# Active BandPass filter

### Aim

Study of the Active Band Pass Filter and to evaluate
•       Low cutoff frequency f_L.
•     High cutoff frequency f_H.
•     3 dB Bandwidth
•     Plot the frequency response of Band Pass Filter.

### Apparatus

• Analog board of AB52.
• DC power supplies \$+\$ 12V, \$−\$ 12V from external source or ST2612 Analog Lab.
• Function generator or ST2612 Analog Lab.
• Oscilloscope Caddo 802 or equivalent.
• Digital Multimeter.
• 2 mm Patch Cords.
Theory
An electric filter is a frequency selective circuit that passes electric signals of specific band of frequencies and attenuates signal of frequencies outside this band. Depending on the type of elements used in their construction filters may be classified as passive or active filters. Elements used in passive filters are resistors, capacitors and inductors.
• Active filter consists of active components such as Op-amp, transistors with passive elements
• Procedure

- Connect Ohmmeter between Test Point 1 and Gnd. Adjust resistance value to approximately 17K Ohms by varying the potentiometer P1 to set the Low cut off frequency (\$f_L\$) at 200Hz.
- Connect Ohmmeter between Test Point 3 and Test Point 4. Adjust resistance value to approximately 800 ohms by varying the potentiometer P2 to set the High cut off frequency (\$f_H\$) at 20 KHz.
- Connect + 12V and − 12V DC power supplies at the indicated position from external source or ST2612 Analog Lab.
- Switch ‘On’ the Power Supply.
- Connect a sinusoidal signal of amplitude 1V (p-p) of frequency 1 KHz to the Test Point \$V_{in}\$ of Band-Pass Filter from external source or ST2612 Analog Lab.
- Observe output on Oscilloscope by connecting Test Point \$V_{out}\$ out to Oscilloscope.
- Increase the frequency of input signal step by step and observe the effect on output \$V_{out}\$ on Oscilloscope.
- Decrease the frequency of input signal step by step and observe the effect on output \$V_{out}\$ on Oscilloscope.
- Tabulate values of \$V_{out}\$, gain, gain (dB) at different values of input frequency shown in Observation Table.
- Plot the frequency response of Band-Pass Filter using the data obtained at different input frequencies.
- Perform the same procedure at different Cut-off frequencies.