Electronics Lab - Day 4 cntd.

Lab 2-4 : Low Pass Filter

At an input voltage of 4V, we figured that the maximum output voltage at the 3dB point would be 2.8V. Calculating the 3dB point using f=1/(2pi*RC) we found that f3dB = 1061 Hz and experimentally, we found that Vout = 2.8V when f=800Hz.

We were also asked the find the phase shifts for the 3dB point, at very low frequencies and at very high frequencies.

At a low frequency (f=50 Hz) we found the phase shift to be almost zero.

At the 3dB point, we measured the phase shift to be around pi/6=30 degrees. (It should be around 45 degrees).

And at a high frequency (f=10 kHz) we found that phase shift to be just about 90 degrees.

We were also asked to measure the attenuation levels at different frequencies.

f=20*f3dB = 16 kHz --> Vout = 80 mV

f=10*f3dB = 8 kHz --> Vout = 400 mV

f=4*f3dB = 3.2 kHz --> Vout = 1.84 V

f=2*f3dB = 1.6 kHz --> Vout = 1.08 V

Lab 2-5 : High Pass Filter

Because we used the same components for our high pass filter as we did for the low pass filter, the calculations for the cutoff frequency were the same where fo= 1061 Hz. We found that the frequency at which Vout = 2.8 V (which is Vin/sqrt(2)) is f = 1.2 kHz.

We also measured the attenuations at frequencies well below the cutoff frequency.

f=60 Hz --> Vout = 248 mV

f=50 Hz --> Vout = 224 mV

f=40 Hz --> Vout = 184 mV

We also measured the limiting phase shifts for the high pass filter.

At low frequencies (f=40 Hz) the phase shift was 90 degrees.

At high frequencies (f= 10 kHz) the phase shift was zero.

These limiting phase shifts are, not surprisingly, opposite of those that we found for the low pass filter.