RU2525120C2 - Multichannel filtration unit - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to radio electronics and can be used as a preselector stage. Proposed unit comprises differential transformer. Primary of the latter has two output terminals. Differential secondary has tree output terminals. First group of N band filters is connected to first output of differential winding. Second group of N band filters is connected to third output of differential winding. Outputs of band filter of first and second groups make the outputs of filtration unit. Note here that first and second capacitors are connected to first output of transformer primary. Second output of first capacitor is connected to input potential terminal of filtration union. Second outputs of second capacitor and primary are integrated with common bus. Second output of differential winding is connected to third capacitor with its second output connected to common bus.

EFFECT: decreased working attenuation in preselector bandwidth.

1 dwg

Description

The proposed device relates to electronics and can be used as a preselector in professional radio receivers.

In the mainline radio communication technology, when implementing preselectors, a differential system is often used, which consists of a differential transformer, a balanced resistor connected to the middle terminal of the secondary differential winding, and two groups of bandpass filters connected to the differential winding, the filter outputs are the outputs of the preselectors [1].

Such a device provides simultaneous signal processing on each of several channels and a high level of isolation between the filters of the first and second groups. This device is the closest to the proposed technical solution and is selected as a prototype.

The disadvantage of the prototype device is that the attenuation introduced by the differential system in the pass bands of each of the filters can reach 5 ÷ 6 dB or more in real conditions.

The objective of the invention is to reduce the operational attenuation in the passband of the preselector.

The problem is solved in that in the known circuit of a multi-channel filtering unit containing a differential transformer, the primary winding of which has two leads, the secondary differential winding has three leads, the first group of N bandpass filters is connected to the first terminal of the differential winding, and the third differential terminal is connected windings connected to the second group, consisting of M band-pass filters, the outputs of the band-pass filters of the first and second groups are the outputs of the filtering unit, in addition the first, second and third capacitors are driven, while the first and second capacitors are connected to the first output of the primary winding of the differential transformer, the second output of the first capacitor is connected to the input potential terminal of the filtration unit, the second conclusions of the second capacitor and primary winding are connected to the common bus, the second differential output the windings are connected to a third capacitor, the second terminal of which is connected to a common bus.

Comparative analysis shows that the claimed technical solution differs from the prototype in that the first, second and third capacitors are additionally introduced into the device, while the first and second capacitors are connected to the first terminal of the differential transformer primary winding, the second terminal of the first capacitor is connected to the input potential terminal of the unit filtering, the second terminals of the second capacitor and the primary winding are connected to a common bus, the second terminal of the differential winding is connected to the third condensate yell, a second terminal of which is connected to the common bus.

When comparing the claimed device not only with the prototype, but also with other technical solutions known in science and technology, no solutions were found that have similar characteristics.

The drawing shows an electrical diagram of the proposed device. The filtering unit consists of a differential transformer 1, the first 2 and second 3 capacitors are connected to its primary winding, the first group of bandpass filters 4 is connected to the first output of the differential winding, the second group of bandpass filters 5 is connected to the third output of the differential winding, and the second differential winding is connected to a third capacitor 6, the second terminal of which is connected to a common bus. The second terminal of the first capacitor is connected to the input potential terminal of the device, and the second terminal of the second capacitor and the second terminal of the communication winding are connected to a common bus, the outputs of the bandpass filters are independent outputs of the filtering unit.

The device operates as follows.

In [1], a differential system was considered operating in the mode when the balanced resistance R ₀ is equal to the resistance of the signal source R. Provided that all windings of the differential transformer have the same number of turns, the input resistance of the system from the side of connecting the filters of the first group Z ₂ will be determined the ratio

$$Z_2=\frac{\mathrm{four}{R}_{0}R+R{Z}_3+R_0{Z}_3}{R+R_0+Z_3},\text{where (1)}$$

Z ₃ is the input resistance of the system from the side of turning on the filters of the second group, R ₀ is the balanced resistance, R is the resistance of the signal source.

This mode of operation of the system ensures independence of the resistance Z ₂ and Z ₃ from each other, to match the bandpass filters connected to the output of the system, they must have input resistances close to twice the resistance of the signal source (Z ₂ = Z ₃ = 2R). The working attenuation that the differential system introduces, provided that the transformer is ideal, is 3 dB.

In the presented device, the operating mode of the differential system is used, when the resistance Z ₂ = 4R, Z ₃ = jωL ₀ is inductive. The balance resistance R ₀ in accordance with the formula (1) we get equal

$$R_0=R\frac{\mathrm{four}R+j3\omega L_0}{j\omega L_0}=3R+\frac{\mathrm{four}{R}^2}{j\omega L_0}(2)$$

.As follows from (2), the balanced resistance is realized by the serial connection of the 3R resistor and the capacitance numerically equal $$C_0=\raisebox{1ex}{$L_0$}\!\left/ \!\raisebox{-1ex}{$\mathrm{four}{R}^2$}\right.$$

.

It can be shown that the transfer function module (by emf) in the direction from the signal source to the first output of the system loaded with resistance Z ₂ = 4R will be determined by the expression

$$|\; |\; |T|\; |\; |=\frac{\sqrt{64+\mathrm{twenty}Q+Q^2}}{2\left(\mathrm{four}+Q^2\right)},\text{where (3)}$$

- приведенная добротность индуктивности L₀. $$Q=\raisebox{1ex}{$\omega L_0$}\!\left/ \!\raisebox{-1ex}{$R$}\right.$$

- reduced quality factor of inductance L ₀ .

, а рабочее затухание а_р≤0,7 дБ.If Q≤1, then $$|\; |\; |T|\; |\; |\ge 0.92$$

, and the working attenuation a _p ≤0.7 dB.

In the real scheme of the filtering unit, when the input impedance of the filters of the second group is inductive at the frequencies of the passbands of the filters of the first group, the working attenuation introduced by the differential system at these frequencies can be less than 3 dB. If the filters of the 1st and 2nd groups have characteristic impedance for which it is inductive in the delay band, the use of this mode of operation allows to improve the transmission coefficient of the filters of both groups in their pass bands.

We also note that when modeling a preselector operating in this mode, the active part of the balance resistance had a slight effect on the preselector parameters, since the capacitive component in the circuit R ₀ prevails over the active one, and a resistor of 3 R can be excluded. In addition, the average value of ωL ₀ in real circuits is less than 0.5 R, and, therefore, Q≤0.5.

The proposed device also introduced an additional half-bandpass filter, consisting of the first 2 and second 3 capacitors and an inductor connected in parallel with the second capacitor. The half-link band is designed so that its bandwidth is significantly greater than the operating bandwidth of the preselector. The inductance coil of this filter, connected to an ideal differential transformer, shunts it and allows the use of a differential transformer with more convenient parameters for practice.

During experimental verification of the operation of the proposed device, it was found that in the frequency range 30 ÷ 80 MHz it is possible to obtain filters whose working attenuation in the passband does not exceed 1.5 ÷ 2 dB with the quality factor of the transformer and inductance coils included in the bandpass filters 100 ÷ 150 units ., while the attenuation in the delay bands is reduced compared to the attenuation of these filters operating outside this system.

The source of information

1. Pleshkov N.G., Zingerenko A.M., Lavrish B.C., Klimovich V.F., Isakson B.K. Telecommunication technology. Ed. VKAS, Leningrad, 1951, pp. 101-105, 277-279.

Claims (1)

A multi-channel filtering unit containing a differential transformer, the primary winding of which has two leads, the secondary differential winding has three leads, the first group of N bandpass filters is connected to the first terminal of the differential winding, and the second group of M band winders is connected to the third terminal of the differential winding filters, the outputs of the bandpass filters of the first and second groups are the outputs of the filtering unit, characterized in that to the first output of the primary winding of the differential About the transformer, the first and second capacitors are connected, the second terminal of the first capacitor is connected to the input potential terminal of the filtration unit, the second terminals of the second capacitor and the primary winding are connected to the common bus, the second terminal of the differential winding is connected to the third capacitor, the second terminal of which is connected to the common bus.