MATLAB functions for calculating circuit values for 4th order Butterworth filter consisting of two Rauch filters in series.
First choose a C5 value for each Rauch filter.
Then calculate m value upper limits with your desired values of shaping parameter Q and voltage gain G. For a butterworth filter the Q values must be 0.541 and 1.307 respectively. The G values must multiply together to give the desired overall passband small-signal voltage gain.
m_a = m(0.541, 1)
m_b = m(1.307, 100)In this case a passband small-signal voltage gain of 100 (40dB) is required so the two gain values are chosen as 1 and 100.
The next step is to choose a value of m for each filter from the upper limits calculated.
The last step is to plot a Bode plot of the filter. This will also print out values for each passive component in each filter as well as its individual transfer function.
bode(H(C5_a, C5_b, G_a, G_b, m_a, m_b));replacing the arguments with the chosen ones.