting one of the outputs of the adder 223 and the inverter 224 according to the signal BPFS1 and the signal BPFS2 for controlling the gain conversion. A multiplexer 226 for converting the? And an adder 227 for outputting the output of the multiplexer 226 and the output of the delayer 221 to output a luminance signal amplified by a predetermined level.

The inverter 224 inverts the code according to the frequency conversion characteristic to the high frequency side.

Referring to the operation and effect of the present invention configured in this way in detail as follows.

In order to be compatible with three signal systems (NTSC, PAL, SECAM) and S-VHS signals having different frequency bands, the position of the frequency band characteristics must be variable according to each method.

According to the present invention, if the high pass correction circuit 210 amplifies or delays only the components of the high pass by inputting the luminance signal Y and then selects and outputs the band characteristics according to the control signal C _O , the center frequency conversion circuit 220 is performed. By varying the frequency band characteristics synthesized with the high pass correction circuit 210, the high pass is finally corrected to output an amplified signal.

Here, the aperture correction emphasizes only the high pass component so the low pass component is cut off.

The high pass correction circuit 210 is an active filter having a band characteristic centering on Ws / 4 with a frequency characteristic of any magnitude as shown in FIG. 5, and the frequency characteristic is expressed as in Equation (1) below. Substituting 1) into Eq. (2) gives the impulse response function as Eq. (3).

From this impulse response function, the impulse response is obtained as shown in the table of FIG.

When the luminance signal Y is input to the high pass correction circuit 210 having the above characteristics and the amplification level for the same band characteristic is changed by adjusting the gain parameter α in the amplifier 211, the delay unit 212 to 215 Delayed sequentially) and the adder 216 sums the output of the amplifier 211 and the output of the delayer 215, and the adder 217 outputs the output of the delayer 213 and the output of the adder 216. The sum is input to the multiplexer 218.

By this operation, the transfer function for the impulse response function such as equation (3) is expressed as equation (4).

In addition, the S-VHS signal is sequentially passed through the delayers 212 and 213 without filtering, and only the delay time is adjusted and then input to the multiplexer 218.

By this operation, the transfer function is expressed as Eq. (5).

Accordingly, the path of the multiplexer 218 is changed according to the control signal C _O to determine whether to correct the high pass. In the case of the high pass correction, the output signal of the adder 217 is selected to the center frequency conversion circuit 220. When outputting and only adjusting the delay time, the output signal of the delayer 213 is selected and output to the center frequency conversion circuit 220.

That is, the high frequency correction circuit 210 having a center amplitude of 2α inputs the basic high frequency corrected signal centered on Ws / 4 to the center frequency conversion circuit 220.

In the center frequency conversion circuit 220, the frequency characteristic function of the center frequency conversion circuit 220 is increased so that the frequency characteristics synthesized with the high frequency correction circuit 210 are obtained in the form as shown in FIGS. Must be a function

First, when the center frequency conversion circuit 220 has an amplitude characteristic as shown in FIG. 9 (a) and (b), when the band characteristic synthesized with the high frequency correction circuit 210 is moved to the low side, FIG. Has an amplitude characteristic such as

The frequency characteristic of FIG. 8 (a) and (b) is represented by equation (6), and the impulse response is expressed by equation (7).

Here, β is an adjustment value for setting the center frequency of gain correction.

The impulse response to Equation (7) is obtained as shown in Table 10 (a).

In this case, the gain of the center frequency conversion circuit 220 has the same range as in Equation (6) to Equation (8), and the β value may vary within a range of 0 to 1/2.

Here, the β value selects a value of 1/4 or 1/2 as the control signal BPFS ₀ for the convenience of digital processing.

Therefore, the transfer function obtained by shifting the predetermined time T on the time axis so that the impulse response of equation (7) satisfies the causality is as shown in equation (9) (10).

In addition, when the frequency band characteristic of the center frequency conversion circuit 220 has an amplitude characteristic as shown in FIG. 9 (D) (D), the amplitude characteristic synthesized with the high pass correction circuit 210 is represented by (C) in FIG. It is possible to obtain the characteristic of moving to the high side as

The amplitude characteristic of FIG. 9C is expressed as Equation (11), and the impulse response is expressed as Equation (12).

Here, the β value selects a value of 1/4 or 1/2 as the control signal BPFS ₀ as in the case of frequency conversion to the low frequency side.

The impulse response to Equation (12) is obtained as shown in the table of FIG.

Therefore, the transfer function obtained by shifting the impulse response of equation (12) by a predetermined time T on the time axis so as to satisfy the causality is as shown in equations (13) and (14).

That is, when the output signal of the high pass correction circuit 210 is input, the center frequency conversion circuit 220 sequentially delays the delays 221 and 222 and then outputs the high pass correction circuit 210 by the adder 223. The synthesized signal is input to the multiplexer 225 and the synthesized signal is input to the multiplexer 225, and the inverter 224 is inverted according to a frequency conversion characteristic from the inverter 224 to the multiplexer 225.

The multiplexer 225 selects _one of an output signal of the low pass adder 223 and an output signal of the high pass inverter 224 according to the control signal BPFS ₁ and outputs the result to the multiplexer 226.

The multiplexer 225 is high when Selecting side by a control signal (BPFS ₁₎ outputs a signal -1/2 (1 + Z ^-2) and select the low-side 1/2 (1 + Z ^-2 Will output a signal of).

Thereafter, when the multiplexer 225 selects the high or low side signal, the multiplexer 226 changes the β value to 1/4 or 1/2 by selecting a path according to the control signal BPFS ₀ . .

As a result, the adder 227 obtains the difference between the output signal of the multiplexer 226 and the output signal of the delayer 221, thereby outputting the amplified signal with high frequency correction.

That is, the output of the adder 227 can be obtained as shown in Equations (9) (10) (13) and (14).

As described above, the center frequency conversion circuit 220 has four frequency characteristics by the control signals of the control signals BPFS ₁ and BPFS ₀ , and is combined with the high frequency correction circuit 210 to show 2.2 as shown in FIG. 5. It has a frequency characteristic centered between the frequency bands of MHz and 3.8MHz, respectively.

Therefore, the present invention can adjust the frequency band to be amplified in improving the resolution by amplifying the high range in the video signal system of NTSC, PAL, SECAM.

As described in detail above, the present invention can improve the resolution by amplifying the high range of the luminance signal in the NTSC, PAL, and SECAM video signal systems having different frequency bands, and the S-VHS signal, and furthermore, gain parameter (α). By adjusting, it is possible to adjust the correction level of the high range in each frequency band.

Therefore, the present invention can be applied to a digital video device such as a digital TV (TV) or a computer to improve sharpness by amplifying a high range of a luminance signal regardless of each signal system.

Claims (8)

A video apparatus which amplifies the high range of a luminance signal to improve clarity, comprising: high frequency correction means for amplifying only a high frequency component after removing a low frequency range from a luminance input Y, and controlling the output signal Y _H of the high frequency correction means; A variable band digital filter (VBPF) comprising a center frequency conversion unit configured to have different bands by synthesizing according to (BPFS ₁ , BPFS ₀ ) and converting the maximum amplification position to the high or low frequency side. 2. A variable band digital filter (VBPF) according to claim 1, wherein the high pass correction means and the center frequency conversion means are constituted by cascade connections. 2. A variable band digital filter (VBPF) according to claim 1, wherein the high pass correction means is an active filter having a frequency characteristic of the following formula around Ws / 4. Where α is a gain parameter. 2. The variable band digital filter (VBPF) according to claim 1, wherein the high frequency correction means has two transfer functions for the case of the high frequency correction and the delay adjustment as shown below. 5. The high frequency correction means according to any one of claims 1 to 4, wherein the high pass correction means includes: an amplifier 211 for amplifying the luminance signal Y according to the gain?, And a delay for sequentially delaying the output of the amplifier 211. Adders 216 for adding up the outputs of the delay unit 215 and the output of the amplifier 211, and the output of the adder 216 at the output of the delay unit 213. When the high frequency is corrected according to the adder 217 to subtract and the control signal C ₀ , the output of the adder 217 is selected and the output of the delayer 213 is selected when only the delay time is adjusted. A variable band digital filter (VBPF) comprising a multiplexer 218 outputted by means. The variable band digital filter (VBPF) according to claim 1, wherein the center frequency converting means has a band characteristic that is combined with the output of the high frequency correcting means and moves to the low side and the high side as shown in the following formula. However, β is variable within the range of 0 and 1/2. The variable band digital filter (VBPF) according to claim 1, wherein the center frequency converting means obtains a transfer function such as the following formula by moving the impulse response to the low and high frequencies by a predetermined time (T). 8. The frequency converter according to claim 6 or 7, wherein the center frequency converting means includes delayers 221 and 222 for sequentially delaying the output Y _H of the high pass correcting means, and an output of the delay 222 and the high pass. An adder 223 for summing the outputs of the correction means, an inverter 224 for inverting the sign of the output signal of the adder 223, and a signal BPFS1 for controlling the high and low conversions. A multiplexer 225 for selecting one of the outputs of the 223 and the inverter 224, a multiplexer 226 for converting the output gain of the multiplexer 225 according to the signal BPFS0 for controlling the gain conversion, A variable band digital filter (VBPF) comprising an adder (227) for outputting the output of the multiplexer (226) and the output of the delayer (221) to output a luminance signal amplified by a predetermined level.