The low-pass filter is designed to obtain an amplitude-frequency response in which the attenuation is directly proportional to the frequency. Such filters are built using passive elements: capacitors, resistors and inductors.
Instructions
Step 1
To assemble the simplest low-pass filter, connect a resistor between its input and output, and a capacitor between the output and the common wire.
Step 2
Convert the values of the elements into SI units: resistance in ohms, capacitance in farads. Calculate the cutoff frequency of the simplest filter using the formula: F = 1 / (2πRC), where F is the frequency (Hz), π is the number "pi", 3, 1415926535 (dimensionless value), R is the resistance of the resistor (Ohm), C is the capacitance capacitor (F).
Step 3
To change the characteristic of the filter, adjust the resistor and capacitor values. This can be done empirically, by removing the frequency response after each alteration, or by substituting various values into the formula and calculating the result each time. With an increase in the resistance of the resistor, the beginning of the characteristic descends along the vertical axis to the origin, and with an increase in the capacitance of the capacitor, the angle between this line and the abscissa axis increases (if the latter characterizes the frequency in the graph).
Step 4
Some low-pass filters have variable response. An example of such a device is a tone control. To collect it, include another resistor in the filter - a variable. Connect it between the bottom plate of the capacitor and the common wire.
Step 5
Resistors used in low-pass filters are useful in weak signal processing circuits. If the filter is located after the power amplifier, their use is undesirable, since it leads to a decrease in the efficiency. If you are developing a device for splitting the signal spectrum into bands for feeding to several speakers (crossover), use chokes in its low-pass filters instead of resistors. At the same time, capacitors can be excluded from such filters - they are useful in high-pass filters.
