26-09-2013, 03:20 PM
To verify the characteristics of Low pass and High pass filter
CUTOFF FREQUENCY
As stated above, the circuit has two roles: to pass the desired low frequency signals and stop the
unwanted high frequency signals. But at what frequency does the filter change its behavior from
passing the low ones to stopping the high ones. This is called the cut-off frequency.
SPICE FILE
Vin 1 0 AC 10V
Rf 1 2 4.0
CF 2 3 2.0uF
Lf 3 0 127uH
.AC DEC 20 100Hz 1MEG
.PROBE
.END
This time we did not use 1V for the input voltage. Therefore, we will need to have PROBE
actually divide the input into the output to get the gain. We show this gain in decibels.
Notice that the gain below the resonant frequency of 10 kHz slopes upward at 40 dB/decade.
When we plot the phase shift of this filter, we only need to specify the phase angle of the output
voltage since the input voltage was specified at 0 degrees.