KR100312413B1 - Look-up table based digital pulse shaping filter - Google Patents

Abstract

1. TECHNICAL FIELD OF THE INVENTION

The present invention relates to a digital waveform shaping filtering apparatus using a look-up table method.

2. The problem to be solved by the invention

In the present invention, a digital waveform shaping filtering device can significantly reduce the area of a chip by using a look-up table without storing the tap coefficients and storing the result in a memory to filter the digital waveform shaping filter. The purpose is to provide.

3. Summary of Solution to Invention

The present invention includes: in-phase filtering means for selecting predetermined tap coefficients according to in-phase symbols input from the outside, and then adding and outputting multiplexed signals by multiplexing the selected tap coefficients; Orthogonal filtering means for selecting the predetermined tap coefficients according to an orthogonal symbol input from the outside and then adding and outputting the multiplexed signals by multiplexing the selected tap coefficients; And first adding means for adding and outputting the signal filtered by the in-phase filtering means and the signal filtered by the quadrature filtering means.

4. Important uses of the invention

The present invention is used to remove interference in a high speed transmission system or the like.

Description

Look-up table based digital pulse shaping filter

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital waveform shaping filtering device used to remove interference in a high speed transmission system, and more particularly, to a digital waveform shaping filtering device using a look-up table method.

In general, a waveform shaping filter is widely used to reduce the influence of a transmission medium when implementing a transceiver for a wired / wireless communication, and is generally implemented using a transversal filter structure that is easy to implement.

In this case, however, multiplying the input and tap coefficients is essential for each tap of the filter, which requires hardware that is proportional to the number of taps and tap coefficients and the word length of the input. Due to the high speed operation was inadequate.

In addition, the type filter plays a role of changing the type of data to be transmitted to a specific type in order to minimize interference on a transmission line and to allocate a transmission frequency band in a high speed transmission system.

In addition, the conventional waveform shaping digital filter consists of a unit delay element (i.e., a D-flip-flop), a multiplier, and an adder. The total sum of the products of the input data and the tap coefficient inside the filter is equal to the output value of the filter. do.

However, in the case of the conventional waveform shaping digital filter, the number of multipliers has a problem that the area of the integrated circuit becomes too large and consumes too much power in performing the calculation operation by the above-described calculators.

Accordingly, the present invention has been made to solve the above problems, in implementing a digital waveform shaping filter, by using a look-up table stored in the memory to filter the tap coefficients without multiplying them, It is an object of the present invention to provide a digital waveform shaping filtering device that can significantly reduce the area of the chip.

1 is a block diagram of a digital waveform shaping filtering apparatus using a look-up table method according to an exemplary embodiment of the present invention.

2 is a characteristic diagram showing a raised-cosine Nyquist pulse used as a general waveform shaping pulse.

3 is a structural diagram of a memory for storing tap coefficients input to the in-phase filter of FIG.

4 is a structural diagram of a memory for storing tap coefficients input to an orthogonal filter of FIG.

Explanation of symbols on the main parts of the drawings

110: in-phase filter 120: quadrature filter

130: adder

According to the present invention for achieving the above object, in the digital filtering device, after selecting predetermined tap coefficients according to in-phase symbols input from the outside, the selected tap coefficients are multiplexed to add and multiplex signals In-phase filtering means; Orthogonal filtering means for selecting the predetermined tap coefficients according to an orthogonal symbol input from the outside and then adding and outputting the multiplexed signals by multiplexing the selected tap coefficients; And first adding means for adding and outputting the signal filtered by the in-phase filtering means and the signal filtered by the quadrature filtering means.

When the input of the transversal filter is limited to a specific value, the result of multiplying the tap coefficient of the filter with the input in advance without storing the multiplier is stored in the look-up table, and then the filter input is selected as the multiplexer's selection signal. In order to output the data of the look-up table by using a multiplexer instead of a multiplier, high-speed operation and hardware can be reduced.

In particular, the baseband Nyquist pulse used for waveform shaping is the right function, and the in-phase and quadrature pulses of the passband Nyquist pulse are also the right function and the odd function, respectively. It can be reduced below.

Accordingly, the present invention is to reduce the memory required to store the value multiplied by the filter input and the tap coefficient to "tap number / (tap number / 2 + 1)" when the digital filter of the look-up table method is implemented.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention.

1 is a configuration diagram of an apparatus for filtering digital waveform shaping using a look-up table method according to an exemplary embodiment of the present invention.

As shown in FIG. 1, the digital waveform shaping filtering apparatus of the present invention selects predetermined tap coefficients according to an in-phase symbol input from the outside, and then multiplexes the selected tap coefficients by multiplexing them. In-phase filter 100 that adds and outputs one signal, and selects predetermined tap coefficients according to quadrature symbols input from the outside, and then adds and outputs multiplexed signals by multiplexing the selected tap coefficients. Orthogonal filter 200 and an adder 300 for adding and outputting the signal filtered by the in-phase filter 100 and the signal filtered by the orthogonal filter 120.

Here, the in-phase symbol and the orthogonal symbol have -3, -1, +1, and +3 values, respectively.

The in-phase filter 100 may include a delay unit 110 for delaying the in-phase symbol according to a clock input from the outside, and a memory (in accordance with the in-phase symbol delayed and transmitted through the delay unit 110). (Not shown) selectors 120, 130, 140, 150 for selectively transmitting the tap coefficients (-3C, -C, + C, + 3C) stored in advance, and the multiplexed signal input from the outside. And multiplexers 161 to 164 for multiplexing the respective output signals of the selectors 120, 130, 140, and 150, and an adder 170 for adding the output signals of the multiplexers 161 to 164. do.

The delay unit 110 includes a D-flip flop 111 for delaying the in-phase symbol according to the clock and a D-flip flop for delaying the in-phase symbol delayed through the D-flip flop 111 according to the clock. A flip-flop 112 and a D-flip-flop 113 for delaying in-phase symbols delayed through the D-flip-flop 112 according to the clock.

The selector 120 selectively transmits tap coefficients (-3C, -C, + C, + 3C) stored in the memory to the multiplexer 161 according to the in-phase symbol. And the tap coefficients (-3C, -C, + C, + 3C) stored in the memory according to the in-phase symbols transmitted through the D-flip-flop 111 and selectively to the multiplexer 162. The tap coefficients (-3C, -C, + C, + 3C) stored in the memory according to the selectors 125 to 128 and the in-phase symbols transmitted through the D-flip-flop 112, respectively. Tap coefficients stored in the memory (-3C, -C, + C) according to selectors 129 to 132 selectively passing to 163 and in-phase symbols passed through the D-flip-flop 113 , Selectors 133 through 136 that selectively pass + 3Cs to multiplexer 164.

The quadrature filter 200 includes a delay unit 210 for delaying the orthogonal symbol according to a clock input from the outside, and a tap stored in the memory according to in-phase symbols delayed and transmitted through the delay unit 210. Selection units 220, 230, 240 and 250 for selectively transmitting coefficients -3C, -C, + C, and + 3C, and selection units 220, 230, 240 according to a multiplexed signal input from the outside. And multiplexers 261 to 264 for multiplexing the respective output signals of the signals 250 and an adder 270 for adding the output signals of the multiplexers 261 to 264.

The delay unit 210 includes a D-flip flop 211 for delaying the orthogonal symbol according to the clock and a D-flip for delaying the orthogonal symbol delayed through the D-flip flop 211 according to the clock. A flop 212 and a D-flip flop 213 for delaying orthogonal symbols delayed through the D-flip flop 212 in accordance with the clock.

The selector 220 selectors 221 to 224 selectively transfer tap coefficients -3C, -C, + C, and + 3C stored in the memory to the multiplexer 261 according to the orthogonal symbol. And a selector for selectively passing tap coefficients (-3C, -C, + C, + 3C) stored in the memory to the multiplexer 162 according to the orthogonal symbols transmitted through the D-flip-flop 211. Multiplexer 263 the tap coefficients (-3C, -C, + C, + 3C) stored in the memory in accordance with the orthogonal symbols passed through the D-flip-flop 212 (225-228). Tap coefficients stored in the memory (-3C, -C, + C, + 3C) according to the selectors 229 to 232 for selectively passing through to the orthogonal symbols transmitted through the D-flip-flop 113 To selectors 233 to 236 for selectively passing the signals to the multiplexer 264.

Referring to the operation of the digital waveform shaping filtering apparatus using the look-up table method of the present invention having the structure as described above is as follows.

The in-phase filter 100 filters the in-phase symbols using the tap coefficients stored in the memory and transmits the in-phase symbols to the adder 300.

The orthogonal filter 200 filters the orthogonal symbol using the tap coefficients stored in the memory and transmits the orthogonal symbol to the adder 300.

In this way, the filtered in-phase symbol and the orthogonal symbol are added by the adder 300 and transmitted to the outside.

2 is a characteristic diagram showing a raised-cosine Nyquist pulse used as a general waveform shaping pulse.

Referring to FIG. 2, the additional bandwidth is 0.2, the in-phase pulse is a result of multiplying the baseband pulse by a cosine value, and the quadrature pulse is a result of multiplying the baseband pulse by a sine value.

As can be seen from the figure, the in-phase pulse is the right function and the orthogonal pulse is the odd function, and in the case of the passband digital waveform shaping filter, the sum of the product of the input and the sample value of each pulse is the final output.

First, look at the in-phase pulse, the result of multiplying the input symbol (that is, +3, +1, -1, -3) by the sampling value of the pulse, the look-up table is the number of samples, the number of input symbols And a memory corresponding to the multiplication value multiplied by the number of bits necessary to express the sample value.

In this case, considering that the in-phase pulse is a right function, since the sample values of the left half and the right half of the pulse are the same, if only one of the same sample values is taken and used, the look-up table adds 1 by dividing the number of samples by 2 Only the memory corresponding to the multiplication value multiplied by the number of bits necessary to express the value, the number of input symbols and the sample value is required.

For example, a 33-tap transversal filter is used, each tap is represented by 20 bits, and the input symbols are +3, +1, -1, -3. However, using the structure developed in the present invention, only 1360-bit memory is required.

Of course, orthogonal pulses can also reduce memory in the same way as in-phase pulses.

However, since the orthogonal pulse is an odd function, that is, the left half and the right half have the same magnitude and different signs, only the sample value of the left half multiplied by a positive input is equal to the right half sample value multiplied by a negative input. This is different.

3 is a structural diagram of a memory for storing tap coefficients input to an in-phase filter of FIG. 1.

4 is a structural diagram of a memory for storing tap coefficients input to an orthogonal filter of FIG. 1.

Although the technical idea of the present invention has been described in detail according to the above preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

As described above, the present invention has the following effects.

First, the chip area can be significantly reduced by significantly reducing the amount of memory by using the symmetry characteristic of the filter in the process of storing the tap coefficients in the look-up table. Second, the chip area can be greatly reduced by not using a multiplier using a lookup table method. Third, the amount of adder is obtained by extracting four filter values for one filter input from the lookup table using the points where each tap coefficient samples the filter at four times the symbol rate and accumulating them four times using one adder. Can significantly reduce the Fourth, by using the external interface, it is possible to change, save, and read a small number of tap coefficient values stored in the memory so that it can be used in general for the waveform shaping filter for communication where the tap coefficient value should be changed according to the intended use. .

Claims (4)

In the digital filtering device, In-phase filtering means for selecting predetermined tap coefficients according to in-phase symbols input from the outside and then adding and outputting the multiplexed signals by multiplexing the selected tap coefficients; Orthogonal filtering means for selecting the predetermined tap coefficients according to an orthogonal symbol input from the outside and then adding and outputting the multiplexed signals by multiplexing the selected tap coefficients; And First adding means for adding and outputting the signal filtered by the in-phase filtering means and the signal filtered by the quadrature filtering means; Digital waveform shaping filtering device using a look-up table method comprising a. The method of claim 1, The in-phase filtering means, A plurality of delay means for sequentially delaying the in-phase symbols according to a clock input from the outside; A plurality of selection means for selectively transferring the predetermined Tap coefficients according to each in-phase symbol transmitted through the plurality of delay means; A plurality of multiplexing means for multiplexing tap coefficients selected by said plurality of selecting means according to a multiplexing signal input from the outside; And Second adding means for adding output signals of the multiplexing means to output to the first adding means; Digital waveform shaping filtering device using a look-up table method comprising a. The method of claim 1, The orthogonal filtering means, A plurality of delay means for sequentially delaying the orthogonal symbols according to a clock input from an outside; A plurality of selection means for selectively transferring the predetermined tap coefficients according to each orthogonal symbol transmitted through the plurality of delay means; A plurality of multiplexing means for multiplexing tap coefficients selected by the plurality of selecting means in accordance with a multiplexed signal input from the outside; And Second adding means for adding output signals of the multiplexing means to output to the first adding means; Digital waveform shaping filtering device using a look-up table method comprising a. The method according to any one of claims 1 to 3, The in-phase symbol and the orthogonal symbol are each, Digital waveform shaping filtering device using a look-up table method characterized in that the value -3, -1, +1, +3.