SU1434538A1 - Digital filter - Google Patents

Abstract

The invention relates to radio engineering and m. used in multi-tier filters. The purpose of the invention is to simplify the center frequency tuning. The digital filter contains five su 4mators 1,3,4,6,7, two elements 8.9 delay, four multipliers 12,15,13,14, inputs 16,17, outputs 18,19, To achieve the goal, two more are entered adder 2.5 and jjba element 10.11 delay. The digital filter can be used as a notch filter or a bandpass filter. The transition from one type of filter to another is accomplished by selecting the appropriate input and output of the device. 2 Il.

Description

RF Entry

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I Invention retracts to radio technology and can be used in multi-link filters.

The purpose of the invention is to simplify the center frequency tuning.

FIG. 1 shows an electrical circuit diagram of a digital filter; in fig. 2 - digital filter graph.

The digital filter contains the first 1, the sixth 2, the second 3, the third 4, the fifth 5, the fourth 6 and the fifth 7 total piii, the first 8, the second 9, the third 10 and the fourth 11 delay elements, the first 12, the third 13, the fourth 14 and the second 15 multipliers, the first 16 and the second 17 inputs and the first 18 and second 19 outputs.

The digital filter works as follows.

: If the digital filter uses B1 as a notch filter, then at low frequencies, where the change of signals within one or even two periods of quantization is very small, the transfer coefficients of the first B, second 9, third 10 and fourth 14 delay elements can be | one. The value of the signal at the output of the sixth adder 2 will mainly be determined by the coefficient. The transmissions in the following branches are: first 1 adder 1 — the first delay element 8 — second. adder 3 - the second element 9 for dfrzhki - the third adder 4 the third 3jiieMeHT 10 delay - the fourth ele 11 delay - the fourth sum is 6; the third adder 4 is the fourth adder 6; the sixth adder 2 - the first multiplier 12 - the second adder 3 - the second delay element 9 - the third adder 4 - the third delay element 10 - the second multiplier 15 the sixth adder 2.

Elementary summation over the above branches m gives a total transfer coefficient, approximately equal to one.

At high frequencies (close to half the quantization frequency), the coefficients of the first 8, second 9, third 10, and fourth 11 delay elements tend to minus one. The summation of the transmission coefficients for the indicated branches m and in this case gives the total coefficient, the value of which is approximately equal to one.

At medium frequencies, due to the phase shift in the first 8, second 9, third 10 and fourth 11 delay elements, the depth of frequency-dependent negative feedbacks increases due to branches: the second multiplier 15 the seventh adder 5 the fourth multiplier 14 the third adder 4 second multiplier 15 - seventh adder 5 - fourth multiplier 14 - first adder 1, second multiplier 15 - seventh adder 5 - third multiplier 13 - third adder 4, second multiplier 15 seventh adder 5 - third multiplier 13 - sixth cyiviMHTop 2 - first multiply Tel 12 - second adder 3, a result medium frequency attenuation occurs filter gain, but at some frequency, ijoTopart determined by the values of the coefficients of the first 12 and second multipliers 15, it becomes equal to zero. The steepness of the frequency response of the filter is determined by the degree of compensation of the samples at the output of the fourth adder 6 by changing the values of the coefficients of the third 13 and fourth 14 multipliers, which determine the notch height. Thus, the output of the fourth adder b is the output of the notch filter.

I

If a digital filter is used

As a band-pass filter, taking into account the above X approximations, the transmission coefficient at both low and high frequencies (up to half the quantization frequency) will be mainly determined by the four branches ЕЕ: the first adder 1 - per, - the delay element 8 is the second adder 3 — the second delay element 9 — the third adder 4 — the third delay element 10 — the fourth delay element 11 — a five adder 7; first input 16 - third adder 4 - fifth adder 7 second input 17 - third. adder 4 - the third delay element 10 - the fourth delay element 11 - the fifth adder 7-, the first adder 1 - the first delay element 8 - the second adder 3 - the second delay element 9 - the third, the adder 4 - the fifth adder 7. Elementary summation over the above branches m both at low and at high frequencies

gives the total transmission coefficient1), and the transmission patient is approximately zero. This is due to the fact that at the inverting and non-inverting inputs of the fifth adder 7 at the considered frequencies the signal samples are approximately equal in amplitude and practically compensate each other,

When considering mid frequencies, the -) frequency response for a bandpass filter will be determined by the same frequency-dependent feedback as in the case of a notch filter. The steepness of the frequency response of the bandpass filter

pf 21-2Z + Z

1 -2od (2A + B) (2A L) + 2A + B-1) (.2A-B) + (1 -2V) Z

g

Q j

This is achieved by the degree of compensation of the samples at the output of the fifth adder 7 by changing the values of the coefficients of the third 13 and fourth 14 multipliers. The central frequency is then controlled by two identical first 12 and second 15 multipliers.

Thus, the output of the fifth adder 7 is the output of the bandpass filter.

The transfer functions of the digital filter found using the graph (Fig. 2) in the Z-dart are:

-four

l-AciZ + 2Z -4ftLZ Vz

IRF () 1-2oi (2A + ByZ-4-2 (2Aci42A + B-) Z

-2ciC2A-B) Zoi, is the multiplication factor of the first 12 and second 15 multipliers;

B - multiplication factors

third 13 and fourth 14 multipliers,

Claims (1)

Invention Formula . A digital filter comprising in series the first torus, the first delay element, the second adder, the second delay element, the third adder and the fourth adder, the fifth adder, the output of which is the first output of a digital filter, the first multiplier, the output of which is connected to the second input of the second the second multiplier, the output of which is connected to the subtractive input of the fourth adder, the third multiplier, the output of which is connected to the second summing input of the third adder, and the fourth multiplier, ichayuschiys in that, in order to simplify the center frequency adjustment, it administered serially connected third delay element having an input cos dinene with a subtracting input of the p adder, and a fourth delay element. -2ciC2A-B) Z + (T-2B) Z5 0 5 0 5 0  the output of which is connected to the third input of the fourth adder, with the summing input of the fifth adder and the first subtractive input of the first adder, the first summing input of which is connected to the subtractive input of the third adder and is the first input of the digital filter, and the second subtractive input is connected to the third summing input of the third adder and connected to the output of the fourth multiplier, the sixth adder, the first subtractive input of which is connected to the second summing input of the first adder, with the fourth summing input The third adder is the second input of the digital filter, the second is subtracted. the input is with the output of the third multiplier, and the output is connected to the input of the first multiplier, as well as the seventh adder, the summed input of which is connected to the output of the second multiplier, the subtracting input is connected to the fifth the input of the third adder and the output of the fourth delay element, and the input connected to the inputs of the third and fourth multipliers, while the output of the fourth adder is the second output of the digital filter. B code L (R ffljfXffdPijo 2 ГI f /) (--- el.L) (Pus. 2