SU441640A1 - Band-pass filter - Google Patents

Description

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The invention relates to radio engineering and can be used in radio engineering devices, in particular, in telemetry for the purpose of switching information channels, in automation as a relay circuit with a frequency selective effect.

Known bandpass RC-filter containing a double T-shaped bridge.

A disadvantage of the known filter is that it is not possible to obtain a pulse voltage at the output in a narrow frequency band.

The purpose of the invention is to obtain a pulse output in a narrow frequency band.

This goal is achieved by introducing a Schmitt trigger into the filter, with two T-bridge resistors connected in series being simultaneously part of the base divider of the first Schmitt trigger transistor, and the midpoint of the bridge is connected through a capacitor to a common power supply bus.

The drawing shows a schematic diagram of the proposed band-pass RC filter.

The band-pass RC filter with a pulse output on the Schmitt trigger is made on transistors 1 and 2. The series-connected resistors 3 and 4 of the double T-bridge connected between the collector and the base of transistor 1 are part of the base divider of transistor 1 consisting of resistors 3 , 4 and 5. The midpoint of resistors 3 and 4 is connected through a capacitor 6, which is an element of a double T-shaped bridge, to a common power supply bus. The input signal is fed through a resistor 7 (which is an element of a double T-shaped bridge, which is fine tuned to the selected frequency) connected to the midpoint of two capacitors 8 and 9 connected in series (elements of a double T-shaped bridge) that are connected in parallel to the resistors 3 and 4. An output signal is output from the collector 10 from the collector of transistor 2.

The scheme works as follows.

At the initial moment when power is applied, transistor 1 is in the ajar state due to bias, which is determined by the base divider consisting of resistors 3, 4 and 5. Transistor 2 is open. When a sinusoidal signal of a varying frequency between the collector and the base of transistor 1 is fed into the input through resistor 7, deep negative AC feedback is applied, which is carried out through resistors 3, 4 and capacitors 8, 9, which are elements of a double T-shaped bridge and there is no signal at the output of the circuit. As the frequency approaches

the signals to the natural frequency of the double T-shaped bridge, which is tuned by resistor 7, negative feedback decreases, and at a frequency close to the natural frequency of the double T-shaped bridge, it becomes so small that a Schmitt trigger is triggered, and further The physical process of the Schmitt trigger occurs normally. As the input frequency of the double T-bridge's own frequency passes and the negative feedback loop is removed from it, the alternating current loop is restored, and at a certain OOS depth, a sharp (relay) drop to the output pulse signal is detected at the circuit output.

The output pulse signal is removed from the collector of transistor 2 through a capacitor 10.

Subject invention

A band-pass RC filter containing a double T-bridge, characterized in that, to obtain a pulse output in a narrow frequency band, a Schmitt trigger is inserted into the filter, with two resistors connected in series in the above-mentioned T-bridge the first transistor of the 1Lmitt trigger, and the midpoint of the bridge is connected via a capacitor to a common power supply line.

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