Band-pass lc-filter with controlled transmission bandwidth

FIELD: physics.

SUBSTANCE: band-pass LC-filter with controlled transmission bandwidth which consists of first and second inductor coils whose first leads are connected to a first capacitor and a third inductor coil whose second leads are connected to a common bus, also contains fourth and fifth inductor coils, second and third capacitors and two varicaps, where the fourth inductor coil is connected to the input potential terminal of the filter and the second lead of this coil is connected to first leads of the second capacitor and the first varicap. The fifth inductor coil is connected to the output potential terminal of the filter and the second lead of this coil is connected to first leads of the third capacitor and the second varicap. Second leads of the varicaps, second and third capacitors are connected to the common bus.

EFFECT: control of transmission bandwidth during operation.

2 dwg

 

The invention relates to electronics and can be used in professional radio receiving devices, measurement techniques.

In modern transceiver devices trunk radio uses different types of selectors, vypolnennye using band-pass LC-filter for suppression of radio interference and the formation of the spectra of the radiated signals. As bandpass filters used several well-known schemes, of which the closest to the proposed solution is a system comprising first and second inductors, the first conclusions which are interconnected and also connected to the third inductor and the first capacitor, the second set of conclusions which are connected to a shared bus [1], C, table 3.

This option scheme is selected as a prototype, because it has a higher attenuation at frequencies above the bandwidth (in comparison with other parts of bandpass LC filters).

The disadvantage of this filter is that it has the first class on the characteristic impedance and the first class on attenuation, and can only be used to implement a constant bandwidth.

The objective of the invention is to improve the Squareness ratio of the amplitude-frequency characteristics of the filter and RA is the expansion of its functionality, namely regulate its bandwidth during operation.

The problem is solved in that in the filter containing the first and second inductors, the first conclusions which are interconnected and also connected to the third inductor and the first capacitor, the second the third coil and the capacitor are connected with a common bus, inputs of the fourth and fifth inductors, second and third capacitors, the first and second varicaps are given, while the fourth inductor is connected to the input potential terminal of the filter, the second terminal of this coil is connected with the second output of the first inductor, the second capacitor and the first VariCam, the fifth inductor connected to the output potential terminal of the filter, the second terminal of the fifth inductor connected to the second output of the second inductor, a third capacitor and a second Maricopa, main conclusions of the second and third capacitors, the first and second varicaps are given connected to a common bus.

Apostolically analysis shows that the proposed solution differs from the prototype in that the device additionally introduced the fourth and fifth inductors, second and third capacitors, the first is the first and the second varicaps are given, and fourth cause inductance is connected to the input potential terminal of the filter, the second terminal of this coil is connected with the second output of the first inductor, the second capacitor and the first VariCam, the fifth inductor connected to the output potential terminal of the filter, the second terminal of the fifth coil is connected with the second output of the second inductor, a third capacitor and a second Maricopa, main conclusions of the second and third capacitors, the first and second varicaps are given is connected to the shared bus.

When the comparison of the proposed solutions not only prototype, but also with other known technical solutions in science and technology, not found solutions with similar characteristics.

The figure 1 shows the electric diagram of the proposed device. Bandpass LC filter with adjustable bandwidth consists of the first inductor 1, the second inductor 2, the first conclusions which are interconnected and connected to the first conclusions of the third inductor 3 and the first capacitor 4, the latter findings are connected to a common bus, the fourth inductor 5 is connected to the input potential terminal of the filter, the second conclusion of this inductance is connected to the second output of the first coil and the first conclusions of the second capacitor 6 and the PE the first varicap 7, the fifth inductor 8 is connected to the potential output terminal of the filter, the second terminal of this coil is connected with the second output of the second coil 2, with the first findings of the second capacitor 9 and the second varicap 10, the second terminals of the capacitors 6 and 9 and varicaps are given 7 and 10 are connected with a common bus.

The device operates as follows.

Part of a filter consisting of inductive elements 1, 2, 3 and capacitor 4, 6, 9, is a symmetrical circuit (coils 1 and 2, as well as the capacitors 6 and 9 are chosen equal) and in accordance with the bisection theorem Bartlett [2] str÷174 can be represented in the form of a symmetrical bridge equivalent, in whose branches included reactance Zaand Zin. Frequency dependence of the impedance Zaand Zinshown in figure 2A, figure 2B shows the frequency dependence of the characteristic impedance of this filter.

As can be seen from the graphs of figure 2, the bandwidth of the filter is located between the frequencies ω1and ω3the filter has a second-class resistance and the second class is the attenuation, while prototypes have first class on attenuation and first-class resistance. Compared with the prototype, it has a greater attenuation in the band of delaying and steeper slopes of the attenuation characteristics of the business in Addition, the characteristic phase shift at frequency ω2equal to π radians. This, in turn, means that the choice of loads of the filter on the inlet and outlet arbitrarily, but are equal to each other, working on the attenuation of the filter at frequency ω2will be zero (see formula 4.1 and 4.2 p.194 [3]). Therefore, in this scheme, the simultaneous change of the load resistance on the input RH1and the output RH2provided that RH1=RH2=R0<Z0(here Z0the characteristic impedance of the filter at frequency ω2see figure 2a) reduces the bandwidth of the filter due to the increase of the Z0/R0(which also follows from formula 4.1 and 4.2 of [3]) when the offset frequency ω2. This position is verified experimentally, thus reducing the bandwidth of the filter is almost proportional to the ratio Z0/R0.

In order to install the required load resistance of the filter at constant values of the external load resistances in the device, which operates the filter on the inlet and outlet of the device put the links of the low-pass filters (LPF), each of which is made in the form of coil inductance and varicap. When the capacitance of varicap changes the cutoff frequency of LPF and changes the input weather resistance is compared with the U-shaped side low-pass filter.

It has been found that the filter frequency to 30 MHz with a bandwidth of 1 MHz when the change in capacitance low-pass filter 6 to 21 pF when the inductance of each 2,4 mH bandwidth decreased 9 times.

Thus, changing the value of the control voltage on the varicaps are given in the proposed scheme filter in a fairly wide range to adjust the bandwidth.

Sources of information

1. Černá HI inductive coupling and transformation in electric filters. Svyazist, 1962.

2. Guillemin E.A. Synthesis of passive circuits. Ed. "Communication", M., 1970.

3. Beletsky A.F. Theoretical foundations of electrical communication means, ch. III. Synthesis of reactive two-port and electrical filters. Svyazist, 1959.

Bandpass LC filter with adjustable bandwidth, comprising first and second inductors, the first conclusions which are connected between themselves and with the third inductor and the first capacitor, the second the third inductor and the first capacitor connected to a common bus, wherein the circuit device further introduced the fourth and fifth inductors, second and third capacitors, the first and second varicaps are given, while the fourth inductor is connected to the input potential of the terminal device, and a second output is coupled to the second output of the first inductor, with the first findings of the second capacitor and the first varicap, the fifth inductor connected to the output potential of the terminal unit and the second output is connected with the second output of the second inductor to the first output of the third capacitor and the first output of the second varicap, main conclusions of the second and third capacitors, the first and second varicaps are given connected to a common bus.



 

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