ENGD1025 Electronics CAE & Programme Fundamentals Assignment, De Montfort University, UK

Title - Passive RC Band pass Filters

Band Pass Filter - The band pass filter allows only frequencies that are between two cut-off frequencies to pass through them. They filter out the low and high frequencies and are used in audio systems to filter a specific band of frequencies. The cut-off frequency of the high-pass filter stage is setup to be lower than the cut-off frequency of the low-pass filter stage. The passive band-pass filter is made up of two resistors and two capacitors as shown.

Calculate the cut-off frequencies from the above resistor and capacitor values:

f_H = 1/(2πR₂C₂) and f_L = 1/(2πR₁C₁)

The lower cut-off and higher cut-off frequency in a band pass filter is the frequency below which, and beyond which, the output signal is greatly attenuated respectively. These frequencies are given by the expressions above. At both cut-off frequencies the output voltage is 70.7% of that of ~V_in and -3dB below the maximum.

1. Run the AC Sweep using Vac for the input voltage (10V) and plot the frequency response, gain and phase shift.

(Simulation settings -> AC sweep -> logarithmic -> from 10Hz to 1Meg, points/dec = 1000)

2. Calculate the theoretical cut-off frequency and compare with the simulation value. Note down the max output voltage also.

3. Use Vsin (Amplitude 10V, Frequency 10 Hz) and show the input and output waveforms.

(Simulation settings -> Time Domain -> Run to Time = 500ms, Maximum step-size = 10u)

4. Use Vsin (Amplitude 10V, Frequency 1 Meg Hz) and show the input and output waveforms.

(Simulation settings -> Time Domain -> Run to Time = 0.01ms, Maximum step-size = 0.01u)

5. Use Vsin (Amplitude 10V, Frequency 3 KHz) and show the input and output waveforms.

(Simulation settings -> Time Domain -> Run to Time = 3ms, Maximum step-size = 0.1u)

6. Try to design a band-stop filter with a stop band between 1KHz and 10KHz.