To study the frequency response of first order low pass filter. Apparatus: • 741c Op Amp. • Resistors • Capacitor • Function generator • Oscilloscope • Power supply Diagram: [pic] Theory A high-pass filter, or HPF, is an LTI filter that passes high frequencies well but attenuates (i. e. , reduces the amplitude of) frequencies lower than the filter’s cutoff frequency. The actual amount of attenuation for each frequency is a design parameter of the filter. It is sometimes called a low-cut filter or bass-cut filter.
The simple first-order electronic high-pass filter shown in Figure 1 is implemented by placing an input voltage across the series combination of a capacitor and a resistor and using the voltage across the resistor as an output. The product of the resistance and capacitance (R? C) is the time constant (? ); it is inversely proportional to the cutoff frequency fc, at which the output power is half the input power. That is, [pic] [pic] Figure 1: A passive, analog, first-order high-pass filter, realized by an RC circuit PROCEDURE: Connect the circuit according to circuit diagram. • Provide ±15v to the circuit. • Provide input at pin 3 of IC through a resistor. • Connect oscilloscope at pin 6 of IC. • Observe the output on oscilloscope. Observations and calculations [pic] OUTPUT WAVEFORMS: [pic] [pic] Response at 10Khz Response at 1Khz [pic] Conclusion: • High pass filters are the filters that allow the higher frequencies to pass and block the lower frequencies. High pass filters are used in single sideband communication systems to eliminate the lower sideband. • It is to be noted that the input peak to peak voltage is maintained at 10 and we get the 18volts at the output peak to peak. So [pic] • The cutoff frequency for a high-pass filter is that frequency at which the output (load) voltage equals 70. 7% of the input (source) voltage. Above the cutoff frequency, the output voltage is greater than 70. 7% of the input, and vice versa.