SU1492451A1 - Digital band-pass filter - Google Patents

Abstract

The invention relates to radio engineering. The purpose of the invention is to simplify the adjustment and increase speed. The filter contains adders 1–4, algebraic adders 5–8, delay delays 9–12, and multipliers 13–16. The goal is achieved by the fact that the parameter α, which controls the center frequency, is the same for all links. In this case, the coefficients B _{1I of the} links are equal to each other, which facilitates adjustment of the filter bandwidth. 2 Il.

Description

Lgod

15

The invention relates to radio engineering and can be used in communication technology, automation and other areas for filtering signals given by a digital code.

The aim of the invention is to simplify the tuning and increase the speed of the bandpass digital filter .10

FIG. 1 shows a structural electrical bandpass digital filter circuit; fig 2 is his graph.

The band-pass digital filter contains the first to fourth adders 1-A, the first to fourth algebraic adders 5-8, the first to fourth delay elements 9-12, and the first to fourth multipliers 13-16.20

Band-pass digital filter works as follows.

The input signal is subtracted from the contents of the second delay element 10 in the third algebraic adder 7 and the result is multiplied by the coefficient b in the fourth multiplier 16. The signal from the output of the fourth multiplier 16 is added to the input signal in the fourth adder 4. In the fourth algebraic adder 8 the signal from the fourth the adder 4 is added to the content of the second delay element 10, the content of the 35 is subtracted from this amount

the fourth delay element 12 and the result is multiplied by the factor b- in the first multiplier 13, the signal from the output of which is added to sig25

thirty

five

0

0

five

five

0

cash from the output of the fourth adder | 4 in the first adder 1. The signal from the output of the first adder I is added to the contents of the second delay element 10 in the second adder 2, the signal from the output of which is multiplied by the coefficient c1 and in the second multiplier 14 the result of the first delay element 9 is subtracted algebraic adder 5. The signal from the output of the first adder 1 is recorded in the first delay element 9, the signal from the output of the first algebraic adder 5 is recorded in the second delay element 10, the signal from the output of the second adder 2 is added with erzhimym fourth delay element 12 in the third adder, the result is output as a digital bandpass filter and is multiplied by a factor in a third multiplier 15. The second algebraic adder 6 content third delay element 11 is subtracted from the signal The yields. Yes, the third multiplier I5, the signal from the output of the second adder 2 is recorded in the third delay element 11, the signal from the output of the second algebraic adder 6 is recorded in the fourth delay element 12. Further, the bandpass digital filter operation is repeated for new input values.

Starting from the graph (figure 2), find the transfer function of the proposed bandpass digital filter

f

H (Z)

(l-bi) Cl + bitj ()

1- (o (, + c (+ b (c1,) + fl /, b, (l + b,)) Z- + (l + bi (b,, -eft (l + b,)) Z - Ji (2ba + b, (I + l) Z

+ b, Z-

20

The main application of the device is associated with the condition o (, o (j ej. Then

H (Z)

d-bJcubjXi-z-)

l-rf (2 + b, (l-t-)) z- + (l + bi) (b, +0 (1 + 4, - (2b g + b, (1 bj) Z-3 +

Let be

Hfp) Pj (p) ij

U)

dW; p + W |.

There is a transfer function of an analog low-pass filter prototype with a cut-off frequency of 57. To go to a bandwidth digital transceiver, use the transform

g

, (l + b,)) Z- + (l + bi (b,, -eft (l + b,)) Z

20

the transfer function takes the form

Z

h (1)

Where

  2e (Z + Z - Z i cos be;

le

-g

c / i ctg 2 Making this substitution at j. one ,

get a digital filter with pOTOHnHCHoti

frequency of arcos c and polpgoG

51492451

D0 2arctgi7, The transfer function of the digital filter is written as

(l-z-)

 i (-Z-) -b (l-2rfZ +) + uj. (d-Z)

4 1-in ((2 + b ,;; (l + bj;)) Z- + (H-b4i) (b, j + c ((I + b, i) (2b5; + b ,, (1+ B,;)) E Z

A comparison of expressions (1) and (3) shows that they differ by a constant factor, the coefficients b ,, - depend only on the parameters of the low-pass filter, and the parameter / that controls the center frequency is the same for; all links.

For some classes of filters, for example, Butterworth filters, the condition 1l} with 1 Wo and the coefficients b, of the links are equal to each other, which makes it easy to adjust the bandwidth of the bandpass digital filter. From the properties of the applied frequency conversions and the comparison of expressions (1) and (3), it follows that to provide a transmission level of 0 dB, a scale factor 2 is set at the input frequency of the proposed bandpass digital filter, independent of the filter coefficients. This can also be verified by direct substitution of Z cos 0j- jsinfl into expression (1)

followed by replacement

cos in

d.

Formula

the invention

A bandpass digital filter comprising a serially connected first multiplier, a first adder, a first delay element, a first algebraic adder, a second delay element, a second adder and a third adder, the output of which is the output of a band-pass digital filter, the second multiplier, output

H (Z)

P H. (Z)

25

KoTopoj o is connected to the non-injecting input of the first algebraic

adder, serially connected

third multiplier and second al

40

A hebraic adder, characterized in that, in order to simplify the restructuring and speed performance of a bandpass digital filter, a third and fourth delay elements and a third algebraic adder, a fourth multiplier, a fourth adder and a fourth algebraic adder, whose output co35 is connected to the input of the first multiplier, are introduced and the output of the first adder is connected to the second input of the second adder, the output of which is connected to the input of the second multiplier and through the third delay element with the investment The second input of the second algebraic adder, whose output is connected via the fourth delay element to the second input of the third adder and the 45 rotating input of the fourth algebraic adder, the second non-inverting input of which is connected to the output of the second delay element and the non-inverting input of the third algebraic adder, the inverting input of which is input digital bandpass filter and is connected to the second input of the fourth adder, the output of which is connected to

55 to the second input of the first adder, and the output of the third adder is connected to (INPUT of the third multiplier.

Editor A. Shandor

Compiled by S. Muzychuk Tehred L. Serdyukova

Order 3892/55

. Circulation 884

VNIIPI State Committee for Inventions and Discoveries at the State Committee on Science and Technology of the USSR 113035, Moscow, Zh-35, Raushsk nab. 4/5

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Corrector I. Muska

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Claims (1)

Claim A bandpass digital filter containing a first multiplier, a first adder, a first delay element, a first algebraic adder, a second delay element, a second adder and a third adder, the output of which is the output of a bandpass digital filter, and a second multiplier whose output is wedged to the non-inverting input of the first algebraic adder, connected in series • the third multiplier and the second algebraic adder, with the fact that, in order to simplify the adjustment and increased In order to speed the bandpass digital filter, the third and fourth delay elements and the third algebraic adder, the fourth multiplier, the fourth adder and the fourth algebraic adder are introduced in series, the output of which is connected to the input of the first multiplier, and the output of the first adder is connected to the second input of the second adder, output which is connected to the input of the second multiplier and through the third delay element with an inverting input of the second algebraic adder, the output of which is connected through four the fourth delay element with the second input of the third adder and the inverting input of the fourth algebraic adder, the second non-inverting input of which is connected to the output of the second delay element and the non-inverting input of the third al50 of the algebraic adder, the inverting input of which is the input of the bandpass digital filter and connected to the second input of the fourth adder, the output of which is connected to the 55 second input of the first adder, and the output of the third adder is connected to the input of the third multiplier.