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Non-inverting filter: zero at 8, pole at 4, gain 2

Short answer

The transfer function is T(s)=(s+8)/(s+4). Using non-inverting topology with R1 to ground and R2||C feedback: set R1=R2=25 kΩ, C2=10 µF, giving DC gain 2, HF gain 1, zero at −8, pole at −4.

Realize an active filter using non-inverting op-amp configuration with zero at 8, pole at 4 and DC gain of 2.

The required function (zero at s=−8s=-8, pole at s=−4s=-4) is

T(s)=Ks+8s+4,T(0)=K⋅84=2⇒K=1T(s) = K\frac{s+8}{s+4}, \qquad T(0) = K\cdot\frac{8}{4} = 2 \Rightarrow K = 1

So T(s)=s+8s+4T(s) = \dfrac{s+8}{s+4}: DC gain 2, HF gain 1.

Non-inverting configuration: Z1Z_1 from the inverting input to ground, Z2Z_2 from output to inverting input:

T(s)=1+Z2Z1T(s) = 1 + \frac{Z_2}{Z_1}

Use Z1=R1Z_1 = R_1 and Z2=R2∥C2Z_2 = R_2 \parallel C_2:

T(s)=1+R2R1(1+sR2C2)=s+1R2C2(1+R2R1)s+1R2C2T(s) = 1 + \frac{R_2}{R_1(1+sR_2C_2)} = \frac{s + \frac{1}{R_2C_2}\left(1 + \frac{R_2}{R_1}\right)}{s + \frac{1}{R_2C_2}}
          +---R2---+
          |        |
          +---||---+
          |   C2   |
   +------+-|-\    |
   |        |  >---+---- Vo
  R1  Vin---|+/
   |
  GND

Matching:

1R2C2=41+R2R1=84=2⇒R1=R2\begin{aligned} \frac{1}{R_2C_2} &= 4 \\ 1 + \frac{R_2}{R_1} &= \frac{8}{4} = 2 \Rightarrow R_1 = R_2 \end{aligned}

Normalized: C2=1C_2 = 1 F, R1=R2=0.25 ΩR_1 = R_2 = 0.25\ \Omega.

Practical values: choose C2=10 μC_2 = 10\ \muF: R2=14×10−5=25 kΩ=R1R_2 = \dfrac{1}{4 \times 10^{-5}} = 25\ \text{k}\Omega = R_1.

Answer: R1=R2=25 kΩR_1 = R_2 = 25\ \text{k}\Omega, C2=10 μC_2 = 10\ \muF; DC gain 2, HF gain 1, zero at −8, pole at −4.

✓ Answer checked by Claude Sonnet 5.5

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