An active LC band pass filter includes a single LC pair and a plurality of active amplifiers providing a number of separate resonance circuits.

The active amplifiers compensate ohmic losses, high frequency skin effects, and high frequency radiation. Each circuit has a resonance frequency that is adjustable by changing only the parameters of one of more active amplifiers. The filter has very high adjustable quality value Q, very low shape factors S, a relatively high signal-to-noise ratio, and a very large voltage gain that increases with frequency. High frequency performance is not affected by the quality of the LC pair, being limited only by the high frequency performance of the amplifier components. Also disclosed is a method for processing an electronic signal using the active LC band pass filter.

The present invention relates to a band pass filter comprising of active components and L, C elements, or an active L (inductance) C (capacitance) band pass filter, and more particularly to an active LC band pass filter, which, under high frequency, improves the Q value (quality factor), selectivity (i.e. shape factor) and voltage gain of a loop, and which uses an inductor-capacitor pair for the tuning of selected frequencies from single tuning, dual tuning to multiple tuning, and in which change of tuning frequency can be made easily. the active LC band pass filter of the present invention has a high frequency performance that is no longer determined primarily by the parameters of the L, C elements but by the frequency characteristics of the amplifier component. The circuit can maintain superior performance as long as the amplifier is able to operate properly under the operating frequency.

The active LC band pass filter wherein said active components are inserted into a resonance circuit comprising LC in serial or parallel connection to compensate for the loss of resonance energy in said resonance circuit at high frequency so that said resonance circuit has improved resonance performance, higher Q value, higher selectivity, better signal-to-noise ratio, and increased output voltage amplification power. The circuit output voltage amplification increases as the working frequency increases.

In a heterodyne wireless receiving system, the gain at the high-frequency stage is generally designed to be small. The general practice is to put the primary gain task on the intermediate frequency amplification of the fixed frequency, so that the integrated system can work stably, to satisfy the gain requirement of the integrated system. In order to improve the sensitivity of the integrated system, a common practice is to use a large antenna or add an antenna amplifier or, in a scenario that is technically more complex, use a double-resonance amplifier made of two variable capacitance diodes with electric tuning at the input stage to have small-power amplification of the high frequency. It is for this reason that a high-performance stable input unit with high voltage gain, good selectivity, powerful noise suppression capability and high sensitivity, wherein multiple independent-tuning sub-channels can be made easily, is good for both wired and wireless receiving systems. Such input unit is suitable for wideband transmission with multiple sub-channels. The active LC resonance amplifier described above is an idea unit.

Generally, a passive band pass filter formed by passive serial or parallel LC resonance has a circuit Q value that will decrease as the work frequency increases such that the resonance performance of the circuit degrades. This degradation can be primarily attributed to the influence of radiation emitted by the circuit connection wire, circuit elements and components, as well as the skin effect of the circuit when working under high-frequency conditions. In such conditions, one will see an increase in the ohm loss of the circuit. The capacitor will consume ohms and distribute inductors in addition to eliminating its capacitance and inductance characteristic. The inductor will consume ohms and distribute capacitors in addition to eliminating its inductance characteristic and ohm loss. The consumption will increase when the work frequency increases, leading to degradation in the quality of the circuit.

The results of analysis of the active LC band pass filter of the present invention using our theory are supported by experiments. An example of frequency response curve of the dual resonance at the main frequency of 765 kHz by using an ordinary terylene capacitor to connect in series with an ordinary hollow capacitor made of a singe strand of thin enameled copper wire available in the market. In this experiment, the input is 0.95mV and output is 2776mV. Therefore, the voltage amplifying power is 2922, i.e. voltage gain is 69dB. The measured bandwidth is BW0.7 = 12 kHz at -3dB and is BW0.1 = 117 kHz at -20dB. The loop has quality factor of Q=232 and shape factor of S=9.7, which is very difficult to achieve with a single tuning loop made of a pair of passive L and C.

It is evident that the resonance unit made of the active LC filter of the present invention can be directly used to replace the original passive LC resonance unit in the input unit of a superheterodyne receiving system. This simple replacement can significantly improve the receiving sensitivity and selectivity as well as SNR of the receiving system, without changing the original layout of the superheterodyne receiving system. The receiving sensitivity of a receiving system depends only on the SNR of the system, which is mainly determined by the performance of the receiving system at the very initial stage. Amplifications at subsequent stages after the first stage amplifying unit do not have much effect on improvement of the SNR of the first stage unit. This simple improvement will dramatically improve the receiving performance of a superheterodyne receiving system. Of course, other types of wireless communication mobile phones can also use the active LC resonator as a high-frequency amplifying unit to be connected immediately following the antenna to significantly increase their receiving sensitivity, narrowing the distance between network stations, reduce the number of network stations and reduce the amount of cellular phone communication frequency radiations to cellular phone users which in turn reduce the risk of damage to users due to exposure, if any. All of these are most simple, convenient, direct applications where best results can be achieved most easily.
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