Design a Digital Butterworth LPF with 2 dB passband attenuation at afrequency of 20 rad/sec and atleast 10 dB stopbad attenuation at 30rad/sec

To design a Digital Butterworth Low Pass Filter (LPF) with specific attenuation requirements, follow these steps:

Step 1: Determine the filter order The filter order is determined by the desired stopband attenuation. In this case, we need at least 10 dB stopband attenuation. For a Butterworth filter, the filter order can be calculated using the formula:

N = (log(10^(A/10) - 1)) / (2 * log(ωc))

Where: N = filter order A = stopband attenuation in dB (10 dB in this case) ωc = cutoff frequency in rad/sec (30 rad/sec in this case)

Substituting the values, we get:

N = (log(10^(10/10) - 1)) / (2 * log(30))

Simplifying the equation, we find:

N ≈ 2.5

Since the filter order must be an integer, we round up to the nearest whole number. Therefore, the filter order is 3.

Step 2: Calculate the cutoff frequency The cutoff frequency is the frequency at which the filter starts attenuating the signal. In this case, the cutoff frequency is 20 rad/sec.

Step 3: Determine the transfer function coefficients The transfer function of a Butterworth filter can be calculated using the following formula:

H(z) = K / ((z - p1) * (z - p2) * ... * (z - pn))

Where: H(z) = transfer function K = gain factor z = complex variable p1, p2, ..., pn = poles of the filter

For a Butterworth filter, the poles are located on the unit circle in the complex plane. The distance of each pole from the origin is equal to the cutoff frequency. In this case, the poles can be calculated as:

p1 = e^(j * ωc) p2 = e^(-j * ωc) p3 = -1

Where j is the imaginary unit.

Step 4: Determine the gain factor The gain factor can be calculated by evaluating the transfer function at the cutoff frequency. In this case, we want 2 dB passband attenuation at 20 rad/sec. Therefore, the gain factor can be calculated as:

K = 10^(A/20) ≈ 1.5849

Step 5: Implement the filter Using the calculated transfer function coefficients, implement the digital Butterworth LPF in your desired programming language or software.

Note: The above steps provide a general guideline for designing a Butterworth LPF. The actual implementation may vary depending on the specific programming language or software you are using.