Aim: Designing a First Order High pass filter using op amp.
Apparatus Required: 741 IC, Multimeter, CRO, Dual power supply (15-0-15 V), Resistors, Capacitor, and connecting wires.
Theory: A first-order active high-pass filter is an electronic circuit designed to pass high-frequency signals while attenuating low-frequency signals. Similar to the low-pass filter, it consists of an active element, typically an operational amplifier (op-amp), combined with passive components such as resistors and capacitors. This type of filter is called “first-order” because it provides a roll-off rate of +20 dB/decade or +6 dB/octave.
Working Principle:
The input signal (Vin) is applied to the inverting (-) input terminal of the op-amp through resistor R. The non-inverting (+) input terminal is usually connected to the ground (GND) or a reference voltage. The resistor R provides input impedance to the circuit. The output signal (Vout) is taken from the output terminal of the op-amp.
The resistor R is connected in series with the capacitor C, forming a high-pass filter network. At low frequencies, the impedance of the capacitor is low, causing most of the input signal to be dropped across it, resulting in a low output voltage. As the frequency increases, the impedance of the capacitor decreases, allowing more of the input signal to pass through to the output. This effect attenuates low-frequency signals and passes high-frequency signals to the output.
Frequency Response:
The cutoff frequency (fc) of the filter is the frequency at which the output voltage is attenuated by -3 dB (approximately 70.7% of the input voltage). It is determined by the values of the resistor (R) and capacitor (C) according to the formula:
fc = 1/(2piRC)
Advantages:
- Flexibility: The cutoff frequency of the filter can be easily adjusted by changing the values of the resistor and capacitor.
- Low Output Impedance: The output impedance of the op-amp is typically low, providing a stable output signal.
- High Accuracy: Active filters offer higher accuracy and precision compared to passive filters
Circuit Diagram:
Precautions:
- Do not connect more than 15 v DC supply
- Always check the Dual power supply with a multimeter before connecting it to the circuit
- Connect an input supply such that the corresponding output remains within the range +14 to -14 volts
- Connections should be neat and tight
