RU2780811C1 - Tunable band notch filter - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: invention relates to the field of radio engineering and can be used to suppress unwanted signals (interference) in communication and radar systems, incl. in the functional units of power amplifiers. In particular cases, digitally controlled resistors or digital potentiometers can be used as these auxiliary resistors. A notch filter with a tunable bandwidth contains an input (1) and an output (2) of the device, a terminating resistor (3), a series LC oscillatory circuit (4) with the first (5) and second (6) outputs, including a frequency-setting capacitor (7) and inductance (8), wherein the first output of the terminating resistor (3) is connected to the input (1) of the device, and its second output is connected to the output of the device (2) and is connected to the first output (5) of the series LC oscillatory circuit (4). The second output of the terminating resistor (3) is connected to the output of the device (2) through the first (9) buffer amplifier, the output (2) of the device is connected through an additional voltage divider (10) to the input of the second (11) buffer amplifier, the output of which is connected to the second output (6) series LC oscillating circuit (4).

EFFECT: creation of a notch filter, which provides for bandwidth adjustment not by changing the parameters of the frequency-setting inductance 8 or capacitor 7, but by controlling the resistance of auxiliary resistors.

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Description

The invention relates to the field of radio engineering and can be used to suppress unwanted signals (interference) in communication and radar systems, incl. in the functional units of power amplifiers.

Currently, notch filters [1–8] are implemented both on the basis of operational amplifiers [2] and in the form of passive (LC) RF and microwave frequency selection devices [5–8].

Modern RF and microwave power amplifiers for communication systems with amplitude modulation have increased requirements for the level of non-linear distortion. To ensure control of the level of non-linear distortions in the operating mode, it is advisable to use the built-in power detector with the proposed notch filter, which eliminates the fundamental harmonic signal at the input of the power detector. This allows you to determine the power level of harmonic distortion. Microwave power amplifiers are most often made on the basis of GaAs technological processes, therefore, the development of circuitry for rejection filters and their active (amplifying) elements, taking into account the specifics of GaAs technological processes, is an urgent task.

The closest prototype of the proposed device is the classical notch filter of Fig. 1 published on the Practical Electronics website (URL: https://www.ruselectronic.com/passive-filters/#LC). This circuit solution is also presented in a large number of articles and specialized monographs, for example, [2,8]. It contains an input 1 and an output 2 of the device, a terminating resistor 3, a series LC oscillating circuit 4 with the first 5 and second 6 outputs, including a frequency-setting capacitor 7 and an inductance 8, the first output of the terminating resistor 3 is connected to input 1 of the device, and its second output connected to the output of device 2 and connected to the first output 5 of the serial LC of the resonant circuit 4.

A significant disadvantage of the known device of FIG. 1 is that bandwidth tuning in it can be realized only by changing the parameters or inductance 8 or capacitor 7. This limits the scope of the known RF circuit, which cannot be used as a digitally controlled IP module.

The main objective of the proposed invention is to create a notch filter, which provides for bandwidth adjustment not by changing the parameters of the frequency-setting inductance 8 or capacitor 7, but by controlling the resistance of the auxiliary resistors included in the circuit. In particular cases, digitally controlled resistors or digital potentiometers can be used as these auxiliary resistors.

The task is achieved by the fact that in the notch filter of FIG. 1, containing input 1 and output 2 of the device, a terminating resistor 3, a series LC oscillatory circuit 4 with the first 5 and second 6 outputs, including a frequency-setting capacitor 7 and an inductance 8, the first output of the terminating resistor 3 is connected to input 1 of the device, and its second the output is connected to the output of device 2 and is connected to the first output 5 of the serial LC oscillatory circuit 4, new elements and connections are provided - the second output of the terminating resistor 3 is connected to the output of device 2 through the first 9 buffer amplifier, the output 2 of the device is connected through an additional voltage divider 10 with the input of the second 11 buffer amplifier, the output of which is connected to the second output 6 of the serial LC oscillatory circuit 4.

Figure 1 shows a classic notch filter - a prototype, published, for example, on the site "Practical Electronics" (URL: https://www.ruselectronic.com/passive-filters/#LC).

In FIG. 2 shows a diagram of the claimed device in accordance with paragraph 1 and paragraph 2 of the claims.

In FIG. 3 is a diagram of the notch filter of FIG. 2 in the MicroCap simulation environment for the particular case of choosing the numerical values of inductance 8 and capacitor 7.

In FIG. 4 shows the amplitude-frequency and phase-frequency characteristics of the proposed notch filter of FIG. 3.

The tunable notch filter of FIG. 2 contains input 1 and output 2 of the device, a terminating resistor 3, a series LC oscillatory circuit 4 with the first 5 and second 6 outputs, including a frequency-setting capacitor 7 and an inductance 8, the first output of the terminating resistor 3 is connected to input 1 of the device, and its second output is connected to the output of device 2 and is connected to the first output 5 of the serial LC oscillatory circuit 4. The second output of the terminating resistor 3 is connected to the output of device 2 through the first 9 buffer amplifier, the output 2 of the device is connected through an additional voltage divider 10 to the input of the second 11 buffer amplifier, the output which is connected to the second output 6 of the serial LC oscillatory circuit 4.

In FIG. 2, in accordance with paragraph 2 of the claims, an additional voltage divider 10 is implemented on the first 12 and second 13 auxiliary resistors, the common node of which is connected to the input of the second 11 buffer amplifier.

In FIG. 2, signal source 14 is connected between input 1 of the device and the common bus of power supply 15.

The operation of the circuit of Fig. 2 and its compliance with the claimed properties is confirmed by the results of computer simulation in the MicroCap environment presented in FIG. 4. As shown in FIG. 4 by changing the resistance of the resistor R5 included in the structure of the additional voltage divider 10 in the circuit of FIG. 2 at constant values of the frequency-setting capacitor 7 and inductance 8, the bandwidth of the notch filter changes.

Thus, the claimed device has significant advantages in comparison with the prototype and can be used in frequency selection devices with digital control.

REFERENCES

1. Practical electronics: site. - URL: https://www.ruselectronic.com/passive-filters/#LC.

2. Loskutov, E.D. Circuitry of analog electronic devices: study guide / E.D. Loskutov. - Saratov: Higher education, 2016. - 264 p. - Text: electronic // Electronic library system IPR BOOKS: [website]. - URL: https://www.iprbookshop.ru/44037.html (date of access: 09/17/2021). - Access mode: for authorization. users - Fig. 8.21

3. Patent RU 2520422, 2014

4. Patent SU 1417178, 1988

5. Electric LC filters: website. - URL: http://bourabai.kz/toe/filters.htm. - Rice. 6.

6. https://www.chegg.com/homework-help/questions-and-answers/need-matlab-code-one-rlc-filter-instructions-want-lanalyzing-frequency-response-circuit-bo-q19396304

7. https://www.chegg.com/homework-help/questions-and-answers/experiment-52-rlc-filters-function-generator-figure-54-experiment-52-rlc-band-pass-filter- -q32336352

8. Modern theory of filters and their design / ed. G. Temesha and S. Mitra: per. from English. / ed. cand. tech. Sciences I.N. Teplyuk with a preface by Dr. tech. Sciences A.A. Lanne. - Publishing house "Mir", Moscow, 1977. - 560 p.

Claims (2)

1. A notch filter with a tunable bandwidth, containing an input (1) and an output (2), a terminating resistor (3), a series LC oscillatory circuit (4) with the first (5) and second (6) terminals, including a frequency-setting capacitor (7 ) and inductance (8), wherein the first terminal of the terminating resistor (3) is connected to the input (1), and its second terminal is connected to the output (2) and connected to the first terminal (5) of the series LC oscillatory circuit (4), characterized in that that the second output of the terminating resistor (3) is connected to the output (2) through the first (9) buffer amplifier, the output (2) is connected through an additional voltage divider (10) to the input of the second (11) buffer amplifier, the output of which is connected to the second output (6) series LC oscillating circuit (4). 2. A notch filter with a tunable bandwidth according to claim 1, characterized in that the additional voltage divider (10) contains the first (12) and second (13) auxiliary resistors, the common node of which is connected to the input of the second (11) buffer amplifier.

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