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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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