SU1169148A1 - Recursive digital filter - Google Patents

Abstract

A RECURSIVE DIGITAL FILTER containing a first adder connected in series, a first delay line, a third adder, and a fourth adder, the output of which is connected to the input of the first multiplier, the fifth adder, the second, third, and fourth multipliers, are different in that simplifying adjustment of the notch band with a constant opacity band, the output of the third adder is connected to the input of the second multiplier, the output of which is connected to the inputs of the third and fourth multipliers and with the combined first inputs the first and fourth adders, the second inputs of which are combined and are the input of a recursive digital filter, the output of the fifth adder, the codes of the first and fourth multipliers, are to the second, third and fourth inputs of the second adder, respectively, then the fourth multiplier is connected to the output the second multiplier, and the second input of the third adder is connected to the input of the recursive digital filter.

Description

The invention relates to radio engineering and can be used in communication technology, automation, measurement technology. The purpose of the invention is to simplify the adjustment of the notch frequency at a constant opacity band. FIG. 1 shows the structural electrical circuit of the recursive digital filter in FIG. 2 - graph of a recursive digital filter. The recursive digital filter contains the first 1, second 2, third 3, quarter A and fifth fifth adders, the first 6 and second 7 lines of delay, the first 8, second 9, third 10, fourth 11 multipliers. Recursive digital filter works as follows. The input signal is fed to the corresponding inputs of the first, third, fourth and fifth adders 1, 3.4 and 5. At low frequencies, the signal changes both at the output and at the input of a recursive digital filter within one or even two quantization periods insignificantly, the transmission coefficient of the links of lines 6 and 7 of the delay can be considered approximately equal to one. Taking into account the fact that multiplication factors 8 and 9 are very small, since they are normalized by the quantization frequency, the signal value is mainly determined by the branches: the sum of the torus 3 is the multiplier 10 is the multiplier 11; adder 5 - adder 2 - delay line - adder 3 - multiplier 10 - multiplier 11J adder 1 - delay line 6 - adder 2 - delay line 7 - adder 3 - multiplier 10 multiplier 11 (Fig. 1), Elementary summation of transmissions along these branches m gives a total transmission coefficient of approximately equal to the multiplier of 11. When considering sufficiently high frequencies of the signal, the transmission coefficients of links of lines 6 and 7 delay to 1. By analogy with the previous one, the sum of transmissions on the above branches gives a total transmission coefficient, also approximately p an explicit to the coefficient multipliers 11. At the medium frequencies due to the phase shift in the lines 6 and 7, the delay is its attenuation. The steepness of the frequency response of a recursive digital filter is determined by the depth of the negative feedback formed by the multiplier 9, the transmission coefficient of which in this case determines the band of the filter. The recursive digital filter rejection frequency is determined by the frequency-dependent recursive digital filter feedbacks formed by multiplier 8. The signal level in the transparency bands is determined by the multiplier 11. All the summation and multiplication operations are performed in a recursive digital filter in the time interval between two adjacent signal values, i.e. in the period of its quantization, equal to the delay time of lines 6 and 7 of the delay. The operation of the proposed recursive digital filter can be understood using its graph shown in FIG. 2. Based on this graph using the Meson formula, the transfer function of the filter in the r-plane is equal to. 1 -.211; where L, b (-1) BoZ P, LBD .Z P hbB "Z -, (-l), 2BoZ L4 BO (-OZ P aG, b and h are the normalized no frequent. multipliers coefficients 8.9 and 11. Transform expression (1), we have V, 1 + (b-2) ZVz, n (n) h TTl + CB i -JrirF - 2) In order to evaluate the frequency properties of the recursive digital filter, The resulting expression (2) should be transformed into the P-plane. Do this by using the exact-transformation () 2 Transform H (Z) H (- (L-2) rGH 1 + 5 + (b-a-2P-g "-Z-: fiZ- b () + Z-b °

i-z

as a result we get

 )

Ihp

T (pbh

 h.

 arch chr p + pa + b

From expression (3) you can find the frequency of notching

Wo 4b, (4)

transparency bar

Uw a

(five)

and transmission coefficient in transparency bands

k h. (6)

By transferring the digital function of the function of (Z), you can make a difference equation

hs -r hich-2) + x1; c-2 (7)

-a-a-2lii n4l-y h-2 y

The exponentials (4-7) clearly indicate that the parameter 1az can be set equal to the coefficient b, without changing the parameters CO and k.

Claims (1)

A RECURSIVE DIGITAL FILTER containing a first adder, a first delay line, a third adder, and a fourth adder, the output of which is connected to the input of the first multiplier, the fifth adder, the second, third, and fourth multipliers, which differs in that simplifying the adjustment of the notch band with a constant opacity band, the output of the third adder is connected to the input of the second multiplier, the output of which is connected to the inputs of the third and fourth multipliers and to the combined first inputs of the first the first and fourth adders, the second inputs of which are combined and are the input of a recursive digital filter, the output of the fifth adder, the outputs of the first and fourth multipliers are connected to the second, third and fourth inputs of the first adder, respectively, while the input of the fourth multiplier is connected to the output of the second multiplier, and the second the input of the third adder is connected to the input of a recursive digital filter. Figure 1