SU1233263A1 - Band-pass filter - Google Patents

Abstract

The invention relates to radio engineering and can be used in radio receiving and radio measuring devices as a narrowband filter. The purpose of the invention is to reduce the level of intrinsic noise. The device contains an adder 1, a wideband band-pass filter (D1PF) 2, two attributes (A) 3, 8, a subtractor 4, controlled by A 5, an integrating filter 6 and a phase discriminator (PD) 7. The input signal and interference mixture in adder 1 is added with an output voltage of A 3. This total voltage goes to one input of the subtractor 4 and through the serially connected SPF 2, controlled by A 5 and A 8 to the other input of the subtractor, body 4. The output voltage of the subtractor 4 through series-connected PD 7 and integrating filter 6 is fed to the control The ny input of the controlled A 5, the output voltage of which is fed to the input A3, to the other input of the PD 7 and to the output of the device. The goal is achieved by the introduction of an adder and A 8. 2 Il. W% 3 OW 00 ON 00 iNd about: with

Description

Fig. /

The invention relates to radio engineering and can be used in radio receivers as well as in radio measuring equipment as a narrowband filter.

The purpose of the invention is to reduce the intrinsic noise level of the band pass filter.

Figure 1 shows the functional diagram of the bandpass filter; Fig, 2 is an example of the implementation of the input part of the bandpass filter when connected directly to the antenna-feeder path,

The device (FIG.) Contains the sum of a torus I, a wideband band-pass filter 2,, first attenuator 3, subtractor (jyn equal attenuator 5, integrating filter 6, phase discriminator 7 and second attenuator 8,

The bandpass filter works the same way.

The input signal and noise mix in the adder .1 is added to output 1 to 1M of the attenuator 3 voltage. The resulting total voltage is fed to the input of the wideband bandpass filter 2 and to the input of the subtractor 4, the output voltage of the filter 2 through the controlled attenuator 5 postpattates to the bandpass output filter, to the attenuator 3, to the phase discriminator 7 and through the attenuator 8 to the input of the subtractor 4, the output voltage of which goes to the second input of the phase discriminator 7, the output voltage of the phase discriminator 7 through the integral s filter 6 is supplied to a control input of the controllable attenuator 5.

The transfer function of the bandpass filter is

“:) -. i-bW-iijIM-XKr

and

where K is the transfer functti sum

torus 1;

Kj (jo) is the transfer function of a wideband bandpass filter 2 5

K, .K ,. - transfer functions corresponding to 9

the first attenuator 3 and a par with its attenuator 5,

When used as a broadband bandpass filter 2 single resonant amplifier with a transfer function

V y k

K, (jto) - where CE g 2Q - -1J-l

generalized detuning; Q, fd- quality factor and tuning frequency of the resonant amplifier;

f is the frequency of the input signal;

 transmission coefficient at the resonant frequency, we have

K (jco) fl№ --.- i. , (2)

i,.

 .

It can be seen from formula (2) that the equivalent Q-factor of the bandpass filter is increased compared with the wideband bandpass filter 2 in

Tk; k; k; t p. The limiting possibilities for narrowing the bandwidth of a bandpass filter are determined by the condition:

1- K, K, K 1. (3) This condition simultaneously P1No determines the stability limit of the positive feedback loop. In fulfillment of the conditions

TO,

  L

(four)

narrow bandwidth is provided.

The stabilization of the relation (4) is implemented by the tracking system, the sensitive element of which is the phase discriminator 7, and the controlling element is the integrating filter 6. At the tuning frequency of the wideband

2oi 0 and, as follows from (2)

KiSaK.

Pic 17

 8bJX in

1-K, K, K5

(five)

Subtractor output voltage 4

(l-KiK Ke) K ,,. J. (5)

and and,

i-KjK Ky

where K is the transfer function of the second attenuator 8, From expressions (5) and (6) it follows that at. the phases of the voltages and U at the inputs of the phase discriminator 7 coincide j and, with I, are opposite. In the first case, the signal at the output of the phase discriminator 7

has a positive sign, the signal at the output of the integrating filter 6 increases, which leads to an increase in the transmission coefficient K of the controlled attenuator 5, and, consequently, of magnitude. In the second case, on the contrary, K and are reduced. Thus, the steady state of the servo system is observed when the condition

.5 -k;

(7)

When connecting a band-pass filter directly to the antenna-feeder path, the preferred implementation of the adder 1 and the first attenuator 3 is shown in Fig. 2, where it is indicated: ЕЯ - antenna emf; Sd, respectively, the capacity of the antenna and

C. connecting cable; C in; and

The input and feedback capacitances are respectively. The transmission coefficient of the first attenuator 3 is equal to

CjDc ..

TO

 C + CBV + C „p + C

The capacitance values of the capacitors C ,, and Co are chosen so that the depletion

to bake

the fulfillment of the condition necessary to prevent the input signal from passing directly to the output of the bandpass filter (through the first attenuator 3), in this case, respectively, К „« 1.

Fyg.2

VNIIPI Order 2781/56 Circulation 816

Random polygons pr-tie, Uzhgorod, st. Project, 4

The intrinsic noise level of a bandpass filter connected to the antenna-feeder path (figure 2) is determined by the noise level of wideband bandpass filter 2, which allows the use of this bandpass filter in radio receivers with increased sensitivity.

Claims (1)

Invention Formula Bandpass filter containing broadband bandpass filter output. which is connected to the input of the controlled attenuator, and sequentially connected subtractor, phase discriminator and integrating filter, the output of which is connected to the control input, a controlled attenuator, as well as the first attenuator, characterized in that, with a value of less than X noise, a second attenuator and adder are added, the first input which is the input of a bandpass filter, and the output is connected to the input of a broadband bandpass filter and to the first input of the subtractor, the second input of which is connected to the second input of the phase discriminator controlled attenuator and through the first attenuator t with the second input of the adder, while this controlled attenuator is the output of a bandpass filter. Subscription